JP5347372B2 - Exhaust gas purification system and exhaust gas purification method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control system heating a section carrying catalyst to uniform temperature and quickly and efficiently using purification function of the catalyst in the exhaust emission control system provided with an exhaust emission control device such as an NOx conversion catalyst device, an oxidation catalyst device, and a filter device with catalyst. <P>SOLUTION: In the exhaust emission control system 1 provided with the exhaust emission control device 10 carrying catalyst converting harmful components in exhaust gas G, an outer circumference of the section carrying catalyst of the exhaust emission control device 10 is covered by a heater 31 and a conductive part of a heater 31 is divided in a longitudinal direction to make current applied to the heater 31 pass in the circumference direction. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to an exhaust gas purification system and an exhaust gas purification method provided with an exhaust gas purification device in which a heater is disposed on the outer periphery of a portion carrying a catalyst.

  One device for purifying exhaust gas from an internal combustion engine is a NOx purification catalyst device for purifying NOx (nitrogen oxide) in the exhaust gas. In one of these NOx purification catalyst devices, an alkali metal or alkaline earth metal is supported together with a noble metal, NO (nitrogen monoxide) in exhaust gas containing excess oxygen is oxidized and adsorbed on the catalyst as a nitrate, There is an apparatus carrying a NOx occlusion reduction type catalyst for purifying NOx. This NOx occlusion reduction type catalyst occludes NOx when the exhaust gas is in a lean air-fuel ratio state with excess oxygen, and releases the occluded NOx in a rich air-fuel ratio state where the oxygen concentration is low or the air-fuel ratio is less than 1. The released NOx is reduced in a reducing atmosphere to reduce NOx.

  Moreover, as another device of the exhaust gas purification device, it cannot occlude NOx, but mainly supports precious metals and oxidizes and removes CO (carbon monoxide) and HC (hydrocarbon) by its oxidation action. There is an oxidation catalyst device. Furthermore, there is a filter device with a catalyst that collects PM (particulate matter) in exhaust gas and oxidizes and removes it with an oxidation catalyst supported on a filter or a PM oxidation catalyst.

  By using these exhaust gas purification devices, NOx, CO, HC, PM and other harmful components in the exhaust gas discharged from the internal combustion engine are purified, and the amount of these harmful components released into the atmosphere is reduced. However, it has been reduced to below the emission standard.

  However, in an exhaust gas purification system (exhaust gas aftertreatment system) using these catalysts, it is necessary to raise the temperature of the catalyst to a temperature at which the catalyst is activated and a purification reaction is possible. Depending on the type of catalyst, the catalyst generally starts its purification reaction when a temperature of 200 ° C. to 250 ° C. is reached. Therefore, until the temperature of the catalyst reaches this activation temperature, there is a problem that harmful components in the exhaust gas cannot be removed by catalytic reaction, and the harmful components are discharged into the atmosphere as they are. In other words, in an exhaust gas purification system using a catalyst, if the time to reach the temperature at which the catalyst starts the purification reaction is short, the amount of harmful components released into the atmosphere can be reduced accordingly.

  Therefore, in the exhaust gas purification system including these NOx purification catalyst device, oxidation catalyst device, and filter device with catalyst, when the temperature of the catalyst is low, such as immediately after the engine is started, the time to reach the activation temperature is shortened. Therefore, it is conceivable that exhaust gas is concentrated and flowed to the inner peripheral portion of the catalyst to reduce the portion carrying the catalyst to be heated.

  In this connection, a flow path control mechanism is provided upstream of the catalyst, and when the exhaust gas temperature is low, the exhaust gas flow is concentrated at the center of the catalyst so that the catalyst temperature reaches the activation temperature quickly. In addition, when the exhaust gas temperature is high, the exhaust gas is concentrated in the periphery of the catalyst, and even if the exhaust gas becomes hot, a catalytic converter for a diesel engine that prevents the formation and accumulation of sulfate in the catalyst is proposed. (For example, refer to Patent Document 1).

  In this diesel engine catalytic converter, it is considered effective to provide a plurality of cooling fans on the outer surface of the catalytic converter housing, and in order to suppress the generation of sulfate, the exhaust gas is discharged when the exhaust gas reaches a high temperature. Instead of flowing in the central part of the catalyst, the catalyst is passed through in a concentrated manner at the periphery of the catalyst having a low temperature.

  However, maintaining the temperature of the outer peripheral portion at a low temperature is considered to be effective in suppressing the formation of sulfate, but it is necessary to raise the temperature of the entire catalyst above the activation temperature of the catalyst for NOx purification. Therefore, lowering the temperature of the outer peripheral portion is not preferable from the viewpoint of NOx purification. In addition, when desulfurizing by raising the temperature in order to remove the sulfate generated in the catalyst, there is a problem that it is difficult to increase the temperature of the outer peripheral portion of the catalyst and to desulfurize and regenerate the outer peripheral portion.

  If the exhaust gas temperature is lower than the oxidation catalyst activation temperature, a high-temperature exhaust gas treatment unit carrying the oxidation catalyst is provided in the center and a low-temperature exhaust gas treatment unit equipped with heating means is provided in the periphery. The exhaust gas is heated above the oxidation catalyst activation temperature and flowed to the low temperature exhaust gas processing section to improve the exhaust gas purification efficiency at start-up and when the exhaust gas temperature decreases, and the exhaust gas When the temperature is equal to or higher than the oxidation catalyst activation temperature, an automobile exhaust gas treatment device that stops the operation of the heating means and flows exhaust gas to the high-temperature exhaust gas treatment unit to purify harmful components by the oxidation catalyst. It has been proposed (see, for example, Patent Document 2).

  In this automobile exhaust gas treatment device, when the exhaust gas temperature is high, the exhaust gas is flowed through the high temperature exhaust gas treatment unit and the low temperature exhaust gas treatment unit to purify it. In such a case, the path is switched to flow into the peripheral low temperature exhaust gas processing section via the heating means. As a result, the exhaust gas is heated to a temperature higher than the catalyst activation temperature by the heating means, and the heated exhaust gas flows into the low-temperature exhaust gas processing section for purification.

  However, in general, because of the heat dissipation, the central part of the catalyst is likely to be at a high temperature, and the peripheral part is likely to be at a low temperature. The configuration of the processing apparatus has a problem of poor thermal efficiency.

  On the other hand, the present inventor, as a means for shortening the temperature rise time of the catalyst at the outer peripheral portion, arranges the electric heater so as to cover the outer periphery of the outer peripheral portion that is likely to be low temperature, and energizes this heater, We considered heating the outer periphery from the outside.

  In connection with the arrangement of the heater on the outer peripheral side, a diesel patty in which an energizing wire mesh is wound around the outside of a ceramic fiber material made of randomly laminated nonwoven fabric that collects particulates contained in exhaust gas of a diesel engine. A curate filter has been proposed (see, for example, Patent Document 3).

  In this diesel particulate filter, the exhaust gas is allowed to flow from the outer peripheral side of the current-carrying wire mesh to the inner peripheral side ceramic fiber material, and the filter body is heated by energizing the current-carrying wire mesh and collected in the ceramic fiber material. The filter is regenerated by incineration by heating.

However, simply providing an energizing wire mesh on the outer periphery of the exhaust gas purifying device will cause the entire outer periphery to be heated uniformly when energizing and heating the energizing wire mesh. For this reason, the heat generated by the catalytic reaction of harmful components in the exhaust gas is transferred to the downstream side by the movement of the exhaust gas, so the downstream temperature becomes higher than the upstream temperature, and the catalyst of the exhaust gas purification device Cannot be heated to a uniform temperature. If the catalyst does not reach a uniform temperature, during the purification of the harmful components of normal exhaust gas that is not regenerated, activation is incomplete in the low temperature part, and there is a problem of sulfate accumulation in the high temperature part. At the time of desulfurization treatment in which the temperature needs to be increased, the desulfurization treatment is incomplete at the low temperature portion, and the problem of catalyst deterioration occurs at the high temperature portion.
JP-A-10-299465 JP 2002-295233 A Japanese Patent Laid-Open No. 08-312328

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a catalyst in an exhaust gas purification system including an exhaust gas purification device such as a NOx purification catalyst device, an oxidation catalyst device, and a filter device with a catalyst. An object of the present invention is to provide an exhaust gas purification system and an exhaust gas purification method that can heat the temperature of a supported portion to a uniform temperature and can efficiently use the purification function of a catalyst quickly.

