WO2005080763A1

WO2005080763A1 - Electric heater having improved durability

Info

Publication number: WO2005080763A1
Application number: PCT/KR2004/002152
Authority: WO
Inventors: Jae-Won Hwang; Seok Kim; Kae-Hee Oh; Gye-Won Jang; Won-Tae Kim; Bong-Kun Kang; Do-Yon Yang
Original assignee: Il Jin Electric Co., Ltd.
Priority date: 2004-02-23
Filing date: 2004-08-26
Publication date: 2005-09-01
Also published as: KR20050083467A; DE112004002758T5; CN1926314A; KR100586052B1

Abstract

The present invention relates to a durable electric heater, designed to change a local resistance non-symmetrically distributed in a heating element to a resistance symmetrically distributed therein by attaching at least one heating element to each section divided in the heating element or by varying amplitude of the heating element, thereby ensuring that the heating element has a uniform temperature distribution at a bent portion of the heating element or at a contact portion between the heating element and a mantle.

Description

ELECTRIC HEATER HAVING IMPROVED DURABILITY

Technical Field

The present invention relates to a durable electric heater, and more particularly to a durable electric heater, designed to change a local resistance non- symmetrically distributed in a heating element to a resistance symmetrically distributed therein by attaching at least one heating element to each section divided in the heating element or by varying amplitude of the heating element, thereby ensuring that the heating element has a uniform temperature distribution at a bent portion of the heating element or at a contact portion between the heating element and a mantle. Background Art

