JP3956728B2 - NOx purification device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a NOx purification device that purifies NOx in exhaust gas of an internal twist engine, and in particular, a NOx purification device for an internal combustion engine in which a device for spraying an exhaust gas reducing agent is disposed upstream of a reduction catalyst provided in an exhaust system. About.
[0002]
[Prior art]
The NOx in the exhaust gas discharged from the internal twisting engine is purified by the NOx purification device. In particular, the NOx purification device used in the diesel engine places a urea SCR catalyst (NOx catalyst) in its exhaust system, and its upstream side. There is known a device provided with a reducing agent supply means. This reducing agent supply means supplies urea water (urea water) to the exhaust system, and urea contained therein is hydrolyzed and thermally decomposed as shown in the following formula (1) to release NH3.
[0003]
(NH ₂ ) 2 CO + H ₂ O → 2NH ₃ + CO ₂ ... (1)
Ammonia (NH ₃ ) generated by hydrolysis is supplied as a reducing agent to the SCR catalyst (NOx catalyst). As a result, the SCR catalyst can purify NOx in an oxygen-excess atmosphere.
By the way, as described above, the urea water addition type NOx purifying apparatus uses urea water that is easy to handle instead of directly supplying ammonia used as a reducing agent to the exhaust passage, and atomizes the urea water for transportation. The air flow is supplied to the exhaust passage, that is, supplied to the exhaust passage using an air assist method, and the hydrolyzed ammonia is supplied to the SCR catalyst.
[0004]
[Problems to be solved by the invention]
By the way, in the NOx purification device employing the air assist method, urea water is put on the air flow for conveyance flowing in the supply passage, and the urea water is supplied to the exhaust passage from the injector at the downstream end of the supply passage. A carrier air supply means 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 means is opened between the air supply means and the injector. Here, the mist-like urea water blown out and added to the supply passage from the addition port of the urea water addition pipe easily adheres to the inner wall surface of the supply passage, and this solids when water is evaporated by the influence of the air flow for transportation. This solid matter generation itself cannot be avoided.
In particular, when a NOx purification device employing an air assist system is mounted on a vehicle, the supply passage through which the air for conveyance flows is often curved or the cross-sectional area of the flow path changes. In the vicinity of the mouth and the injector, a portion where the air stream line is disturbed or a spiral portion (turbulent flow) is likely to occur, and urea water tends to adhere to such a portion.
[0005]
If this urea water adhesion state continues, moisture will evaporate each time and the amount of solidification will increase, which will reduce the cross-sectional area of the air flow path at that part, possibly closing the flow path and causing the so-called urea plugging phenomenon Thus, there is a problem that the urea water addition type reducing agent supply means does not operate properly and the NOx purification function stops.
[0006]
Moreover, when the control means of such a NOx purification device is provided with a plugging detection means in advance, this plugging detection means detects, for example, the air pressure in the supply passage through which the carrier air flows, and this is a predetermined value when the plugging occurs. If it exceeds the value, it is immediately determined that there is a failure in the NOx purification device. For this reason, even if 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 insignificant. It is easy to increase.
The present invention provides a NOx purification device for an internal combustion engine that can prevent the frequency of stoppage of the NOx purification device from increasing excessively due to the urea plugging phenomenon in the NOx purification device that performs urea water addition based on the above problems. With the goal.
[0007]
[Means for Solving the Problems]
According to a first aspect of the present invention, there is provided an 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 the exhaust system via the supply passage. A reducing agent supply means for supplying urea water to the 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, a temperature sensor for detecting the temperature of the urea water , 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 pressure or flow rate in the supply passage, and the control means to operate the air supply means to generate pressurized air. determining clogging presence of the supply passage in accordance with the detected pressure or flow by the air supply state detecting means supplies, and, by the temperature sensor of the same judgment operation Issued urea water temperature when less than the predetermined temperature characterized by comprising a judgment means for inhibiting. In the supply passage for supplying urea by putting pressurized air on the exhaust system, the water content of urea water evaporates and solidifies at the inner wall or the like, which may clog the flow path, that is, the urea plugging phenomenon may occur . Here, the clogging failure can be easily determined and dealt with according to the pressure or flow rate.