In order to achieve the above object, an exhaust gas purification system of the present invention is an exhaust gas purification system comprising an exhaust gas purification device carrying a catalyst for purifying harmful components in the exhaust gas, the catalyst of the exhaust gas purification device. Enclose the outer periphery of the part carrying the heater with a heater that uses a material whose energization resistance increases as the temperature rises, and divide the energized part of the heater in the longitudinal direction so that the current flowing through the heater flows in the circumferential direction In addition, each of the divided heaters is electrically connected in parallel to the energizing electrode, and the portion carrying the catalyst of the exhaust gas purifying device is connected to the outer peripheral portion and the central tube by a cylindrical partition wall having a heat shielding structure. Divided into two parts, a first valve is provided between the exhaust passage of the internal combustion engine and the outer peripheral part, and a second valve is provided between the exhaust passage and the central cylinder part, and the catalyst of the central cylinder part The temperature of When the first index temperature to be marked is equal to or lower than the first determination temperature set in advance, the first valve is closed and the second valve is opened to allow the exhaust gas to flow only through the central tube portion. When the temperature exceeds one judgment temperature, the first valve is opened while the second valve is opened, and exhaust gas is allowed to flow through both the central tube portion and the outer peripheral portion, and the heater is energized while being heated. When the temperature of the outer peripheral portion is adjusted to perform desulfurization treatment, the first index temperature indicating the temperature of the catalyst in the central cylinder portion is equal to or lower than the second determination temperature set in advance. The valve is closed and the second valve is opened to allow the exhaust gas to flow only through the central tube portion. After the first index temperature exceeds the second determination temperature, the first index temperature becomes equal to the second determination temperature. The first that is the sum of the times exceeded The first valve and the second valve are kept in the open / closed state until the sulfurization treatment time has passed the first determination time set in advance, and the first desulfurization treatment time has passed the first determination time. When the first valve is opened and the second valve is closed, the exhaust gas is allowed to flow only to the outer peripheral portion and the heater is energized to adjust the energization amount while adjusting the temperature of the outer peripheral portion, Further, when the energization current to the heater that raises the temperature of the outer peripheral portion exceeds a preset determination current value, a second desulfurization treatment time that is the sum of the times when the energization current exceeds the determination current value is preset. Until the elapse of the second determination time, the open / closed state of the first valve and the second valve and the temperature adjustment by the heater are continued as they are, and when the second desulfurization processing time elapses the second determination time, Finish desulfurization treatment As described above, the exhaust gas is caused to flow to the outer peripheral portion by opening the first valve, and the exhaust gas is caused to flow to the central cylinder portion by opening the second valve .

  According to this configuration, the amount of heat dissipated through the catalyst container of the exhaust gas purification device can be supplemented by heating by energizing the heater, and the temperature decrease of the entire outer peripheral portion of the portion carrying the catalyst can be suppressed. it can. In addition, the outer peripheral portion of the portion carrying the catalyst can be heated by energizing the heater without being dependent on the heat quantity of the exhaust gas from the internal combustion engine, and the temperature can be maintained within the activation temperature range. The time until the temperature rises can be significantly shortened. Accordingly, it is possible to significantly reduce the emission amount of harmful components released until the catalyst is heated to the activation temperature range.

In general, the temperature on the downstream side of the exhaust gas purification device is higher than that on the upstream side due to the heat generated by the catalytic reaction, but by flowing the heater current in parallel in the circumferential direction, the exhaust gas purification device The amount of electric current can be changed for each longitudinal direction of the exhaust gas, and as the exhaust gas moves from the upstream side to the downstream side, different heating can be performed, and the temperature of the catalyst can be maintained uniformly throughout. Easily. In other words, when a general heater material whose energization resistance increases as the temperature rises is used as the heater material, the amount of current increases in a portion where the temperature is low and the energization resistance value is small, and heating can be performed efficiently. In a portion where the energization resistance value is high and the amount of current is reduced, heating can be suppressed.

  According to this configuration, when the exhaust gas temperature is low, such as during warm-up operation or low-load operation, the exhaust gas is allowed to flow only in the central cylinder part, and the temperature of the catalyst in the central cylinder part is quickly brought to the activation temperature or higher. be able to. On the other hand, when the exhaust gas volumetric flow rate increases and the exhaust gas flows also to the outer peripheral part, the delay in the temperature rise of the catalyst on the outer peripheral part becomes remarkably large. Thus, it is possible to prevent a delay in the temperature rise of the catalyst on the outer periphery. That is, in this two-divided structure, the effect of providing a heater on the outer peripheral portion is particularly great.

  Further, immediately after the start of the internal combustion engine, when exhaust heat from the internal combustion engine is transmitted to the portion carrying the catalyst by the exhaust gas to raise the temperature of the catalyst, the exhaust gas is concentrated at the central portion. In this case, since a cylindrical partition wall having a heat insulation structure is provided between the outer peripheral portion and the central cylindrical portion, in other words, a heat retaining ring is provided, the heated portion can be limited to the central cylindrical portion having a reduced heat capacity. it can.

  Therefore, since the heat capacity to be heated is reduced and the heat transfer from the central tube portion to the outer peripheral portion is reduced, the time required for raising the temperature to the activation temperature can be shortened. In addition, even when the temperature of the outer peripheral part needs to be raised and the heater is heated by energizing the heater, the cylindrical partition wall of the heat shielding structure reduces the heat capacity of the heating part and the center from the outer peripheral part. Since heat transfer to the cylindrical portion is reduced, the temperature of the outer peripheral portion can be raised in a short time.

  In the exhaust gas purification system, the temperature of the outer peripheral portion of the portion carrying the catalyst is estimated from the amount of current flowing to the heater, and the amount of current supplied to the heater is controlled based on the estimated value, The temperature of the portion carrying the catalyst is controlled.

  The resistance of the heater changes depending on the temperature of the place where it is placed, and the amount of current applied at a constant voltage changes according to the resistance. Therefore, the amount of current can be used as a temperature sensor signal. By controlling the applied voltage while estimating the temperature, a more appropriate temperature distribution can be made relatively easily.

  Even when not energized, if a low voltage that does not lead to heating is applied to the heater, a weak current flows. By detecting this weak current, the temperature of the heater part is obtained from this weak current, and the catalyst The temperature of the outer peripheral portion of the portion carrying the catalyst can be easily controlled by estimating the outer peripheral temperature of the portion carrying the catalyst, and controlling the on / off of the energization voltage and the energization amount according to the estimated value.

  In the exhaust gas purification system, the activation temperature of the catalyst is estimated by measuring the energization current of the heater, and the degree of deterioration of the catalyst is estimated from the activation temperature.

  In addition, when the catalyst is activated and a catalytic reaction occurs, reaction heat is generated and the temperature starts to rise. By measuring the heater energization current at the start of this temperature rise, the activation temperature of the catalyst is measured. The degree of increase can be estimated. On the other hand, the activation temperature, which is the starting temperature of the catalytic reaction, gradually shifts to the high temperature side due to deterioration of the catalyst. Therefore, the degree of catalyst deterioration can be grasped from the change in energization current at the start of temperature rise of the heater current value closely related to the catalyst temperature. In addition, by dividing the heater in the exhaust gas flow direction (longitudinal direction of the exhaust gas purification device) and arranging several rows, it becomes possible to grasp the deterioration state of the catalyst in more detail.

And, in the exhaust gas purification method for achieving the above object, the part carrying the catalyst of the exhaust gas purification device is divided into the outer peripheral part and the central cylindrical part by the cylindrical partition wall of the heat shielding structure, A first valve is provided between the exhaust passage of the internal combustion engine and the outer peripheral portion, a second valve is provided between the exhaust passage and the central cylinder portion, and the first valve is opened to allow the exhaust gas to flow to the outer peripheral portion. The exhaust gas is caused to flow through the central cylinder by opening the second valve, and the outer periphery of the outer periphery is wrapped with a heater that uses a material that increases energization resistance when the temperature rises. Exhaust gas purification in which the energized portion of the heater is divided in the longitudinal direction so that the current flowing through the heater flows in the circumferential direction, and each of the divided heaters is electrically connected in parallel to the energized electrode System exhaust When the first index temperature indicating the temperature of the catalyst in the central cylinder portion is equal to or lower than a first determination temperature set in advance, the first valve is closed and the second valve is opened to exhaust the exhaust gas. When the first index temperature exceeds the first determination temperature when the first index temperature exceeds the first cylindrical portion, the first valve is opened while the second valve is open, and the exhaust gas is discharged from the central cylindrical portion and the outer peripheral portion. When the desulfurization treatment is performed by adjusting the energization amount while heating by energizing the heater and heating the heater, the first temperature indicator of the temperature of the catalyst in the central cylinder portion is used. When the index temperature is equal to or lower than a second determination temperature set in advance, the first valve is closed and the second valve is opened to allow exhaust gas to flow only through the central tube portion, and the first index temperature is equal to the second determination temperature. After exceeding, the first index temperature The first valve and the second valve are kept open and closed until the first desulfurization treatment time, which is the sum of the times over which the second determination temperature has been exceeded, has passed a preset first determination time. When the first desulfurization processing time has passed the first determination time, the first valve is opened and the second valve is closed to allow exhaust gas to flow only to the outer periphery and to heat the heater. While adjusting the energization amount to adjust the temperature of the outer peripheral portion, and further when the energization current to the heater that raises the temperature of the outer peripheral portion exceeds a preset determination current value, the energization current becomes the determination current value Until the second desulfurization processing time, which is the sum of the times exceeding the predetermined time, has passed the second determination time set in advance, the open / close state of the first valve and the second valve and the temperature adjustment by the heater are continued as they are, During the second desulfurization process The desulfurization process is terminated when the second determination time elapses .

