JPH08170524A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PURPOSE: To improve warming up performance of a catalyst in an exhaust emission control device for an internal combustion engine. CONSTITUTION: An exhaust emission control device for an internal combustion engine is provided with a exhaust gas purifying light off catalyst 34 which is provided downstream from the electrically heating catalyst 33 of an exhaust passage 32, a deterioration degree detecting means 35 for detecting a catalyst deterioration degree R, and a warming up control means 36 for stopping electrification of the electrically heating catalyst 33 according to the detected catalyst deterioration degree R.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in an exhaust gas purification device for an internal combustion engine using an electrically heated catalyst.

[0002]

2. Description of the Related Art In an automobile internal combustion engine or the like, in order to purify exhaust gas, feedback control is performed so that an air-fuel ratio becomes a stoichiometric air-fuel ratio, and HC and C are provided in an exhaust passage.
A system equipped with a three-way catalyst that simultaneously oxidizes O and reduces NO has been widely put into practical use. However, immediately after starting when the engine is cold, the temperature of the exhaust gas is low,
Exhaust gas is not sufficiently purified by the three-way catalyst.

[0003] Therefore, conventionally, there is an exhaust gas purifying apparatus using an electrically heated catalyst as shown in Fig. 12 for the purpose of early activation of the catalyst during warm-up (see Japanese Patent Laid-Open No. 4-279718).

To explain this, an electrically heated catalyst 21 for purifying exhaust gas is installed in the exhaust passage 29 of the engine 27. The electrically heated catalyst 21 is energized by the control unit 24 during warm-up.

A temperature sensor 23 for detecting the temperature of the electrically heated catalyst 21 is provided. The control unit 24
When the electric heating catalyst 21 is energized during warm-up and its temperature rises above a predetermined value, it is determined that the catalyst has been sufficiently activated, and the energization is stopped.

Further, in response to a failure of the temperature sensor 23, the control unit 24 calculates a limit time for energizing the electrically heated catalyst 21 according to the engine cooling water temperature and the like, and the energization time reaches the calculated limit time. Then, it is determined that the electrically heated catalyst 21 has been sufficiently activated, and the energization of the electrically heated catalyst 21 is stopped.

[0007]

By the way, the catalytic performance of the electrically heated catalyst 21 tends to deteriorate as the deterioration thereof progresses. For example, the temperature T50 required to purify exhaust gas by 50% is greatly increased. Become higher.

However, such an electrically heated catalyst 2
In the exhaust gas purification apparatus using No. 1, the electrically heated catalyst 21
Since the catalyst temperature or the energization time detected during warm-up is controlled regardless of the deterioration degree of the electric heating catalyst 21, the energization time of the electric heating catalyst 21 may be too long or too short depending on the deterioration degree of the electric heating catalyst 21. There is a nature.

Further, in the exhaust gas purification device in which a large capacity light-off catalyst is installed on the downstream side of the electrically heated catalyst in the exhaust passage, the light-off catalyst is made effective during warm-up in response to the progress of catalyst deterioration. Can't work, HC, CO
The amount of emissions of carbon dioxide increases, and fuel consumption deteriorates.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems and improve the catalyst warm-up performance in an exhaust gas purification apparatus for an internal combustion engine.

[0011]

An exhaust gas purification apparatus for an internal combustion engine according to claim 1 is an electric heating system for exhaust gas purification, which is installed in an exhaust passage 32 of an engine 31 and heated by energization, as shown in FIG. The catalyst 33, an exhaust purification light-off catalyst 34 installed downstream of the electrically heated catalyst 33 in the exhaust passage 32, and a deterioration degree detection means 35 for detecting the catalyst deterioration degree R.
And a warm-up control means 36 that energizes the electrically heated catalyst 33 during warm-up and stops energization of the electrically heated catalyst 33 according to the detected catalyst deterioration degree R.

In the exhaust gas purifying apparatus for an internal combustion engine according to claim 2, as shown in FIG. 14, the temperature TE of the electrically heated catalyst 33 is increased.
And a second catalyst temperature detecting means 42 for detecting the temperature TL of the light-off catalyst 34.
When the temperature TE of the electrically heated catalyst 33 detected during warm-up when the catalyst deterioration degree R is equal to or lower than a predetermined value rises to a reference value TEC or higher, energization of the electrically heated catalyst 33 is stopped, and the catalyst deterioration degree R is a predetermined value. When the temperature TL of the light-off catalyst 34 rises above the reference value TLC during a larger warm-up period, the electrically heated catalyst 3
Switching means 43 for stopping the energization of No. 3 of FIG.