[0008]
In particular, if the urea water is at a low temperature, the saturation concentration decreases, and it is not possible to expect the dissolution and discharge of the clogged portion of the supply passage with such a low temperature urea water. The determination of whether or not the supply passage is clogged by a simple determination means is prohibited, and the temperature rises.
Preferably, in the NOx purification device for an internal combustion engine according to claim 1 , further comprising a heater for increasing the temperature of the urea water, and the determination means, when the urea water temperature detected by the temperature sensor is less than a predetermined temperature, The heater may be operated.
[0009]
In this case, when the urea water is lower than the predetermined temperature, the temperature of the urea water is increased by operating the heater, and the clogged portion of the supply passage can be easily dissolved and discharged with the urea water having a high saturation concentration.
[0010]
Preferably, in the NOx purification device for an internal combustion engine according to claim 1 , further comprising a heater for increasing the temperature of the urea water, and when the urea water temperature detected by the temperature sensor is less than a predetermined temperature, the determination means When the heater is activated and the urea water temperature detected by the temperature sensor is determined to be equal to or higher than a predetermined temperature after the heater is activated, it may be determined whether the supply passage is clogged.
In this case, when the urea solution is lower than the predetermined temperature, the determination unit operates the heater to increase the temperature of the urea water, and when the urea water temperature exceeds the predetermined temperature, the urea water dissolves and discharges the clogged portion of the supply passage. Therefore, it is possible to accurately determine whether the supply passage is clogged by the determination means.
[0011]
According to a second aspect of the present invention, in the NOx purification 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, the reducing agent supply The supply of urea water by the means is prohibited.
When the determination means determines a clogging failure that requires a flow path recovery process of the supply passage with pressurized air, the supply of urea water is prohibited, so that unnecessary operation of the NOx purification device can be stopped, and for example, to the passenger By encouraging maintenance at repair shops, environmental considerations are promptly made.
[0012]
According to a third 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, and a reducing agent for supplying urea water via a supply passage communicating with the exhaust system upstream of the NOx catalyst. Control for controlling the operation of the supply means, the air supply means for supplying pressurized air from the supply passage upstream of the supply site of urea water supplied from the reducing agent supply means, the reducing agent supply means and the air supply means Means, air supply state detection means for detecting pressure or flow rate in the supply passage, operating the air supply means by the control means to supply pressurized air and pressure or flow rate detected by the air supply state detection means And determining means for determining whether or not the supply passage is clogged, and when the determination means determines that the supply passage is clogged, After the base agent supply means is operated and urea water is supplied, the air supply means is operated to supply pressurized air and the supply passage is clogged according to the pressure or flow rate detected by the air supply state detection means. The presence or absence is determined.
As described above, when the determination unit determines that the supply passage is clogged, by temporarily supplying urea water, the solidified and clogged urea is dissolved and discharged in the supply passage, and then clogging is performed again. Therefore, if it is clogged so that it can be dissolved, erroneous determination of abnormality can be prevented and NOx purification can be achieved. Even if urea water is once supplied, solidified urea cannot be dissolved and discharged in the supply passage. Sometimes it is possible to accurately diagnose urea clogging by determining clogging.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
An internal combustion engine NOx purification device as an embodiment of the present invention will be described below with reference to FIG. The internal combustion engine NOx purification device (hereinafter simply referred to as NOx purification device) is mounted on an exhaust system 2 of a multi-cylinder diesel engine (hereinafter simply referred to as engine) 1 mounted on a vehicle (not shown).