  The “first index temperature” refers to the temperature of the catalyst in the central cylinder portion itself or a temperature indicating the temperature. This is because it is often difficult to directly measure the temperature of the catalyst. Instead, a temperature closely related to the temperature of the catalyst, for example, the temperature of the exhaust gas flowing into the central cylinder or the central cylinder is used. The temperature of the exhaust gas flowing out may be used. Therefore, “first index temperature” is expressed as an expression including the temperature used instead.

  The first determination temperature is a temperature equal to or higher than the activation temperature of the catalyst, and is a temperature within a range of 200 ° C. to 300 ° C., for example, set to 250 ° C., depending on the type of catalyst.

  According to this method, at the time of warm-up operation or low load operation immediately after engine start, the first index temperature is low and the exhaust gas volumetric flow rate is also small. It is possible to quickly raise the temperature of the catalyst in the tube portion and shorten the time until activation. In addition, when the first index temperature is high and the exhaust gas volume flow rate is large, the exhaust gas is flowed through both the central tube portion and the outer peripheral portion, the volume of the portion through which the exhaust gas passes is increased, and the space velocity relative to the exhaust gas is increased. The catalyst reaction can be promoted by increasing the time during which the exhaust gas contacts the catalyst.

In addition, when exhaust gas is allowed to flow to the outer periphery, the energization amount is adjusted while the heater is energized and heated to adjust the temperature of the outer periphery, so the outer periphery is heated from the outer periphery to quickly reach the activation temperature. The temperature can be raised, and after the temperature rise, the amount of energization can be adjusted to maintain the temperature of the catalyst at the outer peripheral portion within the activation temperature range.

Further, in the above exhaust gas purification method, when the desulfurization treatment is performed, when the first index temperature indicating the temperature of the catalyst in the central cylinder portion is equal to or lower than the preset second determination temperature, the first valve is set. The first valve temperature exceeds the second determination temperature after the first valve temperature exceeds the second determination temperature after the first valve temperature exceeds the second determination temperature by closing and opening the second valve. The first valve and the second valve are kept open and closed until the first determination time set in advance, which is the sum of the times, has passed, and the first desulfurization time is When the first determination time has elapsed, the first valve is opened, the second valve is closed, exhaust gas is allowed to flow only to the outer peripheral portion, and the heater is energized to adjust the energization amount while heating the outer periphery. Adjust the temperature of the When the second index temperature indicating the temperature of the catalyst at the outer peripheral portion exceeds a preset third determination temperature, the second desulfurization treatment is the sum of the time when the second index temperature exceeds the third determination temperature until passage of a second determination time period is preset, the first valve opening and closing state of the second valve the temperature adjustment by the heater as it continues, the second desulfurization treatment time is the second determination time After elapses, the desulfurization process is terminated.

  The “first index temperature” refers to the temperature of the catalyst in the central cylinder portion itself or a temperature indicating the temperature thereof. The “second index temperature” refers to the temperature of the catalyst in the outer peripheral portion itself or the temperature thereof. Say the temperature to do. This is because it is often difficult to directly measure the temperature of the catalyst. Instead, a temperature closely related to the temperature of the catalyst, for example, the temperature of the exhaust gas flowing into the central cylinder or the outer periphery or the center The temperature of the exhaust gas flowing out from the cylinder part or the outer peripheral part may be used. Therefore, the expression including the temperature used instead is expressed as “first index temperature” and “second index temperature”.

The second determination temperature and the third determination temperature are temperatures equal to or higher than the temperature at which the desulfurization treatment of the catalyst in the central cylinder portion or the outer peripheral portion can be performed, and depending on the type of the catalyst, a range of 650 ° C to 750 ° C For example, 700 ° C. and 650 ° C. Note that the third determination temperature is usually set lower than the second determination temperature because of thermal degradation.

  The first determination time is the time until the desulfurization treatment of the catalyst in the central cylinder portion is completed, and the second determination time is the time until the desulfurization treatment of the catalyst in the outer peripheral portion is completed. These times are set based on the results of experiments conducted in advance. In general, the second determination time is longer than the first determination time because barium used in the NOx occlusion reduction catalyst for low temperature is more easily desorbed than potassium used in the NOx occlusion reduction catalyst for high temperature. Set short.

  According to this method, in the desulfurization process that requires the catalyst to be at a high temperature, the first index temperature exceeds the second determination temperature until it exceeds the first determination time, due to the heat shielding structure of the cylindrical partition wall. Exhaust gas is allowed to flow through the central tube portion where heat retention is high and the temperature rises quickly, and the desulfurization process of the central tube portion is completed. Further, when the desulfurization process of the central cylinder part is completed, the exhaust gas is flowed to the outer peripheral part where the temperature rise of the catalyst is likely to be delayed as compared with the central cylindrical part, and the desulfurization process of the outer peripheral part is performed intensively. Therefore, desulfurization of the entire catalyst can be performed efficiently. Further, when exhaust gas is allowed to flow to the outer periphery, the temperature of the outer peripheral portion is adjusted by adjusting the energization amount while energizing and heating the heater, so that the temperature of the catalyst at the outer peripheral portion can be quickly desulfurized. The temperature can be maintained at a high temperature.

  For example, in a NOx occlusion reduction type catalyst, the NOx purification performance deteriorates due to sulfur adsorption. This sulfur adsorption occurs at temperatures below about 600 ° C, while desulfurization requires high temperatures above about 650 ° C. Therefore, the adsorption of sulfur extends to the outer periphery of the catalyst which does not easily reach a high temperature. However, in the desulfurization, the catalyst temperature needs to be further increased. However, since the outer peripheral portion does not easily reach a high temperature, there is a problem that sulfur tends to remain.

  In order to solve this problem, in the present invention, a cylindrical heat shield structure (partition wall) is provided between the inner side and the outer side in the radial direction of the portion supporting the catalyst to form a central cylindrical portion and an outer peripheral portion, and desulfurization is performed. In the latter half of the treatment, only the outer periphery is desulfurized, and the exhaust gas is difficult to pass through and the outer periphery where the temperature is difficult to rise is persistently desulfurized, so that sufficient desulfurization can be performed over the entire catalyst. It becomes like this.

  As a result, it is possible to reduce the time and number of reduction processes necessary for maintaining the purification performance of the catalyst, in other words, the regeneration process for recovering the purification capacity of the catalyst, thereby reducing the fuel consumption required for the regeneration process. . Therefore, the capacity of the catalyst mounted on the vehicle can be reduced to ensure the mountability and reduce the cost. In addition, in the desulfurization treatment, it is possible to suppress the deterioration of the catalyst due to the central cylinder portion being exposed to an excessively high temperature by heating only the outer peripheral portion of the catalyst that is easily cooled to a high temperature.

  Furthermore, since the heater is provided around the outer periphery, the temperature of the catalyst at the outer periphery can be increased more efficiently during the desulfurization process.

  Further, in the above exhaust gas purification method, an energization current amount of the heater is used as the second index temperature. The resistance of the heater varies depending on the temperature of the place where the heater is disposed, and the amount of current that is energized at a constant voltage varies depending on the resistance. Therefore, the amount of current can be used as a temperature sensor signal. Even when not energized, if a low voltage that does not lead to heating is applied to the heater, a weak current flows. By detecting this weak current, the temperature of the heater part is obtained from this weak current, and the catalyst Can be estimated.

  According to the exhaust gas purification system of the present invention, in the exhaust gas purification device using a catalyst such as a NOx purification catalyst device, an oxidation catalyst device, a filter device with a catalyst, etc., considering the temperature dependence of the purification performance of the catalyst, The purification performance of the catalyst can be used quickly and efficiently.

  According to this configuration, the amount of heat dissipated from the exhaust gas purification device can be supplemented by heating with the heater, and the temperature drop of the portion carrying the catalyst can be suppressed. In addition, the temperature of the outer peripheral portion of the portion carrying the catalyst can be raised by heating with a heater and maintained in the activation temperature range without depending on the amount of heat of the exhaust gas. Almost can be eliminated. Therefore, it is possible to significantly reduce the emission of harmful components that are released before the catalyst is heated to the activation temperature range.

  In addition, the heaters divided in the longitudinal direction can be heated differently for each longitudinal direction by flowing current in parallel in the circumferential direction, and the heating at the low temperature part and the heating at the high temperature part are suppressed. Thus, it is relatively easy to raise the temperature of the catalyst in a short time and maintain it uniformly as a whole.

