JP2014105645A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control device of an internal combustion engine capable of surely reducing and purifying NOx.SOLUTION: An exhaust gas is introduced into intake air (S10) by operating one or both of EGR valves, injection of urea water is started from an urea water injector when an exhaust gas temperature between the urea water injector and an ammonia adsorption catalyst is within a prescribed temperature range (S12), and an ammonia adsorption amount Wn adsorbed in the ammonia adsorption catalyst is less than a prescribed amount (S14), and ammonia generated in hydrolysis of the urea water is adsorbed by the ammonia adsorption catalyst (S16). The injection of urea water is terminated (S18) in any of a case when the EGR is not introduced, a case when the exhaust gas temperature is outside of the prescribed range, and a case when the ammonia adsorption amount Wn is the prescribed amount or more.

Description

  The present invention relates to an exhaust gas purification apparatus for an internal combustion engine, and more particularly to ammonia adsorption control.

In diesel engines and lean-burn gasoline engines, the amount of nitrogen oxide (NOx) discharged into the exhaust gas increases because the mixture of fuel and air contains a large amount of oxygen.
Therefore, conventionally, in a diesel engine or a lean burn gasoline engine, a selective reduction catalyst, a NOx trap catalyst, or the like is provided in the exhaust passage. Particularly in a diesel engine, the amount of NOx emission increases during high rotation speed and high load operation. Therefore, ammonia water (NH3) generated by adding urea water to the exhaust gas in the exhaust passage and hydrolyzing the urea water A selective reduction catalyst device (SCR system) that reduces and purifies NOx is used.

  In such a selective catalytic reduction catalyst device, as disclosed in Patent Document 1, when forced regeneration of the diesel particulate filter is performed, the amount of ammonia that can reduce and purify NOx discharged from the internal combustion engine is reduced from the urea water injector to the urea. Water is supplied into the casing (exhaust passage), and NOx is reduced and purified by an ammonia selective reduction type NOx catalyst (selective reduction type catalyst device). When the diesel particulate filter is not forcibly regenerated, the urea water injector is set so that the adsorption amount of ammonia in the selective catalytic reduction device is equal to or less than the upper limit adsorption amount of ammonia that can be adsorbed by the selective catalytic reduction device. The amount of urea water supplied into the exhaust passage is adjusted.

Special table 2009-270449 gazette

In the exhaust purification device of Patent Document 1, when forced regeneration of the diesel particulate filter is not performed, urea water is supplied from the urea water injector into the exhaust passage, and ammonia is adsorbed to the selective catalytic reduction catalyst device. ing.
However, the amount of ammonia adsorbed to the selective catalytic reduction device varies depending on the amount of ammonia supplied to the selective catalytic reduction device after the urea water is hydrolyzed and the amount of NOx discharged from the internal combustion engine.

  Therefore, for example, when there is a large amount of NOx discharged from the internal combustion engine, such as during high speed / high load operation of the internal combustion engine, ammonia is desorbed from the ammonia adsorption catalyst disposed upstream of the selective catalytic reduction catalyst. When the technology of Patent Document 1 is applied to an exhaust purification device that reduces and purifies NOx, the amount of ammonia supplied to the ammonia adsorption catalyst changes, so that the amount of ammonia adsorbed required during high-speed / high-load operation of the internal combustion engine It takes time to become.

Therefore, even if the internal combustion engine operates at a high speed and a high load, and the NOx emission amount increases, the ammonia adsorption amount in the ammonia adsorption catalyst is small. Therefore, the selective reduction type catalyst sufficiently reduces and purifies NOx. This is not preferable because NOx that is not reduced and purified may be released to the atmosphere.
The present invention has been made to solve such problems, and an object of the present invention is to provide an exhaust purification device for an internal combustion engine that can reliably reduce and purify NOx.

  In order to achieve the above object, in the exhaust gas purification apparatus for an internal combustion engine according to claim 1, the selective reduction catalyst for reducing and purifying nitrogen oxides contained in the exhaust gas discharged from the internal combustion engine with ammonia, and the selective reduction An ammonia adsorption catalyst that is disposed upstream of the type catalyst, adsorbs the ammonia, and desorbs the ammonia at a temperature higher than the ammonia desorption temperature of the selective catalytic reduction catalyst, and urea water upstream of the ammonia adsorption catalyst Urea water supply means for supplying the ammonia water, and ammonia adsorption control means for controlling the operation of the urea water supply means, wherein the ammonia adsorption control means comprises at least a discharge amount of nitrogen oxides discharged from the internal combustion engine or Depending on the temperature of the exhaust gas, when the ammonia adsorption catalyst is in an environment where the ammonia is easily adsorbed with respect to the urea water supply, And supplying from said urea water supply unit the urea water to the amount or more ammonia required for reducing and purifying nitrogen oxides contained in exhaust gas discharged from the internal combustion engine is generated.

  Further, in the exhaust gas purification apparatus for an internal combustion engine according to claim 2, in claim 1, the internal combustion engine includes exhaust gas recirculation means for recirculating the exhaust gas to an intake passage of the internal combustion engine, and the ammonia adsorption catalyst includes the exhaust gas purification device. The environment in which ammonia is easily adsorbed is a state in which the exhaust gas recirculation means is operated and the exhaust gas is recirculated in the intake passage of the internal combustion engine.

  According to a third aspect of the present invention, there is provided an exhaust gas purification apparatus for an internal combustion engine according to the first or second aspect, further comprising a diesel particulate filter for removing particulate matter in the exhaust gas upstream of the urea water supply means. The environment in which the ammonia is easily adsorbed on the catalyst is a state in which regeneration control of the diesel particulate filter is being performed.