In the exhaust gas purifying apparatus for an internal combustion engine according to claim 3, as shown in FIG. 15, a reference value TEC and a reference value TLC are provided.
Setting means 44 for setting the respective values according to the catalyst deterioration degree R
Is provided.

In the exhaust gas purifying apparatus for an internal combustion engine according to claim 4, as shown in FIG. 16, the temperature TE of the electrically heated catalyst 33 is set.
Catalyst temperature detection means 51 for detecting the temperature, target value setting means 52 for setting a target value KC of a value obtained by integrating the product of the energization time and the temperature of the electrically heated catalyst 33 according to the catalyst deterioration degree R, and the detected catalyst. Of the temperature TE and the energization time of the electrically heated catalyst 33 are integrated to calculate a value K, and when the calculated integrated value K exceeds a set target value KC, the electrically heated catalyst 33 is energized. Energization stopping means 54 for stopping the
Is provided.

[0015]

The mode of deterioration of the catalyst is classified into permanent deterioration that occurs due to a decrease in the specific surface area due to thermal deformation of the washcoat and a decrease in the degree of dispersion of the noble metal, and temporary deterioration that occurs due to the oxidation or reduction of the catalyst metal.

The catalytic performance of the electrically heated catalyst 33 tends to deteriorate as compared with the light-off catalyst 34 as the catalyst deteriorates, and the catalyst temperature at which the desired conversion is obtained rises significantly. To do. That is, when the catalyst deterioration degree R is smaller than the predetermined value during warm-up, the electrically heated catalyst 33 is activated before the light-off catalyst 34, while when the catalyst deterioration degree R is larger than the predetermined value during warm-up, the light-off catalyst is activated. 34 is activated before the electrically heated catalyst 33.

The present invention has been made by paying attention to the deterioration characteristics of the catalyst. In the exhaust gas purification apparatus for an internal combustion engine according to claim 1, the warm-up control means 36 energizes the electrically heated catalyst 33 during warm-up. Then, according to the detected catalyst deterioration degree R, the power supply to the electrically heated catalyst 33 is stopped and the warm-up is finished.

In this way, the time during which the electric heating catalyst 33 is energized is appropriately controlled in accordance with the catalyst deterioration degree R, so that the time during which the electric heating catalyst 33 is energized is insufficient during warm-up or is unnecessary. Is prevented from becoming too long, and the catalysts 33, 3
4 can be activated early, and power can be saved.

In the exhaust gas purifying apparatus for an internal combustion engine according to claim 2, the switching means 43 detects the temperature T of the electrically heated catalyst 33 when the catalyst deterioration degree R is equal to or less than a predetermined value during warm-up.
When E rises above the reference value TEC, the electric heating catalyst 33 is de-energized and the warm-up is terminated.

When the catalyst deterioration degree R is smaller than a predetermined value during warm-up, the electrically heated catalyst 33 is activated before the light-off catalyst 34. Therefore, when the temperature TE of the electrically heated catalyst 33 reaches the activation temperature TEC, electric Stop energizing the heating catalyst 33,
Exhaust gas is purified mainly by the electrically heated catalyst 33.

On the other hand, the switching means 43 controls the temperature TL of the light-off catalyst 34 during warm-up when the catalyst deterioration degree R is larger than a predetermined value.
When is higher than the reference value TLC, the electric heating catalyst 33 is de-energized and the warm-up is terminated.

When the catalyst deterioration degree R is higher than the predetermined value, the light-off catalyst 34 is activated before the electric heating catalyst 33. Therefore, when the outlet temperature TL of the light-off catalyst 34 reaches the activation temperature TLC, The electricity supply to the electrically heated catalyst 33 is stopped, and the exhaust gas is purified mainly by the light-off catalyst 34.

In the exhaust gas purifying apparatus for an internal combustion engine according to claim 3, the setting means 44 includes a reference value TEC and a reference value TLC.
Are set according to the catalyst deterioration degree R, respectively.

As the catalyst deterioration progresses, the catalyst temperatures at which the electric heating catalyst 33 and the light-off catalyst 34 can obtain the desired conversion rates rise, so that the reference value TEC and the reference value TLC are deteriorated respectively. By setting in accordance with the degree R, it is possible to prevent the energization time of the electrically heated catalyst 33 from becoming insufficient or becoming unnecessarily long during warm-up.