The engine 1 includes an engine control device (an engine ECU 10 that constitutes a main control unit in the figure) 3, and a NOx purification device is provided in the exhaust system of the engine 1. An engine ECU 10 of the engine control device 3 and an exhaust gas control device (hereinafter simply referred to as an exhaust system ECU) 4 constituting a control unit of the NOx purification device are mutually connected by a CAN mutual communication system (hereinafter simply referred to as a communication line) 5. It is connected so that it can communicate.
[0014]
In FIG. 1, an 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 a NOx purification device that is an exhaust gas aftertreatment device. And an exhaust system.
In FIG. 1, an engine ECU 10 used by the engine 1 is connected to 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. Here, the crank angle information Δθ is used in the engine ECU 10 for derivation of the engine speed Ne and for fuel injection timing control described later.
[0015]
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 and the like, and sends a control signal to the fuel adjustment unit 11 via a line (not shown). To function.
The fuel injection system includes a fuel adjusting unit 11 that injects fuel with an injector 12 in a combustion chamber (not shown), and this part is controlled by an engine ECU 10 that functions as a fuel control unit n2.
[0016]
The fuel discharge amount adjusting unit 121 supplies high-pressure fuel from the engine-driven high-pressure fuel pump 123 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 in accordance with 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 an injector 12 connected to a common rail 122 via an electromagnetic valve Vp. The electromagnetic valve Vp is connected to the engine ECU 10 and can adjust the fuel injection amount and the injection timing in accordance with the output D (injn) signal of the fuel control unit n2. Only one connection line between the electromagnetic valve Vp and the engine ECU 10 is shown.
[0017]
Here, the fuel control unit n2 obtains the basic fuel injection amount INJb according to the engine speed Ne and the accelerator pedal opening θa (corresponding to the lever opening θr), and for example, each of water temperature and atmospheric pressure according to the operating conditions. The fuel injection amount INJn (= INJb + dt + dp) is derived by adding the correction values dt and dp. Further, the injection timing is derived by adding a correction corresponding to the operating condition to a known basic advance value. After that, an output D (injn) signal corresponding to the calculated injection timing and fuel injection amount INJ is set in a fuel injection driver (not shown), and is output to the electromagnetic valve Vp of the fuel adjustment unit 11 to inject fuel from the injector 12. To control.
[0018]
The exhaust system 2 of the engine 1 includes a NOx purification device.
The NOx purification device outputs an SCR catalyst 17 that is a NOx catalyst mounted in the middle of the exhaust pipe 16, an urea water addition nozzle 18 disposed upstream thereof, and a NOx concentration Snoxf upstream of the addition nozzle 18. A sensor 19, 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 are provided. For the catalyst temperature, an estimated value of the catalyst temperature may be calculated and used in consideration of correlated parameters such as the engine speed and fuel amount, the operation time for each engine operation 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, passes through the exhaust pipe 28 equipped with the NOx catalytic converter 27 downstream thereof, and is released into the atmosphere through a muffler (not shown).
[0019]
The NOx catalytic converter 27 includes a honeycomb-shaped ceramic catalyst carrier (not shown) in a casing, and a catalytic metal (for example, vanadium) for functioning as the SCR catalyst 17 is supported on the carrier. The SCR catalyst 17 can selectively reduce NOx in the exhaust gas by adsorbing ammonia (NH 3) from a reducing agent supply means described later. Here, when the SCR catalyst 17 is in an ammonia adsorption state, the NOx in the exhaust gas is subjected to the reaction of the following formula (2) at a high temperature, that is, the following formula (2) at a high temperature, and the formula (3) at a low temperature. The denitration reaction between nitrogen oxides can be promoted.
[0020]
4NH ₃ + 4NO + O ₂ → 4N ₂ + 6H ₂ O (2)
2NH ₃ + NO + NO ₂ → 2N ₂ + 3H ₂ O (3)
A urea water supply device 29 as a reducing agent supply means for supplying urea water through a supply passage rn and a high-pressure air tank 32 as an air supply means are mounted in the exhaust path E of the exhaust pipe 28.
