WO2004067927A1

WO2004067927A1 - Fumes reducing device for diesel engines and method of manufacturing the same

Info

Publication number: WO2004067927A1
Application number: PCT/KR2003/002276
Authority: WO
Inventors: Jae-Won Hwang; Soek Kim; Seung-Joo Choe; Do-Yon Yang
Original assignee: Iljin Electronic Co., Ltd
Priority date: 2003-01-27
Filing date: 2003-10-27
Publication date: 2004-08-12
Also published as: DE10394082B4; DE10394082T5; AU2003273113A1

Abstract

Disclosed herein are an exhaust gas aftertreatment device for diesel engines using an electric heater and a method of manufacturing the same. The device burns PMs contained in exhaust gas discharged from an internal combustion engine, especially a diesel engine, so that pollutants are not discharged to the air. An electric heater (4) for spatially non-uniformly distributing thermal capacity is attached to at least one catalyst unit (7, 8) for activating a catalyst or improving a conversion efficiency of nitric oxide/nitrogen dioxide at a low temperature. The electric heater (4) is divided into a plurality of segments so that electric current is supplied continuously or selectively to the respective segments on the basis of the amount of PMs collected at the segments, whereby energy consumption is minimized. The electric heater is manufactured by stacking strips (60). Each of the strips comprises corrugated strip parts (61) and flat strip parts (62). The corrugated and flat strip parts are alternately arranged.

Description

FUMES REDUCING DEVICE FOR DIESEL ENGINES AND METHOD OF MANUFACTURING THE SAME

Technical Field

The present invention relates to an exhaust gas aftertreatment device for diesel engines using an electric heater and methods of manufacturing the same. More particularly, the present invention relates to an exhaust gas aftertreatment device which is capable of burning the particulate matter(PM) contained in exhaust gas from an internal combustion engine, especially a diesel engine, so that pollutants are not discharged to the air, and a method of manufacturing the same.

Background Art

As well known to those skilled in the art, there are exhausted a large amount of hazardous particles when fuel is burned in an internal combustion engine, which generates power necessary to drive a vehicle. Especially for a diesel engine, the temperature of fuel injected into the engine is increased due to the compression work of a piston. As a result, the fuel is made autoignition, and is therefore incompletely burned. Consequently, there is exhausted a large amount of noxious pollutants (hereinafter, referred to as "PM"), such as particulate matter, nitrogen oxides(NOχ), unburned or partially burned hydrocarbons(HC), carbon monoxide(CO), and offensive aromatic substances. The fuel that is not completely burned in the combustion process of the diesel engine is discharged together with exhaust gas of the vehicle into the air. Such exhaust gases are diffused in the air, and therefore are inhaled into the lung of people, thereby causing bronchial trouble and even cancer.

Recently, such air pollution has come to the forefront as one of the problems urgently requiring a solution. Furthermore, regulation of exhaust gas discharged from vehicles has become increasingly strict in connection with environmental standards in all countries of the world.

For the aforementioned reasons, a vehicle using diesel fuel generally includes a pre-treatment device applied to an exhaust pipe thereof, through which exhaust gas is discharged to the air, or other parts thereof, for reducing a pollutant contained in exhaust gas before the exhaust gas is discharged to the air in order to prevent environmental pollution. In addition, it is inevitably required that a aftertreatment device for purifying the exhaust gas be further applied to the vehicle equipped with the diesel engine as regulations on the exhaust gas are tightened.

The aftertreatment device means a device for alternately blocking a passage of a ceramic substrate, which is principally applied to a gasoline engine, to filter solid noxious substance, such as PM, when it passes through the ceramic substrate. In the case that the ceramic filter is used for a long period of time without replacing it, however, particulate matter contained in the exhaust gas is collected beyond the receptive capacity of the filter. As a result, the back pressure of the exhaust system is increased, by which the filter is damaged or the output of the engine is lowered. In order to solve the above-mentioned problem, therefore, it is required to provide, in front oft he filter, an additional device for periodically burning and removing the collected PMs, or a catalyst for decreasing the regeneration temperature of the PMs.

As t he a foresaid P Ms b urning o r o xidizing system m ay b e u sed a s ystem for directly increasing the temperature of the exhaust gas to the temperature at which the PMs are oxidized, or a system for decreasing the temperature at which they are oxidized. The system for directly increasing the temperature of the exhaust gas directly heats the exhaust gas by means of an electric heater or a light oil burner, and the system for decreasing the temperature at which the PMs are oxidized uses a catalyst or a fuel additive.

A detailed description will now be given of a conventional exhaust gas purification system for the diesel engine equipped with an electric heater with reference to Fig. 1.

Fig. 1 is a side view showing the structure of a conventional exhaust gas purification system using the electric heater. As shown in Fig. 1, the conventional exhaust gas purification system comprises: a canister 2 provided at the middle of an exhaust pipe 1 of a vehicle and having an inlet, through which the exhaust gas is introduced into the canister 2, and an outlet, through which the exhaust gas is discharged from canister 2; a ceramic filter 3 mounted in the canister 2 and formed in the shape of honeycomb channels; and an electric heater 4 proved in front of the ceramic filter 3 for heating the ceramic filter 3 when the electric heater 4 is energized.

Around the ceramic filter 3 are arranged pressure sensors (not shown) for measuring the pressure of the gas. The pressure sensors are electrically connected to an electronic control unit (ECU) 5, which controls the electric power supplied to the electric heater 4.

In the conventional exhaust gas purification system with the above-stated construction, particulate matter contained in the exhaust gas discharged to the air through the exhaust pipe of the vehicle is collected by means of the ceramic filter 3, and the collected particulate matter is heated to a generation available temperature by means of the electric heater 4. In this way, the exhaust gas is purified.

In the canister 2 of the exhaust gas purification system are mounted sensors, including pressure sensors and temperature sensors, for sensing whether more than a prescribed amount of the particulate matter is collected by means of the ceramic filter 3. In the case that more than a prescribed amount of the particulate matter is collected by means of the ceramic filter 3 as a result of detection by means of the sensors, the electric heater 4 i s o perated b y means o f the e lectronic control unit 5 to h eat the e xhaust g as discharged from the engine up to a high temperature, for example, of approximately 500 to 700 ^°C so that the particulate matter collected by means of the ceramic filter 3 is burned and removed. As described above, the ceramic filter 3 must be heated to a high temperature of approximately 500 to 700 ^°C by means of the electric heater 4 in order to regenerate PM in the ceramic filter 3. Furthermore, such heating operation of the ceramic filter 3 by means of the electric heater 4 must be repeatedly performed while the vehicle is driven. Consequently, the electric power consumption of the conventional electric heater 4 is great.

The term "regeneration" means a process for collecting the PMs by means of the filter, burning the collected them so that the filter is restored to the state for collecting the PMs again. Therefore, the filter is regenerated (returned to its original state) but the PMs are simply oxidized. As can be understood from the above description, the supply of the electric energy t o t he c onventional e lectric h eater 4 is c ontrolled a s a w hole b y means o f the electronic control unit 5 whenever ignition and heating operations are performed. In other words, the entire ceramic filter 3 is always heated by means of the electric heater 4. Consequently, a large amount of energy may be unnecessarily consumed whenever the electric heater is operated.

Moreover, the conventional electric heater is manufactured as a single body. Consequently, the entire electric heater must be replaced even when a part of the electric heater i s damaged, which increases the cost of replacing or repairing the exhaust gas purification system.

Timing of the regeneration of the filter is determined on the basis of the back pressure from the engine or between both ends of the filter or the temperature sensors, and the electric heater is entirely energized whenever the filter is regenerated. Consequently, the durability of the electric heater may be deteriorated.

There occurs thermal load at the filter due to overheating the electric heater when the filter is regenerated. Consequently, the filter may be damaged.

Furthermore, the electric heater is operated only when the pressure of the exhaust gas is above a prescribed value. Consequently, it is impossible to predict the regeneration of the filter in a particular condition. Even when the filter is regenerated, the regeneration or collection is unevenly carried out since the amount of the fumes cannot be accurately controlled. As a result, a large amount of the collected PMs are oxidized at a time when the filter is regenerated in the case that the amount of fumes is large, whereby a lot of heat is generated. Consequently, it is difficult to thermally control the filter by means of the conventional electric heater. This is because the conventional systems' aims are not at reducing the energy consumption of the heater but at completely regenerating the filter.

