JP3379267B2 - Exhaust gas purification device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust emission control device for an engine of an automobile or the like.

[0002]

2. Description of the Related Art A catalyst device carrying a noble metal (platinum, rhodium, etc.) or another metal has been conventionally used for purification of exhaust gas from an automobile. The catalytic converter purifies exhaust gas by causing harmful components in exhaust gas (HC, CO, NO _X) oxide, or reduced.

Of these, the purification of HC by a catalyst is
Exhaust gas temperature has a strong effect and generally requires a temperature of 350 to 400 ° C or higher. Therefore, immediately after the engine is started, the exhaust gas temperature is low and the catalyst has an activation temperature (normally 350 to
Since the temperature does not reach 400 ° C or higher), the purification of HC by the catalytic device is hardly performed. In addition to this, there is a problem that a large amount of HC is released to the atmosphere when the temperature of exhaust gas is low because the amount of HC emitted is very large when the engine is cold.

In order to solve the above problems, a catalyst device is installed in the exhaust system of the engine, and HC discharged during cold engine (hereinafter referred to as cold HC) is adsorbed on the upstream side or the downstream side thereof. H containing the adsorbent
Purification devices equipped with a C trapper have been proposed (JP-A-4-17710, JP-A-2-135126, JP-A-6-66130, etc.).

In the exhaust gas purifying apparatus according to Japanese Patent Application Laid-Open No. 2-135126, an adsorbing device using a zeolite adsorbent is arranged on the upstream side of the catalytic device, the catalytic device and the adsorbing device are used together, and the exhaust gas is low in temperature. At this time, the cold HC is adsorbed by the adsorbent, and when the exhaust gas has a high temperature, the HC desorbed from the adsorbent and the HC discharged from the engine are purified by the catalyst device.

Further, in the exhaust gas purifying apparatus according to Japanese Unexamined Patent Publication No. 4-17710, an HC trapper containing an adsorbent is arranged in a bypass flow passage in parallel with the main flow passage, and the HC trapper is provided downstream of the catalyst device. A flow path switching valve that switches between the bypass flow path including the bypass flow path and the main flow path is provided. Then, immediately after the engine is started, for a predetermined time,
The flow passage switching valve is operated to allow the exhaust gas to flow to the bypass flow passage side, during which cold HC is adsorbed by the HC trapper.

On the other hand, at a high temperature when cold HC is desorbed from the adsorbent, the flow path switching valve is operated so that exhaust gas flows through the main flow path, and at this time, the downstream side of the HC trapper and the intake pipe of the engine are connected to each other. The negative pressure of the intake pipe of the engine is applied to the HC desorption reflux pipe connecting the two, and the desorbed HC is sucked into the intake pipe and burned again in the engine.

Further, in the exhaust gas purifying apparatus according to Japanese Patent Laid-Open No. 6-66130, a bypass passage having an adsorbing device and a main passage having no adsorbing device are provided on the upstream side of the catalyst device, and the adsorbing device is further provided. An air-fuel ratio sensor is provided in the exhaust passage on the upstream side and on the upstream side of the catalyst device downstream of the adsorption device. When the downstream air-fuel ratio (A / F) is smaller than the upstream air-fuel ratio by a predetermined value or more, it is determined that the adsorption device is abnormal.

[0009]

However, the exhaust gas purifying device disclosed in JP-A-2-135126 or JP-A-6-66130 in which an adsorption device is arranged upstream of the catalyst device has the following problems. There is. This is because the adsorption device located on the upstream side is likely to reach a high temperature, and the following problems occur in the thermal characteristics and heat resistance of the adsorption device.

Generally, the adsorbent has a higher gas adsorbing performance at lower temperatures, and desorbs adsorbed HC and the like at higher temperatures. In the above structure, the desorption phenomenon occurs before the activation temperature of the catalyst device, and the HC or the like that has been adsorbed is released to the atmosphere without being purified. Further, when the adsorption device is arranged on the upstream side, there is a problem that activation of the catalytic device on the downstream side is delayed due to its heat capacity.

On the other hand, there is a problem that the exhaust emission control device disclosed in Japanese Patent Laid-Open No. 2-135126 or Japanese Patent Laid-Open No. 4-17710 does not have a function of self-diagnosing the abnormality of the device. Therefore, in the exhaust gas purification device, there is a problem that the operation is continued even if a failure occurs in the adsorption device or the flow path switching valve.

