JP3277698B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in an exhaust gas purifying apparatus for an internal combustion engine in which an adsorbent for adsorbing unburned HC is interposed in an exhaust system.

[0002]

2. Description of the Related Art Catalytic devices such as three-way catalysts are frequently used as exhaust gas purifying devices for internal combustion engines. However, when the exhaust gas temperature is low immediately after starting at a low temperature, the catalyst is not activated. Purification can hardly be expected. Therefore, the unburned HC generated while the catalyst is not activated is temporarily adsorbed by the adsorbent, and after the catalyst is activated, the adsorbed unburned HC is desorbed. An exhaust gas purifying apparatus that performs the above-described operation is proposed in, for example, Japanese Patent Application Laid-Open No. 63-68713.

[0003] In the device described in this publication, a bypass passage is arranged in parallel with a main exhaust passage provided with a catalyst device on the upstream side of the catalyst device, and HC is provided in the bypass passage.
An adsorbent is interposed, and a switching valve is provided at an upstream branch portion of both passages so as to control the flow of exhaust gas into the bypass passage.

[0004] In general, HC adsorbents are those that chemically adsorb HC, and there are temperatures at which HC is easily adsorbed and temperatures at which it is desorbed. Current adsorbents have a relatively low HC desorption temperature, which results in the desorption of HC before the catalyst reaches the activation temperature. Therefore, when the exhaust gas temperature rises and reaches the desorption temperature, especially during the period below the catalyst activation temperature, the exhaust flow path is switched by the switching valve so that the exhaust gas does not pass through the HC adsorbent. Then, when the catalyst reaches the activation temperature, the switching valve is again switched to the bypass passage side to start desorption of HC.

[0005]

In an exhaust gas purifying apparatus in which unburned HC is adsorbed by the adsorbent as described above, it has conventionally been impossible to detect the amount of adsorbed unburned HC actually adsorbed. It was possible. For this reason, for example, it is difficult to perform an optimal treatment at the time of desorption.

[0006] For example, when the exhaust gas temperature of the internal combustion engine rises and HC is desorbed from the adsorbent as described above, the air-fuel ratio becomes rich for the catalyst, and HC cannot be sufficiently purified. Therefore, at the time of HC desorption, 2
It is considered that secondary air is introduced. However, since the secondary air introduction amount and the introduction period are set regardless of the amount of HC, whether the secondary air is excessively large or small is determined. In either case, either NOx or HC tends to deteriorate.

[0007] When the amount of adsorbed HC is large, it is preferable to perform desorption under operating conditions in which the amount of exhaust gas is large, since it is possible to reduce the influence on the catalyst. Neither can the separation operation condition be selected according to the amount of adsorption.

[0008]

As shown in FIG. 1, an exhaust gas purifying apparatus for an internal combustion engine according to the present invention includes an adsorbent 2 interposed in an exhaust passage 1 for adsorbing unburned HC, and an adsorbent 2 for adsorbing unburned HC. Means 3 for detecting the exhaust gas temperature at the outlet side of the adsorbent 2, means 4 for detecting the length of time during which the exhaust gas temperature at the outlet side of the adsorbent 2 is maintained at a temperature corresponding to the exhaust dew point, Means 5 for detecting the amount of heat per unit time given to
Means 6 for calculating the amount of water evaporated from the adsorbent 2 based on the exhaust dew point period and the amount of heat, and means 7 for calculating the amount of unburned HC adsorbed on the adsorbent 2 based on the amount of water.
And, it is characterized by having.

In particular, in the invention of claim 2, the amount of heat per unit time given to the adsorbent 2 is determined as the difference between the amount of heat flowing into the adsorbent 2 and the amount of heat released from the adsorbent 2. I have.

[0010] In the invention according to claim 3, there is further provided a main exhaust passage provided with a catalyst device, a bypass passage provided in parallel with the main exhaust passage on the upstream side of the catalyst device and provided with the adsorbent. Based on a switching valve for controlling the flow of exhaust gas into the bypass passage and the calculated unburned HC amount,
Means for setting parameters at the time of HC desorption.

[0011] In particular, in the invention of claim 4, a secondary air supply device for supplying secondary air upstream of the catalyst device at the time of HC desorption is provided. The time and the exhaust gas amount of the internal combustion engine are set based on the calculated unburned HC amount.

According to the fifth aspect of the present invention, the degree of opening of the switching valve is set based on the unburned HC amount as a parameter at the time of HC desorption.

