JPH06200750A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To increase the reliability of an exhaust emission control device by providing a main passage and a by-pass passage with an adsorbent interposed therein, in parallel upstream of the catalyst of an exhaust passage, and controlling the exhaust flow ratio of both passages from the degree-of-degradation of the catalyst, the exhaust gas temperature, and the like according to the operating state of an engine so as to desorb HC from the adsorbent according to the degree of degradation. CONSTITUTION:Part of the exhaust passage 13 of an engine 11 is formed of a main passage 13a and a by-pass passage 14 with an adsorbent 15 interposed therein. A pre-three-way catalyst 19a and a main three-way catalyst 19b are provided upstream and downstream of both passages 13a, 14, and oxygen sensors 21a, 21b are provided. The degree-of-degradation of the three-way catalyst 19b is obtained from the oxygen sensors 21a, 21b, and the opening of a control valve 16 is controlled by the output of an exhaust gas temperature sensor 22. When the temperature of the exhaust gas is low, the exhaust gas is made flow mainly to the adsorbent 15 side, and part of the exhaust gas is made flow to the catalyst 19b side to accelerate temperature rise. Upon exceeding the specified temperature, a flow ratio on the by-pass passage 14 side is made zero. The opening of the control valve 16 is regulated according to the operating state so as to desorb HC from the adsorbent 15. The reliability of an exhaust emission control device is thus increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purification apparatus for an internal combustion engine, and more particularly, to an unburned HC contained in the exhaust gas of an engine, which is temporarily adsorbed and desorbed by an adsorbent at a low temperature and exhausted after activation. The present invention relates to a technology in which an exhaust purification catalyst is used as a countermeasure in an apparatus that purifies with a purification catalyst.

[0002]

2. Description of the Related Art In an internal combustion engine for a vehicle, in order to purify exhaust gas, HC (unburned gas) and CO in the exhaust gas are oxidized into H ₂ O and CO ₂ in the exhaust passage, while NO _X is converted into N ₂ . An exhaust gas purification catalyst called a three-way purification catalyst that reduces and purifies is installed. By the way, of the harmful components in the exhaust gas, H
The discharge amount of C is particularly susceptible to the exhaust temperature. In other words, even if a noble metal catalyst is used, it is generally 3
A catalyst temperature of 00 ° C or higher is required. Therefore, in the exhaust gas purification device only including the three-way catalyst, it is difficult to purify the HC by the catalyst when the exhaust gas temperature is low, such as immediately after the engine is started cold.

Therefore, as a conventional exhaust gas purifying apparatus for a vehicle, for example, as shown in JP-A-62-174522, for adsorbing HC in the exhaust passage on the upstream side of the exhaust gas purifying catalyst. It has been proposed to interpose the adsorbent. That is, when the adsorbent has a low temperature,
By utilizing the fact that it has the property of adsorbing the adsorbent and desorbing the adsorbed HC when the temperature becomes high, a bypass passage in which the adsorbent is interposed is connected in parallel to a part of the exhaust passage upstream of the exhaust purification catalyst. The main passage and the bypass passage are selectively opened and closed, and the bypass passage is opened to adsorb HC at the adsorbent at a low temperature before the exhaust purification catalyst is activated.
After the bypass passage is closed once, the temperature becomes high and the exhaust purification catalyst is activated, and then the bypass passage is opened again to desorb the adsorbed HC and the exhaust purification catalyst purifies it. As the adsorbent, for example, a monolith carrier coated with zeolite has been proposed because zeolite has excellent adsorbability.

[0004]

By the way, in an exhaust gas purification apparatus provided with such an adsorbent, as shown in FIG. 8, the catalyst is activated unless the exhaust gas at a higher temperature is exhausted as the exhaust gas purification catalyst deteriorates. However, even if the catalyst is sufficiently activated, the purification efficiency of the catalyst will decrease, but since the control was not modified according to the deterioration, sufficient purification was not performed and exhaust emission worsened. Was causing problems.

The present invention has been made in view of the above-mentioned conventional problems, and exhaust gas emission is controlled by controlling the timing and the amount of desorption of HC from the adsorbent in accordance with the degree of deterioration of the catalyst. It is an object of the present invention to provide an exhaust emission control device for an internal combustion engine, which can prevent the deterioration of the engine.