Further, in the exhaust gas purification apparatus for an internal combustion engine according to claim 4, in any one of claims 1 to 3, the environment in which the ammonia is easily adsorbed by the ammonia adsorption catalyst is the exhaust gas flowing into the ammonia adsorption catalyst. The temperature is in a predetermined temperature range.
Further, in the exhaust gas purification apparatus for an internal combustion engine according to claim 5, in any one of claims 1 to 4, the environment in which the ammonia is easily adsorbed by the ammonia adsorption catalyst is adsorbed by the ammonia adsorption catalyst. The ammonia amount is less than a predetermined value.

  Further, in the exhaust gas purification apparatus for an internal combustion engine according to claim 6, in any one of claims 1 to 5, a first concentration for detecting the concentration of the nitrogen oxide in the exhaust gas upstream of the urea water supply means. A detection means, and a second concentration detection means for detecting the concentration of the nitrogen oxides in the exhaust gas downstream of the selective reduction catalyst, wherein the ammonia adsorption control means is a detection value of the second concentration detection means. However, if it is equal to or greater than the detection value of the first concentration detection means, the urea water supply from the urea water supply means is terminated.

  According to the invention of claim 1, when the ammonia adsorption catalyst is in an environment in which ammonia is easily adsorbed with respect to the supply of urea water depending on at least the amount of nitrogen oxide discharged from the internal combustion engine or the temperature of the exhaust gas, Since urea water is supplied from the urea water supply means so that more ammonia than the amount necessary for reduction and purification of nitrogen oxides contained in the exhaust gas discharged from the internal combustion engine is generated, the ammonia adsorption catalyst reliably adsorbs ammonia. It becomes possible to make it.

Therefore, ammonia can be adsorbed on the ammonia adsorption catalyst. For example, the ammonia adsorbed on the ammonia adsorption catalyst can be removed at a high rotational speed and high load of the internal combustion engine that emits a large amount of nitrogen oxide. The ammonia can be supplied to the selective reduction catalyst and the nitrogen oxides can be reliably reduced and purified.
According to the second aspect of the present invention, the environment in which ammonia is easily adsorbed by the ammonia adsorption catalyst is in a state where the exhaust gas recirculation means is operated and the exhaust gas is recirculated in the intake passage of the internal combustion engine.

In this way, by supplying urea water from the urea water supply means during operation of the exhaust gas recirculation means, during the operation of the exhaust gas recirculation means, the amount of nitrogen oxide discharged from the internal combustion engine decreases, There is no need to actively reduce and purify nitrogen oxides with the selective reduction catalyst.
Therefore, by setting the amount of urea water supplied from the urea water supply means to a necessary amount for adsorbing to the ammonia adsorption catalyst, it is possible to reduce the consumption of urea water while reliably adsorbing ammonia to the ammonia adsorption catalyst.

  Therefore, ammonia can be adsorbed by the ammonia adsorption catalyst. For example, the ammonia adsorbed on the ammonia adsorption catalyst can be removed at a high rotational speed and high load of the internal combustion engine that emits a large amount of nitrogen oxide. The ammonia can be supplied to the selective reduction catalyst and the nitrogen oxides can be reliably reduced and purified. And since the consumption of urea water can be reduced, the capacity | capacitance of the tank which stores urea water can be made small, or if the capacity | capacitance of a tank is the same, the space | interval until replenishment of urea water can be lengthened.

According to the invention of claim 3, the environment in which ammonia is easily adsorbed by the ammonia adsorption catalyst is in a state where the regeneration control of the diesel particulate filter is being performed.
Thus, by supplying urea water from the urea water supply means during the regeneration control of the diesel particulate filter, the amount of nitrogen oxides discharged from the internal combustion engine increases during the regeneration control of the diesel particulate filter. However, although it is necessary to reduce and purify nitrogen oxides with a selective reduction catalyst, the temperature of the exhaust gas is high in order to burn the particulate matter deposited in the diesel particulate filter.

Accordingly, the temperature of the exhaust gas is high, and the urea water supplied from the urea water supply means is in a state where it is easily hydrolyzed to become ammonia. Therefore, the urea water is reliably supplied to the ammonia adsorption catalyst as ammonia gas. It becomes possible.
Therefore, ammonia can be adsorbed by the ammonia adsorption catalyst. For example, the ammonia adsorbed on the ammonia adsorption catalyst can be removed at a high rotational speed and high load of the internal combustion engine that emits a large amount of nitrogen oxide. The ammonia can be supplied to the selective reduction catalyst and the nitrogen oxides can be reliably reduced and purified.

According to the invention of claim 4, an environment in which ammonia is easily adsorbed by the ammonia adsorption catalyst is in a state where the temperature of the exhaust gas flowing into the ammonia adsorption catalyst is within a predetermined temperature range.
Accordingly, for example, the lower limit of the predetermined temperature range is the temperature at which urea water is hydrolyzed to ammonia, and the upper limit of the predetermined temperature range is the temperature at which ammonia starts to desorb from the ammonia adsorption catalyst, and the exhaust gas temperature is within the predetermined temperature range. By supplying urea water from the urea water supply means sometimes, the urea water can be hydrolyzed into ammonia and adsorbed on the ammonia adsorption catalyst, so that the ammonia adsorbed on the ammonia adsorption catalyst can be prevented from desorbing. Thus, ammonia can be reliably adsorbed on the ammonia adsorption catalyst.

Therefore, ammonia can be adsorbed on the ammonia adsorption catalyst, so that the ammonia adsorbed on the ammonia adsorption catalyst is desorbed at a high rotation speed and high load of the internal combustion engine where the amount of nitrogen oxide emitted from the internal combustion engine is large. Thus, ammonia can be supplied to the selective catalytic reduction catalyst, and nitrogen oxides can be reliably reduced and purified.
According to the invention of claim 5, the environment in which ammonia is easily adsorbed by the ammonia adsorption catalyst is set to a state where the amount of ammonia adsorbed by the ammonia adsorption catalyst is smaller than a predetermined amount.

