JP2021021352A - Exhaust emission control device and exhaust emission control method - Google Patents

Abstract

To suppress the discharge of HC discharged from an HC trap material while being unpurified.SOLUTION: An HC trap material and a heat generation material 3 for generating heat by the occlusion of an oxidation catalyst and oxygen are arranged in an exhaust emission passage 2. When a temperature of the HC trap material is equal to a prescribed temperature or lower, the heat generation of the heat generation material 3 is suppressed by lowering the oxygen density of exhaust emission which flows into the heat generation material 3, and when the temperature of the HC trap material exceeds the prescribed temperature, the heat generation material 3 is made to generate heat by raising the oxygen density. When the purification of the exhaust emission is finished, oxygen is discharged from the heat generation material 3 by lowering the oxygen density, and a self-heat generation property of the heat generation material 3 is maintained by holding an environment of the heat generation material 3 in a state that the oxygen density is lowered up until a succeeding start of the purification of the exhaust emission.SELECTED DRAWING: Figure 1

Description

The present invention relates to an exhaust gas purification device and an exhaust gas purification method.

Regarding the purification of the exhaust gas of an engine, it is known that the temperature of an oxidation catalyst that oxidizes HC (hydrocarbon), CO, etc. in the exhaust gas is raised by a chemical heat storage material. For example, Patent Document 1 utilizes the fact that a chemical heat storage material that reversibly undergoes an exothermic reaction and endothermic reaction with water vapor and the like and an oxidation catalyst are placed next to each other, and the chemical heat storage material reacts with water vapor and the like in exhaust gas to generate heat. It is described that the temperature of the oxidation catalyst is raised. The document also describes that when the engine is stopped, the engine is operated by fuel cutting to exhaust the exhaust gas from the exhaust pipe, and then the valve provided on the downstream side of the catalyst is closed. This is to prevent the chemical heat storage material from reacting with water vapor to generate heat after the engine is stopped.

Japanese Unexamined Patent Publication No. 2011-252464

By the way, an exhaust gas purification system using an oxidation catalyst and an HC trap material in combination is known. This is because when the exhaust gas temperature is low and the oxidation catalyst is not activated, HC in the exhaust gas is adsorbed on the trap material, and when the exhaust gas temperature rises, the activated oxidation catalyst is used to release the HC in the exhaust gas from the trap material. Oxidize and purify the released HC.

However, since the HC trap material gradually releases HC as the temperature rises, it tends to result in a large amount of HC being discharged unpurified before the oxidation catalyst is activated. That is, there is a problem that the temperature at which the HC trap material starts to release HC and the temperature at which the oxidation catalyst becomes active do not always match.

Therefore, the present invention suppresses the HC released from the HC trap material from being discharged unpurified.

In order to solve the above problems, the present invention uses a self-heating material that generates heat when oxygen is occluded, and rapidly raises the temperature of the oxidation catalyst when the HC trap material starts to release HC.

The exhaust gas purification device disclosed herein is a device that purifies exhaust gas containing HC.
An HC trap material that is provided in the exhaust gas passage through which the exhaust gas flows and traps the HC,
An oxidation catalyst provided in the exhaust gas passage for oxidizing the HC released from the HC trap material and the HC contained in the exhaust gas,
A self-heating material provided in the exhaust gas passage and self-heating when oxygen is occluded for heating the oxidation catalyst,
By lowering the oxygen concentration of the exhaust gas flowing into the self-heating material when the temperature correlated with the temperature of the HC trap material is equal to or lower than the predetermined temperature before the HC trap material starts to release HC. A self-heating control means that suppresses the self-heating of the self-heating material and causes the self-heating by increasing the oxygen concentration when the temperature correlated with the temperature of the HC trap material exceeds the predetermined temperature.
When the purification of the exhaust gas is completed, the self-heating material recycling means for recovering the self-heating property of the self-heating material by releasing oxygen from the self-heating material by lowering the oxygen concentration.
It is characterized by being provided with a self-heating maintenance means for maintaining the self-heating property of the self-heating material by keeping the atmosphere of the self-heating material in a state where the oxygen concentration is lowered until the next start of purification of the exhaust gas. To do.

In this exhaust gas purification device, when the temperature correlated with the temperature of the HC trap material is equal to or lower than the predetermined temperature, the self-heating of the self-heating material is suppressed, and when the temperature exceeds the predetermined temperature, the self-heating is generated.

Therefore, when the exhaust gas temperature is low, it is possible to prevent the HC trap material from being heated by the heat generated by the self-heating material. That is, it is possible to avoid accelerating the release of HC from the HC trap material. Therefore, it is prevented that HC is discharged unpurified before the activation of the oxidation catalyst. Then, the temperature of the oxidation catalyst can be raised in a short time by the heat generated by the self-heating material before the HC trap material starts to release HC. Due to the activation of the oxidation catalyst as the temperature rises, the amount of HC discharged unpurified is reduced.

Further, according to this exhaust gas purification device, when the purification of the exhaust gas is completed, oxygen is released from the self-heating material to recover the self-heating property, and this self-heating property is started to purify the next exhaust gas. Can be maintained up to. Therefore, the self-heating material can be repeatedly used so as to be effective in purifying the exhaust gas.