[0006]

Therefore, according to the present invention, as shown in FIG. 1, an exhaust gas purification catalyst is provided in an exhaust passage of an engine, and a part of the exhaust gas passage upstream of the exhaust purification catalyst is provided. Main passage and unburned HC in exhaust gas connected in parallel to the main passage
An exhaust flow rate ratio control means for controlling the flow rate ratio of exhaust gas between the main passage and the bypass passage, and a bypass passage having an adsorbent having a function of adsorbing at a low temperature and desorbing at a high temperature. In an exhaust gas purification device for an internal combustion engine, comprising:
Deterioration degree detecting means for detecting the degree of deterioration of the exhaust gas purification catalyst, operating state detecting means for detecting the operating state of the engine, exhaust temperature detecting means for detecting the temperature state of the exhaust gas, including the degree of deterioration and the exhaust temperature Exhaust flow ratio setting means for setting an exhaust flow ratio according to the operating state of the engine based on the conditions, and the exhaust flow ratio control means for obtaining the exhaust flow ratio set by the exhaust flow ratio setting means. It is configured to be controlled by.

Further, the exhaust flow rate ratio setting means, depending on the deterioration degree of the exhaust purification catalyst obtained by the deterioration degree detecting means, desorbs the HC adsorbed by the adsorbent at a catalyst temperature per unit time. Of the HC desorption amount, the exhaust flow rate ratio is set based on the unit desorption amount, and the time for maintaining the set exhaust flow rate ratio is obtained. The exhaust flow rate ratio may be controlled to be maintained at the set value for a predetermined time at the temperature of the start catalyst or higher.

Further, the deterioration degree detecting means is means for detecting the deterioration degree of the exhaust purification catalyst based on the ratio of the fluctuation cycle of the air-fuel ratio detection value at the upstream inlet portion and the downstream outlet portion of the exhaust purification catalyst. You can also Further, the deterioration degree detection means may be means for detecting the deterioration degree of the exhaust gas purification catalyst based on the exhaust gas temperatures at the upstream inlet portion and the downstream outlet portion of the exhaust gas purification catalyst.

[0009]

According to this structure, before the exhaust gas temperature detected by the exhaust gas temperature detecting means reaches the temperature at which the exhaust gas purification catalyst is activated, the bypass passage is opened and the adsorbent adsorbs HC in the exhaust gas. Let After that, until the exhaust gas purification catalyst is activated, the exhaust flow rate ratio control means closes the bypass passage and guides the exhaust gas to the main passage. During this time, the exhaust gas temperature reaches the temperature at which HC is desorbed from the adsorbent, but since the exhaust gas is not guided by closing the bypass passage, desorption is not performed.

On the other hand, according to the deterioration degree of the exhaust gas purification catalyst obtained by the deterioration degree detecting means, the H adsorbed on the adsorbent
When the desorption start catalyst temperature and desorption amount of C are set, and when the desorption start catalyst temperature of the HC is reached, the exhaust flow rate ratio control means opens the bypass passage to allow the exhaust gas to flow in and remove the HC adsorbed by the adsorbent. The exhaust gas flow rate ratio is controlled so that the set HC desorption amount is obtained according to the operating state of the engine.

As described above, by controlling the timing and the amount of desorption of HC from the adsorbent according to the degree of deterioration of the catalyst, it is possible to maintain excellent exhaust gas, particularly HC purification performance. Further, when the degree of deterioration of the exhaust purification catalyst is detected based on the ratio of the fluctuation cycle of the air-fuel ratio detection value at the upstream inlet portion and the downstream outlet portion of the exhaust purification catalyst, the exhaust purification performance is directly determined. Since the degree of deterioration can be detected with high accuracy, and the degree of deterioration can be accurately detected regardless of the operating state, the reliability of the exhaust emission control device can be increased.

Further, when the degree of deterioration of the exhaust purification catalyst is detected based on the exhaust temperatures at the upstream inlet and the downstream outlet of the exhaust purification catalyst, the product cost can be increased with a simpler configuration. It becomes possible to suppress.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. First, referring to FIG. 2, the overall configuration of the exhaust gas purification device according to the present invention will be described. A part of the exhaust passage 13 of the engine 11 is composed of a main passage 13a and an exhaust bypass passage 14 connected in parallel with the main passage 13a. An adsorbent 15 is formed in the exhaust bypass passage 14. The adsorbent 15 is formed, for example, by coating a monolithic ceramic carrier with a substance having an adsorbing property such as zeolite, activated carbon, or γ-alumina.

The exhaust inlet 14 of the bypass passage 14
In a, a control valve 1 as means for controlling the flow rate ratio of exhaust gas between the main passage 13a and the bypass passage 14 by continuously controlling the opening ratio between the main passage 13a and the bypass passage 14 is provided.
6 is provided. The control valve 16 includes, for example, a diaphragm type actuator, and is formed such that the valve opening degree is controlled by the actuator based on a signal from the control unit 17.

