Abstract:
A manually resettable thermostat has several individual thermostats which have respective manually resettable calibration temperature stacked one above the other and formed an integrative assembly. The thermostat can apply to the thermostatic system that need several different manually resettable calibration temperatures so the space of the system is saving and the operation of the thermostat is easy.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to bimetal snap-action type temperature control devices and more particularly, to a thermostat device, which has multiple manually resettable thermostat units arranged in a stack for working individually at different temperature ranges, and which allows a user to reset all the manually resettable thermostats at a time through one single action. 
         [0003]    2. Description of the Related Art 
         [0004]    According to the design of a conventional manually resettable bimetal snap-action thermostat, the bimetal snap-action spring plate is caused to curve from a first position to a second position when the temperature rises over a predetermined temperature. When the temperature drops below the predetermined temperature, the bimetal snap-action spring plate returns from the second position to the first position. At this time, the switch circuit is not reset, and an external force must be applied to reset the thermostat. This type of manually resettable thermostat has the advantages of high reliability and ease of use. Therefore, this type of manually resettable thermostat is intensively used in different fields. However, this type of manually resettable thermostat is workable only at one single temperature point. For multiple temperature control point application, multiple manually resettable thermostats shall be used. In case there is no sufficient installation space for multiple manually resettable thermostats, the aforesaid conventional design becomes useless. 
         [0005]    For example, when designing an automatic rice cooker, as shown in FIG.  5 , it is necessary to rapidly increase the heating temperature to a first temperature point t 1 , i.e., the food safety temperature about 60˜75° C. to kill microbes in rice, and then to lower the heating power for enabling the heating temperature to be increased slowly to a second temperature point t 2 , i.e., the saturation temperature about 85˜95° C. to have rice be well cooked, and then to lower the heating temperature to a third temperature point t 3 , i.e., the warm-keeping temperature about 60˜65° C. It is the most economic and convenient way to detect the first temperature point t 1  and the second temperature point t 2  by means of the use of a snap-action type thermostat. However, when the temperature drops, the snap-action type thermostat does not return to its former position automatically, i.e., it cannot let the heating temperature drop to the warm-keeping temperature point t 3  to keep the cooked rice warm. This warm-keeping temperature point t 3  is lower than the saturation temperature point t 2 . For the control of the first temperature point t 1  and the second temperature point t 2 , a manually resettable thermostat can be used. The best installation position for thermostat between the electric heater and the cooker is the center area. However, the available space around this center area is limited. In a rice cooker, this space is sufficient for accommodating one single manually resettable thermostat. When multiple manually resettable thermostats are arranged together, the resetting mechanism will be complicated. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention has been accomplished under the circumstances in view. It is the main object of the present invention to provide a thermostat device, which is suitable for use in a temperature control system that requires control of multiple temperature points and, which is easy to operate and saves much installation space. 
         [0007]    To achieve this and other objects, the thermostat device comprises a plurality of manually resettable thermostat units arranged in a stack. The manually resettable thermostat units act at different temperature ranges. Each manually resettable thermostat unit comprises a thermoconducting top cover, a bottom cover, an intermediate structure set in between the thermoconducting top cover and the bottom cover, a smoothly arched bimetal snap-action spring plate for switching on/off a circuit subject to change in temperature, a center push rod inserted axially slidably inserted through the respective intermediate structure. The smoothly arched bimetal snap-action spring plate, the thermoconducting top cover and the bottom cover each have a center through hole for the passing of the respective center push rod. The center through hole of the thermoconducting top cover of one lower manually resettable thermostat unit allows the center push rod of the adjacent upper manually resettable thermostat to pass such that said manually resettable thermostat units work individually at a respective different temperature range and are simultaneously manually resettable. The manually resettable thermostat units are arranged in a stack in such an order that the manually resettable thermostat unit that is disposed at a lower side acts at a relatively lower temperature range than the manually resettable thermostat unit that is disposed at an upper side. 
         [0008]    The thermostat device further comprises a thermoconducting housing surrounding the manually resettable thermostat units and disposed in connection with the thermoconducting top covers of the manually resettable thermostat units for quick transfer of heat energy to keep the thermoconducting top covers of the manually resettable thermostat units at a same temperature. 
