JPH0693843A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To secure the HC purifying performance by accurately grasping the degree of deterioration of an adsorbent which adsorbs HC in exhaust of an internal combustion engine. CONSTITUTION:An HC adsorbent 5 is provided in a bypass passage 6 connected with a main passage 4 in parallel in the upstream of an exhaust emission purifying catalyst 3 in an exhaust passage 2. At the time when water temperature detected by a water temperature sensor 11 is above a specified value, idle operation in which an idle switch 12 is turned ON is done, and temperature of the adsorbent detected by a temperature sensor 10 is low and less than the specified value, air-fuel ratio is concentrated and clamped and the by-pass passage 6 is opened by a control valve 7 to make the adsorbent 5 adsorb HC. The degree of deterioration of the adsorbent 5 is estimated based on the variation of output of an air-fuel ratio sensor 8 at this time, alarm is given in accordance with the degree of deterioration, and the degree of opening of the control valve 7 is controlled to perform fail-safe.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine, and more particularly to an improvement of an apparatus having a function of temporarily adsorbing HC in exhaust gas.

[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 an exhaust emission control device for vehicles,
As disclosed in Japanese Patent Application Laid-Open No. 63-68713, there has been proposed one in which an adsorbent for adsorbing HC is interposed in the exhaust passage on the upstream side of the exhaust purification catalyst. This one utilizes the fact that the adsorbent adsorbs HC at low temperatures and desorbs the adsorbed HC at high temperatures, so that the adsorbent is provided in a part of the exhaust passage upstream of the exhaust purification catalyst. The inserted bypass passages are connected in parallel to selectively open and close the main passage and the bypass passage, and the bypass passage is opened at a low temperature before activation of the exhaust gas purification catalyst to cause HC to be adsorbent. After adsorbing, and once closing the bypass passage, 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. It has become. As the adsorbent, for example, a monolith carrier coated with zeolite has been proposed because zeolite has excellent adsorbability.

[0004]

By the way, in the exhaust gas purification apparatus provided with such an adsorbent, even if the adsorbent is deteriorated and its adsorbing ability is lowered, it is not adsorbed by the adsorbent at a low temperature and even an exhaust gas purifying catalyst is used. Although the amount of HC that is not purified increases, the conventional device does not have a self-diagnosis function for detecting the degree of deterioration of the adsorbent, and thus has a problem that it is not possible to cope with such a decrease in HC purification performance. Was there.

The present invention has been made in view of the above conventional problems, and has an internal combustion engine capable of suppressing deterioration of HC purification performance by providing a self-diagnosis function for detecting the degree of deterioration of the adsorbent. It is an object of the present invention to provide an exhaust emission control device.

[0006]

Therefore, the present invention is based on FIG.
As shown in FIG. 3, an exhaust gas purification catalyst is provided in the exhaust gas passage of the engine, and a part of the exhaust gas passage upstream of the exhaust gas purification catalyst is connected in parallel to the main passage and the main passage to adsorb HC in the exhaust gas at low temperature. And a means for controlling the opening ratio between the main passage and the bypass passage, and a means for detecting the engine temperature. The bypass passage is opened at a low engine temperature so that HC in the exhaust gas is adsorbed by the adsorbent, and then the bypass passage is closed. After reaching the temperature at which the exhaust purification catalyst is activated, the bypass passage is opened again. In an exhaust gas purification device for an internal combustion engine, which is opened to desorb HC adsorbed on an adsorbent and which is purified by an exhaust gas purification catalyst, means for detecting the temperature of the adsorbent, and exhaust gas downstream of the adsorbent From the predetermined component of the air-fuel ratio While providing a means for detecting, after the operation of desorbing HC from the adsorbent, when the engine temperature is equal to or higher than a predetermined value and the adsorbent temperature is equal to or lower than a predetermined value, a substantially steady operating condition is satisfied, Deteriorates the degree of deterioration of the adsorbent based on the speed of change in the enrichment direction of the air-fuel ratio detected by the air-fuel ratio detection means at that time while the air-fuel ratio is concentrated and fixed and the bypass passage is opened. And a judging means.

[0007]

After the HC is sufficiently desorbed from the adsorbent, the adsorbent is kept at a temperature equal to or lower than the predetermined temperature under a stable operating condition where the engine temperature is equal to or higher than a predetermined value, that is, the air-fuel ratio is hard to change. When the adsorption condition is satisfied by, the air-fuel ratio is concentrated and fixed, and the bypass passage is opened to allow the exhaust gas to flow through the adsorbent to adsorb the HC in the exhaust gas.

As a result, the exhaust gas whose HC concentration has increased due to the enrichment of the air-fuel ratio flows into the bypass passage and circulates through the adsorbent. However, when the degree of deterioration of the adsorbent has not progressed and the adsorption capacity is high. Since the ratio of adsorbed HC in the exhaust gas is high, the concentration rate of the air-fuel ratio detected by the air-fuel ratio detection means is low, but when the adsorbent deteriorates and the adsorption capacity decreases, the air-fuel ratio decreases. The concentration of the air-fuel ratio detected by the detection means is accelerated.

