JPH11270329A - Reducing agent feeder for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately and easily detect plug up of an HC feeder for annexing HC into an exhaust pipe. SOLUTION: This feeder is provided with a lean NOx catalyst 17 for reducing NOx to the exhaust pipe 16 of an internal combustion engine under the existance of reducing agent of oxygen excess ambient atmosphere and HC feeders 19, 31, 33 for feeding HC to the exhaust gas flowing in to the catalyst, while these HC feeders 19, 31, 33 are composed of a feeding passage 31 for feeding the liquid reducing agent and an injection means 19 for injecting the liquid reducing agent fed from the passage 31 into the exhaust pipe 16. In this case, a temperature sensor 34 is provided inside the exhaust pipe on the lower stream side of the injection means 19 and the degree of plug up is detected correspondingly to the temperature detected by the temperature sensor 34.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reducing agent supply device for purifying NOx in exhaust gas in an excess oxygen state discharged from an internal combustion engine, and further, the clogging of the reducing agent supply device. This is related to the abnormality detection for detecting the error.

[0002]

2. Description of the Related Art There is known an exhaust gas purifying apparatus for an internal combustion engine provided with an NOx catalyst for purifying nitrogen oxides (hereinafter, NOx) contained in exhaust gas in an excess oxygen state in an engine exhaust passage. The NOx catalyst exhibits a high NOx purification rate in a predetermined temperature range. Therefore, when the temperature of the NOx catalyst is within the above-mentioned predetermined temperature range, NOx is reduced to nitrogen by a reducing agent (generally, hydrocarbon, that is, HC, hereinafter referred to as HC) in the exhaust gas. Reduced to N
Purify Ox. That is, in order to secure a high NOx purification rate, it is preferable that the HC concentration in the exhaust gas is set to an optimum concentration according to the NOx amount and the exhaust gas temperature. For example, Japanese Patent Application Laid-Open No. 05-113116 discloses that NO in exhaust gas.
HC that is added to exhaust gas by an HC supply device so that the HC concentration becomes optimum according to the x concentration and the catalyst temperature.
A supply device and HC supply control are disclosed.

[0003]

However, if the supply of HC is continued, part of the HC is solidified (that is, a deposit is deposited) on the supply passage in the HC supply device due to the heat of the exhaust gas, and the HC is supplied. There has been a problem that it adheres to the addition wall surface and eventually blocks the passage in the HC supply device. Therefore, in order to detect whether or not clogging has occurred in any of the passages in the HC supply device, it has been desired to detect whether or not desired HC has actually been injected into the exhaust pipe. But,
The supplied HC was mixed with the exhaust gas in the exhaust pipe, and the HC amount could not be accurately detected. Accordingly, an object of the present invention is to provide an abnormality detection device that detects clogging of an HC addition device by estimating the amount of added HC by utilizing an endothermic effect generated when HC changes from a liquid to a gas. It is in.

[0004]