Generally, an internal combustion engine for a vehicle discharges a great quantity of harmful exhaust gas when burning fuel, and a catalyst is used for reducing the amount of exhaust gas. The catalyst is usually coated on a metal substrate. The metal substrate is manufactured by alternately laminating a corrugated strip and a flat strip, each being made of a thin metal plate, winding the laminated metal strips, and brazing the metal strips in a vacuum furnace with a metal brazing filler applied to the wound metal strips for increasing the binding force between the metal strips. At this time, the metal strips are bonded to each other by brazing the flat/corrugated strips, which are previously wound as an integral component and then inserted in a can. As with the conventional ceramic substrate, the metal substrate produced by brazing is formed with extremely minute apertures. Particularly, according to a recent trend of strengthening regulations aimed at reduction of exhaust gas emissions, in case of a gasoline engine, there is an exhaust gas emissions reducing method, in which the catalyst is located adjacent to the engine in order to reduce the amount of unburned hydrocarbons discharged during a cold start or idling of the engine. Alternatively, there is another exhaust gas emission-reducing method using an electric heater based on the principle of the metal substrate, which activates the catalyst in a short period of time by heating the electric heater during the cold start. Meanwhile, in case of a diesel engine, a diesel particulate filter is used to reduce smoke of the diesel engine. As for a technology available for the diesel particulate filter, there are a trapping technology using a ceramic filter, and a regeneration technology for periodically oxidizing or burning trapped smoke. Recently, the electric heater having the metal substrate has been employed for the regeneration technology. At this time, the electrical heater used for the regeneration technology generally has several sheets of thin plates stacked on each other, which are used when manufacturing the metal substrate, as described above. Meanwhile, when manufacturing the electrical heater using the metal substrate, corrugated strips having different cell sizes are alternately laminated, and are then bonded to each other. Fig. 1 shows a conventional electric heater, which comprises a heating element having strips laminated therein, a mantle separating the heating element into several regions, and electrodes to supply power to the heating element. Fig. 2 shows a conventional heating element having the strips laminated therein. Each of the strips 10 and 20 of the heating element used in the conventional electric heater is corrugated to form cells thereon, each of which has a size different from that of the other strip, and the strips are alternately laminated on each other. The heating element has a predetermined number of laminated layers and a predetermined width according to a predetermined capacity. The heating element can be formed to have a bent portion and a straight portion, and thus, it can be used not only in a straight portion of the electric heater, but also in a bent portion of the electric heater. Fig. 3 is a photograph illustrating the heating element generating heat when electric current is applied to the bent portion of the heating element. A light portion in the photograph has a high temperature, and a dark portion in the photograph has a low temperature. Fig. 4 is a diagram illustrating the electric current flowing in an S -shaped bent portion of the heating element, Fig. 5 is a diagram illustrating the electric current flowing in an L-shaped bent portion of the heating element, and Fig. 6 is a diagram illustrating the electric current flowing in a straight portion of the heating element. That is, when the resistance is temporarily varied at the bent portion, the electric current tends to flow to a portion having a lowest resistance in the bent portion. On the contrary, generation of heat is mainly concentrated on a portion having a higher resistance at the bent portion. Fig. 7 is a schematic diagram illustrating the heating element, the bent portion of which is divided into several sections in order to find resistance distribution at respective sections. Ω l, Ω2, and Ω3 indicate different resistances caused by shape differences of the sections. Accordingly, as the sections Ω 1 and Ω 5 have the same shape, sections Ω 1 and Ω 5 have the same resistance, and as sections Ω2 and 4 have the same shape, sections Ω2 and Ω4 have the same resistance. Meanwhile, in the case of the section Ω 3, since the left side is a pathway through which the electric current can flow in a shortest distance, the left side of the pathway has a higher temperature distribution than the right side of the pathway when the electric heater generates heat. As a result, such a higher and non-symmetrical temperature distribution in the heating element causes the endurance of the heating element at the section Ω3 to be reduced. Fig. 8 shows the section Ω 3 having three regions divided in the section Ω 3 of the bent portion in the horizontal direction, in which Region 1 has a higher temperature than that of Region 3. Accordingly, it can be appreciated that even in the same section Ω 3, the heating element has different temperatures depending on the regions divided in the section 3 when the electric current is applied to the electric heater, thereby generating a difference of thermal endurance. Fig. 9 is a schematic diagram illustrating the heating element bent and attached to a mantle, in which the heating element is divided into several sections. In order to provide a lot of contact portions between the heating element and the mantle, the strips of the heating element has a serpentine shape. Accordingly, in the conventional heating element, the number of the contact portions is the highest at a section Ω l, and is then gradually decreased towards a section Ω5. As a result, the resistance is gradually increased from a section Ω2 towards sections Ω3, Ω4, and 5, and thus, the electric current flows not to the heating element but to the mantle provided at an outer portion of the heating element, so that heat is not generated in the sections Ω 3, Ω4, and Ω 5. Furthermore, at a contact portion between the section Ω 2 and the mantle, electric current is maximized, providing a major and primary cause of temperature increase, thereby reducing the endurance of the heating element. Fig. 10 is a photograph showing a state of generating heat at a contact portion between the mantle and the heating element when applying the electric current to the electric heater. As can be seen in Fig. 10, the temperature is remarkably reduced towards portions 3, 4 and 5 after a portion 2. As a result, due to differences of the thermal endurance at the contact portions between the mantle and the heating element or at the bent portion of the heating element, some regions of the electric heater are broken, completely incapacitating the electric heater. Disclosure of the Invention

Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a durable electric heater, designed to change a local resistance non-symmetrically distributed in a heating element to a resistance symmetrically distributed therein by attaching at least one heating element to each section divided in the heating element or by varying amplitude of the heating element, thereby ensuring that the heating element has a uniform temperature distribution at a bent portion of the heating element or at a contact portion between the heating element and a mantle. In accordance with an aspect of the present invention, the above and other objects can be accomplished by the provision of an electric heater, comprising: a heating element with a plurality of strips laminated in the heating element to form a bent portion and a straight portion; at least one mantle separating the heating element into a central portion of the heating element and an outer portion of the heating element while contacting the heating element; and at least one electrode electrically connected to the heating element to supply power to the heating element, generating heat in the electric heater, wherein the bent portion of the heating element or a contact portion between the mantle and the heating element has different resistances according to a position in the heating element. The heating element may have at least one reinforcing heating element of a predetermined length attached thereto in order to provide the different resistances according to the position in the heating element. The different resistances according to the position in the heating element may cause a change of a contact area between the mantle and the heating element. The change of the contact area between the mantle and the heating element may cause change of amplitude of the heating element at the contact portion between the mantle and the heating element.

