JP2003293738A - NOx CLEANING DEVICE FOR INTERNAL COMBUSTION ENGINE - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a NOx cleaning device for effectively suppressing the occurrence of ammonia slip while maintaining a high NOx cleaning factor. <P>SOLUTION: When ammonia or urea water is supplied to a NOx catalyst 17, provided in an exhaust system 2 for an engine 1 for adsorbing the ammonia and selectively reducing NOx in exhaust gas, with reducer supply means 29, a target NOx cleaning factor Mη is derived by target NOx cleaning factor deriving means, in accordance with the operated condition of the engine 1 and a catalyst temperature Tg of the NOx catalyst 17, an actual NOx cleaning factor η of the NOx catalyst 17 is derived by actual NOx cleaning factor deriving means 44, and an ammonia addition amount DNH<SB>3</SB>of the reducer supply means 29 is controlled by control means 45, depending on a comparison result of the target NOx cleaning factor Mη with the actual NOx cleaning factor η. <P>COPYRIGHT: (C)2004,JPO

Description

DETAILED DESCRIPTION OF THE INVENTION [0001] [0001] The present invention relates to an exhaust gas containing oxygen
Equipped with NОx catalyst having NОx purifying action under excess atmosphere
The present invention also relates to an NОx purification device for an internal combustion engine. [0002] 2. Description of the Related Art Urea water is added to exhaust gas for hydrolysis.
Ammonia generated by or directly added ammonia
Purifying device using as a reducing agent of a selective reduction catalyst
Is known. Such an NОx purification device is
When mounted on a vehicle equipped with an internal combustion engine such as a gin,
Exhaust gas in the exhaust system of Seki
Selective reduction catalyst capable of purifying NOx under ambient atmosphere, so-called urea
An SCR catalyst (hereinafter referred to as “NОx catalyst”) is provided,
Urea water or ammonia is used as a reducing agent from the upstream side of the catalyst.
So that it is added to the exhaust gas and supplied to the NОx catalyst.
Make up. Generally, NOx purification in a NOx purification device
The conversion rate largely depends on the performance of the NОx catalyst,
The N @ x catalyst using ammonia as a reducing agent as described above is
In the region where the temperature exceeds about 350 ° C., N
It has the property of reducing Ox. [0003] When urea water is added to exhaust gas,
As a result of hydrolysis and thermal decomposition as in (1),
Near (NH3) is generated.     (NH2) 2CO + H₂O → 2NH₃+ CO₂... (1) Ammonia (NH3) and nitrogen oxides (N
Оx) depends on the level of the catalyst temperature, that is,
Equation (2) is mainly used at high temperature, and equation (3) is mainly used at low temperature.
It is known that each response takes place.     4NH₃+ 4NO + O₂→ 4N₂+ 6H₂O ... (2)     2NH₃+ NO + NO₂→ 2N₂+ 3H₂O · · · · (3) The N @ x catalyst using ammonia as a reducing agent is shown in FIG.
As shown by the solid line in FIG. 5, the absorption of ammonia into the NОx catalyst
Since the NOx purification rate is higher as the deposition amount is higher, NО
To obtain a high purification rate of the x catalyst, control the ammonia adsorption
It is preferable to control. Ammo that can be adsorbed on NОx catalyst
There is a limit in the near adsorption amount, and the adsorption indicated by a solid line L1 in FIG.
The limit value depends on the catalyst temperature. [0004] SUMMARY OF THE INVENTION
When a NОx purification device having an x catalyst is mounted on a vehicle,
The vehicle changes its operating state from moment to moment.
Flow rate of exhaust gas, NОx amount in exhaust gas,
Since the change in the medium temperature is large, NОx corresponding to the operating state
Ammonia supply to the catalyst is required. NОx catalyst
If the ammonia supply cannot correspond to the operating state, for example
If the supply amount of ammonia is small, the ammonia
The amount of adsorption is insufficient and sufficient N が x reduction cannot be performed.
