JP7298364B2 - Exhaust gas purification device and exhaust gas purification method - Google Patents

Description

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

2. Description of the Related Art It is known to raise the temperature of an oxidation catalyst that oxidizes HC (hydrocarbons), CO, etc. in exhaust gas by using a chemical heat storage material to purify engine exhaust gas. For example, in Patent Document 1, a chemical heat storage material that undergoes reversible exothermic and endothermic reactions with water vapor or the like and an oxidation catalyst are placed next to each other, and the chemical heat storage material reacts with water vapor or the like in the exhaust gas to generate heat. is described to raise the temperature of the oxidation catalyst. The document also describes closing a valve provided on the downstream side of the catalyst after discharging the exhaust gas from the exhaust pipe by operating the engine with the fuel cut when the engine is stopped. This prevents the chemical heat storage material from reacting with water vapor and generating heat after the engine is stopped.

JP 2011-252464 A

By the way, an exhaust gas purification system using both an oxidation catalyst and an HC trap material is known. When the temperature of the exhaust gas is low and the oxidation catalyst is not activated, the HC in the exhaust gas is adsorbed by the trap material. Oxidatively purifies released HC.

However, since the HC trap material gradually releases HC as its temperature rises, a large amount of unpurified HC is likely to be discharged before the oxidation catalyst is activated. In other words, the problem is that the temperature at which the HC trap material begins to release HC does not necessarily match the temperature at which the oxidation catalyst becomes active.

Therefore, the present invention prevents the HC released from the HC trap material from being discharged in an unpurified state.

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

An exhaust gas purification device disclosed herein is a device for purifying exhaust gas containing HC,
an HC trap material provided in an exhaust gas passage through which the exhaust gas flows to trap the HC;
an oxidation catalyst provided in the exhaust gas passage for oxidizing HC released from the HC trap material and HC contained in the exhaust gas;
a self-heating material that is provided in the exhaust gas passage and that heats itself when absorbing oxygen for heating the oxidation catalyst;
By reducing 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 a predetermined temperature before the HC trap material starts releasing HC. self-heating control means for suppressing self-heating of the self-heating material and causing the self-heating by increasing the oxygen concentration when the temperature correlated with the temperature of the HC trapping material exceeds the predetermined temperature;
self-heating material regeneration means for releasing oxygen from the self-heating material by lowering the oxygen concentration to recover the self-heating property of the self-heating material when the purification of the exhaust gas is completed;
self-heating property maintaining means for maintaining the self-heating property of the self-heating material by maintaining the atmosphere of the self-heating material in a state where the oxygen concentration is lowered until the next exhaust gas purification is started ;
The self-heating material regeneration 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. It is characterized by setting the reduction degree and the reduction time of the oxygen concentration of the exhaust gas .

In this exhaust gas purifier, the self-heating of the self-heating material is suppressed when the temperature correlated with the temperature of the HC trapping material is below a predetermined temperature, and self-heating occurs when the temperature exceeds the predetermined temperature.

Therefore, when the temperature of the exhaust gas is low, the HC trap material is prevented from being heated by the heat generated by the self-heating material. That is, the premature release of HC from the HC trapping material can be avoided. Therefore, unpurified HC is prevented from being discharged before the oxidation catalyst is activated. 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 trapping material starts releasing HC. The amount of unpurified HC discharged decreases due to the activation accompanying the temperature rise of the oxidation catalyst.

In addition, according to this exhaust gas purifying device, when 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 used to start purification of the next exhaust gas. can be maintained up to Therefore, the self-heating material can be used repeatedly so as to effectively purify the exhaust gas.

Further, the exhaust gas purification device disclosed herein is a device for purifying exhaust gas containing HC,
an HC trap material provided in an exhaust gas passage through which the exhaust gas flows to trap the HC;
an oxidation catalyst provided in the exhaust gas passage for oxidizing HC released from the HC trap material and HC contained in the exhaust gas;
a self-heating material that is provided in the exhaust gas passage and that heats itself when absorbing oxygen for heating the oxidation catalyst;
means for determining the amount of HC flowing into the HC trapping material from when the HC trapping material starts trapping HC;
When the HC inflow amount is less than or equal to a predetermined value, the self-heating of the self-heating material is suppressed by reducing the oxygen concentration of the exhaust gas flowing into the self-heating material, and the HC inflow amount exceeds a predetermined value. self-heating control means for causing the self-heating by increasing the oxygen concentration in the coke;
self-heating material regeneration means for releasing oxygen from the self-heating material by lowering the oxygen concentration to recover the self-heating property of the self-heating material when the purification of the exhaust gas is completed;
self-heating property maintaining 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 purification of the exhaust gas is started. do.

