JP2003013786A - Exhaust emission purifier of engine and its computer program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To set proper quantity of a reducing agent capable of providing the maximum NOx purifying rate in an exhaust emission purifier of an engine furnished with a plurality of NOx purifying catalysts 22, 23 in series. SOLUTION: A temperature change of the upstream side NOx purifying catalyst 22 within specified time after practicing quantity increase of the reducing agent is estimated, and a temperature change of the downstream side NOx purifying catalyst 23 is estimated. Hereafter, optimum reducing agent quantity with which the NOx purifying rate by the both NOx purifying catalysts 22, 23 is computed in accordance with the estimated temperature change of the upstream side NOx purifying catalyst 22 and the temperature change of the downstream side NOx purifying catalyst 23. Consequently, it is possible to decide the optimum quantity of the reducing agent with which the NOx purifying rate by the both NOx purifying catalysts 22, 23 becomes highest in accordance with the temperature change of the upstream side NOx purifying catalyst 22 and the temperature change of the downstream side NOx purifying catalyst 23.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust emission control system for an engine.

[0002]

[Prior Art] Diesel engine and gasoline engine
NO emitted from_X(Nitrogen oxide) of the engine
NO placed in the exhaust passage_XReduction purification by purification catalyst
Has been done. This NO_XAs shown in Figure 2, the purification catalyst
NO as temperature rises_XPurification rate rises to a specific temperature
Maximum NO degree_XIndicates the purification rate, higher than the specified temperature
On the side, as the temperature rises, NO_XPurification rate decreases
It has characteristics. Also, this kind of NO_XWith purification catalyst
Increases NO when the amount of reducing agent in the exhaust gas is increased._XReturn of
It is known that purification proceeds efficiently. But a lot
When the reducing agent is supplied, the heat of oxidation reaction of the reducing agent causes
NO_XPurification catalyst temperature rises, rather NO _XPurification rate
May decrease.

On the other hand, Japanese Patent Laid-Open No. 9-317524
In the publication, fuel is injected into the combustion chamber near the top dead center of the compression stroke.
After injection, a small amount of fuel is injected into the combustion chamber after the main injection
NO by shooting_XWhile supplying the reducing agent to the purification catalyst,
This NO_XPurification catalyst is maximum NO _XThan the temperature that shows the purification rate
When the temperature is low, the post injection amount is increased, and when the temperature is high,
It is disclosed that the post injection amount is reduced. Sanawa
Chi, NO_XWhat temperature zone is the purification catalyst in?
Therefore, the post-injection amount is made different, and the NO_X
This is to prevent excessive temperature rise of the purification catalyst.

[0004] According to the prior art, which is advantageous in the NO _X purification that by controlling the supply amount of the reducing agent by post injection to suppress the Atsushi Nobori of the NOx purification catalyst, in practice the reducing agent supply amount There is a difficult problem as to how much to set.
That is, when the NO _X purification catalyst is in a temperature zone higher than the temperature showing the maximum NO _X purification rate, if the reducing agent supply amount is reduced, the excessive temperature rise of the NO _X purification catalyst is suppressed, but It is impossible to improve the NO _X purification rate by the supply, and if the reducing agent supply amount is increased, the N
Although the O _X purification rate increases, the catalyst temperature rises sharply and the NO _X purification rate decreases. Therefore, the present applicant predicts the temperature change of the NO _X purification catalyst within a predetermined time from when the amount of reducing agent in the exhaust gas supplied to the NO _X purification catalyst is increased, and the predicted NO _X purification catalyst It is proposed to supply an optimal amount of reducing agent according to the NO _X purification performance after the reducing agent is supplied for a predetermined time by setting the optimal reducing agent supply amount according to the temperature change. (Japanese Patent Application No. 2000-237958)

[0005]

[SUMMARY OF THE INVENTION However, even the proposed of the present applicant, if it is arranged in series in the exhaust passage a plurality of the NO _X purification catalyst, the downstream-side NO _X purification catalyst downstream of the final NO _X There was a problem that purification was not always optimal. That is, among the plurality of NO _X purification catalysts, only the upstream NO _X purification catalyst temperature is focused, and the reducing agent supply amount is set based on the predicted upstream NO _X purification catalyst temperature so as not to cause an excessive temperature rise. Then, the NO _X purification rate in the upstream NO _X purification catalyst becomes high, but the upstream NO _X purification rate increases.
_Since the exhaust gas temperature lowers due to the effect of heat radiation in the exhaust passage between the _X purification catalyst and the downstream NO _X purification catalyst,
The temperature of the downstream NO _X purification catalyst decreases, and the NO _X purification rate of the downstream NO _X purification catalyst decreases. Conversely, if only the downstream NO _X purification catalyst temperature is focused and the reducing agent supply amount is set based on the predicted downstream NO _X purification catalyst temperature so as not to cause excessive temperature rise, the upstream NO _X purification catalyst The amount of the reducing agent becomes inappropriate, and the NO _X purification rate of the upstream NO _X purification catalyst decreases.

The present invention has been made in consideration of the above problems. The problem is that the exhaust gas of an engine in which a plurality of NO _x purification catalysts are provided in series and an appropriate amount of reducing agent can be set. To provide a purification device.

[0007]

In order to achieve the above object, the present invention has the following means for solving the problem. That is, the first configuration of the present invention is a catalyst that reduces and purifies NO _{X in} exhaust gas by supplying a reducing agent, and the NO _X purification rate increases as the temperature rises, and becomes the maximum at a specific temperature. A reducing agent in which a plurality of NO _X purification catalysts, which show the NO _X purification rate, and whose NO _X purification rate decreases as the temperature rises on the higher temperature side than the specific temperature, are arranged in series in the exhaust passage of the engine. Temperature predicting means for predicting a temperature change of the upstream side NO _x purification catalyst within a predetermined time from the supply of R, and a first temperature predicting means for predicting a temperature change of the downstream side NO _x purification catalyst within a predetermined time after the supply of the reducing agent. and 2 temperature prediction means, the both NO _X purification catalyst based on the temperature change and the temperature change of the downstream-side NO _X purification catalyst upstream NO _X purification catalyst that has been predicted by the first temperature prediction means and the second temperature prediction means The optimal reducing agent amount setting means for setting the optimal reducing agent amount that maximizes the NO _x purification rate by the above, and the optimal reducing agent amount set by the optimal reducing agent amount setting means are provided on the upstream side NO _x purification catalyst and the downstream side. A reducing agent supply means for supplying the NO _X purification catalyst is provided. According to the first configuration of the present invention, with respect to each of the upstream side NO _X purification catalyst and the downstream side NO _X purification catalyst, it is possible to predict the temperature change of the NO _X purification catalyst that changes within a predetermined time after the supply of the reducing agent. together, it is possible to predict the NO _X purification rate of the NO _X purification catalyst that varies based on temperature of the predicted NO _X purification catalyst to change. Then, based on the predicted both NO _X purification rates, it is possible to set the optimum reducing agent amount that maximizes the overall NO _X purification rate obtained by the both NO _X purification catalysts.

