Patent Publication Number: US-5892428-A

Title: Thermal actuator

Description:
FIELD OF THE INVENTION PRESENT 
     The present invention relates to a kind of actuator, and more particular to a thermal actuator that can automatically provide an actuating action once the temperature of a predetermined surrounding zone is overheated or over-cold. It is a universal device adapted to the overheat of various apparatus and appliances, such as an electrical circuit breaker, a motor, a refrigerator, a freezing storage, a coffee maker, a heater, a computer, and etc.. 
     BACKGROUND OF THE PRESENT INVENTION 
     Most electrical appliances break down because of overheating. Overheating of an appliance or a circuit frequently causes fire or electrical shock. In order to provide a kind of protection, most houseware appliances install a fuse to prevent the overheating of the electrical wires. For the building circuitry, the bi-metal type breaker is the most common device installed in the control panel to prevent the overheating of the electrical wiring. 
     In the other words, those conventional thermal protectors are substantially the electrical current protection for preventing overheating of the electrical wiring. However, the surroundings around the electrical appliance has nothing for protecting against overheating or over-cold. For example, a pot of a coffee maker may also be overheated if there is no more coffee therein. It will also create danger of fire or breaking down situation. A halogen floor lamp would generate a great amount of heat therearound that has a high risk of burning stuff like the curtain around. Moreover, it is well known that the CPU of a computer generates heat during operation. If the heat accumulates around the CPU to a certain extent, the CPU will be malfunctioned. Also, a heater is an appliance for generating heat. However, the user can only control the heat by setting the power output or the timer control. It is relatively expensive and difficult to control the heater according to the actual temperature around the heater. 
     In fact, every electrical appliance that generates heat needs a thermal guard to prevent the surrounding being overheated or over-cold. It would be a remarkable matter if there is an inexpensive device that can cut the circuit or switch off the appliance if the surrounding thereof is too hot. It not only can prolong the service life of the appliance, but also can help the user to avoid unreasonable hazard or damages. 
     SUMMARY OF THE PRESENT INVENTION 
     It is thus a main object of the present invention to provide a thermal actuator which can provide an actuating action to break a circuit or to switch off the appliance when the temperature of a predetermined surrounding zone is higher than a safe temperature. 
     A further object of the present invention is to provide a thermal actuator which is a universal device adapted for installing in most kinds of electrical circuitry or appliances. 
     Yet another object of the present invention is to provide a thermal actuator which has a relatively economic structure and is easy to install. 
     In order to accomplish the above objects, the present invention provides a thermal actuator which comprises a thermal detector, an actuator unit and a connecting circuit for electrically connecting the thermal detector and the actuator unit. 
     The thermal detector comprises a first contact member made of electrical conducting material, a second contact member made of thermostatic metal and an insulating connector connected between a connecting end of the second contact member and the first contact member. The second contact member which is normally remained not in contact with the first contact member has a contact end which would bend towards and press against the first contact member when the temperature around the thermal detector reaches a predetermined value. 
     The actuator unit comprises an actuating piece made of thermostatic metal strip, a conducting terminal piece connected to the actuating piece, an insulating sleeve covering a portion of the actuating piece, and an electrical heat wire wrapping around the insulating sleeve which has one end connected to the actuating piece. 
     The connecting circuit comprises a first conducting wire connected between the first contact member of the thermal detector and the conducting terminal piece of the actuator unit, a first terminal, a second conducting wire connected between the second contact member of the thermal detector and the first terminal, a second terminal electrically connected with another end of the electrical heat wire. The first and second terminals are adapted to connect to the electrical circuit of an electrical appliance or any electrical circuitry. 
     Whereby, when the second contact member is normally remained not in contact with the first contact member, the thermal actuator of the present invention is an open circuit and does not function. However, when the second contact member bends to contact with the first contact member due to overheated or over-cold surroundings around the thermal detector, the thermal actuator is close and the electric current flows to the actuator unit. The heat wire wrapped the actuating piece generates heat to increase the temperature around the actuating piece. When the temperature around the actuating piece increases to a predetermined extent, the actuating piece bends so as to provide an actuating action. If the actuator unit is installed close to a switch or a breaker, the actuating action of the actuating piece can activate the switch to turn off the the breaker to cut the electric supply. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a thermal actuator in accordance with a preferred embodiment of the present invention, wherein the dotted lines indicated the displacement of the second contact member. 
