JP3304678B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine.

[0002]

Using BACKGROUND ART An exhaust gas purifying catalyst disposed in an exhaust passage of an internal combustion engine, HC in the exhaust gas, CO, exhaust gas purification device for purifying harmful components such as NO _X are generally known. Exhaust purification catalysts generally do not exhibit exhaust purification performance unless they have a specific activation temperature or higher. Therefore, when the catalyst temperature is low, harmful components in exhaust gas may pass through the catalyst and be released to the atmosphere. Therefore, an HC adsorbent that adsorbs HC components in exhaust gas at low temperature and releases HC components adsorbed at high temperature is disposed upstream of the exhaust purification catalyst in the exhaust passage to prevent HC components from being released into the atmosphere at low temperatures. An exhaust gas purifying device designed to perform the above has been devised. In these devices, when the exhaust gas temperature is low and the exhaust purification catalyst has not reached the activation temperature, such as when the engine is started, the HC component in the exhaust gas is adsorbed by the HC adsorbent on the upstream side of the exhaust purification catalyst. After the exhaust gas temperature rises and the exhaust gas purification catalyst reaches the activation temperature, both the HC component in the exhaust gas and the HC component released from the HC adsorbent are reduced to the downstream side. It purifies with an exhaust purification catalyst.

[0003] As this type of exhaust gas purifying apparatus, for example, there is an apparatus described in Japanese Utility Model Laid-Open No. 4-1617. Exhaust purification system of this publication, the NO _X purification catalyst which selectively purify NO _X by consuming HC component in an oxidizing atmosphere is arranged in an exhaust passage, arranging an HC adsorbent in the exhaust passage on the upstream side At the same time, a control means is provided for causing the HC adsorbent to adsorb HC in the operating region where the amount of HC is large in the exhaust gas and releasing HC from the HC adsorbent in the operating region where the amount of HC is small in the exhaust gas. In the device disclosed in the publication, for example, in a region where the exhaust gas temperature is low immediately after the start of the engine and the HC component in the exhaust gas is relatively large, HC is adsorbed by the HC adsorbent, and the engine exhaust gas temperature is high and the HC gas in the exhaust gas is high. In the operation region where the components are relatively small, the HC adsorbed from the HC adsorbent is released.

[0004] NO _X purification catalyst exhaust temperature, such as immediately after engine startup is low region has not reached the activation temperature, can not purify NO _X by consuming HC components in the exhaust NO _X
Even if the HC component is supplied to the purification catalyst, it may pass through the catalyst without being consumed by the catalyst. Further, even if the NO _X purification catalyst reaches the activation temperature, if the amount of HC component in the exhaust gas is small, it is not possible to sufficiently purify NO _X. Therefore, in the device of the publication, when the exhaust gas temperature is low and the catalyst has not reached the activation temperature, the HC component in the exhaust gas is adsorbed by the HC adsorbent, and the exhaust gas temperature is high and the catalyst has reached the activation temperature. the adsorbed HC can be released from the HC adsorbent when, while preventing atmospheric emission of HC at low temperatures, thereby improving the purification efficiency of the NO _X at a high temperature.

[0005]

However, an HC adsorbent is arranged upstream of the exhaust purification catalyst as in the apparatus disclosed in Japanese Utility Model Application Laid-Open No. 4-1617, and the exhaust gas passing through the HC adsorbent is used as the exhaust purification catalyst. In the case where the exhaust gas is made to flow, there is a problem that the temperature rise of the exhaust gas purification catalyst becomes slow and it takes time for the exhaust gas purification catalyst to reach the activation temperature after the engine is started.

[0006] For example, the exhaust purification catalyst is cold at the time of cold start of the engine, and is heated by the exhaust gas passing after the engine is started to reach the catalyst activation temperature. If it is made to flow into the exhaust purification catalyst after passing through the adsorbent, the heat of the exhaust gas is taken by the HC adsorbent when passing through the HC adsorbent on the upstream side,
The temperature of the exhaust gas flowing into the exhaust purification catalyst becomes low. Therefore, the temperature rise of the exhaust purification catalyst on the downstream side is delayed, and it is delayed to reach the activation temperature after the engine is started, and it takes time until the exhaust purification action is started after the engine is started. For this reason, during this time, there is a problem that the exhaust gas is not sufficiently purified and the exhaust properties are deteriorated.