[0008] In the second configuration of the present invention, the downstream NO _X purification and estimating means for estimating the amount of reducing agent catalyst outlet, the estimated by the estimation means the downstream NO _X purification catalyst outlet of the reducing agent When the amount exceeds the preset upper limit,
An optimal reducing agent amount correcting means for correcting the optimal reducing agent amount set by the optimal reducing agent amount setting means is provided so that the estimated reducing agent amount becomes equal to or less than the upper limit value. According to the second configuration of the present invention, since the amount of reducing agent can be regulated by the upper limit value, it is possible to suppress the excessive reducing agent from being discharged as HC.

In the third structure of the present invention, the estimating means includes first estimating means for estimating the reducing agent amount at the outlet of the upstream NO _X purification catalyst, and upstream estimated by the first estimating means. composed of the second estimation means for estimating the amount of reducing agent downstream NO _X purification catalyst outlet based on the amount of reducing agent on the side NO _X purification catalyst outlet, it is so. According to the third configuration of the present invention, the reducing agent amount at the downstream NO _X purification catalyst outlet is estimated in consideration of the reducing agent amount at the upstream NO _X purification catalyst outlet estimated by the first estimating means. The amount of reducing agent can be estimated in consideration of consumption of the reducing agent in the upstream NO _X purification catalyst.

According to the fourth aspect of the present invention, the first
The estimating unit is configured to make an estimation based on the temperature change of the upstream NO _X purification catalyst predicted by the first temperature predicting unit and the exhaust gas flow rate. According to the fourth configuration of the present invention, the amount of reducing agent at the outlet of the upstream NO _X purification catalyst is estimated in consideration of the exhaust gas flow rate, so the exhaust gas flow rate changes and the HC discharged from the engine changes. Even so, the amount of reducing agent can be properly estimated.

According to the fifth aspect of the present invention, the above-mentioned second aspect is used.
The estimating means is configured to make an estimation based on the temperature of the downstream NO _X purification catalyst predicted by the second temperature predicting means and the exhaust gas flow rate. According to the fifth configuration of the present invention, the amount of reducing agent at the outlet of the upstream NO _X purification catalyst is estimated in consideration of the exhaust gas flow rate, so the exhaust gas flow rate changes and the HC discharged from the engine changes. Even so, the amount of reducing agent can be properly estimated.

Further, in the sixth configuration of the present invention, the reducing agent supply means supplies the reducing agent by the auxiliary injection for additionally injecting the fuel in the expansion stroke or the exhaust stroke after the main injection of the fuel. is there. According to the sixth configuration of the present invention, it is possible to supply the reducing agent amount by the auxiliary injection that additionally injects the fuel in the expansion stroke or the exhaust stroke.

According to a seventh aspect of the present invention, there is provided a computer program incorporated in hardware resources including a computer, the computer program causing the upstream NO _X purification catalyst within a predetermined time from the supply of the reducing agent. Temperature prediction procedure for predicting a temperature change of the downstream NO _x purification catalyst within a predetermined time from the supply of the reducing agent, a first temperature prediction procedure for predicting a temperature change of 2 Upstream NO _X predicted by the temperature prediction procedure
An optimum reducing agent amount setting procedure for setting an optimum reducing agent amount that maximizes the NO _X purification rate by both NO _X purification catalysts based on the temperature change of the purification catalyst and the temperature change of the downstream NO _X purification catalyst, The optimum reducing agent of the amount set by the reducing agent amount setting procedure reduces and purifies NO _X in the exhaust gas,
As the temperature rises, the NO _X purification rate rises to show the maximum NO _X purification rate at a specific temperature, and on the higher temperature side than the specific temperature, the NO _X purification rate decreases as the temperature rises. The above-mentioned hardware resource is made to execute the reducing agent supply procedure for supplying to the side NO _X purification catalyst and the downstream side NO _X purification catalyst. According to the seventh configuration of the present invention, with respect to each of the upstream side NO _X purification catalyst and the downstream side NO _X purification catalyst, it is possible to predict the temperature change of the NO _X purification catalyst that changes within a predetermined time after the supply of the reducing agent. together, it is possible to predict the NO _X purification rate of the NO _X purification catalyst that varies based on temperature of the predicted NO _X purification catalyst to change. And the predicted both NO
Based on the _X purification rate, it is possible to set the optimum amount of reducing agent that maximizes the overall NO _X purification rate obtained by both NO _X purification catalysts.

[0014]

According to the present invention, it is possible to set an appropriate amount of reducing agent in a catalyst including a plurality of NO _X purification catalysts in series.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows the overall construction of an exhaust emission control device A for a diesel engine according to an embodiment of the present invention, and 1 is an engine body of a multi-cylinder diesel engine mounted on a vehicle. The engine body 1 has a plurality of cylinders 2 (only one is shown), and a piston 3 is reciprocally fitted in each cylinder 2 so that the cylinder 2 and the piston 3 allow the respective cylinders 2 to reciprocate. A combustion chamber 4 is formed. Further, a fuel injection valve 5 is arranged in a substantially central portion of the upper surface of the combustion chamber 4 with its front injection hole facing the combustion chamber 4, and the injection hole is opened / closed at a predetermined injection timing for each cylinder. The fuel is directly injected into the combustion chamber 4.

The fuel injection valve 5 is connected to a common common rail (storage chamber) 6 for storing high-pressure fuel, and a high pressure supply pump 8 driven by a crankshaft 7 is connected to the common rail 6. . This high-pressure supply pump 8
Is the common rail 6 detected by the pressure sensor 6a.
It operates so that the internal fuel pressure is maintained at a predetermined value or higher. A crank angle sensor 9 for detecting the rotation angle of the crank shaft 7 is provided. The crank angle sensor 9 is provided with a plate to be detected (not shown) provided at an end of the crank shaft 7 and an outer periphery thereof. The electromagnetic pickup is arranged so as to face each other, and the electromagnetic pickup outputs a pulse signal in response to passage of protrusions formed at predetermined angles all around the outer circumference of the plate to be detected. Has become.

Reference numeral 10 denotes an intake passage for supplying intake air filtered by an air cleaner (not shown) to the combustion chamber 4 of the engine body 1. The intake passage 10 is branched to a passage connected to each cylinder on the downstream side thereof. Each of the branched passages is connected to the combustion chamber 4 of each cylinder 2 via an intake port. Further, the intake passage 10 is provided with an intake pressure sensor 10a for detecting a supercharging pressure supplied to each cylinder 2. In the intake passage 10, a hot film type air flow sensor 11 for detecting the flow rate of intake air taken into the engine body 1 and a blower 12 for compressing intake air driven by a turbine 21 described later are arranged in this order from the upstream side to the downstream side.
An intercooler 13 that cools the intake air compressed by the blower 12 and an intake throttle valve 14 that throttles the cross-sectional area of the intake passage 10 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.
Similar to the R valve 24, the magnitude of the negative pressure acting on the diaphragm 15 is adjusted by the negative pressure controlling solenoid valve 16, so that the opening degree of the valve is adjusted. Further, the intake throttle valve 14 is provided with a sensor (not shown) for detecting the opening thereof.