According to the first aspect of the present invention, a lean NOx catalyst for reducing NOx in the presence of a reducing agent in an oxygen-excess atmosphere in an exhaust pipe of an internal combustion engine and an exhaust gas flowing into the catalyst are provided. A reducing agent supply device for supplying the reducing agent, the reducing agent supply device including a supply passage for supplying a liquid reducing agent and an injection unit for injecting the liquid reducing agent supplied from the passage into the exhaust pipe; In the reducing agent supply device for the internal combustion engine, a temperature sensor is provided in an exhaust pipe on the downstream side of the injection means, and a degree of clogging of the reducing agent supply device is detected according to a temperature detected by the temperature sensor. According to the above invention, when the liquid reducing agent in the reducing agent supply device is added to the exhaust gas, a change in the exhaust gas temperature caused by an endothermic effect that occurs when the liquid turns into a gas is detected, and the amount of change is detected from the change amount. The degree of clogging in the reducing agent supply device is detected.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, 1 is an engine body, 2 is a piston, 3 is a combustion chamber, 4 is a spark plug, 5 is an intake valve, 6 is an intake port, 7 is an exhaust valve, and 8 is exhaust gas. Each port is shown. The intake ports 6 are connected to surge tanks 10 via corresponding intake manifolds 9, and each intake manifold 9 is provided with a fuel injection valve 11 for injecting fuel into the intake port 6. The surge tank 10 is connected to an air cleaner 13 via an intake duct 12, and a throttle valve 14 is arranged in the intake duct 12. On the other hand, the exhaust port 8 is connected to the exhaust manifold 1
5 and an exhaust pipe 16 are connected to a casing 18 containing a lean NOx catalyst 17. Here, lean NO
The x catalyst 17 is composed of a zeolite supporting a transition metal or a noble metal, and is a selective reduction type NOx catalyst that reduces NOx in exhaust gas in the presence of HC in an oxidizing atmosphere.
Or at least one selected from alkali metals, alkaline earths, and rare earths, and a noble metal such as platinum are supported on an alumina carrier, absorb NOx in excess of oxygen, and release absorbed NOx when oxygen decreases. A storage-reduction type NOx catalyst or the like for reducing HC in exhaust gas by exhaust gas is considered. An HC supply valve 19 as a reducing agent supply device is provided in the exhaust pipe 16 on the upstream side of the lean NOx catalyst 17. Further, a passage 30 for supplying liquid HC to the HC supply valve 19,
A HC 31 and a three-way valve 33 are provided, and the liquid HC is vaporized by a nozzle in the HC supply valve 19 and is injected and added into the exhaust gas of the exhaust pipe 16. HC is supplied from a fuel tank (not shown) to the passage 30 by a pump.
3, only the necessary amount is supplied to the passage 31 and the rest is supplied to the passage 3.
2 returns to the fuel tank. Here, the reducing agent, that is, HC in this system is light oil in the case of a diesel engine, and gasoline in the case of a gasoline engine, but is not limited thereto, and may be a system provided with an HC tank in advance. As used herein, the terms "upstream" and "downstream" refer to the flow of exhaust gas flowing through the exhaust pipe 16, and the present invention primarily includes an excess of oxygen, such as a diesel or lean burn engine. Applied to internal combustion engines that emit exhaust gas.

The electronic control unit 40 is composed of a digital computer and is connected to each other via a bidirectional bus 41. A ROM (read-on memory) 42, a RAM (random access memory) 43, and a CPU (microprocessor)
44, an input port 45 and an output port 46. A pressure sensor 28 that generates an output voltage proportional to the absolute pressure PM in the surge tank 10 is mounted in the surge tank 10, and the output voltage of the pressure sensor 28 is input to an input port 45 via an AD converter 47. You. Also,
The input port 45 is connected to the crank angle sensor 30 that generates an output pulse every time the crankshaft of the engine body 1 rotates, for example, 30 degrees. The CPU 44 calculates the engine speed of the engine body 1 based on the output pulse.
Further, an upstream temperature sensor 32 for generating an output voltage proportional to the exhaust gas temperature is attached to the upstream side of the HC supply valve 19, and the output voltage of the upstream temperature sensor 32 is supplied to an input port via an AD converter 48. 45 is input. A downstream temperature sensor 34 for generating an output voltage proportional to the exhaust gas temperature in consideration of the HC temperature just injected from the HC supply valve 19 is also provided downstream of the HC supply valve 19,
The output voltage of the downstream temperature sensor 34 is
Through the input port 45. The position of the downstream temperature sensor 34 is provided near the HC supply valve 19 and in the HC injection direction in order to detect the exhaust gas temperature in consideration of the HC temperature just injected from the HC supply valve 19.
On the other hand, the output port 46 controls the amount of HC injected from the HC supply valve 19 through the drive circuit 50.
3 is controlled.

[0007] The lean NOx catalyst 17 exhibits a predetermined high NOx purification rate within a predetermined temperature range. As shown in FIG. 2 showing the relationship between the catalyst temperature and the NOx purification rate, a predetermined temperature range W in the present embodiment is used.
Is the lower limit temperature value T1 at which the NOx purification rate becomes about 35% or more.
And the upper limit temperature value T2. Therefore, in the present embodiment, the predetermined temperature range W indicating a high NOx purification rate is defined as a temperature range indicating a NOx purification rate of about 35% or more. However, this is not a limitation of the present invention. In FIG. 2, the catalyst temperature indicating the maximum NOx purification rate is defined as Tm.

