JP2003269145A - NOx PURIFICATION DEVICE OF INTERNAL COMBUSTION ENGINE - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an NOx purification device of an internal combustion engine capable of preventing stop frequency of the NOx purification device due to a urea plucking phenomenon in the NOx purification device from needlessly increasing. <P>SOLUTION: This device is provided with: an NOx catalyst 17 installed in an exhaust system 2 of an engine 1 for selectively reducing NOx; a feed passage rn located in the upstream of the NOx catalyst and communicating with the exhaust system 2; a urea water feed device (reducer feed means) 29 for feeding urea water to the exhaust system through the feed passage rn; a high-pressure air tank 32 (air feed means) for feeding compressed air to the exhaust system 2 from an upstream position of a feed position (g) of the urea water; a control means for controlling the operation of the feed device 29; an air pressure sensor 24 (air feed state detection means) for detecting pressure pa in the feed passage rn; and a determination means for feeding the compressed air after adding the urea water by the control means and for determining the presence of clogging of the feed passage according to the pressure pa detected by the sensor 24. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a NOx purifying device for purifying NOx in exhaust gas of an internal twist engine, and more particularly to a device for spraying an exhaust gas reducing agent on the upstream side of a reduction catalyst provided in an exhaust system. The present invention relates to a NOx purification device for an internal combustion engine.

[0002]

2. Description of the Related Art NOx in exhaust gas discharged from an internal twisting engine
Is purified by a NOx purification device, and in particular, a NOx purification device used in a diesel engine has a urea SCR catalyst (NOx catalyst) in its exhaust system, and a reducing agent supply means is arranged upstream of the urea SCR catalyst. Has been. This reducing agent supply means supplies urea water (urea water) to the exhaust system, and urea contained therein is hydrolyzed and pyrolyzed as shown in the following formula (1) to release NH3.

(NH ₂ ) 2CO + H ₂ O → 2NH ₃ + CO ₂ ... (1) Ammonia (NH ₃ ) generated by hydrolysis is supplied to the SCR catalyst (NOx catalyst) as a reducing agent. This allows the SCR catalyst to purify NOx in an oxygen excess atmosphere. By the way, as described above, in the urea water addition type NOx purifying device, instead of directly supplying ammonia used as a reducing agent to the exhaust passage, urea water that is easy to handle is used, and the urea water is atomized for transportation. Is supplied to the exhaust passage by being carried by the air flow, that is, is supplied to the exhaust passage using the air assist method, and the ammonia hydrolyzed there is added to S
Supplying to the CR catalyst.

[0004]

By the way, in the NOx purifying device adopting the air assist system, urea water is placed on the carrier air flow flowing in the supply passage, and the urea water is introduced into the exhaust passage from the injector at the downstream end of the supply passage. To supply. A carrier air supply unit is connected to an upstream portion of the supply passage, and an addition port of a urea water addition pipe extending from the reducing agent supply unit is opened between the air supply unit and the injector. here,
The atomized urea water blown from the addition port of the urea water addition pipe and added to the supply passage is likely to adhere to the inner wall surface of the supply passage, which easily becomes solid matter when water is evaporated due to the influence of the air flow for transportation. However, this solid generation itself cannot be avoided. In particular, when the NOx purification device adopting the air assist system is mounted on the vehicle, the supply passage through which the air for transportation is often curved or the flow passage cross-sectional area is changed. Near the mouth and injectors,
A portion where the air flow line is disturbed or a swirl portion (turbulent flow) is likely to occur, and urea water is likely to adhere to such a portion.

If this state of adhesion of urea water continues, the water content evaporates each time and the amount of solidification increases, which narrows the cross-sectional area of the air flow path at that part, and in some cases the flow path is closed, so-called urea plugging. A phenomenon occurs, which causes the urea water addition type reducing agent supply means to not operate properly, and NO
There is a problem that the x purification function stops.