This exhaust gas purifier controls the oxygen concentration of the exhaust gas flowing into the self-heating material based on the amount of HC flowing into the HC trap material, not the temperature of the HC trap material. It is different from a purifier. The predetermined value, which is the threshold for changing and controlling the oxygen concentration, can be, for example, an amount of HC that is smaller than the amount that the HC trapping material can trap without releasing HC. Therefore, by the time the HC trapping material begins to release HC, it becomes easier to activate the oxidation catalyst, and it is possible to prevent HC from being discharged in an unpurified state. In addition, according to this exhaust gas purifying device, when 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 used to start purification of the next exhaust gas. can be maintained up to Therefore, the self-heating material can be used repeatedly so as to effectively purify 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 storage increases, which is advantageous for rapid heating of the oxidation catalyst, and the release of oxygen at a relatively low temperature (300°C or less) enables recovery of the self-heating material. be advantageous to

In one embodiment, the self-heating property 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. The atmosphere of the self-heating material can be kept in a state where the oxygen concentration is lowered by preventing outside air from entering the exhaust gas passage by the on-off valve.

In one embodiment, the self-heating material regeneration 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 the above-described method for reducing the oxygen storage amount to a predetermined value. The reduction degree and reduction time of the oxygen concentration of the exhaust gas flowing into the self-heating material are set. This is advantageous in reliably recovering the self-heating property of the self-heating material.

According to the present invention, by controlling the oxygen concentration of the exhaust gas flowing into the self-heating material having self-heating properties, based on the temperature correlated with the temperature of the HC trap material or the amount of HC flowing into the HC trap material, Self-heating of the self-heating material is suppressed and self-heating occurs, and when exhaust gas purification is completed, oxygen is released from the self-heating material to recover its self-heating property, and the next exhaust gas purification is started. Since the self-heating property is maintained until the HC trap material starts releasing HC, it becomes easy to activate the oxidation catalyst, and it is possible to prevent unpurified HC from being discharged. Also, the self-heating material can be used repeatedly to effectively purify the exhaust gas.

FIG. 1 is an overall configuration diagram of an engine exhaust gas purifier. FIG. 4 is a control flow diagram regarding self-heating of a self-heating material. Graph diagram showing H ₂ -TPR test results of a self-heating material. FIG. 4 is a graph showing changes over time in temperature reached by self-heating of a self-heating material. Graph diagram showing H ₂ -TPR test results of a self-heating material. FIG. 4 is a graph showing the temperature reached by self-heating of the self-heating material. 2 is a graph showing changes over time in THC and the like in Example 1. FIG. FIG. 2 is a graph showing temporal changes in THC and the like in Example 2. FIG. FIG. 10 is a graph showing changes over time of THC and the like in Example 3. FIG. Graph diagram showing the HC purification rate of Example 1-3. FIG. 4 is a graph showing changes in vehicle speed over time in WLTP mode; FIG. 4 is a graph showing changes over time such as vehicle speed when the engine is started in the WLTP mode; FIG. 4 is a graph showing temporal changes in vehicle speed and the like when the engine is stopped in WLTP mode;

EMBODIMENT OF THE INVENTION Hereinafter, the form for implementing this invention is demonstrated based on drawing. The following description of preferred embodiments is merely exemplary in nature and is not intended to limit the invention, its applications or uses.

