JP2001221035A - Exhaust emission control device for engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To precisely decide deterioration of an NOx adsorber even in the case when a specified amount of the NOx adsorber and a large amount of an oxygen adsorber are arranged in an exhaust air passage. SOLUTION: This exhaust emission control device for an engine furnished with a reducing agent increasing means 38 to increase a reducer to be supplied to a NOx reducing catalyst 22 is constituted to carry out control to increase the reducer to be supplied to the NOx reducing catalyst 22 for a previously set first period of time and to restrain increase of the reducing agent for a previously set second period of time by the reducing agent increasing means 38 in the case where temperature of the NOx reducing catalyser 22 assumed by a catalyst temperature assuming means 37 is lower than standard temperature by having the catalyst temperature assuming means 37 to assume temperature of the NOx reducing catalyst 22.

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 engine mounted on an automobile or the like.

[0002]

2. Description of the Related Art Conventionally, as shown in Japanese Patent Application Laid-Open No. 9-317524, for example, a catalyst device is arranged in the upstream side of an exhaust passage and a second catalyst is arranged in series downstream of the first catalyst device. A first cylinder group connected upstream of the first catalyst device and a second cylinder connected to an exhaust passage between the first catalyst device and the second catalyst device. In a nitrogen oxide purifying apparatus for an internal combustion engine comprising a group, a main fuel injection command for generating engine output and a post fuel injection command for supplying hydrocarbon (HC) are provided for each cylinder by a fuel injection means. By emitting the fuel, the amount of post-fuel injection is adjusted in accordance with the temperatures of the first catalyst device and the second catalyst device determined by the catalyst temperature determination means, and the nitrogen oxides (NOx ) To maximize the purification rate It has been made.

[0003]

As described above, in addition to the main injection of the fuel corresponding to the operation state of the engine, the post-fuel injection is performed to increase the HC in the exhaust gas, so that the heating of each catalyst device is reduced. In a configuration in which the purification rate of NOx is improved while suppressing it, during a normal operation in which the catalyst is activated, a reducing agent composed of HC or the like is reacted with NOx to form N2.
Although Ox can be purified, there is a problem that NOx cannot be purified effectively when the catalyst temperature is in an inactive state where it is low and when the catalyst temperature is higher than a certain value.

That is, when the temperature of the NOx reduction catalyst is low and in an inactive state, even if a reducing agent composed of HC or the like is present, the NOx reduction effect of the catalyst cannot be sufficiently obtained, and the NOx reduction catalyst cannot be obtained. When the temperature of the catalyst is high, the reducing agent is oxidized by oxygen in the exhaust gas to form N 2
Since the reduction action of Ox cannot be obtained, as shown by the solid line in FIG. 5, the NOx purification rate shows a peak when the temperature of the NOx reduction catalyst reaches a predetermined value. In any state of high temperature, the purification rate of NOx tends to decrease.

[0005] When the temperature of the NOx reduction catalyst is higher than the peak time, the NOx reduction catalyst is in an active state.
It is possible to purify NOx in exhaust gas by securing the amount of reducing agent for reducing
When the temperature of the NOx reduction catalyst is lower than the peak time, the NOx reduction catalyst is in an inactive state. Therefore, even if the amount of the reducing agent in the exhaust gas is increased, the reduction rate of NOx cannot be improved. There has been a problem that NOx in exhaust gas cannot be effectively purified.

In view of such circumstances, the present invention effectively reduces NOx in exhaust gas even when the temperature of the NOx reduction catalyst disposed in the exhaust passage is low and the exhaust gas reduction catalyst is in an inactive state. It is an object of the present invention to provide an exhaust gas purification device for an engine which can be purified by reduction.

[0007]

The invention according to claim 1 is
Combustion control means for controlling the combustion state of the fuel so as to obtain the required output of the engine, and at least NOx purification by reacting NOx and a reducing agent in an oxygen-rich atmosphere having a high oxygen concentration and disposed in an exhaust passage of the engine In an exhaust gas purifying apparatus for an engine, comprising: a NOx reduction catalyst to be reduced, and a reducing agent increasing means for increasing a reducing agent supplied to the NOx reduction catalyst, a catalyst temperature estimating means for estimating the temperature of the NOx reducing catalyst If the catalyst temperature estimated by the catalyst temperature estimating means is lower than the reference temperature, the reducing agent increasing means sets the NO for a predetermined first period.
The amount of the reducing agent supplied to the x reduction catalyst is increased, and the amount of the reducing agent is prevented from increasing over a second period set in advance.