In addition, when the control means of such a NOx purifying device is provided with plugging detection means in advance, this plugging detection means detects, for example, the air pressure in the supply passage through which the transport air flows, and this occurs. If the value exceeds the predetermined value at, it is immediately determined that the NOx purification device has a failure. Therefore, even when the urea plugging phenomenon occurrence part can be easily dissolved and the passage can be restored to the communication state, it is determined that there is a failure, and the stop frequency of the NOx purification device is undesired. It is easy to increase. Based on the above problems, the present invention provides a NOx purification device for an internal combustion engine that can prevent an excessive increase in the stop frequency of the NOx purification device due to the urea plugging phenomenon in the NOx purification device that adds urea water. With the goal.

[0007]

According to a first aspect of the present invention, there is provided a NOx catalyst provided in an exhaust system of an internal combustion engine for selectively reducing NOx in exhaust gas, a supply passage communicating with the exhaust system upstream of the NOx catalyst, Reducing agent supply means for supplying urea water to the exhaust system through the supply passage, air supply means for supplying pressurized air to the exhaust system from a portion upstream of the urea water supply portion in the supply passage, and the reduction Control means for controlling the operation of the agent supply means and the air supply means, air supply state detection means for detecting the pressure or flow rate in the supply passage, and the control means for operating the air supply means to supply pressurized air. Along with this, there is provided a determining means for determining whether or not the supply passage is clogged according to the pressure or the flow rate detected by the air supply state detecting means. In the supply passage for supplying urea by putting pressurized air on the exhaust system, the water content of the urea water evaporates and solidifies at the inner wall or the like, which may cause clogging of the flow path, that is, a urea plugging phenomenon may occur. Here, before the judgment of such clogging by pressurized air, once urea water is supplied, the solidified urea is dissolved in the supply passage and the clogged urea is dissolved and discharged. If possible clogging, it is possible to prevent erroneous determination of abnormality and purify NOx, and it is possible to prevent the stop region of the NOx purification device from unnecessarily expanding.

According to a second aspect of the present invention, in the NOx purifying device for an internal combustion engine according to the first aspect, a temperature sensor for detecting the temperature of the urea water is provided, and the determination means is the urea detected by the temperature sensor. When the water temperature is lower than a predetermined temperature, the determination operation of the determination means is prohibited. In this case, when the urea water is at a low temperature, the saturation concentration decreases, and it is not possible to expect dissolution and discharge of the clogging portion of the supply passage with such low-temperature urea water. It is prohibited to determine whether or not the supply passage is clogged by such determination means, and waits for the temperature to rise. Preferably,
The NOx purifying device for an internal combustion engine according to claim 2,
A heater that raises the temperature of the urea water may be provided, and the determination unit may operate the heater when the temperature of the urea water detected by the temperature sensor is lower than a predetermined temperature.

In this case, when the urea water is below a predetermined temperature,
The heater can be operated to raise the temperature of the urea water, and the urea water having a high saturation concentration can easily dissolve and discharge the clogging portion of the supply passage.

Preferably, in the NOx purifying device for an internal combustion engine according to claim 2, a heater for raising the temperature of the urea water is provided, and the judging means has a urea water temperature detected by the temperature sensor lower than a predetermined temperature. At this time, when the heater is operated and it is determined that the urea water temperature detected by the temperature sensor is equal to or higher than a predetermined temperature after the heater is operated,
It may be determined whether or not the supply passage is clogged.
In this case, the determination means activates the heater to raise the temperature of the urea water when the temperature of the urea water is lower than the predetermined temperature, and when the temperature of the urea water exceeds the predetermined temperature, the urea water dissolves and discharges the clogging part of the supply passage. Can be easily and reliably performed, and the presence or absence of clogging of the supply passage can be accurately determined by the determination means.

