Abstract:
A glow plug may include: i) a hollow plug housing that is mounted on a plug mount in an insulation status; ii) a center shaft that is fixed to one end of the plug housing in an insulation status and receives power from the outside; iii) a heating unit that is connected to the center shaft and the other end of the plug housing, and generates heat using a potential difference; and iv) a connecting unit that insulates the plug mount and the center shaft, is coupled to the plug mount, and electrically connects with center shaft with the plug housing.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority of Korean Patent Application Number 10-2012-0036933 filed Apr. 9, 2012, the entire contents of which application is incorporated herein for all purposes by this reference. 
     BACKGROUND OF INVENTION 
     1. Field of Invention 
     An exemplary embodiment of the present invention relates to an electric thermostat of a cooling system in a vehicle, More particularly, the present invention relates to a glow plug that allows the heating temperature of an electric thermostat to rapidly reach a desired temperature. 
     2. Description of Related Art 
     In general, thermostats for vehicles can be disposed between an engine and a radiator, and function to maintain a coolant at an appropriate temperature by automatically opening/closing in accordance with a change in temperature of the coolant and controlling the flow rate of the coolant flowing to the engine. 
     In the related art, most of thermostats for vehicle are mechanical thermostat structured such that the expansion force of was, which expands in accordance with the temperature of a coolant, is transmitted to a piston and a valve is opened/closed by the force. 
     However, such mechanical thermostats operates in the way of operating in accordance with opening/closing temperatures set as regulation temperatures of a coolant, that is, in the way of simply opening/closing the valve only at predetermined temperatures. Accordingly, considering the recent tendency that the performance and efficiency of vehicles are gradually increased, there is a limit in actively dealing with changes in driving circumstances and other conditions. 
     Currently, variable control types of electric thermostats that maintain the temperature of the engine coolant in an optimal status while making up for the drawbacks of the mechanical thermostats have been developed, 
     The electric thermostats can keep an engine optimally cooled, by controlling the temperature of the engine coolant in accordance with the driving circumstances such as the status of load applied to the vehicle, and can be expected to improve fuel efficiency and reduce exhaust gas in comparison to the mechanical thermostats. 
     An example of the electric thermostats has a structure in which wax and a film resistance type of film are included, heat is generated by a heater supplied with power, the wax is expanded by the heat of the heater, and a piston is pushed by the expansion force, such that a value is operated. 
     The electric thermostats using the film resistance type of heater or other heaters in the related art take 50˜70 seconds to reach a desired temperature of 300-350° C. 
     Therefore, there is a problem in the related art in that as it takes a lot of time to increase the heating temperature of the heater to a desired temperature, it is difficult to control the temperature of the coolant in real time and it is also difficult to improve fuel efficiency of a vehicle. 
     The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art. 
     SUMMARY OF INVENTION 
     Various aspects of the present invention provide for a glow plug having advantages of being able to he used as a heater that generates heat and to be mounted on a plug mount made of a non-conductive material in an electric thermostat. 
     Various aspects of the present invention provide for an electric thermostat that can minimize that time for increasing the heating temperature of a heater to a desired temperature, control the temperature of a coolant in real time in accordance with the driving conditions of a vehicle by improving control responsiveness, and maximize fuel efficiency of the vehicle. 
     Various aspects of the present invention provide for a glow plug that may include: i) a hollow plug housing that is mounted on a plug mount in an insulation status; ii) a center shaft that is fixed to one end of the plug housing in an insulation status and receives power from the outside; iii) a heating unit that is connected to the center shaft and the other end of the plug housing, and generates heat using a potential difference; and iv) a connecting unit that insulates the plug mount and the center shaft, is coupled to the plug mount, and electrically connects with center shaft with the plug housing. 
     The connecting unit may include: a connector that is integrally coupled to the plug and has integral positive (+) and negative (−) terminal members; a first terminal coupler that is fitted in the connector, electrically connected with the positive (+) terminal member, and coupled with the center shaft; and a second terminal coupler that is fitted in the connecter, separately from the first terminal connector, electrically connected with the negative (−) terminal member, and coupled with one end of the plug housing. 