Reference numeral 20 denotes exhaust gas from the combustion chamber 4 of each cylinder 2.
Exhaust passage to exhaust each cylinder through exhaust manifold
It is connected to two combustion chambers 4. In this exhaust passage 20
Is the acid in the exhaust gas in order from the upstream side to the downstream side.
Linear O to detect elementary concentration₂The sensor 17 and the exhaust flow
The turbine 21 that is recirculated and the HC and CO in the exhaust gas
And NO_XUpstream NO that can purify_XPurification catalyst 22 and below
Flow side NO_XA purification catalyst 23 is provided respectively.
Also, upstream NO_XUpstream and downstream of the purification catalyst, NO upstream _XPurification
Temperature sensor for detecting the temperature of the catalyst catalyst inlet and outlet
The sensors 18 and 19 are provided respectively.

The above upstream NO_XThe purification catalyst 22 is arranged in the axial direction.
A honeycomb structure coat having a large number of through holes extending in parallel.
Do not form a catalyst layer on the wall surface of each through hole of the gellite carrier.
The catalyst layer is zeolite and precious metals such as Pt.
The genus (catalyst metal) is dried and supported by the spray dry method.
The catalyst powder thus formed is supported on the carrier by a binder.
It is formed by Downstream NO_XPurification catalyst 23
Is divided into 2 bets, and the upstream N
O_XA catalyst similar to the purification catalyst 22 is arranged, and is provided on the downstream side.
Is similar to the above with precious metals such as Pt in beta zeolite.
A catalyst with a high HC adsorption capacity is supported by the method
Has been done. As mentioned above, downstream NO_XPurification catalyst 23
Is composed of two different catalysts and its total capacity
Is upstream NO_XNO downstream from the purification catalyst_XPurification catalyst
Has been made larger. Also, downstream NO _XOf the purification catalyst 23
Maximum NO_XThe catalyst temperature indicating the purification rate is the upstream NO_Xpurification
Maximum NO of catalyst 22_XHigh against the catalyst temperature, which indicates the purification rate
I'm sick.

FIG. 2 schematically shows temperature characteristics relating to the NO _X purification rate and the HC purification rate by the upstream NO _X purification catalyst 22. That is, the NO _X purification rate rises as the catalyst temperature rises to reach the specific temperature (200
The maximum NO _X purification rate is shown at about 300 ° C.), and the NO _X purification rate decreases as the temperature rises on the higher temperature side than the specific temperature. The HC purification rate increases as the catalyst temperature rises, and after about 300 ° C, the HC purification rate remains almost constant.
Purification rate (purification rate close to 100%). In addition, downstream NO
_{Although the X} purification catalyst 23 is not disclosed, the maximum NO
_The only difference is that the specific temperature indicating the _X purification rate is higher than that of the upstream NO _X purification catalyst 22, and the tendency of the temperature characteristics regarding the NO _X purification rate and the HC purification rate itself is the upstream NO.
It is similar to the _X purification catalyst 22.

An exhaust gas recirculation passage (hereinafter referred to as an EGR passage) 23 for recirculating a part of exhaust gas to intake air branches from a portion of the exhaust passage 20 upstream of the turbine 21,
The downstream end of the EGR passage 23 is connected to the intake passage 10 on the downstream side of the intake throttle valve 14. EGR passage 23
An exhaust gas recirculation amount control valve (hereinafter referred to as an EGR valve) 24 whose opening can be adjusted is arranged near the downstream end in the middle of the intake air intake while adjusting a part of the exhaust gas in the exhaust passage 20 by the EGR valve 24. It is designed to be returned to the passage 10.

The EGR valve 24 is of a negative pressure responsive type, and the negative pressure passage 27 is connected to the negative pressure chamber of the valve box. The negative pressure passage 27 is connected to a vacuum pump 29 via a negative pressure controlling solenoid valve 28, and the solenoid valve 2
8 is a negative pressure passage 27 according to a control signal from an ECU described later.
The negative pressure type EGR valve drive negative pressure is adjusted by connecting / disconnecting the valve, thereby linearly adjusting the opening of the EGR passage 23.

The turbocharger 25 is a VGT (Variable Geometry Turbo), to which a diaphragm 30 is attached, and a solenoid valve 3 for negative pressure control.
By adjusting the negative pressure acting on the diaphragm 30 by 1, the cross-sectional area of the exhaust gas passage for the turbine 21 is adjusted, and the efficiency of the turbine 21 is adjusted to be optimum according to the operating state.

The fuel injection valve 5, the high pressure supply pump 8, the intake throttle valve 14, the EGR valve 24, the turbocharger 25, etc.
Control unit (Engine Control Unit: E below)
It is configured to operate based on a computer program stored in a memory within the CU 35. On the other hand, the ECU 35 has an output signal from the pressure sensor 6a, an output signal from the crank angle sensor 9, an output signal from the pressure sensor 10a, an output signal from the air flow sensor 11, and an O2 sensor 17. The output signal, the output signals from the temperature sensors 18 and 19, and the EG
An output signal from a lift sensor 26 of the R valve 24 and an output signal from a sensor (not shown) that detects the engine water temperature are input.

The fuel injection amount and the fuel injection timing of the fuel injection valve 5 are controlled according to the operating state of the engine body 1, and the common rail pressure, that is, the fuel injection pressure is controlled by the operation of the high pressure supply pump 8. In addition to this, control of the exhaust gas recirculation amount by the operation of the EGR valve 24,
The operation control (VGT control) of the turbocharger 25 is performed.

In fuel injection control, main injection control and post-injection control are performed. First, the main injection control will be described. In the memory of the ECU 35, a stored target torque map in which the optimum value of the target torque is experimentally determined with respect to changes in the accelerator opening and the engine speed, and the target torque map, intake air amount, and engine speed are stored. The stored fuel injection map in which the optimum value of the fuel injection amount is experimentally determined with respect to the change is stored. Then, a target torque is obtained based on the accelerator opening detected by the accelerator opening sensor 32 and the engine speed detected by the crank angle sensor 9, and the target torque, the engine speed and the air flow sensor 11 are detected. A basic fuel injection amount is calculated based on the intake air amount. Furthermore, the fuel injection amount is corrected according to the engine water temperature, atmospheric pressure, etc.,
Find the final fuel injection amount. Then, the valve opening time of each fuel injection valve 5 is determined based on the fuel injection amount and the common rail pressure detected by the pressure sensor 6.