[0013]

When the exhaust gas temperature is low such as immediately after the start of the internal combustion engine, unburned HC is adsorbed by the adsorbent 2 when the exhaust gas passes through the adsorbent 2. This type of adsorbent 2 is considered to adsorb HC by chemical bonding, and the degree of adsorption varies depending on the pore diameter of the adsorbent 2 and the HC molecular diameter. Therefore, in the adsorbent 2 that mainly adsorbs HC, water (H
₂ O) a strong bonding force between the adsorbent 2 from differences in molecular size can not be obtained, they quickly away the addition of heat. Further, as shown in the characteristic diagram of FIG. 3, the adsorbed HC also has a lower adsorbing ability as the temperature becomes higher, and eventually is completely desorbed. In particular, when the warming-up of the engine advances and the exhaust gas temperature at the outlet side of the adsorbent 2 exceeds the temperature corresponding to the exhaust dew point (the temperature at which the moisture in the exhaust gas becomes liquid), the temperature of the adsorbent 2 suddenly increases. As a result, the adsorbed HC suddenly desorbs. This temperature change is caused by the evaporation of the moisture adsorbed by the adsorbent 2. In other words, while moisture remains in the adsorbent 2, the exhaust heat is used for evaporating the moisture. Therefore, until the moisture completely evaporates, the temperature of the outlet side of the adsorbent 2 corresponds to the exhaust dew point. Is maintained. Then, when the moisture completely disappears, the temperature of the adsorbent 2 rapidly rises, and the adsorbent 2 turns to the HC desorbing action.

Here, the moisture adsorbed on the adsorbent 2 is, like the unburned HC, given from the exhaust gas passing through the adsorbent 2 at a low temperature, as shown in FIG. Unburned H adsorbed on the adsorbent 2 with the passage of exhaust gas
The amount of C and the amount of water are in a proportional relationship with each other (the slope varies depending on the type of the adsorbent 2). Therefore, if the amount of water adsorbed is known, the amount of adsorbed unburned HC can be known.

As described above, the heat while the temperature on the outlet side of the adsorbent 2 is maintained at a temperature corresponding to the exhaust dew point is used for evaporating the adsorbed moisture. Therefore, in the present invention, during this time, the amount of water is obtained from the amount of heat given to the adsorbent 2, and the amount of HC adsorption is calculated.

The amount of heat given to the adsorbent 2 is equal to the amount of heat flowing in as exhaust heat unless heat is radiated to the outside.
In practice, some heat is dissipated. Therefore, claim 2
Then, the heat quantity actually given to the adsorbent 2 is obtained as the difference between the heat quantity flowing into the adsorbent 2 and the heat release quantity flowing out of the adsorbent 2.

According to the third aspect of the present invention, the desorption from the adsorbent 2 is controlled by the switching valve. However, based on the unburned HC adsorption amount calculated as described above, the time of desorption of HC is determined. Various parameters are set.

For example, in claim 4, as the parameters for desorbing HC, the amount and time of introduction of the secondary air are optimally set in accordance with the amount of HC adsorption. Furthermore, the amount of exhaust gas of the internal combustion engine when desorption is to be performed is set, and desorption is performed under operating conditions that result in this amount of exhaust gas.

Further, the opening degree of the switching valve is controlled according to the calculated HC amount.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below in detail with reference to the drawings.

FIG. 2 shows an embodiment of an exhaust gas purification apparatus according to the present invention. For example, an exhaust manifold 12 of an internal combustion engine 11 composed of an electronically controlled fuel injection type gasoline engine is provided.
A main exhaust passage 13 is connected, and a catalyst device 14 utilizing a three-way catalyst is interposed in the middle of the passage. Further, on the upstream side of the catalyst device 14, the main exhaust passage 1
A bypass passage 15 is provided in parallel with 3, and an adsorbent device 16 is provided in the middle of the passage. The adsorbent device 16 has an adsorbent 17 for adsorbing unburned HC inserted in a casing. As the adsorbent 17, for example, γ-alumina activated carbon obtained by coating granular activated carbon with porous alumina is used. Can be An inlet side temperature sensor 18 for detecting the adsorbent inlet side temperature Tf and an outlet side temperature sensor 19 for detecting the adsorbent outlet side temperature Tr are provided on the inlet side and the outlet side of the adsorbent device 16, respectively. I have.

A switching valve 20 for controlling the flow of exhaust gas into the bypass passage 15 is provided at the upstream branch portion of the bypass passage 15. The switching valve 20 is, for example, a butterfly valve type, and is configured to be electromagnetically opened and closed.