  Therefore, for example, when the predetermined amount of ammonia is the limit amount of ammonia that can be adsorbed to the ammonia adsorption catalyst that is unable to adsorb ammonia to the ammonia adsorption catalyst, the amount of ammonia adsorbed on the ammonia adsorption catalyst becomes the predetermined amount. Since urea water is not supplied from the supply means, it is possible to prevent ammonia from flowing out downstream of the ammonia adsorption catalyst without being adsorbed by the ammonia adsorption catalyst, and as a result, was not adsorbed by the ammonia adsorption catalyst. It is possible to prevent ammonia from being discharged outside the vehicle.

Further, according to the invention of claim 6, when the concentration of nitrogen oxides in the exhaust gas downstream of the selective catalytic reduction catalyst is equal to or higher than the concentration of nitrogen oxides in the exhaust gas upstream of the urea water supply means, ammonia adsorption The control is terminated.
The first and second concentration detecting means generally have characteristics that are influenced by ammonia. When the concentration of nitrogen oxides in the exhaust gas downstream of the selective catalytic reduction catalyst is equal to or higher than the concentration of nitrogen oxides in the exhaust gas upstream of the urea water supply means, urea supplied from the urea water supply means Water is hydrolyzed to become ammonia, and the ammonia is not adsorbed by the ammonia adsorption catalyst, and is discharged without being used for the reduction and purification of nitrogen oxides by the selective reduction catalyst, and the second concentration detection means is influenced by the ammonia. Is the case. That is, when the concentration of nitrogen oxides in the exhaust gas downstream of the selective catalytic reduction catalyst is equal to or higher than the concentration of nitrogen oxides in the exhaust gas upstream of the urea water supply means, urea water is excessive from the urea water supply means. The case where it is supplied to.

  Therefore, if the concentration of nitrogen oxides in the exhaust gas downstream of the selective catalytic reduction catalyst is equal to or higher than the concentration of nitrogen oxides in the exhaust gas upstream of the urea water supply means, urea water is supplied excessively from the urea water supply means. It is determined that ammonia is not adsorbed by the ammonia adsorption catalyst and is not used for reduction and purification of nitrogen oxides by the selective reduction catalyst, and is discharged, and the ammonia adsorption control is terminated. It is possible to prevent ammonia from being discharged out of the vehicle without being adsorbed and not being used for reduction and purification of nitrogen oxides by the selective reduction catalyst.

1 is a schematic configuration diagram of an engine to which an exhaust gas purification apparatus for an internal combustion engine according to the present invention is applied. It is a control flowchart of ammonia adsorption control which the engine control unit of the exhaust gas purification apparatus of the internal combustion engine which concerns on 1st Example of this invention performs. It is a control flowchart of ammonia adsorption control which the engine control unit of the exhaust gas purification apparatus of the internal combustion engine which concerns on 2nd Example of this invention performs. It is a control flowchart of ammonia adsorption control which the engine control unit of the exhaust gas purification apparatus of the internal combustion engine which concerns on 3rd Example of this invention performs.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram of an engine 1 to which an exhaust gas purification apparatus for an internal combustion engine is applied.
As shown in FIG. 1, an engine (internal combustion engine) 1 is a multi-cylinder direct injection internal combustion engine (for example, a common rail diesel engine). Specifically, high pressure fuel accumulated in the common rail is used as fuel for each cylinder. The fuel nozzle is supplied to the injection nozzle 2 and can be injected from the fuel injection nozzle 2 into the combustion chamber 3 of each cylinder at an arbitrary injection timing and injection amount.

Each cylinder of the engine 1 is provided with a piston 4 that can slide up and down. The piston 4 is connected to the crankshaft 6 via a connecting rod 5. A flywheel is provided at one end of the crankshaft 6.
An intake port 7 and an exhaust port 8 are communicated with the combustion chamber 3.
The intake port 7 is provided with an intake valve 9 that communicates and shuts off the combustion chamber 3 and the intake port 7. Further, the exhaust port 8 is provided with an exhaust valve 10 for performing communication between the combustion chamber 3 and the exhaust port 8 and shutting off.

An intake manifold 11 that distributes the sucked air to each cylinder is provided upstream of the intake port 7 so as to communicate therewith. Further, an exhaust manifold 12 that collects exhaust gas discharged from each cylinder is provided downstream of the exhaust port 8.
The intake manifold 11 upstream of the branch for distributing the intake air to each cylinder of the intake manifold 11 is provided with an oxygen concentration sensor 13 for detecting the oxygen concentration so that the sensor portion projects into the intake manifold 11. . Further, an intake air temperature sensor 14 for detecting the temperature of intake air taken into the combustion chamber 3 is provided downstream of the air-fuel ratio sensor 13 so as to protrude into the intake manifold 11.

  A high-pressure EGR passage (exhaust gas recirculation means) for returning a part of the high-temperature / high-pressure exhaust gas to the intake air so that the intake manifold 11 and the exhaust manifold 12 communicate with each other, that is, introducing high-temperature / high-pressure EGR gas into the intake air. 15 is provided. The high pressure EGR passage 15 is connected to an intake manifold 11 upstream of the oxygen concentration sensor 13 via an EGR valve (exhaust gas recirculation means) 16 that adjusts the amount of high temperature / high pressure exhaust gas returning to the intake air, that is, the flow rate of EGR gas. Connected. The high-pressure EGR passage 15 is provided with an EGR cooler (exhaust gas recirculation means) 17 that cools the exhaust gas introduced into the intake manifold 11.