In the exhaust gas purification apparatus for an internal combustion engine according to claim 4, the energization stopping means 54 detects the detected catalyst temperature TE.
The value K obtained by integrating the product of the electric current of the electric heating catalyst 33 and
When the target value KC set in advance is exceeded, the electrically heated catalyst 33
Turn off the power supply to and finish warming up.

As a result, it is possible to prevent the energization time of the electrically heated catalyst 33 from becoming short and unnecessarily long during warm-up.

[0027]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

As shown in FIG. 1, a fuel injection valve 5 is attached to the intake passage 8 of the engine 7 and injects fuel in response to a signal from the controller 4.

In the exhaust passage 9, an electrically heated catalyst (EHC) that simultaneously oxidizes HC and CO in the exhaust gas and reduces NOx
1 and a light-off catalyst (LOC) 6 are installed side by side in series.

The electrically heated catalyst 1, which is provided as a means for forcibly heating the catalyst, is installed upstream of the exhaust passage 3 and has a heater function of generating heat when energized. The capacity of the electrically heated catalyst 1 is set smaller than that of the light-off catalyst 6 at a predetermined ratio.

The light-off catalyst 6 installed downstream of the electrically heated catalyst 1 in the exhaust passage 3 has no heater function and is heated by the exhaust gas introduced through the electrically heated catalyst 1.

The electrically heated catalyst 1 and the light-off catalyst 6 are composed of a platinum-based three-way catalyst in which platinum (Pt) is mainly supported as a catalyst metal on each carrier. Further, the electrically heated catalyst 1 and the light-off catalyst 6 may be composed of a palladium-based three-way catalyst in which palladium (Pd) is mainly supported as a catalyst metal on each carrier and other ceria or the like is supported.

First and second oxygen sensors 2 and 3 for detecting the oxygen concentration in the exhaust gas are installed upstream of the electrically heated catalyst 1 and downstream of the light-off catalyst 6 in the exhaust passage 3.

FIG. 4 shows how the internal temperatures of the electrically heated catalyst 1 and the light-off catalyst 6 change when the electrically heated catalyst 1 is energized. The electrically heated catalyst 1 and the light-off catalyst 6 rise together with the passage of the energization time.

A first temperature sensor 13 for detecting the outlet temperature TE of the electrically heated catalyst 1 and a second temperature sensor 14 for detecting the outlet temperature TL of the light-off catalyst 6 are installed in the exhaust passage 3.

The controller 4 receives signals from the first and second oxygen sensors 2 and 3, the first and second temperature sensors 13 and 14, and the water temperature sensor 12 that detects the engine cooling water temperature TW, respectively. It

Although not shown, the controller 4 inputs detection signals such as the engine intake air amount and the number of revolutions, calculates the basic fuel injection amount Tp that brings the air-fuel ratio close to the stoichiometric air-fuel ratio, and calculates the basic oxygen injection amount of the first oxygen sensor 2. A detection signal is input and feedback control is performed so that the fuel injection amount falls within a narrow range centered on the theoretical air-fuel ratio in a predetermined stoichiometric range. Feedback control is performed so that the air-fuel ratio of the air-fuel mixture supplied to the engine 7 falls within a narrow range centered on the theoretical air-fuel ratio, so that the catalysts 1 and 6 work effectively and HC and C in the exhaust gas are discharged.
Oxidation of O and reduction of NOx are performed simultaneously.

When the catalysts 1 and 6 are exposed to a high-temperature exhaust gas atmosphere that is leaner than the stoichiometric air-fuel ratio, the catalyst conversion rate decreases due to the oxidation of the catalyst metal, so-called temporary deterioration occurs. In addition to the temporary deterioration, the electrically heated catalyst 1 has a so-called permanent deterioration in which the catalyst conversion rate decreases due to physical factors such as a decrease in specific surface area due to thermal deformation of the washcoat and a decrease in dispersity of the catalyst metal. Get up.

FIG. 5 shows an electrically heated catalyst 1 and a light-off catalyst 6.
It shows that the catalyst performance changes as the deterioration of the catalyst progresses. The catalyst performance is represented by the temperature T50 required to purify the exhaust gas by 50%, and as the deterioration progresses, the electric heating catalyst 1 has a significantly higher T50 than the light-off catalyst 6, and the catalyst performance is Tends to get worse.

The present invention has been made by paying attention to the deterioration characteristic of the catalyst, and the controller 4 inverts the outputs of the first oxygen sensor 2 and the second oxygen sensor 3 to rich lean. The deterioration degrees R of the catalysts 1 and 6 are detected by comparing the cycles, and the time during which the electrically heated catalyst 1 is energized during warm-up is controlled in accordance with the deterioration degree R.