In catalyzed filter system, which is one of the applications to the gas purification system, PMs are collected by means of a catalyst-coated filter disposed downstream of the exhaust gas, and then the filter is regenerated when the temperature of the catalyst-coated filter is increased to the catalytic activation temperature, for example, approximately 350 ^°C . This system has a problem in that the PMs are continuously collected without regeneration when the engine is operated at a lower temperature for a long period of time, and thus the filter is clogged or damaged due to the increase of the back pressure.

When the temperature inside the filter is increased temporarily above a prescribed temperature due to excessive collection of the PMs, the PMs are oxidized and it releases a large amount of heat, by which the filter may be damaged. Thus, there are too disadvantages in this system. One is that the PM is not oxidized at lower temperature and the other is that controlling of the regeneration time is not available.

In an exhaust gas purification system using the combination of an oxidation catalyst and a diesel filter, the oxidation catalyst is placed at ahead of diesel filters. The filters continuously collect the PMs, while the oxidation catalyst oxidizes nitric oxide (NO) contained in the exhaust gas to substitute nitrogen dioxide (NO₂).

The n itrogen d ioxide ( NO₂) o btained b y t he o xidization se rves to o xidize t he collected PMs.

In this system, it is determined whether the PMs are regenerated or not on the basis of the generated amount of nitrogen dioxide (NO₂). The generation of the nitrogen dioxide (NO₂) is mainly influenced by the temperature.

Fig. 2 shows that nitrogen dioxide (NO₂) generated in the above-mentioned system effectively reacts with PMs at a low temperature as compared to oxygen (O₂). The oxidized nitrogen dioxide (NO₂) has excellent oxidizing power, and thus the oxidized nitrogen dioxide (NO₂) can easily oxidize the PMs even at a low temperature.

However, the generated amount of the oxidized nitrogen dioxide (NO₂) is limited by the temperature of the exhaust gas and the discharged amount of nitric oxide (NO).

The oxidized nitrogen dioxide (NO₂) serves to lower the temperature at which the PMs are oxidized (approximately 650 ^°C) to approximately 250 ^°C in an atmosphere of oxygen (O₂) as shown in Fig. 2.

A conversion efficiency of nitric oxide (NO)/nitrogen dioxide (NO₂) is determined on the basis of the temperature of the oxidation catalyst disposed in front of the filter. It can be seen from Fig. 3 that the conversion efficiency of nitrogen dioxide (NO₂) is highest when the temperature of the catalyst is approximately 300°C . In other words, the conversion efficiency of nitrogen dioxide (NO₂) is deteriorated when the temperature of the catalyst is above or below 300 ^°C .

As indicated in Fig. 2, the fumes are oxidized when the temperature of the exhaust gas is between 250 and 450 °C, and the filter is not regenerated when the temperature of the exhaust gas is between 450 and 650 ^°C or below 250 ^°C . Thirdly, in an oxidation catalyst-engine control(post-injection)-fuel additive system adoptable for a common-rail injection system for diesel engines, which has been commercially used recently, the temperature of the exhaust gas is increased approximately 100^°C by means of the Diesel Oxidation Catalyst(DOC), fuel is injected again at the end of the exhaust stroke so that the temperature of the exhaust gas is increased by approximately 150 to 200 ^°C, and the temperature at which the PMs are regenerated is decreased to 450 °C by means of the fuel additive so that the PMs are regenerated. The common-rail injection system is a system for electronically controlling the injection timing and amount of the fuel as compared to the conventional mechanical injection system. Specifically, the fuel is injected only once in the course of compression and expansion, and the engine is operated by the compression temperature generated by such injection in the conventional mechanical injection system. On the other hand, post-injection is electronically performed after the fuel is burned by means of the main injection so that the temperature of the exhaust gas is increased at the end of the exhaust stroke by means of the post-injected fuel in the common-rail injection system.

In the oxidation catalyst-engine control(post-injection)-fuel additive system, however, the regeneration of the PM is not effectively performed when the temperature of the exhaust gas is below 250 ^°C .

A plurality of thin plates, which are used for manufacturing a metal substrate, are overlapped in the electric heater. A process of manufacturing the electric heater using the metal substrate is performed by alternately stacking corrugated strips with different cell sizes and joining the stacked strips. However, the junctions are not uniform, whereby the joining force is deteriorated after the braze work. Also, it is inconvenient to wind the corrugated strips, and the corrugated strips are manufactured while not only the specific resistance of the strips is not uniform but they are not uniform structurally and electrically as well. Consequently, it is difficult to practically use the electric heater.

In the case that the s ecific resistance of the strips is not uniform, excessive current passes along a part of the strips as compared to the rest of them, by which the temperature of the strips becomes non-uniform, or the temperature of the strips is partially increased. Consequently, the thermal durability is decreased at a part of the strips.

Considering the functions of a conventional electrode part and a heater mantle part, the electrode which connects the strips to a power supply, has low contact resistance, excellent insulation from the surroundings, and excellent mechanical/thermal W

durability. The mantle part, which serves to connect a ground of the power supply to the strips, should also have sufficient thermal/mechanical strength.

The conventional electrode has a very low degree of shock or vibration tolerance as compared to the electrode using a ceramic insulating material. Also, the electrode is joined with the inner mantle. Consequently, the heater must be replaced as a w hole w hen the e lectrode i s d amaged orb ro en. The m antle se rves to e lectrically connect the strips and the outside. The mantle is attached to the hot wires by means of brazing.

In this case, the corrugated strips are connected to the flat mantle. Hence, the strips and the mantle are very weak mechanically and thermally. Also, the specific resistance of the mantle cannot be easily changed on the basis of the amount of electric current passing along the hot wires.

There is further provided a radiation prevention unit or a metal substrate in addition to the electric heater in order to carry out the final assembly. At this time, there is used an insulation pin for electrically insulating the radiant heat prevention unit and the electric heater while maintaining the mechanical strengths of the radiation prevention unit and the electric heater. However, the structure of the insulation pin and thus the manufacturing process of the insulation pin are complicated with the result that the cost of the insulation pin is high when it is commercially used. Manufacturing the electric heater using the metal substrate is carried out by alternately stacking corrugated strips with different cell sizes and joining the stacked strips. However, the brazed points are not uniform, whereby the joining force is deteriorated after the braze work.

Also, the contraction rate of the strip varies when the corrugated strip is formed from a flat strip in the case that the corrugated strips with different cell sizes are stacked. Consequently, it is difficult to control the resistance of each strip.

Through the strip having a lowered contraction rate flows a large amount of electric current, whereby the temperature of the strips themselves becomes non-uniform, or the joining force at the specific parts of the strips is deteriorated. In manufacturing the metal substrate, a flat strip is supplied from a flat strip supplying unit and a corrugated strip is supplied from a corrugated strip supplying unit. The flat strip and the corrugated strip are alternately stacked and wound. At this time, the flat and corrugated strips must be simultaneously used so as to insert the flat and corrugated strips into the outer can part. Therefore, it is difficult to wind and join the flat and corrugated strips.

In the case that the flat strip is manufactured by means of gears, there is provided a p rescribed c learance b etween t he g ears. When the c learance b etween t he gears is too small, the gears and the strip may be worn. When the clearance between the gears is too large, tension at the strip supplying unit or at the strip extracting unit is decreased, whereby the strip slides. Consequently, the yield rate of the corrugated strip is deteriorated.

Furthermore, the braze work of the metal substrate is carried out after the flat and corrugated strips are prepared and wound, respectively. As a result, the junctions at the brazed parts of the strips are uniform; however, the strips must be supplied so that they are wound while constant tensions are applied to the strips. Besides, the gears or strips are worn due to the abrasion between the corrugated strip and the gears.

In manufacturing the electric heater using the metal substrate, the junctions, which are to be brazed, are non-uniform when the corrugated strips have different cell densities, and thus the strength of the strips is deteriorated when they are joined to each other.

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 exhaust gas aftertreatment device for diesel engines wherein an electric heater is not used as a main heating source but an auxiliary heating source for activating a catalyted filter or oxidation catalyst so that the thermal durability of the electric heater is improved, the operation of the engine and the state of the filter are continuously monitored so that the most appropriate regenerating system can be applied on the basis of the operation of the engine and the state of the filter, and a method of manufacturing the same.

With the electric heater, which is applied to the exhaust gas aftertreatment device for diesel engines, heat necessary to regenerate the PMs in a conventional DPF system is supplemented, whereby the purification is accomplished even at a low temperature.