Therefore, the degree of deterioration of the adsorbent is determined based on the enrichment rate of the air-fuel ratio.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 2 showing the configuration of an embodiment of the present invention, an exhaust gas purification catalyst (three-way catalyst) is provided in an exhaust passage 2 of an internal combustion engine 1.
3, a part of the exhaust passage 2 upstream of the exhaust purification catalyst 3 is composed of a main passage 4 and a bypass passage 6 connected in parallel with the main passage 4 and having an adsorbent 5 interposed therein. Has been done. At the upstream branch point between the main passage 4 and the bypass passage 6, an electromagnetic control valve 7 is interposed as a means for controlling the opening ratio of the main passage 4 and the bypass passage 6.
An air-fuel ratio sensor 8 as an air-fuel ratio detecting means for linearly detecting the air-fuel ratio is provided downstream of the adsorbent 5 in the bypass passage 6.
Is installed.

Further, in the exhaust passage 2 upstream of the control valve 7, there is an air-fuel ratio sensor 9 for ON / OFF detection of the air-fuel ratio which is richer or leaner than the stoichiometric air-fuel ratio for normal air-fuel ratio feedback control. It is installed. Further, a temperature sensor 10 is attached to the adsorbent 5 as a means for detecting the temperature of the adsorbent 5. In addition, a water temperature sensor 11 is provided as a means for detecting the engine temperature, and an idle switch 12 is provided for detecting the idle operation of the engine when it is turned on at a predetermined opening of the throttle valve or less. 13 is input to the control unit 13, the control unit 13 controls various engines based on the signals detected by these sensors, and also performs self-diagnosis of the adsorbent 5 according to the present invention. Fail-safe control is performed based on the self-diagnosis result.

The self-diagnosis of the deterioration of the adsorbent 2 by the control unit 13 will be described with reference to the flow chart shown in FIG. The self-diagnosis routine corresponds to deterioration determining means. In step (denoted as S in the figure. The same applies hereinafter) At 1, the cooling water temperature T _W detected by the water temperature sensor 11
Is determined to be equal to or greater than the predetermined value T.

When T _W ≧ T ₀ , the routine proceeds to step 2, where it is judged whether or not the operation of desorbing HC from the adsorbent 5 is completed. This may be performed by storing the history of the control valve 7 closing the bypass passage 6 after warming up the bypass passage 6 and making a determination based on the history. If it is determined that the desorption operation has been completed, the process proceeds to step 3 and the temperature sensor 10
It is determined whether the temperature T _C of the adsorbent 5 detected by is less than the predetermined value T ₁ . The predetermined value T ₁ is set to a temperature sufficiently lower than the temperature at which HC is desorbed from the adsorbent 5, and the adsorbent 5 can have a sufficient adsorption capacity. It should be noted that the adsorbent temperature is naturally high immediately after the completion of HC desorption, but since the bypass passage 2 is closed thereafter, the temperature decreases. Therefore, instead of mounting the temperature sensor 10 that directly detects the adsorbent temperature, the accuracy is slightly inferior, but after the desorption operation is completed, the control valve 7 is closed for a predetermined time. The cost may be reduced by indirectly detecting by making a determination.

If it is determined that the adsorbent temperature T _C is less than the predetermined value T ₁ , the process proceeds to step 4 and the idle switch
Judgment is made based on the ON / OFF state of 12 as to whether or not it is in the idle operation state. If it is determined that the engine is in the idle operation state, the process proceeds to step 5 and the feedback control of the air-fuel ratio from the stoichiometric air-fuel ratio is performed to control the air-fuel ratio to be thicker than the stoichiometric air-fuel ratio through the fuel supply amount control (not shown). Switch.

In step 6, the control valve 7 is driven to open the bypass passage 6 and the exhaust gas is passed through the adsorbent 5.
In step 7, the change in the output state of the air-fuel ratio sensor 8 on the downstream side of the adsorbent 5 is read for a predetermined time and the output pattern is detected. In step 8, a response time constant (corresponding to the enrichment speed of the air-fuel ratio) is calculated from the output pattern.

In step 9, the deterioration degree of the adsorbent 5 is estimated from the response time constant calculated in step 8. That is, since the upstream air-fuel ratio sensor 9 is feedback-controlled to the theoretical air-fuel ratio before opening the bypass passage 6,
The air-fuel ratio detected by the downstream air-fuel ratio sensor 8 is maintained at a substantially stoichiometric air-fuel ratio. When the bypass passage 6 is opened from this state, the HC in the exhaust is adsorbed by the adsorbent 5, but when the degree of deterioration of the adsorbent 5 advances and the HC adsorbing ability is low, the HC in the exhaust passing through the adsorbent 5 is adsorbed. The concentration is increased in a short time, the air-fuel ratio concentration speed detected by the air-fuel ratio sensor 8 is accelerated, and the response time constant is small. On the other hand, when the adsorbent 5 has not deteriorated, the adsorbent 5 has a high HC adsorbing capacity, so the HC concentration in the exhaust gas passing through the adsorbent 5 increases slowly, and the air-fuel ratio sensor 8 detects The detected air-fuel ratio enrichment speed is slow and the response time constant is large (see Fig. 4). As a result, the degree of deterioration of the adsorbent 5 can be estimated according to the magnitude of the calculated response time constant.