FIG. 2 shows a routine for detecting the deterioration degree R of the catalysts 1 and 6.

Explaining this, first, in step S1, feedback control is performed so that the air-fuel ratio falls within a narrow range centered on the theoretical air-fuel ratio, and it is determined whether or not it is in a diagnostic region where a predetermined exhaust temperature can be obtained. .

In steps S2 and S3, the rich lean inversion frequency F1 of the first oxygen sensor 2 installed upstream of the catalysts 1 and 6 and the second oxygen sensor 3 installed downstream of the catalysts 1 and 6. The inversion frequency F2 of the rich lean of is read respectively.

As shown in FIG. 6, as the degree of deterioration of the catalysts 1 and 6 progresses and the catalyst conversion rate approaches 0%, the reversal cycle ratio F2 / F1 approaches 1. When the catalysts 1 and 6 are functioning normally, the oxygen in the exhaust gas is stored, and therefore the oxygen contained in the upstream exhaust gas cannot be directly detected downstream of the catalysts 1 and 6. However, when the catalysts 1 and 6 deteriorate, the oxygen in the upstream exhaust flows to the downstream as it is, so the output reversal number of the downstream oxygen sensor 3 approaches the reversal number of the output of the upstream oxygen sensor 2. come.

In step S4, this inversion period ratio Fr
Is calculated as F2 / F1.

In step S5, the catalyst deterioration degree R is retrieved from the map shown in FIG. 7 based on the cycle ratio Fr.

In step S6, the catalyst deterioration degree R retrieved
Is stored.

In step S7, the catalyst deterioration degree R retrieved
Is compared with a predetermined value, and when it is determined that the catalyst deterioration degree R is larger than the predetermined value, the process proceeds to step S8, and the progress of catalyst deterioration is displayed on a display device (not shown).

Next, a routine for controlling energization of the electrically heated catalyst 1 shown in FIG. 3 will be described.

At the start of the engine 7, the electrically heated catalyst 1 is first energized in step S11 as an ignition switch (not shown) is turned on.

In step S12, the catalyst deterioration degree R is compared with a predetermined value, and if it is determined that the catalyst deterioration degree R is within the predetermined value, the process proceeds to step S16 and subsequent steps, in accordance with the outlet temperature TE of the electrically heated catalyst 1. Control energization stop.

In step S16, the outlet temperature TE of the electrically heated catalyst 1 detected by the first temperature sensor 13 is read.

Subsequently, in step S17, the energization stop outlet temperature (reference value) T corresponding to the deterioration degree R is calculated from the map shown in FIG.
Search EC. The energization stop outlet temperature TEC is a temperature at which the electrically heated catalyst 1 is sufficiently activated.

Subsequently, in step S18, the electrically heated catalyst 1
When the outlet temperature TE is determined to be equal to or lower than the energization stop outlet temperature TEC, the electric heating catalyst 1 is continuously energized, and the outlet temperature TE is the energization stop outlet. When it is determined that the temperature exceeds the temperature TEC and rises, the process proceeds to step S19 to stop the energization of the electrically heated catalyst 1 and finish the warm-up.

In this way, in the operating state where the catalyst deterioration degree R is smaller than the predetermined value, the electric heating catalyst 1 is activated before the light-off catalyst 6, so that the temperature T of the electric heating catalyst 1 is increased.
When E reaches the activation temperature TEC, the electricity supply to the electrically heated catalyst 1 is stopped, and the exhaust gas is mainly purified by the electrically heated catalyst 1.

On the other hand, when it is determined in step S12 that the catalyst deterioration degree R is larger than the predetermined value, step S13.
After that, the energization stop is controlled according to the outlet temperature TL of the light-off catalyst 6.

In step S13, the outlet temperature TL of the light-off catalyst 6 detected by the second temperature sensor 14 is read.

Subsequently, at step S14, the energization stop outlet temperature (reference value) T corresponding to the deterioration degree R is calculated from the map shown in FIG.
Search LC. The energization stop outlet temperature TLC is a temperature at which the light-off catalyst 6 is sufficiently activated.

Subsequently, in step S15, the light-off catalyst 6
When the outlet temperature TL is determined to be equal to or lower than the energization stop outlet temperature TLC, the electric heating catalyst 1 is continuously energized, and the outlet temperature TL is the energization stop outlet. If it is determined that the temperature has risen above the temperature TLC, the process proceeds to step S19 to stop the energization of the electrically heated catalyst 1 and finish the warm-up.