If the supply amount is too large and exceeds the adsorption limit, NОx
Ammonia not adsorbed by the medium is discharged into the atmosphere
A phenomenon called ammonia slip easily occurs. Book
The present invention provides a method for reducing ammonia while maintaining a high NОx purification rate.
Internal combustion that can effectively suppress the occurrence of aslip
An object of the present invention is to provide a NOx purification device for an engine. [0005] SUMMARY OF THE INVENTION An internal combustion engine according to the present invention
NOx purifying devices are provided in an exhaust system of an internal combustion engine.
N that adsorbs monia and selectively reduces NOx in exhaust gas
Supply ammonia or urea water to Ox catalyst and NOx catalyst
Reducing agent supply means, the operating state of the internal combustion engine, and NO
x of the catalyst temperature of the catalyst or a parameter correlated to the catalyst temperature
The purpose of deriving the target NOx purification rate as a reference based on one
Target NOx purification rate deriving means and actual NOx by the NOx catalyst
Means for deriving an actual NOx purification rate for deriving a purification rate;
and the target NOx purification rate derived by the x purification rate deriving means.
NOx purification derived by the actual NOx purification rate deriving means
System for controlling the reducing agent supply means according to the comparison result with the conversion rate
Control means. According to the present invention, the target NОx
Supply of reducing agent according to the result of comparison between conversion rate and actual N 実 x purification rate
Since the amount of addition is corrected by the means, the return of NOx emission
An appropriate amount of reducing agent so that the required amount of ammonia is absorbed
Can be supplied. [0006] DESCRIPTION OF THE PREFERRED EMBODIMENTS Internal combustion engine as an embodiment of the present invention
The NOx purification device of Seki will be described. In FIG.
Indicates a diesel engine mounted on a vehicle (not shown)
(Hereinafter referred to as “engine”). Engine 1 is engine
The output control is performed by the gin controller 5. En
The gin control device 5 is, here, a well-known
Of the intake air flow from the airflow sensor and the fuel system
Fuel injection amount, fuel injection timing, engine speed, etc.
A signal indicating that the child is in a dark state is sent to the exhaust gas control device 4.
I'm working. Exhaust gas control device 4 and engine control device
5 is a well-known microcomputer whose main part is composed
Are connected so that they can communicate with each other via a control communication line.
Is tied. [0007] The NOx purifying device is an exhaust manifold of the engine 1.
To the exhaust pipe 28 that connects to the hold 25 and composes the exhaust system
NO that is provided to selectively reduce NOx in the exhaust gas 24
Supply ammonia to x catalyst 17 and NOx catalyst 17
The reducing agent supply means 29 and the
Monia basic addition amount D_NH3Derivation of basic additive amount
Means 42 and a base based on the catalyst temperature Tg of the NOx catalyst 17.
The target NOx purification rate for deriving the reference target NOx purification rate Mη
Actual NOx purification by the conversion rate deriving means 43 and the NOx catalyst 17
Actual NOx purification rate deriving means 44 for deriving the conversion rate η;
Target NOx derived by the NOx purification rate deriving means 43
Derived by the purification rate Mη and the actual NOx purification rate deriving means 44
In accordance with the result of comparison with the actual NOx purification rate η
And control means 45 for controlling the supply means 29. [0008] The NOx catalyst 17 is a catalyst supporting catalyst having a honeycomb structure.
A catalyst component is attached to the body.
Stored in the casing of the NOx catalytic converter 27
Have been. As the NOx catalyst 17 which is a selective reduction catalyst
Are vanadium-based, platinum-based, and zeolite-based.
The NOx catalyst 17 uses ammonia (NH₃)
This is for selectively reducing NOx in the gas 24,
In the monia adsorption state, NOx in the exhaust gas 24 is touched.
According to the medium temperature, that is, at a high temperature, the above equation
(2) When the temperature is low, the reaction of the above formula (3) is mainly performed.
