JP2007263055A - Exhaust purification device - Google Patents

Abstract

The present invention relates to an exhaust emission control device, which can improve responsiveness in exhaust gas temperature control with a simple configuration and realize efficient filter regeneration.
An exhaust purification device for regenerating a filter by controlling the temperature of an exhaust purification filter (2) interposed on the exhaust passage (10) of the engine, on the upstream side of the filter (2) on the exhaust passage (10). The oxidation catalyst 1 includes an oxidation catalyst 1 disposed in a single interposed casing, and temperature detection means 3 provided inside the casing and detecting the exhaust temperature inside the casing as a catalyst internal temperature _Tc. Are the first oxidation catalyst portion 1a upstream of the exhaust passage 10 relative to the position where the temperature detecting means 3 detects the in-catalyst temperature _Tc , and the second oxidation catalyst portion 1b downstream of the exhaust passage 10 relative to the position. And the second oxidation catalyst unit 1b has a heat capacity large enough to absorb at least a predetermined amount of variation in the exhaust temperature in the first oxidation catalyst unit 1a.
[Selection] Figure 1

Description

  The present invention relates to an exhaust gas purification apparatus suitable for use in purifying exhaust gas from an engine, particularly a diesel engine.

Conventionally, as a post-treatment device for a diesel engine mounted on a vehicle, a diesel particulate filter (DPF, hereinafter abbreviated as a filter) that collects particulate matter (particulate matter, hereinafter abbreviated as PM) contained in exhaust gas. And an exhaust gas purification device having an oxidation catalyst for oxidizing and removing PM on the filter has been developed. In this exhaust purification device, NO ₂ is generated from NO in exhaust gas using an oxidation catalyst, and PM collected on the filter is reacted with NO ₂ to continuously incinerate and remove PM, To play. In addition, such a method of continuously removing PM by incineration is referred to as a continuous regeneration method (for example, Patent Document 1).

  On the other hand, the exhaust gas temperature is unlikely to rise under Japanese driving conditions where there is a lot of vehicle traffic (for example, low load and low rotation), and if the filter temperature does not rise to the temperature required for PM combustion, There is a possibility that PM is not sufficiently removed by incineration. Therefore, a forced regeneration type that forcibly incinerates PM by intentionally maintaining the filter temperature at a necessary temperature has been developed. As a forced regeneration type exhaust gas purification device, for example, a device in which an external heat source such as a heater is provided in the filter, or a device in which the filter temperature is raised by raising the exhaust gas temperature has been developed.

  In addition, a method has been proposed in which unburnt fuel is supplied to an oxidation catalyst provided upstream of the filter (upstream of the exhaust passage) by adding fuel (HC) to the exhaust gas, and the temperature of the filter is raised by the oxidation heat. ing. Since the calorific value of unburned fuel can be directly used for raising the temperature of the filter, this is expected as a technique that can obtain good thermal efficiency and suppress deterioration of fuel consumption.

  By the way, the PM combustion speed on the filter, that is, the regeneration speed, becomes slower as the filter temperature (or the exhaust gas temperature flowing into the filter) is lower. On the other hand, if the filter temperature is too high, cracks and erosion occur on the filter surface. May be easier. Therefore, in order to regenerate the filter efficiently, temperature control is performed so that a good PM combustion rate can be obtained and the temperature fluctuation of the filter is kept within a temperature range where there is no risk of cracking or melting of the filter. It is preferable to carry out.