Brief Description of the Drawings

The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: Fig. 1 shows a conventional electric heater; Fig. 2 shows an example of a conventional heating element having strips laminated therein; Fig. 3 is a photograph illustrating the heating element having the strips laminated therein when electric current is applied to a bent portion of the heating element; Fig. 4 is a diagram illustrating electric current flowing in an S-shaped bent portion of the heating element having the strips laminated therein; Fig. 5 is a diagram illustrating electric current flowing in an L-shaped bent portion of the heating element having the strips laminated therein; Fig. 6 is a diagram illustrating electric current flowing in a straight portion of the heating element having the strips laminated therein; Fig. 7 is a schematic diagram illustrating the bent portion of the heating element divided into five sections; Fig. 8 is a schematic diagram illustrating a Ω 3 section of the heating element shown in Fig. 7 and having three regions divided in the Ω 3 section in the horizontal direction; Fig. 9 is a schematic diagram illustrating the heating element bent and attached to a mantle, in which the heating element is divided into several sections; Fig. 10 is a photograph showing a state of heat generation in a contact portion between the mantle and the heating element when applying electric current to the electric heater; Fig. 11 is a schematic diagram illustrating the heating element having a reinforcing heating element attached thereto in a predetermined region; Fig. 12 shows an example of the heating line having the reinforcing heating elements attached to strips of the heating element according to the present invention; Fig. 13 is a photograph showing an example of the heating element of Fig, 11 applied to the practical use when applying electric current to the electric heater; Fig. 14 is a graphical representation depicting a temperature at the bent portion of the heating element of the present invention and the conventional heating element; Fig. 15 shows an example of the heating element of Fig. 11 , which has reinforcing heating elements attached to strips of the heating element and is attached to a mantle, providing a contact portion between the mantle and the heating element; Fig. 16 is a photograph showing the example of Fig. 15 when applying electric current to the electric heater; Fig. 17 is a graphical representation depicting a temperature at the contact portion between the mantle and the heating element of the present invention and the conventional heating element; Fig. 18 is a schematic diagram illustrating a hot spot portion where the temperature is highest in the contact portion between the mantle and the heating element; Fig. 19 is a schematic diagram illustrating a hot spot portion of Fig. 18, which is enhanced in structure; Fig. 20 is a diagram, with which the contact area between the conventional heating element and the mantle can be calculated; Fig. 21 is a diagram, with which the contact area between the conventional heating element and the mantle when amplitude of the heating element is reduced can be calculated. Best Mode for Carrying Out the Invention

Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings. Fig. 11 is a schematic diagram illustrating a preferred embodiment of the present invention, in which a reinforcing heating element 11 is attached to a predetermined section of a strip 10 of a heating element. That is, when forming the heating element by laminating strips, the heating element is formed to have a different resistance at a bent portion of the heating element. At this time, the reinforcing heating element has a corrugated shape with the same number of cells as that of the strip in the same strip layer of the heating element, as shown in Fig. 11, and one or more such reinforcing heating elements are attached to the strips of the heating element, respectively. Due to the reinforcing heating elements attached to the strips of the heating element, sections Ω 1 and Ω 3 have a different resistance from that of a section Ω2. This is attributed to the fact that, even with the same material, a larger unit area allows electric current to flow easily and lowers the resistance. That is, since the section Ω 2 has a large unit area, the electric current can easily flow, and the resistance is decreased. Fig. 12 shows an example of the heating element having the reinforcing heating elements attached to the strips of the heating element according to the present invention. In this example, the reinforcing heating elements, each having the same number of cells as that of the strip in the same strip layer of the heating element, are attached to the strips constituting the heating element, so that, when activating the electric heater, a temperature distribution of the heating element is largely extended to Region 3. This phenomenon can be confirmed from Fig. 13, which is a photograph of the shape of the heating element of Fig. 12. Considering the reason of uniform distribution of heat generation as shown in Fig. 13, the reinforcing heating elements are attached to the strips of the heating element in order to change the resistance in the heating element around the entirety of the bent portion, while gradually increasing the length of the reinforcing heating elements from an innermost portion of the heating element before the bent portion at Region 1 toward an outer portion of the heating element. That is, since the large unit area causes the resistance to be lowered, the resistance is gradually decreased from the innermost portion towards the outer portion. Accordingly, by reducing the resistance at the outer portion of the bent heating element, the electric current tending to flow inwardly is guided to flow outwardly, so that heat generated at the bent portion of the heating element can be distributed to the outer portion of the bent portion. Fig. 14 is a graphical representation depicting a temperature at the bent portion of the heating element of the present invention and of the conventional heating element. As shown in Fig. 14, it can be appreciated that the temperature at Region 3 is decreased by about 250 ^°C . Meanwhile, at Region 1, although the temperature is slightly decreased compared with the conventional heating element, thermal endurance can be achieved due to reduction in temperature at -egion 1. Fig. 15 shows an example of the heating element of Fig. 11 , which has reinforcing heating elements attached to the strips of the heating element, and is attached to a mantle, thereby providing a contact portion between the mantle and the heating element, wherein the reinforcing heating elements are attached to sections 2, Ω 3, Ω4, and Ω 5 to have the same resistance as that of a section Ω l. As with the case wherein the reinforcing heating elements are attached to the strips of the heating element having the bent portion, each of the reinforcing heating elements has the same number of cells as that of a strip in the same strip layer of the heating element. Fig. 16 is a photograph showing the example of Fig. 15 when applying electric current to the electric heater. Fig. 17 is a graphical representation depicting the temperature at the contact portion between the mantle and the heating element of the present invention and of the conventional heating element. As shown in Fig. 17, it can be appreciated that the temperature is decreased by about 250 ^°C, which is the maximum extent to which the temperature can be decreased. That is, it can be appreciated that the resistance distribution is significantly extended towards the sections Ω2, Ω 3, Ω4, and