According to a third aspect of the present invention, in the NOx purifying device for an internal combustion engine according to the first aspect, when the determination means determines that the clogging failure requires a flow path recovery process of the supply passage, It is characterized in that the supply of urea water by the reducing agent supply means is prohibited. When the determination unit determines a clogging failure that requires the flow path recovery process of the supply passage by the pressurized air, the supply of the urea water is prohibited, so that the unnecessary operation of the NOx purification device can be stopped and, for example, for the passenger. Environmental considerations are promptly made by promoting maintenance at a repair shop.

A fourth aspect of the present invention is an NOx catalyst provided in an exhaust system of an internal combustion engine for selectively reducing NOx in exhaust gas,
Reducing agent supply means for supplying urea water via a supply passage communicating with the exhaust system upstream of the NOx catalyst, and pressurized air from the supply passage upstream of a supply portion of urea water supplied from the reducing agent supply means. For supplying air, a control means for controlling the operation of the reducing agent supply means and the air supply means, an air supply state detection means for detecting a pressure or a flow rate in the supply passage, and the air supply means by the control means. And supplying pressurized air, and further comprising a determining means for determining whether or not the supply passage is clogged according to the pressure or the flow rate detected by the air supply state detecting means, the determining means is When it is determined that there is clogging, the control means operates the reducing agent supply means to supply urea water, and then the air supply means is operated to supply pressurized air. And judging the clogging presence of the supply passage in response to pressure or flow detected by the air supply state detection means with. in this way,
When the determining means determines that the supply passage is clogged, once the urea water is supplied, the solidified and clogged urea in the supply passage is dissolved and discharged, and then the clogging is determined again. If it is a clog that can be dissolved, it is possible to prevent erroneous determination of abnormality and purify NOx.
Even if the urea water is supplied, when the solidified urea cannot be dissolved and discharged into the supply passage, the clogging is determined, and thus the urea clogging can be accurately diagnosed.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION A NOx purifying apparatus for an internal combustion engine as an embodiment of the present invention will be described below with reference to FIG. The NOx purification device for the internal combustion engine here (hereinafter simply referred to as NO
x purification device) is a multi-cylinder diesel engine (hereinafter simply referred to as engine) mounted on a vehicle (not shown) 1
It is attached to the exhaust system 2 of. The engine 1 includes an engine control device (the engine ECU 10 forming a main control unit is shown in the drawing) 3 and a NOx purification device is provided in an exhaust system of the engine 1. The engine EC of the engine control device 3
The U10 and an exhaust gas control device (hereinafter simply referred to as an exhaust system ECU) 4 which constitutes a control unit of the NOx purification device are interconnected by a CAN intercommunication system (hereinafter simply referred to as a communication line) 5 so that they can communicate with each other.

In FIG. 1, the engine 1 includes a fuel injection system that adjusts the amount of fuel supplied to a combustion chamber (not shown), a fuel supply system that adjusts the discharge amount of a fuel pump, and an NOx purification system that is an exhaust gas aftertreatment device. And an exhaust system having a device. In FIG. 1, an engine ECU used by the engine 1
An accelerator pedal opening sensor 9 that detects an accelerator pedal opening θa of the engine 1 and a crank angle sensor 15 that detects crank angle information Δθ are connected to the engine 10. Here, the crank angle information Δθ is used by the engine ECU 10 to derive the engine speed Ne and is also used for fuel injection timing control described later.

The engine ECU 10 has a large number of ports in its input / output circuit, takes in detection signals from the accelerator pedal opening sensor 9, the crank angle sensor 15, etc., and controls the fuel adjustment section 11 via a line (not shown). It functions to send out a signal. The fuel injection system is provided with a fuel adjustment unit 11 for injecting fuel by an injector 12 into a combustion chamber (not shown), and the same unit functions as a fuel control unit n2.
It is controlled by U10.