<Overview of exhaust gas purifier>
As shown in FIG. 1, the exhaust gas purifier of this embodiment purifies exhaust gas discharged from an engine 1 of a vehicle. In the exhaust gas passage 2 of the engine 1, a heating element 3, an oxidation catalytic converter 4, a particulate filter 5, an SCR (Selective Catalytic Reduction) catalyst 6, a slip catalyst 7 and an exhaust passage valve ( On-off valves 8 are arranged in order from the upstream side in the exhaust gas flow direction. The exhaust gas purifier includes a controller 9 using a microcomputer for controlling 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 heating element 3 includes a self-heating material that releases oxygen when the air-fuel ratio of the exhaust gas is rich, absorbs oxygen when the air-fuel ratio is lean, and generates heat by itself. 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 it is particularly preferable to use a CeZrBi composite oxide. 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, from the viewpoint of improving self-heating property. The CeZrBi composite oxide preferably supports a catalytic metal such as Rh. Supporting Rh can promote the steam reforming reaction or the water gas shift reaction, and the hydrogen obtained from the reaction facilitates the low-temperature reduction of the self-heating material (releasing self-heating property by releasing oxygen). In addition, by supporting Rh, the oxygen in the vicinity of Rh is activated, so that the oxygen storage and release performance of the self-heating material increases even at low temperatures, which is advantageous for self-heating. The amount of Rh supported on the CeZrBi composite oxide is preferably 0.01% by mass or more and 20% by mass or less.

In the catalytic converter 4, an HC trapping material that traps HC in the exhaust gas, and an oxidation catalyst for oxidizing the HC released from the HC trapping material and HC, CO, and NO in the exhaust gas are carried on the honeycomb support. It becomes Zeolite is preferably used as the HC trap material, and β-zeolite is particularly preferably used. As the oxidation catalyst, for example, it is preferable to employ 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, a transition metal such as Zr or a Ce-containing oxide whose heat resistance is improved by a rare earth metal such as Nd can be preferably used.

The HC trapping material and the oxidation catalyst can be mixed and supported on the honeycomb carrier. The HC trapping material and the oxidation catalyst can be supported on the honeycomb carrier in layers such that the former is the lower layer and the latter is the upper layer, or the former is the upper layer and the latter is the lower layer. Alternatively, the HC trapping material and the oxidation catalyst can be carried on the honeycomb carrier in tandem such that the former is positioned upstream and the latter is positioned downstream thereof.

The self-heating material can also be supported on the honeycomb carrier of the catalytic converter 4 without making it separate from the catalytic converter 4 . For example, both can be carried on the honeycomb carrier in tandem such that the self-heating material is located upstream and the oxidation catalyst is located downstream. Alternatively, both can be supported on the honeycomb carrier in layers such 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. This filter 5 is formed by carrying a PM combustion catalyst on a filter body that traps PM. The PM combustion catalyst promotes combustion of PM trapped 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 alternately provided in parallel. It is a wall-flow type that flows out into the adjacent exhaust gas outflow passage through the pores of the partition wall. The filter body is made of _inorganic porous materials such as cordierite, SiC, _Si3N4 , Sialon, _AlTiO3 . The PM combustion catalyst includes a catalyst in which Pt is supported on activated alumina, a Zr-based composite oxide and a Rh-doped Ce-containing Zr-based composite oxide (Rh is a crystal lattice point or between lattice points of a Ce-containing Zr-based composite oxide. Rh-arranged compound), etc. can be employed.

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 employ urea-SCR, which employs urea as a precursor of NH ₃ as a reducing agent. The urea water is supplied to the upstream side of the SCR catalyst 6 from a urea water tank (not shown). As the SCR catalyst 6, it is preferable to employ a catalyst component in which a catalyst metal that reduces NOx using _NH3 as a reducing agent is supported on zeolite that traps _NH3 . As catalyst metals for NOx reduction, Fe, Cu, Ti, V, W and the like are preferable.

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

The exhaust passage valve 8 opens and closes the exhaust gas passage 2 downstream of the slip catalyst 7 . The exhaust passage valve 8 is opened during exhaust gas purification and 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. When the purification of the exhaust gas is finished, the self-heating property of the self-heating material is restored (oxygen is released from the self-heating material) by means for regenerating the self-heating material, which will be described later. After that, the exhaust passage valve 8 is closed, and the outside air is allowed to enter the exhaust gas passage 2, thereby maintaining the self-heating property of the self-heating material until the next purification of the exhaust gas is started. It constitutes exothermic maintenance means.