According to the above configuration, when the temperature of the NOx reduction catalyst is estimated to be lower than the reference temperature by the catalyst temperature estimating means, the reducing agent increasing means increases the amount of the NOx reducing catalyst over the first period set in advance. The control to increase the amount of the reducing agent supplied to the NOx reduction catalyst and to suppress the increase in the amount of the reducing agent over a second period set in advance are performed, thereby promoting the NOx reduction by the NOx reduction catalyst. Is exerted, and NOx in the exhaust gas is effectively purified.

According to a second aspect of the present invention, in the exhaust gas purifying apparatus for an engine according to the first aspect, the reference temperature is:
It is set to the inactive temperature of the NOx reduction catalyst at which the NOx purification rate becomes less than a predetermined value.

According to the above configuration, when the temperature of the NOx reduction catalyst is estimated to be lower than the reference temperature by the catalyst temperature estimating means and it is confirmed that the NOx reduction catalyst is in an inactive state, the reduction of the NOx reduction catalyst is performed. After increasing the amount of the reducing agent supplied to the NOx reduction catalyst over a first period set in advance by the agent increasing means, control is executed to suppress the increase in the reducing agent over a second period set in advance. Will be done.

According to a third aspect of the present invention, in the exhaust gas purifying apparatus for an engine according to the first or second aspect, the reducing agent increasing means uses a fuel injection valve arranged in a combustion chamber of the engine to exhaust gas from an expansion stroke. The control for injecting fuel at a predetermined time during the stroke is executed for each predetermined cylinder over the first period.

According to the above configuration, when the temperature of the NOx reduction catalyst is estimated to be lower than the reference temperature by the catalyst temperature estimating means, the fuel injection valve disposed in the combustion chamber of the engine causes the exhaust gas to be discharged from the expansion stroke. At a predetermined time during the stroke, control for increasing the amount of reducing agent in the exhaust gas is executed by, for example, post-injecting fuel for each predetermined cylinder over the first period.

[0014] The invention according to claim 4 is the above-mentioned claims 1-3.
In the exhaust gas purifying apparatus for an engine according to any one of the above, the reducing agent increasing means sets the period longer than the first period when the NOx reduction catalyst is in an active state and the engine is in a steady operation state. N over the third period
This is configured to increase the amount of the reducing agent supplied to the Ox reduction catalyst.

According to the above configuration, when the catalyst temperature estimating means confirms that the NOx reduction catalyst is in the active state at the reference temperature or higher, the third period set to a period longer than the first period. The control for increasing the amount of the reducing agent supplied to the NOx reducing catalyst is performed over a period of time, so that the amount of the reducing agent in the exhaust gas is further increased as compared with the case where the temperature of the NOx reducing catalyst is lower than the reference temperature. Will be done.

[0015] The invention according to claim 5 is the above-mentioned invention.
The exhaust gas purification device for an engine according to any one of the above, further comprising a NOx reduction catalyst in which zeolite supports a catalyst metal.

According to the above configuration, in both the normal operation state in an oxygen-excess atmosphere and the inactive state in which the temperature of the NOx reduction catalyst is low, the trapping in the pores of zeolite as a porous material. By reducing the NOx in the exhaust gas using the reduced agent such as HC, the NOx can be effectively purified.

[0017]

FIG. 1 shows an example in which an exhaust gas purifying apparatus for an engine according to the present invention is applied to a diesel engine mounted on an automobile. The main body 1 of the engine is
It has a plurality of cylinders (only one is shown in the figure) 2, and a piston 3 is inserted into each cylinder 2 so as to be able to reciprocate, and a combustion chamber 4 is defined inside each cylinder 2 by the piston 3. ing. A fuel injection valve 5 is provided substantially at the center of the upper surface of the combustion chamber 4.
Is disposed, and fuel is directly injected into the combustion chamber 4 of each cylinder 2 at a predetermined timing. Further, a water temperature sensor 1 for detecting a temperature of a cooling water of the engine so as to face a water jacket (not shown) of the engine body 1.
8 are provided.

Each of the fuel injection valves 5 is connected to a common rail 6 for storing high-pressure fuel. The common rail 6 is provided with a pressure sensor 6a for detecting an internal fuel pressure (common rail pressure) and a crankshaft. A high-pressure supply pump 8 driven by 7 is connected. This high-pressure supply pump 8 controls the fuel supply pressure,
The fuel pressure in the common rail 6 detected by the pressure sensor 6a is, for example, about 20 M during the idling operation of the engine.
The pressure is maintained at Pa or higher, and is maintained at 50 MPa or higher during other operations.