In addition, since a general heater material often shows a characteristic that the energization resistance increases as the temperature rises, the use of this heater material usually causes the reaction heat of the catalyst during the heating process of the exhaust gas purification device. The temperature of the part carrying the catalyst on the downstream side becomes faster, but if the temperature on the downstream side rises and the temperature of the heater in that part becomes higher than the temperature of the heater in the other part, the energization resistance of that part Since the energization resistance of other parts is larger than the energization resistance of the other parts, even if energization is performed in parallel at a constant voltage, the energization current is reduced by the amount of energization resistance and the amount of heat generation is reduced. Heated.

  Further, according to the exhaust gas purification method of the present invention, in an exhaust gas purification device using a catalyst such as a NOx purification catalyst device, an oxidation catalyst device, a catalyst-equipped filter device, etc., warm-up operation or low load operation immediately after engine startup In this case, the exhaust gas is allowed to flow through the central cylinder portion having good heat retention, and the catalyst in the central cylinder portion can be quickly heated to shorten the time until activation.

Also, when the exhaust gas volume flow rate is large, the exhaust gas is allowed to flow through both the central cylinder part and the outer peripheral part, the volume of the part through which the exhaust gas passes is increased, the space velocity relative to the exhaust gas is reduced, and the exhaust gas The catalytic reaction can be promoted by increasing the time of contact with the catalyst. When exhaust gas is allowed to flow through the outer peripheral portion, the energizing amount is adjusted while the heater is energized and heated to adjust the temperature of the outer peripheral portion. Therefore, the outer peripheral portion is heated from the outer peripheral side to quickly rise to the activation temperature. The temperature of the catalyst at the outer peripheral portion can be maintained within the activation temperature range by adjusting the energization amount after the temperature rise.

  Hereinafter, an exhaust gas purification system and an exhaust gas purification method according to embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows a configuration of an exhaust gas purification system 1 according to an embodiment of the present invention. This exhaust gas purification system 1 is one of a NOx purification catalyst device, an oxidation catalyst device, a catalyst-equipped filter device in which an exhaust passage 2 of an engine (internal combustion engine) carries a catalyst that purifies harmful components in the exhaust gas G, or The exhaust gas purification device 10 formed by several combinations is arranged and configured.

When the exhaust gas purification device 10 is a NOx purification catalyst device carrying a NOx occlusion reduction type catalyst, in order to purify NOx in the exhaust gas G , it is formed of a monolith catalyst. A catalyst coat layer of aluminum oxide, titanium oxide or the like is provided on a carrier such as a cordierite honeycomb of the monolith catalyst. This catalyst coat layer is configured to carry a NOx occlusion reduction catalyst comprising a catalyst metal such as platinum (Pt) or palladium (Pd) and a NOx occlusion material (NOx occlusion material) such as barium (Ba).

The NOx occlusion reduction type catalyst, oxygen concentration of the high exhaust gas G state, i.e., when the air-fuel ratio lean state, the NOx in the exhaust gas G NOx occlusion material occludes the NOx in the exhaust gas G Purifies and releases the stored NOx when the oxygen concentration is low, the air-fuel ratio is in an air-fuel ratio rich state smaller than 1, or the air-fuel ratio is in an air-fuel ratio stoichiometric state of 1. By reducing by the catalytic action, NOx outflow into the atmosphere is prevented.

In this NOx occlusion reduction type catalyst, if the air-fuel ratio lean state continues, the NOx occlusion material changes to nitrate. Therefore, before the NOx occlusion capacity is saturated, the regeneration control for bringing the exhaust gas G into the air-fuel ratio rich state is performed. The NOx occlusion capacity is restored by releasing and reducing the occluded NOx.

When the exhaust gas purification device 10 is an oxidation catalyst device that supports an oxidation catalyst, the exhaust gas G is oxidized by HC (hydrocarbon) to raise the exhaust gas temperature, or the NO ( In order to easily purify NOx (nitrogen oxide) by oxidizing NO (nitrogen monoxide) to NO ₂ (nitrogen dioxide), an oxidation catalyst such as platinum is supported on a porous ceramic honeycomb structure or the like. Is formed.

Further, when the exhaust gas purification device 10 is a filter device with a catalyst, in order to purify PM (particulate matter) in the exhaust gas G , a porous ceramic honeycomb channel (exhaust gas passage) is used. It is formed of a monolith honeycomb wall flow type filter or the like in which the inlet and the outlet are alternately sealed. A catalyst such as platinum or cerium oxide is supported on the filter so as to promote the oxidation of PM and HC at a relatively high temperature and to adsorb HC at a relatively low temperature. PM in the exhaust gas G is collected by the porous ceramic wall of the catalyst-equipped filter device.

In this filter device with a catalyst, in order to prevent the amount of collected PM from increasing and pressure loss to increase, when the collected amount of PM exceeds a predetermined collected amount or before and after the filter device with catalyst When the differential pressure exceeds a predetermined differential pressure amount, exhaust gas temperature control is performed to raise the exhaust gas temperature and to raise the temperature of the filter device with catalyst to the PM combustion temperature or higher . In the exhaust gas temperature raising control, air-fuel ratio rich control including unburned fuel supply control is performed.

As shown in FIGS. 1 and 3, the exhaust gas purifying device 10 carrying the catalyst is divided into two parts, an outer peripheral part 11 and a central cylindrical part 12, and a partition wall which is a cylindrical ring in the gap. 13 is formed and arranged in a heat shield structure. Further, a heat insulating structure 14 having a heat insulating property for heat insulation is provided around the outer peripheral portion 11. The heat retaining structure 14 is formed of a foam material or the like containing a large amount of air, and is configured to enhance the heat retaining property and the heat shielding property (heat insulating property) and also serve as a container for storing the catalyst carrier. By providing the heat retaining structure 14, the temperature of the catalyst can be raised more efficiently during the activation of the catalyst and the desulfurization process.

When the central cylindrical portion 12 is formed in a cylindrical shape, the outer peripheral portion 11 is provided around the periphery, and the exhaust gas purification device 10 is formed in a cylindrical shape, the outer diameter of the central cylindrical portion 12 and the outer peripheral portion 11 are formed. The ratio of the outer diameters is set in consideration of the use conditions of the catalyst based on the temperature raising time. In other words, the ratio of the cross-sectional area of the central cylindrical portion 12 to the cross-sectional area of the outer peripheral portion 11 is set in consideration of the use conditions of the catalyst based on the temperature rise time.

For example, the cross-sectional area of the part supporting the catalyst is made the same, and the volume of the central cylindrical part 12 and the volume of the outer peripheral part 11 are formed to be equal, and the catalyst is supported without changing the amount of heat necessary for heating the catalyst. If the exhaust gas G is allowed to flow only through the central cylinder portion 12 so that the heat capacity of the portion is halved, in this case, the catalyst temperature Tc1 is set to a predetermined temperature (for example, 200 ° C.) immediately after the engine is started. The time required to raise the temperature to about 50% is reduced to about half, and the emission of harmful components in the exhaust gas G until the catalyst is activated can be reduced.
As shown in FIG. 4, the cylindrical partition wall 13 is formed in a ring shape by bending a double wall structure formed by two plates 13 b and 13 c sandwiching a corrugated plate 13 a therebetween. The both ends of the gas tank are closed so that the exhaust gas G cannot flow in and out. The ring-shaped corrugated plate 13a reduces the contact area between the two plates 13b and 13c to reduce heat transfer due to heat conduction, and is formed between the corrugated plate 13a and the double walls 13b and 13c. The space portion 13d is filled with air, and the heat shielding property is increased by the air having low thermal conductivity.

  Further, a first valve 16 is provided in the first passage 15 between the exhaust passage 2 and the outer peripheral portion 11 of the engine, and a second valve 18 is provided in the second passage 17 between the exhaust passage 2 and the central cylinder portion 12. By opening the first valve 16, the exhaust gas G flows through the outer peripheral portion 11, and by opening the second valve 18, the exhaust gas G flows through the central cylinder portion 12.

According to this configuration, the parts 11 and 12 carrying the catalyst are divided into two parts by the cylindrical partition wall 13 having a heat shielding structure, and the heat capacity of each part 11 and 12 is reduced. When the temperature Tc1 of the catalyst needs to be quickly raised to the activation temperature or higher, the exhaust gas G is allowed to flow only on the side of the central cylindrical portion 12 where the heat capacity of the portion carrying the catalyst is reduced compared to the whole, The catalyst temperature Tc1 can be quickly raised to activate the catalyst. As a result, the time until activation is shortened, and the release amount of harmful components in the exhaust gas G into the atmosphere can be reduced accordingly.

At this time, a cylindrical partition wall 13 provided between the outer peripheral portion 11 and the central cylindrical portion 12 is formed in a heat shield structure, and the movement of heat is suppressed to move from the central cylindrical portion 12 to the outer peripheral portion 11. Since the amount of heat to be reduced is reduced, the heat of the exhaust gas G can be efficiently used to raise the temperature of the central tube portion 12, and the temperature Tc1 of the catalyst in the central tube portion 12 can be quickly raised accordingly. Further, the heat retaining structure 14 also indirectly contributes to the temperature rise of the central cylinder portion 12.

