JP2003035131A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize effective simultaneous reproduction of purifying means of an exhaust emission control device of an internal combustion engine provided with DPF(diesel particulate filter) and the NOx absorbent. SOLUTION: In simultaneous regeneration, the region determination is made on the basis of air quantity Qaexh in combustion residual gas and temperature TDPF of the DPF. When no DPF deterioration occurs, even after making exhaust air/fuel ratio rich by post injection (FTVC=0), regeneration is conducted by the post jet; while when DPF deterioration by the post-injection possibly occurring (FTVC=1) is taken into account, the post-injection quantity for DPF reproduction is read. By so doing, the required intake air quantity Qareq to make the exhaust air/fuel ratio rich is calculated (S26).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purification apparatus for removing particulate matter and nitrogen oxides from exhaust gas of an internal combustion engine such as a diesel engine, and more particularly to a regeneration technology for such an exhaust gas purification apparatus. .

[0002]

2. Description of the Related Art Particulate matter (hereinafter referred to as PM) from exhaust gas
As an exhaust gas purifying apparatus for an internal combustion engine, which is provided with a means for removing nitrogen oxides (hereinafter, NOx), there is one described below (see Japanese Patent Laid-Open No. 9-53442). A diesel engine according to a conventional technique includes an oxidation catalyst, a diesel particulate filter (hereinafter, DPF), and a NOx absorbent in the exhaust system in order from the upstream. Of these, the oxidation catalyst oxidizes unburned fuel (hydrocarbon) and carbon monoxide contained in the exhaust gas to render them harmless, and the DPF removes PM from the exhaust gas. Further, the NOx absorbent has a function of removing NOx from the exhaust gas, and absorbs NOx contained in the exhaust gas when the exhaust air-fuel ratio is a high air-fuel ratio indicating lean.

In such an exhaust emission control device, the DPF has a P
If M continues to be collected, it eventually becomes clogged and the exhaust pressure becomes excessive. Therefore, it is necessary to regularly remove the accumulated PM. To achieve this, fuel is injected during the exhaust stroke to supply hydrocarbons to the exhaust gas and the exhaust temperature is raised. As a result, the DPF is regenerated by promoting the reaction between nitrogen dioxide (hereinafter referred to as NO2) obtained by oxidizing NO in the exhaust gas in the oxidation catalyst and PM on the DPF.

Even if NOx is continuously absorbed by the NOx absorbent, the absorption capacity of the NOx absorbent reaches its limit, and
The inflowing NOx is discharged as it is. Therefore, it is necessary to remove the absorbed NOx here as well. Here, the NOx absorbent has a rich exhaust air-fuel ratio.
In such a state, it has a property of releasing absorbed NOx. The released NOx reacts with the hydrocarbons in the exhaust gas to be reduced and rendered harmless. Therefore, conventionally, fuel is injected during the exhaust stroke in order to periodically make the exhaust air-fuel ratio rich.

[0005]

According to such an exhaust emission control device, PM and NOx can be removed from the exhaust gas, and the accumulated PM and the like can be processed and regenerated if necessary. There are the following problems. That is, when there is a further demand for regeneration of the NOx absorbent during regeneration of the DPF, simply injecting additional fuel to make the exhaust air-fuel ratio rich will impair the performance of the oxidation catalyst. It can happen. This is because the excess oxygen that has not contributed to combustion and the fuel (hydrocarbon) additionally injected to regenerate the NOx absorbent react with the oxidation catalyst to generate heat. During regeneration of the DPF, the oxidation catalyst is heated to a high temperature by burning the fuel to promote the oxidation of NO2 and PM. Further, if heat is further generated, the temperature of the oxidation catalyst rises excessively and deteriorates depending on conditions. It will end up.

When the oxidation catalyst deteriorates, not only cannot it fulfill its essential role of purifying hydrocarbons and carbon monoxide, but also the oxidation reaction of NO becomes slow. If this happens, NO2 will not be sufficiently supplied to the DPF, so that PM will not be easily burned (oxidized) and will not be regenerated, and the exhaust pressure will become high, which may make engine operation difficult. Further, regarding the DPF, regardless of whether the DPF to be used has high heat resistance, a type using silicon carbide or the like having good collection efficiency is weak against heat, and therefore is excessively heated through an oxidation catalyst. If the generated exhaust gas flows in, it may deteriorate.

In order to facilitate combustion of accumulated PM, DP
There is a method of installing F supporting an oxidation catalyst.
In this case, when the fuel is further injected for the regeneration of the NOx absorbent during the regeneration of the DPF, the DPF will be excessively heated as described above. Excess oxygen that did not contribute to combustion and fuel injected for regeneration of the NOx absorbent are D
This is because it reacts on PF. Since the DPF of the type using silicon carbide or the like is weak against heat, excessive heating will significantly deteriorate its performance.

In order to avoid deterioration of the oxidation catalyst and DPF when there is a further demand for regeneration of the NOx absorbent during regeneration of the DPF as described above, the air-fuel ratio of the exhaust gas flowing into the NOx absorbent is made rich. Therefore, it is possible to reduce the combustion air-fuel ratio (air-fuel ratio of the air-fuel mixture formed in the combustion chamber). According to this method, the smoke performance tends to deteriorate as compared with the case where fuel is injected during the exhaust stroke, but DP
Since F is provided, it is not a problem.

However, when the combustion air-fuel ratio becomes rich when the DPF is regenerated, the exhaust gas flowing into the oxidation catalyst does not contain oxygen, so that the oxidation reaction does not occur. Therefore, the amount of heat required to heat the DPF cannot be obtained,
There is a problem that the DPF is not regenerated. As a result, when the secondary air or the like is not supplied, it can be said that it is suitable for regeneration of the DPF that the combustion air-fuel ratio is made lean and oxygen is left and additional fuel is injected after combustion.