Further, the exhaust gas purifying apparatus disclosed in Japanese Patent Laid-Open No. 6-66130 determines the abnormality of the adsorbing device on the basis of the air-fuel ratio sensors installed on the upstream side and the downstream side of the adsorbing device. However, since the monitoring is performed during the adsorption reaction, that is, when the engine is cold, there is a problem that accurate failure diagnosis cannot be performed until the warm-up state of the air-fuel ratio sensor is completed. The present invention has been made in view of the above conventional problems, and provides an exhaust gas purification device for an engine that can effectively suppress the emission of harmful components in exhaust gas and can accurately determine a device failure. It is the one we are trying to provide.

[0013]

According to a first aspect of the present invention, there is provided a catalyst device arranged upstream of an exhaust passage of an engine for purifying exhaust gas, and an adsorption device arranged downstream of the catalyst device for adsorbing harmful gas components in exhaust gas. A device, an openable and closable reflux means for connecting a downstream side of the adsorption device to an upstream side of the catalyst device, and a first direct communication of the downstream side of the catalyst device to the exhaust port side without passing through the adsorption device. A flow path, a second flow path that connects the downstream side of the catalyst device to the exhaust port side through the adsorption device, and causes the exhaust gas to flow through the second flow path when the temperature of the exhaust gas is below a predetermined value. An exhaust gas purifying apparatus for an engine, comprising: a switching means for circulating the exhaust gas in the first flow path and opening the recirculation means when the temperature of the exhaust gas exceeds a predetermined value. Exhaust gas upstream of the adsorption device An exhaust gas sensor for detecting a gas component or the like in the exhaust gas that fluctuates due to the operation of the adsorption device is provided in each of the passages, and the two exhaust gases are received immediately after the recirculation means is opened upon receiving the output signal of the exhaust gas sensor. A time measuring means for measuring a time te until the outputs of the gas sensors coincide with each other, and a failure judging means for judging a device failure when the measurement time te is out of a predetermined range are provided. Located in the engine exhaust purification system.

The first point that is most noticeable in the first invention is that the adsorbing device is provided on the downstream side of the catalyst device, and the first flow path with the adsorbing device and the second flow path without the adsorbing device are provided. Is switched by the temperature of the exhaust gas, and when the exhaust gas is further circulated in the first flow path, the recirculation means is operated (opened) at the same time. The second point that is most noticeable is that an exhaust gas sensor that detects gas components in exhaust gas that fluctuates due to the operation of the adsorption device is provided on the recirculation means and the upstream side of the adsorption device. is there.

The gases in the exhaust gas that fluctuate due to the operation of the adsorption device include HC, O ₂ , air-fuel ratio and the like, and the gas sensors include HC sensor, oxygen sensor, air-fuel ratio sensor and the like. And the third point that is most noteworthy is
The time measuring means for measuring the time te until the outputs of the two gas sensors coincide with each other, and the failure determining means for determining that the device is in failure when the time te is out of a predetermined range are provided. . The procedure by which the failure determination means determines a device failure from the time te will be described later in the next section.

On the other hand, the second aspect of the present invention is a catalyst device arranged upstream of the exhaust passage of the engine for purifying exhaust gas, and an adsorption device arranged downstream of the catalyst device for adsorbing harmful gas components in the exhaust gas. And an openable / closable reflux means for connecting the downstream side of the adsorption device to the upstream side of the catalyst device, and a first flow for directly communicating the downstream side of the catalyst device with the exhaust port side without passing through the adsorption device. A passage, a second flow passage that connects the downstream side of the catalyst device to the exhaust port side through the adsorption device, and causes the exhaust gas to flow through the second flow passage when the temperature of the exhaust gas is a predetermined value or less, An exhaust emission control device for an engine, comprising: a switching means for circulating the exhaust gas in the first flow path and opening the recirculation means when the temperature of the exhaust gas exceeds a predetermined value. Exhaust on the upstream side of the device The a road, exhaust gas sensor for detecting gas components in the exhaust gas varies by the operation of the suction device is provided respectively, the output signal of the exhaust gas sensor, after open the recirculation means, the Sucking
Correlation calculating means for calculating the degree of correlation between the outputs of the two exhaust gas sensors within the time period during which the harmful gas component is desorbed from the adsorbing means, and the device for the case where the degree of the correlation does not reach a certain level. An exhaust emission control device is provided with a failure determination means for determining a failure.

What is most noticeable in the second invention is that
In addition to the most remarkable first and second points in the first aspect of the invention, the correlation calculating means and the failure determining means are provided. That is, the exhaust emission control device receives the output signal of the exhaust gas sensor and calculates the degree of correlation between the outputs of the two exhaust gas sensors within a predetermined time after opening the recirculation means, and the correlation calculation means. There is provided a failure determination means for determining that the device is in failure when the degree of the above does not reach a certain level. The index for calculating the degree of correlation includes a correlation ratio and a correlation coefficient.