Further, when the temperature Tg of the exhaust gas G increases and the volumetric flow rate of the exhaust gas G increases, the exhaust gas G is allowed to flow to the outer peripheral portion 11 side while flowing the exhaust gas G to the central cylinder portion 12. By increasing the volume of the portion carrying the catalyst through which the exhaust gas G passes, the space velocity with respect to the exhaust gas G can be lowered, and the time for the exhaust gas G to contact the catalyst can be lengthened to promote the catalytic reaction. Thereby, sufficient purification is performed against harmful components of the exhaust gas G.

  Further, in order to measure the temperature Tc1 of the catalyst in the central cylindrical portion 12, a thermocouple 19 as a temperature sensor is disposed at the outer peripheral portion on the downstream side of the central cylindrical portion 12, and the temperature Tc2 of the catalyst in the outer peripheral portion 11 is measured. In order to do this, the thermocouple 20 is arranged at the outer peripheral portion on the downstream side of the outer peripheral portion 11. Further, in order to measure the temperature Tg of the exhaust gas G flowing into the exhaust gas purification device 10, a thermocouple 21 is disposed in the exhaust passage 2 upstream of the exhaust gas purification device 10.

The measured values Tc1, Tc2, and Tg of these thermocouples 19, 20, and 21 are input to an engine control unit (ECU) 3 that controls the operation of the engine. Based on these measured values Tc1, Tc2, and Tg, The opening and closing operation of the first valve 16 and the second valve 18 is performed. In addition, when the energization current of the net heater 31 as described below is used instead of the thermocouple 20 that detects the temperature of the outer peripheral portion 11, the thermocouple 20 is not necessary.

In the present invention, as shown in FIG. 5, the entire outer peripheral portion 11 that is the inside of the heat retaining structure 14 is wrapped with a net-like heater (heater) 31 formed by braiding a small-diameter wire into a net shape, The periphery is wrapped with an insulating seal mat 32 having electrical insulation and airtightness. At the same time, the energized portion of the net heater 31 is divided into the longitudinal direction of the exhaust gas purification device 10 (passage direction of the exhaust gas G) so that the current flowing through the net heater 31 flows in the circumferential direction. To do. The net heater 31 has, for example, a heater wire diameter of, for example, about 0.5 mm and an interval of several mm so that heating with a power of several kilowatts can achieve a temperature difference of about 400 degrees is possible. A plurality of knitted net-like heaters 31 are arranged in the longitudinal direction and wound around the outer peripheral portion 11. The divided net heaters 31 are electrically connected to the energizing electrodes 31a in parallel. The two energizing electrodes 31a are inserted and fixed in the electrode mounting grooves 11a provided at the mating portions of the net heater 31 and the insulating seal mat 32 with the insulator 11b interposed therebetween.

To draw the outside of the container of the powered electrode 31a is an exhaust gas purifying device 10, as shown in FIGS. 6 and 7, scissors ceramic insulating tube 31b, the ceramic insulating seal plate 31c, etc., electrical insulating fixed to the thermal insulation structure 14 while ensuring both sealability against sexual and exhaust gas G, the take-out portion of the conducting electrode 31a, a voltage adjustment and control unit for adjusting the applied voltage by a lead wire 33 as shown in FIG. 8 The voltage adjustment and control unit 34 is connected to a battery 36 serving as a power source by a lead wire 35. The voltage adjustment and control unit 34 is configured to control the voltage applied to the net heater 31 to adjust the amount of energization current and raise the temperature of the outer peripheral portion 11. The control of the applied voltage is performed by a control signal output from the engine control device 3.

This net heater 31 is not formed by a single net heater (resistor R) 31X as shown in FIG. 9, but as shown in FIG. Resistance r = R × n ) 31 is formed, and heating in each longitudinal direction is enabled by flowing current in parallel in the circumferential direction.

  In the example of FIG. 10, it is divided into five in the longitudinal direction, and even if the temperature of the resistance at one location rises, the influence on the overall resistance is only one fifth, and the resistance value as a whole increases. This is limited to the case where the overall temperature of the outer peripheral portion 11 rises and the resistance values of many parts increase.

Further, in the configuration of the net-like heater 31, rather than making the resistance of the entire portion with a single resistor, a plurality of resistance lines are knitted to disperse the portions where the energization resistance is generated, so It becomes the composition which covers the part. Therefore, even when the exhaust gas purification device 10 is relatively large, it is possible to detect the resistance change due to the temperature change of the resistance covering the whole by the change in the current amount of energization. Therefore, if an energization current value is detected in a state where the applied voltage to the resistance value of the net heater 31 is a constant voltage, a value close to the average temperature of the entire outer periphery of the outer peripheral portion 11 can be estimated.

  According to this configuration, by passing a current in parallel to the net-like heater 31 divided in the longitudinal direction, the catalyst temperature and the temperature of the net-like heater 31 having a close relationship with the outer peripheral surface of the portion carrying the catalyst. Can be uniformly heated in a short time from a state where the temperature is lower than the target temperature.

That is, when a general heater material whose energization resistance increases as the temperature rises is used, the temperature of the portion carrying the downstream catalyst is usually increased in the heating process of the exhaust gas purification device 10. In this configuration, when the temperature on the downstream side rises and the temperature of the net-like heater 31 in that part becomes higher than the temperature of the net-like heater 31 arranged in the other part, the energization resistance in that part becomes lower in the other part. Since it becomes larger than the energization resistance , even if energization is performed in parallel at a constant voltage, the energization current becomes smaller and the amount of heat generation is reduced by the increase in the energization resistance, so that the temperature becomes uniform.

For example, a NOx occlusion reduction type catalyst has a temperature range in the oxidation reaction from NO to NO _2, and in order to adsorb NO ₂ in the form of NO ₃ , it is 500 ° C. or less (this temperature value is somewhat different depending on the type of catalyst). Change). Therefore, when maintaining the catalyst temperature above the activation temperature, the exhaust gas to heat the inlet side of the G, but easily outlet temperature increases by catalytic reaction heat will be preferable not to heat the net By dividing the energized portion of the net heater 31 in the longitudinal direction so that the current flowing through the heater 31 flows in the circumferential direction, the temperature of the entire catalyst of the exhaust gas purification device 10 is equal to or higher than the activation temperature. And it becomes possible to maintain below 500 degreeC.

Next, regarding the net heater 31, a case where the input power is obtained from the data of the heater material manufacturer and the heater wire diameter is obtained will be described. When a portion carrying a catalyst is mounted inside a cylindrical heater and heating is performed from the outer peripheral surface, the heating area S has an outer diameter of 190.5 mm (7.5 inches) of the portion carrying the catalyst. ) From 177.8 mm (7.0 inches) to S = π × 0.1905 × 0.1778 = 0.106 m ² .

  Here, from the design results of a practical furnace that takes heat dissipation into the outer periphery into consideration, about 14 kW is required to heat in 6 minutes until the temperature rises to 800 ° C.

  Based on this, the necessary resistance R2 is R2 = 28 × 28 / 14,000 = 0.056Ω as 28 V applied voltage, and assuming that the length of the heater is 0.6 m and the number is n, r2 = 0.56 Xn. Assuming that n = 50, r2 = 0.056 × 50 = 2.8Ω, and the wire diameter of the heater material close to this value is 0.63 mmφ. The resistance of the heater material is 4.154 Ω / m, and at 0.6 m, the resistance is 2.49 Ω.

  In addition, when the temperature rise is 400 ° C. for 6 minutes instead of the temperature rise of 800 ° C. for 6 minutes, the power becomes about 4 kW in consideration of the heat radiation amount, and the resistance R3 = 28 × 28/4. 000 = 0.196Ω, and when n = 50, r3 = 50 × 0.196 = 9.8Ω, and the wire diameter of the heater material close to this value is 0.315 mmφ. The resistance of the heater material is 16.62 Ω / m, and 10 Ω at 0.6 m.

  Further, the temperature of the outer peripheral portion of the portion carrying the catalyst is estimated from the amount of current flowing through the net heater 31, and the amount of current supplied to the net heater 31 is controlled based on this estimated value to carry the catalyst. It is configured to perform temperature control of the part.

  That is, the resistance of the net-like heater 31 changes depending on the temperature at the place where it is arranged, and the amount of current that is energized at a constant voltage changes according to the resistance, so that the amount of current can be used as a signal for the temperature sensor. Therefore, the applied voltage is controlled while estimating the temperature of the outer peripheral portion from this amount of current. As a result, a more appropriate temperature distribution can be achieved relatively easily.

  Note that, even when the current is not energized, a weak current flows if a low voltage that does not reach heating is applied to the net-like heater 31. Therefore, by detecting this weak current, the portion of the net-like heater 31 is detected from this weak current. The temperature of the outer periphery of the portion carrying the catalyst is estimated, and the temperature of the outer peripheral portion of the portion carrying the catalyst is controlled by controlling the ON / OFF of the energization voltage and the energization amount according to the estimated value.