The crankshaft 7 is provided with a crank angle sensor 9 for detecting the rotation angle. The crank angle sensor 9 includes a plate to be detected provided at the end of the crankshaft 7 and an electromagnetic pickup disposed to face the outer periphery of the plate. And outputs a pulse signal by detecting the passage of the projection formed on the substrate.

The downstream end of the intake passage 10 connected to the engine body 1 branches off for each cylinder 25 via a surge tank (not shown), and this branching part is connected to each cylinder 2 via an intake port. Are connected to the combustion chamber 4. Further, the surge tank is provided with an intake pressure sensor 10a for detecting a pressure of intake air supplied into each cylinder 2.

In the intake passage 10, in order of its upstream side,
A hot film airflow sensor 11 for detecting a flow rate of intake air sucked into the engine body 1;
1, a blower 12 for compressing intake air, an intercooler 13 for cooling air compressed by the blower 12, and an intake throttle valve 1 for changing a flow area of intake air.
4 and 4 are provided.

The intake throttle valve 14 is a butterfly valve provided with a notch so that intake air can flow even in a fully closed state. Like the EGR valve 24 described later, a solenoid valve 16 for negative pressure control is provided. The degree of opening of the valve is adjusted in accordance with the magnitude of the negative pressure acting on the diaphragm 15 being adjusted. Further, the intake throttle valve 14 is provided with a sensor for detecting the valve opening.

The upstream end of the exhaust passage 20 connected to the engine body 1 branches off for each cylinder 2, and this branch is connected to the combustion chamber 4 of each cylinder 2 via an exhaust port. I have. The exhaust passage 20 has, in order from the upstream side, a λO ₂ sensor (not shown) whose output rapidly changes at the stoichiometric air-fuel ratio, a turbine 21 driven by the exhaust flow, and at least one of the exhaust gas. NOx reduction catalyst 22 for reducing and purifying NOx, and NOx reduction catalyst 22
And a NOx sensor 19 for detecting the NOx concentration in the exhaust gas passing through the NOx sensor.

The NOx reduction catalyst 22 has a cordierite carrier formed in a honeycomb structure having a large number of through holes extending parallel to each other along the flow direction of exhaust gas.
The catalyst layer is formed on the wall surface of each through hole. Specifically, the catalyst layer is formed by supporting platinum (Pt) and rhodium (Rh) as a support material such as MFI-type zeolite (ZSM5) as a porous material.

The NOx reduction catalyst 22 converts NOx into CO or HC when the mixture in the combustion chamber 4 is lean and the oxygen concentration in the exhaust gas is high (4% or more).
It is configured to react with a reducing agent composed of the above and purify. The NOx reduction catalyst 22 has a three-way catalyst function even when the oxygen concentration is low.

The blower 11 provided in the intake passage 10 and the turbine 21 provided in the exhaust passage 20
, A variable geometry turbo (VGT) configured to change the nozzle cross-sectional area of the exhaust passage 20
Is constituted.

An exhaust gas recirculation passage (hereinafter, referred to as an EGR passage) 23 for recirculating a part of the exhaust gas to the intake passage 10 is connected to the exhaust passage 20 on the upstream side of the turbine 21. A downstream end of the EGR passage 23 is connected to the intake passage 10 on the downstream side of the intake throttle valve 14, and a downstream end of the EGR passage 23 is configured to have a valve opening adjustable. A pressure-operated exhaust gas recirculation amount control valve (hereinafter, referred to as an EGR valve) 24 is provided.
The amount of exhaust gas recirculated to the intake passage 10 by the valve 24 is adjusted.

In the EGR valve 24, a valve body (not shown) is urged in a closing direction by a spring.
The opening degree of the EGR passage 23 is linearly adjusted by being driven in the opening direction by the diaphragm 24a. That is, a negative pressure passage 27 is connected to the diaphragm 24a, and the negative pressure passage 27 is connected to a vacuum pump (negative pressure source) 29 via an electromagnetic valve 28 for negative pressure control. When the electromagnetic valve 28 communicates or blocks the negative pressure passage 27, the negative pressure for driving the EGR valve is adjusted, and the EGR valve 24 is driven to open and close. The EGR valve 24 has a lift sensor 2 for detecting the position of the valve body.
6 are provided.