When the exhaust gas temperature is relatively low, such as in a diesel engine, the temperature rise of the downstream exhaust purification catalyst is delayed for the same reason even if the exhaust gas temperature rises during acceleration. At times, the exhaust gas purification operation of the exhaust gas purification catalyst is not started immediately, which causes a problem that exhaust gas purification during acceleration becomes insufficient. The present invention solves the above problems,
When an HC adsorbent is arranged upstream of the exhaust purification catalyst to adsorb HC in exhaust gas until the catalyst reaches the activation temperature,
It is an object of the present invention to provide an exhaust gas purifying apparatus capable of preventing unpurified HC components from being released into the atmosphere due to a delay in reaching an activation temperature of a downstream side exhaust gas purifying catalyst.

[0008]

[0009]

According to the first aspect of the present invention, there is provided an exhaust gas purification device for purifying at least a hydrocarbon component in exhaust gas flowing when the temperature is equal to or higher than a predetermined temperature, which is disposed in an exhaust passage of an internal combustion engine. In an exhaust gas purifying apparatus for an internal combustion engine, comprising: a catalyst; and an HC adsorbent disposed in an exhaust passage upstream of the exhaust gas purifying catalyst and adsorbing hydrocarbons in the exhaust gas flowing into the exhaust gas purifying catalyst. Is changed in a direction perpendicular to the axis of the exhaust passage so that the average value of the heat flow rate of the exhaust gas passing through the HC adsorbent is set to be larger in the portion where the heat capacity is small than in the portion where the heat capacity is large. An exhaust gas purification device for an internal combustion engine is provided.

According to the second aspect of the present invention, an exhaust purification catalyst disposed in an exhaust passage of an internal combustion engine for purifying at least a hydrocarbon component in exhaust gas flowing when the temperature is equal to or higher than a predetermined temperature, and the exhaust purification catalyst Located in the exhaust passage upstream of the catalyst,
An HC adsorbent for adsorbing hydrocarbons in the exhaust gas flowing into the exhaust gas purifying device for an internal combustion engine, the heat receiving device transmitting heat of exhaust gas received to a part of the exhaust gas purifying catalyst to another portion of the catalyst. And the average flow velocity of the exhaust gas passing through the portion of the HC adsorbent that is located immediately upstream of the heat receiving portion, except for the position of the heat receiving portion, An exhaust gas purification device for an internal combustion engine is provided, wherein the exhaust gas purification device is set at a position that is larger than an average flow velocity of exhaust gas passing through the portion.

[0011]

[0012]

[0013]

[Action] is the thermal capacity per unit volume of the HC adsorbent in the exhaust gas purification device according to claim 1 is changed in a direction perpendicular to the exhaust passage axis, an average value of the flow velocity of the exhaust gas passing through the HC adsorbent, the heat capacity It is set so that it is small in a large part and large in a part with a small heat capacity. Therefore, HC
The flow rate of exhaust gas passing through the portion having a small heat capacity of the adsorbent is larger than the flow rate of exhaust gas passing through the portion having a large heat capacity. HC
Since the temperature of the adsorbent quickly rises in the portion where the heat capacity of the adsorbent is small, and the temperature of the exhaust gas passing through the portion where the heat capacity is small decreases, the temperature of the downstream side remains high without being deprived of heat by the HC adsorbent. The amount of exhaust reaching the exhaust purification catalyst increases.

According to a second aspect of the present invention, the heat receiving portion for transmitting the heat of the exhaust gas to the downstream side exhaust purification catalyst is disposed immediately downstream of a portion where the average flow velocity of the exhaust gas passing through the HC adsorbent is increased. Therefore, the flow rate of exhaust gas coming into contact with the heat receiving section becomes larger than that of the other sections, and the amount of heat transferred from the heat receiving section to the exhaust gas purification catalyst increases.