  Upstream of the intake manifold 11, an air cleaner 18 that removes fresh dust sucked from the uppermost stream, an intercooler 20 that cools the compressed fresh air, and a flow rate of the fresh air are adjusted. An electronically controlled throttle valve 39 for adjusting the flow rate of low-pressure EGR gas introduced from a low-pressure EGR passage 41, which will be described later, and a compressor (not shown) of a turbocharger 19 that compresses fresh air sucked using exhaust energy The housing is connected to the intake manifold 11 via the intake pipe 21. An electronically controlled throttle valve 22 for adjusting the flow rate of EGR gas introduced from the high pressure EGR passage 15 is disposed between the intake manifold 11 and the intake pipe 21. The electronically controlled throttle valves 22 and 39 are provided with throttle position sensors 23 and 40 for detecting the degree of opening of the throttle valve.

The intake pipe 21 between the air cleaner 18 of the intake pipe 21 and the compressor housing of the turbocharger 19 is provided with an intake temperature sensor 38 that detects the temperature of the intake air so as to protrude into the intake pipe 21. Yes.
Downstream of the exhaust manifold 12, a turbine housing (not shown) for introducing exhaust gas into the turbocharger 19 and an exhaust pipe 24 are provided so as to communicate with each other.

  In the exhaust pipe 24, an oxidation catalyst 25 that oxidizes oxidizable components in the exhaust gas in order from the upstream, a diesel particulate filter 26 that collects and burns particulate matter mainly composed of graphite in the exhaust gas, and ammonia Is temporarily adsorbed, and when the exhaust gas temperature becomes equal to or higher than a predetermined temperature (400 ° C.), the ammonia adsorption catalyst 27 that desorbs the adsorbed ammonia and the nitrogen oxide (hereinafter referred to as NOx) in the exhaust gas are reduced and purified using ammonia. The selective reduction catalyst 28 is provided so as to communicate with it. Note that the oxidation catalyst 25 and the diesel particulate filter 26 are disposed in a casing 29. Further, the ammonia adsorption catalyst 27 and the selective reduction catalyst 28 are disposed in the casing 30.

  The ammonia adsorption catalyst 27 is made of a zeolite that does not contain metal ions (for example, Cu and Fe), that is, a zeolite having a Bronsted acid point. The catalyst capacity of the ammonia adsorption catalyst 27 is set to be equal to or less than the catalyst capacity of the selective reduction catalyst 28. When the temperature of the catalyst is lower than a predetermined temperature (400 ° C.), the ammonia adsorption catalyst 27 adsorbs ammonia generated by hydrolysis of urea water injected from the urea water injector 36 described later, and the temperature of the catalyst is a predetermined temperature. If it becomes above, it has the characteristic of desorbing the adsorbed ammonia. That is, when the exhaust gas temperature becomes equal to or higher than the predetermined temperature and the temperature of the ammonia adsorption catalyst 27 becomes equal to or higher than the predetermined temperature, the ammonia adsorption catalyst 27 desorbs ammonia and supplies ammonia to the downstream selective reduction catalyst 28.

  The selective reduction catalyst 28 is composed of a zeolite containing metal ions (for example, Cu or Fe), that is, a zeolite having a Lewis acid point. The selective reduction catalyst 28 has a function of adsorbing and desorbing ammonia supplied to the selective reduction catalyst 28 in addition to the function of reducing and purifying NOx. The selective reduction catalyst 28 is formed by ammonia desorbed from the ammonia adsorption catalyst 27, ammonia generated by hydrolysis of urea water injected from the urea water injector 36, or ammonia adsorbed on the selective reduction catalyst 28. NOx in exhaust gas is reduced and purified. The selective catalytic reduction catalyst 28 starts desorption of ammonia when the temperature of the catalyst is about 200 ° C. to 300 ° C.

Between the turbocharger 19 of the exhaust pipe 24 and the casing 29, an oxygen concentration sensor 31 for detecting the oxygen concentration in the exhaust gas is provided so as to protrude into the exhaust pipe 24.
An exhaust gas temperature sensor 32 that detects the temperature of the exhaust gas flowing into the oxidation catalyst 25 is provided upstream of the oxidation catalyst 25 in the casing 29 so as to protrude into the casing 29. An exhaust temperature sensor 33 that detects the temperature of the exhaust gas flowing out from the oxidation catalyst 25 is provided between the oxidation catalyst 25 of the casing 29 and the diesel particulate filter 26 so as to protrude into the casing 29. An exhaust gas temperature sensor 34 that detects the temperature of the exhaust gas flowing out from the diesel particulate filter 26 is provided downstream of the diesel particulate filter 26 in the casing 29 so as to project into the casing 29.

  Between the diesel particulate filter 26 and the ammonia adsorption catalyst 27 in the exhaust pipe 24, that is, between the casing 29 and the casing 30 of the exhaust pipe 24, a NOx sensor (first concentration detection) that detects the concentration of NOx in the exhaust gas. Means) 35 is provided so as to protrude into the exhaust pipe 24. A urea water injector (urea water supply means) 36 is provided between the NOx sensor 35 of the exhaust pipe 24 and the casing 30 so as to protrude into the exhaust pipe 24. Note that the detection value of the NOx sensor 35 is influenced by ammonia due to the characteristics of the sensor. That is, the detected value of the NOx sensor 35 outputs a high detected value (NOx concentration) when the concentration of ammonia becomes high even if the concentration of NOx in the exhaust gas is constant.

  The urea water injector 36 injects urea water for supplying ammonia to the ammonia adsorption catalyst 27 and the selective reduction catalyst 28 into the exhaust pipe 24. The urea water is supplied from a urea water tank (not shown) provided outside. The distance from the urea water injector 36 to the ammonia adsorption catalyst 27 is set to be longer than the distance necessary for the urea water injected from the urea water injector 36 to be hydrolyzed to generate ammonia. Therefore, the urea water injected from the urea water injector 36 undergoes hydrolysis and generates ammonia before reaching the ammonia adsorption catalyst 27.