  Furthermore, the activation temperature of the catalyst is estimated by measuring the energization current of the net heater 31, and the degree of catalyst degradation is estimated from this activation temperature.

  In other words, the catalyst has a characteristic that the activation temperature, which is the starting temperature of the catalytic reaction, gradually shifts to a high temperature side due to deterioration. On the other hand, when the catalyst is activated and the catalytic reaction occurs, the reaction heat Since the temperature starts to rise and the electric resistance of the net heater 31 starts to increase, the activation current of the catalyst is measured by measuring the current flowing to the net heater 31 at the start of this temperature rise. The extent of the rise can be estimated. Therefore, the degree of catalyst deterioration can be grasped from the change in energization current at the start of temperature increase of the current value of the net heater 31 having a close relationship with the catalyst temperature. Note that, by arranging the net heater 31 in the flow direction of the exhaust gas G (longitudinal direction of the exhaust gas purification device 10), it becomes possible to grasp the deterioration state of the catalyst in more detail.

  Further, when the exhaust gas purification device 10 is constituted by a NOx purification catalyst device and a NOx occlusion reduction type catalyst is used as the catalyst, the central cylinder portion 12 carries potassium as a NOx occlusion material, and the outer peripheral portion 11 is supported. Is preferably configured to support barium as the NOx storage material. According to this configuration, high-temperature (450 ° C. to 550 ° C.) potassium is often passed through the high-temperature exhaust gas, and is provided in the central cylinder portion 12 having a high average temperature during the NOx purification treatment. Since the low temperature exhaust gas passes through the outer peripheral portion 11 where the average temperature is low during the NOx purification treatment, the NOx occlusion performance is more efficiently achieved with different catalyst components. Can be demonstrated.

  Next, an exhaust gas purification method in the exhaust gas purification system 1 having the above configuration will be described. In a normal operation state, both the first valve 16 and the second valve 18 are opened, the exhaust gas G is caused to flow through both the outer peripheral portion 11 and the central cylinder portion 12, and harmful components in the exhaust gas G are catalyzed. Purify. In addition, the exhaust gas G for warm-up operation, low-load operation, etc. is low temperature, and it is necessary to activate the catalyst quickly, and desulfurization treatment to recover the catalyst from sulfur poisoning requires the catalyst to be at a high temperature. If there is, the first valve 16 and the second valve 18 are controlled as follows according to each case.

First, the warm-up operation and the low load operation will be described with reference to the control flow of FIG. When the engine is started and the control flow shown in FIG. 11 is called from the advanced control flow, the temperature (first index temperature) Tg of the exhaust gas G and the preset first determination temperature T1 are input in step S11. Is done. In step S12, it is determined whether or not the temperature Tg of the exhaust gas G is equal to or lower than the first determination temperature T1. In the control flow of FIG. 11, the temperature Tg of the exhaust gas G flowing into the central cylindrical portion 12 is used as the first index temperature that indicates the temperature of the catalyst in the central cylindrical portion 12 . Note that the temperature Tc1 measured by the thermocouple 19 can also be used.

  If it is determined in step S12 that the temperature Tg of the exhaust gas G is equal to or lower than the first determination temperature T1 (YES), the process goes to step S13, the first valve 16 is closed, and the second valve 18 is opened. As a result, the exhaust gas G is allowed to flow only through the central cylinder portion 12. After this control, after a preset time (time related to the interval of checking the exhaust gas temperature Tg) has elapsed, the process returns to step S11.

If it is determined in step S12 that the temperature Tg of the exhaust gas G exceeds the first determination temperature T1 (NO), the process goes to step S14 to open the first valve 16 and open the second valve 18, that is, the second valve. The first valve 16 is opened while 18 is open. As a result, the exhaust gas G flows through both the central cylinder portion 12 and the outer peripheral portion 11. After this control, after a preset time (time related to the interval of checking the exhaust gas temperature Tg) has elapsed, the process returns to step S11.

  If this step S11 to step S13 or step S11 to step S14 is repeatedly executed and the engine is stopped, an interrupt is generated, the end process of step S15 is performed, and the control flow returns to the advanced control flow. With the end of the flow, the control flow of FIG. 11 is also ended.

  In the present invention, when the first valve is opened in step S14 and the exhaust gas G starts to flow through the outer peripheral portion 11, the net heater 31 is energized to heat the outer peripheral portion 11 from the outside, and the catalyst in the outer peripheral portion 11 is The temperature is raised to quickly reach the activation temperature or higher, and after reaching the activation temperature, the temperature is maintained within the activation temperature range.

With the above control, when the first index temperature Tc1 indicating the temperature of the catalyst in the central cylinder portion 12 is equal to or lower than the first determination temperature T1 set in advance, the first valve 16 is closed and the second valve 18 is opened, and the exhaust gas G When the first index temperature Tc1 exceeds the first determination temperature T1, the first valve 16 is opened with the second valve 18 open, and the exhaust gas G is discharged from the outer periphery to the central cylinder portion 12. The temperature of the outer peripheral part 11 is adjusted by flowing the current through both the parts 11 and adjusting the energization amount while energizing and heating the net heater 31.

  According to this configuration, at the time of warm-up operation or low load operation immediately after engine startup, the temperature Tg of the exhaust gas G is low and the volumetric flow rate of the exhaust gas G is small, so that the exhaust gas G is added to the central cylinder portion 12 with good heat retention. And the temperature of the catalyst in the central cylinder portion 12 can be quickly raised. Further, when the temperature Tg of the exhaust gas G is high and the volumetric flow rate of the exhaust gas G is large, the exhaust gas G is allowed to flow through both the central cylindrical portion 12 and the outer peripheral portion 11 to increase the volume of the portion through which the exhaust gas G passes. By reducing the space velocity with respect to the exhaust gas G, the time during which the exhaust gas G contacts the catalyst can be lengthened to promote the catalytic reaction. At the same time, the outer peripheral portion 11 is heated by the net heater 31 disposed on the outer periphery of the outer peripheral portion 11 so that the temperature of the catalyst in the outer peripheral portion 11 can be quickly raised and maintained within the activation temperature range. Accordingly, the time until the catalyst is activated can be shortened, and the amount of harmful components in the exhaust gas G released into the atmosphere before the catalyst is activated can be reduced.

  The first determination temperature T1 is a temperature equal to or higher than the activation temperature of the catalyst, and is a temperature within a range of 200 ° C. to 300 ° C., depending on the type of the catalyst, and is set to 250 ° C., for example.

Note that the control flow of FIG. 11 is effective when the engine is started or in a low load operation . However, when the temperature Tg of the exhaust gas G rises from the low load operation to the high load operation, a step is performed. Since both the first valve 16 and the second valve 18 of S14 are opened, it is not always necessary to stop the control flow of FIG.

  Next, the case of desulfurization treatment in which the temperature of the catalyst needs to be increased will be described with reference to the control flow of FIGS. The control flow in FIG. 12 and the control flow in FIG. 13 are one control flow connected by A at the lower end of FIG. 12 and A at the upper end of FIG.

In the exhaust gas purification system 1, when performing the desulfurization process, the control flow of FIG. 11 is switched to the control flow of FIGS. Here, the measured temperature Tc1 of the thermocouple 19 is used as the first index temperature, and the measured temperature Tc2 of the thermocouple 20 is used as the second index temperature, but the exhaust gas G is used as the first index temperature and the second index temperature. The temperature Tg may be used.

  The control flow in FIG. 12 and FIG. 13 is a control in the case of performing the desulfurization process. When started, in step S21 in FIG. 12, a first index temperature Tc1 that indexes the temperature of the catalyst in the central cylinder portion 12 is preset. A second determination temperature T2 and a preset first determination time t1 are input. Next, in step S22, it is determined whether or not the first index temperature Tc1 is equal to or lower than the second determination temperature T2.

If it is determined in step S22 that the first index temperature Tc1 is equal to or lower than the second determination temperature T2 (YES), the process proceeds to step S23, where the first valve 16 is closed and the second valve 18 is opened. As a result, the exhaust gas G is allowed to flow only through the central cylinder portion 12. After performing this control, after a preset time ( time related to the check interval of the first index temperature Tc1 ) has elapsed, the process returns to step S21.

  If the first index temperature Tc1 exceeds the second determination temperature T2 in the determination in step S22 (NO), it is the sum of the times when the first index temperature Tc1 exceeds the second determination temperature T2 in step S24. The first desulfurization treatment time td1 is counted. In the next step S25, it is determined whether or not the first desulfurization treatment time td1 has passed a preset first determination time t1. If it is determined in step S25 that the first desulfurization treatment time td1 has not passed the first determination time t1 (NO), the preset time (the first desulfurization treatment time td1 is checked as it is). After a lapse of (time related to the interval), the process returns to step S21.