In this case, a method is conceivable in which temperature detection means for detecting the actual exhaust temperature in the vicinity of the filter is provided, and the amount of unburned fuel added is controlled while confirming the detected exhaust temperature. For example, as shown in FIG. 5, an oxidation catalyst 11 on the exhaust passage 15 of the engine E, a filter 12 disposed downstream thereof, and a temperature sensor 13 for detecting the exhaust temperature between the oxidation catalyst 11 and the filter 12 The amount of unburned fuel added is controlled while feeding back the actual exhaust temperature immediately before flowing into the filter 12 (near the inlet) to the control device 14. Thereby, the actual filter temperature and exhaust temperature can be controlled within a predetermined temperature range, and the filter 12 can be efficiently regenerated.
Japanese Patent Laid-Open No. 2003-13730

However, in the conventional feedback control as described above, the filter temperature may not be sufficiently controlled within a predetermined temperature range in a state where the disturbance (external action affecting the control result) is large.
For example, the exhaust temperature of the vehicle varies greatly depending on the operating state of the engine E. FIG. 6 shows an example of fluctuations in the exhaust temperature near the inlet of the filter 12 when a vehicle equipped with the exhaust purification device of FIG. 5 suddenly increases the traveling speed. In this example, the exhaust temperature suddenly rises as the vehicle starts, causing overshoot, and the exhaust temperature reaches a temperature range where the filter 12 is easily melted. After that, feedback control is performed so that the exhaust temperature approaches the target temperature by feedback.However, when the vehicle enters a traveling state at a substantially constant speed, the exhaust temperature decreases and the undershoot occurs. 6, the filter 12 falls to a temperature region where the regeneration speed of the filter 12 is low.

Thus, in the exhaust temperature control of the vehicle, even if feedback control based on the exhaust temperature near the inlet of the filter 12 is performed, it is difficult to stabilize the inlet temperature of the filter 12 depending on the traveling state of the vehicle. There is a problem that there may be cases.
Further, in a general exhaust gas purification apparatus, the capacity of the oxidation catalyst 11 is set to be relatively large so as to clear the standard defined by the exhaust gas regulations, so that the heat capacity is large. Therefore, the exhaust temperature fluctuation near the inlet of the filter 12 occurs with a slight delay in time with respect to the heat generation fluctuation in the oxidation catalyst 11. That is, it takes a relatively long response time from when the amount of unburned fuel added is changed by feedback control to when temperature fluctuation is detected by the temperature sensor 13.

  For example, FIG. 7 is a graph showing test results of actual exhaust temperature fluctuations near the inlet of the filter 12 when the amount of unburned fuel added is varied. Here, it can be seen that when the fuel addition amount is increased or decreased stepwise, a wavy temperature fluctuation delayed by about one cycle relative to the increase / decrease period is detected, and the delay time is approximately 25 seconds. As described above, in the exhaust purification apparatus, there is a problem that it is difficult to obtain good control responsiveness due to a response delay due to the heat capacity of the oxidation catalyst 11 and it is difficult to suppress overshoot and undershoot of the exhaust temperature near the inlet of the filter 12.

  The present invention has been made in view of such a problem, and an object of the present invention is to provide an exhaust purification device that can improve responsiveness in exhaust temperature control with a simple configuration and can realize efficient filter regeneration.

  In order to achieve the above object, an exhaust emission control device according to the present invention (Claim 1) is an exhaust emission control device that regenerates the filter by controlling the temperature of an exhaust purification filter interposed on an exhaust passage of the engine. An oxidation catalyst disposed in a single casing interposed upstream of the filter on the exhaust passage, and provided inside the casing, and detects the temperature inside the catalyst as the temperature inside the catalyst. Temperature detection means, and the oxidation catalyst includes a first oxidation catalyst portion upstream of the exhaust passage from a position where the temperature detection means detects the temperature, and a downstream side of the exhaust passage from the position. And a second oxidation catalyst part, and the second oxidation catalyst part has a heat capacity large enough to absorb a fluctuation of at least a predetermined amount of the exhaust temperature in the first oxidation catalyst part. Yes.

In addition, it is so preferable that the heat capacity of a 2nd oxidation catalyst part is large compared with the heat capacity of a 1st oxidation catalyst part. That is, in this case, the amount of heat stored in the second oxidation catalyst portion increases, and the heat transfer rate to the downstream side of the second oxidation catalyst portion becomes slower.
Furthermore, it is preferable that a fuel supply amount adjusting means for adjusting an addition amount of unburned fuel supplied to the oxidation catalyst based on the temperature in the catalyst detected by the temperature detecting means is provided.