  A NOx sensor (second concentration detection means) 37 that detects the concentration of NOx in the exhaust gas flowing out from the selective reduction catalyst 28 is disposed downstream of the selective reduction catalyst 28 in the exhaust pipe 24, that is, downstream of the casing 30. It is provided so as to protrude into 24. Similar to the NOx sensor 37, the NOx sensor 37 is influenced by ammonia due to the characteristics of the sensor. That is, the detection value of the NOx sensor 35 outputs a high detection value (NOx concentration) when the concentration of ammonia becomes high even if the concentration of NOx in the exhaust gas is constant.

  A part of the low-temperature and low-pressure exhaust gas is returned to the intake air so that the intake pipe 21 between the electronically controlled throttle valve 39 and the turbocharger 19 and the exhaust pipe 24 downstream of the diesel particulate filter 29 communicate with each other. That is, a low-pressure EGR passage (exhaust gas recirculation means) 41 for introducing low-temperature and low-pressure EGR gas into the intake air is provided. The low-pressure EGR passage 41 has an EGR valve (exhaust recirculation means) 42 that adjusts the amount of exhaust gas that returns to intake air, that is, the flow rate of EGR gas, and an EGR cooler (exhaust gas recirculation means) 43 that cools the exhaust gas that returns to intake air. And an EGR filter (exhaust gas recirculation means) 44 that removes foreign substances from the exhaust gas that is returned to the intake air.

  The fuel injection nozzle 2, oxygen concentration sensors 13, 31, intake air temperature sensors 14, 38, EGR valves 16, 42, electronically controlled throttle valves 22, 39, throttle position sensors 23, 40, and exhaust temperature sensors 32, 33, 34 NOx sensors 35 and 37, urea water injector 36, various sensors for detecting the operating state of the engine 1, an accelerator position sensor for detecting the degree of operation of an accelerator pedal operated by a driver of a vehicle on which the engine 1 is mounted, and the like. The various devices are control devices for performing overall control of the engine 1 and include an input / output device, a storage device (ROM, RAM, nonvolatile RAM, etc.), a timer, a central processing unit (CPU), and the like. It is electrically connected to the engine control unit (ammonia adsorption control means) 50 configured. That. The engine control unit 50 controls the operation of the engine 1 by controlling the operation of various devices based on information from various sensors.

On the input side of the engine control unit 50, oxygen concentration sensors 13, 31, intake temperature sensors 14, 38, throttle position sensors 23, 40, exhaust temperature sensors 32, 33, 34, NOx sensors 35, 37, and accelerator position sensor Sensors such as these are electrically connected, and detection information from these various devices and various sensors is input.
On the other hand, on the output side of the engine control unit 50, the fuel injection nozzle 2, the EGR valves 16, 42, the electronically controlled throttle valves 22, 39, and the urea water injector 36 are electrically connected.

Thus, the engine control unit 50 determines the fuel injection amounts and injection timings of the pre-injection, main injection and after-injection from the fuel injection nozzle 2 based on the detection values of the sensors, the EGR valves 16 and 42, and the electronically controlled throttle valve. The opening degree of 22, 39 and the injection amount of urea water from the urea water injector 36 are optimally controlled, and the engine 1 is controlled with high accuracy.
Further, the engine control unit 50 calculates the pressure difference from the pressure of the exhaust gas upstream and downstream of the diesel particulate filter 26 detected by a pressure sensor (not shown), and when the pressure difference becomes a predetermined pressure difference, When a forced regeneration button or the like (not shown) is operated by the control, the diesel particulates that burn the particulate matter accumulated in the diesel particulate filter 26 by controlling the injection amount and the injection timing of the fuel from the combustion injection nozzle 2 are controlled. Perform filter regeneration processing.

Further, when the engine control unit 50 determines that the NOx emission amount is larger than the operating state of the engine 1 or the NOx concentration detected by the NOx sensor 35, supply of ammonia to be supplied to the ammonia adsorption catalyst 27 and the selective reduction catalyst 28. The injection amount of urea water injected from the urea water injector 36 is increased so that the amount increases. Further, the engine control unit 50 determines the ammonia based on the operating state of the engine 1, the exhaust gas temperature between the urea water injector 36 and the ammonia adsorption catalyst 27, the amount of ammonia adsorbed in the ammonia adsorption catalyst 27, and the like. When it is determined that the environment is such that ammonia is easily adsorbed by the adsorption catalyst 27, ammonia adsorption control is performed in which urea water is injected from the urea water injector 36 and ammonia generated by hydrolysis of the urea water is adsorbed to the ammonia adsorption catalyst 27. carry out.
[First embodiment]
Next, ammonia adsorption control in the engine control unit 50 of the exhaust gas purification apparatus for an internal combustion engine according to the first embodiment of the present invention will be described.

FIG. 2 is a control flowchart of ammonia adsorption control in the engine control unit 50 of the exhaust gas purification apparatus for an internal combustion engine according to the first embodiment of the present invention.
As shown in FIG. 2, in step S10, whether or not EGR is being introduced (corresponding to a state in which the exhaust gas recirculation means of the present invention is operated and exhaust gas is recirculated in the intake passage of the internal combustion engine). Is determined. Specifically, it is determined whether or not the exhaust gas is introduced into the intake air by operating either or both of the EGR valves 16 and 42. If the determination result is true (Yes) and either or both of the EGR valves 16 and 42 are operated to introduce exhaust gas into the intake air, the process proceeds to step S12. If the determination result is negative (No) and neither of the EGR valves 16, 42 is operating, and the exhaust gas is not introduced into the intake air, the process proceeds to step S18.

