JP2013142367A - Exhaust emission control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control device capable of effectively restraining the generation of an ammonia slip when operated in an unsteady state of the rotating speed of an engine since a load variation in the engine is large.SOLUTION: An exhaust emission control device includes an NOx purifying means 17 arranged in an exhaust pipe 10 for exhausting exhaust gas guided from an engine 1 and reducing and purifying nitrogen oxides in the exhaust gas flowing in the exhaust pipe 10. The NOx purifying means 17 has an NHflow rate calculating means for calculating a flow rate of ammonia oxidizable by an NHslip catalyst 21, a first function generating means for calculating a flow rate of the exhaust gas including ammonia corresponding to the flow rate of the ammonia calculated by the NHflow rate calculating means by presetting a relationship between the flow rate of the ammonia oxidizable by the NHslip catalyst 21 and the flow rate of the exhaust gas including the ammonia of the flow rate, and an exhaust gas flow rate control means for controlling the flow rate of the exhaust gas guided to the NHslip catalyst 21 according to the flow rate of the exhaust gas calculated by the first function generating means.

Description

  The present invention relates to an exhaust purification device that reduces and purifies nitrogen oxides contained in exhaust gas.

  Generally, a work machine such as a hydraulic excavator that operates with an engine includes a traveling body, a swiveling body disposed above the traveling body, a cab that is provided on the swiveling body and on which an operator rides, And a front work machine that is attached to the front of the revolving structure and performs work such as excavation by the operation of an operator in the cab. The above-described swivel body includes an engine room disposed behind the cab, the above-described engine disposed in the engine room, and an exhaust pipe that discharges exhaust gas led from the engine to the outside. ing.

  Here, since the exhaust gas discharged from the exhaust pipe contains harmful substances such as carbon monoxide (CO), nitrogen oxides (NOx), and soot, these harmful substances are contained in the revolving structure. An exhaust purification device for treating various substances is provided. Specifically, the exhaust purification device includes NOx purification means that is provided in the exhaust pipe and reduces and purifies nitrogen oxides contained in the exhaust gas flowing through the exhaust pipe.

This NOx purifying means decomposes nitrogen oxides contained in the exhaust gas into water and nitrogen, thereby reducing the concentration of nitrogen oxides in the exhaust gas. The NOx purification means includes, for example, a NOx catalyst provided in the exhaust pipe, and an ammonia supply means that is disposed upstream of the NOx catalyst in the exhaust pipe and supplies ammonia (NH ₃ ) into the exhaust pipe. Yes. The ammonia supplied by the ammonia supply means undergoes a reduction reaction with nitrogen oxides contained in the exhaust gas in the NOx catalyst, thereby decomposing and purifying the nitrogen oxides into harmless water and nitrogen.

  As one of the prior arts of the exhaust gas purification device that processes and purifies nitrogen oxides and the like contained in the exhaust gas, in addition to the NOx catalyst and ammonia supply means described above, the upstream side of the NOx catalyst in the exhaust pipe A pre-treatment device arranged in the above, an ammonia supply control means for controlling the supply of ammonia by the ammonia supply means, and a temperature detection means for detecting the temperature between the NOx catalyst in the exhaust pipe and the pre-treatment device, When the temperature detected by the temperature detection means is lower than the predetermined temperature, the ammonia supply control means prohibits the supply of ammonia from the ammonia supply means, and detects the temperature detection means regardless of the prohibition of the ammonia supply. There is known an exhaust emission control device that releases the prohibition and starts supplying ammonia when the temperature rise rate reaches a predetermined rate (for example, See Patent Document 1).

  In this prior art exhaust purification device, ammonia is supplied into the exhaust pipe by the ammonia supply means using urea water. Specifically, the ammonia supply means is disposed upstream of the NOx catalyst, for example, in a urea water tank for storing urea water, and injects urea water supplied from the urea water tank into the exhaust pipe. And injection means for performing. The urea water injected by this injection means is hydrolyzed by the heat of the exhaust gas, so that ammonia is generated in the exhaust pipe.

However, not all of the produced ammonia necessarily reacts with the nitrogen oxides in the exhaust gas in the NOx catalyst, and the surplus ammonia that does not react depending on the conditions in the exhaust pipe is caused to flow into the exhaust gas and the NOx catalyst A so-called ammonia slip that passes through the gas and is directly released into the atmosphere may occur. Therefore, in the exhaust purification device, an oxidation catalyst that oxidizes unreacted ammonia led from the NOx catalyst, that is, an NH ₃ slip catalyst is provided on the downstream side of the NOx catalyst. Therefore, the exhaust purification device prevents ammonia derived from the NOx catalyst from being decomposed into harmless nitrogen (N ₂ ) and water vapor (H ₂ O) in the NH ₃ slip catalyst and released into the atmosphere.

In addition, when the temperature of the exhaust gas passing through the NOx catalyst is low, such as when the engine starts, the temperature of the NOx catalyst does not increase, and the ammonia adsorption ability by the NOx catalyst decreases, so the above-described ammonia slip Is likely to occur. In the above-described prior art exhaust purification device, the ammonia supply control means controls the supply of urea water according to the temperature detected by the temperature detection means, thereby reacting with the nitrogen oxides contained in the exhaust gas. An optimal amount of ammonia is produced. Therefore, even if ammonia does not react with the nitrogen oxides in the exhaust gas by the NOx catalyst and becomes surplus, it is not excessively discharged from the NOx catalyst and is sufficiently treated by the NH ₃ slip catalyst.