<About the controller>
The controller 9 of this 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 the temperature correlated with the temperature of the HC trap material of the catalytic converter 4 (hereinafter simply referred to as "catalyst temperature"). In this embodiment, the temperature of the exhaust gas flowing into the heating element 3 is used as the catalyst temperature and 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 correlated with the temperature of the self-heating material (hereinafter referred to as "self-heating material correlated temperature").

-Self-heating control-
The HC trap material using β-zeolite begins to release the trapped HC when its temperature reaches around 120°C. On the other hand, the light-off temperature (the temperature at which the purification rate reaches 50%) for HC purification of the oxidation catalyst is generally around 200.degree. Therefore, even if the engine 1 is started and the HC trap material begins 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 will not progress. is discharged without purification.

Therefore, in the present embodiment, the temperature before the HC trap material substantially starts releasing HC is set as the temperature threshold (predetermined temperature) for changing and controlling the oxygen concentration, and self-heating is performed by A/F control. The material is made to generate heat by absorbing oxygen, and the temperature of the oxidation catalyst rises rapidly.

Specifically, the controller 9 controls the A/F according to the operating state of the engine. 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 oxygen concentration of the exhaust gas is low, the self-heating material does not substantially occlude oxygen, thereby suppressing the self-heating. That is, self-heating property 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, , for a few seconds). Oxygen is supplied to the self-heating material by this A/F correction to the lean side. As a result, the self-heating material absorbs oxygen and generates heat, and the temperature of the oxidation catalyst rapidly rises due to the heat, and the HC released from the HC trap material can be oxidized and purified (catalyst activity transformation).

Here, the first temperature T1 is set so that the self-heating property of the self-heating material is used to quickly raise the temperature of the oxidation catalyst as when the engine 1 is cold-started. It is a temperature threshold for determining whether or not to maintain until reaching 2 temperature T, that is, whether or not to correct the A/F to the rich side. Therefore, T1<T2.

The correction to the lean side of the A/F may be terminated when the temperature of the oxidation catalyst exceeds the light-off temperature instead of being terminated by the above time control.

The above-described A/F control by the above-described controller 9 suppresses the self-heating of the self-heating material by reducing the oxygen concentration of the exhaust gas flowing into the self-heating material when the catalyst temperature is equal to or lower than the second temperature T2. , self-heating control means for causing the self-heating by increasing the oxygen concentration when the catalyst temperature exceeds the second temperature T2.

Here, instead of the catalyst temperature, the A/F is the amount of HC flowing into the HC trapping material after the HC trapping material starts trapping HC in a state where the self-heating material has self-heating properties. 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 self-heating properties is less than 1% by mass when the HC inflow amount is equal to or less than a predetermined value. Correction to the rich side is performed. Therefore, since the oxygen concentration of the exhaust gas is low, the self-heating material does not substantially occlude oxygen, thereby suppressing the self-heating. That is, self-heating property 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 )to correct. Oxygen is supplied to the self-heating material by this A/F correction to the lean side. As a result, the self-heating material absorbs oxygen and generates heat, and the temperature of the oxidation catalyst rapidly rises due to the heat, and the HC released from the HC trap material can be oxidized and purified (catalyst activity transformation).

The HC inflow amount can be detected based on the operation history from the start of operation of the engine 1 . The predetermined value for the inflow amount of HC may be an amount of HC that is smaller than the amount that the HC trapping material can trap without releasing HC. The HC trap amount of 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 trapping material is obtained from the catalyst temperature, and the amount of HC that is a predetermined amount smaller than the calculated amount of HC is used as the predetermined value for the inflow amount of HC.

－Recycling of self-heating materials－
By the way, in order for the self-heating material to generate heat, the self-heating material must be in a reduced state (a state in which oxygen can be occluded). However, the self-heating material is in a state of absorbing oxygen after self-heating. Therefore, as it is, the self-heating material cannot generate heat by occluding oxygen. Therefore, in this embodiment, when the purification of the exhaust gas is completed, regeneration is performed to recover the self-heating property of the self-heating material 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 to stop based on the vehicle speed (current vehicle speed) 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 greater than a predetermined value, it is predicted that the engine 1 will stop, and the time until the engine stops is predicted based on the vehicle speed and deceleration. Here, the self-heating property of the self-heating material is recovered by releasing oxygen from the self-heating material by reducing the oxygen concentration of the exhaust gas flowing into the self-heating material to a predetermined value or less. On the other hand, the release of oxygen from the self-heating material becomes possible when the temperature of the self-heating material is higher than the predetermined temperature.