[0018]

[Operation and effect] In the exhaust emission control device of the first and second inventions,
When the catalyst device does not operate at low temperature, exhaust gas is
After the harmful gas is adsorbed by flowing through the flow path and the catalytic device is operated, the harmful gas desorbed from the adsorbing device is returned to the upstream of the catalytic device through the recirculation means to return to the catalytic device together with the harmful component in the exhaust gas. Purify by.

In the exhaust gas purifying apparatus of the first and second inventions, since the adsorbing device is located on the upstream side of the catalytic device, it does not hinder the heating of the catalytic device, and the temperature rise of the adsorbing device itself is relatively high. Therefore, the performance of the adsorption device can be effectively exhibited. Therefore, the harmful gas can be effectively purified as long as the exhaust emission control device is operating normally.

In the exhaust gas purifying apparatus of the first invention, there are the first gas sensor arranged in the recirculation means and the second gas sensor arranged in the exhaust passage, and the first gas sensor is arranged in the first passage after the operation of the recirculation means via the time measuring means. The time width te until the outputs of the gas sensor and the second gas sensor become the same is measured. The reason for measuring the time te is as described below.

When the device is operating normally, the gas component desorbed from the adsorber is added to the exhaust gas in the flow path of the recirculation means. Therefore, during desorption of the adsorber, the first gas sensor The output becomes larger than the output of the second gas sensor (see FIG. 5). When the desorption of the adsorbed gas in the adsorption device is completed, the outputs of the first and second exhaust gas sensors match (see FIG. 6). Therefore, when the device is operating normally, the time te measured by the time measuring means falls within a predetermined value range corresponding to the operating condition of the engine.

Therefore, the failure determination means is provided with the time t.
It is possible to determine whether or not e is within a predetermined range, and by this, it is possible to accurately determine that there is some failure such as a malfunction of the suction device or an abnormality of the switching means. Therefore, the exhaust emission control device does not operate for a long period of time with a failure. As described above, according to the first aspect of the present invention, it is possible to provide an exhaust emission control device that can effectively suppress the emission of harmful components in exhaust gas in a normal state and can accurately determine a device failure.

On the other hand, the exhaust emission control device of the second invention is provided with a correlation calculation means and a failure determination means. As described above, when the device is operating normally, the output of the first exhaust gas sensor becomes larger than that of the second exhaust gas sensor during desorption of the adsorption device, and the first exhaust gas sensor and the second exhaust gas sensor There is a strong correlation between the outputs of the gas sensors (see Figure 5).

On the other hand, when a failure occurs in the adsorbing device, the recirculation means, etc., the correlation between the output of the first exhaust gas sensor and the output of the second exhaust gas is greatly lost. For example, when the recirculation means fails and falls into the normally closed or normally open state, the correlation between the outputs of both exhaust gas sensors is large when the catalyst device operates and enters the desorption process of the adsorption device. Decrease (see FIG. 13).

Therefore, the exhaust emission control device can determine the failure of the device based on the degree of correlation calculated by the correlation calculation means. As described above, according to the second aspect of the present invention, it is possible to provide an exhaust emission control device that can effectively suppress the emission of harmful components in exhaust gas in a normal state and can accurately determine a device failure.

[0026]

【Example】

Example 1 An exhaust emission control device according to an example of the present invention will be described with reference to FIGS. In this example, as shown in FIG. 1, a catalyst device 11 arranged upstream of the exhaust passage 30 of the engine 51 for purifying exhaust gas, and a harmful gas component in the exhaust gas arranged downstream of the catalyst device 11 Adsorption device 12 for adsorption
And an openable / closable recirculation unit 15 that connects the downstream side of the adsorption device 12 to the upstream side of the catalyst device 11, and the first side that directly connects the downstream side of the catalyst device 11 to the exhaust port side without passing through the adsorption device 12. A flow path 31 and a second flow path 32 that connects the downstream side of the catalyst device 11 to the exhaust port side via the adsorption device 12,
When the temperature of the exhaust gas is equal to or lower than a predetermined value, the exhaust gas is circulated in the second flow path 32, and when the temperature of the exhaust gas is higher than the predetermined value, the exhaust gas is circulated and recirculated in the first flow path 31. It is the exhaust gas purification device 1 of the engine 51 having switching means for opening the means 15.