By the main injection control as described above, fuel corresponding to the target torque of the engine is supplied, and the average air-fuel ratio in the engine combustion chamber 4 is lean (A / F ≧ 1).
(8, oxygen concentration is 4% or more).

Next, the post injection will be described. During steady operation (when the accelerator opening change is small), upstream NO _X
In order to supply the reducing agent component for promoting the NO _X reduction purification to the purification catalyst 22 and the downstream NO _X purification catalyst 23, the post-injection in which a small amount of fuel is injected is performed in the expansion stroke or the exhaust stroke after the main injection. After that, the injection amount is determined to be an optimum value that maximizes the NO _X purification rate by the upstream NO _X purification catalyst 22 and the downstream NO _X purification catalyst 23, as described later.

The post-injection may be performed each time the main injection is performed for each cylinder, but may be appropriately thinned out. For example, when the main injection is performed for each cylinder in a predetermined order, the post-injection may be performed once every five main injections.

The feature of the present invention is that the post-injection amount setting for setting the post-injection amount as the optimum reducing agent amount that maximizes the NO _X purification rate by the upstream NO _X purification catalyst 22 and the downstream NO _X purification catalyst 23. The injection amount setting means is described later with reference to the block diagram of FIG.

That is, the post-injection amount setting means is
Data storage means A storing data necessary for calculation, and
The amount of reducing agent was increased by injection over a predetermined time Δt
Sometimes upstream NO rises_XAmount of temperature change Δ of the purification catalyst 22
First temperature predicting means B for calculating T, and the first temperature predicting means
The temperature change amount ΔT calculated by the means B and the temperature sensor
Based on the current temperature detected by 18, the above predetermined
Upstream NO within time Δt_XNO by purification catalyst 22
_XThe first NO to calculate the purification rate_XPurification rate calculation means C, and
The amount of reducing agent was increased by injection over a predetermined time Δt
Sometimes downstream NO rises_XAmount of temperature change Δ of the purification catalyst 23
Second temperature prediction means D for calculating T, and the second temperature prediction
A temperature change amount ΔT calculated by the means D and a temperature sensor
The above-mentioned predetermined value based on the current temperature detected by 19
Downstream NO within time Δt_XNO by purification catalyst 23
_XSecond NO to calculate the purification rate_XPurification rate calculation means E and each
HC / NO_XNO in ratio_XBoth of the above NO based on the purification rate
_XNO by purification catalyst _XOptimum H for highest purification rate
C / NO_XOptimal post-injection amount setting means for selecting and setting the ratio
F and the upstream NO calculated by the first temperature predicting means B
_XThe temperature change amount ΔT of the purification catalyst 22 and the upstream NO_XPurification touch
HC / NO at medium 22 inlet_XBased on the ratio and the above predetermined time
NO upstream in the interval Δt_XPurification at the purification catalyst 22
First estimating means for estimating the amount of HC discharged without being discharged
G and HC emissions estimated by the first estimating means G
Quantity, that is, downstream NO_XHC / NO at the inlet of the purification catalyst 23
_XAnd the second temperature change amount prediction means D.
Downstream NO_XBased on the temperature change amount ΔT of the purification catalyst 23
The downstream NO within the predetermined time Δt._XPurification catalyst 2
Estimate the amount of HC emission that is discharged without purification in 3
The second estimating means H and the second estimating means H
Compare the amount of discharged HC with the maximum allowable maximum value,
Post-injection so that the estimated HC emissions do not exceed the upper limit
A post-injection amount correction means I for setting a correction amount for correcting the amount,
HC / N set by the optimum post injection amount setting means F
O_XRatio, NO estimated based on the operating state of the engine_X
It is set by the generation amount and the optimum post-injection amount correction means I.
The final post-injection amount is set based on
After-injection amount setting means J is provided. The above data description
Storage means A stores data stored in the memory of the ECU 35.
And each of the means B to J is a memory of the ECU 35.
Stored in the memory and set according to the processing cycle set for each method.
A computer program that is executed.

The above HC / NO _x ratio is the engine NO
It is the ratio of the reducing agent supply amount HC to the _X generation amount, and the reducing agent supply amount HC is the reducing agent amount supplied to the NO _X purification catalyst by the main injection and the post injection. The reducing agent supply amount H
C is the sum of the amount of HC that is discharged to the exhaust passage without burning during combustion based on the main injection and the amount of HC that is supplied to the exhaust passage by the secondary injection. The predetermined time Δt is for predicting the influence that appears when the reducing agent amount is supplied by the post-injection as a temperature change of the upstream NO _x purification catalyst 22 and the downstream NO _x purification catalyst 23. A time at which a change appears, for example, about 30 seconds to 60 seconds may be set as Δt. However, since the time required for the temperature change to appear differs depending on the magnitude of the exhaust gas amount, Δt may be set shorter as the engine speed increases.

[0034] The data stored in the unit A, the post-injection amount upstream NO required to compute _X purification catalyst 22 about heating rate data a1, downstream NO _X purification catalyst 23 about heating rate data a2, upstream NO _X purification catalyst 22 Regarding the purification performance data b1 regarding the downstream NO _X purification catalyst 23, the HC emission amount data c1 regarding the upstream NO _X purification catalyst 22, and the HC emission amount data c2 regarding the downstream NO _X purification catalyst 23.

As shown in FIG. 4, the temperature increase rate data a1 shows how the temperature increase rate VT of the upstream NO _X purification catalyst 22 changes when the HC / NO _X ratio changes, and the relationship between the two. And is set experimentally in advance.
Since this relationship differs depending on the engine speed Ne, it is set in relation to the engine speed.

The temperature increase rate data a2 is the temperature increase rate data a.
1 has the same meaning as that of 1, but since the target catalyst is the downstream NO _X purification catalyst 23 having a large capacity, as shown in FIG. 5, when the HC / NO _X ratio changes, The temperature increase rate VT of the upstream NO _X purification catalyst 22 is set smaller than the temperature increase rate data a1.

As shown in FIG. 6, the purification performance data b1 is N when the temperature of the upstream NO _X purification catalyst 22 changes.
It shows the temperature characteristic of the NO _X purification rate, which is how the O _X purification rate changes, and is experimentally set in advance. Since the temperature characteristic of the NO _X purification rate differs depending on the magnitude of the HC / NO _X ratio, a plurality of different HC / NO _X ratios are obtained.
It is set about the ratio.

The purification performance data b2 is the purification performance data b
1 but shows the same meanings as the catalyst of interest, purification on the performance data b1, the maximum NO _X purification rate with the catalyst temperature is high as the maximum NO _X purification rate is low downstream NO _X Since it is the purification catalyst 23, as shown in FIG. 7, the maximum NO _X purification rate is the purification performance data b.
The value is set to be lower than 1, and the catalyst temperature at which the maximum NO _X purification rate is obtained is increased.

