JPH0693830A - Exhaust gas purifying device for engine - Google Patents

Abstract

(57) [Summary] [Purpose] It is necessary to raise the temperature of the adsorbent before the desorption operation in advance so that the temperature of the exhaust gas that reaches the catalyst for exhaust purification immediately after the desorption operation starts decreases. To prevent. An adsorbent that adsorbs HC in exhaust gas is interposed in a bypass passage that bypasses the main exhaust passage. Then, after the adsorbent has adsorbed (S21 to 30), if the desorption is OK (S62), the temperature of the adsorbent 24 is raised prior to the desorption operation of the adsorbent 24 (S71). Then, after that, the outflow control valve 51 is opened, and the exhaust gas flows from the adsorbent 24 to the exhaust gas purification catalyst 22 (S65).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention efficiently purifies unburned gas components desorbed from an unburned gas adsorbent by not lowering the temperature of the exhaust gas supplied to an exhaust gas purification catalyst. The present invention relates to an engine exhaust purification device.

[0002]

2. Description of the Related Art In order to purify engine exhaust gas, a catalyst is often arranged in the exhaust passage of the engine, but the operating temperature or activation temperature of this catalyst is relatively high, for example, 300 ° C. or higher. It is high, and exhaust gas cannot be sufficiently purified below this activation temperature. Therefore, when the engine temperature is low when the exhaust temperature, that is, the temperature of the catalyst is low, in order to sufficiently purify the exhaust gas, an unburned gas adsorbent (hereinafter referred to as an adsorbent) for adsorbing unburned gas that operates at a low temperature is placed upstream of the catalyst. There has been proposed a device provided in an exhaust passage so that the flow of exhaust gas from an engine can be switched according to the exhaust temperature (see Japanese Patent Laid-Open No. 63-68713, etc.).

The above adsorbent can adsorb unburned gas at low temperatures, but its adsorbing ability gradually decreases as the exhaust temperature rises, and the adsorbed gas component begins to be released from around 100 ° C., for example. is doing.

[0004]

In the purification device having the adsorbent and the catalyst for purifying the exhaust gas in the exhaust passage as described above, the unburned gas component in the exhaust gas is efficiently discharged immediately after the cold start. It will be adsorbed by the adsorbent. By the way, in the temperature range from the temperature at which desorption starts from the adsorbent (for example, 100 ° C) to the temperature at which the catalyst starts the reaction (for example, 300 ° C), the unburned unburned gas adsorbed when exhaust gas is passed through the adsorbent. Since the gas is desorbed and the catalyst is inactive, the exhaust gas is allowed to flow directly to the catalyst and not to the adsorbent in the temperature range.

In the temperature range, the amount of unburned gas discharged from the engine is relatively small. Here, when the unburned gas from the adsorbent is started to be purified after the catalyst is activated, the temperature of the adsorbent is lowered because it is cut off from the exhaust, so the exhaust gas temperature of the exhaust passing through the adsorbent is lowered. Will also decrease.

Therefore, the exhaust gas having the lowered temperature flows into the activated catalyst, which lowers the temperature of the catalyst, deactivates the catalyst and makes it impossible to purify unburned gas from the adsorbent. Therefore, there is a fear that the conversion efficiency of the catalyst for purifying the exhaust gas may decrease. The present invention has been made in view of such a conventional problem, and an exhaust gas purification catalyst is provided in an exhaust passage downstream of an exhaust passage in which an adsorbent for adsorbing unburned gas is provided. In the exhaust gas purifying apparatus for an engine, the temperature of the exhaust gas that reaches the catalyst for exhaust gas purification immediately after the desorption operation is started by raising the temperature of the adsorbent material in advance before the desorption operation from the adsorbent material. It is an object of the present invention to provide an exhaust gas purifying apparatus for an engine, which is capable of stably purifying an unburned gas by an exhaust gas purifying catalyst by preventing the deterioration of the exhaust gas.

[0007]

Therefore, the exhaust emission control system for an engine according to the present invention is, as a first technical means,
An unburned gas adsorbent for adsorbing unburned gas in exhaust gas is constructed by including first and second branch passages that branch into an engine exhaust passage and then join again. And disposing an exhaust gas purification catalyst in the exhaust passage downstream of the confluence of the first and second branch passage portions,
An inflow control valve for controlling the inflow of the exhaust gas into the second branch passage portion and an outflow control valve for controlling the outflow of the exhaust gas from the second branch passage portion are provided. When the desorption of the fuel gas is started, the prohibition means for closing the outflow control valve is provided for a predetermined time after switching the inflow control valve so that the exhaust gas flows into the second branch passage portion.

As a second technical means, the opening speed of the outflow control valve is slower than the opening speed of the inflow control valve when starting the desorption of the unburned gas from the unburned gas adsorbent. You may provide the deceleration means to do. Further, as a third technical means, an air-fuel ratio detecting means for detecting an air-fuel ratio of the exhaust gas on the downstream side of the unburned gas adsorbent is provided, and when the rich state is detected by the air-fuel ratio detecting means, a prohibiting means is provided. Alternatively, the deceleration means may be activated.

[0009]

According to the above construction, the unburned gas adsorbent for adsorbing the unburned gas in the exhaust is arranged in the second branch passage portion. When the catalyst is cold, the exhaust gas is circulated through the second branch passage portion and guided to the adsorbent, so that the unburned gas is trapped in the adsorbent when the temperature is low. Then, when the temperature of the catalyst rises and is activated, the unburned gas trapped in the adsorbent is desorbed from the adsorbent.