Further, the exhaust gas purification device disclosed herein is a device for purifying exhaust gas containing HC.
An HC trap material that is provided in the exhaust gas passage through which the exhaust gas flows and traps the HC,
An oxidation catalyst provided in the exhaust gas passage for oxidizing the HC released from the HC trap material and the HC contained in the exhaust gas,
A self-heating material provided in the exhaust gas passage and self-heating when oxygen is occluded for heating the oxidation catalyst,
A means for determining the amount of HC inflow into the HC trap material from the start of the HC trap material, and
When the HC inflow amount is equal to or less than a predetermined value, the oxygen concentration of the exhaust gas flowing into the self-heating material is lowered to suppress the self-heating of the self-heating material, and the HC inflow amount exceeds the predetermined value. The self-heating control means that causes the self-heating by increasing the oxygen concentration,
When the purification of the exhaust gas is completed, the self-heating material recycling means for recovering the self-heating property of the self-heating material by releasing oxygen from the self-heating material by lowering the oxygen concentration.
It is characterized by being provided with a self-heating maintenance means for maintaining the self-heating property of the self-heating material by keeping the atmosphere of the self-heating material in a state where the oxygen concentration is lowered until the next start of purification of the exhaust gas. To do.

The point that this exhaust gas purification device controls the oxygen concentration of the exhaust gas flowing into the self-heating material based on the amount of HC inflow into the HC trap material, not the temperature of the HC trap material, is the exhaust gas described above. It is different from the purification device. The predetermined value, which is the threshold value for changing and controlling the oxygen concentration, can be, for example, an amount of HC smaller than the amount that the HC trap material can trap without releasing HC. Therefore, it becomes easy to activate the oxidation catalyst by the time the HC trap material starts to release HC, and it is possible to prevent HC from being discharged unpurified. Further, according to this exhaust gas purification device, when the purification of the exhaust gas is completed, oxygen is released from the self-heating material to recover the self-heating property, and this self-heating property is started to purify the next exhaust gas. Can be maintained up to. Therefore, the self-heating material can be repeatedly used so as to be effective in purifying the exhaust gas.

In one embodiment, the self-heating material is a CeZr-based composite oxide containing Bi. The Ce molar ratio is preferably 0.4 or more, and the Bi molar ratio is preferably 0.2 or less. As a result, the amount of self-heating associated with oxygen occlusion increases, which is advantageous for rapid heating of the oxidation catalyst, and oxygen can be released at a relatively low temperature (300 ° C or lower), so that the self-heating material can be recovered. It will be advantageous to.

In one embodiment, the self-heating maintaining means is provided in the exhaust gas passage and is configured by an on-off valve that prevents outside air from entering the exhaust gas passage. By preventing the intrusion of outside air into the exhaust gas passage by the on-off valve, the atmosphere of the self-heating material can be kept in a state where the oxygen concentration is lowered.

In one embodiment, the self-heating material regenerating means obtains the oxygen storage amount of the self-heating material based on the temperature correlated with the temperature of the self-heating material, and reduces the oxygen storage amount to a predetermined value. Set the degree of reduction and the reduction time of the oxygen concentration of the exhaust gas flowing into the self-heating material. This is advantageous in surely recovering the self-heating property of the self-heating material.

The exhaust gas purification method disclosed herein is a method for purifying the exhaust gas containing HC flowing through the exhaust gas passage.
An HC trap material that traps the HC in the exhaust gas passage, an oxidation catalyst for oxidizing the HC released from the HC trap material and HC contained in the exhaust gas, and an oxidation catalyst for heating the oxidation catalyst. Place a self-heating material that self-heats when storing oxygen,
By lowering the oxygen concentration of the exhaust gas flowing into the self-heating material when the temperature correlated with the temperature of the HC trap material is equal to or lower than the predetermined temperature before the HC trap material starts to release HC. Suppresses the self-heating of the above self-heating material,
When the temperature correlated with the temperature of the HC trap material exceeds the predetermined temperature, the oxygen concentration is increased to cause the self-heating material to generate heat.
When the purification of the exhaust gas is completed, oxygen is released from the self-heating material by lowering the oxygen concentration.
It is characterized in that the self-heating property of the self-heating material is maintained by keeping the atmosphere of the self-heating material in a state where the oxygen concentration is lowered until the next start of purification of the exhaust gas.

According to this, it becomes easy to activate the oxidation catalyst by the time the HC trap material starts to release HC, and it is possible to prevent HC from being discharged unpurified. In addition, the self-heating material can be repeatedly used so as to be effective in purifying the exhaust gas.

According to the present invention, by controlling the oxygen concentration of the exhaust gas flowing into the self-heating material having self-heating property based on the temperature correlated with the temperature of the HC trap material or the amount of HC flowing into the HC trap material. When the self-heating material is suppressed and self-heating is generated and the purification of the exhaust gas is completed, oxygen is released from the self-heating material to restore the self-heating property, and the purification of the next exhaust gas is started. Since the self-heating property is maintained until, it becomes easy to activate the oxidation catalyst by the time the HC trap material starts to release HC, and it is possible to prevent the HC from being discharged unpurified. In addition, the self-heating material can be repeatedly used so as to be effective in purifying the exhaust gas.