As shown in FIG. 8, the HC emission amount data c1 indicates that the unpurified HC / NO _X ratio indicating how the unpurified HC / NO _X ratio changes when the temperature of the upstream NO _X purification catalyst 22 changes. _It shows the temperature characteristic of the _X ratio, and is experimentally set in advance. The temperature characteristic of this unpurified HC / NO _X ratio is that the HC / NO _X at the inlet of the upstream NO _X purification catalyst 22
Since the ratio varies depending on the size of the
It is set for the NO _x ratio. The HC / NO _X ratio at the inlet of the upstream NO _X purification catalyst 22 can be obtained from, for example, the engine speed and the fuel injection amount.

The HC emission amount data c2 has the same meaning as the HC emission amount data c1, but is different in that the target catalyst is the downstream NO _X purification catalyst 23 having a large capacity, so that it is shown in FIG. As shown, the unpurified HC / NO _x ratio is generally set to be smaller than the HC emission amount data c1.

The first temperature predicting means B is given the engine speed Ne and a plurality of different HC / NO _X ratios at that time, and each HC / NO _{X is} calculated from the temperature increase rate data a1 shown in FIG.
For the ratio, the temperature increase rate VT is read, and the temperature change amount ΔT (= VT × Δ) is calculated based on the temperature increase rate VT and the predetermined time Δt.
Find t).

The first NO _X purification rate calculation means C is for each HC /
Given the amount of temperature change ΔT for the NO _X ratio and the current catalyst temperature Tc, the upstream NO _X for each HC / NO _X ratio is given.
NO _X when the purification catalyst 22 makes the temperature change amount ΔT
The change in the purification rate is read from the purification performance data b1 shown in FIG. 6, and the NO _X purification efficiency for a predetermined time Δt, that is, the average NO _X purification rate is calculated here.

For example, HC / NO_X= 5 and HC / NO_X
= 3, the former is the latter
Since the degree of reducing agent is larger than that of
The heating rate VT obtained from the data a1 is also high.
Therefore, the temperature change amount ΔT also increases. Shown in FIG.
Current upstream NO_XPurification catalyst 22 temperature Tc is the touch
Maximum NO of medium 22_XThan the peak temperature To that indicates the purification rate
If Tc1 is high, HC / NO_X= 5
Since the temperature change amount ΔT is large, a predetermined time Δt
Upstream NO at the time of passing_XPurification catalyst 22 temperature is Tc5
But HC / NO _X= 3, the predetermined time Δt seconds has elapsed
Upstream NO at the time of_XThe temperature of the purification catalyst 22 is lower than that of Tc5.
It has a low Tc3. HC / NO_X= 2, temperature change
After the lapse of a predetermined time Δt seconds, the amount ΔT becomes smaller.
Upstream NO_XPurification catalyst 22 temperature is lower than Tc3
It becomes Tc2.

Such upstream NO_XRise of purification catalyst 22
NO when changes occur_XCheck the change in purification rate over time
Then, as shown in FIG. 10, HC / NO_XWhen = 5, return
Initially NO when the original drug was supplied_XHighest purification rate
However, the temperature change amount ΔT is large and the upstream NO_XPurification catalyst 22 temperature
As the temperature rises sharply, NO_XFast purification rate
It will drop significantly over time. HC / NO_XWhen = 3, return
NO due to the supply of the base drug_XThe degree of purification rate increase is HC / NO
_XHowever, the amount of temperature change ΔT is much smaller
NO because it is not big_XThe degree of reduction of the purification rate is small. H
C / NO_X= 2, the amount of reducing agent is small, but temperature change
Since the amount ΔT is also small, NO even if time elapses. _XPurification rate
Does not drop much.

After all, for each of HC / NO _x = 5, 3, 2, the average NO _x purification rate for the predetermined time Δt is shown in FIG.
Among them, the maximum NO _X purification rate area within a predetermined time Δt is HC / NO _X = 3, which is the highest.

The second temperature predicting means D makes the same prediction as the first temperature predicting means B, but the temperature increase rate data a2 shown in FIG. 5 is used for the prediction.

The second NO _X purification rate calculation means E is operated by the first NO
_{The same} calculation as the _X purification rate calculation means C is performed, but the purification performance data b2 shown in FIG. 7 is used for the calculation.

Such downstream NO_XRise of purification catalyst 23
NO when changes occur_XCheck the change in purification rate over time
As shown in FIG. 11, HC / NO_X= 5, 3, 2
In either case, NO over time_XPurification rate is slow
Shows characteristics that gradually increase, and upstream NO_XN of the purification catalyst 22
O_XPurification rate (HC / NO_X= When 5 is selected)
NO appearing after supply_XNo significant decrease in purification rate
Yes. This is downstream NO_XThe temperature of the purification catalyst 23 is used for heat dissipation
Therefore upstream NO_XLower than the purification catalyst 22 and
Flow NO_XThe capacity of the purification catalyst 23 is upstream NO_XPurification catalyst 22
Within a predetermined time Δt
Since the temperature change amount ΔT of the _XPurification touch
This is because the temperature rise of the medium 23 is small.

In the optimum post-injection amount setting means F, the first N
The average NO _X purification rate of O _X purification rate calculating means upstream NO computed by C _X purification catalyst 22, and the average NO _X purification rate of the downstream NO _X purification catalyst 23 calculated by the first 21NO _X purification rate calculating means E HC / NO with the maximum value
Select and set the _X ratio. That is, every each HC / NO _X ratio, an average NO _X purification rate shown in FIG. 10, by adding the average NO _X purification rate shown in FIG. 11, the summed average NO _X purification rate Of these, the HC / NO _x ratio that maximizes the NO _x purification rate is set.

As described above, the optimum post injection amount setting means F sets the HC / NO _X ratio that maximizes the NO _X purification rate. However, when the temperature of the upstream NO _X purification catalyst 22 or the temperature of the downstream NO _X purification catalyst 23 is lower than the specific temperature at which the NO _X purification rate becomes maximum, the HC emission amount may become the allowable upper limit value or more. . Therefore, since it is necessary to suppress the HC emission amount to the upper limit value or less, it is set by the optimum post-injection amount setting unit F by the first estimating unit G, the second estimating unit H, and the optimum post-injection amount correcting unit I described later. HC /
Correct the NO _X ratio.

First, in the first estimating means G, as shown in FIG. 8, the temperature change amount ΔT of the upstream NO _X purification catalyst 22 calculated by the first temperature predicting means B and the temperature sensor 1 are calculated.
HC with respect to the temperature of the upstream NO _x purification catalyst 22 after a lapse of a predetermined time Δt obtained from the current temperature detected by
The unpurified HC / NO _x ratio is estimated from the emission data c1. The unpurified HC / NO _X ratio temperature characteristics, upstream NO _X
Since different depending on the magnitude of the purifying catalyst 22 inlet of HC / NO _X ratio, unpurified HC / NO _X in accordance with the HC / NO _X ratio
The ratio is set as data. The HC / NO _X ratio at the inlet of the upstream NO _X purification catalyst 22 can be estimated from the engine speed and the fuel injection amount.