Here, in the first technical means according to the present invention, when the desorption of the unburned gas from the adsorbent is started, the prohibiting means causes the inflow control valve to exhaust the exhaust gas to the second branch passage portion. The outflow control valve is closed for a predetermined time after switching to inflow. Therefore, when desorption from the adsorbent is started by flowing the exhaust to the adsorbent, first, only the inflow control valve is opened and the exhaust flows into the second branch passage portion. Therefore, when the inflowing exhaust gas and the adsorbent come into contact with each other, the adsorbent receives the heat of the exhaust gas and is warmed up, and the temperature of the adsorbent itself rises.

Then, after a lapse of a predetermined time from the switching of the inflow control valve, the closing of the outflow control valve is released,
The outflow control valve is opened, and the exhaust gas flows from the adsorbent to the exhaust gas purification catalyst. At this time, since the desorption from the adsorbent has started, the unburned gas desorbed from the adsorbent will be purified by the catalyst, but the temperature of the adsorbent itself is rising, and the desorption is therefore Since the temperature of the unburned gas also rises, the catalyst can be kept active without being cooled by the desorbed unburned gas. Thus, the unburned gas desorbed from the adsorbent is sufficiently purified without deteriorating the purifying ability of the exhaust purification catalyst arranged in the exhaust passage on the downstream side of the unburned gas adsorbent, Stable purification performance can be obtained under all operating conditions.

Further, the unburned HC is easily desorbed, the time lag when the closing of the outflow control valve is released can be reduced, and the desorption control can be facilitated. Further, as a second technical means, when a deceleration means for slowing the valve opening speed of the outflow control valve as compared with the valve opening speed of the inflow control valve is provided, the inflow control valve is immediately opened and the outflow control valve is opened. It opens slowly. Therefore, both the inflow control valve and the outflow control valve are opened when exhaust gas is flowed to the adsorbent to start desorption from the adsorbent,
Since the inflow control valve opens immediately and the outflow control valve opens slowly, the exhaust gas that has flowed into the second branch passage portion is not opened.
Is suppressed from flowing out from the branch passage portion of. Therefore,
When the inflowing exhaust gas and the adsorbent come into contact with each other, the adsorbent receives the heat of the exhaust gas and is warmed up, and the temperature of the adsorbent itself rises.

Then, since the outflow control valve gradually opens thereafter, the exhaust gas flows from the adsorbent to the exhaust gas purifying catalyst. At this time, since desorption from the adsorbent has started,
The unburned gas desorbed from the adsorbent will be purified by the catalyst, but the temperature of the adsorbent itself is rising, and the temperature of the unburned gas desorbed is also rising. Is not cooled by desorbed unburned gas and can maintain its activity.

As a third technical means, when air-fuel ratio detecting means for detecting the air-fuel ratio of the exhaust gas on the downstream side of the unburned gas adsorbent is provided, the air-fuel ratio detecting means detects a rich state. When this occurs, the prohibiting means or the speed reducing means operates, and the exhaust gas flowing into the second branch passage portion is discharged to the second branch passage portion.
Does not flow out or is suppressed from flowing out from the branch passage part of.

Here, as the unburned gas trapped in the adsorbent, unburned HC is the main component, and since the HC acts as a reducing agent, when a predetermined amount of unburned HC is desorbed, a predetermined amount of unburned HC is released. The reducing material will be supplied. Then, the air-fuel ratio detecting means for detecting the air-fuel ratio of the exhaust gas on the downstream side of the unburned gas adsorbent detects that the air-fuel ratio is rich.

That is, the desorbed HC causes the air-fuel ratio to change from lean to rich. Here, when the prohibiting means or the speed reducing means operates, the exhaust gas flowing into the second branch passage portion does not flow out from the second branch passage portion.
Since the outflow is suppressed, the desorbed unburned gas does not flow out of the second branch passage portion or the outflow is suppressed. Therefore, the amount of HC supplied to the catalyst is suppressed, and the rich state of the air-fuel ratio is detected only when a predetermined amount of HC is supplied to the catalyst.

Therefore, the supply of HC to the catalyst is judged by detecting that the air-fuel ratio is rich, and in that case, whether the unburned gas is allowed to flow out from the second branch passage portion by the prohibiting means or the speed reducing means. By suppressing the outflow, the inflowing exhaust gas is prevented from being exhausted at once, and the contact with the adsorbent causes the adsorbent to be warmed up by the heat of the exhaust, and the temperature of the adsorbent itself. Rises.

Since the temperature of the unburned gas desorbed from the adsorbent whose temperature has risen also rises, the catalyst can be kept active without being cooled by the desorbed unburned gas.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. 1, which shows a system configuration of a first embodiment according to claim 1 of the present invention, an exhaust passage 13 connected to an exhaust manifold 12 of an engine 11 is provided with an exhaust purification pre-catalyst 21 and a main catalyst 22. Set up. Then, after bifurcating from the exhaust passage on the downstream side of the pre-catalyst 21 (the branch point is 13a), it joins again on the upstream side of the main catalyst 22 (the merge point is 13b). A branch passage portion 15 and a second branch passage portion 16 are provided, and an unburned gas adsorbent (hereinafter simply referred to as an adsorbent) 24 is disposed in the second branch passage portion 16.