  If it is determined in step S25 that the first desulfurization treatment time td1 has passed the first determination time t1 (YES), the process proceeds to step S26 in FIG. 13 via A, and the first valve 16 is opened and the second valve is opened. 18 is closed and the exhaust gas G is allowed to flow only to the outer peripheral portion 11.

  In the next step S27, a second index temperature Tc2 that indicates the temperature of the catalyst on the outer peripheral portion 11, a preset third determination temperature T3, and a preset second determination time t2 are input. In the next step S28, it is determined whether or not the second index temperature Tc2 is equal to or lower than the third determination temperature T3. If it is determined in step S28 that the second index temperature Tc2 is equal to or lower than the third determination temperature T3 and does not exceed the third determination temperature T3 (YES), a preset time (interval for checking the second index temperature Tc2) After a lapse of (time related to), the process returns to step S27.

  If it is determined in step S28 that the second index temperature Tc2 exceeds the third determination temperature T3 (NO), in the next step S29, the total time for which the second index temperature Tc2 exceeds the third determination temperature T3. The second desulfurization treatment time td2 is counted. In the next step S30, it is determined whether or not the second desulfurization treatment time td2 has passed a preset second determination time t2. If it is determined in step S30 that the second desulfurization treatment time td2 has not passed the second determination time t2 (NO), the preset time (check of the second desulfurization treatment time td2) is left as it is. After the elapse of the time related to the interval, the process returns to step S27.

If it is determined in step S30 that the second desulfurization processing time td2 has passed the second determination time t2 (YES), the process goes to step S31 to reset the first desulfurization processing time td1 and the second desulfurization processing time td2, etc. After completion of the desulfurization process , return to the advanced control flow .

Normally, the third determination temperature T3 is set lower than the second determination temperature T2 , and the second determination time t2 is set shorter than the first determination time t1 . This is because barium used in the low-temperature NOx storage reduction catalyst is more easily desorbed than potassium used in the high-temperature NOx storage reduction catalyst. Depending on the type of catalyst and the exhaust gas purification device 10, for example, the second determination temperature T2 is set to about 700 ° C. to 750 ° C., and the third determination temperature T3 is set to about 650 ° C. to 700 ° C. The determination time t1 is set to about 480 s to 600 s, and the second determination time t2 is set to about 180 s to 300 s.

In the present invention, when the first valve 16 is opened in this step S26 and the exhaust gas G starts to flow through the outer peripheral portion 11, the net heater 31 is energized to heat the outer peripheral portion 11 from the outside, and the catalyst in the outer peripheral portion 11 is heated. Is quickly raised to the third determination temperature T3 or higher.

In addition, when the current I of the net heater 31 is used instead of the second index temperature Tc2 that indicates the temperature of the catalyst on the outer peripheral portion 11 measured by the thermocouple 20, the second index temperature Tc2 in FIG. Instead of, the energization current I is used, and the determination current value Ic is used instead of the third determination temperature T3. In this case, in the control flow of FIG. 13, steps S27 and 28 become steps S27A and 28A of the control flow of FIG.

In this case, even if the temperature rises locally and the resistance at one location increases, the influence on the overall resistance is small, and the overall resistance value is large because the outer peripheral portion carrying the catalyst. This is limited to the case where the overall temperature of 11 increases and the value of many resistances increases. The net-like heater 31 is resistance is dispersed, as in the exhaust gas purifying device 10, when the object for detecting the temperature is high, even for a constant voltage changes in the resistance value of the net-like heater 31 Thus, by detecting the energization current I as the overall current value, control using a value close to the overall average temperature becomes possible.

With this control, when the desulfurization process is performed, when the first index temperature Tc1 indicating the temperature of the catalyst in the central cylinder portion 12 is equal to or lower than the preset second determination temperature T2, the first valve 16 is closed and the second The sum of the time when the first index temperature Tc1 exceeds the second determination temperature T2 after the first index temperature Tc1 exceeds the second determination temperature T2 after the valve 18 is opened and the exhaust gas G is allowed to flow only through the central cylinder portion 12. The first valve 16 and the second valve 18 are kept open and closed until the first desulfurization treatment time td1 that is set in advance passes a first determination time t1, and the first desulfurization treatment time td1 is the first desulfurization treatment time td1. When the determination time t1 has elapsed, the first valve 16 is opened, the second valve 18 is closed, the exhaust gas G is allowed to flow only to the outer peripheral portion 11, and the net heater 31 is energized to adjust the energization amount while heating. The outer periphery 1 The second index temperature Tc2 exceeds the third determination temperature T3 when the second index temperature Tc2 indicating the temperature of the catalyst of the outer peripheral portion 11 exceeds the preset third determination temperature T3. Until the second desulfurization treatment time td2, which is the sum of the times, passes the preset second determination time t2, the open / close state of the first valve 16 and the second valve 18 and the temperature adjustment by the net heater 31 are continued as they are. When the second desulfurization treatment time td2 has passed the second determination time t2, the desulfurization treatment is terminated.

According to the exhaust gas purification method in the case of this desulfurization process, in the desulfurization process that requires the catalyst to be at a high temperature, from when the first index temperature Tc1 exceeds the second determination temperature T2 until it exceeds the first determination time t2. The exhaust gas G is completely flowed through the central cylindrical portion 12 having a high heat retention and a fast temperature rise due to the heat insulating structure of the cylindrical partition wall 13 until the desulfurization treatment of the central cylindrical portion 12 is completed. Although the heat retaining property is good depending on the structure, the exhaust gas G is entirely supplied to the outer peripheral portion 11 where the temperature rise of the catalyst is likely to be delayed as compared with the central cylindrical portion 12, and the outer peripheral portion 11 is heated by energizing the net heater 31. 11 desulfurization treatment can be performed intensively.

  Therefore, in the desulfurization process of the central cylinder part 12, since the heat transfer from the central cylinder part 12 is suppressed by the partition wall 13, the heat treatment time of the central cylinder part 12 can be reduced, and the outer peripheral part 11 In the desulfurization process, the heat transfer from the outer peripheral part 11 is suppressed by the partition wall 13 and the heat retaining structure 14, and further, the heating is performed by the net heater 31, so that the heat treatment time of the outer peripheral part 11 is remarkably reduced. Can do. Therefore, the temperature of each part can be quickly raised, the entire catalyst can be efficiently desulfurized, and the time and fuel consumption required for the desulfurization process can be reduced.

  In addition, in the first half of the desulfurization treatment, only the central cylinder portion 12 is desulfurized, and in the second half of the desulfurization treatment, only the outer peripheral portion 11 is desulfurized while being heated by the net heater 31, so By sufficiently desulfurizing the outer peripheral portion 11 of the catalyst that is difficult to rise, sufficient desulfurization can be performed over the entire catalyst. Therefore, the purification ability can be maintained in a good state.

  As a result, it is possible to reduce the time and number of reduction processes necessary for maintaining the purification performance of the catalyst, in other words, the regeneration process for recovering the purification capacity of the catalyst, thereby reducing the fuel consumption required for the regeneration process. . Therefore, the capacity of the catalyst mounted on the vehicle can be reduced to ensure the mountability and reduce the cost. Further, in the desulfurization treatment, it is possible to suppress the deterioration of the catalyst due to the central cylinder portion 12 being exposed to an excessively high temperature by heating only the outer peripheral portion 11 of the catalyst that is easily cooled to a high temperature.

In the control flow of FIG. 12 and FIG. 13 (or FIG. 14) described above, the number of desulfurization treatments is the same for the central cylindrical portion 12 and the outer peripheral portion 11, but the desulfurization treatment is further performed for the outer peripheral portion 11. If it is configured so as to be performed separately from the central cylindrical portion 12, the number of treatments of the outer peripheral portion 11 which is relatively difficult to adsorb sulfur can be reduced, so that the fuel consumption can be further reduced.

  According to the exhaust gas purification system 1 having the above-described configuration, the exhaust gas purification device 10 using a catalyst such as a NOx purification catalyst device, an oxidation catalyst device, or a filter device with a catalyst takes into account the temperature dependence of the purification performance of the catalyst. Thus, the purification performance of the catalyst can be utilized quickly and efficiently.

  According to this configuration, the amount of heat dissipated from the exhaust gas purification device 10 can be supplemented by the heating by the net heater 31, and the temperature drop of the portion supporting the catalyst can be suppressed. Further, the temperature of the outer peripheral portion 11 of the portion carrying the catalyst can be raised by heating by the net heater 31 and maintained in the activation temperature range without depending on the heat quantity of the exhaust gas G. Almost no heating time can be eliminated. Therefore, it is possible to significantly reduce the emission of harmful components that are released before the catalyst is heated to the activation temperature range.

  In addition, the net-like heater 31 divided in the longitudinal direction can be heated differently for each longitudinal direction by flowing an electric current in parallel in the circumferential direction. Since the suppression of heating can be easily performed, the temperature of the catalyst can be raised in a short time and maintained relatively uniformly as a whole.