     The heating unit may include: a heating tube that is coupled to the other end of the plug housing; and a coil unit that has one end connected to the center shaft in the heating tube and the other end connected to the heating tube. 
     Various aspects of the present invention provide for a glow plug that may be fixed to a predetermined plug mount and may include: i) a hollow plug housing that is mounted on a plug mount, insulated from the plug mount; ii) a center shaft that is fixed to one end of the plug housing, insulated from the plug housing, and receives power from the outside; iii) a heating tube that is coupled to the other end of the plug housing; iv) a coil unit that has one end connected to the center shaft in the heating tube and the other end connected to the heating tube; v) a connector that insulates the plug mount and the center shaft, is coupled to the plug mount, and has integral positive (+) and negative (−) terminal member; vi) a first terminal coupler that is fitted in the connector, electrically connected with the positive (+) terminal member, and coupled with the center shaft; and vii) a second terminal coupler that is fitted in the connecter, separately from the first terminal connector, electrically connected with the negative (−) terminal member, and coupled with one end of the plug housing. 
     The plug housing may be coupled with the second terminal coupler with a predetermined gap from the inner circumference of the plug mount. 
     A spacing that spaces the plug housing may be formed at the plug mount. 
     One end of the plug housing may be coupled to the center shaft through a sealing member. 
     The center shaft and the second terminal coupler may be insulated by an insulating washer. 
     A first elastic deformable portion that elastically presses the center shaft may be integrally formed at the first terminal coupler. 
     A second elastic deformable portion that elastically presses one end of the plug housing may be integrally formed at the second terminal coupler. 
     The first terminal coupler may be formed in a cylindrical Shape and may have a first cutting line that is longitudinally formed to be long in order to apply an elastic force to the connector. 
     The second terminal coupler may he formed in a cylindrical shape and may have a second cutting line that is longitudinally formed to be long in order to apply an elastic force to the connector. 
     A first connection groove connected with the positive (+) terminal member may be formed at the first terminal coupler. 
     A second connection groove connected with the negative terminal member may be formed at the second terminal coupler. 
     The coil unit may include a heating coil with one end connected to the heating tube and the other rend connected to the center shaft. 
     The coil unit may include: a heating coil that is connected to the heating tube and generates heat; and a temperature control coil that is connected to the heating coil and the center shaft and controls a heating temperature of the heating coil. 
     Various aspects of the present invention provide for an electric thermostat that controls the temperature of a coolant for an engine of a vehicle and may include i) a valve housing that is connected with a plurality of channels through which the coolant for an engine flows; ii) a wax case that is disposed in the valve housing and has a wax space; iii) a glow plug that is inserted in wax filled in the wax space and generates heat by receiving power from the outside; iv) a driving body that is moved by expansion of the wax due to heat from the glow plug; and v) a valve assembly that opens/closes the channels by the movement of the driving body, in which the glow plug may be electrically connected with the power, insulated from the valve housing. 
     The glow plug may include: a cylindrical plug housing that is mounted on a plug mount integrally formed with the valve housing, in an insulation status; a center shaft that is fixed to one end of the plug housing in an insulation status and receives power from the outside; a heating unit that is connected to the center shaft and the other end of the plug housing, and generates heat using a potential difference; and a connecting unit that insulates the plug mount and the center shaft, is coupled to the plug mount, and electrically connects with center shaft with the plug housing. 
     The connecting unit may include: a connector that is integrally coupled to the plug and has integral positive (+) and negative (−) terminal members; a first terminal coupler that is fitted in the connector, electrically connected with the positive (+) terminal member, and coupled with the center shaft; and a second terminal coupler that is fitted in the connecter, separately from the first terminal connector, electrically connected with the negative (−) terminal member, and coupled with one end of the plug housing. 
     According to various aspects of the present invention, the glow plug may be disposed on the plug mount in an insulation status and can electrically connect the center shaft with the heating tube through the first and second terminal coupler of the connecting unit. 
     Since the glow plug can also be mounted on a plug mount made of a non-conductive material, unlike common plugs in which positive (+) power is connected to a plug body and negative (−) power is connected to the plug mount  1  made of a conductive material, it is possible to remove the limit conditions of the material of the plug mount. 