[0021]
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 the addition nozzle 18 facing the exhaust path E is connected to the downstream end. Thus, urea water is sprayed toward the downstream side, that is, toward the upstream opening side of the NOx catalytic converter 27. A urea water addition position g, which will be described later, is disposed upstream of the supply site f as a urea addition position by the addition nozzle 18 and downstream of the air tank 32. The air tank 32 is connected to a compressed air supply means (not shown) so that the air pressure is always kept constant. The supply passage rn of the supply pipe 31 passes the air valve 33 from the air tank 32 and flows out the pressurized air to the exhaust passage E. The downstream end opening of the urea water pipe 34 on the urea water supply device 29 side communicates with the addition position g in the intermediate portion of the supply passage rn. As shown in FIGS. 1 and 2, the urea water pipe 34 opens at the downstream end at the upstream in the vicinity of the curved portion 311 of the supply passage rn. The urea water pipe 34 has a urea water tank 35 connected to the upstream end thereof, and supplies urea water in the urea water tank 35 to the supply passage rn side via the urea water supply unit 37.
[0022]
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 into the compressed air. The supply pipe 31 includes curved portions 311 and 312 on the downstream side of the addition position g, and the addition nozzle 18 is provided at the downstream end thereof. In such a supply pipe 31, the flow line fl of the air flow is curved at the inner wall face f0 of the urea water pipe 34 at the addition position g and the inner wall faces of the curved parts 311 and 312, and the spiral part fs is formed in a part thereof. As will be described later, the urea plugging phenomenon occurs over time in each of these portions, and the cross-sectional area of the flow channel is easily narrowed as will be described later.
Further, a heater 21 for heating urea water is attached to the urea water tank 35, and the heater 21 is driven and controlled by the exhaust system ECU 4.
[0023]
The urea water supply unit 37, the air valve 33, and the heater 21 are connected to the exhaust system ECU 4 and driven and controlled. In addition, the heater 21 may be attached to the urea water supply part 37 side other than the urea water tank 35, for example.
An air pressure sensor 24 serving as an air supply state detecting means for outputting the air pressure pa in the supply pipe 31 is provided at the downstream end of the supply pipe 31 (in the vicinity of the addition nozzle 18). A urea water temperature sensor 38 that outputs Tura is provided, and these outputs are supplied to the exhaust 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. A control signal is sent to the unit 37 and the heater 21. In addition, data can be exchanged with the engine ECU 10 via the CAN communication line 5.
[0024]
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 particularly has a NOx purification control function.
Next, the NOx purification control processing of the engine ECU 10 and the NOx purification device of FIG. 1 will be described along the control routines of the NOx purification processing of FIGS.
[0025]
When driving the engine 1 of a vehicle (not shown) equipped with a NOx purification device, the engine ECU 10 displays self-check results of related devices and sensors that are appropriately driven by a plurality of control systems, for example, a fuel injection system and a fuel supply system. In the normal (OK) state, the fuel pressure control unit n1 uses the fuel discharge amount adjusting unit 121 and the fuel control unit n2 uses the fuel adjusting unit 11 according to the input value of each sensor. Each control according to the operation range is executed, and the sensor outputs and the like obtained at that time are also transmitted to the exhaust system ECU 4.
[0026]
On the other hand, the exhaust system ECU 4 repeats the main routine of FIG. 3 for each predetermined control cycle simultaneously with the turning on of the engine key. Here, key-on is confirmed in step sa, and when step sb is reached, the catalyst temperature tg, NOx concentration Snoxf, intake air amount Ua from the engine ECU 10 and other data are taken in, and it is determined whether or not it is an appropriate value. Otherwise, a failure indicator lamp (not shown) is driven, and normally proceeds to step sc. In step sc, a clogging check process is performed. After that, in step sd, a NOx purification process is executed, and in step se, other known control processes are executed, and the process returns.