Overall configuration diagram of the engine exhaust gas purification device. Control flow diagram about self-heating of self-heating material. Graph showing the _H 2-TPR test results of self-heating material. The graph which shows the time-dependent change of the reached temperature by self-heating of self-heating material. Graph showing the _H 2-TPR test results of self-heating material. The graph which shows the reached temperature by self-heating of self-heating material. The graph which shows the time-dependent change of THC and the like of Example 1. FIG. The graph which shows the time-dependent change of THC and the like of Example 2. The graph which shows the time-dependent change of THC and the like of Example 3. The graph which shows the HC purification rate of Example 1-3. The graph which shows the time-dependent change of the vehicle speed in the WLTP mode. The graph which shows the time-dependent change such as the vehicle speed at the time of starting the engine of the WLTP mode. The graph which shows the time-dependent change such as the vehicle speed when the engine is stopped in the WLTP mode.

Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. The following description of preferred embodiments is merely exemplary and is not intended to limit the invention, its applications or its uses.

<Overview of exhaust gas purification device>
As shown in FIG. 1, the exhaust gas purifying device of the present embodiment purifies the exhaust gas discharged from the engine 1 of the vehicle. In the exhaust gas passage 2 of the engine 1, a heating element 3, an oxidation catalyst converter 4, a particulate filter 5, an SCR (Selective Catalytic Reduction) catalyst 6, a slip catalyst 7, and an exhaust passage valve (each of which constitutes an exhaust gas purification device) The on-off valve) 8 is arranged in order from the upstream side in the exhaust gas flow direction. The exhaust gas purification device includes a controller 9 using a microcomputer that controls the oxygen concentration of the exhaust gas flowing into the heating element 3 and the exhaust passage valve 8. The engine 1 may be either a diesel engine or a gasoline engine.

The exothermic body 3 includes a self-heating material that releases oxygen when the air-fuel ratio of the exhaust gas is rich, occludes oxygen in a lean state, and self-heats, and this self-heating material is supported on a honeycomb carrier. .. As the self-heating material, a CeZr-based composite oxide can be preferably used, and in particular, a CeZrBi composite oxide is preferably used. From the viewpoint of improving self-heating, the CeZrBi composite oxide preferably has a Ce molar ratio of 0.3 or more and 0.75 or less, and a Bi molar ratio of 0.1 or more and 0.3 or less. The CeZrBi composite oxide preferably carries a catalyst metal, for example, Rh. By supporting Rh, a steam reforming reaction or a water-gas shift reaction can be promoted, and hydrogen obtained in the reaction facilitates low-temperature reduction of the self-heating material (releases oxygen to restore self-heating). Further, by supporting Rh, the oxygen storage / release performance of the self-heating material is enhanced even at a low temperature by activating oxygen in the vicinity of Rh, which is advantageous for self-heating. The Rh loading amount of the CeZrBi composite oxide is preferably 0.01% by mass or more and 20% by mass or less.

The catalyst converter 4 supports a honeycomb carrier with an HC trap material that traps HC in the exhaust gas, and an oxidation catalyst for oxidizing HC released from the HC trap material and HC, CO, and NO in the exhaust gas. It becomes. Zeolite is preferably used as the HC trap material, and β-zeolite is particularly preferable. As the oxidation catalyst, for example, it is preferable to use a catalyst in which Pt and / or Pd is supported on a mixture of activated alumina and an OSC (Oxygen Storage capacity) material (oxygen storage capacity material). As the OSC material, for example, a Ce-containing oxide whose heat resistance is improved by a transition metal such as Zr or a rare earth metal such as Nd can be preferably adopted.

The HC trap material and the oxidation catalyst can be mixed and supported on the honeycomb carrier. Further, the HC trap material and the oxidation catalyst can be supported on the honeycomb carrier in a layered manner so that the former becomes the lower layer and the latter becomes the upper layer, or the former becomes the upper layer and the latter becomes the lower layer. Alternatively, the HC trap material and the oxidation catalyst can be tandemly supported on the honeycomb carrier so that the former is located on the upstream side and the latter is located on the downstream side thereof.

The self-heating material can also be supported on the honeycomb carrier of the catalyst converter 4 without being separated from the catalyst converter 4. For example, both can be tandemly supported on the honeycomb carrier so that the self-heating material is located on the upstream side and the oxidation catalyst is located on the downstream side thereof. Alternatively, both can be supported in layers on the honeycomb carrier so that the self-heating material is the lower layer and the oxidation catalyst is the upper layer.

The particulate filter 5 collects and removes PM (Particulate Matter) contained in the exhaust gas. The filter 5 has a PM combustion catalyst supported on a filter body that collects PM. The PM combustion catalyst promotes the combustion of PM collected in the filter body. The filter body has a honeycomb structure in which an exhaust gas inflow passage with a closed downstream end and an exhaust gas outflow passage with a closed upstream end are provided alternately in parallel, and the exhaust gas flowing into the exhaust gas inflow passage passes through. It is a wall flow type that flows out to the adjacent exhaust gas outflow passage through the pores of the partition wall. Filter body, cordierite, SiC, _Si 3 _{N 4,} sialon, is formed of an inorganic porous material such as ALTIO _3. As the PM combustion catalyst, a catalyst in which Pt is supported on active alumina, a Zr-based composite oxide and a Zr-based composite oxide containing Rh-doped Ce (Rh is between the crystal lattice points or lattice points of the Ce-containing Zr-based composite oxide). A mixture or the like with a compound in which Rh is arranged) can be adopted.