The present invention has been made in view of the above circumstances, and an object thereof is to include means for collecting PM contained in exhaust gas and means for absorbing NOx contained in exhaust gas. In the exhaust gas purification device for an internal combustion engine, these means are effectively regenerated simultaneously. The present invention also aims to efficiently achieve simultaneous regeneration of these means.

It is another object of the present invention to realize such simultaneous reproduction with a simple structure.

[0012]

Therefore, in the invention described in claim 1, the exhaust gas purifying apparatus for an internal combustion engine has the following (a):
(E) means are included. That is, (a) particle collecting means for collecting the particulate matter contained in the exhaust gas,
(B) NO contained in the exhaust gas provided downstream of the particle collecting means and included in the exhaust gas when the exhaust air-fuel ratio is a high air-fuel ratio indicating lean
NOx absorption means that absorbs x while releasing and reducing the absorbed NOx according to the decrease in the exhaust air-fuel ratio, (c) a specific component that is provided upstream of the particle collection means or itself and that is included in the exhaust gas. Based on the judgment results by the oxidation time oxidizing means, (d) the particle collecting means and the NOx absorbing means, respectively, and the (e) regeneration time judging means. And N
This is a simultaneous regeneration means for supplying hydrocarbons to the exhaust gas and reducing the exhaust air-fuel ratio to a low air-fuel ratio indicating a rich concentration based on the supply amount when the Ox absorbing means is regenerated together.

According to the second aspect of the invention, the feed amount of the hydrocarbon is adjusted based on the temperature of the particle collecting means. In the third aspect of the invention, the amount of hydrocarbon supply is adjusted so that the particle collecting means has a predetermined temperature suitable for its regeneration. In the invention described in claim 4, the lower the temperature of the particle collecting means, the more the amount of hydrocarbons supplied.

According to the fifth aspect of the present invention, the hydrocarbon feed rate is adjusted based on the deviation of the temperature of the particle collecting means from the predetermined temperature. In the invention according to claim 6, when the deviation exceeds a predetermined value, the supply amount of hydrocarbons is adjusted so that the deviation falls within the predetermined value or less. In the invention according to claim 7, the predetermined temperature is set to be equal to or higher than the lower limit temperature for regenerating the particle collecting means.

In the invention according to claim 8, the predetermined temperature is set to be equal to or lower than the deterioration limit temperature of the particle collecting means. In the invention according to claim 9, when the supply amount of hydrocarbons is adjusted to keep the deviation within the predetermined value, the predetermined temperature is set to an intermediate temperature between the lower limit regenerable temperature and the deterioration limit temperature of the particle collecting means. And the predetermined value is set to a value that is half the difference between the lower limit temperature and the deterioration limit temperature.

According to the tenth aspect of the present invention, in the internal combustion engine having the fuel injection valve facing the cylinder, the fuel injection valve is driven at a predetermined timing from the expansion stroke to the exhaust stroke,
Supply hydrocarbons. According to the invention described in claim 11, in the internal combustion engine including the intake throttle valve, the intake air amount is controlled to reduce the exhaust air-fuel ratio.

According to the twelfth aspect of the present invention, when the particle collecting means and the NOx absorbing means are both regenerated,
When the particle collecting means is in a predetermined low temperature state and the maximum air amount contained in the combustion residual gas is below a predetermined amount, the intake air amount is set to the maximum and the hydrocarbon supply amount is increased. Reduce the exhaust air-fuel ratio. The "combustion residual gas" refers to a gas produced by combustion in a cylinder, and when a hydrocarbon for regeneration is supplied after combustion, the exhaust gas contains the combustion residual gas and this hydrocarbon. Is formed. Further, the "maximum air amount" is the amount of air contained in the combustion residual gas obtained without operating a means (for example, EGR or intake throttle) for reducing the oxygen concentration of the combustion residual gas in a certain operating state. To tell.

According to the invention of claim 13,
(A) Particle trapping means for trapping particulate matter contained in the exhaust gas, (b) included in the exhaust gas when the exhaust air-fuel ratio is a high air-fuel ratio indicating lean, provided downstream of the particle trapping means. NOx absorption means for absorbing NOx stored therein and releasing and reducing the absorbed NOx according to the decrease in the exhaust air-fuel ratio,
(C) An oxidizing means which is provided upstream of the particle collecting means or itself and which oxidizes a specific component contained in the exhaust gas,
And (d) In the exhaust gas purifying apparatus for an internal combustion engine, comprising the regeneration timing determining means for determining that the particle trapping means and the NOx absorbing means are in the regeneration timing, the both means are based on the determination result by the regeneration timing determining means. The hydrocarbon is supplied to the exhaust gas when the gas is regenerated together, and the minimum amount of oxygen for reaching the temperature necessary for the particle collection means to regenerate is supplied to the particle collection means based on the supply amount. As described above, the exhaust air-fuel ratio is reduced to the low air-fuel ratio indicating the rich concentration.

[0019]

According to the inventions of claims 1 and 13, when the particle trapping means and the NOx absorbing means are both regenerated at the same time, the simultaneous regeneration means first removes the hydrocarbons supplied to the exhaust gas. The quantity is determined. Then, the exhaust air-fuel ratio is reduced to rich based on this supply amount. Therefore, the exhaust gas flowing into the oxidizing means can contain only oxygen in an amount smaller than that required to burn the supplied hydrocarbons. Therefore, since excessive heat generation does not occur in the oxidizing means and the particle collecting means is not excessively heated, deterioration of these means can be prevented. Then, since the particle collecting means is heated within an appropriate range and the remaining hydrocarbons are supplied to the NOx absorbing means, these can be effectively regenerated simultaneously.