Systematically, the electric heater can be used to improve a conversion efficiency of nitrogen dioxide (NO₂) at a low temperature in combination with a catalyzed filter, an oxidation catalyst and a filter. The electric heater can also be used in a DPF system for regenerating the PM by means of the post-injection of the engine so that regeneration of the PMs is accomplished even at a low temperature. Thus, the electric heater is disposed in front of a conventional catalyst (for example, an oxidation catalyst or a deoxidation catalyst) or a conventional catalyzed filter so that the electric heater can be operated below the range of the temperature at which the regeneration of the PMs is effected by means of the heat from the exhaust gas.

The e lectric h eater d oes not d irectly b urn the P Ms c ollected b y m eans o f the filter. The electric heater is operated only when the activation energy of the catalyst is insufficient. Consequently, only the catalyst is operated at the temperature at which the conventional catalyst is activated.

Structurally, the electric heater is divided into a plurality of segments such that electric energy is effectively supplied to the segments of the electric heater on the basis of the amount of the collected PMs. Consequently, unnecessarily wasted energy is reduced when the electric heater is operated, and the damaged part of the electric heater can be replaced without replacing the entire electric heater when the electric heater is out of order.

When the electric heater is operated, the temperature of the exhaust gas is increased to the temperature for activating the catalyst, which is different from the conventional electric-heating system.

The collected PMs are regenerated on the basis of synthetic determination of the information obtained from the filter and the engine.

The control unit serves to monitor regeneration process in general and to operate the electric heater while no thermal load is applied to the fllter.

It is another object of the present invention to provide a method of manufacturing an electric heater comprising a step of forming strips by means of a jig, thereby solving the problem that the yield rate of the above-mentioned device is decreased due to the change in length and shape of the strips deformed during brazing. It is another object of the present invention to provide an electric heater wherein a mantle of the electric heater has easily changeable specific resistance, mechanical strength at the junctions between the mantle and strips is excellent, and insulation from a radiant heat prevention unit is excellent. It is yet another object of the present invention to provide the corrugated structure of metal substrate so that joining strength between the strips is increased when the metal substrates are brazed.

Especially, the electric heater with joining force more excellent than the conventional electric heater can be manufactured using the method of the present invention when it is applied to the electric heater using the metal substrate as well as the metal substrate.

In a ccordance w ith t he p resent i nvention, the a bove a nd o ther o bj ects c an b e accomplished by the provision of a exhaust gas aftertreatment device for diesel engines, which regenerates PMs by means of a catalyst, wherein an electric heater for spatially non-uniformly distributing thermal capacity is attached to at least one catalyst unit for activating a catalyst or improving a conversion efficiency of nitric oxide (NO)/nitrogen dioxide (NO₂) at a low temperature.

According to the present invention, the electric heater is disposed in front of a catalyst or catalyzed filter of an exhaust pipe of a vehicle for heating the catalyst to the temperature at which the catalyst is activated when particulate matter of the exhaust gas collected by means of the filter is regenerated using the catalyst under the control of an electronic control unit.

Distributing the thermal capacity spatially non-uniformly is supplying heat energies having different thermal capacities to segmented areas on the basis of the sectional center of the inside of the exhaust pipe.

The catalyst unit comprises an oxidation catalyst and a catalyzed filter.

The electric heater is divided into a center segment and a surrounding segment. The surrounding segment comprises a plurality of segment parts, which are arranged radially around the center segment. To the respective segments is supplied electric current continuously or selectively so that the PMs collected at the segments are burned.

The r atio o f t he c enter se gment a nd the su rrounding se gment in t erms o f the radius is preferably approximately 0.6 : 0.4, and the ratio of the center segment and the surrounding segment in terms of the electric current supply to the respective segments is preferably approximately 0.8 : 0.2.

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 is a side view showing the structure of a conventional exhaust gas purification system equipped with an electric heater;

Fig. 2 is a graph showing PMs regeneration rates in atmospheres of oxygen (O₂) and nitrogen dioxide (NO₂);

Fig. 3 is a graph showing a conversion efficiency of nitrogen dioxide (NO₂) on the basis of the temperature of exhaust gas; Fig. 4a is a front view of a series-type electric heater showing the structure of heating elements thereof;

Fig. 4b is a side view of the series-type electric heater showing the structure of the heating elements thereof;

Fig. 4c is another front view of the series-type electric heater showing the structure of the heating elements thereof;

Fig. 5a is a front view of a parallel-type electric heater showing the structure of heating elements thereof;

Fig. 5b is a side view of the parallel-type electric heater showing the structure of the heating elements thereof; Fig. 5c is another front view of the parallel-type electric heater showing the structure of the heating elements thereof;

Fig. 6a is an equivalent circuit diagram showing respective electrodes of the series-type electric heater electrically connected to a power supply;

Fig. 6b is an equivalent circuit diagram showing respective electrodes of the parallel-type electric heater electrically connected to a power supply;

Fig. 7 is a side view_s in section, of a conventional exhaust gas purification system equipped with an electric heater of the prior art;

Fig. 8 is a side view, in section, of an exhaust gas purification system equipped with an electric heater of the present invention, which is applied to a catalyzed filter; Fig. 9 is a side view, in section, of an exhaust gas purification system equipped with an electric heater of the present invention, which is applied to an oxidation catalyst and a catalyzed filter;

Fig. 10 is a side view, in section, of an exhaust gas purification system equipped with an electric heater of the present invention, which is applied to an oxidation catalyst and a filter;

Fig. 11 is a conceptional view showing an apparatus for manufacturing a strip according to the present invention; Fig. 12 is a schematic view showing a process of stacking strips;

Fig. 13 is a view showing conventional stacked strips; Fig. 14 is a view showing strips stacked according to the present invention; Figs. 15a and 15b are conceptional views showing another apparatus for manufacturing a strip according to the present invention; Fig. 16 is a view showing the maximum and minimum values of clearance between gears;

Fig. 17a is a graph showing the clearance on the basis of phases; Fig. 17b is a view showing corrugation formed by the change of the clearance; Figs. 18a to 18d are views showing amplitude adjustment of the corrugation on the basis of clearances a and b, respectively;

Fig. 19 is a graph showing the change of specific resistance on the basis of the amplitudes;

Fig. 20a is an exploded perspective view of a separable heater showing heating elements of the electric heater and a jig for accommodating the hot wires; Fig. 20b is an assembled perspective view of the separable heater showing the heating elements accommodated in the jig;

Fig. 20c is a partially enlarged view of the jig; Fig. 20d is a partially enlarged view of the strips shown in Fig. 20a; Fig. 21 is an assembled perspective view of a single electric heater showing a heating element accommodated in a jig;

Fig. 22a is an assembled perspective view of a separable electric heater showing heating elements accommodated in a jig;

Fig. 22b is an enlarged view of the C portion shown in Fig. 22a; Fig. 22c is an enlarged view of the D portion shown in Fig. 22b; Fig. 22d is a view showing the assembly of the ends of the heating elements and mantles;

Fig. 23 is an assembled perspective view of imier and outer mantles of the electric heater; Fig. 24a is a perspective view of an electrode;

Fig. 24b is a perspective view illustrating the assembly operation of the electrode;

Fig. 24c is a view showing an electrode according to a first preferred embodiment of the present invention;

Fig. 24d is a view showing an electrode according to a second preferred embodiment of the present invention;

Fig. 25 a is an exploded perspective view illustrating the assembly operation of the accommodated heating elements, the mantles, and the electrodes; Fig. 25b is an assembled perspective view of the accommodated heating elements, the mantles, and the electrodes;

Fig. 26a is an exploded perspective view illustrating the assembly operation of the inner and outer heating elements and the mantles by means of connection pins;

Fig. 26b is an assembled perspective view of the inner and outer heating elements and the mantles, which are connected by means of connection pins;

Fig. 27a is an exploded perspective view showing a socket and a socket rest;

Fig. 27b is an assembled perspective view showing the heating elements connected to each other by means of the socket;

Fig. 28a is a view of an insulation pin according to a first preferred embodiment of the present invention;

Fig. 28b is a view of an insulation pin according to a second preferred embodiment of the present invention;

Fig. 28c is a view of an insulation pin according to a third preferred embodiment of the present invention; Fig. 28d is a view of an insulation pin according to a fourth preferred embodiment of the present invention;

Fig. 28e is a view of an insulation pin according to a fifth preferred embodiment of the present invention;

Fig. 28f is a view of an insulation pin according to a sixth preferred embodiment of the present invention;

Fig. 29a is an exploded perspective view illustrating the assembly operation of a radiant heat prevention unit and an electric heater assembly; Fig. 29b is an assembled perspective view of the radiant heat prevention unit and the electric heater assembly;

Fig. 30a is an exploded perspective view illustrating the assembly operation of a part of the electric heater and an outer can part; and Fig. 30b is an assembled perspective view of the part of the electric heater and the outer can part.