Oxygen concentration sensors 21 and 22 for detecting O ₂ which is a gas component in the exhaust gas which fluctuates due to the operation of the adsorption device 12 are provided in the recirculation means 15 and the exhaust passage upstream of the adsorption device 12, respectively. ing. Further, the time measuring means 41 which receives the output signals of the oxygen concentration sensors 21 and 22 and measures the time te from immediately after the opening of the reflux means 15 until the outputs of the oxygen concentration sensors 21 and 22 coincide, It has a failure determination means 42 for determining that the apparatus is out of order when it is out of a predetermined range.

A supplementary explanation will be given below for each of them. As shown in FIG. 1, in the exhaust passage 30 of the engine 51, the catalyst device 11 is arranged immediately after the exhaust manifold 52. Further, a large diameter portion 300 is provided in the exhaust passage 30 downstream of the catalyst device 11, and a second flow passage 32 and a first flow passage 31 that accommodate the adsorption device 12 are formed therein.

The adsorption device 12 is made of a ceramic such as stainless steel or cordierite, and has a semi-cylindrical shape matching the shape of the large diameter portion 300. As shown in FIG. 2, a large number of parallel through holes 121 are provided, and a zeolite-based adsorbent is supported on the adsorbent-supporting layer 120 at the rear part.
On the other hand, no adsorbent is loaded on the adsorbent-free layer 129 located on the front side. The adsorbing device 12 may have an elliptical shape or a rectangular shape according to the shape of the large diameter portion 300.

Then, as shown in FIG. 1, the adsorption device 12
Immediately after the rear end, a first opening / closing means 13 which constitutes a switching means is arranged. The catalyst device 11 and the adsorption device 1
The distance from 2 is such that the time when the catalyst device 11 is heated by the exhaust gas to reach the activation temperature and the time when the adsorbent carried by the adsorption device 22 is heated and loses the adsorption function are substantially equal to each other. Is set to.

The adsorption device 12 is separated and held between the first flow path 31 and the first flow path 31 by a partition wall 123. As shown in FIG. 2, the partition wall 123 is provided with an opening 124. A rectifying plate 125 is provided on the upstream side of the adsorbing device 12 to make the flow velocity distribution of the exhaust gas flowing through the adsorbing device 12 uniform and to enhance the adsorbing efficiency.
The partition wall 123 and the current plate 125 may have an integrated structure as shown in FIG. 2 or may be separated.

Then, as shown in FIG.
A recirculation flow path 35 branches off from the rear part of the recirculation flow path 35. It has, and communicates with the exhaust manifold 52.

A first oxygen concentration sensor 21 is installed upstream of the reed valve 26 in the return flow passage 35.
Further, an operation member 14 for operating the first opening / closing means 13 is provided on the pedestal 140 at the rear part of the adsorption device 12, and the first opening / closing means 13 includes the shaft 141 and the crank 1.
It is connected to the movable piece 145 of the operating member 14 via 42, the pivot and the arm 144.

The operating member 14 is installed away from the adsorption device 12 by the pedestal 140, the heat of the exhaust gas is not directly radiated, the heat quantity transmitted through the shaft 141 and the pedestal 140 is small, and the operating member 14 is cooled by the outside air. Since it is easy to be damaged, it is difficult for obstacles to occur. The operating member 14 communicates with the surge tank 53 upstream of the engine 51 via the intake pipes 361 and 362 to supply a negative pressure for operating the operating member 14. The first electromagnetic valve 27 is arranged at the boundary between the intake pipes 361 and 362.

The directional valve 25 of the return flow passage 35 is a valve which allows only the flow of exhaust gas from the downstream side of the adsorption device 12 toward the upstream side of the catalyst device 21. On the other hand, the second opening / closing means 2
4 operates by a diaphragm or the like that responds to negative pressure.
The second opening / closing means 24 supplies the negative pressure to the surge tank 53 via the intake pipes 371, 372.
A second electromagnetic valve 28 is provided between the intake pipes 371 and 372 and communicates with the intake pipe 362.

The outputs of the oxygen concentration sensors 21 and 22 rapidly increase in the latch region (small air-fuel ratio) as shown in FIG. 3, corresponding to the air-fuel ratio of the exhaust gas. Further, a temperature sensor 43 for detecting the temperature of exhaust gas is installed,
Electronic control unit (ECU) 40 for operating the switching means
The output signal is sent to. The time measuring means 41 and the failure determining means 42 are formed in an electronic control unit (ECU) 40 having a built-in microcomputer.
Receives signals from the oxygen concentration sensors 21 and 22 and the temperature sensor 43, and operates the first and second solenoid valves 27 and 28 to perform the first and second
The second opening / closing means 13 and 24 are controlled.