The fuel injection valve 5, the high-pressure supply pump 8, the intake throttle valve 14, the EGR valve 24, the turbocharger 25 and the like are provided with an engine control unit (hereinafter referred to as EC).
The operating state is controlled in accordance with a control signal output from the U) 35. In addition, the EC
U35 indicates the output signal of the pressure sensor 6a, the output signal of the crank angle sensor 9, the output signal of the air flow sensor 11, the output signal of the water temperature sensor 18, and the operation amount of the accelerator pedal operated by the driver. The output signal of the accelerator sensor 32 to be detected is input.

The ECU 35 includes a combustion control means 36 for controlling the combustion state of the fuel so as to obtain the required output of the engine, a catalyst temperature estimating means 37 for estimating the temperature of the NOx reduction catalyst 22, and a NOx reduction catalyst. Reducing agent increasing means 38 for increasing the amount of reducing agent such as HC supplied to 22;
Exhaust gas recirculation control means 39 for controlling the amount of exhaust gas recirculation by driving the EGR valve 24 according to the operating state of the engine.

The combustion control means 36 controls the injection amount and the injection timing of the fuel injected from the fuel injection valve 5 according to the operating state of the engine, and controls the common rail pressure adjusted by the high-pressure supply pump 8, That is, by controlling the fuel injection pressure and controlling the amount of intake air adjusted by the intake throttle valve 14, the combustion state of the fuel is controlled so that the required output of the engine is obtained.

The catalyst temperature estimating means 37 is provided, for example, based on the engine speed detected in response to the output signal of the crank angle sensor 9 and the engine load detected in response to the output signal of the accelerator sensor 32. An estimated value of the temperature of the NOx reduction catalyst 22 corresponding to the engine operating state is read from a preset map, or the above-mentioned value is determined based on the operating state of the engine and the exhaust gas temperature detected by an exhaust gas temperature sensor (not shown). NOx reduction catalyst 22
And the estimated value is used as the reducing agent increasing means 38.
Is configured to be output.

The reducing agent increasing means 38 controls a predetermined timing between the expansion stroke and the exhaust stroke, for example, the ATDC 30 in addition to the main fuel injection executed by the combustion control means 36.
By controlling the fuel injection valve 5 so as to perform post-injection of fuel at any time within a range of up to 90 °, HC or CO discharged from the combustion chamber 4 to the exhaust passage 20 can be used. The amount of the reducing agent is increased, and the increased amount of the reducing agent is controlled in accordance with the temperature of the NOx reduction catalyst 22.

That is, it is determined that the temperature of the NOx reduction catalyst 22 estimated by the catalyst temperature estimating means 37 is lower than a preset reference value.
If the NOx purification rate is considered to be less than the predetermined value due to the inactive state, the NOx reduction rate is supplied to the NOx reduction catalyst 22 over a first period set in advance to about 0.1 to 100 seconds. While increasing the reducing agent,
The control for suppressing the increase in the amount of the reducing agent is repeatedly executed over a set second period set to about seconds. The amount of the reducing agent at this time is set according to the amount of RawNOx in the exhaust gas, but is set to 5% or less of the fuel consumption corresponding to the required output in order to prevent deterioration of fuel efficiency.

Further, it is determined that the temperature of the NOx reduction catalyst 22 estimated by the catalyst temperature estimating means 37 is equal to or higher than the reference temperature, the NOx reduction catalyst 22 is activated, and the NOx purification rate is equal to or higher than a predetermined value. When it is confirmed that the state is such that the reducing agent supplied to the NOx reduction catalyst 22 is increased over a third period set longer than the first period, The control for suppressing the increase in the amount of the reducing agent is repeatedly executed over a fourth period set to a time shorter than two periods.

The control operation executed in the engine exhaust gas purification apparatus will be described with reference to the flowcharts shown in FIGS. When the above control operation starts,
First, after the data detected by each sensor is input (step S1), the main injection amount Qb and main injection timing Ib of the fuel corresponding to the operating state of the engine are read from a preset map and set (step S1).
2) The estimated catalyst temperature TCat is obtained by the catalyst temperature estimating means 37 (step S3).

Next, it is determined whether or not the estimated value TCat of the catalyst temperature is lower than a predetermined reference temperature TCat0 (step S4). If the determination is YES, the reducing agent increasing means 38 determines A first period TAL previously set to about 0.1 to 100 seconds is input as a period TA for increasing the reducing agent, and a period TB for suppressing the increase of the reducing agent is set to about 1 to 100 seconds in advance. The input second period TBL is input (Step S
5).