Best Mode for Carrying Out the Invention

Now, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Referring to Figs. 4a to 4c, which show the structure of an electric heater, the center heater part of the electric heater is energized tlirough an anode, and the surrounding heater parts of the electric heater are selectively energized through cathodes 121, 122, 123 and 124, so that the center heater part and at least one of the surrounding heater parts are simultaneously operated. As described above, the electric heater comprises the center heater part and the surrounding heater parts surrounding the center heater part. Consequently, one or more heater parts are operated when necessary.

To the electric heater is securely fixed a radiant heat prevention unit by means of insulation pins 171 and 172. The radiant heat prevention unit is disposed in front of the electric heater for preventing the radiant heat from the electric heater in the case that it is not catalyst- coated. The radiant heat prevention unit is disposed in the rear of the electric heater, and serves as an oxidation catalyst that is activated by means of the heat from the electric heater in the case that it is catalyst-coated. Referring to Fig. 6a, which shows the electric structure of a series-type electric heater, electric current flows from Vcc to SI, S2, S3 and S4. Consequently, R1+R2, R1+R3 ... are successively heated when the electric heater is operated. Alternatively, R1+R2+R3, R1+R2+R3+R4, or R1+R2+R3+R4+R5 may be heated. In other words, the electric heater can be operated on the basis of the condition of the engine or the filter. Referring to Fig. 6b, which shows the electric structure of a parallel-type electric heater, electric current flows from Vcc to SI, S2, S3, S4, and S5. Consequently, R1+R2, R1+R3 ... are successively heated when the electric heater is operated.

Regardless of how the electric heater is operated, it is preferable that the center segment of the electric heater is concentrically heated. This is because the flow of the exhaust gases in the exhaust pipe, which is interpreted as a Newton fluid, is concentrated to the center segment of the electric heater.

The present invention is characterized by the device for accomplishing the regeneration of the PMs using the electric heater with the above-stated construction even at the regions where the aforesaid regeneration is not carried out. According to the present invention, the system basically c omprises the electric heater and the catalyzed filter.

The regeneration is accomplished considering the state of the engine in addition to the temperature and back pressure of the exhaust gas.

The construction of the system, to which the electric heater is applied, is indicated in Table 1. The comparison is made in terms of the range of the regeneration temperature.

[Table 1] Comparison of the range of the regeneration temperature of the respective systems

In System A, which basically comprises the oxidation catalyst and the filter, the PMs are oxidized using the nitrogen dioxide (NO₂) generated by means of the oxidation catalyst as an oxidizing agent.

According to System A, the degree of the regeneration is determined on the basis of the amount of the nitrogen dioxide (NO₂), and the conversion efficiency of the nitrogen dioxide (NO₂) by means of the oxidation catalyst is the highest at the temperature of the exhaust gas of 250 to 450 "C . Consequently, the PMs are oxidized at the temperature mentioned above.

On this account, there is needed an additional heating source for supplying heat necessary to increase the conversion efficiency of the nitrogen dioxide (NO₂) so that the PMs are oxidized at a low temperature, i Embodiment 1, therefore, the electric heater is used to activate the oxidation catalyst at a low temperature so that the conversion efficiency of the nitrogen dioxide (NO₂) is increased. Consequently, the PMs can be oxidized even at the low temperature in Embodiment 1.

In System B, which regenerates the PMs only using the catalyzed filter, the PMs are oxidized when the temperature of the exhaust gas is approximately 350 ^°C . In Embodiment 2, the electric heater is applied to System B. The electric heater is used to activate the catalyst at a low temperature. Consequently, the PMs can be oxidized even at the low temperature in Embodiment 2.

In System C, which basically comprises the fuel additive, the oxidation catalyst, and the filter, the PMs are reduced at the temperature of the exhaust gas of above 250 ^°C . In Embodiment 3, therefore, the PMs can be oxidized using the electric heater.

The above-stated embodiments will now be described in more detail with reference to the accompanying drawings. Fig. 7 shows an exhaust gas purification system equipped with a conventional electric heater 4. As shown in Fig. 7, the electric heater 4 is disposed in front of the filter 9. Consequently, the fumes collected by means of the filter 9 are regenerated only by means of the heater 4.

The reference numeral V indicates a mat, which is used to keep the fllter 9 warm, and the reference numeral 20 indicates a clamp, which is used to fix the electric heater 4.

Fig. 8 shows Embodiment 1 in which the electric heater 4 of the present invention is attached to a catalyzed filter system. As shown in Fig. 8, the electric heater 4 of the present invention is disposed in front of a catalyzed filter 8. In front of the electric heater 4 is disposed a radiant heat prevention unit 10 for shielding the radiant heat from the electric heater.

As described above, the electric heater 4 is used only to activate the catalyzed filter 8. That is to say, the electric heater 4 is not used in the total range of the operation of the engine. Consequently, Embodiment 1 i s very useful because of the fact that energy consumption is reduced.

Fig. 9 shows Embodiment 2 in which the electric heater 4 of the present invention is applied to the oxidation catalyst and the catalyzed filter. In Embodiment 2, nitric oxide (NO) is oxidized by means of the oxidation catalyst 7 to obtain nitrogen dioxide (NO₂). The PMs are regenerated using the nitrogen dioxide (NO₂) as an oxidizing agent by means of the catalyzed filter 8. The electric heater 4 is used only to activate the catalyzed filter 8. In this case, a metal substrate, which is used as a radiant heat prevention unit disposed in front of the electric heater, is coated with the oxidation catalyst. Consequently, the oxidation catalyst is not additionally required.

Fig. 10 shows Embodiment 3 in which the electric heater 4 of the present invention is applied to a system comprising the oxidation catalyst 7 and the filter 9.

The electric heater 4 is used to supply heat to the oxidation catalyst 7 so that the nitric oxide (NO) is converted into the nitrogen dioxide (NO₂) by means of the oxidation catalyst.

In this case, the metal substrate is coated with the oxidation catalyst 7, which is disposed in the rear of the electric heater 4.

The above embodiments of the present invention have different power consumption of the heating source and the different operating methods as compared to the conventional regeneration system using the electric heater. Consequently, the regeneration may be accomplished on the basis of the state of the engine and the filter. According to the present invention, the PMs are oxidized on the basis of five states, which are indicated in Table 2.

State 1 is a low speed/high load state, h this state, the engine torque is below 1800 rpm, and the engine load rate is 70 to 100%. Also, the temperature of the exhaust gas from the engine is high, and the back pressure (pressure of the exhaust gas) is low. In State 1, the temperature is above at which the catalyst is activated. As a result, the electric heater is not basically operated, and therefore the PMs are regenerated by means of the catalyst disposed in the rear of the electric heater.

State 2 is a low speed/low load state. In this state, the engine torque is below 1800 φm, and the engine load rate is 0 to 30%. Also, the back pressure rate (the current back pressure/the highest pressure x 100) is at least below 30. hi State 2, the temperature of the exhaust gas from the engine is low, and the back pressure is low. Consequently, the electric heater is used as an additional heating source for heating the catalyst. The electric heater is smoothly operated since the flow rate of the exhaust gas is low. The e lectric h eater b asically h eats t he c atalyst t o t he t emperature a t w hich t he catalyst is activated, not directly combusting the PMs.

State 3 is a middle speed/high load state. In this state, the engine torque is 1800 to 3500 rpm, and the engine load rate is 70 to 100%. Also, the temperature of the exhaust gas is high, and the back pressure is medial.

Consequently, the electric heater is not basically operated in this state. The PMs are regenerated by means of the catalyst disposed in the rear of the electric heater.

Since the back pressure is basically medial, the electric heater may be auxiliarily used when the amount of the PMs is large or the combustion of the PM is not smoothly performed due to the temperature of the exhaust gas.

The flow rate of the exhaust gas is medial, and thus the R1+R2 heating is basically used. If necessary, the temperature of the heating source may be increased to the R1+R2+R3 heating. State 4 is a middle speed/load state, hi this state, the engine torque is 1800 to

3500 rpm, and the engine load rate is 30 to 70%>. Also, the temperature of the exhaust gas is medial, and the back pressure is medial.

