JP3855444B2 - Reducing agent supply device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND 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 relates to abnormality detection for detecting clogging of the reducing agent supply device. It is.
[0002]
[Prior art]
2. Description of the Related Art There is known an exhaust gas purification device for an internal combustion engine provided with an NOx catalyst for purifying nitrogen oxide (hereinafter referred to as NOx) contained in exhaust gas in an excessive oxygen state in an engine exhaust passage. The NOx catalyst exhibits a high NOx purification rate in a predetermined temperature range. Accordingly, when the temperature of the NOx catalyst is within the predetermined temperature range, NOx is converted into nitrogen by a reducing agent (generally hydrocarbons or HC is used, hereinafter referred to as HC) in the exhaust gas. To reduce NOx. That is, in order to ensure a high NOx purification rate, it is preferable to set the HC concentration in the exhaust gas to an optimum concentration according to the NOx amount and the exhaust gas temperature. For example, Japanese Patent Laid-Open No. 05-113116 discloses an HC supply device and an HC supply for adding HC to exhaust gas by an HC supply device so as to obtain an optimum HC concentration according to the NOx concentration and catalyst temperature in the exhaust gas. Control is disclosed.
[0003]
[Problems to be solved by the invention]
However, if HC is continuously supplied, a part of HC is solidified (that is, deposits are deposited) on the supply passage in the HC supply device due to the heat of the exhaust gas, and adheres to the HC addition wall surface. There was a problem of clogging the passage in the HC supply device. Therefore, in order to detect whether 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. However, the supplied HC is mixed with exhaust gas in the exhaust pipe, and the amount of HC cannot 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 HC added by utilizing the endothermic effect that occurs when HC changes from liquid to gas. There is.
[0004]
[Means for Solving the Problems]
According to claim 1 of the present invention, a lean NOx catalyst that reduces NOx in the presence of a reducing agent in an oxygen-excess atmosphere in an exhaust pipe of an internal combustion engine, and a reducing agent supply device that supplies the reducing agent to exhaust gas flowing into the catalyst. The reducing agent supply apparatus comprises: a supply passage for supplying a liquid reducing agent; and a reducing agent supply apparatus for an internal combustion engine comprising an injection means for injecting the liquid reducing agent supplied from the passage into an exhaust pipe. A temperature sensor is provided in the exhaust pipe on the downstream side of the injection means, and the degree of clogging of the reducing agent supply device is detected according to the temperature detected from 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, the exhaust gas temperature change caused by the endothermic action that occurs when the liquid is changed to gas is detected. The degree of clogging in the reducing agent supply device is detected.
[0005]
DETAILED DESCRIPTION OF THE INVENTION
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 an exhaust port. The intake port 6 is connected to a surge tank 10 via a corresponding intake manifold 9, and a fuel injection valve 11 that injects fuel into the intake port 6 is attached to each intake manifold 9. The surge tank 10 is connected to an air cleaner 13 via an intake duct 12, and a throttle valve 14 is disposed in the intake duct 12. On the other hand, the exhaust port 8 is connected to a casing 18 containing a lean NOx catalyst 17 via an exhaust manifold 15 and an exhaust pipe 16. Here, the lean NOx catalyst 17 is made of a zeolite on which a transition metal or a noble metal is supported, and is on a selective reduction type NOx catalyst that reduces NOx in exhaust gas in the presence of HC in an oxidizing atmosphere, or on an alumina carrier. At least one selected from alkali metals, alkaline earths, and rare earths and a noble metal such as platinum are supported, absorbs NOx under excess oxygen, releases the absorbed NOx when oxygen decreases, and emits NOx in the exhaust gas. An NOx storage reduction catalyst that reduces to HC is conceivable. The exhaust pipe 16 on the upstream side of the lean NOx catalyst 17 is provided with an HC supply valve 19 that is a reducing agent supply device. Furthermore, passages 30 and 31 for supplying liquid HC to the HC supply valve 19 and a three-way valve 33 are provided. The liquid HC is vaporized by a nozzle in the HC supply valve 19 and injected into the exhaust gas of the exhaust pipe 16. Is done. HC is supplied from a fuel tank (not shown) to the passage 30 by a pump, and a required amount is supplied to the passage 31 by a three-way valve 33, and the rest is returned to the fuel tank by a passage 32. 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. In this specification, the terms “upstream” and “downstream” refer to the flow of exhaust gas flowing in the exhaust pipe 16, and the present invention mainly includes an excess of oxygen such as a diesel engine or lean burn engine. It is applied to an internal combustion engine that exhausts exhaust gas.