An exhaust bypass passage 14 is provided in the exhaust passage 13.
A pre-three-way catalyst 19a and a main three-way catalyst 19b as exhaust purification catalysts are provided on the upstream side of the exhaust inlet 14a and the downstream side of the exhaust outlet 14b, respectively. Oxygen sensors 21a and 21b for detecting the exhaust state flowing into the main three-way catalyst device 19b are provided at the upstream inlet portion and the downstream outlet portion of the main three-way catalyst device 19b.

The adsorbent 15 and the main three-way catalyst device 1
Exhaust temperature sensors 22 and 20a are provided at the upstream inlet of 9b, and the adsorbent 15 and the main three-way catalyst device 19 are provided.
The temperature of the exhaust gas flowing into b is detected. The control unit 17 is provided with the functions of deterioration degree detection means, exhaust flow rate ratio control means, and exhaust flow rate ratio setting means as software.

The engine load Tp and the rotation speed Ne
Various signals of the detection value of 1, the oxygen sensor value, the adsorbent 15 and the exhaust temperature of the main three-way catalyst device 19b are input to the control unit 17, and various controls are performed based on the input signals. Next, the routine for determining the HC desorption starting temperature T1, the HC desorption amount M1, and the desorption required time t1 based on the degree of deterioration of the catalyst according to the first embodiment of the present invention will be described with reference to the flowchart shown in FIG. To do.

First, in step 1 (hereinafter referred to as "S1"), the fluctuation period (rich / lean inversion per unit time is calculated based on the output values of the oxygen sensors 21a and 21b provided upstream and downstream of the exhaust purification catalyst. The number of times f1 and f2 are detected, and the deterioration degree D1
Find (= f2 / f1). Here, as the deterioration of the catalyst progresses, the number of reversals of the oxygen sensor 21b on the downstream side increases, so that the deterioration degree D1 also increases.

Next, at S2, the HC desorption starting temperature T1, the HC desorption amount M1 and the desorption required time t1 are set based on the deterioration degree D1. That is, first, since the exhaust gas temperature at which the catalyst exhibits sufficient activity increases as the deterioration progresses, the exhaust temperature at which the catalyst exhibits a 50% conversion rate is set as the activation temperature at which exhaust purification is at least achieved. The activation temperature is obtained based on the temperature D1 and is set as the HC desorption start temperature T1.

Next, the relational expression M1 = m0 of the HC desorption amount M1
The HC desorption amount M1 is determined from × 100 / (100-50). Here, m0 represents the allowable amount of HC emission per unit time. Then, the HC desorption required time t1 is determined from the relational expression of t1 = M0 / M1. Here, M0 represents the HC adsorption capacity (maximum adsorption amount), which is uniquely determined by the HC adsorbent loading amount.

Since the deterioration degree is detected by taking the ratio of the output values of the oxygen sensors 21a and 21b in this way, the exhaust gas purification performance is directly detected, so that the deterioration degree detection accuracy becomes high. Moreover, since the degree of deterioration can be accurately detected regardless of the operating state, the reliability of the exhaust gas purification device can be increased. In the above, S1 has a function as a deterioration degree detecting means.

Next, according to the flow chart shown in FIG.
A routine for HC adsorption / desorption processing will be described. First, S1
At 0, after the engine is started, the exhaust gas temperature sensor 22 detects the exhaust gas temperature Ta at the inlet of the HC adsorbent. In S11, it is determined whether the exhaust gas temperature Ta is lower than the predetermined value To. If Ta <To, the process proceeds to S12, in which the control valve 16 provided in the exhaust passage 13 is opened by a predetermined opening to allow the exhaust gas to flow mainly to the adsorbent 15 side to adsorb HC in the exhaust gas and Part to the exhaust purification catalyst 19b side to promote the temperature rise of the catalyst. If Ta ≧ To, the process proceeds to S13.

In S13, since the temperature of the exhaust gas flowing into the adsorbent 15 exceeds the predetermined value, the control valve 16 is opened to the predetermined opening 2 (the exhaust flow rate ratio on the side of the bypass passage 14 is zero), and all the exhaust gas is used as the exhaust purification catalyst. Flow to the 19b side. In S14, the exhaust temperature sensor 20a detects the exhaust temperature Tc at the upstream inlet portion of the exhaust purification catalyst 19b.