Further, it is preferable that the temperature detecting means detects the temperature in the catalyst in the vicinity of a position where the temperature is substantially the highest in the exhaust flow direction inside the casing.
In addition, it is preferable that the first oxidation catalyst part has a larger amount of the catalyst noble metal supported than the second oxidation catalyst part.
Note that it is preferable that the amount of the catalyst noble metal supported by the first oxidation catalyst portion is larger than the amount of the catalyst noble metal supported by the second oxidation catalyst portion. In this case, the oxidation reaction of the unburned fuel is further promoted in the first oxidation catalyst part, and the temperature raising action in the second oxidation catalyst part becomes smaller.

  According to the exhaust purification device of the present invention (Claim 1), since the second oxidation catalyst portion having a heat capacity is disposed between the position of the temperature detection means to be controlled and the filter, the vicinity of the filter inlet A sudden change in the exhaust gas temperature can be suppressed. That is, for example, even when the exhaust gas temperature suddenly rises due to a sudden change in the operation region, heat is temporarily stored in the second oxidation catalyst unit having a large heat capacity, and heat downstream from the second oxidation catalyst unit. The transmission speed becomes slow. Thereby, the amount of overshoot near the filter inlet can be reduced, and the filter can be prevented from being melted. Conversely, even if the exhaust gas temperature suddenly drops, the amount of undershoot near the filter inlet can be reduced, and the filter can be efficiently regenerated in a short time.

In addition, since control is performed by detecting the exhaust temperature inside the casing as the temperature of the oxidation catalyst, compared with control based on the exhaust temperature near the filter inlet on the downstream side of the oxidation catalyst, Responsiveness to temperature changes can be improved.
Moreover, according to the exhaust emission control device of the present invention (Claim 2), the temperature of the oxidation catalyst and the filter can be increased or decreased with a simple configuration of adjusting the fuel injection amount.

Moreover, according to the exhaust emission control device of the present invention (Claim 3), since the substantially maximum temperature inside the casing (that is, the entire oxidation catalyst) can be controlled, thermal deterioration of the catalyst can be suppressed. In addition, compared with the case where the exhaust temperature near the filter inlet is the control target, the thermal reaction at the oxidation catalyst can be accurately grasped, and accurate control is possible.
Further, according to the exhaust emission control device of the present invention (claim 4), the exhaust temperature near the filter inlet is less susceptible to temperature fluctuations by the second oxidation catalyst unit, while the response delay due to the heat capacity of the second oxidation catalyst unit. It becomes easy to be influenced by. In other words, it is possible to reduce the temperature raising action by the second oxidation catalyst unit with respect to the exhaust gas heated through the first oxidation catalyst unit. That is, the exhaust gas at the controlled exhaust temperature can be supplied to the vicinity of the filter inlet without further raising the temperature in the second oxidation catalyst unit, and the controllability of the exhaust temperature in the filter can be improved. Moreover, an effective suppression tendency can be given to the fluctuation | variation of exhaust temperature.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. 1 to 4 show an exhaust emission control device as an embodiment of the present invention. FIG. 1 is a schematic configuration diagram showing the configuration of the exhaust emission control device, and FIG. FIG. 3 is a graph showing the exhaust temperature distribution, FIG. 3 is a graph showing the fluctuation of the running speed and the exhaust temperature near the filter inlet when the vehicle equipped with this device is started, and FIG. 4 shows the unburned fuel addition amount periodically in this device. It is a graph which shows the response delay of the exhaust temperature near filter entrance at the time of changing to.