  In step S12, it is determined whether or not the exhaust gas temperature is within a predetermined temperature range. Specifically, based on the temperature of the exhaust gas discharged from the diesel particulate filter 26 detected by the exhaust temperature sensor 34, the exhaust gas temperature between the urea water injector 36 and the ammonia adsorption catalyst 27 (the temperature of the exhaust gas of the present invention). And the determined exhaust gas temperature is within a predetermined temperature range. If the exhaust gas temperature estimated with the determination result being true (Yes) is within the predetermined temperature range, the process proceeds to step S14. On the other hand, if the exhaust gas temperature estimated as the result of determination is NO (No) is not within the predetermined temperature range, the process proceeds to step S18. The lower limit value of the predetermined temperature range is set to a temperature at which urea water is hydrolyzed to ammonia (for example, 200 ° C.). The upper limit value of the predetermined temperature range is set to a temperature at which ammonia starts to desorb from the ammonia adsorption catalyst 27 (for example, 400 ° C.).

  In step S14, it is determined whether or not the ammonia amount adsorbed in the ammonia adsorption catalyst, that is, the ammonia adsorption amount Wn is less than a predetermined amount. If the determination result is true (Yes) and the ammonia adsorption amount Wn is less than the predetermined amount, the process proceeds to step S16. If the determination result is NO (No) and the ammonia adsorption amount Wn is not less than the predetermined amount, the process proceeds to step S18. The predetermined amount is set to a limit amount of ammonia that can be adsorbed by the ammonia adsorption catalyst 27.

In step S16, urea water injection from the urea water injector 36 is started. That is, urea water is injected from the urea water injector 36, and ammonia generated by hydrolysis of the urea water is adsorbed to the ammonia adsorption catalyst 27. Then, the process returns to step S10.
In step S18, the urea water injection from the urea water injector 36 is terminated. Then, this routine is returned.

  Thus, in the exhaust gas purification apparatus for an internal combustion engine according to the first embodiment, either or both of the EGR valves 16 and 42 are operated to introduce the exhaust gas into the intake air, and the urea water injector 36 and the ammonia adsorption catalyst 27. When the ammonia adsorption amount Wn adsorbed in the ammonia adsorption catalyst is less than the predetermined amount, the urea water injection from the urea water injector 36 is started, Ammonia generated by hydrolysis of urea water is adsorbed on the ammonia adsorption catalyst 27.

  Since the ammonia adsorption catalyst 27 is made of zeolite having a Bronsted acid point, for example, the vehicle suddenly accelerates, the engine 1 becomes a high load operation, the temperature of the exhaust gas rises, and the temperature of the ammonia adsorption catalyst 27 When the temperature exceeds a predetermined temperature (400 ° C.), the adsorbed ammonia is desorbed. In the selective catalytic reduction catalyst 28, the amount of emissions increased due to high load operation of the engine 1 due to ammonia desorbed from the ammonia adsorption catalyst 27 and ammonia generated from urea water injected from the urea water injector 36. NOx discharged from the engine 1 is reduced and purified.

Thus, during the introduction of EGR, that is, when the exhaust gas is introduced into the intake air, the urea water is supplied from the urea water injector 36, so that the amount of NOx discharged from the engine 1 is reduced during the introduction of EGR. Therefore, there is no need to actively reduce and purify NOx by the selective reduction catalyst 28.
Therefore, the urea water supplied from the urea water injector 36 is set to a supply amount necessary for adsorbing to the ammonia adsorption catalyst 27, so that the ammonia adsorption catalyst 27 is reliably adsorbed with ammonia and the consumption of urea water is reduced. it can.

  Therefore, ammonia can be adsorbed on the ammonia adsorption catalyst 27. For example, the ammonia adsorbed on the ammonia adsorption catalyst 27 is removed at a high rotational speed and high load of the engine 1 where the amount of NOx emitted from the engine 1 is large. The ammonia can be supplied to the selective catalytic reduction catalyst 28 and NOx can be reliably reduced and purified. And since the consumption of urea water can be reduced, the capacity | capacitance of the tank which stores urea water can be made small, or if the capacity | capacitance of a tank is the same, the space | interval until replenishment of urea water can be lengthened.

  Further, the exhaust gas temperature between the urea water injector 36 and the ammonia adsorption catalyst 27 is set such that the lower limit value is set to a temperature at which urea water is hydrolyzed to ammonia (for example, 200 ° C.), and the upper limit value is set to the ammonia adsorption catalyst 27. When the urea water is supplied from the urea water injector 36 when the temperature is within a predetermined temperature range set to a temperature at which ammonia starts to desorb (for example, 400 ° C.), the urea water is hydrolyzed into ammonia, and the ammonia is adsorbed. Since the ammonia adsorbed on the ammonia adsorption catalyst 27 can be prevented from desorbing since it can be adsorbed on the catalyst 27, the ammonia can be surely adsorbed on the ammonia adsorption catalyst 27.

Therefore, ammonia can be reliably adsorbed on the ammonia adsorption catalyst 27, so that the ammonia adsorbed on the ammonia adsorption catalyst 27 can be reduced at a high rotational speed and high load of the engine 1 where the amount of NOx discharged from the engine 1 is large. By desorption, ammonia can be supplied to the selective reduction catalyst 28, and NOx can be reliably reduced and purified.
When the ammonia amount adsorbed on the ammonia adsorption catalyst 27, that is, the ammonia adsorption amount Wn is less than a predetermined amount set to the limit ammonia amount that can be adsorbed on the ammonia adsorption catalyst 27, the urea water injector 36 supplies the urea water. Since the supply is not performed, it is possible to prevent ammonia from flowing out downstream of the ammonia adsorption catalyst 27 without being adsorbed by the ammonia adsorption catalyst 27. As a result, ammonia that has not been adsorbed by the ammonia adsorption catalyst 27 is removed from the outside of the vehicle. Can be prevented from being discharged.
[Second Embodiment]
Next, ammonia adsorption control in the engine control unit 50 of the exhaust gas purification apparatus for an internal combustion engine according to the second embodiment of the present invention will be described.