In S15, it is determined whether the exhaust temperature Tc is lower than the desorption start temperature T1 obtained in the above routine. If Tc <T1, the exhaust gas purification catalyst 19
Since b has not yet reached the activation temperature, the steps from S13 are repeated once more so that the amount of discharged HC does not exceed the allowable value. If Tc ≧ T1, the activation temperature is reached, so the control valve 16 is opened to release HC.

Next, in S16, the valve of the control valve 16 is adjusted so that the HC desorption amount M1 per unit time obtained in the above routine is obtained according to the operating condition of the engine (engine load Tp, engine speed Ne). Control the opening. In S17, it is determined whether or not the desorption time t1 calculated in the above routine has elapsed since the desorption started. Then, if the desorption time t1 has elapsed, the control valve 16 is opened to the predetermined opening 2 in S18 and all the exhaust gas is allowed to flow to the exhaust gas purification catalyst 19b. If the desorption time t1 has not yet elapsed, from S14. Repeat the routine.

In the above, the HC desorption starting temperatures T1, H
For the C desorption amount M1 and desorption required time t1, the calculated values at the previous operation are used. Incidentally, here, S14 functions as an exhaust gas temperature detecting means, and S16 functions as an exhaust gas flow rate ratio controlling means. Next, the subroutine for determining the valve opening degree of the control valve 16 shown in S16 will be described with reference to the flowchart shown in FIG.

First, in S20, the load Tp and the rotation speed Ne of the engine are detected. Next, in S21, the exhaust flow rate Q1 is searched from the map based on the detected load Tp and the rotational speed Ne. In S22, the bypass passage flow rate Qb1 is calculated from the relational expression of Qb1 = k · M1. still,
Here, k is a constant, and Qb1 and M1 show a substantially proportional relationship.

In S23, the valve opening V01 of the control valve 16 is searched from the map based on Q1 and Qb1 obtained in the above step. The valve opening degree of the control valve 16 is V01.
HC per unit time by controlling so that
It is possible to control the desorption amount M1.
In addition, this S20 is S21-
The subroutine up to S23 has a function as an exhaust flow rate ratio setting means, and the subroutines at S20 to S23 have a function as an exhaust flow rate ratio control means.

In this way, by controlling the timing and the amount of desorption of HC from the adsorbent 15 in accordance with the degree of deterioration of the exhaust gas purification catalyst 19b, it is possible to maintain good exhaust gas, especially HC purification performance. it can. Next, a second embodiment will be described based on FIGS. 6 and 7. As shown in FIG. 6, the oxygen sensor 21a of the first embodiment is eliminated, and the oxygen sensor 21b is replaced with an exhaust gas temperature sensor 20b. Other configurations are the same as those of the first embodiment. Therefore, the same reference numerals are given and the description thereof is omitted. That is, exhaust temperature sensors 20a and 20b are provided at the upstream inlet portion and the downstream outlet portion of the main three-way catalyst device 19b, and the temperature of the exhaust gas that flows into the main three-way catalyst device 19b and flows out from the catalyst device 19b. To detect.

Next, according to the flow chart shown in FIG.
The HC desorption starting temperature T1, the HC desorption amount M1 and the desorption required time t1 based on the degree of deterioration of the catalyst according to the second embodiment of the present invention.
A routine for determining is explained. First, in S1A, the exhaust temperature of the exhaust purification catalyst is detected by the exhaust temperature sensors 20a and 20b provided upstream and downstream of the exhaust purification catalyst. Then, in the detected value, the exhaust temperature T1 of the catalyst upstream when the exhaust temperature of the catalyst downstream becomes higher than the exhaust temperature of the catalyst upstream is set as the HC desorption start temperature. still,
Here, as the catalyst deteriorates, the exhaust temperature T upstream of the catalyst increases.
Since 1 gradually changes to a high temperature, T1 represents the degree of deterioration at the same time.

Next, in S2, as in the first embodiment, the HC desorption amount M1 is calculated based on the HC desorption start temperature T1.
And the desorption required time t1 are set respectively. In this way, when the degree of deterioration is detected from the detection values of the exhaust gas temperature sensors 20a and 20b, it is possible to suppress an increase in product cost with a cheaper configuration.

[0032]

As described above, according to the present invention,
The desorption start catalyst temperature and the desorption amount of the HC adsorbed by the adsorbent are set according to the deterioration degree of the exhaust gas purification catalyst obtained by the deterioration degree detection means, and when the desorption start catalyst temperature of the HC is reached. The exhaust gas flow ratio control means opens the bypass passage to allow the exhaust gas to flow in to desorb the HC adsorbed by the adsorbent, and at the same time, to obtain the set HC desorption amount according to the operating state of the engine. Since it is configured to control the flow rate ratio, it is possible to maintain excellent exhaust gas, particularly HC purification performance.