In this state, the electric heater is auxiliarily used since the catalyst is not activated, and the flow rate of the exhaust gas is medial. Since the flow rate of the exhaust gas is medial, the R1+R2 heating is basically used. If necessary, the temperature of the heating source may be increased to the R1+R2+R3 heating.

State 5 is a high speed/low load state. In this state, the engine torque is above 3500 φm, and the engine load rate is 0 to 30%>. Also, the temperature of the exhaust gas is medial, and the back pressure is very high.

In t his s tate, i t i s v ery difficult to e ombust the PMs by m eans o f a ny existing catalysts, and the back pressure is very high. Consequently, the filter may be damaged unless the PMs are immediately combusted in State 5.

The electric heater of the present invention has a very high flow rate, and thus a large amount of energy is used when the electric heater is operated.

Consequently, the electric heater is operated such that Rl, R2, R3, R4 and R5 are simultaneously heated in this state, whereby the fumes are effectively combusted with the maximum heat capacity.

In the regeneration of the PMs in the respective states, the operation of the engine and the state of the filter are basically monitored, and the timing of the operation of the electric heater and the amount of electric current to be applied are determined on the basis of the monitored data.

Once the timing and the period of the regeneration are determined by means of the electronic control unit, the temperature and the back pressure between both ends of the filter are monitored to determine whether the regeneration is to be performed. The electric heater is operated again if necessary. When the back pressure of the engine is suddenly increased or it is determined that the regeneration is not smoothly performed by means of the catalyst, the electric heater is operated even before the regeneration timing of the PMs so that the activation of the catalyst is accelerated. In this way, the PMs are oxidized.

Consequently, the regeneration of the PMs is avoidable when the PMs are excessively collected since a prescribed amount of the PMs are always collected and oxidized according to the present invention. ^' The construction of hot wires constituting the electric heater will now be described in detail. The heating elements are constructed by stacking several strips in various forms. For example, the heating elements may be constructed as shown in Figs. 18a to l8d.

However, the conventional heating elements are generally manufactured by alternately stacking and joining corrugated strips with different cell sizes. As a result, the junctions are not uniform.

According to the present invention, there is provided a strip 60 c omprising a corrugated strip part 61 and a flat strip part 62 wherein the corrugated strip part 61 and the flat strip part 62 are alternately arranged so that the junctions are uniform when the strips are joined.

Between the corrugated part and the flat part of the strip may be provided an offset of a prescribed length.

When the strips each formed by alternately arranging the corrugated strip part and the flat strip part are stacked, the upper strip is stacked on the lower strip in such a manner that the corrugated strip part is formed at one side of each of the upper and lower strips, and the flat strip part is formed at the other side of each of the upper and lower strips.

In order to solve the above-mentioned problem, the corrugated strip part and the flat strip part are alternately formed at a constant rate. Preferably, the rate of the corrugated strip part and the flat strip part is approximately 1 : 1.

Also, the offset is provided between the corrugated strip part and the flat strip part to avoid the interference between the corrugated strip part and the flat strip part when the strips are wound. The offset may be changed on the specification of the corrugated strip part.

With the strip as described above, it i s possible to reduce the cell density as compared to the case that only the corrugation is used.

According to the present invention, the corrugated strip part per a unit length is relatively small since the flat strip part is further provided. Consequently, wear of the strip is minimized, and thermal efficiency and flow efficiency are improved.

The wear of the strip will be described in more detail. The strip is generally manufactured by means of gears. The flat strip is supplied from a flat strip supplying unit, and passes through the gears so that the strip is corrugated. When the strip is corrugated, the strip is drawn by means of the gears at a constant tension, on the basis of which the flat strip supplying unit supplies the flat strip while a constant force is applied to the flat strip.

At this time, there occurs friction between the gears and the strip. When the tension is excessive, the gears and the strip are worn due to severe friction between the gears and the strip. As a result, it is required to replace the gears periodically. When the friction is excessive, the cell density may be changed.

According to the present invention, however, the corrugated strip part is not more than a half of the total length (including offset). Consequently, the friction may be reduced by not more than half.

When the electric heater is manufactured using the strips as described above, the area of the junctions is uniformly maintained as compared to the case that the strips with different cell densities are supplied.

Consequently, the present invention has an effect of minimizing the thermal stress due to the local excess of the electric current, which is caused because of the non- uniformity of the cell density.

When the strip is formed, the gears may be changed or cams may be applied to the shafts for driving the gears.

An apparatus for manufacturing the strip comprises: a driving source; a transferring unit operated by means of power from the driving source for transferring a strip material; and at least two gears having gear teeth formed at prescribed parts of the outer c ircumference t hereof, w herein c orragated strip p arts a nd the flat s trip p arts a re alternately formed at the strip material by means of the gear teeth of the gears.

Another apparatus for manufacturing the strip comprises: a driving source; a transferring unit operated by means of power from the driving source for transferring a strip material; at least two gears rotatably engaged with each other for forming corrugation at the strip material; and cams fitted on the shafts of the gears and rotated along with the shafts of the gears for adjusting the clearance between the gears. Fig. 11 shows an apparatus for manufacturing the strip. As shown in Fig. 11, each of the gears has gear teeth partially formed on the outer circumference thereof so that the supplied strip material is formed. Specifically, each of the gears has several parts at which the gear teeth are formed and several parts at which the gear teeth are not formed, and the parts at which the gear teeth are formed and the parts at which the gear teeth are alternately arranged.

In front of the gears is disposed a transferring unit, which comprises transferring rollers 70 and 80 as shown in Fig. 11.

The torque necessary to operate the transferring rollers 70 and 80 is supplied from a driving source 90.

In the strip formed as shown in Fig. 11, the part C indicates a corrugated strip part, the part A indicates a flat strip part, which is not corrugated, and the part B indicates an offset part, by which the corrugated strip part and the flat strip part do not interfere with each other when the strips of the present invention are stacked. A plurality of strips, each of which is formed as shown in Fig. 11, are stacked and joined to each other in such a manner that the corrugated strip parts are joined to the flat strip parts as shown in Fig. 12.

At this time, the value of the offset may be changed considering the cell density and the depth of the gear in order to accomplish total harmony. Fig. 13 is a view showing a metal substrate manufactured by the conventional method.

Fig. 14 is a view showing a metal substrate manufactured using the strip of the present invention.

It can be seen from Fig. 14 that the cell density is increased when the gears with the same height are used. Also, the junctions are very uniform.

Furthermore, the wear of the gears and the strip per a unit length can be reduced to below half when a strip is manufactured.

When the electric heater is manufactured using the strip as described above, uniform junctions are guaranteed as compared to the stacked strips having different cell densities. Also, the specific resistance per a unit length is constant. Consequently, the thermal stress due to the local excess of the electric current is minimized.

Figs. 15a and 15b show another apparatus for manufacturing the strip according to the present invention. As shown in Figs. 15a and 15b, cams are provided at both ends of the gears so that the strip is formed on the basis of the shapes of the cams, which is different from the method of forming the strip by means of the gears as shown in Fig. 11.

As shown in Figs. 15 and 15b, two gears 23 and 24 are provided in the center of the apparatus for manufacturing the strip according to the present invention. A cam 22 is disposed at both ends of one of the gears or at both ends of its driving shaft, and a rotating plate 21 is disposed at the both ends of the other gear or at both ends of its driving shaft. The rotating plate 21 is rotated while it comes into contact with the cam 22. The strip is deformed by means of the gear teeth formed at the gears 23 and 24.

Consequently, the clearance between the gears may be changed from the minimum clearance distance a to the maximum clearance distance b on the basis of the operation of the cam 22, as shown in Fig. 16.

When the strip passes between the gears while the clearance between the gears are changed, the amplitude of the corrugation is changed. The amplitude of the corrugation is changed on the basis of the shape of the cam, as shown in Figs. 17a and 17b.

In Fig. 17a, the reference letter e indicates the clearance.

With the clearances a and b, the strip can be formed as shown in Figs. 18a to 18d.

When the clearance a is equal to the clearance b, the strip can be formed identically to the conventional metal substrate. Furthermore, the total amplitude may be adjusted by changing the absolute amounts of the clearances a and b.

When the clearance a is larger than the clearance b, the strip can be formed as shown in Fig. 18c. This strip can be used for the electric heater and the metal substrate, and the junctions of the strip are uniform.

Especially when the clearance b is zero (b = 0), the strip is partially corrugated and partially flat. Consequently, the strip as shown in Fig. 11 can be obtained.