On the other hand, if the determination in step S4 is NO and it is confirmed that the estimated value TCat of the catalyst temperature is equal to or higher than the reference temperature TCat0, the period TA during which the reducing agent increasing means 38 increases the reducing agent is used. As the first
Third period TAL set to be longer than period TAL
And a fourth period TBH, which is set to be shorter than the second period TBL, as a period TB during which the increase of the reducing agent is suppressed (step S6).

Next, it is determined whether or not the engine is in a steady operation state (step S7). If the determination is NO, a timer for measuring the execution time of the control for increasing the amount of the reducing agent and the control for increasing the amount of the reducing agent is executed. The count value T is set to 0, and the fuel post-injection amount Qp is set to 0 (step S8).

If it is determined YES in step S7 and it is confirmed that the engine is in a steady operation state, it is determined whether or not the count value T of the timer is greater than 0 (step S9), and YES Is determined, it is determined whether or not the count value T of the timer is less than the increasing period TA of the reducing agent (step S1).
0). If the determination in step S9 is NO and it is confirmed that the count value T of the timer is 0, the timer starts counting (step S11), and then proceeds to step S10.

Then, YES is determined in the above step S10, and the count value T of the timer is less than the increasing period TA of the reducing agent, that is, the current control point is within the increasing period TA shown in FIG. If confirmed,
The post-injection amount Qp and the post-injection timing Ip of the fuel according to the operating state of the engine are set by reading out from a preset map or the like (step S12).

On the other hand, if the determination in step S10 is NO, the count value T of the timer is set to the increasing period T of the reducing agent.
If it is determined that the count value is equal to or greater than A, it is determined whether or not the count value T is equal to or greater than the sum (TA + TB) of the increasing period TA of the reducing agent and the increasing suppression period TB (step S).
13).

When the determination in step S13 is NO, the count value T of the timer becomes equal to the reducing agent increasing period T.
If the value is equal to or larger than A and less than the sum (TA + TB), that is, if it is confirmed that the current control point is within the increase suppression period TB shown in FIG. (Step S14). When it is determined that the answer is YES in step S13 and the count value T of the timer is equal to or greater than the sum (TA + TB), the count value T is set to 0 (step S15). The process proceeds to the following step S16.

Next, it is determined whether or not the current time is the main fuel injection timing Ib (step S16), and when the determination is YES, the main fuel injection control is executed (step S1).
7). Next, it is determined whether or not the fuel post-injection amount Qp is set to 0 (step S18). If the determination is YES, the process returns without performing the fuel post-injection and ends the control operation. .

If NO is determined in step S18 and it is confirmed that the post-injection amount Qp of the fuel is set to the predetermined value, it is determined whether or not the present time is the post-injection timing Ip of the fuel. (Step S19), and when it is determined to be YES, the post-injection control of the fuel is executed (step S2).
0).

As described above, the combustion control means 36 for controlling the combustion state of the fuel so that the required output of the engine is obtained.
A NOx reduction catalyst 22 that is disposed in the exhaust passage 20 of the engine and reacts NOx with a reducing agent in an oxygen-rich atmosphere having a high oxygen concentration to purify at least NOx;
In an exhaust gas purification apparatus for an engine, comprising: a reducing agent increasing means 38 for increasing the reducing agent supplied to the Ox reducing catalyst 22; and a catalyst temperature estimating means 37 for estimating the temperature of the NOx reducing catalyst 22. When the temperature TCat of the NOx reduction catalyst 22 estimated by the temperature estimating means 37 is lower than the reference temperature TCat0, the NOx is reduced by the reducing agent increasing means 38 over a first period TA set in advance.
Since the amount of the reducing agent supplied to the x reduction catalyst 22 is increased and the increase in the amount of the reducing agent is suppressed over a preset second period TB, the temperature of the NOx reduction catalyst 22 is low. Even in an inactive state, NOx in the exhaust gas can be effectively reduced and purified.

That is, the NOx reduction catalyst 22, which purifies NOx by reacting NOx with a reducing agent in an oxygen-rich atmosphere having a high oxygen concentration, has a peak NOx purification rate when its temperature becomes constant. It is known that as the activity decreases as the temperature decreases, the NOx purification rate decreases. Therefore, as in the normal case, even if the amount of the reducing agent is increased by the reducing agent increasing means 38, the NOx in the exhaust gas cannot be properly purified.