Ω5. Fig. 18 is a schematic diagram illustrating a hot spot portion where the temperature is highest at the contact portion between the mantle and the heating element, in which the resistance is increased towards the right side, so that electric current does not smoothly flow at the right side, whereby the temperature of the heating element is decreased at the right side. Fig. 19 is a schematic diagram illustrating a hot spot portion, which is enhanced not only in the distribution of the temperature, but also in the endurance at the hot spot portion without attaching the reinforcing heating element to the heating element. That is, reduction in amplitude of the heating element at the contact portion between the mantle and the heating element increases a contact area between the mantle and the heating element, and variation in length of the entire heating element causes reduction in resistance. Fig. 20 is a diagram with which the contact area between the conventional heating element and the mantle can be calculated. The contact area between the heating element and the mantle is calculated as described below. Contact area = Thickness "t" of filler (brazing agent) * Length "L" of contact area * Number of contact surfaces In Fig. 21, the contact area between the heating element and the mantle is increased due to an increase of the contact length by reducing the amplitude of the heating element, even though the same thickness of the filler and the same number of contact surfaces are provided. As a result, reduction in amplitude of the heating element can not only enhance the endurance of the hot spot portion, but also decrease the overall length of the heating element, resulting in reduction of the resistance of the heating element, thereby allowing enhancement of the heating element and uniform distribution of the temperature in the heating element at the same time.

Industrial Applicability

As apparent from the above description, according to the present invention, resistance in the heating element is symmetrically distributed by attaching at least one heating element to each section divided in the heating element or by varying amplitude of the heating element, thereby ensuring that the heating element has a uniform temperature distribution at the bent portion of the heating element or at the contact portion between the heating element and the mantle, resulting in enhancement of the thermal endurance of the heating element. Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims

Claims:

1. An electric heater, comprising: a heating element with a plurality of strips laminated in the heating element to form a bent portion and a straight portion of the heating element; at least one mantle separating the heating element into a central portion of the heating element and an outer portion of the heating element while contacting the heating element; and at least one electrode electrically connected to the heating element to supply power to the heating element, generating heat in the electric heater, wherein the bent portion of the heating element or a contact portion between the mantle and the heating element have different resistances according to a position in the heating element.

2. The electric heater as set forth in claim 1, wherein the heating element has at least one reinforcing heating element of a predetermined length attached thereto in order to provide the different resistances according to the position in the heating element.

3. The electric heater as set forth in claim 1, wherein the different resistances according to the position in the heating element cause a change of a contact area between the mantle and the heating element.

4. The electric heater as set forth in claim 3, wherein the change of the contact area between the mantle and the heating element causes change of amplitude of the heating element at the contact portion between the mantle and the heating element.