Promotes the denitration reaction between ammonia and nitrogen oxides
Things. The NОx catalyst 17 outputs a catalyst temperature Tg.
A catalyst temperature sensor 22 is provided. In addition,
A parameter that correlates to the medium temperature, such as engine
The number of turns, fuel injection amount, operating time for each engine operating area,
Calculate the estimated value of the catalyst temperature considering the outside air temperature and calculate the catalyst temperature.
It may be used as Tg. The reducing agent supply means 29 includes a front N @ x sensor 1
9 and an exhaust pipe 28 between the NОx catalyst 17 and
Urea water is directed toward the upstream opening side of the Ox catalytic converter 27.
The addition nozzle 18 to be sprayed and added,
The connected injection pipe 31 and the upstream end of the injection pipe 31
Supply of compressed air to the blown air tank 32 and the injection pipe 31
The compressed air control valve 33 to be controlled and the compressed air control valve 33
A urea water supply pipe 34 connected to the injection pipe at a downstream position,
A urea water tank 35 containing urea water for addition,
The urea water in the tank 35 is supplied from the urea water supply pipe 34 to the injection pipe 3
1 and a urea water supply unit 37 for metering and supplying
You. These compressed air control valve 33 and urea water supply unit 37
It is connected to the control means 45 by a signal line. The exhaust pipe 28 on the downstream side of the NOx catalyst 17
Is the NOx concentration Snoxr downstream of the NОx catalyst 17.
After the detection, an NОx sensor 26 is provided. Each NО
NOx concentrations Snoxf, Sn from x sensors 19, 26
oxr is output to the actual NOx purification rate deriving means 44. The target NОx purification rate deriving means 43 is, for example,
An eye determined by the catalyst temperature Tg as shown in FIG.
This is a map of the target NОx purification rate Mη.
Deriving the target NOx purification rate Mη correlated to the medium temperature Tg
Output to control means 45. The actual NOx purification rate deriving means 44 calculates each N は x
NOx concentrations Snoxf and Sno from sensors 19 and 26
xr is subjected to a difference process of Snoxf-Snoxr,
Further, the value is divided by Snoxf to obtain the actual NOx purification rate (η).
Is an arithmetic circuit that calculates. The basic addition amount deriving means 42 is shown in FIG.
The amount of ammonia adsorbed on the N @ x catalyst 17 indicated by 2 is satisfied.
Such an addition amount map, and appropriately according to the catalyst temperature Tg.
Basic amount of ammonia added D_NH3Select the control means 4
5 is output. In the present embodiment, the basic addition amount deriving means 42
Target NОx purification rate deriving means 43, actual NОx purification rate deriving means
The exhaust gas control device 4 is configured by the control unit 44 and the control unit 45.
Is done. The control means 45 includes the compressed air control valve 33 and the urea
The driving of the water supply unit 37 is controlled. Next, the NОx control process by the NOx purifying device
The process will be described with reference to the NOx purification processing routine of FIG.
You. Engine of a vehicle (not shown) equipped with a NOx purification device
When the engine 1 is driven, the engine control device 5
Whether the sensors of various control systems related to drive are normal or not
Check whether the check result is normal,
In K), a well-known fuel in accordance with each input value of the above-mentioned related sensor is used.
Sends control signals to the fuel injection system and fuel supply system to execute control
The sensor output and the like obtained at that time are
Also to send. The exhaust gas control device 4 has an engine key
NOx purification in the NOx purification processing routine of FIG.
The processing control is repeated every predetermined control cycle. NOx purification
In the processing routine, key-on is confirmed in step S1,
In step S2, the catalyst temperature Tg, the NOx concentration Snoxf,
Capture Snoxr and other data. In step S3, the NOx concentration Snoxf,
The actual NОx purification rate η is calculated using the Snoxr and the catalyst temperature Tg.