Next, in the second estimating means H, as shown in FIG. 9, the temperature change amount ΔT of the downstream NO _X purification catalyst 23 calculated by the second temperature predicting means D and the temperature sensor 1 are calculated.
Predetermined time Δ found from current temperature detected by 9
From the HC emission amount data c1 with respect to the temperature of the downstream NO _X purification catalyst 23 after the elapse of t, the unpurified HC / N as the exhausted HC amount
Estimate the _Ox ratio. Since this unpurified HC / NO _X ratio temperature characteristic varies depending on the magnitude of the HC / NO _X ratio at the inlet of the downstream NO _X purification catalyst 23, the unpurified HC / NO _X ratio corresponding to each HC / NO _X ratio is used as data. It is set.

Since the HC amount estimated by the second estimating means H becomes the finally discharged HC amount, the estimated HC amount is compared with the maximum allowable upper limit value. Is set in the optimum post-injection amount correction means I so that the post-injection amount is corrected so that does not exceed the upper limit value.

In the final post-injection amount setting means J, the HC / NO _X ratio set by the optimum post-injection amount setting means F, the correction amount set by the optimum post-injection amount correction means I, and the operating condition of the engine are set. The final post-injection amount is calculated from the NO _X amount estimated based on this.

The specific fuel injection processing procedure will be described below with reference to FIG.
This will be described based on the flowcharts shown in FIGS.

In step S1, various sensor outputs such as a crank angle sensor, an air flow sensor, an accelerator opening, and a temperature sensor are read. In step S2, the target torque is set with reference to the map based on the accelerator opening and the engine speed, and the main fuel injection amount is calculated based on the target torque, the engine speed and the intake air amount. Step S3
Then, the main fuel injection timing is set based on the map of the engine speed and the target torque. The main fuel injection timing is basically set near the top dead center of the compression stroke, but if the engine water temperature or engine speed is different, the fuel ignition delay time is different. The higher the number, the earlier the fuel injection timing.

Then, in step S4, each HC / NO _X
For the ratio, the temperature increase rate VT is read from the temperature increase rate data a1 based on the engine speed at that time, and the reducing agent amount is increased at each HC / NO _X ratio based on the temperature increase rate VT for a predetermined time Δt. Amount of change in catalyst temperature that rises per second Δ
Predict T. Then, based on the current catalyst temperature Tc and the amount of temperature change ΔT, the purification performance data b1 is used to determine each HC / N.
The average NO _X purification rate of the upstream NO _X purification catalyst 22 for the Δt seconds at the O _X ratio is predicted.

In the next step S5, each HC / NO _X
As for the ratio, the catalyst temperature change amount ΔT which rises in a predetermined time Δt seconds when the reducing agent amount is continued at each HC / NO _x ratio
And the current temperature of the upstream NO _X ratio purification catalyst 22,
The temperature of the upstream NO _X purification catalyst after a predetermined time Δt seconds is predicted, and the HC emission amount data c is calculated based on the predicted temperature.
The unpurified HC / NO _x ratio as the amount of discharged HC is estimated from 1.

In step S6, the average NO _X purification rate of the downstream NO _X purification catalyst 23 is predicted in the same manner as in step S4, but the data used to obtain the temperature increase rate VT is the temperature increase rate data a2. There are some differences.

At step S7, similarly to step S5, the temperature of the downstream NO _X purification catalyst 23 after a predetermined time Δt seconds is predicted, and the predicted temperature and the unpurified HC / NO obtained at step S5 are calculated. Based on the _X ratio, the unpurified HC / NO _X as the exhausted HC amount is estimated from the HC emission data c2.

[0061] Subsequently, in step S8, adds the upstream NO _X purification catalyst average NO _X purification rate obtained in step S4, a downstream NO _X purification catalyst average NO _X purification rate obtained in step S6, which is the addition HC / NO _X with maximum value
Calculate the ratio. Hereinafter, step S8 will be specifically described based on the flowchart of FIG. Idea is to maintain the NOx purification catalyst temperature near the temperature at which NO _X purification rate is maximized, while predicting the NO _X purification rate H
It is intended to change the C / NO _X ratio at any time.

In step S110 of FIG. 13, the previous H
A value NO _X conv1 is calculated by adding the upstream NO _X purification catalyst average NO _X purification rate and the downstream NO _X purification catalyst average NO _X purification rate for Δt seconds in the C / NO _X ratio.

In step S120, the previous HC
/ NO _X ratio to, by adding a predetermined amount K which is set in advance, and sets a new HC / NO _X ratio HC / NO _X -P, followed
In step S130, the HC set in step 120 is set.
A value NO _X conv2 is calculated by adding the upstream NO _X purification catalyst average NO _X purification rate and the downstream NO _X purification catalyst average NO _X purification rate after Δt seconds in the / NO _X ratio HC / NO _X -P.

In step S130, the previous HC
/ NO _x ratio, a preset predetermined amount K is subtracted, a new HC / NO _x ratio HC / NO _x -M is set, and then,
In S140, the HC / NO set in step S120 is set.
Upstream NO _x after Δt seconds at _X ratio HC / NO _x -M
Purification catalyst average NO _X purification rate and downstream NO _X purification catalyst average N
The value NO _X conv3 is calculated by adding the O _X purification rate.

The obtained average NO _X purification rate NO _X conv
Any of N, NO _X conv2, NO _X conv3
It is determined whether the O _X purification rate is the highest and the HC / NO _X ratio is corrected. Specifically, in step S160, the average NO _X
It is determined whether or not the purification rate NO _X conv2 is larger than NO _X conv1, and if YES, step S17.
At 0, it is determined whether the average NO _X purification rate NO _X conv2 is larger than NO _X conv3. YES in step S170
If it is determined that the HC set in step S120
Since it can be determined that the average NO _X purification rate at the / NO _X ratio HC / NO _X -P is the highest, the HC at Step S180
/ NO _X ratio compared to the previous HC / NO _X ratio by HC / N
Average NO _X purification rate NO _X conv2 at O _X -P and previous H
Correction is performed with a value obtained by multiplying the ratio of the average NO _X purification rate NO _X conv1 in C / NO _X by a constant K2. By this, HC
/ NO _X can be corrected in the increasing direction in which the average NO _X purification rate becomes higher.