According to the second and third aspects of the invention, it is possible to supply the optimum amount of hydrocarbons for regeneration based on the temperature of the particle collecting means. Then, the exhaust air-fuel ratio is reduced based on this supply amount. Therefore, for example, when the amount of hydrocarbons is increased during the simultaneous regeneration, the amount of air contained in the exhaust gas is increased corresponding to the increased amount. Therefore, the amount of heat generated by the oxidizing means can be controlled and the temperature of the particle collecting means can be adjusted. Since most of the oxygen contained in the exhaust gas is consumed in the oxidizing means, the NOx absorbing means can be efficiently regenerated.

According to the fourth aspect of the invention, the lower the temperature of the particle collecting means, the more the amount of hydrocarbons supplied and the larger the amount of heat generated in the oxidizing means. The means can be quickly heated to the proper temperature. On the other hand, when the temperature of the particle collecting means becomes high, the amount of hydrocarbons supplied is reduced and the amount of heat generated by the oxidizing means becomes small, so that deterioration of the particle collecting means due to excessive heating can be prevented.

According to the invention of claim 5, the temperature of the particle collecting means can be adjusted to a predetermined temperature. In particular, by making the predetermined temperature not lower than the reproducible lower limit temperature of the particle collecting means (claim 7), it is possible to ensure that the means is regenerated, and the predetermined temperature is not higher than the deterioration limit temperature of the particle collecting means. By doing so (claim 8), deterioration of this means can be prevented. Here, the lower limit temperature and the deterioration limit temperature of the particle collecting means differ depending on the system to which the present invention is applied, so it is desirable to set them optimally by experiments or the like. Regarding the regenerable temperature, for example, the combination of the oxidation catalyst and DPF described in the above-mentioned prior art is used as the oxidizing means and the particle collecting means, and
When a system (CRF) that oxidizes PM on PF using NO2 generated by an oxidation catalyst as an oxidant,
The DPF can be regenerated at a temperature of 300 ° C or lower. Further, in a system in which an oxidation catalyst is supported on the DPF and oxygen contained in the exhaust gas reacts with PM on the DPF,
Temperatures above 00 ° C are required.

According to the sixth aspect of the present invention, when adjusting the supply amount of hydrocarbons, a buffer region for adjusting the temperature of the particle collecting means is formed near a predetermined temperature, so that stable adjustment can be performed. You can do it. According to the invention of claim 9, when the particle collecting means exceeds the deterioration limit temperature, the supply amount of hydrocarbons is reduced to the deterioration temperature or lower, and when the temperature is lower than the regenerable temperature, This supply amount can be increased to adjust the temperature to a reproducible temperature.

According to the tenth aspect of the present invention, the fuel injection valve for supplying fuel to the engine also covers the hydrocarbon for regeneration, thereby eliminating the need for adding a new device for regeneration. , Control can be simplified. According to the invention of claim 11, means for consuming or separating oxygen contained in the combustion residual gas by controlling the intake air amount to reduce the exhaust air-fuel ratio, and a secondary air. The amount of oxygen supplied to the oxidizing means can be adjusted without providing a supply pump or the like in the exhaust system.

According to the twelfth aspect of the invention, in the simultaneous regeneration, the particle collecting means is in a predetermined low temperature state, and
When the maximum amount of air contained in the combustion residual gas is less than or equal to a predetermined amount, the intake air amount is maximized and the exhaust air-fuel ratio is reduced by increasing the supply amount of hydrocarbons without affecting drivability. Simultaneous playback is possible. Under such conditions, the temperature at which the particle collecting means is heated to a certain extent does not reach the deterioration limit temperature, and since the combustion residual gas contains relatively little oxygen, there is a limit to heat generation in the oxidizing means. Therefore, it can be determined here that the oxidizing means and the particle collecting means are not deteriorated even if the amount of oxygen supplied to the oxidizing means during the simultaneous regeneration is not particularly limited. The exhaust air-fuel ratio can be reduced by increasing the EGR amount or closing the intake throttle valve, but in these cases, the engine generated torque may fluctuate.

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of a diesel engine (hereinafter, engine) 1 including an exhaust gas purification device for an internal combustion engine according to an embodiment of the present invention. A piston 3 is inserted into a cylinder block 2 of the engine 1, and the piston 3 is connected to a crankshaft 5 via a connecting rod (shown by a chain double-dashed line) 4. A cylinder head 6 is fixed on the cylinder block 2, and a combustion chamber 7 is formed between the piston upper surface and the head lower surface.

The intake passage 8 communicates with one side of the combustion chamber 7, and an intake valve 9 is installed at the port. Intake valve 9
Are driven by the intake cam 10. In the intake passage 8,
An air cleaner (not shown), an air flow meter 11, an intake throttle valve (butterfly valve) 12, and a surge tank 13 are installed from upstream. The air flow meter 11 outputs a detection signal corresponding to the intake air amount to an electronic control unit (hereinafter, ECU) 31. The intake throttle valve 12 is an electromagnetic valve and is driven by the drive device 14 based on a control signal from the ECU 31 to control the intake air amount. After passing through the surge tank 13, the intake air is distributed to each cylinder in the manifold portion and is introduced into the cylinder under the control of the intake valve 9.