At the branch point 13a between the first branch passage portion 15 and the second branch passage portion 16, the exhaust gas is the first branch passage portion 15 only or the second branch passage portion 16 is exhausted. only,
Alternatively, an inflow control valve 18 that switches the flow path so as to selectively flow through both the first branch passage portion 15 and the second branch passage portion 16 is interposed. The inflow control valve 18 is operated by an actuator 19 controlled by a control unit 30 having a microcomputer, which will be described later.

Further, an outflow control valve 51 such as a butterfly valve capable of continuously increasing or decreasing the flow rate of exhaust gas passing through the second branch passage portion 16 is interposed in the second branch passage portion 16. The outflow control valve 51 is also operated by an actuator 52 controlled by a control unit 30 containing a microcomputer described later. Adsorbent 24
Is a monolithic ceramic carrier coated with zeolite. The adsorbent 24 is not limited to the monolith shape, and may be, for example, a foam shape, a pellet shape, a mesh shape, and the adsorbent itself is not limited to the zeolite, and is a substance having an adsorbing performance such as activated carbon. I wish I had it.

Here, the main catalyst 22 for purifying the exhaust gas is an ordinary three-way catalyst which has been conventionally used. For example, a catalyst carrier made of ceramics carrying a noble metal such as platinum, palladium or rhodium is used to chemically exhaust the exhaust gas. Is to be oxidized. Further, a main catalyst outlet temperature sensor 32 for determining whether or not each of the pre-catalyst 21 and the main catalyst 22 is activated is provided in the exhaust passage 13 downstream of the main catalyst 22.

An air flow meter 43 for detecting an intake air flow rate controlled by a throttle valve 42 is provided in an intake passage 41 of the engine 11, and an intake manifold 44 has an electromagnetic type for each cylinder. A fuel injection valve 45 is provided, which is driven by an injection pulse signal from the control unit 30 to open the valve, and a fuel regulated to a predetermined pressure by a pressure regulator fed from a fuel pump (not shown) into the intake manifold 44. Supply by injection.

Further, in the exhaust passage 13 between the confluence 13b and the main catalyst 22, the oxygen concentration of the exhaust gas flowing in the exhaust passage 13 is the exhaust gas when the air-fuel ratio of the intake air-fuel mixture is the theoretical air-fuel ratio. An oxygen sensor 36 is provided as an air-fuel ratio detecting means for detecting ON or OFF as to whether it is on the rich side or the lean side, compared with the oxygen concentration. Further, a crank angle sensor 33 that outputs a unit angle signal for each minute unit crank angle in synchronization with the engine rotation and outputs a reference signal for each stroke crank angle period of each cylinder is provided in a distributor or the like. .

An ignition switch for detecting engine start based on the cranking operation of the engine 11
34 is provided. A water temperature sensor 35 for detecting the engine cooling water temperature Tw is provided in the engine 11. Then, the control unit 30 calculates the fuel injection amount from the fuel injection valve 45 according to the detection signals from the various sensors, and outputs an injection pulse signal having a pulse width corresponding to it, thereby producing an air-fuel ratio. Is controlled and the actuators 19 and 52 are controlled to purify the exhaust gas.

Next, as a first embodiment according to the present invention, the control performed by the control unit 30 will be described with reference to FIG.
Also, description will be made with reference to the flowchart shown in FIG. 3 and the time chart shown in FIG. 7. Step 21 (S21 in the figure
Is written. The same applies hereinafter), the engine on / off signal from the ignition switch 34 is input.

In step 22, it is judged whether or not the ignition signal is input. If the ignition signal is input, it is determined that the engine 11 is rotating and the process proceeds to step 23 and thereafter. If it is determined in step 22 that the ignition signal has not been input, it is determined that the engine 11 is not rotating, and the process directly returns.

In step 23, the engine cooling water temperature Tw detected by the water temperature sensor 35 is input. Step
At 24, it is determined whether the cooling water temperature Tw is equal to or higher than a predetermined temperature Tw ₀ . The cooling water temperature Tw is the predetermined temperature Tw.
If it is determined that the value is not ₀ or more, the process proceeds to step 25.

If it is determined in step 24 that the cooling water temperature Tw is equal to or higher than the predetermined temperature Tw ₀ , the temperature is high even if the unburned gas in the exhaust gas is trapped in the adsorbent 24. The unburned gas desorbed from the adsorbent 24 will increase. Therefore, in this case, the process proceeds to step 27. Step 25
Now, operate the actuator 19 and move the inflow control valve 18
Is switched to a position where the exhaust gas flows only through the second branch passage portion 16.

In step 26, the actuator 52 is operated, the outflow control valve 51 is fully opened, and the exhaust gas introduced by the inflow control valve 18 into only the second branch passage portion 16 is discharged. So that all the
The unburned gas in the exhaust is trapped in the adsorbent 24 (Fig. 7
d, e). Then, after the step is executed, the process returns to step 24 again to judge the cooling water temperature Tw.