[0006]
The electronic control unit 40 comprises 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, a CPU (Microprocessor) 44, an input port 45 and an output. A port 46 is provided. 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 the input port 45 via the AD converter 47. The The input port 45 is connected to a 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 this output pulse. Further, an upstream temperature sensor 32 that generates an output voltage proportional to the exhaust gas temperature is mounted on the upstream side of the HC supply valve 19, and the output voltage of the upstream temperature sensor 32 is input to an input port via an AD converter 48. 45. A downstream temperature sensor 34 for generating an output voltage proportional to the exhaust gas temperature taking into account the HC temperature just injected from the HC supply valve 19 is also installed on the downstream side of the HC supply valve 19. The output voltage is input to the input port 45 via the AD converter 49. The downstream temperature sensor 34 is provided in the vicinity of the HC supply valve 19 and in the HC injection direction in order to detect the exhaust gas temperature taking into account the HC temperature just injected from the HC supply valve 19. On the other hand, the output port 46 controls the amount of opening of the three-way valve 33 in order to control the amount of HC injected from the HC supply valve 19 via the drive circuit 50.
[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, the predetermined temperature range W in the present embodiment has a lower limit temperature value T1 and an upper limit temperature value T2 at which the NOx purification rate is about 35% or more. The range between. Therefore, in this embodiment, the temperature range W indicating a predetermined high NOx purification rate is defined as a temperature range showing a NOx purification rate of about 35% or more. However, this does not limit the invention. In FIG. 2, the catalyst temperature indicating the maximum NOx purification rate is Tm.
[0008]
In the present embodiment, when the temperature T of the lean NOx catalyst 17 is within a range between a lower limit temperature value T1 and an upper limit temperature value T2 of a predetermined temperature range W, the HC supply valve 19 is opened to open the HC The three-way valve 33 is controlled so as to be injected. The valve opening time of the HC supply valve 19 is set so as to increase as the amount of NOx in the exhaust gas increases. The amount of NOx in the exhaust gas is estimated as follows, for example. As the engine speed N increases, the amount of exhaust gas discharged from the engine per unit time increases. Therefore, as the engine speed N increases, the amount of NOx discharged 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 as the combustion temperature increases, the engine load increases. As the absolute pressure PM in the surge tank 10 increases, the amount of NOx discharged from the engine per unit time increases. FIG. 3 shows the relationship between the amount of NOx discharged from the engine per unit time obtained by experiment, the absolute pressure PM in the surge tank 10, and the engine speed N. In FIG. 3, each curve represents the same NOx. Indicates the amount. 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. 3 is 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 allow the HC to pass through the lean NOx catalyst without reducing action.
[0009]
FIG. 5 shows a flowchart of the HC supply control according to the embodiment of the present invention. In step S10, the current NOx amount in the exhaust gas is estimated based on FIG. 3 and FIG. Next, the temperature Ts of the lean NOx catalyst 17 is detected. In step S12, it is determined whether or not the temperature is lower than the upper limit temperature value T2, and in step S14, whether or not the temperature is lower than the lower limit temperature value T1. Judging. When it is determined in both the determination steps that the temperature is lower than the upper limit temperature value T2 and higher than the lower limit temperature value T1, the process proceeds to step S16, and the HC supply control is terminated outside this temperature range. When the routine proceeds to step S16, the HC supply valve is opened for a predetermined period so as to inject the HC amount capable of reducing and purifying the NOx amount estimated in S10 into the exhaust pipe 16 from the HC supply valve 19. This valve opening period is determined by the period during which the passage 30 and the passage 31 are communicated by the three-way valve 33, and the three-way valve 33 is controlled based on the amount of HC that can reduce and purify the NOx amount. Then, another routine A is operated while HC is being injected from the HC supply valve 19. In the present embodiment, the temperature value of the upstream temperature sensor 32 provided on the upstream side of the HC supply valve 19 is the temperature Ts of the lean NOx catalyst.