[0015]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a sectional view showing one embodiment of the exhaust gas purification apparatus of the present invention. In FIG. 1, an exhaust gas purifying apparatus, which is indicated as a whole by 10, includes a housing 11, an exhaust gas purifying catalyst 1 and an HC adsorbent 3 housed therein. The exhaust gas purification device 10 is connected to an exhaust passage 2 of an internal combustion engine 20 such as a diesel engine through a flange 11a of a housing 11.
1 connected. As shown in FIG.
1 is connected to the exhaust passage 21 so that the HC adsorbent 3 is located on the upstream side of the exhaust purification catalyst 1 when viewed from the exhaust flow direction. It passes through the purification catalyst 1.

The HC adsorbent 3 is made of a porous adsorbent containing silica as a main component (eg, SiO ₂ supported between layered crystals of SiO ₄ ), a porous material such as zeolite, etc. It is formed in a cylindrical shape having a directional flow path (cell), and has substantially the same shape as a monolithic carrier used for a normal exhaust gas purification catalyst. Further, as the HC adsorbent 3, a material in which an inorganic porous material such as alumina or silica is supported on the cell wall surface of a monolithic catalyst carrier such as ordinary cordierite can be used. In addition, HC in the exhaust
A catalyst capable of adsorbing the component (for example, a catalyst carrier in which zeolite, alumina, silica, titania, or the like is supported together with the catalyst component) may be used as the HC adsorbent.

The HC adsorbent 3 adsorbs the HC component in the exhaust gas flowing in when the temperature of the adsorbent is low into the porous pores,
H that releases adsorbed HC components when the adsorbent temperature is high
Performs the absorption / release action of C. The HC adsorbent 3 is fixed to the inner surface of the housing 11 via the seal 13 to prevent the exhaust gas from leaking downstream from between the outer periphery of the adsorbent 3 and the inner surface of the housing 11.

[0018] In the as an exhaust gas purifying catalyst 1 disposed HC adsorbent 3 downstream the present embodiment, for example, zeolite ZSM-5 in Fe, NO _X selective reduction with a metal such as Cu is supported by ion-exchange catalyst or _the NO _X selective reducing catalyst zeolite was supported noble metal such as platinum Pt, such as mordenite is used. This NO _X selective reduction catalyst has a high H value under an oxidizing atmosphere (when the exhaust air-fuel ratio is lean).
It is capable of purifying C and CO components alone, and has a selective reduction function of NO _X capable of selectively reducing and purifying NO _X components in exhaust gas even in an oxidizing atmosphere in the presence of an appropriate amount of HC component. The exhaust gas purification catalyst 1 is fixed to the inner peripheral surface of the housing 11 via a heat insulating material 15 to prevent heat transfer from the exhaust gas purification catalyst 1 to the housing 11.

The exhaust gas purifying catalyst 1 changes its exhaust gas purifying ability depending on the temperature. When the temperature is lower than the activation temperature of the catalyst, the exhaust gas purifying ability is significantly reduced. FIG. 2 is a diagram showing an example of a temperature change of the purification rate of the HC and CO components of the exhaust purification catalyst 1. As shown in FIG. 2, the purification rates of HC and CO are determined by a specific activation temperature (FIG. 2).
Below 200 ° C.), the temperature drops sharply. Also,
As will be described later, the NO _X purification rate is exhibited only in a certain narrow temperature range, and the NO _X purification rate is remarkably reduced both at a lower temperature and at a higher temperature than this temperature range (referred to as a NO _X purification temperature window). FIG. 2 shows that the activation temperature of the exhaust purification catalyst 1 is 2
Although the case where the temperature is around 00 degrees C is shown, the activation temperature can be arbitrarily set within a certain range by changing the material, shape, and the like of the exhaust gas purification catalyst.

As described with reference to FIG. 1, in this embodiment, since the diesel engine is used as the internal combustion engine 20, the exhaust gas temperature is generally lower than that of the gasoline engine. In some cases, the activation temperature has not been reached, and the exhaust gas purifying action of the catalyst cannot be obtained.
For this reason, there is a possibility that the HC component in the exhaust gas when the engine exhaust gas temperature is low is not purified and is released to the atmosphere only with the exhaust gas purification catalyst 1.