A fuel injection valve (hereinafter referred to as an injector) 15 is installed facing the upper center of the combustion chamber 7. The injector 15 operates based on a control signal from the ECU 31, and directly injects a predetermined amount of fuel into the cylinder at a predetermined time.
Detection signals from the accelerator sensor 16 and the crank angle sensor 17 are input to the ECU 31, and the ECU 31 sets the injection amount and the injection timing based on the control information. The piston 3 receives the work due to the combustion, and the crankshaft 5 is driven via the connecting rod 4.

The combustion residual gas is released into the atmosphere through the exhaust passage 18. An exhaust valve 19 is installed at the port of the exhaust passage 18. The exhaust valve 19 is driven by an exhaust cam 20. Exhaust passage 18 and surge tank 13 are EGR
A communication valve (hereinafter, referred to as E
GR valve) 22 is installed. The EGR valve 22 is the ECU
The exhaust gas is opened / closed based on a control signal from 31, and when the valve is opened, the exhaust gas whose flow rate is controlled appropriately according to the opening is recirculated to the intake system. EGR suppresses the generation of NOx.

Further, the exhaust passage 18 has an EGR passage 21.
Oxidation catalysts 23, D
The PF 24 and the NOx absorbent 25 are installed. The oxidation catalyst 23 mainly oxidizes unburned fuel (hydrocarbon) and carbon monoxide contained in the exhaust gas. The DPF 24 collects PM floating in the exhaust gas. NOx absorbent 25
Is the N contained in the exhaust gas when the exhaust air-fuel ratio is lean.
N that absorbed Ox and absorbed when the exhaust air-fuel ratio was rich
It releases and reduces Ox. Here, the oxidation catalyst 23 is the oxidizing means according to the present invention, the DPF 24 is the particle collecting means,
The NOx absorbent 25 constitutes each NOx absorbing means. Here, the temperature sensor 26 is installed in the DPF 24,
The detection signal is input to the ECU 31.

The control executed by the ECU 31 will be described below. First, the configuration of this control system will be described with reference to the block diagram shown in FIG. DPF regeneration permission section A
Estimates the amount of PM accumulated in the DPF 24,
It is determined whether or not the reproduction of F24 is necessary. During DPF regeneration, the degree of progress of regeneration is confirmed to determine whether or not regeneration is completed. The determination result of the permission unit A is reflected in the post injection amount calculation unit B.

The post-injection amount calculation unit B, based on the detection signal from the temperature sensor 26 during DPF regeneration,
A post injection amount for detecting the temperature of F24 and controlling the DPF 24 in a predetermined temperature range (in addition to injection for combustion,
The injection amount when the injector 15 additionally injects at a predetermined timing from the expansion stroke to the exhaust stroke is calculated. The calculation result is output to the injector 15 and reflected in the intake air amount calculation unit D.

The injector 15 injects for combustion in the compression stroke, and also injects at a predetermined time from the expansion stroke to the exhaust stroke based on the calculation result in the post injection amount calculation unit B. The NOx absorbent regeneration permission section C
The amount of NOx absorbed in the NOx absorbent 25 is estimated to determine whether or not the absorbent 25 needs to be regenerated. Also,
At the time of regeneration of the absorbent, the progress of the regeneration is confirmed and it is judged whether or not the regeneration is completed. The determination result of the permission unit C is
This is reflected in the intake air amount calculation unit D.

The intake air amount calculation unit D includes a DPF 24 and an N
When both the regeneration of the Ox absorbent 25 is permitted, the intake air amount for making the total exhaust air-fuel ratio including the fuel for the post injection a predetermined air-fuel ratio is calculated. The calculation result of the calculation unit D is output to the intake throttle valve 12 (driving device 14). The intake throttle valve 12 is driven based on the calculation result in the intake air amount calculation unit D, and adjusts the opening area of the intake passage 8.

Next, the control in each of the control blocks A to D will be described in detail with reference to the flowchart. Figure 3
4 is a flowchart of control in the DPF regeneration permitting section A. In S (step) 1, it is determined by the DPF regeneration permission flag FPM whether or not regeneration of the DPF 24 is permitted. If it is determined to be permitted, S7
If it is determined that the license is not permitted, the process proceeds to S2.

At S2, the accelerator opening AVO is calculated based on the output values of the accelerator sensor 16 and the crank angle sensor 17.
And the engine speed Ne. In S3, the PM deposition amount PM per unit time (execution cycle of this routine) is read with reference to the map allocated according to the accelerator opening AVO and the engine speed Ne.

Then, the PM read in S4 is integrated,
The total PM accumulation amount ΣPM in the DPF 24 is calculated. S5
Then, it is determined whether the total PM accumulation amount ΣPM exceeds a predetermined value SLPM indicating the limit accumulation amount of PM of the DPF 24. If it is determined that the time has not been exceeded, it is determined that the time to regenerate the DPF 24 has not yet been reached, and the present flow ends. On the other hand, if it is determined that the value has been exceeded, D
When it is determined that the time to regenerate the PF 24 has been reached, the process proceeds to S6.

In step S6, 1 is assigned to the DPF regeneration permission flag FPM to permit regeneration of the DPF 24, and the total PM accumulation amount ΣPM is reset to prepare for calculation of ΣPM after regeneration is stopped. To reset. This timer TMPM is for grasping the elapsed time from the start of reproduction of the DPF 24. D in S1
If reproduction of the PF 24 is permitted (FPM = 1), S
7, the DPF regeneration time counting timer TMPM is increased by the predetermined interval DLTPM. This interval DLTP
M is 1 if the execution cycle of this routine is 1 second,
When this routine is executed at unequal intervals, the elapsed time from the previous execution is used.