In step 27, the exhaust gas temperature T detected by the main catalyst outlet temperature sensor 32 is input. Step
At 28, it is determined whether the exhaust temperature T is equal to or higher than a predetermined value T ₀ . When it is determined that the exhaust temperature T is not equal to or higher than the predetermined value T ₀ , the process proceeds to step 29. In step 29,
Since the exhaust temperature T is not equal to or higher than the predetermined value T ₀ , the catalyst 22 has not reached the catalyst activation temperature and is in the inactive state (see FIG. 7a). On the other hand, since the adsorbent 24 has a high cooling water temperature Tw, it is considered that the amount of unburned gas desorbed from the adsorbent 24 is also increasing. Therefore, the actuator 19 is operated and the inflow control valve 18 exhausts the first branch passage portion.
The switching operation is performed so that only 15 flows (see FIG. 7d).

In step 30, the actuator 52
Is operated to fully close the outflow control valve 51. At this time, the exhaust gas flows only into the first branch passage portion 15, and in this case the unburned gas contained in the exhaust gas is released to the atmosphere as it is. However, in this temperature region, the unburned gas contained in the exhaust gas is unburned. The amount of gas is small.

That is, in steps 29 and 30, the outflow control valve 51 is fully closed so that the adsorbent
If 24 has reached the desorption temperature of the unburned gas, the adsorbent 24
Even if the amount of unburned gas desorbed from the fuel cell increases, the unburned gas is prevented from being discharged. Then, after the step is executed, the process returns to step 28 again, and the exhaust temperature T is judged.

On the other hand, in step 28, the exhaust temperature T is the predetermined value T
_If it is determined that the value is ₀ or more, the process proceeds to step 61.
The steps described above are the flow relating to the adsorption of the unburned gas by the adsorbent 24. Then, in step 61, it is determined by a routine that is separately executed whether or not the engine 11 is operating in an operating state in which the engine 11 burns leaner than the stoichiometric air-fuel ratio.

A routine for determining the operating state of the engine 11 will be described with reference to FIGS. 4 and 5. FIG. 4 shows a routine for setting the fuel injection amount.
It is executed every 10 msec. In step 41, the engine speed N obtained by calculating the cycle of the unit angle signal is input from the crank angle sensor 33.

In step 42, the intake passage 41 of the engine 11
Intake air flow rate Q from the air flow meter 43 provided in the
Input the signal. In step 43, the basic fuel injection amount Tp equivalent to the theoretical air-fuel ratio is calculated by the following equation based on the engine speed N and the intake air flow rate Q signal. Tp = K · Q / N (where K is a constant) FIG. 5 shows an air-fuel ratio setting routine, which is executed when it is determined that the engine 11 is started by the ignition signal, for example.

In step 51, the exhaust gas temperature T detected by the main catalyst outlet temperature sensor 32, the engine speed N and the basic fuel injection amount Tp are input. At step 52, whether the exhaust temperature T is within a predetermined range ( _TL <T <
T _H ), whether the engine speed N is within a predetermined range (N _L <N <N _H ), and whether the basic fuel injection amount Tp is within a predetermined range (Tp _L <Tp <Tp _H ) To judge.

When it is judged that the exhaust temperature T, the engine speed N and the basic fuel injection amount Tp are within the predetermined ranges, it is judged that it is possible to operate in a leaner state than the stoichiometric air-fuel ratio. Then, the routine proceeds to step 53, where the target air-fuel ratio is set based on the lean operation map. On the other hand, when it is determined that the exhaust temperature T, the engine speed N and the basic fuel injection amount Tp are not within the predetermined ranges, it is determined that the stoichiometric air-fuel ratio should be operated, and the routine proceeds to step 54, where the stoichiometric operation is performed. In order to perform the above, a normal stoichiometric air-fuel ratio is set as the target air-fuel ratio.

Then, in step 55, based on various correction coefficients COEF according to the cooling water temperature of the engine 11, the correction amount of the correction amount Ts according to the battery voltage, and the air-fuel ratio feedback correction coefficient LAMBDA, Fuel injection valve
Air-fuel ratio feedback control is performed to set the fuel injection amount from 45. Now, let us return to the description of the flowcharts of FIGS. 2 and 3 again.

In step 61, it is judged whether or not the operating condition is an operating condition in which combustion is on the lean side of the stoichiometric air-fuel ratio. If it is judged that lean operation is in progress, the routine proceeds to step 62. In step 62, by determining the engine speed N and the basic fuel injection amount Tp, the exhaust gas is caused to flow through the adsorbent 24 based on the map as shown in FIG.
It is determined whether or not the unburned gas adsorbed on 24 can be desorbed. Here, the basic fuel injection amount Tp is a parameter representing the load of the engine 11, and in FIG. 6, OK is an operating region in which control is performed so as to desorb the unburned gas adsorbed by the adsorbent 24, NG is an operation region in which control is performed so as not to desorb the unburned gas adsorbed on the adsorbent 24.

That is, when the lean operation is being performed, NO _X
The amount of HC emission is smaller than that of
Since the C concentration becomes low, the NO _x purification performance of the main catalyst 22 may be deteriorated, so that the unburned gas adsorbed by the adsorbent 24 is desorbed and the NO _{x is} removed by the unburned gas.
Will need to be reduced. Further, when the operating condition is high load and high rotation speed, the exhaust flow rate discharged from the engine 11 also increases, so that the NO in the main catalyst 22 is further increased.
_{Since the X} purification performance may be deteriorated, the exhaust gas can be efficiently purified by desorbing the unburned gas adsorbed by the adsorbent 24.