Therefore, when the controller 9 predicts that the engine 1 will stop, the self Estimate the time required to restore the self-heating properties 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 detected temperature. Then, based on the oxygen storage amount and the exhaust gas flow rate, the amount of oxygen in the exhaust gas flowing into the self-heating material necessary for reducing the oxygen storage amount of the self-heating material to a predetermined value (recovering the self-heating property) is calculated. Set the density reduction degree and reduction time. That is, the time required for recovering 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 or the like, but 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 stops is longer than the time required to recover the self-heating property and the temperature of the self-heating material is higher than a predetermined temperature. 2. The oxygen concentration of the exhaust gas flowing into the self-heating material is set to less than 1% by mass. Then, simultaneously with stopping the engine 1, the exhaust passage valve 8 is closed until the next engine operation starts. 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.

Self-heating material regeneration that restores the self-heating property of the self-heating material by lowering the concentration of oxygen flowing into the self-heating material when the A/F control by the controller 9 when the engine is stopped completes purification of the exhaust gas. constitute 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 purification of the exhaust gas is started, thereby suppressing the self-heating property of the self-heating material. It constitutes a self-heating property maintaining means for maintaining.

<Flow of Control by Controller 9>
As shown in FIG. 2, in step S1 after the start, it is determined whether or not the engine is operating. A/F control is performed (step S3). In subsequent step S4, it is determined whether the catalyst temperature is equal to or lower than the first temperature T1, and if it is equal to or lower than the first temperature, the A/F is corrected to the rich side (step S5). Oxygen storage in the self-heating material is thereby suppressed, so that the self-heating material maintains its self-heating properties.

In subsequent step S6, it is determined whether or not the catalyst temperature has exceeded the second temperature T2, and if so, the A/F is corrected to the lean side (step S7). As a result, the self-heating material starts absorbing oxygen and heats itself. As a result, the temperature of the oxidation catalyst rises rapidly, and HC released from the HC trapping material and HC, CO and NO in the exhaust gas can be oxidized and 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 instead of 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 A/F is lean-corrected when the catalyst temperature exceeds the second temperature T2.

In step 8, it is determined whether engine stop is predicted based on the vehicle speed and its deceleration. When the engine is expected to stop, the self-heating material is capable of releasing oxygen (at a predetermined temperature or higher), and the A/F shifts to the rich side when there is time to release oxygen before the engine stops. 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 A/F is not corrected to the rich side. . 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 recovered. When it is determined in the subsequent step S12 that the engine is stopped, the exhaust passage valve 8 is closed, and the self-heating property of the self-heating material is maintained.

<About self-heating material>
As self-heating materials, a plurality of Rh-supporting CeZrBi composite oxides with different molar ratios of Ce, Zr, and Bi were prepared, and further, a Bi-free Rh-supporting CeZr composite oxide was prepared, and each TPR (temperature rise The low-temperature reducing property and calorific value were evaluated by the reaction method).

FIG. 3 shows the effect of the Ce/Zr molar ratio on the consumption of _H2 as a reducing agent. The figure shows that the Rh-supporting CeZrBi composite oxide can be reduced (capable of releasing oxygen) at 400° C. or less when the Ce/Zr molar ratio is 1 or more.

FIG. 4 shows the influence of the Ce/Zr molar ratio on the calorific value. The figure shows that the Rh-supporting CeZrBi composite oxide generates a large amount of heat when the Ce/Zr molar ratio is 4 or more.

FIG. 5 shows the effect of Bi molar ratio on _H2 consumption. The figure shows that the Rh-supporting CeZrBi composite oxide can be reduced (capable of releasing oxygen) at 400° C. or lower when the Bi molar ratio is 0.2 or lower.

FIG. 6 shows the effect of the molar ratio of Bi on the calorific value. The figure shows that the Rh-supporting CeZrBi composite oxide generates a large amount of heat 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 reduction. It is preferable to adopt a Rh-supported CeZrBi composite oxide, and it is more preferable that the Ce molar ratio is 0.4 or more and 0.75 or less, and the Bi molar ratio is 0.1 or more and 0.2 or less. be able to.