A secondary air supply device 21 is provided upstream of the catalyst device 14 in the main exhaust passage 13. This 2
The secondary air supply device 21 includes, for example, an air pump 22 and 2
And an electromagnetic valve 24 for opening and closing the secondary air passage 23. It should be noted that secondary air may be introduced via a reed valve using exhaust pulsation without using the air pump 22.

The secondary air supply device 21 is controlled by a control unit 25 together with the switching valve 20. The control unit 25 uses a so-called microcomputer system, and controls these switching valves 20 and the like according to a program described later. 2
Reference numeral 6 denotes a water temperature sensor for detecting a cooling water temperature Tw of the internal combustion engine 11, reference numeral 27 denotes an air flow meter for detecting an intake air amount Qa of the internal combustion engine 11, and reference numeral 28 denotes a rotational speed sensor for detecting a rotational speed N of the internal combustion engine 11. Are input to the control unit 25 together with the detection signals of the two temperature sensors 18 and 19 described above. The control unit 25 also controls the fuel injection amount and the like from a fuel injection valve (not shown) based on these detection signals.

FIGS. 5 and 6 are flowcharts showing the flow of the HC adsorption / desorption control executed in the control unit 25. The operation of the exhaust gas purifying apparatus will be described below based on the flowchart.

The process shown in this flowchart is started simultaneously with the start (key-on) of the internal combustion engine, and is repeatedly executed. First, at step 1, the engine cooling water temperature Tw is detected. Then, in step 2, it is determined whether the water temperature Tw read first, that is, the starting water temperature Tw1 is lower than 40 ° C. If the temperature is equal to or higher than 40 ° C., it is determined that the warm-up is to be restarted, and the processing after step 3 is not performed. If the starting water temperature Tw1 is less than 40 ° C., it is considered that the engine is in a cold start and the catalyst is not activated.
In order to adsorb C, the switching valve 20 is switched to the bypass passage 15 in step 3. Thereby, the internal combustion engine 11
The exhaust gas discharged from is passed through the adsorbent 17, where the unburned HC is adsorbed. In addition, the moisture contained in the exhaust gas together with the unburned HC is also adsorbed by the adsorbent 17.

At the same time as the start of the adsorption, steps 4 to 7
In, the calorie given to the adsorbent 17 is calculated. In step 4, the amount of exhaust gas Qe flowing into the adsorbent 17 is calculated from the basic fuel injection amount Tp and the engine speed N by Q
Calculate as e = Tp × N. Note that the basic fuel injection amount T
p is obtained, for example, from the intake air amount Qa and the engine speed N. In step 5, the inlet-side temperature Tf of the adsorbent 17
And the outlet-side temperature Tr are detected. And step 6
Then, the heat amount Hi flowing into the adsorbent 17 is calculated. The inflow heat amount Hi is based on the adsorbent inlet side temperature Tf and the exhaust gas amount Qe.
Is sequentially integrated. That is, Hi
= ΣTf · Qe. In step 7, the heat release amount Ho flowing out of the adsorbent 17 is calculated. This heat release amount Ho is obtained from the difference between the outside air temperature and the temperature of the adsorbent 17, but in this embodiment, the outside air temperature is substituted by the adsorbent outlet side temperature Tr1 at the time of starting, and the adsorbent temperature is used. The average of the exhaust temperatures before and after the adsorbent 17 (that is, the inlet-side temperature Tf and the outlet-side temperature Tr) is used as a substitute. Therefore, Ho = Σ ｛(Tf + Tr) / 2
−Tr1｝ × k1 However, k1 is an appropriate constant.

Next, at step 8, it is determined whether or not the outlet side temperature Tr of the adsorbent 17 has exceeded a temperature corresponding to the exhaust dew point. In this embodiment, the temperature corresponding to the exhaust dew point is set to 80 ° C. That is, in step 8, it is repeatedly determined whether or not the outlet side temperature Tr has exceeded 80 ° C. If the temperature is below 80 ° C., the process returns to step 4, and if it exceeds 80 ° C., the process proceeds to step 9. ing.

Therefore, until the outlet side temperature Tr exceeds 80 ° C., the exhaust gas is introduced into the adsorbent 17, the adsorption of the unburned HC is continued, and the calorific value calculation in steps 4 to 7 is repeatedly executed. You. Here, the above-mentioned inflow heat amount Hi and heat release amount Ho are repeatedly integrated, as described above, and thus have values including a time element in advance. That is, the sum of the inflow heat amount and the heat release amount while the temperature is maintained at the temperature corresponding to the exhaust dew point is always shown.