The fuel discharge amount adjusting unit 121 supplies the high pressure fuel of the high pressure fuel pump 123 driven by the engine to the common rail 122 after making the pressure constant. The fuel discharge amount adjusting unit 121 is connected to the engine ECU 10, and can adjust the discharge amount so that the pressure in the common rail 122 becomes a predetermined pressure pf according to the output D (pf) of the fuel pressure control unit n1. The fuel adjustment unit 11 adopts a common rail system in which high pressure fuel injection is performed by the injector 12 connected to the common rail 122 via the electromagnetic valve Vp. The electromagnetic valve Vp is connected to the engine ECU 10 and outputs the output D (i
njn) signal, the fuel injection amount and the injection timing can be adjusted. Only one connecting line between the electromagnetic valve Vp and the engine ECU 10 is shown.

Here, the fuel control unit n2 determines the engine speed N
The basic fuel injection amount INJb corresponding to e and the accelerator pedal opening θa (corresponding to the lever opening θr) is obtained, and the respective correction values dt and dp of the water temperature and the atmospheric pressure corresponding to the operating conditions are obtained.
Fuel injection amount INJn (= INJb + dt + d
p) is derived. Further, the injection timing is derived by adding a correction according to the operating condition to the known basic advance value. Moreover,
Output D corresponding to the calculated injection timing and fuel injection amount INJ
The (injn) signal is set in a fuel injection driver (not shown) and output to the electromagnetic valve Vp of the fuel adjusting section 11 to control the fuel injection of the injector 12.

The exhaust system 2 of the engine 1 is equipped with a NOx purification device. The NOx purification device outputs an NOx concentration Snoxf upstream of the addition nozzle 18 and an SCR catalyst 17 which is an NOx catalyst mounted in the middle of the exhaust pipe 16, an addition nozzle 18 of urea water arranged upstream thereof. Sensor 1
9, a catalyst temperature sensor 22 that outputs the catalyst temperature tg of the SCR catalyst 17, and an exhaust system ECU 4 that forms a control unit of the NOx purification device. Catalyst temperature is a correlated parameter,
For example, the estimated value of the catalyst temperature may be calculated and adopted in consideration of the engine speed and the fuel amount, the operating time for each engine operating region, and the outside air temperature. Exhaust gas flowing out from the engine 1 to the exhaust passage E passes through the exhaust manifold 25 and NOx downstream thereof.
It passes through an exhaust pipe 28 equipped with a catalytic converter 27 and is released into the atmosphere through a muffler (not shown).

The NOx catalytic converter 27 has a ceramic catalyst carrier having a honeycomb structure (not shown) in a casing, and a catalyst metal (for example, vanadium) for functioning as the SCR catalyst 17 is carried on the carrier. SCR catalyst 1
Reference numeral 7 denotes ammonia (NH
It is possible to adsorb 3) and selectively reduce NOx in the exhaust gas. Here, in the ammonia adsorption state, the SCR catalyst 17 mainly reacts NOx in the exhaust gas according to the level of the ambient temperature, that is, when the temperature is high, the reaction of the following formula (2) and the formula (3) below are mainly performed, and NH3 The denitration reaction with nitrogen oxides can be promoted.

4NH ₃ + 4NO + O ₂ → 4N ₂ + 6H ₂ O (2) 2NH ₃ + NO + NO ₂ → 2N ₂ + 3H ₂ O (3) Supply path rn in exhaust path E of exhaust pipe 28 Aqueous urea supply device 29 as reducing agent supply means for supplying aqueous urea via
Also, a high pressure air tank 32 as an air supply means is mounted.