In S8, it is determined whether or not the DPF regeneration time counting timer TMPM has exceeded a predetermined value SLTMPM indicating regeneration completion. If it is determined that the number has been exceeded, S9
Go to step D and substitute 0 in the DPF regeneration permission flag FPM
After stopping the reproduction of the PF 24, this routine ends.
On the other hand, if it is determined that the predetermined value SLTMPM has not yet been exceeded, this routine is ended and the regeneration of the DPF 24 is continued.

As described above, the present embodiment has a structure in which the regeneration stop of the DPF 24 is determined by the elapsed time from the regeneration start. For more accuracy, DPF24 during regeneration
It is also possible to estimate and correct the amount of PM that has flowed into the. Also, D
Since the regeneration of the PF24 depends on the temperature of the DPF, D
It is also preferable to make the determination based on the elapsed time from when the PF has reached a predetermined temperature or higher. As another method for determining the regeneration stop, it is conceivable to determine the regeneration completion when the differential pressure across the DPF 24 becomes equal to or lower than a predetermined pressure determined according to the inflow gas amount.

FIG. 4 is a flow chart of control in the NOx absorbent regeneration permitting section C. The structure of this routine is
It is basically the same as that shown in FIG. This routine will be briefly described as follows. If the NOx absorbent regeneration permission flag FNO determines in S11 that regeneration of the NOx absorbent 25 is permitted, the process proceeds to S12, in which the accelerator opening AVO and the engine speed Ne are read. Then, in S13, the NOx absorption amount NO per unit time is read by referring to the map allocated according to AVO and Ne. The NO read in S14 is integrated to obtain the total NOx absorption amount ΣNO. Furthermore, the total NO in S15
If it is determined that the x absorption amount ΣNO has exceeded the predetermined value SLNO, and if it is determined that it has not exceeded the predetermined value SLNO, then this flow is ended as it is, while if it is determined that it has exceeded, the time at which the NOx absorbent 25 should be regenerated When it is determined that the value has reached, the process proceeds to S16. In S16, 1 is substituted into the NOx absorbent regeneration permission flag FNO to permit regeneration of the NOx absorbent 25, and the total NO
N for resetting the x absorption amount ΣNO and preparing the calculation of ΣNO after the regeneration is stopped, in order to grasp the elapsed time from the regeneration start
The timer TMNO for counting the Ox absorbent regeneration time is reset.

On the other hand, if the regeneration of the NOx absorbent 25 is permitted in S11 (FNO = 1), the routine proceeds to S17, where NO
x Absorbent regeneration time counting timer TMNO is increased by a predetermined interval DLTNO. This interval DLTNO is set to 0.1 if the execution cycle of this routine is 0.1 seconds,
When this routine is executed at unequal intervals, the elapsed time from the previous execution is used. Then, in S18, the timer TMN
It is determined whether or not O has exceeded the predetermined value SLTMNO. If it is determined that O has exceeded the predetermined value SLTMNO, 0 is substituted for the NOx absorbent regeneration permission flag FNO and the regeneration of the NOx absorbent 25 is stopped. When it is determined that the predetermined value SLTMNO has not been exceeded, this routine is terminated and NO.
x Regeneration of absorbent 25 is continued.

FIG. 5 is a flow chart of control in the intake air amount calculation unit D. In S21, it is determined by the NOx absorbent regeneration permission flag FNO whether or not the regeneration of the NOx absorbent 25 is permitted. If it is determined that the post-injection amount is not permitted, the process proceeds to S27, and the flag FTVC used for the control in the post-injection amount calculation unit B, which will be described later, is set to 1
Is substituted. Then, in S28, the required intake air amount Qare
The q is set to the maximum value MAX, and this routine is finished.
That is, while the regeneration of the NOx absorbent 25 is not permitted, the intake throttle valve 12 is fully opened to maximize the intake air amount. On the other hand, when it is determined that the regeneration of the NOx absorbent 25 is permitted, the process proceeds to S22.

At S22, the temperature T of the DPF 25 is calculated based on the output values of the temperature sensor 26 and the air flow meter 11.
The DPF and the intake air amount Qa are read, and the weight flow rate of the fuel injected for combustion (hereinafter, the combustion fuel amount)
Read Qf. The combustion fuel amount Qf is read from, for example, a map allocated in correspondence with the accelerator opening AVO and the engine speed Ne.

In S23, the amount of air contained in the combustion residual gas (the amount of air sucked into the cylinder is exhausted without contributing to combustion) according to the following equation (1) based on the intake air amount Qa and the combustion fuel amount Qf. It refers to the amount of air, and hereinafter, the amount of air in the combustion residual gas) Qaexh is calculated. C1 is a constant and corresponds to the theoretical air-fuel ratio. Qaexh = Qa−Qf × C1 (1) In S24, the region to which the current operating state belongs is determined by referring to the map allocated in correspondence with the DPF temperature TDPF and the combustion residual gas air amount Qaexh. Temperature TD
In the region where the PF is high and the air amount Qaexh is high,
Substitute 1 for the flag FTVC and proceed to S25.

In S25, the post injection amount Qp calculated by the post injection amount calculating section B is read. And S
At 26, the required intake air amount Qareq is calculated by the following equation (2) based on the combustion fuel amount Qf and the post injection amount Qp. Note that C2 is a constant, and corresponds to the exhaust air-fuel ratio (set to a low air-fuel ratio that indicates richness, about 12.5 for gasoline) necessary for regeneration of the NOx absorbent 25.