[Constitution]
(1) Mechanical configuration The engine E shown in FIG. 1 is a diesel engine using light oil (HC) as fuel. On the exhaust passage 5 of the engine E, an oxidation catalyst (DOC) 1 and a filter (DPF, diesel particulate filter) 2 are installed in order from the upstream side of the flow path of exhaust gas (exhaust gas) discharged from the engine E. Has been. The exhaust emission control device of the present invention includes the oxidation catalyst 1, the filter 2, the catalyst temperature sensor 3, and the control device 4.

The oxidation catalyst 1 is a catalyst disposed in a single casing, oxidizes nitrogen oxide (NO) contained in exhaust gas to generate nitrogen dioxide (NO ₂ ), and supplies this NO ₂ to the filter 2. Is. Further, the oxidation catalyst 1 functions to oxidize unburned fuel (HC) in the exhaust gas to generate heat of oxidation and raise the temperature of the exhaust gas. The oxidation catalyst 1 is divided into an upstream first oxidation catalyst portion 1a and a downstream second oxidation catalyst portion 1b in the casing.

In the space between the first oxidation catalyst portion 1a and the second oxidation catalyst portion 1b, a catalyst temperature sensor (temperature detection means) 3 for detecting the exhaust temperature inside the space as the catalyst internal temperature _Tc is provided. . The detected catalyst temperature T _c is input to the control device 4.
The oxidation catalyst 1 of the present embodiment is coated (coated) with alumina powder on a honeycomb-shaped carrier made of cordierite, ceramics, etc., and supported thereon are fine particles of catalytic noble metal such as platinum, rhodium, and palladium. It has a known structure.

  The filter 2 is a porous filter (for example, a ceramic filter) that collects particulate matter (particulate matter mainly composed of carbon C, PM) in exhaust gas that causes black smoke. As schematically shown in FIG. 1, the inside of the filter 2 is divided into a plurality along the flow direction of the exhaust gas by the wall body, and when the exhaust gas passes through the wall body, PM is collected in the wall body. Thus, the exhaust gas is purified (filtered).

On the filter 2, the collected PM is incinerated under a predetermined temperature condition using NO ₂ supplied from the oxidation catalyst 1 as an oxidizing agent. Thereby, PM accumulated in the wall of the filter 2 is removed, and the filter 2 is regenerated and purified.
The control device (fuel supply amount adjusting means) 4 adjusts the addition amount (HC amount) of unburned fuel supplied to the oxidation catalyst 1 based on the catalyst internal temperature T _c detected by the catalyst temperature sensor 3. Regeneration control (forced regeneration) for forcibly regenerating and purifying the filter 2 is performed.

Further, here, as the regeneration control, feedback control is performed in which the amount of unburned fuel added is adjusted so that the in-catalyst temperature _Tc becomes equal to a predetermined target temperature set in advance. . That is, the control device 4 performs feedback control using the exhaust temperature (intra-catalyst temperature T _c ) in the space (DOC intermediate) between the first oxidation catalyst unit 1a and the second oxidation catalyst unit 1b as a control target. The predetermined target temperature is a temperature in the oxidation catalyst 1 such that the temperature near the inlet of the filter 2 is a temperature at which PM can sufficiently burn (for example, complete combustion). In this embodiment, the target temperature is set to a constant value.

(2) Heat Capacity Characteristics The division position of the oxidation catalyst 1 is such that the second oxidation catalyst portion 1b on the downstream side has a larger heat capacity than the first oxidation catalyst portion 1a on the upstream side. For example, when the oxidation catalyst 1 has the same quality and the same cross-sectional area with respect to the flow direction of the exhaust gas, the oxidation catalyst 1 is divided at a position upstream from the middle between the upstream end and the downstream end.

  In addition, by changing the heat capacity characteristics in the flow direction of the exhaust gas (for example, by increasing the thickness of the honeycomb wall of the carrier toward the upstream side to increase the mass), the displacement is shifted from the middle between the upstream end and the downstream end to the downstream side. It is also possible to divide by position. That is, it can be considered that the heat capacities of the first oxidation catalyst unit 1a and the second oxidation catalyst unit 1b are set so that the heat capacity on the upstream side of the division position is smaller than the heat capacity on the downstream side. . Therefore, the second oxidation catalyst unit 1b has a property that it is more difficult to warm and cool than the first oxidation catalyst unit 1a.