     Since the glow plug is used as a heater that generates heat, it is possible to minimize the time for increasing the temperature of the heater to the desired temperature. 
     Since it is possible to control the temperature of the coolant in real time in accordance with the driving conditions of a vehicle, it is possible to increase fuel efficiency of the vehicle as much as possible by controlling the temperature of the coolant in real time. 
     The methods and apparatuses of the present invention have other features and advantages which will he apparent from or are set forth in more detail in the accompanying drawings, which are incorporated herein, and the following Detailed Description, which together serve to explain certain principles of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view showing the configuration of an exemplary electric thermostat where a glow plug is applied, according to the present invention. 
         FIG. 2  is a perspective view showing an exemplary glow plug that is applied to an electric thermostat according to the present invention. 
         FIG. 3  is a cross-sectional view showing the configuration of the glow plug that is applied to an exemplary electric thermostat according to the present invention. 
         FIG. 4  is a cross-sectional view schematically showing the configuration of an exemplary heating unit that is applied to a glow plug of an electric thermostat according to the present invention. 
         FIG. 5  is an exploded perspective view showing an exemplary y connecting unit that is applied to a glow plug of an electric thermostat according to the present invention. 
         FIG. 6  is a cross-sectional view showing the configuration of an exemplary connector of a connecting unit that is applied to a glow plug of an electric thermostat according to the present invention. 
         FIG. 7  is a cross-sectional view showing the configuration of an exemplary first terminal coupler of a connecting unit that is applied to a glow plug of an electric thermostat according to the present invention. 
         FIG. 8  is a cross-sectional view showing the configuration of an exemplary second connector of a connecting unit that is applied to a glow plug of an electric thermostat according to the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to various embodiments of the present invention(s), examples of which are illustrated in the accompanying drawings and described below. While the invention(s) will be described in conjunction with exemplary embodiments, it will be understood that present description is not intended to limit the invention(s) to those exemplary embodiments. On the contrary, the invention(s) is/are intended to cover not only the exemplary embodiments, but also various alternatives, modifications, equivalents and other embodiments, which may be included within the spirit and scope of the invention as defined by the appended claims. 
     Components unrelated to the description will be omitted in order to obviously describe the present invention, and like reference numerals will be used to describe like components throughout the present specification. 
     Further, in the drawings, the sizes and the thicknesses of the components are exemplarily provided for the convenience of description, the present invention is not limited those shown in the drawings, and the thicknesses are exaggerated to clearly show several parts and regions. 
     Terms used in the specification, giving the names of the components in ‘first’, ‘second’, ‘third’, etc is for discrimination them because the names are the same and they are not limited to the order. 
       FIG. 1  is a cross-sectional view showing the configuration of an electric thermostat where a glow plug is applied, according to various embodiments of the present invention. 
     Referring to FIG,  1 , a glow plug  100  according to various embodiments of the present invention may be generally used to heat air in advance to help ignition of fuel in a diesel engine. 
     However, the glow plug  100  according to various embodiments of the present invention may be applied to a heater that is fixed to a flog mount  1 , generates heat in response to an electric signal, and provides heat around the plug mount  1 . 
     For example, the glow plug  100  according to various embodiments of the present invention may be applied to a heater of an electric thermostat  200  that maintain the temperature of an engine coolant in an optimal state. 
     The electric thermostat  200  is structured to making the heater generate heat by receiving power, expanding wax by using the heat of the heater, and operating a valve by pushing a driving body such as a piston. 
     Meanwhile, various embodiments of the present invention provide the glow plug  100  that can also be mounted on a plug mount  1  made of a non-conductive material, unlike common plugs in which positive (+) power is connected to a plug body and negative (−) power is connected to the plug mount  1  made of a conductive material. 
     That is, since the plug mount  1  should be made of a conductive material to ground the negative (−) power, in common glow plugs, there is a limit in use in accordance with the material of the plug mount  1 . 
       FIG. 2  is a perspective view showing a glow plug that is applied to an electric thermostat according to various embodiments of the present invention and  FIG. 3  is a cross-sectional view showing the configuration of the glow plug that is applied to an electric thermostat according to various embodiments of the present invention. 