As shown in FIGS. 1 and 2, the supply passage rn is formed by a supply pipe 31, an air tank 32 is connected to the upstream end of the supply pipe 31, and an addition nozzle 18 facing the exhaust passage E is connected to the downstream end. Thus, the urea water is sprayed toward the downstream side, that is, the upstream opening side of the NOx catalytic converter 27. A urea water addition position g, which will be described later, is provided at a position upstream of a supply position f as a urea addition position by the addition nozzle 18 and at a downstream position of the air tank 32. A compressed air supply means (not shown) is connected to the air tank 32 so that the air pressure is always kept constant. The supply passage rn of the supply pipe 31 allows the pressurized air to flow from the air tank 32 to the exhaust passage E through the air valve 33. The urea water supply device 29 is provided at the addition position g in the middle of the supply passage rn.
The downstream end opening of the urea water pipe 34 on the side is communicated. As shown in FIGS. 1 and 2, the urea water pipe 34 has a downstream end opening upstream in the vicinity of the curved portion 311 of the supply passage rn.
The urea water pipe 34 has an upstream end connected to a urea water tank 35, and supplies the urea water in the urea water tank 35 to the supply passage rn side via the urea water supply unit 37.

As shown in FIG. 2, the downstream end opening of the urea water pipe 34 opens toward the inner wall surface of the supply pipe 31 at the addition position g, and urea water can be jetted to the compressed air. The supply pipe 31 is provided with the curved portions 311 and 312 on the downstream side of the addition position g.
And an addition nozzle 18 is provided at the downstream end thereof. Such a supply pipe 31 has the inner wall surface f0 facing the urea water pipe 34 at the addition position g, and the curved portions 311 and 312.
The flow line fl of the air flow is curved on each inner wall surface of the above, and a swirl part fs is easily generated in a part thereof, and as described later, urea plugging phenomenon occurs over time in each of these parts, and the flow path cross-sectional area increases. It is a part that is easy to narrow. Further, a heater 21 for heating urea water is attached to the urea water tank 35, and the heater 21 is drive-controlled by the exhaust system ECU 4.

The urea water supply unit 37, the air valve 33, and the heater 21 are connected to the exhaust system ECU 4 and drive-controlled.
The heater 21 may be, for example, a heater other than the urea water tank 35.
It may be attached to the urea water supply unit 37 side. The supply pipe 31 is provided at the downstream end of the supply pipe 31 (near the addition nozzle 18).
The air pressure sensor 24 as an air supply state detecting means for outputting the air pressure pa therein and the urea water temperature sensor 38 for outputting the temperature Tura of the urea water are provided in the urea water tank 35, respectively, and these outputs are exhausted. It is supplied to the system ECU 4. The exhaust system ECU 4 has a large number of ports in its input / output circuit and can input detection signals from the NOx sensor 19, the catalyst temperature sensor 22, the air pressure sensor 24, the urea water temperature sensor 38, etc., and the air valve 33, the urea water supply. A control signal is sent to the section 37 and the heater 21. Moreover, the CAN communication line 5
It is possible to send and receive data to and from the engine ECU 10 via the.

The exhaust system ECU 4 includes an input / output interface 401, a storage unit 402, a non-volatile memory 403 for battery backup, and a central processing unit 404, and in particular, a NOx purification control function. Next, the NOx purification control process of the engine ECU 10 and the NOx purification device of FIG. 1 will be described along with each control routine of the NOx purification process of FIGS. 3 and 4.

When the engine 1 of a vehicle (not shown) equipped with the NOx purifying device is driven, the engine ECU 10 controls a plurality of control systems such as a fuel injection system, a fuel supply system, and related devices and sensors that are appropriately driven. The check result is fetched, and it is confirmed whether it is normal or not. If the check result is normal (OK), the fuel pressure control unit n1 operates the fuel discharge amount adjustment unit 121 and the fuel control unit n according to the input value of each sensor described above.
2 executes the respective controls of the fuel adjusting section 11 according to the operating range, and outputs the respective sensor outputs obtained at that time to the exhaust system ECU.
Also send to 4.