To be newly adsorbed to the NОx catalyst 17 based on the
A) Basic addition amount D as amount_NH3When each is calculated
In both cases, the target NОx purification rate Mη based on the catalyst temperature Tg
From the map which is the target NОx purification rate deriving means 43.
Then, the process proceeds to step S4. In step S4, the actual NОx purification rate η is
The actual NОx purification rate η is compared with the target NОx purification rate Mη.
If the target NОx purification rate Mη is exceeded, the ammonia
Proceed to step S7 because there is a risk of aslip and return
Urea water supply unit 37 to stop and control the agent supply means 29.
To stop the addition of urea water and end this control cycle
I do. The actual NОx purification rate η is equal to the target NОx purification rate Mη.
If not, the process proceeds to step S5. Step
In step S5, actual NОx purification rate = target NОx purification rate M
In the case of η, the basic addition amount of ammonia D_NH3Against
There is no correction, but actual NОx purification rate η <target NОx purification rate M
η, the basic addition amount D_NH3Is the target NОx purification rate
The difference is corrected so as to satisfy Mη, and the reducing agent addition amount (an
Actual amount of monia) D_{N H3}(n) is determined and step
Proceed to S6. In step S6, the reducing agent addition amount D _NH3
(n) or basic addition amount D_NH3Equivalent to the amount of ammonia
So that the amount of urea water to be added can be added.
Drive control of the urea water supply unit 37 of the
To end. As a result, the urea water supply unit 37
A Basic addition amount D_NH3Or the basic addition amount is corrected
Amount of reducing agent added D_NH3(n) Urea adjusted to a corresponding flow rate
Water is discharged from the addition nozzle 18 via the injection pipe 31 to the exhaust pipe.
28. In this embodiment, the actual NОx purification rate η and the target NО
x reducing agent supply means 29 according to the result of comparison with x purification rate Mη.
Is controlled by the control means 45, the actual NОx purification rate η is incorrect.
Even if there is a difference, the basic addition amount of ammonia D_NH3Suitable
The correction required for the reduction of NOx emissions
Apply an appropriate amount of ammonia to NОx
Ammonia is adsorbed on the NОx catalyst 17
While maintaining a high NОx purification rate,
The generation of ammonia slip can be effectively suppressed.
Wear. In this embodiment, in step S4 of FIG.
The actual N 実 x purification rate η exceeds the target NОx purification rate Mη
If there is, the flow proceeds to step S7 and the reducing agent supply means 2
9 to stop and inhibit the addition of urea water
However, the present invention is not limited to such a form. Another control type using the flowchart of FIG.
State. In FIG. 3, steps T1 to T4 are diagrams.
Since the contents are the same as Steps S1 to S4 of Step 2,
The description of these contents is omitted. Also implement this control
, The exhaust gas control device 4 determines the basic addition amount D_NH3
Map information (not shown) indicating the amount of correction for addition / subtraction to
The information is stored in advance in a memory (not shown). In FIG. 3, the steps are sequentially performed from step T1.
Is performed, and in step T4, the actual NОx purification rate
If η exceeds the target NОx purification rate Mη,
Proceeding to T7, the basic addition amount of ammonia D_NH3From
Reduction agent addition amount D after subtracting a predetermined amount_NH3(n)
Proceed to step T6. Actual NОx purification rate η is the target NОx purification
If the ratio is less than the rate Mη, the process proceeds to step T5 where the ammonia
Basic addition amount D_NH3Amount of reducing agent added D
_NH3(n) is determined, and the process proceeds to step T6. Step T
6, the actual NОx purification rate η and the target NОx purification rate Mη
The reducing agent added or subtracted according to the comparison result
Addition D_NH3The amount of aqueous urea corresponding to the amount of ammonia in (n)
The urea water supply unit of the reducing agent supply means 29 is added so that it can be added.
37, and the current control cycle is completed. With this configuration, the urea water supply unit 37
Urea adjusted to a substantial flow rate that has been added or subtracted
Water is discharged from the addition nozzle 18 via the injection pipe 31 to the exhaust pipe.