The SCR catalyst 6 reduces and purifies NOx in the exhaust gas in the presence of a reducing agent. For example, it is preferable to use urea-SCR which uses urea as a precursor of NH ₃ as a reducing agent. It is supplied from a urea water tank (not shown) to the upstream side of the SCR catalyst 6. The SCR catalyst 6, the zeolite to trap NH _3, it is preferable to employ a catalyst component obtained by supporting a catalytic metal to reduce NOx and NH ₃ as a reducing agent. As the catalyst metal for NOx reduction, Fe, Cu, Ti, V, W and the like are preferable.

The slip catalyst 7 is a catalyst that traps and oxidizes (purifies) NH ₃ and its derivatives that pass through (slip) the SCR catalyst 6 without reacting with NOx, that is, prevents the NH _{3 and the} like from slipping. The slip catalyst 7 preferably has a configuration in which a zeolite that traps NH ₃ , an alumina material that supports Pt, and an OSC material that supports Pt are supported on the cell wall of the honeycomb carrier.

The exhaust passage valve 8 opens and closes the exhaust gas passage 2 on the downstream side of the slip catalyst 7. The exhaust gas passage valve 8 is opened at the time of exhaust gas purification, and is closed to prevent outside air from entering the exhaust gas passage 2 from the downstream side from the end of exhaust gas purification to the start of the next exhaust gas purification. At the end of purification of the exhaust gas, the self-heating property of the self-heating material is restored (release of oxygen from the self-heating material) by the self-heating material recycling means described later. After that, the exhaust passage valve 8 is closed to allow outside air to enter the exhaust gas passage 2 to maintain the self-heating property of the self-heating material until the start of purification of the next exhaust gas. It constitutes a means for maintaining heat generation.

<About the controller>
The controller 9 of the present embodiment controls the oxygen concentration of the exhaust gas flowing into the self-heating material by controlling the air-fuel ratio A / F of the engine 1. The oxygen concentration is controlled based on a temperature that correlates with the temperature of the HC trap material of the catalyst converter 4 (hereinafter, simply referred to as “catalyst temperature”). In the present embodiment, the temperature of the exhaust gas flowing into the heating element 3 is adopted as the catalyst temperature, and is detected by the temperature sensor 11. The temperature sensor 11 is provided in the exhaust gas passage 2 on the upstream side of the heating element 3. The temperature sensor 11 is also a sensor that detects a temperature that correlates with the temperature of the self-heating material (hereinafter, referred to as "self-heating material correlation temperature").

-Self-heating control-
The HC trap material using β-zeolite begins to release the trapped HC when the temperature reaches around 120 ° C. On the other hand, the light-off temperature (temperature at which the purification rate reaches 50%) related to HC purification of the oxidation catalyst is generally around 200 ° C. Therefore, even if the engine 1 is started and the HC trap material starts to release HC as the temperature rises due to the heat of the exhaust gas, if the oxidation catalyst is not lighted off, the purification of HC does not proceed, so that most of HC Is discharged without being purified.

Therefore, in the present embodiment, the temperature before the HC trap material substantially starts to release HC is set as the temperature threshold value (predetermined temperature) for changing and controlling the oxygen concentration, and self-heating is performed by A / F control. The material is heated by the occlusion of oxygen so that the temperature of the oxidation catalyst rises rapidly.

That is, the controller 9 controls the A / F according to the operating state of the engine, and when the catalyst temperature detected by the temperature sensor 11 is equal to or lower than the first temperature T1, the self-heating material has self-heating property. The A / F is corrected to the rich side so that the oxygen concentration of the inflowing exhaust gas is less than 1% by mass. In this case, since the self-heating material has a low oxygen concentration in the exhaust gas, it does not substantially occlude oxygen, and thus its self-heating is suppressed. That is, self-heating is maintained.

Then, when the catalyst temperature exceeds the second temperature T2 (predetermined temperature), the A / F is set to the lean side for a predetermined time (for example, so that the oxygen concentration of the exhaust gas flowing into the self-heating material becomes 10% by mass). , For a few seconds) Correct. Oxygen is supplied to the self-heating material by the correction to the lean side of the A / F. As a result, the self-heating material occludes oxygen and generates heat, and the temperature of the oxidation catalyst rises rapidly due to the heat, and the HC released from the HC trap material can be oxidized and purified (catalyst activity). ).

Here, at the first temperature T1, in order to utilize the self-heating material for the rapid temperature rise of the oxidation catalyst as in the case where the engine 1 is cold-started, the oxidation catalyst sets the self-heating property of the self-heating material. It is a temperature threshold for determining whether the temperature should be maintained until the temperature reaches T, that is, whether the A / F should be corrected to the rich side. Therefore, T1 <T2.