As described above, while moisture remains in the adsorbent 17, the exhaust heat is consumed for evaporating the moisture, so that the temperature of the adsorbent 17 is maintained at the exhaust dew point. Therefore, the outlet side temperature Tr is 80 ° C. corresponding to the exhaust dew point.
Maintained near. And when the water completely evaporates,
The temperature of the adsorbent 17 rises sharply, and unburned HC is desorbed.

When it is determined in step 8 that the temperature of the adsorbent 17 has reached the desorption temperature, the process proceeds to step 9 and the switching valve 20 is switched to the main exhaust passage 13 side. As a result, the exhaust gas does not flow to the adsorbent 17.

Next, at step 10, the amount M of unburned HC adsorbed on the adsorbent 17 is calculated. This amount of adsorption M is
The amount of heat Hi and the amount of heat released Ho into the adsorbent 17 described above.
, And is calculated as M = (Hi−Ho) × k2. However, k2 is an appropriate constant. In other words, as described above, the adsorbent 1 is not used until the outlet side temperature Tr exceeds 80 ° C.
The amount of heat given to 7 is considered to have been used for evaporating the moisture, and the value of the amount of heat indicates the amount of moisture. The amount of moisture is proportional to the amount of unburned HC adsorbed M, and thus the amount of adsorbed HC is indicated.

In step 11, the parameters for desorption are set based on the adsorption amount M estimated as described above. Specifically, the secondary air introduction amount Am by the secondary air introduction device 21, the introduction time ta thereof, and the exhaust gas amount Qn of the internal combustion engine 11 at the time of desorption are determined in accordance with maps of predetermined characteristics. . FIG. 7 illustrates characteristics of a map for determining the secondary air introduction amount Am. The larger the adsorption amount M is, the larger the secondary air introduction amount Am is given. FIG. 8 shows a map for determining the introduction period ta of the secondary air. The larger the adsorption amount M is, the longer the introduction period ta is. In addition, as described later, the introduction period ta is also a period during which desorption from the adsorbent 17 is performed. FIG. 9 shows the characteristics of a map for determining the amount of exhaust gas Qn at the time of desorption. Desorption is performed under operating conditions in which the larger the amount of adsorption M, the larger the amount of exhaust gas Qn. . That is, the adsorption amount M is large so that the unburned HC component in the exhaust gas flowing into the catalyst device 14 does not become excessively large, in other words, the air-fuel ratio does not become excessively rich for the catalyst device 14. The higher the speed, the higher the load, the more the desorption is performed.

After setting various parameters in this way, it is determined in step 12 whether or not the engine cooling water temperature Tw has reached 70 ° C. or higher. This temperature is a temperature at which the catalyst can be considered to be activated. If the temperature is 70 ° C. or more, even if the unburned HC is desorbed from the adsorbent 17, the treatment can be performed by the catalyst device 14.

If the engine cooling water temperature Tw is 70 ° C. or higher, the routine proceeds to step 13, where the actual engine operating conditions, specifically, the exhaust gas amount Qe is set to the previously set exhaust gas amount Qn.
Is determined. Then, when this condition is satisfied, the routine proceeds to step 14, where the switching valve 20 is switched to the bypass passage 15 side to allow the exhaust gas to flow to the adsorbent 17. At the same time, in step 15, secondary air is introduced upstream of the catalyst device 14 by the secondary air introduction device 21. The introduction amount at this time is adjusted to the introduction amount Am set previously. Then, it is determined in step 16 whether or not the elapsed time t from the start of the desorption and the introduction of the secondary air has reached the previously set introduction period ta, and when t ≧ ta is satisfied, In Step 17, the introduction of the secondary air is stopped, and in Step 18, the switching valve 20 is switched to the main exhaust passage 13 side.

Thus, a series of control is completed.

As described above, according to the above embodiment, the adsorbent 1
The secondary air can be appropriately supplied in accordance with the amount M of the unburned HC adsorbed to the NOx 7 and NOx or HC can be avoided by avoiding a substantial lean / rich air-fuel ratio on the catalyst device 14 side.
Increase in the amount of wastewater can be prevented. Further, since the desorption is performed on the high-speed and high-load side as the amount of adsorption M increases, even if a relatively large amount of unburned HC desorbs, the change in the composition of the exhaust gas flowing into the catalyst device 14 can be reduced, and There is no performance degradation.

In addition to the parameters shown in the above embodiment, for example, the opening of the switching valve 20 at the time of desorption may be set in accordance with the amount of adsorption M. Specifically, when the amount of adsorption M is large, the ratio of the exhaust gas flowing to the adsorbent 17 is made relatively small, so that rapid desorption can be suppressed.