When the e lectric h eater i s m anufactured u sing the m etal su bstrate, i t i s v ery important to control the total specific resistance.

When the c learance b etween t he g ears is 1 arge a s sh own in F ig. 1 9, the total length of the strip is increased. Consequently, the resistance can be controlled by simple adjustment of the clearance without cutting the strip or adjusting the length of the strip since the value of the resistance is in proportion to the length of the strip.

A method of manufacturing the electric heater, which is formed by stacking the strips, for purifying exhaust gas from a vehicle, is characterized by a step of inserting the strips into a jig having prescribed shapes formed therein. The jig 310 is preferably made of a metal or a ceramic. The jig further has at least one mantle insertion hole, through which at least one mantle for supplying electric current to the strip is inserted. At the edge of the walls of the heating element insertion holes and the mantle insertion hole are formed notches.

The strips are stacked to manufacture the electric heater, which is used in the exhaust gas purification system for vehicles. Specifically, the strip is formed in such a manner that the strip is divided into an inner strip part and an outer strip part. An inner mantle part and an outer mantle part of the mantle, to which electric current is supplied by means of electrodes, are connected to the inner and the outer strip parts. A radiant heat p revention u nit is integrally d isposed o n the m antle a nd t he s trip. As d escribed above, the mantle is preferably divided into at least two mantle parts.

The end of the strip, at which the flat strip part of a prescribed length is formed, is fixed to the mantle by means of a fixing unit. The strip is placed in such a manner that the height of the strip inserted into the mantle is changed to eliminate the interference between the electrode and the heating element so that the specific surface area is increased. The electrode comprises an electrode rod having a bolt tap formed at one end thereof, by which the electrode rod is attached to the mantle, and an electrode ring containing a ceramic therein and securely fitted on the electrode rod. The fixing of the mantle and the strip is accomplished by means of brazing. Alternatively, the fixing of the mantle and the strip may be accomplished by means of the combination of a socket rest formed at a prescribed area of the strip and a socket inserted into the socket rest while the socket comes into contact with the mantle, or otherwise by means of a joining pin. The radiant heat prevention unit is mounted by means of an insulation pin so t hat the r adiant h eat p revention u nit i s e lectric ally i nsulated from t he s trip a nd t he mantle. The length of the mantle for an anode is smaller than the length of the mantle for a cathode. On the outer circumference of the electrode rod, on which the electrode ring is fitted, is formed at least one groove. The insulation pin is inserted through a though-hole of a cylindrical ceramic member. Alternatively, the insulation pin may be divided into two insulation pin parts, which are disposed in the ceramic member while they are spaced apart from each other.

The electric heater of the present invention is used in the exhaust gas purification system for vehicles. The metal strips, each of which is made of a thin plate, are stacked in such a manner that the corrugated and flat strips are alternately stacked. Heating elements obtained from the stacked strips are coated with a solvent or a filler formed in the shape of a sheet. The radiant heat prevention unit is disposed on the heating elements, and the brazing operation is carried out in a vacuum furnace.

In the case of the separable electric heater for independently controlling the inner and outer thermal capacities, there are provided at least two separate heater parts.

Specifically, the separable electric heater is divided into the center segment and the surrounding segment. The center segment is separated from the surrounding segment by means of the mantle. The electrode and the mantle are used to supply electric current between the hot wires so that the electric current flows along the hot wires. The number of the electrodes and the mantles is provided corresponding to the number of the separate heating segments. The heating elements are attached to an outer can part, whereby the total mechanical/thermal strength is increased.

A method of manufacturing the electric heater with the above-stated construction comprises the steps of: stacking strips formed by alternately arranging corrugated and flat strip parts; forming the stacked strips in a prescribed shape; connecting mantles and electrodes to the strips of the prescribed shape; applying a bonding agent to the strips and the mantles; mounting a radiant heat prevention unit on the strips and the mantles; and brazing all the components.

In the step of forming the stacked strips in the prescribed shape, it is difficult to form the stacked strips in the prescribed shape while maintaining constant gap distances. For this reason, there is used a jig having hot wire insertion holes of prescribed shapes formed therein according to the present invention.

It is required that the jig be usable repeatedly. Consequently, the jig is preferably made of a metal or a ceramic. In the case that the jig is made of the metal, there may be applied a ceramic coating after the brazing in order to prevent sticking between the mantles and the jig or the strips and the jig.

In the jig, it is provided at least one mantle insertion hole, into which the mantle electrically connected to the strip for supplying electric current to the strip.

The mantle insertion hole is formed at the outside of the strip so that the mantle is inserted into the mantle insertion hole while the mantle applies some quantity of tight- contact force to the strip. In the case that the strip or the mantle is inserted into the jig, the strip or the mantle may crash into the corner wall of the stacked strip insertion hole or the mantle insertion hole. Consequently, it is preferable that notches are formed at the edge of the walls of the strips insertion hole and the mantle insertion hole.

When the electric heater is manufacture as described above, the mantle is formed in such a manner that the mantle is divided into at least two mantle parts.

The length of the mantle for the anode is smaller than the length of the mantle for the cathode.

As described above, the end of the strip, at which the flat strip part of a prescribed length is formed, is fixed to the mantle by means of the fixing unit. In the conventional method, the end of the stacked strips, which is corrugated, is fixed to the mantle with the result that the fixing force between the strip and the mantle is decreased after the electric heater is repeatedly used.

According to the present invention, the end of the heating elements, which is not corrugated but flat, is fixed to the mantle. Consequently, the fixing force between the heating element and the mantle is improved, and thus the fixing force between the heating element and the mantle is not decreased even after the electric heater is repeatedly used. The corrugated end of the strip is easily and securely fixed to the mantle, whereby the fixing between the strip and the mantle is not loosened or unfastened when the vehicle vibrates. The electrode is connected to the mantle so that electric current is supplied to the strip. At one end of the electrode rod of the electrode is formed the bolt tap, by which the electrode rod is attached to the mantle. The electrode ring of the electrode is fitted on the outer circumference of the electrode rod.

The electrode rod is attached to the mantle for comiecting the heater part to the power supply. It is required that the heating element is electrically insulated from the ground of the engine. Since heat is applied repeatedly to the electrode rod, it is required that the electrode rod have excellent thermal characteristics.

The electrode ring is filled with a ceramic, and on the outer circumference of the electrode rod, on which the electrode ring is fitted, are formed grooves, by which the thermal and electrical characteristics of the electrode ring are improved.

The surface area of the mantle is increased to reduce the contact resistance between the heating element and the mantle. The position where the electrode and the mantle are joined to each other is freely changeable. Also, the structural change of the mantle is accomplished by changing the height of the mantle when the capacity of the electric heater is to be changed.

Furthermore, the height of the strip inserted into the mantle is changed to eliminate the interference between the electrode and the strip so that the specific surface area is increased. Consequently, it is possible to increase the wound number of the strip per a unit area.

The fixing of the mantle and the strip is accomplished by means of brazing, the socket, or the joining pin.

The brazing is carried out in the vacuum furnace. Alternatively, t he fixing o f t he m antle a nd the strip m ay b e a ccomplished b y means of the combination of the socket rest formed at a prescribed area of the strip and the socket inserted into the socket rest while the socket comes into contact with the mantle.

The assembly of the strip and the mantle is mounted to the radiant heat prevention unit by means of the insulation pin. As described above, the insulation pin is inserted through the though-hole of the cylindrical ceramic member. Alternatively, the insulation pin may be divided into two parts, which are disposed in the ceramic member while they are spaced apart from each other.

The insulation pin is provided between the radiant heat prevention unit and the mantle for insulating the radiant heat prevention unit from the mantle, maintaining the mechanical strength between the radiant heat prevention unit and the mantle, and maintaining the entire shape. The insulation pin is preferably made of the combination of a ceramic and a metal. The insulation pin of the present invention is used to maintain the clearance between the radiant heat prevention unit and the mantle as well as the mechanical strength between the radiant heat prevention unit and the mantle.

Fig. 20a shows a heating element for a center segment 301, hot wires for surrounding segment 302, and a jig 310 according to a preferred embodiment of the present invention, which are used when the separable electric heater is manufactured. The structure of the heating element is formed in such a manner that the strips with different cell densities are stacked or the strips with constant periods are stacked as indicated in the enlarged parts A and B of Fig. 20a.

The manufactured jig is provided with the strips insertion holes, an inner mantel insertion hole 304, and an outer mantle insertion hole 303, whereby the mantle and the electrode can be assembled into the jig.