  That is, in the present exhaust purification apparatus, a heat capacity body having a heat capacity large enough to absorb a fluctuation of at least a predetermined amount of the exhaust temperature in the first oxidation catalyst unit 1a is provided downstream of the middle of the DOC that is a feedback sensing target. As a result, fluctuations in the exhaust temperature are stabilized.

(3) Temperature distribution characteristics In the present embodiment, the position where the first oxidation catalyst portion 1a and the second oxidation catalyst portion 1b are divided is the position where the exhaust gas flow direction is substantially the highest in the casing of the oxidation catalyst 1. Is set to Specifically, as shown in FIG. 2, according to the balance between the amount of heat of oxidation heat generated by unburned fuel inside the oxidation catalyst 1 and the amount of heat loss radiated from the casing of the oxidation catalyst 1 to the outside. In the exhaust temperature distribution determined by the above, the first oxidation catalyst portion 1a and the second oxidation catalyst portion 1b are divided in the vicinity of the position where the temperature becomes highest. That is, in the inside of the oxidation catalyst 1, the vicinity of the downstream end portion of the first oxidation catalyst portion 1a and the vicinity of the upstream end portion of the second oxidation catalyst portion 1b are higher in temperature than other portions in the casing.

(4) Precious metal carrying amount characteristics Further, paying attention to the carrying amount of the catalytic precious metal carried on the surface of the oxidation catalyst 1, a larger amount of catalytic precious metal than the precious metal carrying amount of the second oxidation catalyst portion 1b is present in the first oxidation catalyst portion 1a. It is carried on. That is, the temperature rise characteristic of the oxidation catalyst 1 is set so that the amount of heat generated in the second oxidation catalyst unit 1b is smaller than the amount of heat generated in the first oxidation catalyst unit 1a due to unburned fuel.

[Action]
The exhaust emission control device is configured as described above and operates as follows.
First, when regeneration control is started in the control device 4, the in-catalyst temperature _Tc detected by the catalyst temperature sensor 3 is fed back to the control device 4, and the in-catalyst temperature _Tc becomes equal to a preset target temperature. As described above, the amount of unburned fuel supplied to the oxidation catalyst 1 is adjusted.

(1) Action by heat capacity characteristic Here, between the position (intermediate DOC) of the catalyst temperature sensor 3 where the in-catalyst temperature _Tc is detected and the inlet of the filter 2 (DPF inlet), the upstream side A second oxidation catalyst portion 1b having a larger heat capacity than the first oxidation catalyst portion 1a is disposed. For this reason, the second oxidation catalyst unit 1b has a property that it is more difficult to warm and cool than the first oxidation catalyst unit 1a, and the temperature T _c in the catalyst that is the control target of the control device 4 is greatly affected by the disturbance. Even if it fluctuates, the exhaust temperature fluctuation on the downstream side of the second oxidation catalyst portion 1b is attenuated.

For example, as indicated by a thin solid line in FIG. 3, the exhaust of the catalyst internal temperature _{Tc in} the middle of the DOC is so large that the same overshoot as in the conventional exhaust temperature fluctuation example shown in FIG. Assume that the temperature rises rapidly. Even in such a case, in the present exhaust control device, since the heat capacity of the second oxidation catalyst unit 1b is large, the second oxidation catalyst unit 1b that is heated by the amount of heat of the exhaust at the catalyst internal temperature _Tc is difficult to warm. A time delay occurs in the rise of the exhaust temperature downstream of the second oxidation catalyst portion 1b. Further, since the heated second oxidation catalyst portion 1b is difficult to cool, the movement of the amount of heat transmitted from the second oxidation catalyst portion 1b to the exhaust on the downstream side becomes slow.