On the other hand, the exhaust system ECU 4 repeats the main routine of FIG. 3 every predetermined control cycle at the same time when the engine key is turned on. Here, the key-on is confirmed in step sa, and when step sb is reached, catalyst temperature tg, NOx concentration Snoxf, intake air amount U from the engine ECU 10
a, other data is taken in, it is judged whether or not it is an appropriate value, and if it is not normal, a failure indicator light (not shown) is driven, and if it is normal, the routine proceeds to step sc. In step sc, a clogging check process is performed, after that, in step sd, NOx purification process is performed, then in step se, other well-known control process is performed, and the process returns.

When step a1 of the clogging check routine of FIG. 4 showing the clogging check process is reached, the temperature Tura of the urea water is taken in here, and the value exceeds the predetermined temperature Turaβ at which the sufficient urea dissolution performance can be exhibited. Determine if As a result of the determination in step a1, when the temperature of the urea water is low at first, step a2 is reached. Here, the addition amount output DU is fixed to zero (DU = 0), and then step a3
At, it is determined whether the heater driving flag FLGH is on. When the flag FLGH is off (= 0), step a4
In this case, the heater 21 is driven to heat the urea water and the flag FLGH is turned on (= 1). After that, in step a5, the above steps are repeated until the temperature Tura of the urea water exceeds a predetermined temperature Turaβ capable of sufficiently dissolving urea, and when it exceeds, the process proceeds to step a6, the heater 21 is stopped and the heater is being driven. Flag F
LGH is turned off (= 0) and the process returns.

The temperature Tura of the urea water is equal to the predetermined temperature Tura.
After exceeding β, the process proceeds to step a7. Step a7
Then, the air valve 33 is opened to allow the air to flow in the supply passage rn in a constant state. When step a8 is reached, it is determined whether or not the air pressure pa detected by the air pressure sensor 24 exceeds the clogging determination value paα, and the air pressure pa is determined by the determination value pa.
If α or more, it is considered that the supply passage rn is open without clogging, and the process proceeds to step a9.
n is regarded as clogging, and the process proceeds to step a10.

In step a9, the supply passage rn is opened and it is considered that the supply passage rn is in the normal state, and the urea water addition permission is set. As a result, an appropriate amount of ammonia can be supplied to the NOx catalyst 17, and NOx in the exhaust gas can be reduced. In step a8, when it is determined that the flow path is clogged and the process reaches step a10, here, the urea water supply device 2
The cleaning output DU for cleaning the urea water supply unit 37 of No. 9 which is clogged, dissolved and discharged is operated at = DUcr, and the process reaches step a11. In step a11, the timer tn is driven to wait for the elapse of the cleaning time tcr for clogged dissolution discharge, and after the elapse, the process proceeds to step a12. In step a12, the air pressure pa detected by the air pressure sensor 24 is again compared with the clogging determination value paα. Here, if the air pressure pa is below the clogging determination value paα, it is determined to be clogging, and if the air pressure pa is equal to or higher than the clogging determination value paα, it is considered that the supply passage rn is opened, and the process proceeds to step a14.

In step a14, it is considered that the supply passage rn is open and is in a normal state, and the urea water addition permission is set. As a result, ammonia can be supplied to the NOx catalyst 17, and NOx in the exhaust gas can be reduced. If the clogging is not resolved even after the cleaning process for dissolving and discharging the clogging, at step a13,
The clogging failure output is output to the failure indicator lamp rp and turned on, the urea water addition amount output DU (= 0) is held, and the urea water addition prohibition is switched. As a result, when the occupant knows that the addition of ammonia is prohibited by the failure indicator light rp after the clogging failure, the occupant promptly carries out the maintenance of the recovery process for opening the supply passage rn due to the clogging failure, so that the repair shop is promptly repaired. Will transport the vehicle to

Here, after the cleaning, the air pressure pa detected by the air pressure sensor 24 was again judged in step a12 whether or not it exceeds the clogging judgment value paα. However, instead of this, steps a8 and Step a
Each of the 12 clogging determination values paα may be set as follows. That is, by setting the clogging determination value paα in step a8 to be larger than the clogging determination value paβ in step a12, the clogging determination value paα in step a8 can be made relatively large, that is, the clogging determination value paα can be relatively large. If a slight occurrence of the above occurs, the cleaning process can be started promptly, the cleaning ratio can be increased to prevent clogging early, and the frequency of maintenance for opening the supply passage rn can be reduced.