FIG. 3 is a control flowchart of ammonia adsorption control in the engine control unit 50 of the exhaust gas purification apparatus for an internal combustion engine according to the second embodiment of the present invention.
The ammonia adsorption control of the second embodiment is different from the first embodiment in that the NOx sensor disposed between the diesel particulate filter 26 and the ammonia adsorption catalyst 27 after the urea water injection by the urea water injector 36. The difference is that the detected value 35 is compared with the detected value of the NOx sensor 37 disposed downstream of the selective catalytic reduction catalyst 28. Differences from the first embodiment will be described below.

  As shown in FIG. 3, steps S10 to S16 are the same as those in the first embodiment, whether or not EGR is being introduced, whether or not the exhaust gas temperature is within a predetermined temperature range, and the ammonia adsorption catalyst. It is determined whether the ammonia adsorption amount Wn adsorbed therein is less than a predetermined amount. If all the determination results are true (Yes), the urea water injector 36 starts to inject urea water. Then, the process proceeds to step S17.

  In step S <b> 17, the detected value (NOx concentration) Do of the NOx sensor 37 disposed downstream of the selective reduction catalyst 28 is the NOx sensor 35 disposed between the diesel particulate filter 26 and the ammonia adsorption catalyst 27. It is determined whether or not the detected value (NOx concentration) Di is greater. If the determination result is true (Yes) and the NOx concentration Do is greater than the NOx concentration Di, the process proceeds to step S18, the injection of urea water from the urea water injector 36 is terminated, and this routine is returned. If the determination result is NO (No) and the NOx concentration Do is not greater than the NOx concentration Di, the process returns to step S10.

  Thus, in the exhaust gas purification apparatus for an internal combustion engine according to the second embodiment, either or both of the EGR valves 16 and 42 are operated to introduce exhaust gas into the intake air, and the urea water injector 36 and the ammonia adsorption catalyst 27. When the ammonia adsorption amount Wn adsorbed in the ammonia adsorption catalyst is less than the predetermined amount, the urea water injection from the urea water injector 36 is started, Ammonia generated by hydrolysis of urea water is adsorbed on the ammonia adsorption catalyst 27. If the NOx concentration Do is greater than the NOx concentration Di, the urea water injection from the urea water injector 36 is terminated. Further, if the NOx concentration Do is not larger than the NOx concentration Di, it is determined again whether or not EGR is introduced.

  Therefore, the NOx sensor 35 and the NOx sensor 37 generally have characteristics that are influenced by ammonia. When the NOx concentration Do in the exhaust gas downstream of the selective catalytic reduction catalyst 28 becomes larger than the NOx concentration Di in the exhaust gas upstream of the urea water injector 36, the urea water injected from the urea water injector 36 is hydrolyzed. It is decomposed into ammonia, which is not adsorbed by the ammonia adsorption catalyst 27, is exhausted without being used for NOx reduction purification by the selective reduction catalyst 28, and the NOx sensor 37 is affected by the ammonia. . That is, when the NOx concentration Do in the exhaust gas downstream of the selective catalytic reduction catalyst 28 becomes larger than the NOx concentration Di in the exhaust gas upstream of the urea water injector 36, the urea water is excessively supplied from the urea water injector 36. If it is.

Accordingly, when the NOx concentration Do in the exhaust gas downstream of the selective catalytic reduction catalyst 28 becomes larger than the NOx concentration Di in the exhaust gas upstream of the urea water injector 36, urea water is excessively injected from the urea water injector 36 and ammonia is injected. It is determined that the catalyst is not adsorbed by the ammonia adsorption catalyst 27 but is not used for reduction and purification of NOx by the selective reduction catalyst 28, and the injection of urea water from the urea water injector 36 is terminated. It can be prevented that ammonia is not adsorbed by the catalyst 27 and is not used for the reduction and purification of NOx by the selective reduction catalyst 28 and is discharged outside the vehicle.
[Third embodiment]
Next, ammonia adsorption control in the engine control unit 50 of the exhaust gas purification apparatus for an internal combustion engine according to the third embodiment of the present invention will be described.

FIG. 4 is a control flowchart of ammonia adsorption control in the engine control unit 50 of the exhaust gas purification apparatus for an internal combustion engine according to the third embodiment of the present invention.
The ammonia adsorption control of the third embodiment differs from the second embodiment in that the determination of whether or not the EGR is introduced in step S10 is the determination of whether or not the diesel particulate filter is being regenerated. . Differences from the second embodiment will be described below.

  As shown in FIG. 3, in step S <b> 10 ′, it is determined whether or not regeneration control of the diesel particulate filter 26 is being performed (corresponding to a state in which regeneration control of the diesel particulate filter of the present invention is being controlled). If the determination result is true (Yes) and the regeneration control of the diesel particulate filter 26 is in progress, the process proceeds to step S12. If the determination result is negative (No) and the regeneration control of the diesel particulate filter 26 is not in progress, the process proceeds to step S18.

  From step S12 to step S18, as in the second embodiment, whether or not the exhaust gas temperature is within a predetermined temperature range, and the ammonia adsorption amount Wn adsorbed in the ammonia adsorption catalyst is less than the predetermined amount. If all the determination results are true (Yes), the urea water injection from the urea water injector 36 is started. If the NOx concentration Do is not greater than the NOx concentration Di, the determination of the introduction of the exhaust gas into the intake air is performed again. If the NOx concentration Do is greater than the NOx concentration Di, the urea water injection from the urea water injector 36 is terminated.