[0027]
When step c1 of the clogging check routine of FIG. 4 showing the clogging check process is reached, the temperature Tura of urea water is taken here, and it is determined whether the value exceeds a predetermined temperature Turaβ capable of exhibiting sufficient urea dissolution performance. .
If the temperature of the urea aqueous solution is initially low as a result of the determination in step a1, step a2 is reached. Here, the addition amount output DU is fixed to zero (DU = 0), and then it is determined in step a3 whether the heater driving flag FLGH is on. When the flag FLGH is off (= 0), step a4 is reached. Here, the heater 21 is driven to heat the urea water and the flag FLGH is turned on (= 1). Thereafter, in step a5, the above steps are repeated until the temperature Tura of the urea water exceeds a predetermined temperature Turaβ at which urea can be sufficiently dissolved, and if it exceeds, the process proceeds to step a6 to stop the heater 21 and stop the heater being driven. The flag FLGH is turned off (= 0) and the process returns.
[0028]
After the temperature Tura of the urea water exceeds the predetermined temperature Turaβ, the process proceeds to step a7.
In step a7, the air valve 33 is opened to allow air to flow into 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. If the air pressure pa is equal to or higher than the determination value paα, the supply passage rn is regarded as being open without clogging. The process proceeds to step a9, and if it falls below the determination value paα, the supply passage rn is regarded as clogged, and the process proceeds to step a10.
[0029]
In step a9, the supply passage rn is opened, and it is assumed that the supply passage rn is in a 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.
If it is determined in step a8 that the flow path is clogged and step a10 is reached, the cleaning output DU for cleaning that discharges the urea water supply unit 37 of the urea water supply device 29 by clogging is operated at DUcr. a11 is reached. In step a11, the timer tn is driven to wait for the elapse of the cleaning time tcr for clogging and discharging, and after 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 judgment value paα. Here, if the air pressure pa falls below the clogging determination value paα, it is determined that clogging occurs. In step a13, if the air pressure pa is equal to or higher than the clogging determination value paα, the supply passage rn is considered to open, and the process proceeds to step a14.
[0030]
In step a14, it is considered that the supply passage rn is opened and in a normal state, and the urea water addition permission is set. Thereby, ammonia can be supplied to the NOx catalyst 17, and NOx in the exhaust gas can be reduced.
If the clogging is not solved even after the cleaning process for clogging and discharging, in step a13, the clogging fault output is output to the fault indicator lamp rp and turned on, and the urea water addition amount output DU (= 0) ) And switch to prohibiting urea water addition.
As a result, when the passenger knows that the addition of ammonia is prohibited by the failure indicator lamp rp after the clogging failure, the repair factory promptly performs maintenance of the recovery process for opening the supply passage rn due to the clogging failure. For example, the vehicle is transported.
[0031]
Here, after the air pressure pa detected by the air pressure sensor 24 is cleaned, it is determined again in step a12 whether it exceeds the clogging determination value paα. Instead, in steps a8 and a12, Each clogging determination value 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 relatively increased, that is, clogging occurs. If a slight amount of water is generated, the cleaning process can be started promptly, the cleaning ratio can be increased to prevent clogging at an early stage, and the frequency of maintenance for opening the supply passage rn can be reduced.
[0032]
In the above-described embodiment, the supply pipe 31 is provided with the air pressure sensor 24 as an air supply state detection unit that outputs the air pressure pa of the supply passage rn. In step a8, the air pressure pa detected by the air pressure sensor 24 is provided. Whether or not the supply passage rn is clogged is determined based on whether or not the value 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.
[0033]
In this case, duplicated explanation is omitted by executing the same control except that step a8 shown in FIG. 4 is replaced with step a8 ′.