28. Therefore, urea water is supplied to the NОx catalyst 17.
Higher NОx purification rate by eliminating the additive-free state
While effectively suppressing the occurrence of ammonia slip
Can be controlled. [0027] According to the present invention, the target NOx purification rate and the actual
Return NOx emissions according to the comparison result with NOx purification rate
The appropriate amount of ammonia that will be the amount of ammonia needed
High N 、 x purification rate and ammonia
The reduction of the lip can be achieved at the same time.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an overall configuration diagram of an NОx purification device showing one embodiment of the present invention. FIG. 2 is a flowchart showing a routine of NОx purification processing executed by the NОx purification device of FIG. 1; FIG. 3 is a flowchart showing another routine of the NОx purification process executed by the NОx purification device of FIG. 1; FIG. 4 is a characteristic diagram showing a relationship between a target NОx purification rate and a catalyst temperature. FIG. 5 is a characteristic diagram showing a relationship between an ammonia adsorption amount of a NOx catalyst and a NOx purification rate. FIG. 6 is a characteristic diagram showing a relationship between a catalyst temperature of an NОx catalyst and an amount of adsorbed ammonia. [Description of Signs] 1 Internal combustion engine 2 Exhaust system 17 NOx catalyst 24 Exhaust gas 29 Reductant supply means 43 Target NОx purification rate derivation means 44 Actual NOx purification rate derivation means 45 Control means Tg Catalyst temperature η Actual NOx purification rate Mη Reference NOx Purification rate

   ────────────────────────────────────────────────── ─── Continuation of front page    (72) Inventor Kiyoshi Kawatani             5-33-8 Shiba, Minato-ku, Tokyo Mitsubishi Motors             Industrial Co., Ltd. (72) Inventor Satoshi Hiranuma             5-33-8 Shiba, Minato-ku, Tokyo Mitsubishi Motors             Industrial Co., Ltd. (72) Inventor Takeshi Hashizume             5-33-8 Shiba, Minato-ku, Tokyo Mitsubishi Motors             Industrial Co., Ltd. (72) Inventor Reiko Momomeki             5-33-8 Shiba, Minato-ku, Tokyo Mitsubishi Motors             Industrial Co., Ltd. (72) Inventor Shino Saki Ritsuko             5-33-8 Shiba, Minato-ku, Tokyo Mitsubishi Motors             Industrial Co., Ltd. (72) Inventor Shinichi Saito             5-33-8 Shiba, Minato-ku, Tokyo Mitsubishi Motors             Industrial Co., Ltd. (72) Inventor ▲ Taka ▼ Bridge Yoshinori             5-33-8 Shiba, Minato-ku, Tokyo Mitsubishi Motors             Industrial Co., Ltd. F-term (reference) 3G091 AA02 AA18 AA28 AB05 BA14                       CA13 CA17 DB10 EA01 EA05                       EA08 EA09 EA14 EA18 EA30                       EA33 GA06 GB01W GB06W                       GB09W HA36 HA37 HA39                       HA42                 4D048 AA06 AB02 AB07 AC03 AC04                       CC61 DA01 DA02 DA06 DA10                       DA20 EA04

Claims (1)

1. A NOx catalyst provided in an exhaust system of an internal combustion engine for adsorbing ammonia and selectively reducing NOx in exhaust gas, and a reducing agent for supplying ammonia or urea water to the NOx catalyst. Supply means; target NOx purification rate deriving means for deriving a reference target NOx purification rate based on an operating state of the internal combustion engine, and a catalyst temperature of the NOx catalyst or one of parameters correlated to the catalyst temperature; Actual NO for deriving the actual NOx purification rate by the catalyst
x purification rate deriving means, and the target N derived by the target NOx purification rate deriving means.
Control means for controlling the reducing agent supply means in accordance with a comparison result between the Ox purification rate and the actual NOx purification rate derived by the actual NOx purification rate deriving means. Purification device.