Therefore, in the present embodiment, the HC adsorbent 3 is arranged upstream of the exhaust purification catalyst 1 so that the HC
Prevents atmospheric release of components. As described above, the HC adsorbent 3 adsorbs the HC component in the exhaust gas at a low temperature and performs the action of absorbing and releasing the HC component that releases the adsorbed HC component at a high temperature. Therefore, when the exhaust gas temperature of the engine is low, the HC component in the exhaust gas is adsorbed by the HC adsorbent 3 on the upstream side and does not flow out to the downstream side, thereby preventing the HC component from being released into the atmosphere at low temperatures. On the other hand, when the exhaust gas temperature rises, the HC adsorbent 3
However, since the temperature of the exhaust gas purification catalyst 1 on the downstream side also rises with the rise of the exhaust gas temperature and the action of purifying HC and CO components occurs, the HC discharged from the HC adsorbent 3 is released.
The components and the HC and CO components discharged from the engine are purified by the exhaust purification catalyst 1, and are not released to the atmosphere.

However, since the HC adsorbent 3 is disposed on the upstream side of the exhaust purification catalyst 1, another problem may occur. That is, since the exhaust gas from the engine 20 first passes through the HC adsorbent 3 and then reaches the exhaust purification catalyst 1, both the HC adsorbent 3 and the exhaust purification catalyst 1 are used when the engine is cold started. If the temperature is low, the upstream HC
When passing through the adsorbent 3, the temperature of the exhaust gas decreases, causing a problem that the temperature of the exhaust gas purification catalyst 1 on the downstream side increases.

In this embodiment, this problem is solved by setting the heat capacity of the downstream exhaust purification catalyst to be smaller than the heat capacity of the upstream HC adsorbent. When the exhaust gas temperature reaching the exhaust gas purification catalyst on the downstream side is low, the difference between the catalyst and the exhaust gas temperature becomes small, and the amount of heat given to the catalyst from the exhaust gas becomes small. By setting the heat capacity of the catalyst small, even when the amount of heat given from the exhaust gas to the catalyst is small, the temperature of the catalyst quickly rises, so that a delay in the temperature rise of the catalyst is prevented.

FIG. 3A is an enlarged view showing a cross section perpendicular to the axis of the upstream HC adsorbent of this embodiment. As described above, the HC adsorbent 3 has the same structure as a commonly used monolithic catalyst carrier, and is made of a material having a relatively large heat capacity per unit volume, such as cordierite or zeolite, as shown in FIG.
The structure is such that a large number of flow paths (cells) in the axial direction as shown in FIG.

On the other hand, FIG. 3B is an enlarged view showing a cross section perpendicular to the axis of the downstream side exhaust purification catalyst of this embodiment. In this embodiment, the exhaust purification catalyst 1 uses a metal having a relatively small heat capacity per unit volume as a carrier, forms a honeycomb-shaped cell 32 in this metal carrier, and supports a catalyst such as zeolite on the cell wall. It has a configuration in which a component layer is formed.

As is apparent from a comparison between FIGS. 3A and 3B, in the present embodiment, the thickness of the partition wall 32a between the cells 32 of the downstream side exhaust purification catalyst 1 is different from that of the cell 31 of the upstream side HC adsorbent 3. Since it is very thin compared to the thickness of the partition wall 31a,
In the downstream side exhaust purification catalyst 1, the volume of the carrier portion is small, and in the upstream side HC adsorbent 3, the volume of the carrier portion is large. Therefore, the heat capacity of the downstream side exhaust purification catalyst 1 is significantly smaller than the heat capacity of the upstream side HC adsorbent 3 as a whole.

As described above, the upstream HC adsorbent 3
The cell 31 has a large flow path area and a thick wall, and the flow path area of the cell 32 of the downstream exhaust purification catalyst is small and the wall is thin, so that the number of cells per unit area in the exhaust flow direction is the upstream HC adsorbent. In the case of No. 3, the amount is significantly smaller than that of the downstream side exhaust purification catalyst 1. This means that the total cell wall area in contact with the exhaust gas is small in the upstream HC adsorbent 3 and large in the downstream exhaust purification catalyst 1. Thus, the amount of heat given from the exhaust gas to the cell wall surface by the upstream HC adsorbent 3 is reduced, and the decrease in the exhaust gas temperature when passing through the upstream HC adsorbent 3 is reduced.