When it is determined in step 62 that the operation region is such that control is performed so that the vehicle is detached, step 71 to be described later is performed.
Continue below. Further, when it is determined in step 62 whether or not it is in the operation region in which control is performed so as to be detached, the elapsed time after engine start, engine water temperature, etc. may be taken into consideration. Further, when it is determined in step 61 that the lean operation is not being performed, or even when it is determined that the lean operation is being performed in step 61, it is determined in step 62 that it is not in the operation range in which the control is performed so as to be detached. If so, go to step 63.

In step 63, it is judged whether or not the inflow control valve 18 is switched by the actuator 19 so as to desorb the unburned gas which the adsorbent 24 is currently adsorbing. If the adsorbent 24 is not being desorbed, the first
Assuming that the inflow control valve 18 has been switched so that the exhaust gas flows only in the branch passage portion 15, the process returns to step 61 and the operating condition is judged again.

In step 63, when it is determined that the adsorbent 24 is being desorbed, the operating conditions have changed, but the inflow control valve 18 has the first branch passage portion 15 and the second branch passage portion 15. In step 64, it is assumed that the exhaust gas is switched so that the exhaust gas flows through both of the passage portions 16.
After switching the inflow control valve 18 so that the exhaust gas flows only to 15, the process returns to step 61 and the operating condition is judged again.

In step 71, the actuator 19 is operated to turn on the inflow control valve 18 so that the exhaust gas is discharged from the first branch passage portion 15
And the switching operation to the intermediate position so that the second branch passage portion 16 flows. In this state, since the outflow control valve 51 is initially kept fully closed in step 30, the exhaust gas passes through the first branch passage portion 15 and the catalyst 22, but the exhaust gas temperature T Is a predetermined value T ₀ or more, and the catalyst
22 has reached the catalyst activation temperature and is in an active state. Therefore, the unburned gas in the exhaust gas is also reduced by the catalyst and purified by the catalyst 22.

Also, in step 30, the outflow control valve
Since 51 is held in the closed state, the inflow control valve 18 is switched to the intermediate position, so that the second branch passage portion
The flow of exhaust gas flowing into 16 is blocked by the outflow control valve 51. Then, in step 72, the elapsed time t after switching the inflow control valve 18 to the intermediate position in step 71 is counted.

In step 73, it is determined whether or not the elapsed time t has exceeded a predetermined time t ₀ , and if it is determined that it has elapsed, the process proceeds to step 65 and the following steps. In step 65,
The flow rate control valve 51 in the closed state is opened by α ° as the first predetermined angle so that the first predetermined amount of exhaust gas flows to the second branch passage portion 16 and the first predetermined amount of exhaust gas is discharged. Pass through the adsorbent 24. Here, when the unburned HC trapped in the adsorbent 24 is desorbed, the HC acts as a reducing agent, so the exhaust gas becomes rich.

That is, prior to the desorbing operation of the adsorbent 24, the adsorbent 24 is exposed to high temperature exhaust gas in advance.
Increase the temperature of 24 (step 71). Then, after a lapse of a predetermined time t ₀ from the switching of the inflow control valve 18, the closing of the outflow control valve 51 is released, and the outflow control valve 51 is released.
Is opened, and the exhaust gas flows from the adsorbent 24 to the exhaust gas purification catalyst 22 (step 65). At this time, since desorption from the adsorbent 24 has started, the unburned gas desorbed from the adsorbent 24 will be purified by the catalyst 22, but the temperature of the adsorbent 24 itself has risen. Since the temperature of the desorbed unburned gas also rises, the catalyst 22 can be kept active without being cooled by the desorbed unburned gas. Therefore, the adsorbent does not decrease the purifying ability of the exhaust purification catalyst 22 arranged in the exhaust passage downstream of the adsorbent 24.
The unburned gas desorbed from 24 is sufficiently purified, and stable purification performance can be obtained under all operating conditions.

Further, the unburned HC is easily desorbed, the time lag when the closing of the outflow control valve is released can be reduced, and the desorption control can be facilitated. Therefore, steps 71 to 73 and step 65 perform the function of prohibiting means. Then, in step 66, the oxygen concentration of the exhaust gas flowing in the exhaust passage 13 is determined by the oxygen sensor 36 provided in the exhaust passage 13 between the confluence 13b and the main catalyst 22.
Compared with the oxygen concentration of the exhaust gas when the air-fuel ratio of the intake air-fuel mixture is the stoichiometric air-fuel ratio, it is detected whether it is on the rich side or the lean side.

Here, when it is detected that the fuel is on the richer side, the unburned HC trapped in the adsorbent 24 is discharged.
Is desorbed by the first predetermined amount, and it is detected that the oxygen concentration in the exhaust gas is on the rich side, and the routine proceeds to step 67. That is, the oxygen concentration has changed from lean to rich due to the HC desorbed according to the first predetermined amount corresponding to the case where the flow control valve 51 is opened by α °.

In step 67, the oxygen sensor 36 causes the oxygen concentration of the exhaust gas flowing in the exhaust passage 13 to be higher than the oxygen concentration of the exhaust gas when the air-fuel ratio of the intake air-fuel mixture is the stoichiometric air-fuel ratio. Detects whether it is on the rich side or the lean side. Here, only the first predetermined amount corresponding to the case where the flow control valve 51 is opened by α ° is exhausted by the adsorbent 24.
Since it does not flow into the adsorbent, the adsorbent has a temperature in which the amount of heat absorbed from the exhaust gas temperature and the amount of heat exhausted from the adsorbent to the outside are balanced. Then, from the adsorbent 24, set the flow control valve 51 to α °.
When only the amount of HC commensurate with the first predetermined amount corresponding to the desorption amount at the temperature when only opened is completely desorbed,
The supply of unburned HC is reduced again.