Next, the operation procedure of the exhaust purification system 1 will be described with reference to the system configuration diagram of FIG. 1 and the flowchart shown in FIG. In step 601, when the engine 51 is started (ignition on), E
In step 602, the CU 40 opens the first electromagnetic valve 27 so that the intake pipes 361 and 362 communicate with each other. As a result, the negative pressure of the surge tank 53 acts on the operating member 14, pulls the shaft 141, and the first opening / closing means 13 comes to the position shown by the broken line (closing operation).

Immediately after starting the engine 51, the temperature of the exhaust gas is low and the engine 51 discharges the exhaust gas containing a large amount of cold HC. While the temperature of the exhaust gas is low, the catalyst has not reached the activation temperature, and the cold HC flows through the second flow path 32 without being purified by the catalyst device 11. The temperature of the exhaust gas is measured by the temperature sensor 43.
Being monitored by. The exhaust gas flow at this low temperature is the adsorbent (zeolite) unsupported layer 1 of the adsorption device 12.
29 (FIG. 2) flows to the adsorbent support layer 120 and is adsorbed by the adsorbent. Then, the exhaust gas from which the cold HC has been removed after passing through the adsorption device 12 is released to the atmosphere through a muffler (not shown).

Since the exhaust gas passing through the adsorption device 12 is rectified by the rectifying plate 125 as described above, it has a uniform flow velocity distribution and passes through the adsorption device 12. At this time, the ECU 40, as shown in step 603,
The solenoid valve 27 counts the time t after the operation. Then, as shown in step 604, when the engine 51 warms up and a predetermined time ta in which the temperature of the exhaust gas exceeds the operating temperature of the adsorbent has elapsed (t> ta), step 605
At, the ECU 40 closes the first electromagnetic valve 27.

As a result, the supply of negative pressure to the operating member 14 is cut off, and the shaft 141 is pushed out by the urging force of the spring 149. As a result, in step 605, the first opening / closing means 23 restores the state shown by the solid line in FIG. 1, opens the first flow path 31, and closes the second flow path 32. Then, the time elapsed until this step is t (> ta)
As described above, the catalyst device 11 has reached the activation temperature, and the HC in the exhaust gas is purified by the catalyst device 11,
Exhaust gas containing almost no HC is released into the atmosphere through the first flow path 31. In this way, the exhaust emission control device 1 of this example can significantly reduce the emission of HC.

After the first solenoid valve 27 is closed in step 605, the second solenoid valve 28 is opened as shown in step 606. Then, the intake pipe 371 communicates with the surge tank 53, negative pressure is supplied to the second opening / closing means 24,
The second opening / closing means 24 opens. And step 608
As shown in, the timer starts counting again. On the other hand, on the side surface of the adsorption device 12, the exhaust gas that has already become hot flows through the first flow passage 31, and the hot exhaust gas passes through the opening 124 of the partition wall 123 shown in FIG. It is in contact with 120.

Therefore, the heat of the exhaust gas is absorbed by the adsorbent support layer 1
20 is transmitted very well, the temperature of the adsorbent rises, and the desorption of HC is promoted. At this time, since the second opening / closing means 24 has already been opened as described above, the exhaust pulsation generated in the exhaust manifold 52 is passed through the recirculation flow path 35 to the one-way valve 2
5 is intermittently opened.

As a result, the HC desorbed from the adsorbent of the adsorbent-supporting layer 120 of the adsorber 12 flows into the exhaust manifold 52 through the reflux flow passage 35. Then, as shown in FIG. 3, the outputs of the oxygen concentration sensors 21 and 22 are significantly larger when the air-fuel ratio is small (rich) than when the air-fuel ratio is large (lean). Therefore, the output (Vex) of the oxygen concentration sensor 21 installed in the reflux flow path 35 is the same as the adsorption device 12
Of the oxygen concentration sensor 22 installed on the upstream side of the
Compared to n), the amount of desorbed HC increases and the air-fuel ratio decreases, so the value is always large.

When swinging from the rich side to the lean side, the output Vex changes more slowly than the output Vin, and the output difference between both oxygen concentration sensors becomes remarkable (FIG. 5).
5 to 8, the solid line indicates the Vin, the broken line indicates the Vex, the mountain side indicates the rich time, and the valley side indicates the lean time (see FIG. 3).