The correction of the A / F to the lean side may not be terminated by the above time control, but may be terminated when the temperature of the oxidation catalyst exceeds the light-off temperature.

The above-mentioned A / F control by the above-mentioned controller 9 suppresses the self-heating of the self-heating material by lowering the oxygen concentration of the exhaust gas flowing into the self-heating material when the catalyst temperature is the second temperature T2 or less. It constitutes a self-heating control means that causes the self-heating by increasing the oxygen concentration when the catalyst temperature exceeds the second temperature T2.

Here, the A / F is the amount of HC inflow into the HC trap material after the HC trap material starts trapping HC in a state where the self-heating material has self-heating property instead of the catalyst temperature. It can also be controlled based on.

In that case, the controller 9 adjusts the A / F so that the oxygen concentration of the exhaust gas flowing into the self-heating material having the self-heating property becomes less than 1% by mass when the HC inflow amount is equal to or less than a predetermined value. Make corrections to the rich side. Therefore, since the self-heating material has a low oxygen concentration in the exhaust gas, it does not substantially occlude oxygen, and thus its self-heating is suppressed. That is, self-heating is maintained.

Then, when the HC inflow amount exceeds the predetermined value, the A / F is set to the lean side for a predetermined time (for example, several seconds) so that the oxygen concentration of the exhaust gas flowing into the self-heating material becomes 10% by mass. )to correct. Oxygen is supplied to the self-heating material by the correction to the lean side of the A / F. As a result, the self-heating material occludes oxygen and generates heat, and the temperature of the oxidation catalyst rises rapidly due to the heat, and the HC released from the HC trap material can be oxidized and purified (catalyst activity). ).

The HC inflow amount can be detected based on the operation history from the start of operation of the engine 1. The predetermined value related to the HC inflow amount can be a smaller amount of HC than the amount that the HC trap material can trap without releasing HC. The amount of HC trap in the HC trap material depends on the temperature of the HC trap material. Therefore, the amount of HC that can be trapped by the HC trap material may be obtained from the catalyst temperature, and the amount of HC that is a predetermined amount smaller than the amount of HC may be set as a predetermined value related to the amount of inflow of HC.

-Regeneration of self-heating material-
By the way, in order to generate heat of the self-heating material, it is necessary that the self-heating material is in a reduced state (a state in which oxygen can be occluded). However, the self-heating material is in a state of occluding oxygen after self-heating. Therefore, as it is, the self-heating material cannot perform self-heating by occlusion of oxygen. Therefore, in the present embodiment, when the purification of the exhaust gas is completed, the self-heating material is regenerated to recover the self-heating property in order to purify the exhaust gas during the next operation of the engine 1.

That is, the controller 9 predicts the stop of the engine 1 and the time until the stop based on the vehicle speed (current speed of the vehicle) obtained by the vehicle speed sensor 12 and its deceleration. That is, when the vehicle speed is equal to or less than a predetermined value and the deceleration is equal to or more than a predetermined value, the engine 1 is predicted to stop, and the time until the engine is stopped is predicted based on the vehicle speed and the deceleration. Here, the self-heating property of the self-heating material is restored by setting the oxygen concentration of the exhaust gas flowing into the self-heating material to a predetermined value or less and releasing oxygen from the self-heating material. On the other hand, oxygen can be released from the self-heating material when the self-heating material is at a predetermined temperature or higher.

Therefore, when the controller 9 predicts that the engine 1 will stop, the controller 9 self when the oxygen concentration of the exhaust gas flowing into the self-heating material is set to a predetermined value or less based on the self-heating material correlation temperature and the exhaust gas flow rate. Estimate the time required to restore the self-heating of the exothermic material.

Specifically, since the oxygen storage amount of the self-heating material depends on the temperature, the self-heating material correlation temperature is detected by the temperature sensor 11, and the oxygen storage amount of the self-heating material is estimated based on the temperature. Then, based on the oxygen storage amount and the exhaust gas flow rate, the oxygen of the exhaust gas flowing into the self-heating material, which is necessary for reducing the oxygen storage amount of the self-heating material to a predetermined value (restoring the self-heating property), is performed. Set the degree of concentration reduction and the reduction time. That is, the time required to recover the self-heating property of the self-heating material when the oxygen concentration of the exhaust gas flowing into the self-heating material is set to a predetermined value or less is set. The exhaust gas flow rate can be estimated based on the fuel injection amount of the engine 1, etc., but it can also be measured by providing a flow rate sensor.

The controller 9 corrects the A / F to the rich side when the time until the engine 1 is stopped is longer than the time required for recovery of the self-heating property and the temperature of the self-heating material is equal to or higher than the predetermined temperature. , The oxygen concentration of the exhaust gas flowing into the self-heating material is set to less than 1% by mass. Then, at the same time as the engine 1 is stopped, the exhaust passage valve 8 is closed until the next engine operation is started. By closing the exhaust passage valve 8, the self-heating material is prevented from being exposed to the outside air, so that the self-heating property is maintained.