     Referring to  FIGS. 1 to 3 , the glow plug  100  in various embodiments of the present invention basically includes a plug housing  10 , a center shaft  20 , a heating unit  30 , and a connecting unit  60 . 
     In various embodiments of the present invention, the plug housing is provided to mount the components of the glow plug  100  and may be mounted on the plug mount  1  that fixes the entire glow plug  100 . 
     For example, the plug mount  1  may be integrally and/or monolithically formed with a valve housing  110 , which may be made of various materials and is connected to a plurality of channels through which an engine coolant flows, and may be made of a non-conductive material. 
     The plug housing  10  is formed in a hollow case shape with the top and bottom open in the drawings, is mounted in the space inside the plug mount  1 , insulated from the plug mount  1 , and may be provided as a grounding main body that receives negative (−) power from the outside. 
     A thread  11  to be thread-fastened to a predetermined element is formed on the outer surface of the plug housing  10  and a hexagonal head  13  is formed at the top of the plug housing  10 , so that the plug housing  10  having this structure is called a vault in this field. 
     A spacing  5  for insulating the inner circumference of the plug mount  1  and the plug housing  10  may be formed on inner circumference of the plug mount  1 . 
     The spacing  5  spaces the inner circumference of the plug mount  1  at a predetermined distance from the plug housing  10  while the inner circumference of the plug mount  1  is cut, when the plug mount  1  is made of metal. 
     Further, the spacing  5  may space the inner circumference of the plug mount  1  at a predetermined distance from the plug housing  10  by injection molding, when the plug mount  1  is made of plastic. 
     The center shaft  20  is a core that receives positive (+) power from the outside and may be fixed to one end (the top in the drawings) of the plug housing  10 , insulated from the plug housing  10 . 
     The center shaft  20  may be connected with one end of the plug housing  10  through a sealing member  21 . For example, the sealing member  21  may be an O-ring. 
     In various embodiments of the present invention, the heating unit  30  is provided to generates heat, using a potential difference, by receiving power rough the center shall  20  and the plug housing  10 , and includes a heating tube  40  and a coil unit  50 , as shown in  FIG. 4 . 
     The heating tube  40  is formed in a cylindrical shape with the upper end open and the lower end dosed, in the drawings, in which the upper end is inserted in the other end. (lower end in the drawings) of the plug housing  10  or may be coupled to the other end of the plug housing  10 . 
     The heating tube  40  may he forcibly fitted in the other end of the plug housing  10  may be attached to the other end of the plug housing  10  by welding. 
     Further, the lower end of the center shaft  20  may be inserted in the open upper end of the heating tube  40 , insulated from the heating tube  40 , and the lower end of the heating tube  40  may be curved by swaging. 
     The coil unit  50  generates heat, using a potential difference of the power applied from the outside, is disposed in the heating tube  40 , and has on end connected to the lower end of the center shaft  20  and the other end connected to the lower end of the heating tube  40 . 
     The coil unit  50 , as in (a) of FIG,  4 , may include a heating coil  51  connected with the lower end of the heating tube  40  and generating heat, and a temperature control coil  53  connected with the heating coil  51  and the lower end of the center shaft  2 . 0  an controlling the heating temperature of the heating coil  51 . 
     The heating coil  51  may be fixed to the inner circumference of the lower end of the heating tube  40  by laser welding and the temperature control coil  53  may be fixed to the lower end of the center shaft  20  by calking or laser welding. 
     The temperature control coil  53  functions to keep the heating temperature of the heating coil  51  constant by controlling an crease in temperature due to a change in resistivity in accordance with an increase in temperature of the heating coil  51 . 
     In this configuration, the heating coil  51  and the temperature control coil  53  are integrally connected, in which the heating coil  51  is made of a material with large electric resistance and the temperature control coil  53  may be made of a material with small electric resistance in comparison to the heating coil  51 . 
     Alternatively, the coil unit  50  may be implemented only by the heating coil  51  that generates heat, using power applied from the outside, as a modified example, as in (b) of  FIG. 4 . 