In this way, in an operating state in which the degree of catalyst deterioration R is larger than a predetermined value, the light-off catalyst 6 is activated before the electrically heated catalyst 1, so that the outlet temperature TL of the light-off catalyst 6 becomes equal to the activation temperature TLC. When the temperature reaches the
Is stopped and the light-off catalyst 6 mainly purifies the exhaust gas.

As a result, it is possible to avoid unnecessarily energizing the electrically heated catalyst 1 during warm-up, save electric power, and suppress deterioration of the electrically heated catalyst 1 and a battery (not shown).

Next, as another embodiment, the controller 4
Is a value K obtained by integrating the product of the energization time (counter value of the timer) of the electrically heated catalyst 1 and the outlet temperature TE, compares the calculated integrated value K with the target value KC, and the integrated value K is the target value. When it is determined that the temperature exceeds KC, the catalysts 1 and 6 may be sufficiently activated, and the electrically heated catalyst 1 may be deenergized.

FIG. 10 shows a routine for controlling energization of the electrically heated catalyst 1 in this embodiment.

To explain this, when an ignition switch (not shown) is turned on when the engine 7 is started, first, at step S21, the electrically heated catalyst 1 is energized.

Subsequently, in step S22, the target value KC corresponding to the deterioration degree R is retrieved from the map shown in FIG. This target value KC is a target value of a value obtained by integrating the time and temperature required for the deterioration recovery processing of the catalysts 1 and 6. In the map shown in FIG. 11, the target value KC obtained by integrating the product of the energization time and the outlet temperature TE of the electrically heated catalyst 1 in which the catalysts 1 and 6 are sufficiently activated according to the catalyst deterioration degree R is set in advance as an experimental result. It is set based on.

Succeedingly, in the step S23, the integrated value K
Is calculated as an integrated value of the product of the outlet temperature TE and the energization time (count value of the timer).

Then, in step S24, the calculated integrated value K is compared with the target value KC retrieved according to the deterioration degree R, and if it is determined that the integrated value K exceeds the target value KC, the step Proceeding to S25, the electricity supply to the electrically heated catalyst 1 is stopped and the warming up is completed.

In this way, the time during which the electric heating catalyst 1 is energized is properly controlled according to the catalyst deterioration degree R, so that the time during which the electric heating catalyst 1 is energized is insufficient during warm-up or is unnecessary. It is avoided to energize for a long time, and the catalyst 1,6
Can be activated early, power can be saved, and deterioration of the electrically heated catalyst 1 and the battery (not shown) can be suppressed.

As yet another embodiment, the controller 4
Is a configuration for controlling the voltage for energizing the electrically heated catalyst 1 according to the catalyst deterioration degree R and the cooling water temperature TW at the time of starting, and the energization time of the electrically heated catalyst 1 required to obtain the desired catalyst performance. You may make it constant.

[0070]

As described above, the exhaust gas purifying apparatus for an internal combustion engine according to claim 1 energizes the electrically heated catalyst during warm-up and stops energization of the electrically heated catalyst according to the detected catalyst deterioration degree R. As a result, the time for energizing the electrically heated catalyst is properly managed according to the catalyst deterioration degree R, and it is avoided that the electrically energized time of the electrically heated catalyst becomes short during warm-up or becomes unnecessarily long. Early activation of the catalyst and power saving can be achieved.

In the exhaust gas purifying apparatus for an internal combustion engine according to claim 2, when the temperature TE of the electrically heated catalyst detected during warm-up when the catalyst deterioration degree R is equal to or lower than a predetermined value rises above the reference value TEC, While de-energizing, the catalyst deterioration degree R
Temperature TL of the light-off catalyst during warm-up
When the temperature rises above the reference value TLC, the electric heating catalyst is de-energized, so that the catalyst that activates first in accordance with the catalyst deterioration degree R of the electric heating catalyst and the light-off catalyst is activated to activate the catalyst early. And power saving is achieved.

In the exhaust gas purifying apparatus for an internal combustion engine according to claim 3, the reference value TEC and the reference value TLC are set in accordance with the catalyst deterioration degree R, so that the energization time of the electrically heated catalyst is insufficient during warm-up. And avoiding unnecessarily long.