The self-heating material regeneration that restores the self-heating property of the self-heating material by lowering the oxygen concentration flowing into the self-heating material when the above A / F control when the engine is stopped by the controller 9 finishes the purification of the exhaust gas. It constitutes the means. The closing control of the exhaust passage valve 8 by the exhaust passage valve 8 and the controller 9 keeps the atmosphere of the self-heating material in a state where the oxygen concentration is lowered until the next start of purification of the exhaust gas, thereby improving the self-heating property of the self-heating material. It constitutes a self-exothermic maintenance means for maintaining.

<Control flow by controller 9>
As shown in FIG. 2, it is determined in step S1 after the start whether or not the engine is running, and if the engine is running, the process proceeds to step S2 to open the exhaust passage valve 8 according to the engine operating state. A / F control is performed (step S3). In the following step S4, it is determined whether the catalyst temperature is the first temperature T1 or less, and if it is the first temperature or less, the A / F is corrected to the rich side (step S5). As a result, the occlusion of oxygen in the self-heating material is suppressed, and therefore the self-heating material maintains the self-heating property.

In the following step S6, it is determined whether or not the catalyst temperature exceeds the second temperature T2, and if it exceeds, the A / F is corrected to the lean side (step S7). As a result, the self-heating material starts to store oxygen and self-heats. As a result, the temperature of the oxidation catalyst rises rapidly, and HC, HC, CO and NO in the exhaust gas released from the HC trap material can be oxidatively purified.

Here, when it is determined in step S4 that the catalyst temperature is not equal to or lower than the first temperature T1, the process proceeds to step 8 without proceeding to step 6. That is, only when the A / F is corrected to the rich side and the self-heating material maintains the self-heating property, the lean correction of the A / F is performed when the catalyst temperature exceeds the second temperature T2.

In step 8, it is determined whether or not the engine stop is predicted based on the vehicle speed and its deceleration. When the engine is expected to stop, the self-heating material can release oxygen (above the specified temperature), and when there is time required to release oxygen before the engine stops, the A / F is on the rich side. It is corrected (steps S9 to S11). That is, even if the engine is predicted to stop, if the temperature of the self-heating material is too low to release oxygen, or if the time required for oxygen release cannot be secured, the correction to the rich side of the A / F is not performed. .. This is to avoid deterioration of fuel efficiency.

By correcting the A / F to the rich side in step S11, oxygen is released from the self-heating material, and the self-heating property of the self-heating material is restored. When it is determined that the engine is stopped in the following step S12, the exhaust passage valve 8 is closed, and the self-heating property of the self-heating material is maintained.

<About self-heating material>
As a self-heating material, a plurality of Rh-supported CeZrBi composite oxides having different molar ratios of Ce, Zr and Bi are prepared, and further, a Rh-supported CeZr composite oxide containing no Bi is prepared, and each TPR (temperature rise) is prepared. The low temperature reducing property and the exothermic amount were evaluated by the reaction method).

FIG. 3 shows the effect of the Ce / Zr molar ratio on the consumption of H ₂ as a reducing agent. According to the figure, it can be seen that the Rh-supported CeZrBi composite oxide can be reduced (oxygen can be released) at 400 ° C. or lower when the Ce / Zr molar ratio is 1 or more.

FIG. 4 shows the effect of the Ce / Zr molar ratio on the calorific value. According to the figure, it can be seen that the Rh-supported CeZrBi composite oxide has a large calorific value when the Ce / Zr molar ratio is 4 or more.

FIG. 5 shows the effect of the molar ratio of Bi on H ₂ consumption. According to the figure, it can be seen that the Rh-supported CeZrBi composite oxide can be reduced (oxygen can be released) at 400 ° C. or lower when the Bi molar ratio is 0.2 or less.

FIG. 6 shows the effect of the molar ratio of Bi on the calorific value. According to the figure, it can be seen that the Rh-supported CeZrBi composite oxide has a large calorific value when the Bi molar ratio is 0.2 or less.

From FIGS. 3 to 6, the self-heating material has a Ce molar ratio of 0.3 or more and 0.75 or less and a Bi molar ratio of 0.1 or more and 0.3 or less from the viewpoint of heat generation and low temperature reducing property. It is preferable to use the Rh-supported CeZrBi composite oxide, which is more preferably 0.4 or more and 0.75 or less in Ce molar ratio, and more preferably 0.1 or more and 0.2 or less in Bi molar ratio. be able to.

<Rig test>
Prepare a test material that combines an HC trap material and an oxidation catalyst (a test material without a self-heating material) and a test material that combines a self-heating material, an HC trap material, and an oxidation catalyst (a test material with a self-heating material). did. As the self-heating material, Rh-supported Ce _0.64 Zr _0.16 Bi _0.20 O ₂ was used. Each test material is set in a simulated exhaust gas flow reactor, and a simulated exhaust gas containing 1000 ppmC of HC is circulated at a gas temperature of 100 ° C. for 120 seconds, and then the gas temperature is adjusted at a rate of 30 ° C./min. The temperature of the exhaust gas flowing out of the test material (exhaust gas temperature) and the total HC concentration (THC) when the temperature was raised were measured.