In the present embodiment, when the temperature T of the lean NOx catalyst 17 is within the range between the lower limit temperature value T1 and the upper limit temperature value T2 of the predetermined temperature range W, the HC supply valve 19 is opened. Then, the three-way valve 33 is controlled so as to inject HC. The opening time of the HC supply valve 19 is determined by the N
It is set to increase as the Ox amount increases. The NOx amount in the exhaust gas is estimated, for example, as follows.
As the engine speed N increases, the amount of exhaust gas emitted from the engine per unit time increases. Therefore, as the engine speed N increases, the amount of NOx emitted from the engine per unit time increases. Further, as the engine load increases, that is, as the absolute pressure PM in the surge tank 10 increases, the amount of exhaust gas discharged from each combustion chamber 3 increases, and the combustion temperature increases, so the engine load increases, that is, As the absolute pressure PM in the surge tank 10 increases, the amount of NOx discharged from the engine per unit time increases. Figure 3 shows the NOx emissions from the engine per unit time determined by experiments.
Amount, the absolute pressure PM in the surge tank 10, and the engine speed N
In FIG. 3, each curve is the same
The x amount is shown. As shown in FIG. 3, the amount of NOx discharged from the engine per unit time increases as the absolute pressure PM in the surge tank 10 increases, and increases as the engine speed N increases. The NOx amount shown in FIG.
Are stored in the ROM 42 in advance in the form of a map as shown in FIG. However, the upper limit of the amount of HC supplied at one time is set to an amount that does not cause the HC to pass through the lean NOx catalyst without performing the reducing action.

FIG. 5 shows a flowchart of HC supply control according to the embodiment of the present invention. Step S10
In the above, the NOx amount in the exhaust gas at the present time is estimated based on FIGS. Next, the temperature Ts of the lean NOx catalyst 17 is detected. In step S12, it is determined whether the temperature is equal to or lower than the upper limit temperature value T2 of the temperature range W. In step S14, whether the temperature is equal to or higher than the lower limit temperature value T1 of the temperature range W is determined. Judge. If it is determined that the temperature is equal to or lower than the upper limit temperature value T2 and equal to or higher than the lower limit temperature value T1 in both of these determination steps, step S
Proceeding to 16, the HC supply control is ended outside this temperature range. When the process proceeds to step S16, the HC amount that can reduce and purify the NOx amount estimated in S10 is injected from the HC supply valve 19 into the exhaust pipe 16 so that the HC amount is reduced.
The supply valve is opened for a predetermined period. This valve opening period is three-way valve 3
The three-way valve 33 is controlled based on the amount of HC capable of reducing and purifying the NOx amount, which is determined by the period in which the passage 30 and the passage 31 communicate with each other.
Then, another routine A is operated while HC is being injected from the HC supply valve 19. In this embodiment, H
Upstream temperature sensor 3 provided upstream of C supply valve 19
The temperature value of 2 is the temperature Ts of the lean NOx catalyst.

FIG. 6 shows the point of the present invention. Routine A for detecting abnormality of the HC supply valve 19 of the first embodiment.
Is shown. First, in step S20, the exhaust gas temperature Tg is detected by the upstream temperature sensor 32.
Note that the exhaust gas temperature can be estimated from the operating state of the internal combustion engine instead of using the temperature sensor. Next, proceeding to step S22, the exhaust gas temperature Th that takes into account the HC temperature just injected from the HC supply valve 19 is detected by the downstream temperature sensor 34 provided in the vicinity of the HC supply valve 19 and in the HC injection direction. In step S24, the temperature difference between Tg and Th detected above (Tg-Th)
Is greater than or equal to a predetermined value B. Here, the predetermined value B is a value predetermined by an experiment or the like.
The predetermined value B may be changed so as to increase as the amount of C added increases. In this determination step, the temperature difference (Tg-Th)
Is determined to be larger than the predetermined value B,
Assuming that the HC is normally supplied into the exhaust pipe 16, the abnormality detection routine A ends. The reason why it is determined that the HC is being supplied normally is that the passage 31 and the HC supply valve 1
9 is liquid HC, and at the moment HC is injected into the exhaust pipe 16, the HC changes from a liquid to a gas, and when the liquid becomes a gas, the surrounding exhaust gas is absorbed by heat of vaporization that absorbs surrounding heat. The temperature drops. The greater the amount of HC, the greater the amount of decrease in the exhaust gas temperature. By detecting the temperature difference, the amount of HC injected into the exhaust pipe 16 can be estimated. In this determination step, the temperature difference (T
g-Th) is determined to be smaller than the predetermined value B, the desired HC is set in the exhaust pipe 16 for the above-described reason.
The amount is not supplied, and it is determined that clogging or the like has occurred in the passage 31 and the HC supply valve 19. At this time, the process proceeds to step S26 to stop supplying the HC to the passage 31 by controlling the three-way valve 33, and to execute step S28.
This indicates to the driver or the like that the clogging of the HC supply system is abnormal.