         [0009]    The thermostat device further comprises at least one automatically resettable thermostat unit arranged on the top side of the manually resettable thermostat units. 
         [0010]    The thermostat device further comprises a thermal insulative covering surrounding the thermoconducting housing. The thermal insulative covering is preferably prepared from glass fiber cloth. 
         [0011]    Further, the center push rod of each manually resettable thermostat unit has its top end normally kept in flush with the associating thermoconducting top cover, and its bottom end normally kept in flush with the associating bottom cover. 
         [0012]    By means of the aforesaid arrangement, the manually resettable thermostat units work individually at different temperature ranges, however the manually resettable thermostat units are manually resettable at a the same time through one single action. Therefore, the thermostat device of the present invention saves much installation space, and is easy to operate. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a schematic sectional view of a thermostat constructed in accordance with the present invention. 
           [0014]      FIG. 2  is a schematic sectional view of a manually resettable thermostat device in accordance with the present invention. 
           [0015]      FIGS. 3   a - 3   d  are schematic drawings showing different operation status of the manually resettable thermostat device shown in  FIG. 2 . 
           [0016]      FIG. 4  is a schematic sectional view of an alternate form of the manually resettable thermostat device in accordance with the present invention. 
           [0017]      FIG. 5  is a schematic drawing showing the temperature control procedure of the manually resettable thermostat device shown in  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0018]    Referring to  FIG. 1 , a manually resettable thermostat device in accordance with the present invention is shown comprising a thermoconducting metal top cover  10 , an intermediate structure  20 , which has a center guide hole  21 , a bottom cover  30 , a center push rod  40  axially movably inserted through the center guide hole  21  of the intermediate structure  10 , a first accommodation chamber  6  defined in between the thermoconducting metal top cover  10  and the intermediate structure  20 , a second accommodation chamber  7  defined in between the intermediate structure  20  and the bottom cover  30 , a smoothly arched bimetal snap-action spring plate  1  made out of two metals having different thermal expansion coefficients and coupled to the center push rod  40  and suspending in the accommodation chamber  6 , at least one first metal contact  3  fixedly mounted in the second accommodation chamber  7 , and a second metal contact  4  affixed to the center push rod  40  and normally kept in contact with the first metal contact  3 . When reached the designed temperature point, the smoothly arched bimetal snap-action spring plate  1  is caused to make a snap action and to curve in the reversed direction from the upwardly curved first stable state position to the downwardly curved second stable state position. At this time, the reaction force of the snap action of the smoothly arched bimetal snap-action spring plate  1  forces the center push rod  40  downwards, and therefore the second metal contact  4  is moved with the center push rod  40  downwardly away from the first metal contact  3  to open the circuit (see the status of the first thermostat T 1  shown in  FIG. 2 ). 
         [0019]    When the temperature reached the snap-action temperature t 2  of the second thermostat T 2  that is stacked on the first thermostat T 1 , the smoothly arched bimetal snap-action spring plate of the second thermostat T 2  is caused to make a snap action and to curve in the reversed direction from a first stable state position to a second stable state position (see  FIG. 3   a ). At this time, the first thermostat T 1  and the second thermostat T 2  are off. When the temperature starts to drop at this time and when it reaches the working temperature point t 2  of the smoothly arched bimetal snap-action spring plate  1  of the second thermostat T 2  (t 2 &gt;t 1 ), the smoothly arched bimetal snap-action spring plate  1  of the second thermostat T 2  is caused to return to its upwardly curved first stable state position, as shown in  FIG. 3   b . However, this action does not cause the center push rod  40  to displace, and therefore the smoothly arched metal spring plate, referenced by  2 , remains in its downwardly curved second stable state position, and the metal contacts  3  and  4  are kept in the broken circuit status. Further, in  FIG. 1 , the reference sign  5  indicates a metal gasket. 