Figure 7 shows in no test materials self-heating material, the results of the cases was 10 wt% to finish the O ₂ concentration of the simulated exhaust gas from the test beginning (Example 1). Since THC is lower than the inflow HC concentration at the initial stage when the simulated exhaust gas distribution is started, it can be seen that HC is trapped in the HC trap material. After a while, THC gradually increased and became higher than the inflow HC concentration 250 seconds after the start of the test, and THC peaked at 350 seconds. After that, THC decreased, which indicates that the oxidation catalyst was activated and HC was purified.

Figure 8 shows the results of the test materials have self-heating material, the case was 10 mass% to the end of the O ₂ concentration of the simulated exhaust gas from the test beginning (Example 2). In this case, due to the self-heating of the self-heating material, the exhaust gas temperature rises immediately after the start of the test. It is recognized that THC started up immediately after the start of the test because the HC trap material was heated by the self-heating of the self-heating material. Further, it is recognized that the lower THC peak as compared with the case of the test material without the self-heating material (Example 1) is a result of the earlier activation of the oxidation catalyst.

FIG. 9 shows a case (Example 3) in which the O ₂ concentration of the simulated exhaust gas was set to 0% by mass for 120 seconds from the start of the test and then the O ₂ concentration was set to 10% by mass in the test material with the self-heating material. The result is shown. Example 2 of FIG 8, in the treasury heat generating material, is a lean start cases the O ₂ concentration from the test beginning and 10 wt% of the simulated exhaust gas, Example 3 of FIG. 9, in the treasury heat generating material, This is a rich start case in which the O ₂ concentration of the simulated exhaust gas was set to 0% by mass at the beginning of the test.

In the case of the rich start (Example 3) of FIG. 9, the exhaust gas temperature rises when the O ₂ concentration is switched from 0% by mass to 10% by mass, and THC also rises for a moment at the same time. This is recognized as the effect of the self-heating of the self-heating material. After that, THC increased, but its peak height was much lower than that of the lean start case (Example 2) in FIG. It is recognized that this is because the oxidation catalyst was rapidly heated by the self-heating of the self-heating material immediately after the switching of the O ₂ concentration and quickly reached the active temperature. That is, it is the result of efficiently purifying the HC released from the HC trap material by the oxidation catalyst.

As shown in FIG. 10 showing the average HC purification rate in the low temperature range (100 ° C. to 300 ° C.) of Examples 1 to 3, in Example 2 (with self-heating material and lean start), without self-heating material (Example 1). The HC purification rate is higher than that in Example 3, but in Example 3 (rich start with self-heating material), the HC purification rate is even higher than in Example 2 of lean start. From this, it can be seen that maintaining the self-heating property of the self-heating material for a while by rich start and then switching the air-heat ratio of the exhaust gas to lean is effective in improving the HC purification rate.

<Control time chart in WLTP mode>
FIG. 11 shows a change in vehicle speed in the WLTP mode. FIG. 12 shows changes in vehicle speed, gas input temperature (exhaust gas temperature flowing into the oxidation catalyst), catalyst temperature (oxidation catalyst temperature), engine A / F, EGR rate, and THC when the engine is started in the WLTP mode. Is shown.

After the engine is started, the gas input temperature gradually rises, and the gas input temperature rises almost in synchronization with the rise of the vehicle speed (the degree of rise is increasing). On the other hand, the catalyst temperature rises after the rise of the incoming gas temperature. As the catalyst temperature rises, the temperature of the HC trap material also rises and rises, and along with this, HC begins to be released. However, since the catalyst temperature is still low, the released HC is not purified.

In the present embodiment, the A / F becomes lower than the stoichiometric air-fuel ratio (14.7) as shown by the broken line until the temperature of the HC trap material rises to a predetermined temperature (the temperature before the release of HC starts). The self-heating of the self-heating material is suppressed by correcting to the rich side (lowering the oxygen concentration of the exhaust gas). After that, the A / F is corrected to the lean side (increasing the oxygen concentration of the exhaust gas) so as to be higher than the stoichiometric air-fuel ratio as shown by the broken line, and the self-heating material is heated at once by occlusion of oxygen. As a result, the catalyst temperature rises rapidly as shown by the broken line, and by the time the HC trap material begins to release HC, the oxidation catalyst becomes active. As a result, the HC released from the HC trap material is purified by the oxidation catalyst, and the HC is suppressed from being discharged unpurified.

Here, in the present embodiment, the oxygen concentration of the exhaust gas flowing into the self-heating material is changed by controlling the A / F of the engine, but as shown in FIG. 12, the temperature of the HC trap material is a predetermined temperature ( The oxygen concentration of the exhaust gas flowing into the self-heating material is changed by increasing the EGR rate to more than 50% (heavy EGR) until it rises to the temperature before the release of HC) and then lowering the EGR rate. You can also do it. Alternatively, the oxygen concentration may be changed by A / F control and EGR rate control.

FIG. 13 shows changes in vehicle speed, input gas temperature (exhaust gas temperature flowing into the oxidation catalyst), catalyst temperature (oxidation catalyst temperature), engine A / F, EGR rate, and THC when the engine is stopped in the WLTP mode. Is shown.