As shown in FIG. 5, when step a7 is reached from step a7, if the air flow rate Qrn in the supply passage rn detected by an air flow sensor (not shown) is not less than the clogging judgment value Qrnα, the process proceeds to step a9 without clogging. If it falls below, the supply passage rn is determined to be clogged due to urea precipitation, and the process proceeds to step a10. Note that the same determination may be made in step a12.
In this case as well, the same effect as when the air pressure sensor 24 is used can be obtained.
[0034]
【The invention's effect】
As described above, the present invention has a possibility that urea water is attached to the inner wall portion or the like of urea in the supply passage that supplies pressurized air to the exhaust system to solidify the urea, which may clog the flow path. In this case, the clogging failure can be easily determined and dealt with according to the pressure or the flow rate.
[0035]
In particular, if the urea water is at a low temperature, the saturation concentration decreases, and it is not possible to expect the dissolution and discharge of the clogged portion of the supply passage with such a low temperature urea water. The determination of whether or not the supply passage is clogged by a simple determination means is prohibited, and the temperature rises.
[0036]
The invention according to claim 2 stops the unnecessary operation of the NOx purification device because the supply of urea water is prohibited when the determination means determines a clogging failure that requires a flow path recovery process of the supply passage by pressurized air. At the same time, for example, by prompting passengers to perform maintenance at a repair shop, consideration for the environment can be made promptly.
[0037]
In the invention of claim 3 , when the determination means determines that the supply passage is clogged, once the urea water is supplied, the urea solidified and clogged in the supply passage is dissolved and discharged. Since clogging is determined, if it is clogging that can be dissolved, erroneous determination of abnormality can be prevented and NOx purification can be achieved. When it cannot be dissolved and discharged, it is determined as clogged so that urea clogging can be diagnosed accurately.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a NOx purification device and an engine equipped with the same as an embodiment of the present invention.
2 is a partially enlarged cross-sectional view of a supply passage and an exhaust passage used in the NOx purification device of FIG. 1. FIG.
FIG. 3 is a flowchart of a main routine used by the exhaust system ECU of FIG.
4 is a flowchart of a clogging check routine used by the exhaust system ECU of FIG.
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;
[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 part tg catalyst temperature DU addition amount equivalent output g urea water supply part rn supply passage pa pressure

Claims (3)

A NOx catalyst provided in an exhaust system of an internal combustion engine for selectively reducing NOx in the 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 via the supply passage;
An 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;
A temperature sensor for detecting the temperature of the urea water ,
Control means for controlling the operation of the reducing agent supply means and the air supply means;
Air supply state detection means for detecting pressure or flow rate in the supply passage;
The control means operates the air supply means to supply pressurized air, determines whether the supply passage is clogged according to the pressure or flow rate detected by the air supply state detection means, and performs the same determination operation. Determining means for prohibiting when the temperature of the urea water detected by the temperature sensor is lower than a predetermined temperature ,
A NOx purification device for an internal combustion engine, comprising: 2. The internal combustion engine according to claim 1 , wherein when the determination unit determines that the clogging failure requires a flow path recovery process of the supply passage, supply of urea water by the reducing agent supply unit is prohibited. Engine NOx purification device. A NOx catalyst provided in an exhaust system of an internal combustion engine for selectively reducing NOx in the exhaust gas,
A reducing agent supply means for supplying urea water via 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 from a supply site of urea water supplied from the reducing agent supply means;
Control means for controlling the operation of the reducing agent supply means and the air supply means;
Air supply state detection means for detecting pressure or flow rate in the supply passage;
A determination means for operating the air supply means by the control means to supply pressurized air and determining whether the supply passage is clogged according to the pressure or flow rate detected by the air supply state detection means;
When the determination means determines that the supply passage is clogged, the control means operates the reducing agent supply means to supply urea water, and then operates the air supply means to supply pressurized air. And determining whether or not the supply passage is clogged according to the pressure or flow rate detected by the air supply state detection means,
An NOx purification device for an internal combustion engine characterized by the above .

Images