That is, when it is determined in step 67 that the oxygen concentration of the exhaust gas is on the lean side, the supply of unburned HC is reduced, and the oxygen concentration detected by the oxygen sensor 36 changes from rich to lean. Steps that changed
Continue to 69. On the other hand, when it is detected in step 66 that the oxygen concentration of the exhaust gas flowing in the exhaust passage 13 is on the lean side as compared with the oxygen concentration of the exhaust gas when the air-fuel ratio of the intake mixture is the stoichiometric air-fuel ratio. Proceeds to step 68.

In step 68, it is judged whether or not the lean state has continued for a predetermined time or longer. If the lean state has not continued for a predetermined time or longer, in step 66 again,
The oxygen concentration of the exhaust gas flowing through the exhaust passage 13 is determined. Here, the predetermined time in step 68 means the flow control valve
This is the time from when the valve opening / closing control of 51 is performed until the change in oxygen concentration can be read by the oxygen sensor 36. That is, the valve operation of the flow control valve 51, the adsorbent 24
Change in the amount of exhaust gas flowing into the tank, rise in temperature of adsorbent 24, desorption of unburned HC from adsorbent, outflow of HC excess gas and passage of oxygen sensor 36, detection by oxygen sensor 36, rich by control unit 30 It is the time required for the determination, and is basically obtained as a constant in advance by experiments or the like.

If it is determined in step 68 that the lean state has continued for a predetermined time or longer, the α ° as the first predetermined angle set in step 65 is small, so that the unburned fuel to be supplied is supplied. Since the amount of HC is small and the amount of reducing material is small, it is judged that the oxygen concentration of the exhaust gas is on the lean side, and the routine proceeds to step 69. In step 69, it is determined whether or not the valve opening degree of the flow control valve 51 is less than or equal to a predetermined angle (for example, the fully open value).

That is, in the operating state in which combustion is on the lean side of the stoichiometric air-fuel ratio, the oxygen concentration detected by the oxygen sensor 36 once becomes rich and then becomes lean or it is detected for a predetermined time. Whether or not it is detected that the lean state has continued, or in any case, and when the flow control valve 51 still has a margin in the opening direction,
You have advanced to step 70.

That is, in step 70, the oxygen sensor
Since the oxygen concentration detected by 36 is in a lean state, the oxygen concentration detected by the oxygen sensor 36 is high, and the oxygen concentration in the exhaust gas is reduced by desorbing HC again and reducing the HC. However, it can be determined that the exhaust purification catalyst 22 still has a sufficient ability to purify the exhaust.

Therefore, in step 70, the flow control valve
The valve opening of 51 is set to a second predetermined angle (α + β) ° that is gradually increased by β ° from the first predetermined angle α °, and a second predetermined amount of exhaust gas that is increased from the first predetermined amount is exhausted. However, the adsorbent 24 will flow to the adsorbent 24.
The unburned HC is further desorbed from the fuel cell. That is, since unburned HC is not rapidly desorbed from the adsorbent 24, the oxygen concentration in the exhaust gas flowing through the exhaust passage 13 on the downstream side of the adsorbent 24 is equal to the theoretical air-fuel ratio of the intake air-fuel mixture. It is possible to prevent the conversion efficiency of the catalyst 22 for purifying the exhaust gas from being lowered, as compared with the oxygen concentration of the exhaust gas in the case of the air-fuel ratio, without being largely shifted to the rich side.

Therefore, stable exhaust gas purification performance can be obtained under all operating conditions. Where α ° and β
The degree will be described. In the first embodiment, α ° is the initial opening and is set differently from the normal opening increment β °. Here, if unburned HC starts to be desorbed from the adsorbent for some reason before the start of purging, and if the desorbed HC increases sharply in the early stage of purging, the purification performance of the downstream catalyst decreases. Therefore, in order to prevent this, it is desirable to set α ° small. Further, α ° and β ° may not be set only as constant values, but may be changed depending on, for example, operating conditions and exhaust temperature. Further, by gradually increasing β ° according to the number of operations, for example, α, α + β, α + 3β, α + 6β, ...
The valve operation pattern (valve opening degree) may be changed as described above.

Therefore, as described above, according to the first embodiment, the unburned HC is rapidly desorbed from the adsorbent 24 by opening the flow rate control valve 51 by α °. Therefore, it is possible to prevent the conversion efficiency of the catalyst 22 for purifying the exhaust gas from decreasing.
There is also an effect that a stable exhaust gas purification performance can be obtained under all operating conditions.

Further, prior to the desorption operation of the adsorbent 24,
In advance, the temperature of the adsorbent 24 is raised by exposing the adsorbent 24 to high-temperature exhaust, and the temperature of the exhaust reaching the catalyst 22 for exhaust purification immediately after the desorption operation is started is lowered. There is an effect that the exhaust purification catalyst 22 can stably purify unburned gas. Also,
By exposing the adsorbent 24 to high temperature exhaust gas, unburned HC
By facilitating desorption, the time lag at the time of desorption operation can be reduced, and by facilitating the desorption control, the unburned gas can be purified more reliably.