The estimation of the amount of adsorption M is based on the adsorbent 1
7 can also be used to determine the deterioration. For example, when the adsorption amount M equal to or higher than a certain level is not detected during the cold start under the predetermined condition, it is possible to determine that the adsorbent 17 is deteriorated or abnormal.

[0040]

As is apparent from the above description, according to the exhaust gas purifying apparatus for an internal combustion engine according to the present invention, the amount of unburned HC adsorbed by the adsorbent can be easily estimated, This makes it possible to perform appropriate control at the time of separation, determine deterioration of the adsorbent, and the like.

Further, according to the configuration of the second aspect, an error caused by the amount of heat released from the adsorbent is eliminated, and the accuracy of estimating the amount of adsorption is improved.

According to the third aspect of the invention, when desorbing HC by switching the switching valve, various parameters can be made to correspond to the amount of adsorption.

In particular, according to the structure of the fourth aspect, the engine operating conditions at the time of desorption can be made to correspond to the amount of adsorption, the secondary air can be appropriately supplied, and the desorbed HC can be provided.
Can be reliably treated with a catalyst.

Further, according to the structure of the fifth aspect, by controlling the opening degree of the switching valve, it is possible to more appropriately perform the treatment of the desorbed unburned HC with the catalyst.

[Brief description of the drawings]

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

FIG. 2 is a configuration explanatory view showing a mechanical configuration of an embodiment of the exhaust gas purification apparatus according to the present invention.

FIG. 3 is a characteristic diagram showing the relationship between the temperature of the adsorbent and the adsorption rate.

FIG. 4 is a characteristic diagram showing a relationship between an amount of adsorbed HC and an amount of adsorbed moisture.

FIG. 5 is a flowchart showing the flow of control in this embodiment.

FIG. 6 is a flowchart following FIG. 5;

FIG. 7 is a characteristic diagram showing a relationship between an adsorption amount and a secondary air introduction amount.

FIG. 8 is a characteristic diagram showing a relationship between an adsorption amount and a secondary air introduction period.

FIG. 9 is a characteristic diagram showing a relationship between an adsorption amount and an engine exhaust gas amount at the time of desorption.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Exhaust passage 2 ... Adsorbent 3 ... Outlet side exhaust gas temperature detecting means 4 ... Exhaust dew point period detecting means 5 ... Heat amount detecting means 6 ... Moisture amount calculating means 7 ... HC amount calculating means

Continuation of the front page (56) References JP-A-6-101452 (JP, A) JP-A-6-93847 (JP, A) JP-A-6-93846 (JP, A) JP-A-6-93840 (JP) , A) (58) Field surveyed (Int.Cl. ⁷ , DB name) F01N 3/08-3/24

Claims (5)

(57) [Claims] 1. An adsorbent interposed in an exhaust passage and adsorbing unburned HC, means for detecting an exhaust gas temperature on the outlet side of the adsorbent, and the exhaust gas temperature on the outlet side of the adsorbent is set to an exhaust dew point. Means for detecting the length of the period maintained at the corresponding temperature, means for detecting the amount of heat per unit time given to the adsorbent, and evaporating from the adsorbent based on the exhaust dew point period and the amount of heat described above. An exhaust gas purifying apparatus for an internal combustion engine, comprising: means for calculating the amount of water; and means for calculating the amount of unburned HC adsorbed on the adsorbent based on the amount of water. 2. The internal combustion engine according to claim 1, wherein the amount of heat per unit time given to the adsorbent is obtained as a difference between the amount of heat flowing into the adsorbent and the amount of heat released from the adsorbent. Exhaust purification equipment. 3. A main exhaust passage provided with a catalyst device, a bypass passage provided in parallel with the main exhaust passage on the upstream side of the catalyst device and provided with the adsorbent, and exhaust gas flowing into the bypass passage. The internal combustion engine according to claim 1 or 2, further comprising: a switching valve for controlling the amount of unburned HC; and means for setting a parameter for desorbing HC based on the calculated amount of unburned HC. Exhaust purification equipment. 4. A secondary air supply device for supplying secondary air upstream of the catalyst device at the time of desorption of HC, wherein a secondary air introduction amount, an introduction time and an exhaust gas amount of the internal combustion engine are used as parameters at the time of HC desorption. The exhaust gas purifying apparatus for an internal combustion engine according to claim 3, wherein is set based on the unburned HC amount. 5. The exhaust gas purifying apparatus for an internal combustion engine according to claim 3, wherein an opening degree of the switching valve is set based on an unburned HC amount as a parameter at the time of HC desorption.