For example, platinum is supported on a support made of MFI-type zeolite, and the amount of supported platinum is 1.4 g /
The model exhaust gas of the diesel engine having various temperatures, that is, 2
80 ppm NOx, 10% O ₂ , 200 ppm
Gas containing 333 ppm of HC and 333 ppm of HC
Supplied at a space velocity (SV) of 5000 h ^-1
In the case where an experiment for measuring the purification rate was performed, data shown by a solid line A in FIG. 5 was obtained. From this data, when the exhaust gas temperature is about 220 ° C., the NOx purification rate shows a peak, and as the exhaust gas temperature decreases from this peak, the NOx purification rate decreases. At 200 ° C., it can be seen that the NOx purification rate is less than half the peak time.

On the other hand, HC in the above model exhaust gas
A gas whose component is set to 0 is supplied to the NOx reduction catalyst 22 at a space velocity (SV) of 85000 h ^-1 , and the same conditions as those under which the increase of the reducing agent by the reducing agent increasing means 38 is stopped are set. , NOx after 30 seconds have passed
An experiment was performed to measure the purification rate of the oil.
The data as shown in FIG. From this data, HC
By setting the component to 0, the peak of the NOx purification rate can be shifted to the low temperature side, and the exhaust gas temperature becomes lower than 20%.
It was confirmed that a sufficiently high NOx purification rate was obtained even at 0 ° C.

Therefore, when the temperature of the NOx reduction catalyst 22 is lower than the reference temperature from the above data, the NOx reduction catalyst 22 is supplied to the NOx reduction catalyst 22 by the reducing agent increasing means 38 over a first period TA set in advance. After increasing the reducing agent, by suppressing the increasing amount of the reducing agent for a preset second period TB, even when the NOx reduction catalyst 22 is in a low temperature inactive state, the amount of the exhaust gas It can be seen that NOx can be effectively reduced and purified.

When the increase in the amount of the reducing agent is temporarily suppressed as described above, the NOx purification rate is improved only when the concentration of HC in the exhaust gas is reduced. The released HC and the like are released from the gap and discharged into the exhaust gas. The HC and the like react with the NOx in the exhaust gas near the wall surface of the NOx reduction catalyst 22, and the platinum or the like carried on the zeolite. It is considered that this is because the catalytic action for accelerating the above reaction is sufficiently exhibited by removing the HC attached so as to cover the catalytic metal.

For example, a model exhaust gas of a diesel engine having a temperature of 200 ° C. is applied to a NOx reduction catalyst 22 in which platinum is supported on a carrier made of MFI zeolite and the amount of platinum is set to 2 g / l. That is, 280 ppm of NOx, 10% of O ₂ , and 200 pp
m containing CO and 333 ppm of HC
As shown in FIG. 6 (A), after supplying for about 3 seconds at a space velocity (SV) of 85000 h ⁻¹ , the HC component in the model exhaust gas is set to 0, whereby the reducing agent When the change in the NOx purification rate was measured under the same conditions as when the increasing of the reducing agent by the increasing means 38 was stopped, data as shown in FIG. 6B was obtained.
From this data, it can be seen that by stopping the increase of the reducing agent, the NOx purification rate can be temporarily improved.

The criterion for determining whether or not the increase in the reducing agent over the first period TA set in advance as described above and the suppression of the increase in the reducing agent over the second period TB set in advance is performed. The reference temperature TCat0 can be set to various values according to the characteristics of the NOx reduction catalyst 22 and the like, but when the NOx reduction catalyst 22 is inactive, the NOx reduction
In order to effectively purify NOx, the reference temperature TCat0 is set to a value at which the NOx purification rate becomes less than a predetermined value.
It is preferable to set the temperature at which the x reduction catalyst 22 is inactive.

Further, as shown in the above embodiment, the post-injection for injecting fuel at a predetermined timing between the expansion stroke and the exhaust stroke is executed by the fuel injection valve 5 arranged in the combustion chamber 4 of the engine body 1. When the control for increasing the amount of reducing agent in the exhaust gas is performed in the reducing agent increasing means 38, the fuel may be post-injected for each predetermined cylinder 2 over the first period TA. Good. That is, one or a plurality of cylinders 2 are selected from the cylinders 2 to execute the post-injection, or selected in accordance with a preset combustion cycle or a combustion cycle set according to the operating state of the engine. The above-described post-injection may be executed only for the cylinder 2 that has been subjected to the injection.