In the present embodiment, the engine stop is monitored by the vehicle speed and its deceleration, and when the vehicle speed becomes equal to or less than a predetermined value and the deceleration becomes equal to or more than a predetermined value, the engine stops and the time until the stop is predicted. When the engine is predicted to stop, the temperature of the self-heating material is above the specified temperature (the stored oxygen can be released) at that time, and there is time required to release oxygen before the engine is stopped. Occasionally, the A / F is corrected to the rich side (lower the oxygen concentration of the exhaust gas) so that it is lower than the stoichiometric air-fuel ratio (14.7) as shown by the broken line, and the self-heating material is self-heated. Restore sex. That is, oxygen is released from the self-heating material. Immediately after the engine is stopped, the exhaust passage valve 8 is closed.

Regarding the purification of NOx, NSC (NOx storage reduction catalyst) or the like can be adopted instead of the SCR catalyst 6.

1 Engine 2 Exhaust gas passage 3 Heating element (self-heating catalyst)
4 Oxidation catalyst converter (containing HC trap material)
8 Exhaust passage valve (open / close valve)
9 Controller 11 Temperature sensor 12 Vehicle speed sensor

Claims (6)

An exhaust gas purification device that purifies exhaust gas containing HC.
An HC trap material that is provided in the exhaust gas passage through which the exhaust gas flows and traps the HC,
An oxidation catalyst provided in the exhaust gas passage for oxidizing the HC released from the HC trap material and the HC contained in the exhaust gas,
A self-heating material provided in the exhaust gas passage and self-heating when oxygen is occluded for heating the oxidation catalyst,
By lowering the oxygen concentration of the exhaust gas flowing into the self-heating material when the temperature correlated with the temperature of the HC trap material is equal to or lower than the predetermined temperature before the HC trap material starts to release HC. A self-heating control means that suppresses the self-heating of the self-heating material and causes the self-heating by increasing the oxygen concentration when the temperature correlated with the temperature of the HC trap material exceeds the predetermined temperature.
When the purification of the exhaust gas is completed, the self-heating material recycling means for recovering the self-heating property of the self-heating material by releasing oxygen from the self-heating material by lowering the oxygen concentration.
It is characterized by being provided with a self-heating maintenance means for maintaining the self-heating property of the self-heating material by keeping the atmosphere of the self-heating material in a state where the oxygen concentration is lowered until the start of purification of the next exhaust gas. Exhaust gas purification device. An exhaust gas purification device that purifies exhaust gas containing HC.
An HC trap material that is provided in the exhaust gas passage through which the exhaust gas flows and traps the HC,
An oxidation catalyst provided in the exhaust gas passage for oxidizing the HC released from the HC trap material and the HC contained in the exhaust gas,
A self-heating material provided in the exhaust gas passage and self-heating when oxygen is occluded for heating the oxidation catalyst,
A means for determining the amount of HC inflow into the HC trap material from the start of the HC trap material, and
When the HC inflow amount is equal to or less than a predetermined value, the oxygen concentration of the exhaust gas flowing into the self-heating material is lowered to suppress the self-heating of the self-heating material, and the HC inflow amount exceeds the predetermined value. The self-heating control means that causes the self-heating by increasing the oxygen concentration,
When the purification of the exhaust gas is completed, the self-heating material recycling means for recovering the self-heating property of the self-heating material by releasing oxygen from the self-heating material by lowering the oxygen concentration.
It is characterized by being provided with a self-heating maintenance means for maintaining the self-heating property of the self-heating material by keeping the atmosphere of the self-heating material in a state where the oxygen concentration is lowered until the start of purification of the next exhaust gas. Exhaust gas purification device. In claim 1 or 2,
The exhaust gas purification device, wherein the self-heating material is a CeZr-based composite oxide containing Bi. In claim 1 or 2,
The exhaust gas purification device is characterized in that the self-heating maintaining means is provided in the exhaust gas passage and is composed of an on-off valve that prevents outside air from entering the exhaust gas passage. In claim 1 or 2,
The self-heating material regenerating means obtains the oxygen storage amount of the self-heating material based on the temperature correlated with the temperature of the self-heating material, and flows into the self-heating material for reducing the oxygen storage amount to a predetermined value. An exhaust gas purification device characterized in that the degree of reduction and the reduction time of the oxygen concentration of the exhaust gas to be reduced are set. It is an exhaust gas purification method that purifies the exhaust gas containing HC.
In the exhaust gas passage through which the exhaust gas flows, an HC trap material that traps the HC, an oxidation catalyst for oxidizing the HC released from the HC trap material and HC contained in the exhaust gas, and the oxidation catalyst are provided. Place a self-heating material that self-heats when storing oxygen for heating,
By lowering the oxygen concentration of the exhaust gas flowing into the self-heating material when the temperature correlated with the temperature of the HC trap material is equal to or lower than the predetermined temperature before the HC trap material starts to release HC. Suppresses the self-heating of the above self-heating material,
When the temperature correlated with the temperature of the HC trap material exceeds the predetermined temperature, the oxygen concentration is increased to cause the self-heating material to generate heat.
When the purification of the exhaust gas is completed, oxygen is released from the self-heating material by lowering the oxygen concentration.
An exhaust gas purification method characterized in that the self-heating property of the self-heating material is maintained by keeping the atmosphere of the self-heating material in a state where the oxygen concentration is lowered until the next start of purification of the exhaust gas.

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