As a result, the exhaust temperature at the downstream side of the second oxidation catalyst unit 1b, that is, at the DPF inlet, suppresses the amplitude of the temperature fluctuation as shown by the thick solid line in FIG. In the example shown in FIG. 3, the temperature variation amplitude A _{1 in the} middle of the DOC is suppressed to A _{2 at the} DPF inlet, and the temperature variation is within a range close to the target temperature.

(2) Action by Temperature Distribution Characteristic In this exhaust control device, the division position of the first oxidation catalyst unit 1a and the second oxidation catalyst unit 1b, that is, the position in the middle of the DOC is exhausted in the casing of the oxidation catalyst 1. It is set at a position where the maximum temperature is reached in the flow direction. That is, since the exhaust temperature in the middle of the DOC to be controlled is the highest temperature in the casing of the oxidation catalyst 1, the exhaust temperature downstream of the second oxidation catalyst portion 1b is higher than the exhaust temperature in the middle of the DOC. There is nothing.

(3) Action by precious metal loading amount characteristics In addition, in this exhaust control device, a larger amount of catalytic precious metal than the amount of catalytic precious metal supported on the surface of the second oxidation catalyst portion 1b is present on the surface of the first oxidation catalyst portion 1a. It is supported. Therefore, when unburned fuel is supplied to the oxidation catalyst 1 by this regeneration control, the heat generation amount on the upstream side from the middle of the DOC becomes smaller than the heat generation amount on the downstream side.

  That is, the exhaust temperature near the inlet of the filter 2 is less susceptible to temperature fluctuations due to the oxidation reaction of unburned fuel in the second oxidation catalyst unit 1b, and is susceptible to response delay due to the heat capacity of the second oxidation catalyst unit 1b. Will be.

(4) Operation by the position where the catalyst temperature sensor 3 is arranged Further, in the present exhaust control device, the position in the middle of the DOC where the catalyst temperature sensor 3 is arranged, that is, the sensing position of the exhaust temperature to be controlled by feedback control. Compared with the conventional exhaust gas purification apparatus as shown in FIG. 5, the position has moved to the upstream side. That is, paying attention to the heat capacity of the oxidation catalyst 1, for example, if the heat capacity in the entire casing is the same as that of the conventional one, the heat capacity on the upstream side from the sensing position is reduced. Thereby, compared with the conventional one, the temperature fluctuation is detected more quickly by the catalyst temperature sensor 3.

  FIG. 4 is a graph showing test results of actual exhaust temperature fluctuations near the inlet of the filter 2 when the amount of unburned fuel added is increased or decreased in steps. Here, the amount of unburned fuel added shown in the lower part of FIG. 4 is the volume (cubic millimeter) added per stroke in the engine E. Also, the thick solid line in the upper part of FIG. 4 is a graph of the test result of the exhaust control device, and the thin solid line is a graph obtained by superimposing the graph of FIG.

In FIG. 4, when the fuel addition amount is increased or decreased stepwise, a wavy temperature variation delayed by approximately one third of the increase / decrease period is detected, and the delay time is approximately 8 seconds. is there. Thus, it can be seen that the response time of the exhaust gas temperature fluctuation is shortened as compared with the conventional exhaust control device as shown in FIG.
The detected temperature fluctuation information with good response is immediately fed back to the control device 4.

[effect]
According to the exhaust emission control device of the present embodiment, the following effects can be obtained.
(1) Effect due to heat capacity characteristics Even when the temperature T _{c in the} catalyst suddenly changes due to the influence of disturbance, the movement of the heat quantity downstream from the second oxidation catalyst portion 1b becomes slow, and the exhaust temperature fluctuation is suppressed. Therefore, fluctuations in exhaust gas temperature at the DPF inlet can be suppressed. That is, the amount of overshoot near the DPF inlet can be reduced, and the filter 2 can be prevented from being damaged. Also, the amount of undershoot can be reduced, and the regeneration time of the filter 2 can be shortened while maintaining a temperature range with good regeneration efficiency.