Therefore, in this embodiment, the heat capacity of the downstream side exhaust purification catalyst 1 is small, and the decrease in the exhaust gas temperature before reaching the downstream side exhaust purification catalyst 1 is relatively small.
The temperature of the downstream side exhaust purification catalyst 1 quickly rises. In this embodiment, as shown in FIG. 1, the upstream HC adsorbent 3 and the downstream exhaust purification catalyst 1 are arranged with a slight gap 4 therebetween, and the outer periphery of the downstream exhaust purification catalyst 1 and the housing 11 are separated from each other. A heat insulating material 15 is interposed between the inner circumference. Thereby, after the downstream side exhaust purification catalyst 1 reaches the activation temperature and the HC and CO oxidation reactions are started, the downstream side exhaust heat purification catalyst 1 and the upstream side HC adsorbent 3 and the heat transfer through the direct contact with the housing 11 cause the downstream side exhaust heat transfer catalyst 1 to perform the heat transfer. The heat dissipation from the exhaust gas purification catalyst 1 is prevented, and the temperature of the downstream side exhaust gas purification catalyst 1 can be maintained at a high state.

By the way, as described above, the exhaust purification catalyst 1
There in order to purify also the NO _X components not HC, CO components only in the exhaust gas, not only the temperature of the exhaust gas purifying catalyst 1 is equal to or higher than the activation temperature, a relatively narrow temperature range ( there is a need to be entered in the NO _X purification temperature window). FIG. 4 is a diagram illustrating an example of a change in the NO _X purification rate of the exhaust purification catalyst 1 with temperature. As shown in FIG. 4, the NO _X purification rate of the exhaust purification catalyst 1 is within a relatively narrow temperature range (FIG. 4).
In this case, it is exhibited only within the range of about 200 to 250 ° C.), and if it is out of this range, it becomes impossible to sufficiently purify NO _X.

However, since the exhaust gas temperature fluctuates greatly depending on the engine operating condition, in an operating condition in which acceleration and deceleration are repeated, the time during which the exhaust gas purifying catalyst 1 is within the NO _X purifying temperature window decreases, and the NO _X purifying rate as a whole is reduced. Is low. However, in the present embodiment, since the HC adsorbent 3 having a relatively large heat capacity is disposed upstream of the exhaust purification catalyst 1, even if the exhaust gas temperature fluctuates due to the engine operating state, the downstream side exhaust purification catalyst 1 is used. Fluctuations in the temperature of the exhaust gas that arrives are reduced.

FIG. 5 shows an exhaust gas purifying apparatus 1 according to this embodiment.
FIG. 3 is a diagram for explaining a change in the temperature of the exhaust gas flowing into the engine and a change in the temperature of the exhaust gas actually reaching the downstream side exhaust purification catalyst 1. In FIG. 5, the solid line T ₁ indicates the exhaust gas temperature at the inlet of the device 10, and the broken line T ₂ indicates the exhaust gas temperature reaching the exhaust gas purification catalyst 1. By placing the HC adsorbent 3 into the exhaust purification catalyst 1 upstream, for example, an acceleration as shown in FIG. 5, even when the engine exhaust temperatures T ₁ performs the operation to repeat the deceleration as fluctuates greatly, the exhaust gas purification variation of the temperature T ₂ of the exhaust gas reaching the catalyst 1 decreases. That is, even when T ₁ fluctuates beyond the NO _X purification temperature window, the opportunity that the temperature of the exhaust purification catalyst 1 stays within the window (FIG. 5,
Since the number of hatched portions) increases, it is possible to improve the NO _X purification rate as a whole. Further, even when the temperature of the exhaust gas temporarily rises during acceleration or the like and becomes equal to or higher than the temperature at which sulfate is generated by the catalyst, the exhaust gas purification catalyst 1
Is reduced by the HC adsorbent 3 on the upstream side, so that the generation of sulfate in the catalyst can be suppressed.

The HC adsorbent 3 releases adsorbed HC when it exceeds a certain temperature. The HC release temperature can be changed to some extent by changing the material and shape of the adsorbent. . Further, the N of the exhaust purification catalyst 1
O _X purification temperature window is also difficult to expand the width of the window, the same as the material, possible to move the window position somewhat on the high temperature side or the low-temperature side by changing the shape.