     FIG. 2 is a sectional view of a breaker having an actuator unit installed therein according to the above preferred embodiment of the present invention. 
     FIG. 3 is a side view of a floor having a thermal detector mounted near the halogen bulb thereof according to the above preferred embodiment of the present invention. 
     FIGS. 4A and 4B are perspective views of alternative modes of the actuator unit of the present invention. 
     FIG. 5A is a perspective view of the actuator unit installed on to a switch contact according to the above preferred embodiment of the present invention. 
     FIGS. 5B and 5C are perspective views of alternative modes of the actuator unit according to the above preferred embodiment of the present inveniton. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, a thermal actuator according to a preferred embodiment of the present invention is illustrated. The thermal actuator comprises a thermal detector 10, an actuator unit 20 and a connecting circuit 30 for electrically connecting the thermal detector 10 and the actuator unit 20. 
     The thermal detector 10 comprises a first contact member 11 made of electrical conducting material such as brass, a second contact member 12 made of thermostatic metal (bi-metal) and an insulating connector 13 connected between a connecting end 121 of the second contact member 12 and a first end 111 of the first contact member 11. A second end 122 of the first contact member 11 protrudes a first contact point 113 facing to the second contact member 12. The second contact member 12 which is normally remained not in contact with the first contact member 11 has a contact end 122 which protrudes a contact point 123 aligning with the first contact point 113 and facing to the first contact member 11. The second contact member 12 would bend towards and press against the first contact member 11 when the temperature around the thermal detector 10, i.e. the second contact member 12, reaches a predetermined temperature. The predetermined temperature depends on the material nature of the second contact member 12. 
     On the second contact member 12, a circular concave groove 124 is formed. Accordingly, when the second contact member 12 is heated by the hot surrounding, the circular concave groove 124 ensures the contact end 122 of the second contact member 12 bending downwardly toward the first contact member 11. 
     The actuator unit 20 comprises an actuating piece 21 made of thermostatic metal (bi-metal) strip, a conducting terminal piece 22 connected to one end of the actuating piece 21 by spot welding, an insulating sleeve 23 covering a portion of the actuating piece 21, and an electrical heat wire 24 wrapping around the insulating sleeve 23 which has one end 241 connected to the actuating piece 21. The insulating sleeve 23 acts as an insulating layer between the surface of the actuating piece 21 and the heat wire 24 to avoid electrical contact therebetween. 
     The connecting circuit 30 comprises a first conducting wire 31 connected between the first contact member 11 of the thermal detector 10 and the conducting terminal piece 22 of the actuator unit 20, a first terminal 32, a second conducting wire 33 connected between the second contact member 12 of the thermal detector 10 and the first terminal 32, a second terminal 34 electrically connected with a second end 242 of the electrical heat wire 24. The first and second terminals 32, 34 are adapted to connect to the electrical circuit of an electrical appliance or any electrical circuitry. 
     For easy connection, a quick connector 35 is included in the first conducting wire 31. The quick connector 35 consists of two terminal connectors 351, 352, wherein the first terminal connector 351 is connected with the first contact member 11 through a first segment of the first conducting wire 31, and the second terminal connector 352 is connected with the conducting terminal piece 22 through a second segment of the first conducting wire 31. Therefore, the user may separately install the thermal detector 10 and the actuating unit 20 respectively, and then electrically connect them by connecting the first and second terminal connectors 351, 352 together. 
     Whereby, when the second contact member 12 is normally remained not in contact with the first contact member 11, the thermal actuator of the present invention is open and does not function. However, when the second contact member 12 bends to contact with the first contact member 11 due to overheated or over-cold surroundings around the thermal detector 10, the thermal actuator is in a close circuit and the electric current flows to the actuator unit 20. The heat wire 24 wrapped around the actuating piece 21 generates heat to increase the temperature around the actuating piece 21. When the temperature around the actuating piece 21 increases to a predetermined extent, the actuating piece 21 bends so as to provide an actuating action. If the actuator unit 20 is installed close to a switch or a breaker, the actuating action of the actuating piece 21 can activate the switch to turn off of the breaker to cut the electric supply. 