         [0020]    The center push rod  40  is a combination rod comprised of a main shaft  42 , a top guide rod  41  and a bottom guide rod  43 . The top guide rod  41  is inserted through a center through hole  8  of the smoothly arched bimetal snap-action spring plate  1  and the center through hole  11  of the thermoconducting metal top cover  10 . The top guide rod  41  has a shoulder  44  that is kept in contact with the bottom surface of the smoothly arched bimetal snap-action spring plate  1  so that the center push rod  40  can be pushed downwards by the smoothly arched bimetal snap-action spring plate  1  when the smoothly arched bimetal snap-action spring plate  1  is caused to make a snap action and to curve from the upwardly curved first stable state position to the downwardly curved second stable state position. 
         [0021]    The smoothly arched metal spring plate  2  is coupled to the center push rod  40  between the shoulder  44  of the top guide rod  41  and the topmost edge of the main shaft  42 . The arched metal spring plate  2  can be curved from an upwardly curved first stable state position to a downwardly curved second stable state position. However, when the smoothly arched bimetal snap-action spring plate  1  is caused to curve from the downwardly curved second stable state position to the upwardly curved first stable state position, the center push rod  40  does no work, and at this time, the smoothly arched metal spring plate  2  is maintained in the downwardly curved second stable state position. 
         [0022]    As shown in  FIG. 3   c , when the temperature keeps dropping to the level below the working temperature point t 1  of the smoothly arched bimetal snap-action spring plate  1  of the first thermostat T 1 , the smoothly arched bimetal snap-action spring plate  1  of the first thermostat T 1  is caused to return to its upwardly curved first stable state position. At this time, same as the second thermostat T 2 , the metal contacts  3  and  4  of the second thermostat T 2  are kept in the broken circuit status. Referring to  FIG. 3   d , the first thermostat T 1  and the second thermostat T 2  can be reset only when an external force, referenced by the reference sign “f”, is introduced. Upon application of the external force “f”, the first thermostat T 1  and the second thermostat T 2  are simultaneously reset, and the metal contacts  3  and  4  of each of the first thermostat T 1  and second thermostat T 2  are returned to the close circuit status. 
         [0023]    During the assembly process of the present invention, the thermostat of which the smoothly arched bimetal snap-action spring plate has a relatively lower working temperature is provided at the bottom side of the bottom cover of the thermostat of which the smoothly arched bimetal snap-action spring plate has a relatively higher working temperature, keeping the respective center push rods  40  in vertical alignment, as shown in  FIG. 2 . Thus, when the temperature rises to the level of the working temperature of the smoothly arched bimetal snap-action spring plate of the lower thermostat (the first thermostat) T 1 , the respective smoothly arched bimetal snap-action spring plate is caused to curve from the upwardly curved first stable state position to the downwardly curved second stable state position, leaving the upper half of the first accommodation chamber  6  in vacant for the upper thermostat (the second thermostat) T 2 . Therefore, these two stacked thermostats T 1 ; T 2  work independently without interfering with each other. 
         [0024]      FIG. 4  is a schematic sectional view of an alternate form of the manually resettable thermostat device in accordance with the present invention.  FIG. 5  is a schematic drawing showing the temperature control procedure of the manually resettable thermostat device shown in  FIG. 4 . According to this embodiment, T 1  (75° C.) and T 2  (85° C.) are manually resettable thermostats, T 3  (65° C.) is an automatically resettable thermostat. The thermostat T 1  is provided at the bottom side of the thermostat T 2 . The thermostat T 3  is provided at the top side of the thermostat T 2 . Further, a thermoconducting housing F is provided to surround the stacked thermostats T 1 ˜T 3 . The thermoconducting housing F is made of a metal material having high thermal conductivity, for example, copper. Further, the thermoconducting metal top covers  10  of the thermostats T 1 ˜T 3  are bonded to the thermoconducting housing F by, for example, welding, assuring high thermal conductivity. This embodiment further comprises a thermal insulative covering G surrounding the periphery of the thermoconducting housing F to avoid quick dissipation of heat. The thermal insulative covering G is preferably prepared from glass fiber cloth. 
         [0025]    As stated above, the invention provides a thermostat device, which has multiple thermostats arranged in a stack and individually operable at different temperature levels. The thermostat device is easy to operate and saves much installation space, allowing all the thermostats be simultaneously reset through one single action. 
         [0026]    Although particular embodiments of the invention have been described in detail for purposes of illustration, various modifications and enhancements may be made without departing from the spirit and scope of the invention.