Therefore, in this embodiment, the HC release temperature of the upstream HC adsorbent 3 and the lower limit value (200 ° C. in FIG. 4) of the NO _X purification temperature window of the exhaust purification catalyst 1 on the downstream side are matched. The materials and shapes of the HC adsorbent and the exhaust purification catalyst are adjusted. For this reason, while the exhaust gas temperature is low and the downstream exhaust purification catalyst 1 does not reach the activation temperature, the upstream H
Since the HC component in the exhaust gas is adsorbed by the C adsorbent 3 and does not reach the exhaust purification catalyst 1, the situation where the unpurified HC component passes through the exhaust purification catalyst 1 and is released to the atmosphere is prevented. Further, when the exhaust gas temperature rises and the exhaust purification catalyst 1 reaches the activation temperature, HC is released from the upstream HC adsorbent 3, and this HC is moved up by the downstream exhaust purification catalyst 1. Therefore, unpurified HC components are not released to the atmosphere.

Further, in this embodiment, a diesel engine is used as an internal combustion engine 20, the combustion of diesel engine is relatively high NO _X component amount in the high exhaust gas excess air ratio. On the other hand, it is necessary that there is an appropriate amount of HC component in order to purify NO _X in the exhaust gas when using _the NO _X selective reducing catalyst as an exhaust gas purifying catalyst 1. However, increasing the amount of generation of the engine combustion temperature becomes higher when the NO _X, since the generation amount of HC component is reduced at the same time, the exhaust temperature is high region, the temperature of the exhaust gas purifying catalyst 1 is entered in the NO _X purification temperature window If HC components despite there can not purify nO _X in the exhaust gas is insufficient arises.

[0035] In this embodiment, by disposing the HC adsorbent 3 on the upstream side of the exhaust gas purifying catalyst 1 as described above, the HC adsorbent 3 when less NO _X components in the exhaust the exhaust gas temperature is low exhaust The HC component in the exhaust gas is adsorbed and the HC component is released from the HC adsorbent 3 in a region where the exhaust temperature is high and the NO _X component in the exhaust gas increases, so that even in a region where the NO _X component in the exhaust gas increases. it is possible to supply a sufficient HC in the exhaust gas purifying catalyst 1, is carried out sufficiently NO _X purification of the exhaust gas purifying catalyst 1. In this case, the upstream H
The C adsorbent 3 adsorbs a low-concentration HC component in the exhaust gas, and releases the adsorbed HC component in a concentrated form when the exhaust gas temperature is high and the amount of generated NO _X increases.

Next, another embodiment of the present invention will be described.
In this embodiment, the shape and the like of the HC adsorbent 3 are adjusted such that the heat capacity per unit volume of the HC adsorbent 3 on the upstream side changes in a direction perpendicular to the exhaust flow direction. FIG. 6 shows the distribution of the heat capacity of the HC adsorbent 3 of this embodiment. As shown in FIG. 6, in the present embodiment, the heat capacity per unit volume of the upstream HC adsorbent 3 is set to be the smallest near the central axis of the HC adsorbent, and to increase from the center to the outer periphery. Have been. That is, in the HC adsorbent 3 of the present embodiment, the cell partition wall 31a is thinned by reducing the flow path area of the cell 31 and increasing the number of cells per unit area at the center, thereby reducing the heat capacity per unit volume. The cell partition wall 31a is set by increasing the flow path area of the cell 31 toward the outer periphery and decreasing the number of cells.
Is set so that the heat capacity per unit volume gradually increases by increasing the thickness.

Generally, the exhaust flow velocity in the exhaust passage is low near the wall surface of the exhaust passage and large near the center. In particular, when the flow rate of the exhaust gas suddenly increases, such as during acceleration, the difference between the flow velocity in the central portion of the exhaust passage and the flow velocity in the peripheral portion increases. In such a case, the flow rate of exhaust gas passing through the HC adsorbent 3 is large at the center of the HC adsorbent 3 and decreases toward the outer periphery. Therefore, as in this embodiment, H
By setting the heat capacity per unit volume of the C adsorbent 3 to be smaller at the center and larger toward the outer periphery, the flow rate of exhaust gas passing through the HC adsorbent 3 becomes larger as the heat capacity per unit volume becomes smaller.