In the above-described embodiment, the air pressure sensor 24 as an air supply state detecting means for outputting the air pressure pa of the supply passage rn is provided in the supply pipe 31, and step a
In 8, the air pressure pa detected by the air pressure sensor 24
The presence or absence of clogging in the supply passage rn is determined by whether or not exceeds the clogging determination value paα. However, in some cases, instead of the air pressure sensor 24, an air flow rate sensor (not shown) may be used to perform the process of step a8 'as shown in FIG.

In this case, the same control is executed except that step a8 shown in FIG. As shown in FIG. 5, step a7
When the process reaches step a8 ', the air flow rate Qrn of the supply passage rn detected by an air flow rate sensor (not shown) proceeds to step a9 without being clogged if the clogging determination value Qrnα is exceeded.
Is determined to be clogged and the process proceeds to step a10. The same determination may be made in step a12. In this case as well, the same operational effects as when the air pressure sensor 24 is used can be obtained.

[0034]

As described above, according to the present invention, urea is solidified by urea water adhering to the inner wall of the supply passage for supplying urea by putting pressurized air in the exhaust system, and this causes the passage to flow. Even if there is a possibility of clogging, before such clogging is judged by pressurized air, urea water is once supplied to dissolve the solidified urea in the supply passage, Since the clogged urea is dissolved and discharged, if it is a clog that can be dissolved, it is possible to prevent erroneous determination of abnormality and purify NOx, and it is possible to prevent the stop frequency of the NOx purifying device from unnecessarily increasing.

According to the second aspect of the invention, when the urea water is at a low temperature, the saturation concentration is lowered, and it is not possible to expect dissolution and discharge of the clogging portion of the supply passage with such low temperature urea water. In such a case, it is prohibited to determine whether or not the supply passage is clogged by a wasteful determining means, and wait for the temperature to rise.

According to the third aspect of the present invention, the urea water supply is prohibited when the determination means determines a clogging failure that requires the flow passage recovery process of the supply passage by the pressurized air, so that the NOx purification device is unnecessary. The operation can be stopped, and environmental consideration can be promptly made by, for example, urging an occupant to perform maintenance at a repair shop.

According to the invention of claim 4, when the judging means judges clogging of the supply passage, urea water is once supplied to dissolve and discharge the urea solidified and clogged in the supply passage. Then, since the clogging is determined again, if it is a clog that can be dissolved, the erroneous determination of abnormality is prevented and NO is determined.
x purification can be achieved, and once urea water is supplied,
When the solidified urea cannot be dissolved and discharged in the supply passage, the clogging is determined, and thus the urea clogging can be accurately diagnosed.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an NOx purifying device as one embodiment of the present invention and an engine equipped with the same.

2 is a partially enlarged cross-sectional view of a supply passage and an exhaust passage used in the NOx purification device of FIG.

FIG. 3 is a flowchart of a main routine used by the exhaust system ECU of FIG.

FIG. 4 is a flowchart of a clogging check routine used by the exhaust system ECU of FIG.

5 is a main part flowchart of a modified example of a clogging check routine used by the exhaust system ECU of FIG. 1. FIG.