     In this case, one end of the heating coil  51  may be connected to the inner circumference of the lower end of the heating coil  40  by laser welding and the other end of the heating coil  51  may be fixed to the lower end of the center shaft  20  by calking or laser welding. 
     An insulating member  55  may be disposed in the space between the heating tube  40  and the coil unit  50 , inside the heating tube  40 . 
     For example, the insulating member  55  may be magnesium oxide (MgO) powder. The magnesium oxide powder, an insulator, functions to keep the insulation between the heating tube  40  and the coil unit  50 , prevent movement of the coil unit  50 , and transmit the heat generated from the heating coil  51  of the coil unit  50  to the heating tube  40 , 
     In various embodiments of the present invention, the connecting unit  60 , as stated above, is provided to electrically connect the center shaft  20  with the plug housing  10 , and may insulate the plug mount  1  from the center shaft  20  and may be disposed on the plug mount  1 . 
       FIG. 5  is an exploded perspective view showing a connecting unit that is applied to a glow plug of an electric thermostat according to various embodiments of the present invention. 
     Referring to FIGS,  1  to  5 , the connecting unit  60  according to various embodiments of the present invention includes a connector  70 , a first terminal coupler  80 , and a second terminal coupler  90 . 
     In various embodiments of the present invention, the connector  70 , which is inserted in the plug mount  1 , at the upper end of the plug mount  1 , may be coupled to the plug mount  1 , insulating the plug mount  1  from the center shaft  20 . 
       FIG. 6  is a cross-sectional view showing the configuration of a connector of a connecting unit that is applied to a glow plug of an electric thermostat according to various embodiments of the present invention. 
     Referring to  FIGS. 1 to 6 , the connector  70  according to various embodiments of the present invention is made of a plastic material, which is an insulating material, and includes a first portion  71  actually inserted in the plug mount  1  and a second portion  72  integrally and/or monolithically formed with the first portion  71 , perpendicular to the first portion  71 . 
     The second portion  72  has integral positive (+) and negative (−) terminal members  73  and  74  and the connector  70  may be injection-molded to the terminal members  73  and  74 . 
       FIG. 7  is a cross-sectional view showing the configuration of a first terminal coupler of a connecting unit that is applied to a glow plug of an electric thermostat according to various embodiments of the present invention. 
     Referring to  FIGS. 1 to 7 , the first terminal coupler  80  according to various embodiments of the present invention is electrically connected with the center shaft  20  and the positive (+) terminal member  73  and may be fitted in the uppermost portion of the first portion  71  of the connector  70 . 
     Further, the first terminal coupler  80  has a hollow cylindrical shape and is made of a conductive material, and the upper end of the center shaft  20  may be inserted in the first terminal coupler. 
     The first terminal coupler  80  may generate an elastic force against the first portion  71  in close contact with the inner circumference of the first portion  71 , when inserted in the first portion  71  of the connector  70 . A long first cutting line  81  is formed longitudinally from the upper end to the lower end of the first terminal coupling  80 . 
     Further, a plurality of elastic deformable portions  83  for elastically pressing the upper end of the center shaft  20  is integrally and/or monolithically formed with the first terminal coupler  80 . 
     The first elastic deformable portions  83  are formed by cutting a portion of the first terminal coupler  80  to have predetermined wave shapes, so that they can press the center shaft  20  by elastically deforming, when the upper end of the center shaft  20  is inserted into the first terminal coupler  80 . 
     Further, a first connection groove  85  connected with the positive (+) terminal member  73  of the connector  70 , which is stated above, is formed at the first terminal coupler  80 . 
     That is, when the first terminal coupler  80  is inserted into the first portion  71  of the connector  70 , the positive (+) terminal member  73  can be electrically connected with the first terminal coupler  80  while being fitted into the first connection groove  85 . 
       FIG. 8  is a cross-sectional view showing the configuration of a second connector of a connecting unit that is applied to a glow plug of an electric thermostat according to various embodiments of the present invention. 
     Referring to  FIGS. 1 to 8 , a second terminal coupler  90  according to various embodiments of the present invention is electrically connected with the negative (−) terminal member  74  and the plug housing  10  and may be fitted in the first portion  71  of the connector  70 , separately from the first terminal coupler  80 . 