In the exhaust gas purifying apparatus for an internal combustion engine according to claim 4, when the value K obtained by integrating the product of the detected catalyst temperature TE and the energization time of the electrically heated catalyst exceeds the preset target value KC, the electrically heated Since it is configured to stop energizing the catalyst,
It is possible to avoid a shortage of power supply time to the electrically heated catalyst and an unnecessarily long time during warm-up.

[Brief description of drawings]

FIG. 1 is a system diagram showing an embodiment of the present invention.

FIG. 2 is a flowchart showing a control content for similarly determining deterioration of the catalyst.

FIG. 3 is a flow chart showing the control contents for energizing the electrically heated catalyst during warm-up.

FIG. 4 is a schematic diagram showing how the internal temperatures of the electrically heated catalyst and the light-off catalyst change when the electrically heated catalyst is energized.

FIG. 5 is a schematic diagram showing how the catalyst performance changes as the deterioration of the electrically heated catalyst and the light-off catalyst progresses.

FIG. 6 is a characteristic diagram showing the relationship between the inversion period ratio F2 / F1 and the catalyst conversion rate.

FIG. 7 is a map similarly setting the catalyst deterioration degree R based on the inversion period ratio F2 / F1.

FIG. 8 Similarly, based on the deterioration degree R, the energization stop outlet temperature T
Map with EC set.

FIG. 9 Similarly, based on the deterioration degree R, the energization stop outlet temperature T
Map with LC set.

FIG. 10 is a flowchart showing the content of control for energizing the electrically heated catalyst during warm-up in another embodiment.

FIG. 11 is a map in which a target value KC is also set based on the catalyst deterioration degree R.

FIG. 12 is a system diagram showing a conventional example.

FIG. 13 is a diagram corresponding to the claims of the invention according to claim 1.

FIG. 14 is a diagram corresponding to the claims of the invention according to claim 2;

FIG. 15 is a diagram corresponding to the claim of the invention according to claim 3;

FIG. 16 is a diagram corresponding to the claims of the invention according to claim 4;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electric heating catalyst 2 1st oxygen sensor 3 2nd oxygen sensor 4 Controller 5 Fuel injection valve 6 Light-off catalyst 7 Engine 9 Exhaust passage 12 Water temperature sensor 13 1st outlet temperature sensor 14 2nd outlet temperature sensor 31 Engine 32 Exhaust passage 33 Electric heating catalyst 34 Light-off catalyst 35 Degradation degree detecting means 36 Warm-up control means 41 First catalyst temperature detecting means 42 Second catalyst temperature detecting means 43 Switching means 44 Reference value setting means 51 Catalyst temperature detecting means 52 Target value setting means 53 Integrated value calculating means 54 Energization stopping means

Claims (4)

[Claims] 1. An electric heating catalyst for exhaust purification, which is installed in an exhaust passage of an engine and is heated by energization, a light-off catalyst for exhaust purification, which is installed downstream of the electric heating catalyst in the exhaust passage, and a catalyst. Deterioration degree detecting means for detecting the degree of deterioration R, and warm-up control means for energizing the electrically heated catalyst during warm-up and stopping energization of the electrically heated catalyst according to the detected catalyst deterioration degree R are provided. An exhaust emission control device for an internal combustion engine, characterized by: 2. A first catalyst temperature detecting means for detecting a temperature TE of an electrically heated catalyst, a second catalyst temperature detecting means for detecting a temperature TL of a light-off catalyst, and a warm-up in which a catalyst deterioration degree R is a predetermined value or less. When the temperature TE of the electrically heated catalyst detected at the time of the machine rises above the reference value TEC, the electricity of the electrically heated catalyst is stopped, and the temperature TL of the light-off catalyst is changed to the reference value T when the catalyst deterioration degree R is larger than a predetermined value.
The exhaust emission control device for an internal combustion engine according to claim 1, further comprising: a switching unit that stops energization of the electrically heated catalyst when the temperature rises above LC. 3. The exhaust gas purifying apparatus for an internal combustion engine according to claim 2, further comprising setting means for setting the reference value TEC and the reference value TLC in accordance with the catalyst deterioration degree R, respectively. 4. A catalyst temperature detecting means for detecting a temperature TE of an electrically heated catalyst, and a setting means for setting a target value KC of a product of an energization time and a temperature of the electrically heated catalyst integrated according to a catalyst deterioration degree R. And a calculating means for calculating a value K that integrates the product of the detected temperature TE of the electrically heated catalyst and the energization time, and energizing the electrically heated catalyst when the calculated integrated value K exceeds a set target value KC. An exhaust emission control device for an internal combustion engine according to claim 1, further comprising: an energization stopping means for stopping.