If NO is determined in step S170, it can be determined that the average NO _X purification rate at the HC / NO _X ratio HC / NO _X -M set in step S140 is the highest, and thus in step S190. HC / NO and _X ratio to the previous HC / NO _X ratio, HC / NO average in _X -M NO _X purification rate NO _X Conv3 the previous HC / NO _X
The value is corrected by a value obtained by multiplying the ratio with the average NO _X purification rate NO _X conv1 in step 1 by a constant K2. Further, in step S160, NO
If it is determined that the average NO _X
It is determined whether or not the purification rate NOxconv1 is smaller than NOxconv3, and if YES is determined, the step S14 is also performed.
Since it can be determined that the average NOx purification rate at the HC / NO _X ratio HC / NO _X -M set at 0 is the highest, the HC / NO _X ratio is corrected in step S190 as described above.
As a result, HC / NO _X can be corrected in the decreasing direction in which the average NO _X purification rate increases. In step S200, N
If it is determined that from O, the previous HC / NO _X ratio does not correct the HC / NO _X ratio can be determined that the most average NO _X purification rate is the highest in step S210 HC / NO
Maintain the _X ratio at the previous HC / NO _X ratio.

In step S220, step S18
0 / S190 / HC set by HC /
The NO _X ratio is set as a value at which the maximum average NO _X purification rate is obtained.

Returning to FIG. 12, in step S9, the unpurified HC / NO as the exhausted HC amount obtained in step S7.
_It is determined whether or not _X is less than or equal to the upper limit value that is allowable as the amount of discharged HC. If NO is determined in step S9, the correction value for suppressing the exhausted HC amount is set in step S10 by the ratio of the upper limit value to the unpurified HC / NO _X obtained in step S7, and YES in step S9. If it is determined that there is no need to make a correction for suppressing the amount of discharged HC, the process proceeds to step S11.

In step S11, the NO _X amount discharged from the engine is obtained from the engine speed and the fuel injection amount. In the subsequent step S12, the post injection amount is set. Hereinafter, step S11 will be specifically described with reference to the flowchart of FIG.

In step S510 of FIG. 14, the target HC / NO _x ratio that maximizes the average NO _x purification rate obtained in step S8 of FIG. 12 is read, and in step S520, the NO _x obtained in step S11 of FIG. 12 is read. Read emissions.
In step S530, the required HC amount is obtained from the target HC / NO _X ratio and the NO _X emission amount. In step S540, the HC discharged from the engine when the post injection is not performed.
The amount is obtained from the engine speed and the fuel injection amount. In step S550, the post injection amount is obtained. That is, the required HC
Since it is sufficient to inject the amount of HC that is originally insufficient from the engine as the post-injection amount, the value obtained by subtracting the engine exhausted HC amount from the required HC amount is the added HC amount (post-injection amount). ). In step S560, the exhaust gas amount per cycle is obtained from the intake air amount. Then, in step S570,
Determine the final post injection amount. That is, step S55
The amount of HC added obtained in 0 is multiplied by the amount of exhaust gas obtained in step S560 and the correction value (the ratio of the upper limit value to unpurified HC / NO _X ) obtained in step S10 of FIG. In step S580, it is determined whether the final post-injection amount obtained in step S570 is larger than the minimum injection amount with which the linearity of the fuel injection valve 5 is obtained. If YES is determined in step S580, step S57.
The final post-injection amount obtained from 0 is used as it is. If NO is determined in step S580, step S5
At 90, the final post-injection amount obtained at step S570 is multiplied by a predetermined value, for example, 5 times, and at step S600, the thinned-out injection flag is set. That is, when the post-injection amount becomes smaller than the minimum injection amount, the amount injected from the fuel injection valve 5 deviates from the required amount. Therefore, after changing the amount to a larger amount than the minimum injection amount, the number of injections is thinned, and the total injection amount is reduced. The post-injection amount matches the required amount.

Returning to FIG. 12, in step S13, the post fuel injection timing is set based on the post injection amount obtained in step S12. The post-injection timing is, for example, ATDC30-
It is set so that the higher the engine load, the more the 90 ° crank angle range.

In step S14, it is determined whether or not the main fuel injection timing obtained in step S3 has come. If YES is determined, the main fuel injection is executed in step S15. In step S16, it is determined whether or not the post-injection amount set in step S12 is 0 or more, and if NO is determined, it is not necessary to execute the post-injection, so the process ends.

If NO in step S16, it is determined in step S17 whether or not the post-fuel injection timing set in step S13 has come. Step S1
If YES is determined in step 7, it is determined in step S18 whether or not the thinning-out injection flag is set. If NO is determined, it is not necessary to perform thinning-out injection, and thus the post-injection is immediately performed in step S19. . Step S18
If YES is determined in step S20, it is determined in step S20 whether the counter n has been counted up to 5, that is, whether the number of injections is the fifth time. If YES is determined, the counter is reset to 0 in step S21. After resetting, post-injection is executed in step S19. NO in step S18
If it is determined that the counter n is set to 1 in step S22.
The processing is ended without counting up and performing the post injection.

As described above, the upstream NO depends on the post injection amount.
_X purification catalyst 22, sets the amount of reducing agent supplied to the downstream NO _X purification catalyst 23, the amount of overall NO _X purification rate is maximized obtained by the upstream NO _X purification catalyst 22 and the downstream NO _X purification catalyst 23 Therefore, even when a plurality of NO _X purification catalysts are provided, an appropriate amount of reducing agent can be set.

In this embodiment, the HC discharge amount is set to the upstream N
Although the example in which the temperature is determined based only on the temperatures of the O _X purification catalyst 22 and the downstream NO _X purification catalyst 23 is shown, the correction may be performed based on the exhaust gas amount. For example, as shown in FIG. 15, as the amount of exhaust gas increases, the HC purification rate decreases and the amount of HC discharged from the engine increases. Therefore, the amount of HC discharged from the upstream NO _X purification catalyst 22 NO _X
The amount of HC discharged from the purification catalyst 23 may be corrected in the increasing direction. In addition, in the present embodiment, as a reducing agent supply method, a fuel injection valve 5 that injects fuel into a combustion chamber 4 of an engine is used to perform sub-injection that adds fuel to an expansion stroke or an exhaust stroke after main injection. As an example, upstream NO _X
It is also possible to separately provide a supply means for directly supplying the reducing agent to the exhaust passage 20 on the upstream side of the purification catalyst 22, and to supply the reducing agent by the supply means. Further, in the present embodiment, an example in which two NO _X purification catalysts are provided is shown, but three or more NO _X purification catalysts may be provided. Further, in the present embodiment, an example is shown in which the components and capacities of the upstream NO _x purification catalyst and the downstream NO _x purification catalyst are changed, but either one or both may be the same.

[Brief description of drawings]

FIG. 1 is a diagram showing an exhaust emission control device for a diesel engine.

FIG. 2 is a diagram schematically showing temperature characteristics relating to a NO _X purification rate and an HC purification rate of a NO _X purification catalyst.

FIG. 3 is a block diagram showing the configuration of optimum reducing agent amount setting means.