In step 10, the deterioration degree is compared with the reference value K, and if it is determined that the reference value is exceeded, the process proceeds to step 11 to issue an alarm, and if not, without issuing an alarm. Proceeding to step 12, the judgment value is stored in the memory. It should be noted that the determination of deterioration in the idle operation state is most suitable for determining the adsorption performance of the adsorbent because the temperature of the exhaust gas discharged from the engine is low at the time of idling. This is because the desorption from the material becomes active), the exhaust flow rate is stable, and the exhaust air-fuel ratio is also stable, so that a highly accurate determination condition can be created.

On the other hand, the adsorbent 5 thus obtained
Fail-safe is executed according to the deterioration degree of. That is,
As the adsorbent 5 deteriorates, the desorption start temperature of the adsorbed HC decreases and the desorption rate decreases. Therefore, when adsorbing the same amount of exhaust gas as when desorbing the adsorbent 5, desorption is performed. Since a large amount of HC is desorbed and sent to the exhaust gas purification catalyst 3, the exhaust gas cannot be completely purified by the catalyst 3 and the HC purification performance is deteriorated.

In consideration of the above points, the following fail-safe is executed in this embodiment. The fail safe will be described with reference to FIG. In step 21, the deterioration degree of the adsorbent 5 calculated as described above and stored in the memory is read. In step 22, the target temperature rising rate at which the adsorbent 5 is heated during desorption is calculated according to the degree of deterioration.

In step 23, while monitoring the current temperature of the adsorbent 5, the opening of the control valve 7 is controlled so as to approach the target temperature rising rate, and the exhaust flow rate to the bypass passage 6 is controlled. In step 24, the end of desorption from the adsorbent 5 is determined, the opening degree of the control valve 7 is controlled until the desorption is completed, and then this routine is ended after the completion of the desorption.

In this way, by appropriately controlling the temperature rising rate of the adsorbent 5 even if the deterioration progresses,
The desorption amount of HC can be controlled appropriately, and thus good HC purification performance can be maintained. However, if the deterioration progresses to a certain extent or more, it is considered that such a fail-safe will not work well, so it is preferable to replace the adsorbent or regenerate it by an appropriate method. The reference value K for determining the degree of deterioration that gives an alarm in step 10 of FIG. 3 may be set in consideration of this point.

[0022]

As described above, according to the present invention, the air-fuel ratio is enriched under the operating conditions where the air-fuel ratio is stable and adsorbed on the adsorbent, and the air-fuel ratio enrichment speed on the downstream side of the adsorbent is increased. Since it is configured to judge the deterioration state of the adsorbent, it is possible to accurately grasp the degree of deterioration of the adsorbent _, and to maintain good HC purification performance by facilitating appropriate fail-safe, replacement _{, and} regeneration processing. is there.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a configuration of an embodiment of the present invention.

FIG. 3 is a flowchart showing a routine for self-diagnosing the degree of deterioration of the adsorbent according to the embodiment.

FIG. 4 is a diagram showing a change in an output state of an air-fuel ratio sensor due to deterioration of an adsorbent in the same embodiment.

FIG. 5 is a flowchart showing a fail-safe routine according to the degree of deterioration of the adsorbent according to the above embodiment.

[Explanation of symbols]

 1 Internal Combustion Engine 2 Exhaust Passage 3 Exhaust Purification Catalyst 4 Main Passage 5 Adsorbent 6 Bypass Passage 7 Control Valve 8 Air-Fuel Ratio Sensor 10 Temperature Sensor 11 Water Temperature Sensor 12 Idle Switch 13 Control Unit

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location F01N 3/20 R F02D 45/00 368 G 7536-3G

Claims (1)

[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 to a main passage and the main passage to keep HC in the exhaust gas at a low temperature. A bypass passage which is provided with an adsorbent having a function of adsorbing and desorbing at a high temperature, and means for controlling the opening ratio between the main passage and the bypass passage, and means for detecting the engine temperature, And opening the bypass passage at a low engine temperature to adsorb HC in exhaust gas to the adsorbent and then closing the bypass passage, and again after reaching the temperature at which the exhaust purification catalyst is activated In an exhaust gas purification apparatus for an internal combustion engine, in which the adsorbent is desorbed to remove HC adsorbed by the adsorbent, and a means for detecting the temperature of the adsorbent and exhaust gas on the downstream side of the adsorbent are provided. From the predetermined component in the air-fuel ratio While providing a means for detecting, after the operation of desorbing HC from the adsorbent, when the engine temperature is equal to or higher than a predetermined value and the adsorbent temperature is equal to or lower than a predetermined value, a substantially steady operating condition is satisfied, Deteriorates the degree of deterioration of the adsorbent based on the rate of change in the air-fuel ratio enrichment direction detected by the air-fuel ratio detection means at the same time as the air-fuel ratio is concentrated and fixed and the bypass passage is opened. An exhaust emission control device for an internal combustion engine, comprising: a determination unit.