FIG. 7 shows another routine A for detecting an abnormality of the HC supply valve 19 as a second embodiment. First, in step S30, HC is detected by the downstream temperature sensor 34 provided near the HC supply valve 19 and in the HC injection direction.
From the exhaust gas temperature when the fuel is not injected from the supply valve 19, H
The change amount ΔTh that changes to the exhaust gas temperature when the fuel is injected from the C supply valve 19 is detected. Here, the position of the downstream side temperature sensor 34 is the same as that of the first embodiment.
And in the HC injection direction. Next, it is determined whether or not the change amount ΔTh (here, ΔTh is an absolute value) obtained in step S30 is equal to or greater than a predetermined value C. Here, the predetermined value C is a value predetermined by an experiment or the like, but may be changed so that the larger the amount of HC added, the larger the predetermined value C. If it is determined in this determination step that the change amount ΔTh is larger than the predetermined value C, it is determined that HC is normally supplied into the exhaust pipe 16, and
This abnormality detection routine A ends. On the other hand, if the value is equal to or less than the predetermined value C, it is determined that the desired amount of HC has not been supplied into the exhaust pipe 16 for the same reason as in the first embodiment, and clogging or the like has occurred in the passage 31 and the HC supply valve 19. Is determined. At this time, the process proceeds to step S34 and the three-way valve 33
Is stopped to supply HC to the passage 31, and the process proceeds to step S36. In the second embodiment, a heater for burning and removing deposits previously deposited in the nozzles or passages 31 in the HC supply valve 19 is embedded. In step S36, the heaters are operated for a predetermined period to block deposits and the like. Is removed. After heating for a predetermined period in step S36, the three-way valve 33 is opened so that the HC supply valve 19 is opened.
Control. Then, the process returns to step S30 again to perform the abnormality determination. Note that the HC supply control of this embodiment is the same as that of the first embodiment.

By detecting the heat of vaporization that absorbs when the liquid turns into gas, the amount of HC added to the exhaust gas in the exhaust pipe 16 can be estimated, and the clogging of the HC supply valve 19 and the passage 31 can be estimated. The degree can be accurately and easily detected. Furthermore, in the second embodiment, when the clogging is detected, the heating and removing means is provided, so that the addition of HC can be operated for a long time with a minimum heating energy.

[0013]

According to the present invention, the amount of the reducing agent added to the exhaust gas can be estimated by detecting the heat of vaporization absorbed when the reducing agent changes from a liquid to a gas, and the degree of clogging in the reducing agent adding device can be estimated. It can be detected accurately and easily.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing a relationship between a catalyst temperature and a purification rate of HC and NOx.

FIG. 3 is a diagram showing the amount of NOx discharged from the engine body.

FIG. 4 is a diagram showing a map for estimating the amount of NOx discharged from the engine body.

FIG. 5 is a flowchart showing HC supply control.

FIG. 6 is a flowchart illustrating detection of an abnormality in HC supply according to the first embodiment.

FIG. 7 is a flowchart illustrating detection of an abnormality in HC supply according to the second embodiment.

[Explanation of symbols]

 17 NOx catalyst 19 HC supply valve 32 upstream temperature sensor 34 downstream temperature sensor 30, 31 passage 32 return passage 33 three-way valve

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI F02D 41/22 301 F02D 41/22 301M

Claims (1)

[Claims] An exhaust pipe of an internal combustion engine includes a lean NOx catalyst for reducing NOx in the presence of a reducing agent in an oxygen-excess atmosphere, and a reducing agent supply device for supplying the reducing agent to exhaust gas flowing into the catalyst. The agent supply device is a reducing agent supply device for an internal combustion engine comprising a supply passage for supplying a liquid reducing agent, and an injection device for injecting the liquid reducing agent supplied from the passage into an exhaust pipe. A temperature sensor is provided in the exhaust pipe, and clogging detecting means for detecting the degree of clogging of the reducing agent supply device in accordance with the temperature detected by the temperature sensor is provided.