  Further, according to the exhaust gas purification method described above, in the exhaust gas purification device 10 using a catalyst such as a NOx purification catalyst device, an oxidation catalyst device, a filter device with a catalyst, etc., warm-up operation or low load operation immediately after engine startup is performed. In some cases, exhaust gas G is allowed to flow through the central cylindrical portion 12 with good heat retention, and the catalyst in the central cylindrical portion 12 can be quickly heated to shorten the time until activation.

When the volumetric flow rate of the exhaust gas G is large, the exhaust gas G is allowed to flow through both the central cylindrical portion 12 and the outer peripheral portion 11 to increase the volume of the portion through which the exhaust gas G passes, so that the space velocity relative to the exhaust gas G is increased. The catalytic reaction can be promoted by increasing the time during which the exhaust gas G contacts the catalyst. When exhaust gas G is allowed to flow through the outer peripheral portion 11, the energizing amount is adjusted while the net heater 31 is energized and heated to adjust the temperature of the outer peripheral portion 11, so the outer peripheral portion 11 is heated from the outer peripheral side. The temperature can be quickly raised to the activation temperature, and after the temperature rise, the amount of energization can be adjusted to maintain the catalyst temperature Tc2 in the outer peripheral portion 11 within the activation temperature range.

It is a figure which shows the structure of the exhaust-gas purification system of embodiment of this invention. It is a figure which shows the structure of the inlet_port | entrance of the exhaust gas of an exhaust gas purification apparatus. It is a figure which shows the cross section of an exhaust-gas purification apparatus. It is an enlarged view of the ellipse part shown by H of FIG. 3 which shows the structure of the cylindrical partition wall of an exhaust-gas purification apparatus. It is a figure which shows the structure of the net-shaped heater of an exhaust-gas purification apparatus. It is a figure which shows the drawer | drawing-out part structure of the electricity supply electrode of the net-shaped heater of an exhaust-gas purification apparatus. It is an enlarged view of the ellipse part shown by J of FIG. 6 which shows the drawer | drawing-out part structure of the electricity supply electrode of the net-shaped heater of an exhaust-gas purification apparatus. It is a figure which shows the structure of electricity supply of the net-shaped heater of an exhaust-gas purification apparatus. It is a figure which shows typically the state of electricity supply of a single net-shaped heater. It is a figure which shows typically the state of the parallel electricity supply of a some net-shaped heater. It is a figure which shows an example of the control flow in the case of warm-up operation and low load operation of the exhaust gas purification method according to the present invention. It is a figure which shows the first half of an example of the control flow in the case of the desulfurization process of the exhaust gas purification method which concerns on this invention. It is a figure which shows the second half of the control flow of FIG. It is a figure which shows the second half of the control flow of FIG. 12 at the time of using the energization current of a heater.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Exhaust gas purification system 2 Engine exhaust passage 3 Engine control apparatus (ECU)
DESCRIPTION OF SYMBOLS 10 Exhaust gas purification apparatus 11 Outer peripheral part 12 Central cylinder part 13 Partition wall 14 Thermal insulation structure 15 1st channel | path 16 1st valve | bulb 17 2nd channel | path 18 2nd valve | bulb 19, 20, 21 Thermocouple 31 Net-like heater (heater)
32 Insulating seal mat 33, 35 Lead wire 34 Voltage adjustment and control unit 36 Battery (power supply)
G exhaust gas I energizing current Ic determination current value T1 first determination temperature T2 second determination temperature T3 third determination temperature Tc1 first index temperature Tc2 second index temperature Tg exhaust gas temperature t1 first determination time t2 second determination time td1 first desulfurization treatment time td2 second desulfurization treatment time

Claims (4)

In an exhaust gas purification system having an exhaust gas purification device carrying a catalyst for purifying a harmful component in exhaust gas, a material whose energization resistance increases when the temperature of the outer periphery of the portion carrying the catalyst of the exhaust gas purification device rises The heater energized portion is divided in the longitudinal direction so that the current flowing through the heater flows in the circumferential direction, and each of the divided heaters is electrically parallel to the energized electrode. The part carrying the catalyst of the exhaust gas purification device is divided into two parts, an outer peripheral part and a central cylindrical part, by a cylindrical partition wall of a heat shielding structure,
A first valve is provided between the exhaust passage of the internal combustion engine and the outer peripheral portion, and a second valve is provided between the exhaust passage and the central cylinder portion,
When the first index temperature indicating the temperature of the catalyst in the central cylinder portion is equal to or lower than the first determination temperature set in advance, the first valve is closed and the second valve is opened to allow the exhaust gas to flow only in the central cylinder portion. When the first index temperature exceeds the first determination temperature, the first valve is opened while the second valve is open, and exhaust gas is allowed to flow through both the central tube portion and the outer peripheral portion, and the heater. When the desulfurization treatment is performed by adjusting the energization amount while energizing and heating to adjust the temperature of the outer peripheral portion, a first index temperature indicating the temperature of the catalyst in the central cylinder portion is set in advance. 2 or less, the first valve is closed and the second valve is opened to allow the exhaust gas to flow only through the central cylinder, and after the first index temperature exceeds the second determination temperature, The index temperature is the second judgment temperature The first valve and the second valve are kept in the open / closed state until the first determination time set in advance, which is the sum of the obtained time, passes, and the first desulfurization time When the first determination time has elapsed, the first valve is opened, the second valve is closed, exhaust gas is allowed to flow only to the outer periphery, and the heater is energized to adjust the energization amount while heating. When the energizing current to the heater for adjusting the temperature of the outer peripheral portion and raising the temperature of the outer peripheral portion exceeds a preset judgment current value, the sum of the times when the energizing current exceeds the judgment current value Until the second determination time set in advance has elapsed, the open / closed state of the first valve and the second valve and the temperature adjustment by the heater are continued as they are, and the second desulfurization processing time is Second judgment time When the time has elapsed, the exhaust gas is caused to flow to the outer peripheral portion by opening the first valve, and the exhaust gas is caused to flow to the central cylinder portion by opening the second valve so as to end the desulfurization process. Exhaust gas purification system. The temperature of the outer peripheral portion of the portion carrying the catalyst is estimated based on the amount of current flowing to the heater, and the temperature control of the portion carrying the catalyst is controlled based on this estimated value by controlling the amount of current supplied to the heater. The exhaust gas purification system according to claim 1, wherein: The exhaust gas purification system according to claim 1 or 2, wherein an activation temperature of the catalyst is estimated by measuring an energization current of the heater, and a degree of deterioration of the catalyst is estimated from the activation temperature. A portion of the exhaust gas purifying device carrying the catalyst is divided into an outer peripheral portion and a central cylindrical portion by a cylindrical partition wall having a heat shielding structure, and a first valve is provided between the exhaust passage of the internal combustion engine and the outer peripheral portion. A second valve is provided between the exhaust passage and the central tube portion, the exhaust gas is caused to flow to the outer peripheral portion by opening the first valve, and the exhaust gas is passed to the center by opening the second valve. It is configured to flow through the cylinder, and the outer periphery of the outer periphery is encased in a heater that uses a material whose energization resistance increases as the temperature rises, and the heater is energized so that the current flowing through the heater flows in the circumferential direction. An exhaust gas purification method for an exhaust gas purification system in which a portion is provided in the longitudinal direction and each of the divided heaters is electrically connected to the energizing electrode in parallel.
When the first index temperature indicating the temperature of the catalyst in the central cylinder portion is equal to or lower than the first determination temperature set in advance, the first valve is closed and the second valve is opened to allow the exhaust gas to flow only in the central cylinder portion. When the first index temperature exceeds the first determination temperature, the first valve is opened while the second valve is open, and exhaust gas is allowed to flow through both the central tube portion and the outer peripheral portion, and the heater. The temperature of the outer peripheral part is adjusted by adjusting the energizing amount while energizing and heating,
When the desulfurization treatment is being performed, if the first index temperature indicating the temperature of the catalyst in the central cylinder portion is equal to or lower than the second determination temperature set in advance, the first valve is closed and the second valve is opened to exhaust the exhaust gas. A first desulfurization treatment time that is the sum of the time when the first index temperature exceeds the second determination temperature after the gas is allowed to flow only through the central cylinder portion and the first index temperature exceeds the second determination temperature. Until the first determination time set in advance has elapsed, the open and closed states of the first valve and the second valve are continued as they are, and when the first desulfurization processing time has passed the first determination time, The first valve is opened and the second valve is closed to allow exhaust gas to flow only to the outer peripheral portion, and the heater is energized to adjust the energization amount while heating to adjust the temperature of the outer peripheral portion. To the heater to heat up the outer periphery When the electric current exceeds a preset determination current value, the second desulfurization treatment time, which is the sum of the time when the energization current exceeds the determination current value, passes until the second determination time set in advance passes. The exhaust gas purification is characterized in that the open / closed state of the one valve and the second valve and the temperature adjustment by the heater are continued as they are, and the desulfurization process is terminated when the second determination time has passed the second determination time. Method.

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