(2) Effect due to temperature distribution characteristics In this regeneration control, the exhaust temperature downstream of the second oxidation catalyst portion 1b does not become higher than the exhaust temperature in the middle of the DOC, and the inside of the casing (that is, the entire oxidation catalyst 1) ) Is controlled, the thermal deterioration of the oxidation catalyst 1 can be suppressed. In addition, it is possible to ensure that the exhaust temperature at least in the vicinity of the DPF inlet is lower than the exhaust temperature in the middle of the DOC to be controlled, and it is possible to suppress thermal deterioration of the filter 2.

(3) Effect due to precious metal loading amount characteristics The exhaust temperature near the inlet of the filter 2 is less susceptible to temperature fluctuations by the second oxidation catalyst portion 1b, and therefore in the oxidation reaction that occurs with the supply of unburned fuel to the oxidation catalyst 1. In addition, the temperature rising action in the second oxidation catalyst unit 1b can be reduced. That is, the exhaust gas that has reached the target temperature in the DOC intermediate portion (or has approached the target temperature) via the first oxidation catalyst portion 1a is filtered without being further heated by the second oxidation catalyst portion 1b downstream of the exhaust gas. 2 can be supplied to the vicinity of the inlet, and the controllability of the exhaust temperature in the filter 2 can be improved.

  Further, since the exhaust temperature near the inlet of the filter 2 is easily affected by a response delay due to the heat capacity of the second oxidation catalyst unit 1b, an effective suppression tendency can be given to fluctuations in the exhaust temperature.

(4) Effect due to the location of the catalyst temperature sensor 3 Since the catalyst internal temperature T _c inside the oxidation catalyst 1 (intermediate DOC) is detected and regeneration control is performed, as shown in FIG. Compared with control based on the exhaust temperature near the filter 2 inlet (near the DPF inlet) downstream of the oxidation catalyst 1, the response delay due to the heat capacity of the oxidation catalyst 1 is shortened, and the responsiveness to changes in the exhaust temperature is improved. be able to. As a result, the amount of fuel added can be adjusted quickly in response to temperature fluctuations in the exhaust gas due to unexpected disturbance, and overshoot and undershoot can be prevented in advance.
In addition, compared with the case where the exhaust temperature near the inlet of the filter 2 is controlled, the thermal reaction at the oxidation catalyst 1 can be accurately grasped, and control based on accurate calorific value calculation is facilitated.

[Others]
Although one embodiment of the present invention has been described above, the present invention is not limited to such an embodiment, and various modifications can be made without departing from the spirit of the present invention.

For example, in the above-described embodiment, the division position of the oxidation catalyst 1 is characterized and set by the heat capacity characteristic, the noble metal loading amount characteristic, and the temperature distribution characteristic, but at least has a characteristic related to the heat capacity characteristic. It is sufficient that the oxidation catalyst 1 is divided.
That is, it is only necessary that the second oxidation catalyst unit 1b has a heat capacity large enough to absorb a fluctuation of at least a predetermined amount of the exhaust temperature in the first oxidation catalyst unit 1a. In addition, as the heat capacity of the second oxidation catalyst unit 1b is larger than the heat capacity of the first oxidation catalyst unit 1a, the amount of heat stored in the second oxidation catalyst unit 1b increases, and the downstream side of the second oxidation catalyst unit 1b. The heat transfer rate to can be slowed down.

  Further, in the above-described embodiment, the oxidation catalyst 1 is illustrated in which the first oxidation catalyst portion 1a and the second oxidation catalyst portion 1b are divided in the upstream and downstream directions, but instead of such a configuration, for example, It is also conceivable to provide perforations into which the catalyst temperature sensor 3 can be inserted into the single oxidation catalyst 1. In this case, the upstream side from the position of the perforation is the first oxidation catalyst unit 1a, and the downstream side is the second oxidation catalyst unit 1b.