In the portion where the heat capacity is small, the temperature of the HC adsorbent 3 quickly rises, and the temperature of the exhaust gas passing through this portion decreases less. Therefore, the HC adsorbent 3 in the portion where the flow rate of the exhaust gas thus passed is large is small. By setting the heat capacity of the exhaust gas to a small value, the proportion of the exhaust gas having a small temperature decrease with respect to the entire exhaust gas flow rate increases.
The calorific value of the exhaust gas that reaches the downstream side exhaust purification catalyst without being deprived by the adsorbent 3 increases.

Therefore, by changing the heat capacity per unit volume of the HC adsorbent 3 in the direction perpendicular to the exhaust flow as described above, it is possible to raise the temperature of the downstream side exhaust purification catalyst 1 in a short time. It becomes. FIG.
In the example, the size and distribution of the cells are set so that the flow resistance of the HC adsorbent 3 is substantially uniform in a direction perpendicular to the exhaust flow. If the distribution of the size, number, etc. of the cells is set so as to increase the flow rate of the exhaust gas passing through the central portion having a small heat capacity, it is possible to further increase the flow rate. Can be.

Next, still another embodiment of the present invention will be described with reference to FIG. In this embodiment, the upstream HC adsorbent 3 has a concave portion 35 opened at the downstream end surface at the center thereof, and the downstream exhaust purification catalyst 1 has a heat receiving portion fitted into the concave portion. Are formed.
Further, the downstream side exhaust purification catalyst 1 is formed of a metal carrier as in each of the above-described embodiments, and the heat retaining material 17 is disposed between the outer periphery of the projection 37 and the inner periphery of the concave portion 35 of the HC adsorbent 3. Part 37
This prevents direct contact between the outer circumference and the inner circumference of the recess 35. Further, the downstream end face of the HC adsorbent 3 and the exhaust purification catalyst 1
A gap 39 is provided between the upstream end face.

As described above, the flow rate of the exhaust gas passing through the HC adsorbent 3 is greatest near the center, but in this embodiment, the heat receiving section 37 is disposed immediately downstream of the HC adsorbent 3 in this portion. Therefore, the flow rate of exhaust gas passing through the heat receiving section 37 is larger than the flow rate passing through other portions. Further, the portion of the HC adsorbent 3 immediately upstream of the heat receiving portion 37 (the portion forming the bottom of the concave portion 35) is thinner in the exhaust gas flow direction than the other HC adsorbents 3, so that the heat receiving portion is formed at this portion. The temperature of the exhaust gas flowing into the 37 is hardly reduced. Therefore, a large amount of exhaust gas having a higher temperature than other portions of the exhaust gas purification catalyst 1 flows into the heat receiving section 37. Therefore, a large amount of heat is transmitted from the exhaust gas to the heat receiving unit 37. However, in this embodiment, the exhaust gas purifying catalyst 1 including the heat receiving unit 37 uses a metal carrier having good heat conductivity, and thus the heat receiving unit 37 emits heat. The heat received from the catalyst is quickly transmitted to other parts of the carrier, and the entire exhaust purification catalyst 1 quickly rises in temperature.

In particular, when the exhaust gas flow rate suddenly increases at the time of engine acceleration or the like, the exhaust gas flow passing near the center of the HC adsorbent 3 is significantly larger than the exhaust gas flow passing the peripheral portion. The temperature of the exhaust purification catalyst 1 at the time is increased more quickly, and the HC, NO
_{X and the} like can be performed sufficiently without delay.

FIG. 8 shows a modification of the embodiment of FIG. In this embodiment, the central recess 35 of the upstream HC adsorbent 3 is
The adsorbent 3 is open at the upstream end face. The projection 37 is not provided on the downstream side exhaust purification catalyst 1. However, in this case, too, a high temperature and a large amount of exhaust gas flow into the exhaust purification catalyst 1 portion immediately downstream of the concave portion 35 through the central concave portion 35 of the HC adsorbent 3. Heat is transmitted to the entire purification catalyst 1 and the entire exhaust purification catalyst 1 quickly rises in temperature. That is, in the present embodiment, the HC adsorbent 3
The portion of the exhaust gas purification catalyst 1 immediately downstream of the concave portion 35 formed as a function as a heat receiving portion.