The desorbed HC is purified by the catalyst device 11 together with the HC discharged from the engine 51.
Output of both oxygen concentration sensors 21 and 22 (Vex, Vin)
Is compared with Vex> Vi as shown in step 609.
It continues until it is not n. Then, as shown in FIG. 6, after the desorption time of HC has passed, the concentrations of the exhaust gas upstream of the adsorption device 12 and the exhaust gas of the recirculation passage 35 become substantially the same.

When the outputs of both oxygen concentration sensors 21 and 22 become the same, the process proceeds to step 610, the timer count is stopped, and the integrated value t of the timer until this time is measured time te.
Set as. Then, in the next step 611, it is inspected whether or not the measurement time te is within a predetermined range. Generally, the time to completely desorb the adsorption device 12 is
A fixed time zone (tb-α) centered on the central value tb
Since it can be considered that it is between (tb + α), if the measurement time te is within the time zone, the failure determination means 42 determines that the device is normal, and proceeds to step 613.

Then, in step 613, the second electromagnetic valve 28 is closed to close the return flow passage 35 (the second opening / closing means 24
Close). On the other hand, in step 611, when the measurement time te is not within the time zone (tb-α) to (tb + α), the failure determination means 42 determines that the device is in failure, and sets the failure flag in step 612. ， Send a failure signal to the required place. Then, it progresses to step 613 and closes the return flow path 35.

The reasons why the measurement time te does not fall within the predetermined time zone are the malfunctions of the solenoid valves 27, 28 and the opening / closing means 13, 24 constituting the switching means, the deterioration of the adsorption device 12, the reflux flow path. There are 35 clogging. When the exhaust gas purification device 1 functions normally, as shown in FIG. 7, desorption of HC is completed and Vex and Vin
The time te at which is coincident with is within a predetermined range (tb ± α).

However, when the exhaust gas purifying device fails,
When the amount of adsorbed HC is zero, both oxygen concentration sensors 21, 22
The output difference will not appear. In addition, the adsorption device 12
Fig. 8 shows that the adsorption amount in
As shown in, the output difference of the oxygen concentration sensor disappears before (tb-α). Further, if the desorption time of the adsorption device 12 becomes long due to clogging of the reflux flow path 35,
The measurement time te becomes longer than (tb + α). As described above, according to this example, it is possible to provide the exhaust emission control device 1 that can effectively suppress the emission of harmful components in the exhaust gas and accurately determine the device failure.

Example 2 This example is similar to Example 1 except that the oxygen concentration sensors 21 and 22 are used.
It is another embodiment using an air-fuel ratio sensor instead of. The output of the air-fuel ratio sensor is generally as shown in FIG.
The output value with respect to the air-fuel ratio changes gently, and the output does not suddenly change in a narrow range unlike the oxygen concentration sensors 21 and 22 shown in FIG. Therefore, the width of the air-fuel ratio that can be detected by the air-fuel ratio sensor becomes wider, and even when the air-fuel ratio change area changes greatly due to sudden acceleration, etc., it can be identified and more accurate fault diagnosis can be performed. Becomes Others are the same as those in the first embodiment.

Example 3 This example is similar to Example 1 except that the oxygen concentration sensors 21 and 22 are used.
It is another embodiment using an HC concentration sensor that detects the concentration of HC instead of. The output of the HC concentration sensor changes according to the HC concentration in the exhaust gas, as shown in FIG. Therefore, without being affected by changes in the air-fuel ratio,
Since the concentration of HC is directly monitored, Example 1 and Example 2
It is possible to diagnose the failure of the device with higher accuracy. Others are the same as those in the first embodiment.

Embodiment 4 This embodiment is an exhaust gas purification apparatus 1 according to an embodiment of the second invention, and as shown in FIG. 11, in the embodiment 1, the correlation calculation is performed in place of the time measuring means 41 and the failure judging means 42. Means 45
And a failure determination means 46 are provided. ECU 40
The outputs of the first oxygen concentration sensor 21 and the second oxygen concentration sensor 22 are input to the
The correlation coefficient C of both oxygen concentration sensors 21 and 22 after 5 open circuits is calculated. Further, the failure determination means 46 determines whether the device is normal or failed depending on whether or not the correlation coefficient C calculated by the correlation calculation means 45 within a certain time exceeds a predetermined value.

Correlation calculating means 45 and failure judging means 4
An operation procedure of the exhaust emission control device 1 of the present example including No. 6 will be described with reference to FIGS. 11 and 12, focusing on differences from the first embodiment. In the flowchart of FIG. 12, the reflux means 1
The steps up to step 606 for activating 5 are the same as those in the first embodiment (FIG. 4), and the description thereof will be omitted. Next step 6
At 08, the counting of the timer is started and the recirculation means 15
Start measuring time after operation.