FIG. 4 is a temperature rising rate of the upstream NO _X purification catalyst and HC / NO _X
The figure which shows the relationship between a ratio and an engine speed.

FIG. 5 is a temperature rising rate of the downstream NO _X purification catalyst and HC / NO _X
The figure which shows the relationship between a ratio and an engine speed.

FIG. 6 is a diagram showing the temperature characteristics of the NO _X purification rate of the upstream NO _X purification catalyst at each HC / NO _X ratio.

FIG. 7 is a graph showing the temperature characteristics of the NO _X purification rate of the downstream NO _X purification catalyst at each HC / NO _X ratio.

FIG. 8 is a diagram showing unpurified HC / NO _X ratio characteristics with respect to the temperature of the upstream NO _X purification catalyst at each HC / NO _X ratio.

FIG. 9 is a diagram showing unpurified HC / NO _X ratio characteristics with respect to the temperature of a downstream NO x purification catalyst at each HC / NO _X ratio.

FIG. 10 is a diagram showing changes over time in the NO _X purification rate of the upstream NO _X purification catalyst at each HC / NO _X ratio.

FIG. 11 is a diagram showing changes over time in the NO _X purification rate of the downstream NO _X purification catalyst at each HC / NO _X ratio.

FIG. 12 is a flowchart showing an example of fuel injection control.

13 is a flowchart showing an example of detailed control in step S8 of FIG.

14 is a flowchart showing an example of detailed control of step S12 of FIG.

FIG. 15 is a diagram showing an HC purification rate characteristic with respect to an exhaust gas amount.

[Explanation of symbols]

1: Engine body 5: Fuel injection valve 18: Temperature sensor 19: Temperature sensor 22: Upstream NO _x purification catalyst 23: Downstream NO _x purification catalyst B: First temperature prediction means D: Second temperature prediction means F: Optimal reducing agent Quantity setting means (optimum post injection quantity setting means)

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) F02D 41/04 385 F02D 43/00 301H 43/00 301 301J 301T B01D 53/36 101A F term (reference) 3G084 AA01 BA13 BA15 BA24 DA10 DA27 EB11 EB12 EC02 FA08 FA10 FA12 FA20 FA27 FA30 FA37 FA38 3G091 AA02 AA10 AA11 AA18 AA28 AB06 BA04 BA14 BA32 CA02 CA18 CB02 CB03 CB07 DA02 DC01 EA05 EA07 EA08 EA09 EA16 EA17 EA18 EA22 GA06 HA08 HA36 HA42 HB05 HB06 3G301 HA02 HA06 HA11 HA13 JA25 LB11 MA11 MA18 MA27 ND01 NE01 PA04Z PA07Z PA11Z PA16Z PB03Z PB05Z PB08Z PD02Z PD12Z PD15Z PE01Z PE03Z PE08Z 4D048 AA06 AB02 AC10 BA11X BA30X BB02 CC32 CC61 DA01 DA02 DA10 DA13 DA13 DA10 DA13 DA13

Claims (7)

[Claims] 1. NO _{X in} exhaust gas by supplying a reducing agent
The A catalyst for reducing and purifying, NO _X as NO _X purification rate with increasing temperature is increased to the maximum of the NO _X purification rate at a particular temperature, temperature increases in the high temperature side from the specific temperature In the case where a plurality of NO _X purification catalysts whose purification rates are decreasing are arranged in series in the exhaust passage of the engine, the upstream NO _X within a predetermined time from the supply of the reducing agent.
A first temperature predicting means for predicting a temperature change of the purifying catalyst, a second temperature predicting means for predicting a temperature change of the downstream NO _X purifying catalyst within a predetermined time from the supply of the reducing agent, and the first temperature predicting means. And the NO by both NO _X purification catalysts based on the temperature change of the upstream NO _X purification catalyst and the temperature change of the downstream NO _X purification catalyst predicted by the second temperature prediction means.
_The optimum reducing agent amount setting means for setting the optimum reducing agent amount that maximizes the _X purification rate, and the optimum reducing agent in the amount set by the optimum reducing agent amount setting means are used for the upstream NO _X purification catalyst and the downstream NO. An exhaust gas purification apparatus for an engine, comprising: a reducing agent supply means for supplying the _X purification catalyst. 2. The method of claim 1, an estimating means for estimating the amount of reducing agent the downstream NO _X purification catalyst outlet, the amount of reducing agent downstream NO _X purification catalyst outlet estimated by said estimating means preset And an optimal reducing agent amount correcting means for correcting the optimal reducing agent amount set by the optimal reducing agent amount setting means so that the estimated reducing agent amount becomes smaller than the upper limit value. Also, an engine exhaust purification device characterized by the following. 3. The method of claim 2, said estimating means includes first estimating means for estimating the amount of reducing agent in the upstream NO _X purification catalyst outlet, the upstream NO _X purification estimated by the first estimating means An exhaust emission control device for an engine, comprising: second estimating means for estimating the reducing agent amount at the downstream NO _X purification catalyst outlet based on the reducing agent amount at the catalyst outlet. 4. The method according to claim 3, wherein the first estimating means is
An exhaust emission control device for an engine, which is estimated based on a temperature change of the upstream NO _x purification catalyst predicted by the first temperature prediction means and an exhaust gas flow rate. 5. The third estimating means according to claim 3,
An exhaust gas purification apparatus for an engine, which is estimated based on a temperature change of the downstream NO _X purification catalyst predicted by the second temperature prediction means and an exhaust gas flow rate. 6. The reducing agent supply means according to claim 1, wherein the reducing agent supply means supplies the reducing agent by an auxiliary injection for additionally injecting fuel in an expansion stroke or an exhaust stroke after main injection of fuel. Engine exhaust purification device. 7. A set of hardware resources including a computer
And the upstream NO within a predetermined time from the supply of the reducing agent_XPurification
Temperature Prediction Procedure for Predicting Temperature Change of Chemical Catalyst and Reduction
NO on the downstream side within a predetermined time from the supply of agent_XPurification catalyst temperature
Second temperature prediction procedure for predicting change, and the first temperature prediction
Upstream NO predicted by the procedure and the second temperature prediction procedure
_XPurification catalyst temperature change and downstream NO_XPurification catalyst temperature
Both of the above NO based on changes_XNO by purification catalyst_Xpurification
Optimal reducing agent amount that sets the optimal reducing agent amount that maximizes the rate
It is set by the setting procedure and the above-mentioned optimal reducing agent amount setting procedure.
The optimum amount of reducing agent _XReduce and purify,
NO as temperature rises_XPurification rate rises to a certain
Maximum NO at temperature_XIndicates the purification rate, higher than the specified temperature
NO on the warm side as the temperature rises_XThe purification rate has decreased
Going upstream NO_XPurification catalyst and downstream NO_Xpurification
The reducing agent supply procedure for supplying the catalyst to the above hardware
A computer professional characterized by causing resources to execute
Gram.