Next, a second embodiment according to claim 2 of the present invention will be described with reference to the drawings. Since the system configuration is the same as that of the first embodiment shown in FIG. 1,
The description is omitted. Also, the control unit
The control performed by 30 is also the same as the flowcharts shown in FIGS. 2 and 3 except for the steps described below, and therefore the illustration and the description thereof will be omitted.

In the second embodiment, as shown in FIG. 8, if it is determined in step 62 that the operation region is such that control is performed so as to be desorbed, the process proceeds to step 75. Step
At 75, the valve opening speeds of the inflow control valve 18 and the outflow control valve 51 are read from a table (not shown). Here, the valve opening speeds of the inflow control valve 18 and the outflow control valve 51 are determined as shown in FIG. 9, and the valve opening speeds are those for which an optimum solution is obtained in advance by experiments or the like. The set value can be changed according to the operating conditions (exhaust flow rate, exhaust temperature, etc.).

Next, in step 76, the actuator 19
The valve opening speed read in step 75,
The inflow control valve 18 is switched to an intermediate position so that the exhaust gas flows to the first branch passage portion 15 and the second branch passage portion 16. Then, proceed to step 65 and below, and the outflow control valve
The valve opening control of 51 is performed, and the valve opening speed at that time is also controlled according to the valve opening speed read in step 75.

Therefore, in the second embodiment, the opening speeds of the inflow control valve 18 and the outflow control valve 51 at the time of starting the desorption from the adsorbent 24 by flowing the exhaust gas to the adsorbent 24, Since the inflow control valve 18 is opened immediately and the outflow control valve 51 is opened slowly, the second branch passage portion is controlled.
Exhaust gas that has flowed into the 16 is suppressed from flowing out from the second branch passage portion 16. Therefore, when the inflowing exhaust gas comes into contact with the adsorbent 24, the adsorbent 24 receives the heat of the exhaust gas and is warmed up, and the temperature of the adsorbent 24 itself rises.

Then, the outflow control valve 51 is gradually opened, and the exhaust gas flows to the catalyst 22.
Since the desorption from 24 has started, the unburned gas desorbed from the adsorbent 24 is purified by the catalyst. Here, since the temperature of the adsorbent 24 itself has risen and the temperature of the unburned gas desorbed thereby has also risen, the catalyst 22 is not cooled by the desorbed unburned gas and has an activity. Can be kept.

Therefore, it is possible to prevent the conversion efficiency of the catalyst 22 for purifying the exhaust gas from being lowered, and it is possible to obtain a stable exhaust gas purifying performance under all operating conditions. Next, a third embodiment according to claim 3 of the present invention will be described with reference to the drawings. Since the system configuration is the same as that of the first embodiment shown in FIG. 1,
The description is omitted.

The control performed by the control unit 30 is also the same as the flowcharts shown in FIGS. 2 and 3 except for the steps described below, and therefore the illustration and description thereof will be omitted. In the third embodiment, as shown in FIG. 10, when it is determined in step 62 that the operation region is such that control is performed so as to be desorbed, the process proceeds to step 81.

In step 81, the actuator 19 is operated to turn on the inflow control valve 18 so that the exhaust gas flows into the first branch passage portion 15
And the switching operation to the intermediate position so that the second branch passage portion 16 flows. In step 82, the oxygen sensor 36 determines whether the oxygen concentration of the exhaust gas flowing in the exhaust passage 13 is richer than the oxygen concentration of the exhaust gas when the intake air-fuel ratio is the stoichiometric air-fuel ratio. It detects whether it is on the lean side.

If it is judged to be rich, the unburned HC as the reducing material trapped in the adsorbent 24
Is desorbed by a predetermined amount and the oxygen sensor 36 detects that the air-fuel ratio is in a rich state, so that unburned gas is prevented from flowing out from the second branch passage portion 16. That is, the process proceeds to step 83, and the elapsed time t after the inflow control valve 18 is switched to the intermediate position is counted.

In step 84, it is determined whether or not the elapsed time t has exceeded the predetermined time t ₀ , and if it is determined that it has elapsed, the process proceeds to step 65 and thereafter. That is, prior to the desorption operation of the adsorbent 24, the temperature of the adsorbent 24 is raised by exposing the adsorbent 24 to high-temperature exhaust gas in advance (step 83). Then, after the elapse of a predetermined time t ₀ after the switching of the inflow control valve 18, the outflow control valve 51 is released from the closed state, the outflow control valve 51 is opened, and the exhaust gas flows from the adsorbent 24 to the exhaust gas purification catalyst 22. (Step 65).

On the other hand, if it is determined in step 82 that the fuel is not rich, the process jumps to step 65. That is, when the rich state is detected by the oxygen sensor 36 which is the air-fuel ratio detecting means, the unburned HC trapped in the adsorbent 24 is desorbed by a predetermined amount, and if desorption is continued as it is, the temperature of the catalyst 22 is lowered. If there is a fear, the prohibiting means is activated and the exhaust gas flowing into the second branch passage portion 16 does not flow out from the second branch passage portion 16.

Therefore, also in the third embodiment, the adsorbent is
Prior to the desorption operation of 24, the temperature of the adsorbent 24 is raised by exposing the adsorbent 24 to high-temperature exhaust gas in advance, and reaches the exhaust purification catalyst 22 immediately after the desorption operation is started. There is an effect that the temperature of the exhaust gas is prevented from lowering and the exhaust purification catalyst 22 can stably purify the unburned gas.