     The second terminal coupler  90  has a hollow cylindrical shape and is made of conductive material, and one end of the plug housing  10  (upper end in the drawings) may be inserted in the second terminal coupler. 
     In this configuration, the second terminal coupler  90  and the center shaft  20  coupled to the first terminal coupler  80  may be insulated by an insulating washer  99 . 
     Further, the plug housing  10  described above may be coupled to the second terminal coupler  90  with a predetermined gap from the inner circumference of the plug mount  1  by the spacing  5  of the plug mount  1 , which is described above. 
     Meanwhile, the second terminal coupler  90  may generate an elastic force against the first portion  71  in close contact with the inner circumference of the first portion  71 , when inserted in the first portion  71  of the connector  70 . For this configuration, a long second cutting line  91  is formed longitudinally from the upper end to the lower end of the second terminal coupler  90 . 
     Further, a plurality of second elastic deformable portions  93  for elastically pressing one end of the plug housing  10  is integrally and/or monolithically formed with the second terminal coupler  90 . 
     The second elastic deformable portions  83  are formed by cutting a portion of the second terminal coupler  90  to have predetermined wave shapes, so that they can press the plug housing  10  by elastically deforming, when one end of the plug housing  10  is inserted into the second terminal coupler  90 . 
     Further, a second connection groove  95  connected with the negative (+) terminal member  74  of the connector  70 , which is stated above, is formed at the second terminal coupler  90 . 
     That is, when the second terminal coupler  90  is inserted into the first portion  71  of the connector  70 , the negative (−) terminal member  74  can be electrically connected with the second terminal coupler  90  while being fitted into the second connection groove  95 . 
     The glow plug  100  according to various embodiments of the present invention Which is described above is disposed on the plug mount  1  in an insulation status, and can electrically connect the center shaft  20  with the heating tube  40  through the first and second terminal connector  80  of the connecting unit  60 . 
     Therefore, in various embodiments of the present invention, unlike common glow plugs in which the positive (+) power is connected to the plug main body and the negative (−) power is connected to the plug mount  1  made of a conductive material, the glow plug  100  can be mounted even on the plug mount  1  made of a non-conductive material, so that it is possible to remove the limit conditions of the material of the plug mount  1 . 
     The configuration of thermostat  200  where the glow plug according to various embodiments of the present invention which has the configuration described above is described in detail with reference  FIG. 1 . 
     Referring to  FIG. 1 , an electric thermostat  200  according to various embodiments of the present invention, which controls the temperature of an engine coolant of a vehicle, can operate a valve by making a heater generate heat by receiving power, expanding was by using the heat from the heater, and pushing a driving body such as a piston. 
     The electric thermostat  200  according to various embodiments of the present invention has a structure that can rapidly increase the temperature of the heater to a desired temperature by using the glow plug  100  described above, as a heater generating heat. 
     The electric thermostat  200  according to various embodiments of the present invention basically includes a valve housing  110 , a wax case  130 , the glow plug  100  described above, a driving body  150 , and a valve assembly  170 . 
     In various embodiments of the present invention, the valve housing  110  is a part connected with a plurality of channels through which an engine coolant of a vehicle flows. 
     For example, the valve housing  110  may be connected with a radiator-sided channel through which a coolant flowing inside through a radiator, a bypass channel through which the coolant directly circulates to a water pump of an engine without circulating the radiator, and a water pump-sided channel at the inlet through which the coolant flows into the engine. 
     The plug mount  1  where the glow plug  100  according to various embodiments of the present invention is integrally and/or monolithically formed with the valve housing  110 , as a heater that generates heat by receiving power. 
     The valve housing  110  may be made of a conductive material with the plug mount  1  or may be made of a non-conductive material. 
     In various embodiments of the present invention, the wax case  130  may he inserted in the plug mount  1  inside the valve housing  110  and coupled to the plug housing  10  of the glow plug  100 . 
     In this case, the wax case  130  may be made of metal with excellent heat transmission, and may be inserted in the lower end of the plug mount  1  and thread-fastened to the thread  11  of the plug housing  10 , insulated from the plug mount  1 . 