Further, in the above-described embodiment, only the catalyst temperature sensor 3 is provided as a sensor for detecting the exhaust temperature on the exhaust passage 5, but for example, the inlet side or the outlet side of the filter 2 (for example, the filter 2). A new temperature sensor may be provided on the downstream side). In this case, the exhaust gas temperature in the filter 2 can be controlled more accurately.
Further, in the above-described embodiment, the target temperature of the catalyst internal temperature _Tc is set as a predetermined constant value, which is set as the operating state of the engine E, the traveling state of the vehicle, the outside air temperature, etc. It is good also as a structure changed and set according to these conditions. Thereby, fine temperature management according to various conditions becomes possible, and the regeneration efficiency can be further increased.

In the above-described embodiment, it is preferable that the heat capacity of the second oxidation catalyst unit 1b is larger than the heat capacity of the first oxidation catalyst unit 1a. That is, in this case, the amount of heat stored in the second oxidation catalyst portion 1b due to the oxidation reaction of the unburned fuel increases, and heat transfer to the downstream side of the second oxidation catalyst portion 1a becomes slower.
Further, it is preferable that the amount of the catalyst noble metal supported by the first oxidation catalyst portion 1a is larger than the amount of the catalyst noble metal supported by the second oxidation catalyst portion 1b. In this case, the oxidation reaction of the unburned fuel is further promoted in the first oxidation catalyst part 1a, and the temperature raising action in the second oxidation catalyst part 1b is further reduced.

It is a typical block diagram which shows the structure of this exhaust gas purification apparatus. It is a graph which shows the exhaust temperature distribution in the oxidation catalyst of this apparatus. It is a graph which shows the fluctuation | variation of the running speed and the exhaust temperature of filter vicinity vicinity at the time of start of the vehicle provided with this apparatus. It is a graph which shows the response delay of the exhaust temperature vicinity of a filter entrance at the time of changing unburned fuel addition amount periodically in this apparatus. It is a typical block diagram which shows the structural example of the conventional exhaust gas purification apparatus. It is a graph which shows the fluctuation | variation of the exhaust temperature of filter vicinity vicinity at the time of start of the vehicle provided with the conventional exhaust gas purification apparatus. It is a graph which shows the response delay of the exhaust temperature vicinity of a filter entrance at the time of changing the amount of unburned fuel addition periodically in the conventional exhaust purification apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Oxidation catalyst 1a 1st oxidation catalyst part 1b 2nd oxidation catalyst part 2 Filter 3 Catalyst temperature sensor (temperature detection means)
4 Control device (Fuel supply amount adjusting means)
5 Exhaust passage

Claims (4)

An exhaust purification device that regenerates the filter by controlling the temperature of the exhaust purification filter interposed on the exhaust passage of the engine,
An oxidation catalyst disposed in a single casing interposed upstream of the filter on the exhaust passage;
A temperature detecting means provided inside the casing and detecting the temperature inside the casing as a temperature in the catalyst;
The oxidation catalyst includes a first oxidation catalyst portion upstream of the exhaust passage from a position where the temperature detection means detects the temperature, and a second oxidation catalyst portion downstream of the exhaust passage from the position. And having
The exhaust gas purification apparatus, wherein the second oxidation catalyst unit has a heat capacity large enough to absorb a fluctuation of at least a predetermined amount of the exhaust temperature in the first oxidation catalyst unit. 2. The fuel supply amount adjusting means for adjusting the addition amount of unburned fuel supplied to the oxidation catalyst based on the temperature in the catalyst detected by the temperature detecting means. The exhaust emission control device described. The exhaust gas purification apparatus according to claim 1 or 2, wherein the temperature detection means detects the internal temperature of the catalyst in the vicinity of a position where the temperature is substantially maximum in the flow direction of the exhaust gas in the casing. The exhaust emission control device according to any one of claims 1 to 3, wherein the first oxidation catalyst part has a larger amount of the catalyst noble metal supported than the second oxidation catalyst part.

Images