Qareq = (Qf + Qp) × C2 (2) During regeneration of the NOx absorbent 25 (particularly, simultaneous regeneration with the DPF 24), the DPF temperature TDPF is high and the air amount Qaexh in the combustion residual gas is also large. The reason why the exhaust air-fuel ratio is reduced by adjusting the intake air amount in this manner is as follows.

That is, with the intake air amount unchanged,
In the case of only increasing the post injection amount Qp, the oxidation catalyst 2
This is because the amount of oxygen supplied to 3 is too large and the oxidation reaction is performed excessively, which may cause the DPF 24 to exceed the deterioration limit temperature. Therefore, the intake air amount is reduced to reduce the exhaust air-fuel ratio, and the air-fuel ratio of the exhaust gas flowing into the NOx absorbent 25 is adjusted to be rich.

Here, the exhaust air-fuel ratio is made rich by the above method, but the intake air is burned at the stoichiometric air-fuel ratio by Qf and Qp, that is, Qareq = (Qf + Qp) ×
Alternatively, a method may be adopted in which C1 is set and the fuel necessary for enriching the exhaust air-fuel ratio is further supplied by post injection.
Even with such a method, the effects of the present invention can be sufficiently obtained.

Then, the intake throttle valve 12 is driven so as to match the actual intake air amount with the required intake air amount Qareq calculated in S26. As a result, air having a weight flow rate Qareq is sucked into the cylinder, and the injected fuel (weight flow rate Qf) burns. The combustion residual gas includes a part of the intake air remaining without contributing to combustion. Then, post injection is performed at a predetermined time from the expansion stroke to the exhaust stroke,
Exhaust gas containing hydrocarbons for the simultaneous regeneration of the DPF 24 and the NOx absorbent 25 is formed. Since the air-fuel ratio of the exhaust gas is rich, the amount of oxygen contained in the exhaust gas is less than the amount required for the hydrocarbons to completely burn. Therefore, in the oxidation catalyst 23, even if all of this oxygen is consumed, some hydrocarbons will remain without burning. The remaining hydrocarbons pass through the DPF 24 and are supplied to the NOx absorbent 25. This gives D
Since the PF 24 is heated to a reproducible temperature and the exhaust gas flowing into the NOx absorbent 25 becomes rich, both can be effectively regenerated at the same time.

When it is determined in S24 that the DPF temperature TDPF is low and the combustion residual gas air amount Qaexh is also small, 0 is assigned to the flag FTVC and S2 is set.
Go to 8. Then, in S28, the required intake air amount Qareq
Is set to the maximum value MAX, the present routine is ended. Thus, in the regeneration of the NOx absorbent 25 (simultaneous regeneration with the DPF 24), in the region where the DPF temperature TDPF is low and the combustion residual gas air amount Qaexh is small, the intake air amount is maximized and the post The exhaust air-fuel ratio is reduced by increasing the injection amount. Since the DPF 24 has a low temperature, there is a sufficient margin to reach the deterioration limit temperature, and the amount of oxygen supplied to the oxidation catalyst 23 is relatively small. Therefore, even if the post injection amount is increased, the DPF 24 is excessively heated. This is because it can be assumed that there is no risk of deterioration.

As described above, in the present embodiment, in the intake air amount calculation unit D, when the NOx absorbent 25 can be regenerated by post injection only (FTVC = 0), the post injection only is given priority. It was The reason is as follows. That is, in the method of reducing the intake air amount by closing the intake throttle valve 12, a pump loss may occur in the engine and the output may decrease even with the same accelerator opening AVO. With the recent development of control technology, it has become possible to correct the pump loss amount, but it is not always possible to eliminate the torque fluctuation felt by the driver. Therefore, also in the regeneration of the NOx absorbent 25, it is advantageous to use post-injection in which torque fluctuation is unlikely to occur as much as possible.

FIG. 6 is a flow chart of control in the post injection amount calculation section B. In S31, the value of the flag FTVC set by the intake air amount calculation unit D is determined. FT
When it is determined that VC = 0, the process proceeds to S40, and FTVC =
If it is determined to be 1, the process proceeds to S32. When FTVC = 0, the regeneration of the NOx absorbent 25 is permitted, and it is presumed that the DPF 24 is not likely to deteriorate even if the regeneration is performed only by post injection. In S40, the intake air amount Qa and the combustion fuel amount Qf are read. Here, since the intake throttle valve 12 is fully opened, Qa has the maximum value. Then, in S41, based on Qa and Qf, the post injection amount Qp that makes the exhaust air-fuel ratio rich is calculated by the following equation (3).

Qp = (Qa−Qf × C1) / C2 (3) That is, when regeneration of the NOx absorbent 25 is permitted and the DPF 24 is not likely to deteriorate, the DPF
The NOx absorbent 25 is regenerated by making the exhaust air-fuel ratio rich regardless of whether or not regeneration of 24 is permitted and the temperature. At this time,
Some of the hydrocarbons supplied by post injection are DPF2
The remaining hydrocarbons consumed for regeneration of No. 4 are supplied to the NOx absorbent 25 and contribute to regeneration.

On the other hand, in the case of FTVC = 1, the regeneration of the NOx absorbent 25 is not permitted, or even if the regeneration is permitted, the DPF 24 may be deteriorated if only post injection is used. The exhaust air-fuel ratio is made rich by also adjusting. Subsequent S32 to 39 and 4
In No. 2, the post injection amount Qp is only set, and the control for making the exhaust air-fuel ratio rich is not performed. However, NO
When the regeneration of the x-absorbent 25 is permitted, the exhaust air-fuel ratio is made rich in S26 described above, so the regeneration of the NOx absorbent 25 is simultaneously performed.