[Explanation of symbols]

1 engine 2 exhaust system 4 Exhaust system ECU 17 SCR catalyst (NOx catalyst) 22 Catalyst temperature sensor (catalyst temperature detection means) 24 Air pressure sensor (air supply state detection means) 29 Urea water supply device (reducing agent supply means) 31 Supply pipe 37 Urea water supply unit tg catalyst temperature Output equivalent to DU addition amount g Urea water supply site rn supply passage pa pressure

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI Theme Coat (reference) F01N 3/08 B01D 53/34 ZAB 3/22 301 (72) Inventor Kawaya St., Shiba 5-chome, Minato-ku, Tokyo 33-8 ・ Inside Mitsubishi Motors Corporation (72) Inventor Satoshi Hiranuma 5-5 Shiba, Minato-ku, Tokyo 33-8 ・ Inside Mitsubishi Motors Corporation (72) Kenji Kawai 5-5 Shiba, Minato-ku, Tokyo 33-8 ・ Inside Mitsubishi Motors Corporation (72) Inventor Go Hashizume 5-5 Shiba, Minato-ku, Tokyo 33-8 ・ Inside Mitsubishi Motors Corporation (72) Inventor Reiko Momomeki 5-chome Shiba, Minato-ku, Tokyo 33-8 ・ Inside Mitsubishi Motors Corporation (72) Inventor Shinichi Saito 5-5, Shiba, Minato-ku, Tokyo (72) Inventor Mitsubishi Motors Corporation (72) Shinozaki Ritsuko Ritsuko Tokyo Minato Turf 5th 33-8, Mitsubishi Motors Corporation F-term (reference) 3G091 AA18 AA28 AB05 BA14 BA29 BA31 CA05 CA13 CA17 CA22 CB08 DA08 DB10 EA00 EA01 EA07 EA15 EA18 EA24 EA33 FC02 GA06 GB01W HA36 HA39 4D002 AA12 AC37 BA06 BA06 DA70 GA02 GA03 GB06 GB11 4D048 AA06 AB02 AC03 DA01 DA02 DA20

Claims (4)

[Claims] 1. A NOx catalyst provided in an exhaust system of an internal combustion engine for selectively reducing NOx in exhaust gas; a supply passage communicating with the exhaust system upstream of the NOx catalyst; and urea for the exhaust system via the supply passage. Reducing agent supplying means for supplying water, air supplying means for supplying pressurized air to the exhaust system from a position upstream of the urea water supplying part in the supply passage, operation of the reducing agent supplying means and the air supplying means Control means for controlling, air supply state detecting means for detecting pressure or flow rate in the supply passage, pressure control device for operating the air supply means to supply pressurized air and pressure detected by the air supply means or A NOx purifying device for an internal combustion engine, comprising: a determining unit that determines whether or not the supply passage is clogged according to a flow rate. 2. A temperature sensor for detecting the temperature of the urea water, wherein the judging means prohibits the judgment operation of the judging means when the urea water temperature detected by the temperature sensor is lower than a predetermined temperature. A NOx purifying device for an internal combustion engine according to claim 1. 3. The supply of urea water by the reducing agent supply means is prohibited when the determination means determines that there is a clogging failure that requires flow path recovery processing of the supply passage. 1. The NOx purification device for an internal combustion engine according to 1. 4. A NOx catalyst provided in an exhaust system of an internal combustion engine for selectively reducing NOx in exhaust gas, and a reducing agent supply means for supplying urea water through a supply passage communicating with the exhaust system upstream of the NOx catalyst. An air supply means for supplying pressurized air from the supply passage upstream of a supply portion of the urea water supplied from the reducing agent supply means, a control means for controlling the operation of the reducing agent supply means and the air supply means, Air supply state detecting means for detecting a pressure or a flow rate in the supply passage, the control means for operating the air supply means to supply pressurized air, and the pressure or flow rate detected by the air supply state detecting means. And a determination means for determining whether or not the supply passage is clogged, the determination means, when it is determined that the supply passage is clogged, the control means performs the return. Whether or not the supply passage is clogged according to the pressure or flow rate detected by the air supply state detection means while operating the agent supply means to supply the urea water and then operating the air supply means to supply the pressurized air A NOx purification device for an internal combustion engine, which is characterized by: