JPH05195748A - Exhaust gas purification device of internal-combustion engine - Google Patents

Abstract

PURPOSE:To reduce the amount of deposition of exhaust particulates on a catalyst and decrease the service frequency of a heater by holding long the temp. at which the catalyst borne by a filter is activated, and suppress drop in the catalyzing action. CONSTITUTION:An exhaust gas purification device includes two filters 11, 13 for bearing catalyst which are installed in respective exhaust passages 7, 9 arranged in line and coupling an exhaust gas inlet 1a with an exhaust gas outlet 1b, a temp. sensor 23 to sense the exhaust temp. at the inlet to the filters 11, 13, and a valve 15 to open and close the two exhaust passages 7, 9. When the temp. sensed, which has been above the catalyst activation point, becomes below a certain level, a control unit 21 controls the valve 15 so as to close either of the passages 7, 9 for a certain period of time, and thereby the catalyst is kept warm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine equipped with an exhaust particle collecting member for collecting exhaust particles in exhaust gas as the exhaust gas passes through.

[0002]

2. Description of the Related Art Conventionally, for example, as a device for collecting exhaust particulates contained in the exhaust gas discharged from a diesel engine, a filter made of a ceramic foam or the like that adheres and collects when the exhaust gas passes through is provided with a catalyst. There is. An example of such a catalyst filter is Japanese Patent Laid-Open No. 62-2.
There is one described in Japanese Patent No. 0613. This is to form a plurality of exhaust passage portions extending from the exhaust inlet side toward the exhaust outlet side. For each of the plurality of exhaust passage portions, every other exhaust passage portion is closed with a blind plug and at the exhaust outlet side. It is a so-called plugged honeycomb filter in which the part that is not blindly closed on the inlet side is closed by the blind plug and the part that is blindly plugged on the inlet side is open. The exhaust particles are collected by passing through.

In such a catalytic filter, when the amount of trapped exhaust particles increases, the catalytic action lowers and the trapping efficiency as a filter lowers. It is necessary to compulsorily remove the exhaust particulates by burning. In such a regenerator, exhaust gas is bypassed to the filter during normal regeneration, and the amount of gas supplied to the filter is limited to the amount required for combustion to efficiently combust exhaust particulates.

Further, it has been reported that the metal honeycomb catalyst causes clogging due to the accumulation of exhaust particulates during cold running (Fahrzug und Motorentechnik (Germany) 89).
-10p245-258). Therefore, also in this metal honeycomb catalyst, it is necessary to forcibly combust and remove the exhaust particulates by the above-described regeneration device.

On the other hand, in Japanese Patent Publication No. 62-31166, two filters are arranged in parallel, and at the time of regeneration, a passage switching valve provided on the downstream side of the filter is used to form an exhaust passage of the regeneration side filter. It is disclosed that the filter is closed and hot air is supplied to the filter from the downstream side by hot air supply means. In this case, since the two filters are alternately regenerated, the bypass operation of the exhaust gas at the time of regeneration unlike the above-described regeneration device is unnecessary, and the exhaust gas is not directly discharged to the atmosphere at the time of regeneration.

[0006]

In the conventional exhaust gas purifying apparatus as described above, when the exhaust fine particles trapped in the catalyst filter increase and the catalytic action decreases, a regeneration device using a burner or the like is used. Since it is necessary to forcibly combust and remove the exhaust particulates, regeneration will occur frequently when a vehicle equipped with an engine equipped with such an exhaust purification device actually travels. There is a problem in that much energy is required for driving, and the fuel consumption for operating the engine deteriorates.

Therefore, according to the present invention, the temperature at which the catalyst carried on the exhaust particulate collection member is activated is maintained for a longer period,
The purpose is to suppress deterioration of the catalytic action.

[0008]

In order to achieve the above object, the present invention provides a catalyst provided in two exhaust passages arranged in parallel with each other for connecting an exhaust inlet portion and an exhaust outlet portion. An exhaust particulate collection member to be carried, a temperature detecting means for detecting the temperature of the catalyst or a temperature equivalent to the catalyst, an opening / closing means for opening and closing the two exhaust passages, and a temperature detected by the temperature detecting means is a catalyst. When the activation temperature exceeds a predetermined value or less, the control means operates the opening / closing means to close one of the two exhaust passages for a certain period of time.

[0009]

According to the exhaust emission control device having such a structure, when the temperature of the catalyst detected by the temperature detecting means or the temperature equivalent to the temperature of the catalyst becomes a predetermined value or less from the state of exceeding the activation temperature of the catalyst, The control means operates the opening / closing means so as to close one of the two exhaust passages for a certain period of time. As a result, the inflow of the low-temperature exhaust gas into one of the exhaust particulate collection members is blocked, the temperature of the catalyst is maintained, and the activation temperature of the catalyst is maintained for a long time.

[0010]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is an overall configuration diagram of an exhaust emission control device showing an embodiment of the present invention. This exhaust gas purification device includes an exhaust gas inlet portion 1a of an exhaust pipe 1 of a diesel engine which is an internal combustion engine.
And the exhaust outlet portion 1b. Case 3
Is the first exhaust passage 7 on the upper side in the drawing by the partition wall 5 and
The lower second exhaust passage 9 is divided, and an open honeycomb type filter as an exhaust particulate collection member carrying an oxidation catalyst (hereinafter, simply referred to as a catalyst) is carried in each of the exhaust passages 7 and 9. 11 and 13 are attached respectively.

A flow path switching valve 15 as an opening / closing means is provided at the downstream end of the partition wall 5. Flow path switching valve 15
Has one end rotatable about the rotary shaft 17 with respect to the partition wall 5, and is controlled to be opened / closed by an actuator 19 such as a motor installed outside the exhaust pipe 1, and as shown in FIG.
It is set at three positions: an A position shown by a solid line that closes the first exhaust passage 7, a C position shown by a two-dot chain line that closes the second exhaust passage 9, and a B position that is a neutral position parallel to the partition wall 5. It is possible. It normally holds the B position, which is the neutral position. The setting to these three positions is controlled by the control unit 21 including a microcomputer or the like.

On the other hand, a temperature sensor 23 for detecting the exhaust gas temperature is provided near the exhaust gas inlet portion 1a on the opposite side of the flow path switching valve 15.
Is installed. The exhaust gas passing through the temperature sensor 23 is
Immediately after that, the temperature reaches the filters 11 and 13 and passes therethrough, so that the temperature of the filters (catalysts) 11 and 13 depends on the exhaust gas temperature passing therethrough. It has a function as a temperature detecting means for detecting a temperature equivalent to. The detection signal from the temperature sensor 23 is input to the control unit 21.

The control unit 21 lowers the temperature detected by the temperature sensor 23 from a state in which it exceeds the oxidation start temperature at which the catalysts carried by the filters 11 and 13 are activated, to a predetermined value slightly higher than the oxidation start temperature. By the way, the flow path switching valve 15 is switched from the neutral position B to either position A or position C to keep the catalyst warm. For example, when the catalyst start temperature T _CB of exhaust particulates is 350 ° C., the flow path switching determination temperature T _SET is set to 400 ° C., which is slightly higher than T _CB . This 400 ° C. is considered to be a temperature at which the exhaust temperature reaches a sufficient level during vehicle acceleration, although it depends on the engine displacement and vehicle weight. Therefore, it is a temperature that always appears when the vehicle actually travels, and if the temperature at this time can be maintained by the catalyst for a long time, the amount of exhaust particulates reduced by the action of the catalyst will proceed.

Immediately before the exhaust gas inflow side of the filters 11 and 13, heaters 25 and 27, which operate according to a command from the control unit 21, are installed. Heater 2
Reference numerals 5 and 27 operate when the amount of exhaust particulates collected by the filters 11 and 13 exceeds a predetermined amount to forcibly combust and remove the accumulated exhaust particulates to regenerate the filters 11 and 13. .. This reproduction operation is performed by the two filters 11, 1.
3 is performed alternately one by one, but the flow passage switching valve 15 closes the exhaust passage of the filter on the regeneration side to limit the inflow amount of the exhaust gas to the filter on the regeneration side and reliably remove the combustion. The regeneration timing at which the heaters 25 and 27 operate is detected, for example, when the exhaust pressure difference before and after the filters 11 and 13 exceeds a predetermined value, and the control unit 21 operates the heaters 25 and 27 based on this.

Next, the control operation of the control unit 21 will be described with reference to a pattern example of the exhaust temperature detected by the temperature sensor 23 shown in FIG. 2, a time chart corresponding to the change in the exhaust temperature, and a flow chart shown in FIG. The control operation shown in this flowchart is to be performed periodically. The temperature curves shown by the broken line portion and the one-dot chain line portion in FIG. 2 show the exhaust gas temperature when the catalyst is kept warm.

First, the filter 11 or the filter 13
Is being regenerated (step S1), and if it is being regenerated, catalyst heat retention control is not performed. That is, the regeneration operation always has priority over the catalyst heat retention control. When the regeneration is not in progress, the exhaust gas temperature T detected by the temperature sensor 23 is read (step S2), and the read exhaust gas temperature is shown in FIG.
When the flow path switching determination temperature T _SET is exceeded at time t ₁ as in (1) of (b) (step S3), the exhaust gas temperature T is read again at time t ₂ (step S4), and this reading is performed. When the exhaust gas temperature T becomes equal to or lower than the flow path switching determination temperature T _SET (step S5), the timer Tm operates from that point on for a predetermined period t ₀ as shown in (2) of FIG. 2B (step S6).

During the operating period of the timer Tm, the flow path switching valve 15 closes one of the first and second exhaust passages 7 and 9. The selection of the exhaust passage to be closed depends on the state of the flag F ₁ indicating the position of the flow path switching valve 15 immediately before the timer Tm is turned on (step S7). That is, the flag F ₁ is
When it is turned off before the time t ₂ is reached as in (3) of (b), the flow path switching valve 15 is set in (4).
Is set to the A position (step S8), and the first exhaust passage 7 is closed. On the other hand, when the flag F ₁ is on,
The flow path switching valve 15 is set to the C position (step S9), and the second
The exhaust passage 9 is closed. After the flow path switching valve 15 is set to the A position or the C position, the flag F ₁ is switched on and off respectively (steps S10 and S11). This flag F ₁
Is referenced only when the timer Tm changes from off to on, and once referenced, it turns on and off.

That is, the flow path switching valve 15 is the filter 1
When the catalysts loaded on the catalysts 1 and 13 fall below their activation temperature, the catalyst moves from the neutral position B to the position A so as to prevent the exhaust gas from flowing into one of the filters 11, and when the same condition is satisfied next time. , Move to the C position so as to prevent the exhaust gas from flowing into the other filter 13. The closed state of one exhaust passage by the flow passage switching valve 15 is determined by the timer for the period t _0.
When the time t ₃ is exceeded (step S12), the flow path switching valve 15 is fully opened with the neutral position B (step S13), and exhaust gas is passed through both the first and second exhaust passages 7, 9. In FIG. 2, the time t ₄ when the flow path switching valve 15 is in the fully open state is shown.
Then, the exhaust temperature T again exceeds the flow path switching judgment temperature T _SET , and at time t ₅ , the exhaust temperature T thereafter becomes the flow path switching judgment temperature T.
Below _SET , the flow path switching valve 15 is in the C position.

In this way, the exhaust temperature T exceeds the flow path switching judgment temperature T _SET (400 ° C.) (time t ₁ or t).
After ₄ ), the flow passage switching valve 15 is set to the B position, and the exhaust gas is caused to flow through both the filters 11 and 13 to raise the temperature of the catalyst to activate it. Then, when the exhaust gas temperature T becomes equal to or lower than the flow path switching determination temperature T _SET (400 ° C.) (time t ₂ or t ₅ ), the exhaust passage 7 or the exhaust passage 7 is blocked so as to prevent the exhaust gas from flowing into the filter 11 or 13. 9 is closed to prevent low temperature exhaust gas from passing through the filter 11 or 13, and the temperature drop of the catalyst is kept as heat only by itself to keep the temperature as shown by the broken line part and the one-dot chain line part in FIG. In addition, the state where the catalyst reaches the activation temperature (350 ° C. or higher) is maintained for a longer time. When the temperature of the catalyst becomes equal to or lower than the activation temperature at time t ₃ or t ₆ , the flow passage switching valve 15 is set to the B position and fully opened to reduce exhaust resistance and suppress deterioration of fuel consumption of the engine. This is because

The exhaust gas temperature T is not read during the closing period t ₀ of the flow path switching valve 15 in which the timer Tm is on. Therefore, as shown in FIG. 2 (a), the time t ₂₀
Even if the exhaust gas temperature T exceeds the flow path switching judgment temperature T _SET ,
This system does not detect this. The reason for this is to suppress frequent operations of the flow path switching valve 15 and maintain durability.

The closing period t ₀ of the flow path switching valve 15 is constant, but this is the time required for the catalyst temperature to drop from the flow path switching determination temperature T _SET to the catalyst activation start temperature (350 ° C.). Is determined by heat dissipation, and this time can be regarded as almost constant. Since the heat is easily dissipated when the outside air temperature is low, the closing period t ₀ of the flow path switching valve 15 is set shorter to further improve the heat retention effect of the catalyst.

When the exhaust particulates collected in the filters 11 and 13 increase and the exhaust pressure difference before and after the filters 11 and 13 exceeds a predetermined value, the control unit 21
Is given priority over the catalyst heat retention control by the heaters 25, 2
The exhaust particulates collected by the filters 11 and 13 are burnt and removed by operating 7 to regenerate the filters 11 and 13 alternately one by one. When the regeneration of the filters 11 and 13 is completed, the operation returns to the catalyst heat retention mode described above.

Such a reproducing operation mode is used in the filter 1
It is carried out each time exhaust particulate matter collected in the catalysts 1 and 13 is accumulated to some extent, but as described above, in the catalyst heat retention mode, by keeping the temperature at which the catalyst is activated longer, the catalyst is deposited on the catalyst and becomes Since it is possible to reduce the amount of exhaust particulates that obstruct the contact between the exhaust gas and the exhaust gas by oxidative combustion, the heater 2
It is possible to reduce the frequency with which the playback device according to 5, 27 operates. As a result, the energy required to drive the regenerator is reduced, and the reduction in fuel consumption of the engine due to regeneration is suppressed.

Depending on the performance of the catalyst to be used, the weight of the vehicle and the selection of the engine exhaust amount, the exhaust temperature often becomes high above the catalyst activation temperature. Oxidation and combustion can be performed only with a catalyst, and a regenerating device is not required, and a large cost reduction can be achieved.

Further, when the vehicle equipped with the exhaust gas purifying apparatus stops and the power is turned off before the timer Tm is measured until the time t ₀ after starting, the flow passage switching valve 15 is returned to the neutral position B. Instead, one of the exhaust passages 7 or 9 is closed at the time of starting the next engine. Therefore, in order to prevent this, as shown in the flowchart of FIG.
After the engine is started, a reset works to return the flow path switching valve 15 to the neutral B position (step S21). After that, the control operation for keeping the temperature of the catalyst in FIG. 3 starts (step S22).

FIG. 5 is a flow chart showing another embodiment of the present invention. This flowchart includes steps S1 to S5 and S6 to S1 of the flowchart of FIG.
3 is the same as that of FIG. 3 between steps S5 and S6.
Shows the operation added to. In this embodiment, after the exhaust gas temperature exceeds the flow path switching judgment temperature T _SET at time t ₁ and becomes equal to or lower than the flow path switching judgment temperature T _SET at time t ₂ , the filters 11 and 13 are at the regeneration timing. Filter 1
When either one of the filters 1 and 13 approaches the regeneration time, the filters 11 and 13 are regenerated earlier. That is, after step S5 of determining T ≦ T _SET in FIG. 3, it is determined whether the filter 11 is near the regeneration time (step S31) or whether the filter 13 is near the regeneration time (step S32), and the filter 11 Is near the regeneration time, the flow path switching valve 15 is set to the A position to regenerate the filter 11 (step S33), and conversely the filter 1
When 3 is near the regeneration time, the flow path switching valve 15 is set to the C position to regenerate the filter 13 (step S34). When neither of the filters 11 and 13 is close to the regeneration time, the catalyst warming operation after step S6 is performed.

Further, when the flow passage switching valve 15 moves to the position A or the position C when the flow passage switching valve 15 moves to the switching control operation for keeping the temperature of the catalyst near the regeneration time. Regeneration may be performed using this catalyst heat retention.

In the above embodiment, an open honeycomb type filter is used as the catalyst carrier, but other forms such as pellets, plugged honeycomb type filters,
A foam filter made of ceramic or the like may be used.

[0030]

As described above, according to the present invention, when the temperature detected by the temperature detecting means falls below a predetermined value from the state where it exceeds the activation temperature of the catalyst, the opening and closing means keeps it for a certain period of time. , The exhaust gas is prevented from flowing into either of the two catalysts arranged in parallel with each other.
The activation temperature of the catalyst in which the inflow of low-temperature exhaust is blocked is kept longer, and the amount of exhaust particulates deposited on the catalyst can be reduced. As a result, the amount of deposition increases, and the frequency of use of the regenerator when forcibly burning and removing exhaust particulates can be reduced, and in some cases the regenerator can be dispensed with.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of an exhaust gas purification apparatus for an internal combustion engine showing an embodiment of the present invention.

FIG. 2A is an exhaust temperature characteristic diagram, and FIG. 2B is a control time chart in a catalyst heat retention mode corresponding to the exhaust temperature.

FIG. 3 is a flow chart showing a control operation by the control unit of FIG.

FIG. 4 is a flowchart showing a control operation by a control unit at the time of starting the engine.

FIG. 5 is a flowchart showing a control operation according to another embodiment.

[Explanation of symbols]

 1a Exhaust Inlet 1b Exhaust Outlet 7 First Exhaust Passage 9 Second Exhaust Passage 11 and 13 Filter (Exhaust Particle Collection Member) 15 Flow Path Switching Valve (Opening / Closing Means) 21 Control Unit (Control Means) 23 Temperature Sensor (Temperature Detection means)

Claims (1)

[Claims] 1. An exhaust particulate trapping member, which is provided in each of two exhaust passages that are arranged in parallel with each other and connects an exhaust inlet portion and an exhaust outlet portion, and carries a catalyst, and the temperature of the catalyst or the catalyst. Temperature detecting means for detecting a temperature equivalent to the above, an opening / closing means for opening / closing the two exhaust passages, and a temperature detected by the temperature detecting means has fallen below a predetermined value from a state where the temperature exceeds the activation temperature of the catalyst. In this case, the exhaust gas purifying apparatus for an internal combustion engine, further comprising: a control unit that operates the opening / closing unit to close one of the two exhaust passages for a certain period of time.