Next, at step 620, the correlation calculating means 45 causes the first oxygen concentration sensor 2 after the timer is activated.
The correlation coefficient C between 1 and the outputs Vex and Vin of the second oxygen concentration sensor 22 is calculated. The correlation coefficient C is simply expressed as the ratio of the average value of the products (Vex × Vin) of the outputs of the two sensors 21 and 22 and the average value of the squared Vin ² of the output of the second oxygen concentration sensor 22 by the following equation. Can be calculated as follows. C = (Vin × Vex) (Vin × Vin) ⁻¹

The calculation of the correlation coefficient C as described above is continued until the desorption of the adsorption device 12 reaches a certain time ts as shown in step 621. When the time ts is reached in step 621, step 62
Go to 2. In step 622, it is determined whether or not the correlation coefficient C up to the time ts exceeds a predetermined value, for example, 0.5. If not, it is determined to be a failure, a failure flag is set in a step 612, and a recirculation means in a step 613. Closed 15
The control routine ends.

If the correlation coefficient C exceeds the predetermined value in step 622, there is a predetermined correlation between the outputs of the first oxygen concentration sensor 21 and the second oxygen concentration sensor 22, and the device is normal. Then, the circulation means 15 is closed in step 613 without setting the failure flag, and the control routine is completed.

Next, in the case of failure of the exhaust purification system 1,
The correlation coefficient C is significantly reduced, that is, the correlation coefficient C
It is shown based on the measured value that the decrease of the is closely related to the device failure. FIG. 13 shows an example of the correlation coefficient C in the normal state and two failure modes of the reed valve 26. The correlation coefficient C in the normal state is 0.7, which is significantly larger than the predetermined value 0.5, but when the reed valve 26 has a normally open failure (breakage of the valve portion, etc.), C decreases to 0.16. Also, the reed valve 26 has a normally closed failure (valve sticking, etc.)
At that time, C drops to 0.41.

That is, when the valve portion of the reed valve 26 is broken and the recirculation unit 15 is opened, the flow of the exhaust gas in the direction opposite to the normal recirculation of exhaust gas, that is, from the exhaust manifold 52 of the engine to the adsorption device. The flow of exhaust gas downstream of 12 becomes dominant. Therefore, the output Vex of the first oxygen concentration sensor is separated from the oxygen concentration downstream of the catalyst device 11 and Vex> Vin, but the correlation coefficient C with Vin is greatly reduced (C = 0.16). .

Further, for example, when the second opening / closing means 24 of the reed valve 26 falls into the fully closed state, the flow of the exhaust gas of the recirculation means 15 is interrupted, and the first oxygen concentration sensor 21 diffuses from the adsorption device 12. In order to detect the oxygen concentration of the discharged exhaust gas, the output Vex is the output Vi of the second oxygen concentration sensor 22.
The correlation coefficient C with n decreases (C = 0.41). As described above, by monitoring the correlation coefficient C, it is possible to accurately determine the device failure. Others are the same as those in the first embodiment.

As described above, according to this example, it is possible to obtain the exhaust emission control device 1 which can effectively suppress the emission of harmful components in the exhaust gas under normal conditions and can accurately judge the device failure. You can In this example, the predetermined time ts in the flowchart 621 is the time until the adsorption device 12 is completely desorbed, but this time ts may be shorter. For example, the above-mentioned ts may be set to several tens of seconds, the correlation coefficient in step 622 may be checked at intervals of several tens of seconds, and if the condition is satisfied, the failure flag may be immediately set and the failure information may be transmitted (displayed).

[Brief description of drawings]

FIG. 1 is a system configuration diagram of an exhaust emission control device according to a first embodiment.

FIG. 2 is an exploded perspective view of the adsorption device according to the first embodiment.

FIG. 3 is a characteristic diagram of the oxygen concentration sensor according to the first embodiment.

FIG. 4 is a flowchart showing an operation procedure of the exhaust emission control device of the first embodiment.

FIG. 5 shows the outputs (Vex, Vi) of the two oxygen concentration sensors before the completion of desorption of the adsorption device of the exhaust gas purification device of the first embodiment.
The characteristic diagram which shows the change of n).

FIG. 6 shows the outputs (Vex, Vi) of the two oxygen concentration sensors after the desorption of the adsorption device of the exhaust gas purification device of the first embodiment is completed.
The characteristic diagram which shows the change of n).

FIG. 7 is a characteristic diagram showing changes in outputs of two oxygen concentration sensors when the exhaust emission control device of the first embodiment is normal.