     Further, a wax space that is filled with wax  131  is formed in the wax case  130 . 
     The wax  131  is a common thermally expansive material that changes in volume while being liquefied from a solid state, when heat is applied. 
     The heating tube  40  of the glow plug  100  is inserted in the wax space of the wax case  130  and provides heat to the wax  131  in the wax space through the heating tube  40 , 
     For this configuration, a through-hole  133  is formed at the upper portion of the wax case  130  such that the heating tube  40  can be inserted in the wax space through the through-hole. 
     When the wax case  130  is inserted in the lower end of the plug mount  1  and thread-fastened to the thread  11  of the plug housing  10 , the heating tube  40  can be inserted into the wax space through the through-hole  133 . 
     In various embodiments of the present invention, the glow plug  100  with the heating tube  40  is inserted in the wax space of the wax case  130  functions as a heater that generates heat through the heating tube  40  by receiving power from the outside. 
     The glow plug  100  is assembled with the plug mount  1 , insulated from the plug mount  1  of the valve housing  110  and can connect the center shaft  20  with the plug housing  10  through the connecting unit  60 . 
     The glow plug  100  may be electronically controlled by an external controller such as an ECU (Electronic Control Unit). 
     The glow plug  100  in various embodiments of the present invention has the configuration described above, so that the configuration and the assembly structure are not described below. 
     In various embodiments of the present invention, the driving body  150  may be a piston that moves up/down with expansion of the wax  131  by the heat from the glow plug  100 . 
     The driving body  150  may be disposed and moved inside a cylindrical element guide  151  coupled to the lower end (in the drawings) of the wax case  130 . 
     Further, the a rubber movable body  153  may be disposed inside the element guide  151  and on the driving body  150 , the upper portion of the rubber movable body  153  may be filled with transmission liquid, and a diaphragm  157  may be disposed between the upper surface of the transmission liquid  155  and the wax  131 . 
     The space filled with the transmission liquid  155  inside the element guide  151  may include an inclining surface having a diameter gradually decreasing toward the lower portion from the upper portion where the diaphragm  157  is disposed. 
     Therefore, the pressure of the transmission liquid  155  due to deformation of the diaphragm  157  can concentrate on the rubber movable body  153  and the rubber movable body  153  presses the driving body  150  under the rubber movable body, using the force. 
     Therefore, according to this structure, it is possible to accurately control the flow of the coolant, because the expansion pressure of the wax  131  can be transmitted to the driving body  150  without a loss. 
     in various embodiments of the present invention, the valve assembly  170  is provided to selectively open/close the channel through which the engine coolant flows by the movement of the driving body  150 . 
     The valve assembly  170  includes a main valve  181 , an elastic member  185 , and a bypass valve  191 . 
     The main valve  181  is a channel through which the engine coolant by the movement of the driving body  150  and has a function of opening/closing the radiator-sided channel, for example. 
     The radiator-sided. channel is a channel that allows the coolant discharged from an engine to flow into the engine after circulating a radiator. 
     The elastic member  185  is disposed on the bottom of the main valve  181  and has a function of elastically supporting the main valve  181  to the radiator-sided channel. 
     Therefore, unless a force is applied from the outside, the main valve  181  closes the radiator-sided channel by the elastic force of the elastic member  185 . 
     On the other hand, the bypass valve  191  opens/closes a bypass channel, Which does not circulate the radiator, in cooperation with the main valve  181 . 
     The bypass channel is a channel that allows the coolant discharged from the engine to directly flow into a water pump of the engine without passing through the radiator. 
     The bypass valve  191  is disposed under the driving body  150  and can be moved by pressure of the driving body  150 . 
     Further, main valve  181  and the bypass valve  191  according to various embodiments of the present invention may be integrally connected by a frame  193  (generally called a “valve guide” in the field), in which the bypass valve  191  and the main valve  182  are moved together by the pressure of the driving body  150 . 
     On the other hand, the electric thermostat  200  having the configuration according to various embodiments of the present invention may be disposed at the inlet of the engine through which the coolant flows inside. 