Also, between the inner heating element insertion holes and the outer heating element insertion h oles are d isposed c learance maintaining p arts 3 05 for p reventing a short circuit between them when the electric heater is mounted to the engine. Fig. 20b shows the heating element of the electric heater accommodated in the jig- Fig. 20c is a partially enlarged view of the jig 310. At the upper edge of the wall surface of the strip insertion holes or the mantle insertion hole is formed a notch 306 as shown in Fig. 20c. The notch 306 is provided to easily insert the strip. Fig. 20d, which is a partially enlarged view of the strip, shows one example of the processes for stacking the strip.

Usable heating elements include strips with different cell densities, amplitudes and periods. Especially when the strips with different cell densities are stacked, a corrugated part 311 having low density and a corrugated part 312 having high density are alternately stacked. When the strips with different periods are stacked, the strips are stacked while only the phases thereof are changed. The strips have different metal joined parts of different types, respectively.

Fig. 21 is an assembled perspective view showing a jig used when a single electric heater is manufactured and strips inserted in the jig. The process of manufacturing the single electric heater is similar to the process of the manufacturing the separable electric heater except that the number of the mantles of the single electric heater is different from the number of the mantles of the separable electric heater.

Fig. 22a is an assembled perspective view of a separable electric heater showing strips accommodated in a jig, Fig. 22b is an enlarged view of the C portion shown in Fig. 22a, Fig. 22c is an enlarged view of the D portion shown in Fig. 22b, and Fig. 22d is a view showing the assembly of the ends of the hot wires and mantles.

Generally, the corrugated strips 311 and the 312 are directly attached to the mantles. According to the present invention, the end of the strips, at which the flat strip part 314 of a prescribed length is formed, is fixed to the mantle by means of a bolt 327.

Fig. 23 shows the mantles used in the present invention. As shown in Fig. 23, inner mantles are divided into an inner mantle 320 for an anode and an inner mantle 321 for a cathode. In the case of the separable electric heater, the length of the inner mantle for the anode is smaller than the length of the inner mantle for the cathode. In the inner mantle 320 for the anode is inserted an electrode, by means of which the inner mantle 320 is connected to the power supply. The inner mantle 321 for the cathode is connected with the hot wires.

Around the inner mantles are disposed one or more outer mantles 322, which are connected to the electrodes, respectively.

Figs. 24a to 24d respectively show an electrode used in the present invention. At the part of an electrode rod 330, which is filled with a ceramic, are formed grooves, as shown in Fig. 24a, so that the thermal and electrical characteristics of the electrode rod due to the ceramic are improved. At the p art of the electrode rod 330, which is connected to the mantle, is disposed a bolt tap 335, by which the contact resistance is minimized when the electrode rod is connected to the mantle.

As shown in Fig. 24b, the electrode rod 330 is filled with a ceramic 333, which is an insulating material. On the outer circumference of the electrode 330 is fitted an electrode ring 336, which is c onnected to an o uter c an. The c urrent flows along the electrode rod 333, which is an inner part of the electrode, and the electrode ring, which is an outer part of the electrode, is connected to the outer can. The ceramic material serves to insulate the electrode rod 330 and the electrode ring 336 from each other.

Fig. 24c is a sectional view of the electrode shown in Fig. 24b, and Fig. 24d shows another embodiment of the electrode. As shown in Fig. 24d, the insulating ceramic layer 333 is extended to the assembled part or fixed part, whereby breakdown of the insulation is prevented in the course of assembly or fixing.

Fig. 25 shows the assembly of the stacked strips, the mantles, and the electrodes according to the processes as shown in Figs. 20 to 24. The mantles 320, 321 and 322 are inserted into the jig 310 so that the mantles are constantly connected to prescribed positions of the jig 310. Firstly, the inner mantles 320 and 321 are prepared as shown in Fig. 23. The electrode rod prepared as shown in Fig. 24b is connected to the mantle by means of a metal joining or the bolt 332.

Especially, it is required that the outer mantle 322 be electrically insulated when the electrodes are inserted into the inner mantles.

Also, the position of the electrode rod and the position of the joined parts of the strips may be changed so that the specific surface area of the mantles is increased. The width of the strips can also be freely adjusted without great change to the mantles. Fig. 26 sh ows the fixing o f the m antles and the strips. The i nner o ne c ome into direct contact with the mantles so that they are connected to each other by means of brazing. The connection between the inner strip and the outer strip is carried out using several joining pins 315. By means of the joining pins 315, the inner mantles are connected to the inner strips, and the outer mantles are connected to the outer mantles. When the heating element are to be replaced due to the disconnection, they may be fixed to the mantles by means of a socket 340 and a socket rest 341 as shown in Figs. 27a and 27b. At this time, the socket 340 is fixed by means of the socket rest 341.

When the socket is used, it is required to minimize the contact resistance between the socket and the mantles considering the metal characteristics of the socket and the mantles.

After the above-mentioned assembly, to the assembled heater part is mounted a radiant heat prevention unit 373. At this time, it is required that the radiant heat prevention unit 373 is electrically insulated from the heating elements as well as the consideration of the mechanical strength of the radiant heat prevention unit. Figs. 28a to 28f respectively show insulation pins according to various preferred embodiments of the present invention.

Referring to Fig. 28a, an insulation pin 362, which has a square section, is inserted in a hole 361 formed at either end of a circular ceramic member 360. The hole 361 of the ceramic member 360 also has a square section corresponding to the square section of the insulation pin 362.

An insulation pin as shown in Fig. 28b has a circular section. The insulation pin is inserted in a hole having a circular section and fonned at either end of a circular- ceramic member. The hole of the ceramic member also has a circular section corresponding to the circular section of the insulation pin. As shown in Figs. 28a and 28b, two insulation pins are inserted in a single ceramic member in such a manner that the pins are spaced apart from each other by a prescribed distance 364 of approximately 2 to 3 mm (See Fig. 28c) to insulate the pins from each other. The joining strength of the junctions is excellent in the case of the insulation pin having a square section; however, the cost of manufacturing the insulation pin having a circular section is lower. Consequently, it is preferable to use the insulation pin having a square section or a circular section considering the environment where the insulation pin is used. Refening to Fig. 28c, an insulation pin 367, which has a circular section, is inserted in a square ceramic member 365. A distance maintaining piece 369 is attached to either end of a ceramic member to improve the joining strength between an insulation pin 369 and the ceramic member, as shown in Fig. 28d. Fig. 28e shows that a distance- maintaining element 370 of a prescribed size is inserted in a ceramic member to quickly cany out a process of inserting an insulation pin into the ceramic member and to reliably maintain a prescribed distance between the insulation pins. Refening to Fig. 28f, there is shown an offset-type ceramic member 372, which is usually used in the case that the size of the ceramic member is not structurally restrained. The joining strength is improved when this ceramic member 371 is used since metal insulation pins are deeply inserted into the ceramic member.

According to the present invention, the above-described insulation pins may be suitably used on the basis of the use thereof, the cost thereof, and the restriction thereof.

Figs. 29a and 29b respectively show the assembly of a radiant heat prevention unit 373 and the above-described insulation pins. Before the construction of the radiant heat prevention unit 373, a locating operation of pins is carried out so that the mechanical strength can be maintained with the minimum number of pins. Afterward, the insulation pins are inserted into the radiant heat prevention unit 373.

The inserting operation of the insulation pins into the radiant heat prevention unit is carried out by means of an inserting apparatus, the position and the amount of which are properly considered. The radiant heat prevention unit, into which the insulation pins are inserted, is carefully inserted into strip from the outside while a prescribed force is applied to the radiant heat prevention unit. When it is inserted, the radiant heat prevention unit is advanced while being at a right angle to the mantles.

Figs. 3 0a and 3 0b respectively show the final assembly o f the electric heater manufactured according to the present invention. An outer can part 380 for the electric heater is securely connected to electrode rods as shown in Figs. 30a and 30b. Consequently, the total mechanical strength is maintained. Industrial Applicability

As apparent from the above description, the present invention provides a exhaust gas aftertreatment device for diesel engines, to which an electric heater constructed according to the present invention is applied. Consequently, the present invention has an effect of regenerating a filter by means of the electric heater even at a low temperature. Also, the electric heater is used as an auxiliary heating source according to the present invention, whereby energy consumption is reduced as compared to the conventional exhaust gas aftertreatment device using the electric heater as a main heating source. The electric heater of the present invention is divided into a center heater part and surrounding heater parts so that the heater parts can be selectively operated on the basis of the conditions of the engine and the filter, whereby energy consumption is minimized.