At S32, the DPF regeneration permission flag FPM
Thus, it is determined whether the reproduction of the DPF 24 is permitted. If it is determined that the post-injection amount Qp is not permitted, the process proceeds to S42, the post injection amount Qp is set to 0, and then the present routine ends. On the other hand, when it is determined that the regeneration of the DPF 24 is permitted, the process proceeds to S33, the DPF temperature TDPF is read, and the post injection amount Qp is set based on the TDPF in the subsequent steps. The set Qp is read in S25 of FIG. 5 and used to calculate the required intake air amount Qareq.

At S34, the target value TTGT of the DPF temperature is
And the difference between the current DPF temperature TDPF and TDLT (= TT
GT-TDPF) is calculated. In S35, the temperature difference TD
It is determined whether LT is within a proper range (| TDLT | <TSL) (TSL is a threshold temperature indicating a proper range for regenerating the DPF 24). If it is determined to be within the proper range, this routine is ended as it is, and the current post injection amount Qp is maintained. On the other hand, if it is determined that it is not within the proper range, the process proceeds to S36.

In S36, the post injection amount correction amount Qdlt is read based on the temperature difference TDLT. Correction amount Qdt
It is preferable to set l so that it becomes larger as the absolute value of TDLT becomes larger. In S37, the correction amount Qdlt is added to the current post injection amount Qp. When the temperature difference TDLT has a positive value and the DPF temperature TDPF is lower than the target temperature TTGT, Qdlt has a positive value, so the post injection amount Qp is increased. On the other hand, when TDTL has a negative value, Qdlt has a negative value, and therefore the post injection amount Qp
Is reduced. In this way, the TDPF is controlled so as to converge to TTGT.

Here, the target temperature TTGT is the DPF 24.
Renewable temperature (depending on the system, for example,
300 ° C (= minimum reproducible temperature) or higher, and
The temperature is set to a temperature sufficiently lower than the deterioration limit temperature of the DPF 24 (which varies depending on the system, for example, 1000 ° C.). For example, it is desirable to set TTGT to an intermediate value between the reproducible lower limit temperature and the deterioration limit temperature, and to set TSL to a value that is half the difference between these temperatures. Since the lower the reproducible temperature, the higher the regeneration efficiency, it is expected that the regenerable temperature will further decrease in the future.

When it is determined in S38 that the post injection amount Qp is larger than the predetermined value QpMAX indicating the operation limit of the injector 15, Qp is set to Qp in S39.
By substituting MAX, the post injection amount Qp is limited to QpMAX or less. Note that a general method such as PID control may be adopted to calculate the correction amount Qdlt. Further, in the above example, in the post injection amount calculation unit B (flowchart in FIG. 6), Qp becomes 0 when regeneration of the DPF is not permitted (S42). Therefore, the initial value of the post injection amount Qp is 0 when the regeneration is next permitted. In order to speed up the convergence to the target temperature TTGT, it is preferable to use a map in which an initial value is assigned according to the operating state (for example, torque and engine speed).

In the present embodiment, the "reproduction timing determining means" according to the present invention is the steps S21 and 32 of the flow charts shown in FIGS. 5 and 6, and the "simultaneous reproducing means" is the steps S24-28 of both flowcharts. Excluding 27), 37 and 41
Correspond to each. In the above, the combination of the oxidation catalyst 23 and the DPF 24 is used as the oxidation means and the particle collection means, and the oxidation catalyst 23 is arranged upstream of the DPF 24 (C
RF). The present invention is not limited to such a configuration,
A type in which a noble metal having an oxidizing ability is supported on the DPF as the oxidizing means may be used regardless of the upstream oxidation catalyst.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a diesel engine including an exhaust gas purification device for an internal combustion engine according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a control system of the exhaust emission control device of the above.

FIG. 3 is a control flowchart of a DPF regeneration permission unit.

FIG. 4 is a control flowchart of a NOx absorbent regeneration permission unit.

FIG. 5 is a control flowchart of an intake air amount calculation unit.

FIG. 6 is a control flowchart of a post injection amount calculation unit.

[Description of Reference Signs] 1 ... Engine 2 ... Cylinder block 3 ... Piston 6 ... Cylinder head 7 ... Combustion chamber 8 ... Intake passage 9 ... Intake valve 12 ... Intake throttle valve 13 ... Surge tank 14 ... Drive device 15 ... Injector 16 ... Accelerator Sensor 17 ... Crank angle sensor 18 ... Exhaust passage 19 ... Exhaust valve 21 ... EGR passage 22 ... EGR valve 23 ... Oxidation catalyst 24 ... DPF (diesel particulate filter) 25 ... NOx absorbent 26 ... Temperature sensor 31 ... ECU ( Electronic control unit)