     As shown in FIG. 2, in order to enable the person skilled in the art having a better understanding of the present invention, a practical application of the thermal actuator of the present invention is illustrated. The actuator unit 20 is mounted in a breaker switch 40, wherein the thermal detector 10 of the present invention is attached to a predetermined location along the circuit or appliance connected with the breaker 40 for sensing that whether the surroundings around the predetermined location are overheated or over-cold, such as the floor lamp head as shown in FIG. 3. When the temperature of the above mentioned predetermined location accumulating heat to a certain extent, the second contact member 12 bends to contact with the first contact member 11. Then, electric current flows through the heat wire 24 of the actuator unit 20. The actuating piece 21 responds promptly to bend upwards to drive a push rod, which is slidably mounted between the actuating piece 21 and a reboundable switch bar 42 of the breaker switch 40, to move upward and press the switch bar 42 to break off the circuit. 
     As shown in FIG. 3, in order to show the wide application of the present invention, an example of attaching the thermal detector 10 to a lamp head shell 51 of a halogen floor lamp 50 is illustrated. The thermal detector 10 is adhered or screwed to an inner surface of the lamp head shell 51 near the halogen bulb 53, so that if the heat generated by the halogen bulb 53 fails to dissipate and accumulates, the temperature around the lamp head shell 51 will increase. When the surrounding of the lamp head shell 51 becomes too hot to cause hazard situation, the second contact member 12 bends toward and press against the first contact member 11 so as to close the circuit of the thermal actuator. Shortly, the actuator unit 20 will respond to provide an actuating action by the bending actuating piece 21 to turn off the floor lamp 50 (not shown in FIG. 3) or to activate a warning system for the floor lamp 50. 
     FIGS. 4A and 4B illustrate two alternative modes of the thermal detector 10 of the above preferred embodiment. As shown in FIG. 4A, the alternative thermal detector 10a also comprises a first contact member 11a which is an electrical contact terminal mounted on a L-shape insulating connector 13a and connected to the first conducting wire 31. The second contact member 12a has two downwardly indented side strips 121a, 122a connected to a flat central strip 123a, and a contact point 123a is connected to a front end of the flat central strip, 123a. As shown in FIG. 4B, the second alternative thermal detector 10b comprises two curved contact members 11b, 12b arranged and functioned similar to the above embodiment. 
     As shown in FIG. 5A, the actuator unit 20 can be mounted on top of a switch contact member 60 having a switch contact point 61, so that when the actuating piece 21 bends downwardly, an actuating contact point 211 connected to a front end thereof will be rendered to contact with the switch contact point 61 to switch on an appliance (not shown) connected with the switch contact member 60. 
     As shown in FIG. 5B, another alternative mode of the actuator unit 20a is illustrated, which also comprises a S-shape actuating piece 21a made of thermostatic metal strip, a conducting terminal piece 22a connected to one end of the actuating piece 21a to electrically connect with a conducting wire 31a, an insulating sleeve 23a covering a portion of the actuating piece 21a, and an electrical heat wire 24a wrapping around the insulating sleeve 23a which has one end 241a connected to the actuating piece 21a. When the temperature around the actuating piece 21 a increases to a predetermined extent by the electrical heat wire 24a, the S-shape actuating piece 21a will move forward to provide a desired actuation action, illustrated in phantom lines in FIG. 5B. 
     As shown in FIG. 5C, another alternative mode of the actuator unit 20b is illustrated, which also comprises a U-shape actuating piece 21b made of thermostatic metal strip, a conducting terminal piece 22b connected to one end of the actuating piece 21b to electrically connect with a conducting wire 31b, an insulating sleeve 23b covering a portion of the actuating piece 21b, and an electrical heat wire 24b wrapping around the insulating sleeve 23b which has one end 241b connected to the actuating piece 21b. When the temperature around the actuating piece 21b increases to a predetermined extent by the electrical heat wire 24b, the free half of the U-shape actuating piece 21b will move forward to provide an actuation action, illustrated in phantom lines in FIG. 5C. 
     In view of the above disclosure, the thermal actuator of the present invention substantially provides an actuating action when the surrounding around the thermal detector 10 suffers an overheat problem. The designer of the appliance can free to take advantage of this actuating action for responding to the overheat condition. Since the actuator unit 20 that actually provides the actuating action can be installed far away from the thermal detector 10, it is possible to freely attach the thermal detector 10 to any desired location while the actuator unit 20 is installed in the electrical circuit of the appliance. Therefore, it should be noticed that the thermal actuator can be incorporated in any all kinds of electrical circuitry or appliance, such as an electrical circuit breaker, a motor, a refrigerator, a freezing storage, a coffee maker, a heater, a computer, and etc..