[0044]

According to the present invention, when the HC adsorbent is disposed in the exhaust passage on the upstream side of the exhaust purification catalyst to adsorb and release the HC component in the exhaust gas, the exhaust gas on the downstream side is exhausted. This has a common effect that it is possible to prevent unpurified exhaust components from being released into the atmosphere due to a delay in temperature rise of the purification catalyst.

[0045]

That is, according to the first aspect of the present invention, since the exhaust flow rate is large in the portion where the heat capacity per unit volume of the upstream HC adsorbent is small, the exhaust gas which has passed through the portion where the heat capacity is small and whose temperature drop is small is small. The flow rate of
Since the temperature of the exhaust purification catalyst on the downstream side is accelerated, the emission of unpurified exhaust components to the atmosphere is prevented. According to the second aspect of the present invention, the heat receiving portion for transmitting the heat of the exhaust gas to the downstream side exhaust purification catalyst is disposed immediately downstream of the portion where the average flow velocity of the exhaust gas passing through the HC adsorbent is increased. As a result, the flow rate of exhaust gas in contact with the heat receiving section becomes larger than that of the other sections, the amount of heat transferred from the heat receiving section to the exhaust purification catalyst increases, and the temperature of the downstream exhaust purification catalyst rises quickly, so that unpurified exhaust components Is released to the atmosphere.

[0047]

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing one embodiment of an exhaust emission control device of the present invention.

FIG. 2 is a diagram illustrating a change in purification efficiency of HC and CO components of an exhaust purification catalyst depending on temperature.

FIG. 3 is a diagram illustrating the structure of an exhaust purification catalyst and an HC adsorbent.

FIG. 4 is a diagram illustrating a change in NO _X purification efficiency of an exhaust purification catalyst depending on temperature.

FIG. 5 is a diagram illustrating a change in the temperature of exhaust gas flowing into the exhaust purification catalyst in the embodiment of FIG. 1;

FIG. 6 is a diagram illustrating another embodiment of the exhaust gas purification apparatus of the present invention.

FIG. 7 is a diagram illustrating another embodiment of the exhaust gas purification apparatus of the present invention.

FIG. 8 is a diagram illustrating another embodiment of the exhaust gas purification apparatus of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Exhaust purification catalyst 3 ... HC adsorbent 10 ... Exhaust purification device 20 ... Internal combustion engine 21 ... Exhaust passage

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) F01N 3/08-3/38 F01N 9/00-11/00

Claims (2)

(57) [Claims] An exhaust purification catalyst disposed in an exhaust passage of an internal combustion engine for purifying at least a hydrocarbon component in exhaust gas flowing at a predetermined temperature or higher, and disposed in an exhaust passage upstream of the exhaust purification catalyst. An HC adsorbent that adsorbs hydrocarbons in the exhaust gas that flows into the exhaust gas purifying apparatus for an internal combustion engine, wherein a heat capacity per unit volume of the HC adsorbent is changed in a direction perpendicular to the exhaust passage axis. An exhaust gas purifying apparatus for an internal combustion engine, wherein an average value in a portion having a small heat capacity is set to be larger than an average value in a portion having a large heat capacity of an exhaust flow velocity passing through an HC adsorbent. 2. An exhaust purification catalyst disposed in an exhaust passage of an internal combustion engine for purifying at least a hydrocarbon component in exhaust gas flowing when the temperature is equal to or higher than a predetermined temperature, and disposed in an exhaust passage upstream of the exhaust purification catalyst. , An HC adsorbent for adsorbing hydrocarbons in the inflowing exhaust gas, wherein the heat of the exhaust gas received by one part of the exhaust gas purification catalyst is transmitted to another part of the catalyst. A heat receiving portion is formed, and the position of the heat receiving portion is changed such that the average flow velocity of exhaust gas passing through the portion of the HC adsorbent that is located immediately upstream of the heat receiving portion is other than immediately upstream of the heat receiving portion of the HC adsorbent. An exhaust gas purification device for an internal combustion engine, wherein the exhaust gas purification device is set at a position where the average flow velocity of the exhaust gas passing through the portion is larger than the average flow velocity.