<Rig test>
Prepare test material combining HC trap material and oxidation catalyst (test material without self-heating material) and test material combining self-heating material, HC trap material and oxidation catalyst (test material with self-heating material) bottom. Rh-supported Ce _0.64 Zr _0.16 Bi _0.20 O ₂ was used as the self-heating material. Each test material was set in a simulated exhaust gas circulation reactor, and a simulated exhaust gas containing HC of 1000 ppm was passed at a gas temperature of 100°C for 120 seconds, and then the gas temperature was increased 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) were measured when the test material was raised.

FIG. 7 shows the results of a case (example 1) in which the O ₂ concentration of the simulated exhaust gas was set to 10% by mass from the beginning to the end of the test in the test material without the self-heating material. Since the THC concentration is lower than the inflowing HC concentration at the beginning of the flow of the simulated exhaust gas, it can be seen that the HC is trapped in the HC trapping material. After a while, the THC gradually increased, became higher than the inflowing HC concentration at 250 seconds after the start of the test, and peaked at 350 seconds. After that, THC decreased, which indicates that the oxidation catalyst was activated and HC was purified.

FIG. 8 shows the results of a case (example 2) in which the O ₂ concentration of the simulated exhaust gas was set to 10% by mass from the beginning to the end of the test in the test material with the self-heating material. In this case, due to the self-heating of the self-heating material, the exit gas temperature rises immediately after the start of the test. The fact that THC rises immediately after the start of the test is recognized to be due to the fact that the HC trap material was heated by the self-heating of the self-heating material. In addition, the fact that the THC peak is lower than in the case of the test material without the self-heating material (Example 1) is recognized as a result of earlier activation of the oxidation catalyst.

FIG. 9 shows a case (Example 3) in which the _O 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 concentration was set to 10% by mass in the test material with the self-heating material. Show the results. Example 2 in FIG. 8 is a lean start case in which the O ₂ concentration of the simulated exhaust gas is set to 10% by mass from the beginning of the test with the self-heating material, while Example 3 in FIG. 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 rich start (example 3) in FIG. 9, when the O ₂ concentration is switched from 0% by mass to 10% by mass, the outlet gas temperature rises, and THC also rises momentarily at the same time. It is recognized that this is due to the self-heating effect of the self-heating material. After that, THC rises, but the peak height is much lower than 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 O ₂ concentration was switched, and quickly reached the activation temperature. That is, this is the result of efficient purification of HC released from the HC trapping material by the oxidation catalyst.

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

<Control time chart in WLTP mode>
FIG. 11 shows changes in vehicle speed in WLTP mode. Fig. 12 shows changes in vehicle speed, inlet 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 started in WLTP mode. indicates

After the engine is started, the incoming gas temperature gradually rises, and rises substantially in synchronism with the rise of the vehicle speed (the degree of rise increases). On the other hand, the catalyst temperature rises after the rise of the incoming gas temperature. As the temperature of the catalyst rises, the temperature of the HC trapping material also rises, and HC begins to be released accordingly. However, since the catalyst temperature is still low, the released HC is not purified.

In this embodiment, until the temperature of the HC trap material rises to a predetermined temperature (the temperature before HC release starts), the A/F becomes lower than the theoretical air-fuel ratio (14.7) as indicated by the dashed line. is corrected to the rich side (the oxygen concentration of the exhaust gas is lowered) to suppress the self-heating of the self-heating material. After that, the A/F is corrected to the lean side (by increasing the oxygen concentration of the exhaust gas) so that the air-fuel ratio becomes higher than the theoretical air-fuel ratio as indicated by the dashed line, and the self-heating material is caused to generate heat at once by occluding oxygen. As a result, the catalyst temperature rises rapidly as indicated by the dashed line, and the oxidation catalyst becomes active by the time the HC trapping material begins to release HC. As a result, the HC released from the HC trap material is purified by the oxidation catalyst, and the unpurified HC is suppressed from being discharged.