The electric heater can be controlled such that the PMs are oxidized on the basis of several states of the engine, and the electric heater is used as an auxiliary heating source for heating a catalyst, whereby energy consumption is minimized.

In the state of the engine that the temperature of exhaust gas is very low when the regeneration is carried out by means of the catalyst, the entire electric heater is operated. Consequently, the regeneration is effectively carried out although the energy consumption is increased.

When a metal substrate and an electric heater using the metal substrate are manufactured according to the present invention, a strip is prepared in such a manner that some parts of the strip are corrugated and the other parts of the strip are flat. Consequently, it is possible to prevent non-uniformity of the junctions caused when the metal substrate and the electric heater are manufactured. Also, abrasion of gears and the strip is minimized. According to the present invention, the junctions of the metal substrate can be unifonnly maintained, and the metal substrate can be manufactured with smaller cell densities. Furthermore, it is possible to minimize the abrasion of gears and the strip caused when the strip is corrugated. According to the present invention, the junctions are uniformly maintained and the local excess of the electric current is prevented since the electric heater is manufactured with the same cell density. Also, there is provided a prescribed distance between the gears, whereby the total specific resistance is easily adjusted. Since the junctions are uniformly maintained, the brazing operation at the j unctions i s e asily and conveniently performed, and the durability of the junctions after the brazing operation is increased. According to the present invention, hot wires are manufactured using a metal or ceramic jig, which is different from the conventional construction for forming the corrugated strips, whereby it is possible to prevent deterioration of the thermal durability of heating elements due to local difference of the specific resistance generated by the structural non-uniformity, which is caused when the conventional corrugated strips are formed and wound.

When the strips are attached to the mantles according to the present invention, the mantles are fixed to the jig, and a desired force can be easily applied to the mantles. Also, the size of the mantles can be easily changed, whereby the contact resistance between the strips and the mantles is increased, and thus loss of electric energy is actually decreased.

When the strips are attached to the mantles, or the strips are connected to each other, they can be attached to the mantles by m eans of a socket in addition to brazing, whereby thermally and mechanically excellent durability is maintained.

In connection with an electrode, the junctions between a ceramic member and a metal electrode rod are structurally improved. The electrode rod is provided with grooves of prescribed dimensions, and a ceramic insulating material is applied to the electrode rod, whereby damage to the electrode rod due to thermal expansion between the ceramic member and the metal electrode rod is prevented. Furthermore, the present invention provides various insulation pins, which are selectively used on the basis of their applications. Consequently, the structural and electrical characteristics of the insulation pins are improved, and thus the durability of the insulation pins is increased.

Although the prefened embodiments of the present invention have been disclosed for i llustrative p uφoses, 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. A exhaust gas aftertreatment device for diesel engines, wherein an e lectric heater for spatially non-uniformly distributing thermal capacity is attached to at least one catalyst unit for activating a catalyst or improving a conversion efficiency of nitric oxide (NO)/nitrogen dioxide (NO₂) at a low temperature.

2. The device as set forth in claim 1, wherein the catalyst unit is a catalyzed filter, and wherein the electric heater is disposed in front of the filter.

3. The device as set forth in claim 1, wherein the catalyst unit comprises an oxidation catalyst and a catalyzed filter, and wherein the electric heater is disposed between the oxidation catalyst and the catalyzed filter.

4. The device as set forth in claim 1, wherein the electric heater is divided into a center segment and a surrounding segment, the surrounding segment comprising a plurality of segment parts arranged radially around the center segment, and wherein electric cunent is supplied continuously or selectively to the respective segments so that PMs collected at the segments are burned.

5. The device as set forth in claim 4, further comprising a plurality of mantles, wherein one of the mantles surrounding the center segment is connected to an anode, and the mantles of the surrounding segment are connected to cathodes, respectively, so that entire power supply circuits are connected to each other in series.

6. The device as set forth in claim 4, further comprising a plurality of mantles, wherein one of the mantles sunounding the center segment is connected to an anode, and the other mantles of the center segment and the mantles of the sunounding segment are connected to cathodes, respectively, so that entire power supply circuits are connected to each other in parallel.

7. The device as set forth in claim 4, wherein the center and sunounding segments are formed, respectively, by stacking strips.

8. The device as set forth in claim 4, further comprising a radiant heat prevention unit disposed on the mantles and the strips.

9. The device as set forth in claim 7, wherein each of the strips comprises corrugated parts and flat parts, the corrugated and flat strip parts being alternately ananged.

10. The device as set forth in claim 9, wherein each of the strips further comprises offset parts of a prescribed length, each of the offset parts being disposed between the corrugated strip part and the neighboring flat strip part.

11. The device as set forth in claim 9 or 10, wherein the upper strip is stacked on the lower strip such that the corrugated strip part is formed at one side of each of the upper and lower strips, and the flat strip part is formed at the other side of each of the upper and lower strips, when a stacking process is carried out of the strips each formed by alternately arranging the corrugated strip parts and the flat strip parts.

12. The device as set forth in claim 5 or 6, wherein the height of the strip inserted into the mantle is changed to eliminate the interference between the electrodes and the heating elements so that the specific surface area is increased.

13. The device as set forth in claim 5 or 6, wherein the length of the mantle for the anode is smaller than the length of the mantle for the cathode.

14. The device as set forth in claim 12, wherein the electrode comprises an electrode rod having a bolt tap fonned at one end thereof, and an electrode ring containing a ceramic therein and securely fitted on the electrode rod, the electrode rod being attached to the mantle by means of the bolt tap.

15. The device as set forth in claim 14, wherein the electrode rod has at least one groove formed on the outer circumference thereof at the position where the electrode ring is fitted.

16. The device as set forth in claim 7, wherein the fixing of the mantle and the strip is carried out by means of the combination of a socket rest formed at a prescribed area of the strip and a socket inserted into the socket rest while the socket comes into contact with the mantle.

17. The device as set forth in claim 7, wherein the fixing of the mantle and the strip is carried out by means of a joining pin.

18. The device as set forth in claim 8, wherein the radiant heat prevention unit is mounted by means of an insulation pin such that the radiant heat prevention unit is electrically insulated from the strip and the mantle.

19. The device as set forth in claim 18, wherein the insulation pin is inserted through a though-hole of a cylindrical ceramic member.

20. The device as set forth in claim 18, wherein the insulation pin is divided into two insulation parts, the insulation pin parts being disposed in the ceramic member while they are spaced apart from each other.

21. The device as set forth in claim 1, wherein the electric heater is operated such that it supplies different amounts of heating energy on the basis of the below- mentioned five states of the engine.

State 1: a low speed/high load state with engine torque of below 1800 φm and engine load rate of 70 to 100%, State 2: a low speed/low load state with engine torque of below 1800 m and engine load rate of 0 to 30%,

State 3: a middle speed/high load state with engine torque of 1800 to 3500 φm and engine load rate of 70 to 100%>,

State 4: a middle speed/middle load state with engine torque of 1800 to 3500 φm and engine load rate of 30 to 70%,

State 5: a high speed/low load state with engine torque of above 3500 φm and engine load rate of 0 to 30%.

22. A method of manufacturing an electric heater used t o purify exhaust gas from a vehicle, the electric heater being manufactured by stacking strips, the method comprising a step of inserting the strips into a jig having strip insertion holes of prescribed shapes formed therein.

23. The method as set forth in claim 22, wherein the jig is made of a metal or a ceramic.

24. The method as set forth in claim 22, wherein the jig further has at least one mantle insertion hole formed so that at least one mantle for supplying electric current to the strip is inserted into the mantle insertion hole.

25. The method as set forth in claim 22, further comprising notches formed at the edge of the walls of the strip insertion holes and the mantle insertion hole.

26. An apparatus for forming a strip, comprising: a driving source; a transferring unit operated by means of power from the driving source for transfening a strip material; and at least two gears having gear teeth formed at prescribed parts of the outer circumference thereof, wherein corrugated strip parts and flat strip parts are alternately formed at the strip material by means of the gear teeth of the gears.

27. An apparatus for forming a strip, comprising: a driving source; a transfening unit operated by means of power from the driving source for transfening a strip material; at least two gears rotatably engaged with each other for forming corrugation at the strip material; and cams fitted on the shafts of the gears and rotated along with the shafts of the gears for adjusting the clearance between the gears.