[0010]
FIG. 6 shows the points of the present invention, and shows a routine A for detecting an abnormality of the HC supply valve 19 of the first embodiment. First, in step S20, the exhaust gas temperature Tg is detected by the upstream temperature sensor 32. The exhaust gas temperature can be estimated from the operating state of the internal combustion engine instead of using the temperature sensor. Next, the process proceeds to step S22, and an 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, it is determined whether or not the temperature difference (Tg−Th) between Tg and Th detected above is equal to or greater than a predetermined value B. Here, the predetermined value B is a value determined in advance by an experiment or the like, but may be changed so that the predetermined value B increases as the amount of HC added increases. When it is determined in this determination step that the temperature difference (Tg−Th) is larger than the predetermined value B, it is determined that HC has been normally supplied into the exhaust pipe 16, and the abnormality detection routine A is terminated. The reason why HC is normally supplied is liquid HC in the passage 31 and the HC supply valve 19, and the HC changes from liquid to gas at the moment when HC is injected into the exhaust pipe 16. However, the temperature of the surrounding exhaust gas is lowered by the heat of vaporization that absorbs the surrounding heat when the liquid is changed to gas. As the amount of HC increases, the amount of decrease in the exhaust gas temperature increases, and the amount of HC injected into the exhaust pipe 16 can be estimated by detecting the temperature difference. When it is determined in this determination step that the temperature difference (Tg−Th) is smaller than the predetermined value B, the desired amount of HC is not supplied into the exhaust pipe 16 for the above reason, and the passage 31 and the HC supply It is determined that clogging or the like has occurred in the valve 19. At this time, the process proceeds to step S26 to stop the supply of HC to the passage 31 by controlling the three-way valve 33, and at step S28, it is displayed to the driver or the like that the HC supply system is clogged abnormally.
[0011]
FIG. 7 shows another abnormality detection routine A of the HC supply valve 19 as the second embodiment. First, when injecting from the HC supply valve 19 from the exhaust gas temperature when not injected from the HC supply valve 19 by the downstream temperature sensor 34 provided in the vicinity of the HC supply valve 19 and in the HC injection direction in step S30. The amount of change ΔTh changed to the exhaust gas temperature is detected. Here, the position of the downstream temperature sensor 34 is provided in the vicinity of the HC supply valve 19 and in the HC injection direction as in the first embodiment. Next, it is determined whether or not the change amount ΔTh (where 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 determined in advance by experiments or the like, but may be further changed so that the predetermined value C increases as the amount of HC added increases. 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 has been normally supplied into the exhaust pipe 16, and the abnormality detection routine A is terminated. On the other hand, if it is equal to or less than the predetermined value C, the desired amount of HC is not supplied into the exhaust pipe 16 for the same reason as in the first embodiment, and clogging or the like occurs in the passage 31 and the HC supply valve 19. To be judged. At this time, the process proceeds to step S34, the supply of HC to the passage 31 is stopped by controlling the three-way valve 33, and the process proceeds to step S36. In the second embodiment, a heater that burns and removes deposits adhering to the nozzle or passage 31 in the HC supply valve 19 in advance is embedded. In step S36, the heater is operated for a predetermined period to block deposits and the like. Remove. After heating for a predetermined period in step S36, the three-way valve 33 is controlled to open the HC supply valve 19. And it returns to step S30 again and performs abnormality determination.
The HC supply control of this embodiment is the same as that of the first embodiment.
[0012]
The amount of HC added to the exhaust gas in the exhaust pipe 16 can be estimated by detecting the heat of vaporization that is absorbed when the liquid is changed to gas by the above abnormality determination, and the degree of clogging of the HC supply valve 19 and the passage 31 is accurately determined. Good and easy detection. Further, in the second embodiment, when the clogging is detected, the heating removal means is provided, so that the addition of HC can be operated for a long time with the minimum heating energy.
[0013]
【The invention's effect】
In the present invention, the amount of reducing agent added to the exhaust gas can be estimated by detecting the heat of vaporization that is absorbed when the reducing agent changes from liquid to gas, and the degree of clogging in the reducing agent addition device can be accurately and easily determined. Can be detected.
[Brief description of the drawings]
FIG. 1 is a view showing an internal combustion engine equipped with an exhaust gas purifying apparatus according to an embodiment of the present invention.
FIG. 2 is a graph showing the relationship between the catalyst temperature and the 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 showing HC supply abnormality detection according to the first embodiment.
FIG. 7 is a flowchart showing HC supply abnormality detection 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

Claims (1)

An exhaust pipe of an internal combustion engine includes a lean NOx catalyst that reduces NOx in the presence of a reducing agent in an oxygen-excess atmosphere, and a reducing agent supply device that supplies the reducing agent to exhaust gas flowing into the catalyst, the reducing agent supply device being a liquid In a reducing agent supply apparatus for an internal combustion engine comprising a supply passage for supplying a gaseous reducing agent and an injection means for injecting a liquid reducing agent supplied from the passage into the exhaust pipe, the temperature in the exhaust pipe on the downstream side of the injection means A clogging detection unit is provided, which includes a sensor and detects the degree of clogging of the reducing agent supply device according to the temperature detected from the temperature sensor.

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