     However the present invention is not limited to that the electric thermostat  200  is disposed at the inlet of the engine through which the coolant flows inside, and the electric thermostat  200  may be disposed at the outlet of the engine through which the coolant is discharged. 
     The operation of the electric thermostat  200  having the configuration according to various embodiments of the present invention is described hereafter. 
     First of all, when the coolant for an engine is maintained at a predetermined temperature, the main valve  181  has closed the radiator-sided channel by the elastic member  185  and the bypass valve  191  has opened the bypass channel, integrally connected with the main valve  181  by the frame  193 . 
     In this status, the coolant discharged from the engine directly flows into the engine through the bypass channel and the water pump-sided channel without passing through the radiator. 
     In this status, when the temperature of the coolant is increased over a predetermined temperature by the operation of the engine, the ECU gives an instruction of operating the glow plug  100  to open the main valve  181 . 
     Accordingly, external power is applied to the coil unit  50  through the connecting unit  60  of the glow plug  100 , the heating coil  51  of the coil unit  50  rapidly increases to the desired temperature. 
     Therefore, in various embodiments of the present invention, as the heating coil  51  of the coil unit  50  generates heat, the wax  131  increases in volume and the diaphragm  157  being in contact with the wax is deformed by the expansion of the wax  131 . 
     Accordingly, the pressure due to the deformation of the diaphragm  157  is transmitted up to the driving body  150  sequentially through the transmission liquid  155  and the rubber movable body  153 . In this process, the driving body  150  applies pressure to the bypass vale  191 , moving down, and the bypass valve  191  is correspondingly moved down. 
     Therefore, as the bypass valve  191  moves down, the bypass channel is closed by the bypass valve  191 . 
     Further, the main valve  181  integrally connected to the frame  193  opens the radiator-sided valve  181 , moving down with the bypass valve  191 . 
     Therefore, the coolant discharged from the engine flows to the water pump-sided channel through the radiator-sided channel after circulating the radiator, and flows into the engine. The coolant exchanges heat in the radiator in this process, so that the temperature of the coolant decreases. 
     On the other hand, when the temperature of the coolant drops to the predetermined temperature or less, the ECU recognizes the drop of temperature and gives an instruction of stopping the operation of the glow plug  100 . 
     Accordingly, the heating coil  51  of the coil unit  50  stops generating heat, the expanded wax  131  contracts, and the driving body  150  moves up. 
     Therefore, the pressure of the driving body  150  which presses the bypass valve  191  is removed, so that the main valve  181  is moved up by the elastic force of the elastic member  185  and closes the radiator-sided channel and the bypass valve  191  correspondingly opens the bypass channel, moving up. 
     According to the electric thermostat  200  according to various embodiments of the present invention, which was described above, it is possible to maintain the temperature of the coolant at a predetermined temperature by the ECU electronically controlling the electric thermostat  200 . 
     Further, in various embodiments of the present invention, since it is possible to rapidly reach the desired temperature by using the glow plug  100  as a heater that generates heat, it is possible to rapidly and accurately control the temperature of the coolant. 
     Comparing with a test result, it takes 50˜70 seconds to reach the desired temperature of 300-350° C. in the related art using a film resistance type of heater, 
     However, in various embodiments of the present invention using the glow plug  100  as a heater, it can be seen that it takes 30 seconds or less to reach the desired temperature of 350° C., which is remarkably improved in comparison to the related art. 
     Further, in various embodiments of the present invention, it is possible to minimize the time taken to increase up to the desired temperature by using the glow plug  100  in the electric thermostat  200  and it is possible to make the features of the cooling system various, by electronically controlling the amount of heat generated by the heater, using the ECU that performs Pulse Width Modulation (PWM) control. 
     For convenience in explanation and accurate definition in the appended claims, the terms upper or lower, and etc. are used to describe features of the exemplary embodiments with reference to the positions of such features as displayed in the figures. 
     The foregoing descriptions of specific exemplary embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teachings. The exemplary embodiments were chosen and described in order to explain certain principles of the invention and their practical application, to thereby enable others skilled in the art to make and utilize various exemplary embodiments of the present invention, as well as various alternatives and modifications thereof It is intended that the scope of the invention be defined by the Claims appended hereto and their equivalents.