FIG. 8 is a characteristic diagram showing changes in outputs of two oxygen concentration sensors when the adsorption device of the exhaust gas purification device of the first embodiment is abnormal.

FIG. 9 is a characteristic diagram of the air-fuel ratio sensor of the exhaust emission control device according to the second embodiment.

FIG. 10 is a characteristic diagram of the HC sensor of the exhaust purification system of the third embodiment.

FIG. 11 is a system configuration diagram of an exhaust emission control device according to a fourth embodiment.

FIG. 12 is a flowchart showing the operation procedure of the fourth embodiment.

FIG. 13 is a graph showing the value of the correlation coefficient C of the exhaust gas sensor output when the recirculation unit is normal and when it is abnormal in Example 4.

[Explanation of symbols]

1 ... Exhaust gas purification device, 11 ... Catalyst device, 12 ... Adsorption device, 15 ... Reflux means, 21, 22 ... Oxygen concentration sensor, 31 ... the first flow path, 32 ... second flow path,

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI F02D 41/14 310 F02D 41/14 310F 310J 310K (56) Reference JP-A-6-257424 (JP, A) JP-A-6-257424 -66131 (JP, A) JP-A-6-93829 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) F01N 3/08-3/24 F02D 41/14

Claims (6)

(57) [Claims] 1. A catalyst device disposed upstream of an exhaust passage of an engine for purifying exhaust gas, an adsorption device disposed downstream of the catalyst device for adsorbing harmful gas components in exhaust gas, and the adsorption device. An openable / closable reflux means connecting the downstream side of the catalyst device to the upstream side of the catalyst device; a first flow path that directly connects the downstream side of the catalyst device to the exhaust port side without passing through the adsorption device; A second flow path communicating the downstream side of the exhaust gas with the exhaust port side through the adsorption device, and when the temperature of the exhaust gas is below a predetermined value, the exhaust gas is circulated through the second flow path so that the temperature of the exhaust gas is If the specified value is exceeded, the above first
An exhaust emission control device for an engine, comprising: a switching device that allows exhaust gas to flow through a flow path and opens the recirculation device. In the exhaust gas purification device for an engine, the recirculation device and an exhaust passage on an upstream side of the adsorption device operate in the adsorption device. Exhaust gas sensors for detecting the gas components in the exhaust gas that fluctuate due to the exhaust gas sensor are provided respectively, and the time te from when the output of the recirculation means is opened to when the outputs of the two exhaust gas sensors match each other is received. For measuring time, and the measuring time t
An exhaust emission control device for an engine, comprising: failure determination means for determining that the device has failed when e is out of a predetermined range. 2. A catalyst device disposed upstream of an exhaust passage of an engine for purifying exhaust gas, an adsorption device disposed downstream of the catalyst device for adsorbing harmful gas components in exhaust gas, and the adsorption device. An openable / closable reflux means connecting the downstream side of the catalyst device to the upstream side of the catalyst device; a first flow path that directly connects the downstream side of the catalyst device to the exhaust port side without passing through the adsorption device; A second flow path communicating the downstream side of the exhaust gas with the exhaust port side through the adsorption device, and when the temperature of the exhaust gas is below a predetermined value, the exhaust gas is circulated through the second flow path so that the temperature of the exhaust gas is If the specified value is exceeded, the above first
An exhaust emission control device for an engine, comprising: a switching device that allows exhaust gas to flow through a flow path and opens the recirculation device. In the exhaust gas purification device for an engine, the recirculation device and an exhaust passage on an upstream side of the adsorption device operate in the adsorption device. An exhaust gas sensor for detecting a gas component in the exhaust gas that fluctuates due to the exhaust gas sensor is provided, and the output signal of the exhaust gas sensor is input to desorb the harmful gas component from the adsorption means after the recirculation means is opened.
Correlation calculating means for calculating the degree of correlation between the outputs of the two exhaust gas sensor in a time that is, the determining failure determining means that the device failure when the degree of the correlation does not reach a certain level An exhaust emission control device characterized by being provided with. 3. The exhaust emission control device according to claim 2, wherein the correlation calculating means calculates the degree of the correlation by a correlation coefficient. 4. The exhaust gas purifying apparatus for an engine as claimed in claim 1, wherein the exhaust gas sensor is an oxygen sensor. 5. The exhaust gas purifying apparatus for an engine according to claim 1, claim 2, or claim 3, wherein the exhaust gas sensor is an air-fuel ratio sensor. 6. The exhaust gas purifying apparatus for an engine according to claim 1, claim 2, or claim 3, wherein the exhaust gas sensor is an HC sensor.