Further, in the third embodiment, when the oxygen sensor 36 detects the rich state, the prohibiting means is activated, but as the fourth embodiment according to claim 3, the oxygen sensor 36 indicates the rich state. When it is detected, the inflow control valve 18 and the outflow control valve 51 are read from a table (not shown) to open the exhaust gas to the adsorbent 24 to start desorption from the adsorbent 24.
18 and the opening speed of the outflow control valve 51, the inflow control valve
18 may be opened immediately, and the outflow control valve 51 may be controlled to be opened slowly.

Therefore, also in the fourth embodiment, when the inflowing exhaust gas and the adsorbent 24 come into contact with each other, the adsorbent 24 receives the heat of the exhaust and is warmed up, and the temperature of the adsorbent 24 itself rises. Therefore, it is possible to prevent the temperature of the exhaust gas that reaches the exhaust purification catalyst 22 immediately after the desorption operation is started from decreasing and the exhaust purification catalyst 22 to stably purify unburned gas. There is an effect that it becomes possible.

[0075]

As described above, according to the present invention,
When starting the desorption of the unburned gas from the adsorbent, the outflow control valve is closed for a predetermined time after switching the inflow control valve so that the exhaust gas flows into the second branch passage portion by the prohibiting means. Alternatively, both the inflow control valve and the outflow control valve are opened, but the inflow control valve is opened immediately and the outflow control valve is gradually opened by the speed reducing means, or the downstream side of the unburned gas adsorbent is used. The air-fuel ratio detecting means for detecting the air-fuel ratio of the exhaust gas is provided, and when the rich state is detected by the air-fuel ratio detecting means, the prohibiting means or the speed reducing means is operated, so that the inflowing exhaust gas and the adsorbent are By contacting, the adsorbent is warmed up, the temperature of the unburned gas desorbed from the adsorbent also rises, thereby preventing the catalyst from being cooled by the desorbed unburned gas. Activity Dripping.

Therefore, there is an effect that a stable exhaust gas purification performance can be obtained under all operating conditions.

[Brief description of drawings]

FIG. 1 is a system configuration diagram showing an overall configuration of an engine exhaust emission control device according to a first embodiment of the present invention.

FIG. 2 is a flowchart (part 1) explaining the control contents performed by the control unit according to the first embodiment.

FIG. 3 is a flowchart (part 2) explaining the control contents performed by the control unit according to the first embodiment.

FIG. 4 is a flowchart for explaining control contents performed by the control unit according to the first embodiment.

FIG. 5 is a flowchart for explaining the control contents performed by the control unit according to the first embodiment.

FIG. 6 is a map for determining desorption of the adsorbent according to the first embodiment.

FIG. 7 is a time chart explaining the operation of the first embodiment.

FIG. 8 is a flowchart for explaining the control contents performed by the control unit according to the second embodiment of the present invention.

FIG. 9 is a valve opening characteristic diagram for explaining the operation of the second embodiment.

FIG. 10 is a flowchart illustrating the control contents performed by the control unit according to the third embodiment of the present invention.

[Explanation of symbols]

 11 Engine 13 Exhaust passage 15 First branch passage 16 Second branch passage 18 Inflow control valve 22 Main catalyst 24 Adsorbent 30 Control unit 31 Air-fuel ratio sensor 32 Main catalyst outlet temperature sensor 33 Crank angle sensor 35 Water temperature sensor 36 Oxygen sensor 51 Outflow control valve

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

Claims (3)

[Claims] 1. An exhaust passage of an engine is configured to include first and second branch passages that branch into two branches and then join again.
An unburned gas adsorbent for adsorbing unburned gas in the exhaust gas is disposed in the second branch passage portion, and exhaust gas is purified in the exhaust passage downstream of the confluence of the first and second branch passage portions. And an outflow control valve for controlling the inflow of exhaust gas into the second branch passage portion and an outflow control valve for controlling the outflow of exhaust gas from the second branch passage portion. Of the exhaust gas purifying device, wherein a predetermined time has elapsed after switching the inflow control valve so that the exhaust gas flows into the second branch passage portion when starting the desorption of the unburned gas from the unburned gas adsorbent. An exhaust emission control device for an engine, which is provided with prohibiting means for closing the outflow control valve. 2. An exhaust passage of an engine is configured to include first and second branch passages that branch into two branches and then join again.
An unburned gas adsorbent for adsorbing unburned gas in the exhaust gas is disposed in the second branch passage portion, and exhaust gas is purified in the exhaust passage downstream of the confluence of the first and second branch passage portions. And an outflow control valve for controlling the inflow of exhaust gas into the second branch passage portion and an outflow control valve for controlling the outflow of exhaust gas from the second branch passage portion. The exhaust gas purification device of claim 1, wherein when starting desorption of unburned gas from the unburned gas adsorbent, deceleration means for slowing the valve opening speed of the outflow control valve compared to the valve opening speed of the inflow control valve is provided. Exhaust gas purification device for engines characterized by 3. An air-fuel ratio detecting means for detecting an air-fuel ratio of exhaust gas on the downstream side of the unburned gas adsorbent is provided, and when a rich state is detected by the air-fuel ratio detecting means, a prohibiting means or a speed reducing means operates. The exhaust emission control device for an engine according to claim 1 or 2, characterized in that.