Here, in this embodiment, the oxygen concentration of the exhaust gas flowing into the self-heating material is changed by controlling the A/F of the engine. Altering the oxygen concentration of the exhaust gas entering the self-heating material by increasing the EGR rate above 50% (heavy EGR) until the temperature rises to the temperature before HC release begins (heavy EGR), and then decreasing the EGR rate. You can also make Alternatively, the oxygen concentration may be changed by A/F control and EGR rate control.

Fig. 13 shows changes in vehicle speed, inlet 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 WLTP mode. indicates

In this embodiment, the engine stop is monitored based on 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 stop and the time until the engine stop are predicted. When the engine is predicted to stop, the temperature of the self-heating material is at a predetermined temperature or higher (the stored oxygen can be released) at that time, and there is time required for the oxygen to be released before the engine stops. Sometimes, A/F is corrected to the rich side so that it is lower than the theoretical air-fuel ratio (14.7) as indicated by the dashed line (by reducing the oxygen concentration of the exhaust gas), and the self-heating of the self-heating material restore sexuality. That is, oxygen is released from the self-heating material. Immediately after stopping the engine, the exhaust passage valve 8 is closed.

In addition, regarding purification of NOx, instead of the SCR catalyst 6, an NSC (NOx storage reduction catalyst) or the like can be employed.

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 (5)

An exhaust gas purification device for purifying exhaust gas containing HC,
an HC trap material provided in an exhaust gas passage through which the exhaust gas flows to trap the HC;
an oxidation catalyst provided in the exhaust gas passage for oxidizing HC released from the HC trap material and HC contained in the exhaust gas;
a self-heating material that is provided in the exhaust gas passage and that heats itself when absorbing oxygen for heating the oxidation catalyst;
means for determining the amount of HC flowing into the HC trapping material from when the HC trapping material starts trapping HC;
When the HC inflow amount is less than or equal to a predetermined value, the self-heating of the self-heating material is suppressed by reducing the oxygen concentration of the exhaust gas flowing into the self-heating material, and the HC inflow amount exceeds a predetermined value. self-heating control means for causing the self-heating by increasing the oxygen concentration in the coke;
self-heating material regeneration means for releasing oxygen from the self-heating material by lowering the oxygen concentration to recover the self-heating property of the self-heating material when the purification of the exhaust gas is completed;
self-heating property maintaining means for maintaining the self-heating property of the self-heating material by maintaining the atmosphere of the self-heating material in a state where the oxygen concentration is lowered until the next purification of the exhaust gas is started. Exhaust gas purifier. In claim 1 ,
The exhaust gas purifier, wherein the self-heating material is a CeZr-based composite oxide containing Bi. In claim 1 ,
The exhaust gas purifier according to claim 1, wherein the self-heating property maintaining means is provided in the exhaust gas passage and comprises an on-off valve for preventing outside air from entering the exhaust gas passage. In claim 1 ,
The self-heating material regeneration 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. 1. An exhaust gas purifier, characterized in that it sets the degree of reduction and the reduction time of the oxygen concentration of the exhaust gas. An exhaust gas purification device for purifying exhaust gas containing HC,
an HC trap material provided in an exhaust gas passage through which the exhaust gas flows to trap the HC;
an oxidation catalyst provided in the exhaust gas passage for oxidizing HC released from the HC trap material and HC contained in the exhaust gas;
a self-heating material that is provided in the exhaust gas passage and that heats itself when absorbing oxygen for heating the oxidation catalyst;
By reducing 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 a predetermined temperature before the HC trap material starts releasing HC. self-heating control means for suppressing self-heating of the self-heating material and causing the self-heating by increasing the oxygen concentration when the temperature correlated with the temperature of the HC trapping material exceeds the predetermined temperature;
self-heating material regeneration means for releasing oxygen from the self-heating material by lowering the oxygen concentration to recover the self-heating property of the self-heating material when the purification of the exhaust gas is completed;
self-heating property maintaining means for maintaining the self-heating property of the self-heating material by maintaining the atmosphere of the self-heating material in a state where the oxygen concentration is lowered until the next exhaust gas purification is started;
The self-heating material regeneration 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. 1. An exhaust gas purifier, characterized in that it sets the degree of reduction and the reduction time of the oxygen concentration of the exhaust gas.

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