Further, when the deterioration degree detecting means is a means for detecting the deterioration degree of the exhaust purification catalyst based on the ratio of the fluctuation cycle of the air-fuel ratio detection value at the upstream inlet portion and the downstream outlet portion of the exhaust purification catalyst. In addition, since the exhaust purification performance is directly detected, the degree of deterioration can be detected with high accuracy, and the degree of deterioration can be accurately detected regardless of the operating state. You can

Further, when the deterioration degree detecting means is a means for detecting the deterioration degree of the exhaust gas purifying catalyst based on the exhaust gas temperatures at the upstream inlet portion and the downstream outlet portion of the exhaust gas purifying catalyst, a more inexpensive construction is provided. This makes it possible to suppress an increase in product cost.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of the present invention.

FIG. 2 is a system diagram showing the overall configuration of the present invention.

FIG. 3 shows the HC desorption starting temperature T1 and the HC desorption amount M of the present invention.
1 is a flow chart showing a routine for determining 1 and desorption required time t1.

FIG. 4 is a flowchart showing a routine of HC adsorption / desorption processing of the present invention.

FIG. 5 is a flowchart showing a routine for determining a control valve opening degree of an exhaust passage.

FIG. 6 is a system diagram showing the overall configuration of another embodiment of the present invention.

FIG. 7 is a HC desorption starting temperature T1 according to another embodiment of the present invention.
5 is a flowchart showing a routine for determining the amount of desorption of HC M1 and the time required for desorption t1.

FIG. 8 is an explanatory diagram for explaining a relationship between an exhaust temperature and a conversion rate of a catalyst for explaining a conventional example.

[Explanation of symbols]

 11 engine 13 exhaust passage 13a main passage 14 bypass passage 15 adsorbent 16 on-off valve 17 control unit 19a pre-three-way catalyst 19b main three-way catalyst 20a, b exhaust temperature sensor 21a, b oxygen sensor 22 exhaust temperature sensor

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location F02D 41/14 310 K 8011-3G 45/00 314 R 7536-3G

Claims (4)

[Claims] 1. An exhaust gas purification catalyst is provided in an exhaust gas passage of an engine, and a part of an exhaust gas passage upstream of the exhaust gas purification catalyst is connected in parallel with a main passage and unburned HC in the exhaust gas. And an exhaust flow rate ratio control means for controlling an exhaust flow rate ratio between the main passage and the bypass passage, the bypass passage having an adsorbent having a function of adsorbing at a low temperature and desorbing at a high temperature. In an exhaust gas purification apparatus for an internal combustion engine, the deterioration degree detection means for detecting the deterioration degree of the exhaust gas purification catalyst, the operating state detection means for detecting the operating state of the engine, and the exhaust temperature detection for detecting the temperature state of the exhaust gas. Means, and exhaust flow rate ratio setting means for setting the exhaust flow rate ratio according to the operating state of the engine based on conditions including the degree of deterioration and exhaust temperature, the exhaust flow rate ratio set by the exhaust flow rate ratio setting means The above-mentioned elimination as Exhaust purifying apparatus for an internal combustion engine is characterized in that so as to control the flow ratio controller. 2. The exhaust gas flow rate ratio setting means, according to the deterioration degree of the exhaust gas purification catalyst obtained by the deterioration degree detecting means, the desorption start catalyst temperature of the HC adsorbed by the adsorbent per unit time. The HC desorption amount is set, and the exhaust flow rate ratio is set based on the unit desorption amount and the time for maintaining the set exhaust flow rate ratio is obtained.
The exhaust gas purification device for an internal combustion engine according to claim 1, wherein the exhaust gas flow ratio is controlled to be maintained at the set value for a predetermined time at a temperature equal to or higher than the desorption start catalyst temperature. 3. The deterioration degree detecting means is means for detecting the deterioration degree of the exhaust gas purification catalyst based on the ratio of the fluctuation cycle of the air-fuel ratio detection values at the upstream inlet portion and the downstream outlet portion of the exhaust gas purification catalyst. An exhaust emission control device for an internal combustion engine according to claim 1. 4. The internal combustion engine according to claim 1, wherein the deterioration degree detecting means is a means for detecting a deterioration degree of the exhaust gas purification catalyst based on exhaust gas temperatures at an upstream inlet portion and a downstream outlet portion of the exhaust gas purification catalyst. Exhaust purification device.