  Thus, in the exhaust gas purification apparatus for an internal combustion engine according to the third embodiment, regeneration control of the diesel particulate filter 26 is being performed, and the exhaust gas temperature between the urea water injector 36 and the ammonia adsorption catalyst 27 is within a predetermined temperature range. If the ammonia adsorption amount Wn adsorbed in the ammonia adsorption catalyst is less than a predetermined amount, injection of urea water from the urea water injector 36 is started, and ammonia generated by hydrolysis of the urea water is converted into ammonia. Adsorbed on the adsorption catalyst 27. If the NOx concentration Do is not greater than the NOx concentration Di, the determination of the introduction of the exhaust gas into the intake air is performed again. If the NOx concentration Do is greater than the NOx concentration Di, the urea water injection from the urea water injector 36 is terminated.

  By injecting urea water from the urea water injector 36 during regeneration control of the diesel particulate filter 26, during the regeneration control of the diesel particulate filter 26, the amount of NOx discharged from the engine 1 increases, and selective reduction occurs. Although it is necessary to reduce and purify NOx by the type catalyst 28, the temperature of the exhaust gas is high in order to burn the particulate matter deposited in the diesel particulate filter 26.

Therefore, since the temperature of the exhaust gas is high and the urea water injected from the urea water injector 36 is in a state where it is easily hydrolyzed to become ammonia, the urea water is reliably supplied to the ammonia adsorption catalyst 27 as ammonia gas. It becomes possible to do.
Therefore, ammonia can be adsorbed on the ammonia adsorption catalyst 27. For example, the ammonia adsorbed on the ammonia adsorption catalyst 27 is removed at a high rotational speed and high load of the engine 1 where the amount of NOx emitted from the engine 1 is large. The ammonia can be supplied to the selective catalytic reduction catalyst 28 and NOx can be reliably reduced and purified.

Although the description of the embodiment of the invention is finished as above, the embodiment of the present invention is not limited to the above embodiment.
In the above embodiment, the engine 1 is a common rail type diesel engine. However, the present invention is not limited to this, and a lean combustion gasoline engine having an exhaust system that has a relatively large NOx emission amount and a selective reduction catalyst is mounted. Needless to say, this is applicable.

  In the above embodiment, the EGR introduction and the diesel particulate filter 26 are controlled separately, but the present invention is not limited to this. Of course, the EGR introduction and the diesel particulate filter are not limited thereto. The same control flow may be used so that the flow after step S12 is executed when any of the reproduction control of 26 is executed.

1 engine (internal combustion engine)
15 High pressure EGR passage (exhaust gas recirculation means)
16 EGR valve (exhaust gas recirculation means)
17 EGR cooler (exhaust gas recirculation means)
26 Diesel particulate filter 27 Ammonia adsorption catalyst 28 Selective reduction catalyst 35 NOx sensor (first concentration detection means)
36 Urea water injector (urea water supply means)
37 NOx sensor (second concentration detection means)
41 Low pressure EGR passage (exhaust gas recirculation means)
42 EGR valve (exhaust gas recirculation means)
43 EGR cooler (exhaust gas recirculation means)
44 EGR filter (exhaust gas recirculation means)
50 ECU (ammonia adsorption control means)

Claims (6)

A selective reduction catalyst for reducing and purifying nitrogen oxides contained in exhaust gas discharged from an internal combustion engine with ammonia;
An ammonia adsorption catalyst that is disposed upstream of the selective reduction catalyst, adsorbs the ammonia, and desorbs the ammonia at a temperature higher than an ammonia desorption temperature of the selective reduction catalyst;
Urea water supply means for supplying urea water upstream of the ammonia adsorption catalyst;
Ammonia adsorption control means for controlling the operation of the urea water supply means,
The ammonia adsorption control means is an environment in which the ammonia adsorption catalyst easily adsorbs the ammonia with respect to the supply of the urea water depending on at least the amount of nitrogen oxide discharged from the internal combustion engine or the temperature of the exhaust gas. The internal combustion engine is characterized in that the urea water is supplied from the urea water supply means so that ammonia more than an amount necessary for reducing and purifying nitrogen oxides contained in the exhaust gas discharged from the internal combustion engine is generated at a certain time. Exhaust purification equipment. The internal combustion engine includes exhaust gas recirculation means for recirculating the exhaust gas to an intake passage of the internal combustion engine,
The environment in which the ammonia is easily adsorbed by the ammonia adsorption catalyst is a state in which the exhaust gas recirculation means is operated and the exhaust gas is recirculated in the intake passage of the internal combustion engine. Item 6. An exhaust emission control device for an internal combustion engine according to Item 1. An upstream of the urea water supply means, comprising a diesel particulate filter that removes particulate matter in the exhaust gas,
2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the environment in which the ammonia is easily adsorbed by the ammonia adsorption catalyst is a state in which regeneration control of the diesel particulate filter is being performed.   The environment in which the ammonia is easily adsorbed by the ammonia adsorption catalyst is a state in which the temperature of the exhaust gas flowing into the ammonia adsorption catalyst is within a predetermined temperature range. 2. An exhaust emission control device for an internal combustion engine according to item 1.   5. The environment in which the ammonia is easily adsorbed by the ammonia adsorption catalyst is a state in which the amount of ammonia adsorbed by the ammonia adsorption catalyst is less than a predetermined amount. 6. 2. An exhaust gas purification apparatus for an internal combustion engine according to 1. A first concentration detection means for detecting the concentration of the nitrogen oxide in the exhaust gas upstream of the urea water supply means;
A second concentration detecting means for detecting the concentration of the nitrogen oxide in the exhaust gas downstream of the selective catalytic reduction catalyst,
The ammonia adsorption control means terminates the supply of the urea water from the urea water supply means when the detection value of the second concentration detection means is equal to or higher than the detection value of the first concentration detection means. The exhaust emission control device for an internal combustion engine according to any one of claims 1 to 5.

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