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) B01D 46/42 B01D 46/42 B 4D048 53/86 F01N 3/08 A 4D058 53/94 B F01N 3/08 3/20 E 3/24 E 3/20 3/28 301E 3/24 3/36 B 3/28 301 F02D 9/02 Q 3/36 351M F02D 9/02 41/38 B 351 43/00 301H 41 / 38 301K 43/00 301 301T 301W 45/00 314Z B01D 53/36 103B 45/00 314 103C K F term (reference) 3G065 AA01 CA12 DA07 FA03 FA06 GA00 GA05 GA08 GA10 GA46 HA06 JA04 JA09 JA11 KA02 3G084 A15 BA24 BA05 BA05 BA DA10 DA19 EB12 FA02 FA07 FA10 FA27 FA33 FA38 3G090 AA01 BA02 CA01 CA02 CA04 CB02 CB04 CB21 DA13 DA15 DA18 EA02 EA06 3G091 AA02 AA11 AA18 AB02 AB06 AB13 BA04 BA08 BA11 BA14 BA27 BA28 BA32 BA33 BA34 CA02 CA18 CA22 CB02 CB03 CB07 DA01 DA02 DC01 EA05 EA07 EA14 EA22 EA37 FB01 FB07 FC07 HA10 HA19 HA23 HA38 HB05 3G301 HA02 HA13 JA21 JA24 JA25 PE01 NE12Z01 PE12 PE01 PE01 NE12Z01 ND02 PA12 NE01 AZ02 AA06 AA14 AB01 AB02 AB07 AC02 BD03 CC32 CC47 CD05 CD08 DA01 DA02 DA03 DA10 DA13 DA20 EA04 4D058 MA41 MA43 MA52 PA01 PA14 SA08 TA02 TA06

Claims (13)

[Claims] 1. A particle trapping means for trapping particulate matter contained in exhaust gas, and NOx contained in the exhaust gas provided downstream of the means, when the exhaust air-fuel ratio is a high air-fuel ratio indicating lean. NOx absorbing means for releasing and reducing the absorbed NOx according to a decrease in the exhaust air-fuel ratio, and upstream of the particle collecting means or provided itself.
An oxidizing unit that oxidizes a specific component contained in the exhaust gas, a regeneration timing determining unit that determines whether the particle collecting unit and the NOx absorbing unit are in the regeneration period, and both units based on the determination result by the unit. And a simultaneous regeneration means for reducing the air-fuel ratio of the exhaust gas to a low air-fuel ratio showing an excessive concentration based on the supply amount, when regenerating both of them. Exhaust gas purification device for internal combustion engine. 2. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the simultaneous regenerating means adjusts the supply amount of hydrocarbons based on the temperature of the particle collecting means. 3. The internal combustion engine according to claim 1, wherein the simultaneous regenerating means adjusts the amount of hydrocarbons supplied so that the particle collecting means has a predetermined temperature suitable for regeneration thereof. Exhaust purification device. 4. The exhaust gas purifying apparatus for an internal combustion engine according to claim 2, wherein the simultaneous regenerating unit increases the amount of hydrocarbon supplied as the temperature of the particle collecting unit decreases. 5. The exhaust gas of an internal combustion engine according to claim 3, wherein the simultaneous regenerating means adjusts the feed amount of hydrocarbons based on the deviation of the temperature of the particle collecting means from the predetermined temperature. Purification device. 6. The simultaneous reproducing means, when the deviation exceeds a predetermined value, keeps the deviation within the predetermined value.
6. The supply amount of hydrocarbons is adjusted.
An exhaust emission control device for an internal combustion engine as set forth in. 7. The method according to claim 3, wherein the predetermined temperature is equal to or higher than the lower limit of reproducible temperature of the particle collecting means.
Or the exhaust emission control device for an internal combustion engine according to item 6. 8. The predetermined temperature is equal to or lower than a deterioration limit temperature of the particle collecting means.
7. An exhaust emission control device for an internal combustion engine according to any one of 7. 9. The predetermined temperature is set to an intermediate temperature between the lower limit regenerable temperature and the deterioration limit temperature when the simultaneous regeneration means adjusts the feed amount of hydrocarbons to keep the deviation within the predetermined value. At the same time, the predetermined value is set to a value that is half of the difference between the lower limit temperature for regeneration and the lower limit temperature for deterioration, and the exhaust emission control device for an internal combustion engine according to claim 8. 10. An internal combustion engine having a fuel injection valve facing a cylinder, wherein the simultaneous regeneration means drives the fuel injection valve at a predetermined timing from an expansion stroke to an exhaust stroke to supply hydrocarbons. An exhaust emission control device for an internal combustion engine according to any one of claims 1-9. 11. An internal combustion engine having an intake throttle valve,
The exhaust purification system for an internal combustion engine according to any one of claims 1 to 10, wherein the simultaneous regenerating means controls an intake air amount to reduce an exhaust air-fuel ratio. 12. When regenerating both the particle collecting means and the NOx absorbing means, the particle collecting means is in a predetermined low temperature state, and the maximum amount of air contained in the combustion residual gas is a predetermined amount. In the following cases, the simultaneous reproduction means is
The exhaust gas purification device for an internal combustion engine according to any one of claims 1 to 11, wherein the intake air amount is set to a maximum and the exhaust gas air-fuel ratio is reduced by increasing the hydrocarbon supply amount. 13. A particle trapping means for trapping particulate matter contained in exhaust gas, and NOx contained in the exhaust gas when the exhaust air-fuel ratio is a high air-fuel ratio indicating lean, which is provided downstream of the means. NOx absorbing means for releasing and reducing the absorbed NOx according to a decrease in the exhaust air-fuel ratio, and upstream of the particle collecting means or provided itself.
An exhaust gas purification apparatus for an internal combustion engine, comprising: an oxidizing unit that oxidizes a specific component contained in the exhaust gas; and a regeneration timing determining unit that determines that the particle collecting unit and the NOx absorbing unit are in a regeneration period, respectively. When both of the means are regenerated based on the determination result of the regeneration time determination means, a temperature necessary for supplying hydrocarbons to the exhaust gas and regenerating the particle collecting means based on the supply amount. The exhaust gas purification device for an internal combustion engine, characterized in that the exhaust air-fuel ratio is reduced to a low air-fuel ratio showing a rich concentration so that the minimum amount of oxygen for being supplied to the particle collecting means.