When the fuel is post-injected every predetermined cylinder 2 over the first period TA as described above, the post-injection of fuel to all the cylinders 2 is performed. Since it is possible to increase the post-injection amount per operation while reducing the total post-injection amount of the fuel, it is possible to effectively increase the amount of the reducing agent in the exhaust gas with a small amount of fuel, thereby deteriorating the fuel efficiency. Without this, there is an advantage that NOx in the exhaust gas can be reduced and effectively purified by the reducing agent.

It is to be noted that, instead of the above-described embodiment configured to increase the amount of reducing agent in the exhaust gas by performing the post-injection of injecting the fuel at a predetermined time between the expansion stroke and the exhaust stroke as described above. Alternatively, the main injection timing of the fuel corresponding to the engine load may be retarded. That is,
It is also possible to increase the amount of the reducing agent in the exhaust gas by retarding the main injection timing of the fuel corresponding to the engine load as described above to increase the amount of unburned fuel composed of HC or CO or the like. it can. In this case, in order to prevent the ignitability of the fuel from deteriorating, it is preferable to execute a pilot injection for injecting a small amount of fuel in the first half of the intake stroke or the like before performing the main injection of the fuel.

Further, in the multistage injection in which the fuel is divided into a plurality of injections within a predetermined period near the top dead center of the compression stroke, the number of divisions of the fuel injection is reduced or the interruption time of the fuel injection is reduced. By increasing the length, the amount of the reducing agent in the exhaust gas may be increased. That is, in the multi-stage fuel injection as described above, the fuel is intermittently injected to vaporize and atomize the fuel satisfactorily to make the combustion state extremely good, thereby improving fuel efficiency and generating smoke. There is an advantage that can be realized.
When performing the multi-stage injection, the number of divisions of the fuel injection is reduced, or the interruption time of the injection is lengthened to reduce the vaporization and atomization of the fuel, thereby reducing the reducing agent in the exhaust gas. Can be increased.

Further, as shown in the above embodiment, NOx
When the reduction catalyst 22 is in an active state and the engine is in a steady operation state, the NOx reduction catalyst 22 is maintained for a third period TB that is longer than the first period TA.
When the control to increase the amount of the reducing agent supplied to the NOx reducing catalyst 38 is performed in the reducing agent increasing unit 38, the NOx reduction catalyst 22 is inactive compared to when the NOx reduction catalyst 22 is in an inactive state.
The amount of the reducing agent in the exhaust gas can be further increased. Therefore, since the NOx reduction catalyst 22 is in a high-temperature active state, the amount of the reducing agent is insufficient even when the reducing agent such as HC and CO in the exhaust gas is consumed by reacting with the oxygen in the exhaust gas. There is an advantage that the NOx in the exhaust gas can be effectively reduced and purified by the increased amount of the reducing agent in the third period TB without causing a situation in which the exhaust gas has become exhausted.

In the above-described embodiment, the NOx reduction catalyst 22 in which a catalytic metal such as platinum is supported on the zeolite which is a porous material such as the MFI zeolite is disposed in the exhaust passage 20, so that the oxygen-excessive atmosphere is obtained. In both the normal operation state and the inactive state where the temperature of the NOx reduction catalyst 22 is low, the reducing agent such as HC trapped in the pores of the zeolite is used to reduce the exhaust gas. There is an advantage that NOx can be reduced and purified effectively.

In the above-described embodiment, an example in which the present invention is applied to a direct injection type diesel engine in which fuel is directly injected into the combustion chamber 4 has been described. However, a lean burn operation in which an air-fuel mixture thinner than the stoichiometric air-fuel ratio is burned is performed. The present invention is also applicable to a direct injection gasoline engine that performs the following.

Further, instead of the above-described embodiment in which only the NOx reduction catalyst 22 is disposed in the exhaust passage 20, the NOx reduction catalyst 22 for purifying the exhaust gas by reducing NOx in the exhaust gas to N ₂ by a reducing agent, for example. N in the exhaust gas
A structure in which a NOx oxidation catalyst that purifies by oxidizing Ox to NO ₂ may be provided.

[0062]

As described above, the present invention relates to a combustion control means for controlling a combustion state of fuel so as to obtain a required output of an engine, and an oxygen excess having a high oxygen concentration and disposed in an exhaust passage of the engine. A NOx reduction catalyst that purifies at least NOx by reacting NOx and a reducing agent in an atmosphere;
In an exhaust gas purification apparatus for an engine, comprising: a reducing agent increasing means for increasing a reducing agent supplied to the NOx reducing catalyst, a catalyst temperature estimating means for estimating the temperature of the NOx reducing catalyst, wherein the catalyst temperature estimating means When the catalyst temperature estimated by the above is lower than the reference temperature, the reducing agent increasing means increases the amount of the reducing agent supplied to the NOx reduction catalyst over the first period set in advance, and sets the amount of the reducing agent to the preset value. Since the increase in the amount of the reducing agent is suppressed over the second period, even when the NOx reduction catalyst is in an inactive state due to a low temperature, the NOx in the exhaust gas is effectively reduced. There is an advantage that it can be purified.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an embodiment of an exhaust gas purification device for an engine according to the present invention.

FIG. 2 is a flowchart showing a first half of a control operation of the exhaust gas purification device.

FIG. 3 is a flowchart showing a latter half of the control operation of the exhaust gas purification device.

FIG. 4 is a time chart showing a state of control for increasing the amount of HC.

FIG. 5 is a graph showing the relationship between the NOx purification rate and temperature.

FIG. 6 is a time chart showing a correspondence relationship between a change state of the HC concentration and a change state of the NOx purification rate.

[Explanation of symbols]

 Reference Signs List 4 combustion chamber 5 fuel injection valve 20 exhaust passage 22 NOx reduction catalyst 36 combustion control means 37 catalyst temperature estimation means 38 reducing agent increasing means

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02D 41/04 330 F02D 41/34 H 41/34 45/00 312R 45/00 312 B01D 53/36 101B ( 72) Inventor Satoshi Ichikawa 3-1 Shinchi, Fuchu-cho, Aki-gun, Hiroshima F-term (reference) 3G084 AA01 BA00 BA05 BA13 BA15 BA20 CA02 DA10 EB09 FA00 FA08 FA10 FA11 FA20 FA27 FA28 FA29 FA33 FA38 3G091 AA02 AA10 AA11 AA12 AA17 AA18 AA24 AA28 AB02 AB03 AB05 BA03 BA14 BA32 CA13 CA18 CB02 CB03 CB07 DA01 DA02 DA03 DA05 DB06 DB10 DB13 EA00 EA01 EA03 EA05 EA06 EA07 EA16 EA17 EA21 EA30 EA31 EA33 GB01 FA04 GB06W GB09X GB10X GB17X HA10 HA36 HA37 HB03 HB05 HB06 3G301 HA02 HA04 JA25 LB04 LB11 MA18 NE01 NE23 PD12Z 4D048 AA06 AB02 AC02 BA11X BA30X BA33X BB02 DA01 DA02 DA10 DA13 4G069 AA03 BA07A BA07B BA13B BC71A BC71B BC75A BC75B CA03 CA08 CA13 ZA11A ZA11B

Claims (5)

[Claims] 1. A combustion control means for controlling a combustion state of a fuel so as to obtain a required output of an engine.
In the exhaust gas purifying apparatus for an engine comprising a NOx reduction catalyst for purifying at least NOx by reacting Ox and a reducing agent, and a reducing agent increasing means for increasing the reducing agent supplied to the NOx reducing catalyst, A catalyst temperature estimating means for estimating the temperature of the catalyst, wherein when the catalyst temperature estimated by the catalyst temperature estimating means is lower than the reference temperature, the reducing agent increasing means sets the catalyst over a first period set in advance. An exhaust gas purification device for an engine, wherein the amount of the reducing agent supplied to the NOx reduction catalyst is increased by increasing the amount of the reducing agent over a second period set in advance. 2. The exhaust gas purifying apparatus for an engine according to claim 1, wherein the reference temperature is set to an inactive temperature of the NOx reduction catalyst at which the NOx purification rate becomes less than a predetermined value. 3. The control device according to claim 1, wherein the reducing agent increasing means controls the fuel injection valve disposed in a combustion chamber of the engine to inject fuel at a predetermined time between an expansion stroke and an exhaust stroke.
3. The exhaust gas purifying apparatus for an engine according to claim 1, wherein the apparatus is configured to be executed for each predetermined cylinder over a period. 4. The method according to claim 1, wherein the reducing agent increasing means is configured to set a third time period longer than the first time period when the NOx reduction catalyst is in an active state and the engine is in a steady operation state.
The exhaust gas purification apparatus for an engine according to any one of claims 1 to 3, wherein the amount of the reducing agent supplied to the NOx reduction catalyst is increased over a period. 5. NO in which a catalyst metal is supported on zeolite
The exhaust gas purification device for an engine according to any one of claims 1 to 4, further comprising an x reduction catalyst.