JP 2008-128066 A

  Here, when the construction machine such as a hydraulic excavator is operated in an idle state, the load fluctuation of the engine is small and the rotational speed operates in a steady state. On the other hand, the construction machine operates the front working machine to perform work such as excavation, so that the load fluctuation of the engine increases during operation, and the engine speed operates in an unsteady state. For this reason, a sudden increase in the engine speed during operation causes the exhaust gas to be ejected vigorously from the engine, and the amount of exhaust gas discharged from the engine increases. However, the above-described prior art exhaust purification device disclosed in Patent Document 1 does not consider such an engine operating state, and the ammonia supply control means is based on the temperature obtained by the temperature detection means. Even if the supply of water is controlled, there is a possibility that the supply of ammonia generated in the exhaust pipe cannot immediately cope with the increase or decrease in the exhaust gas emission amount exhausted from the engine.

Thus, the prior art exhaust gas purification device disclosed in Patent Document 1 has a large load variation and operates in an unsteady state as when the construction machine performs work such as excavation. Since the balance between the supply amount of ammonia generated by hydrolysis of urea water and the discharge amount of nitrogen oxides contained in the exhaust gas is deteriorated, the excess ammonia without reacting with the NOx catalyst is slipped by NH ₃ There is a concern that the catalyst cannot be sufficiently oxidized and treated, and the occurrence of ammonia slip cannot be effectively suppressed.

  The present invention has been made in view of the actual situation of the prior art as described above, and its object is to effectively suppress the occurrence of ammonia slip when the engine load is large and the engine operates in an unsteady state. An object of the present invention is to provide an exhaust emission control device that can perform the above-described process.

In order to achieve the above object, an exhaust purification apparatus of the present invention includes an exhaust pipe that exhausts exhaust gas led from an engine, and nitrogen included in the exhaust gas that is provided in the exhaust pipe and circulates in the exhaust pipe. and a NOx purifying means for purifying by reducing oxides, the NOx purifying means, and NH ₃ supply means for supplying ammonia to the exhaust pipe, ammonia and exhaust gas supplied by the NH ₃ supply means Exhaust gas comprising at least a NOx catalyst that promotes a reaction with nitrogen oxides and an NH ₃ slip catalyst that is provided downstream of the NOx catalyst and oxidizes ammonia in the exhaust gas led from the NOx catalyst. in purifier, said NOx purifying means, and NH ₃ flow rate calculating means for calculating the flow rate of the oxidizable ammonia by the NH ₃ slip catalyst, the N ₃ the relationship between the flow rate of the oxidizable ammonia slip catalyst and the flow rate of the exhaust gas including ammonia in this flow is set in advance, the exhaust gas containing ammonia in accordance with the flow rate of ammonia calculated by the NH ₃ flow rate calculating means Exhaust gas flow rate calculation means for calculating the flow rate of the exhaust gas, and exhaust gas flow rate control means for controlling the flow rate of the exhaust gas guided to the NH ₃ slip catalyst according to the exhaust gas flow rate calculated by the exhaust gas flow rate calculation means, It is characterized by having.

Thus constituted exhaust gas purification device becomes surplus without reacting with NOx catalyst, NH ₃ relative to ammonia guided to slip catalyst, NH ₃ flow rate calculating means oxidizable ammonia in this NH ₃ slip catalyst The flow rate is calculated. Further, the exhaust gas flow rate calculation means includes a flow rate of ammonia calculated by the NH ₃ flow rate calculation means, a flow rate of ammonia that can be oxidized by a preset NH ₃ slip catalyst, and a flow rate of exhaust gas containing ammonia at this flow rate. Based on this relationship, the flow rate of the exhaust gas containing ammonia at a flow rate that can be oxidized by the NH ₃ slip catalyst is calculated. Since the exhaust gas flow rate control means controls the flow rate of the exhaust gas guided to the NH ₃ slip catalyst according to the exhaust gas flow rate calculated in this way, a sudden increase in the engine speed is prevented. even emissions of exhaust gas discharged from the engine increases going, the amount of ammonia in the exhaust gas guided to the NH ₃ slip catalyst does not become excessive, sufficiently oxidizing ammonia in NH ₃ slip catalyst Can be processed.

In particular, the exhaust emission control device of the present invention directly adjusts the flow rate of exhaust gas led to the NH ₃ slip catalyst by the exhaust gas flow rate control means without adjusting the supply amount of ammonia supplied from the NH ₃ supply means. by large load fluctuation of the engine rotational speed even if the discharge amount of exhaust gas by operating the engine increases and decreases in a non-steady state, in NH ₃ slip catalyst the amount of ammonia introduced to the NH ₃ slip catalyst It is possible to quickly respond within the range of processing capacity. As described above, even when the engine load is large and the engine operates in an unsteady state, the occurrence of ammonia slip can be effectively suppressed.

In the exhaust emission control device according to the present invention, the NH ₃ flow rate calculation means is measured by the temperature measurement means for measuring the temperature of the exhaust gas passing through the NH ₃ slip catalyst, and the temperature measurement means. And a temperature flow rate calculating means for calculating a flow rate of ammonia in accordance with the temperature measured by the temperature measuring means, wherein a relationship between the measured temperature and the flow rate of ammonia that can be oxidized by the NH ₃ slip catalyst is preset. It is characterized by.

In the present invention configured as described above, the ammonia temperature flow rate calculation means is configured such that the temperature measured by the temperature measurement means, the temperature measured by the preset temperature measurement means, and the flow rate of ammonia that can be oxidized by the NH ₃ slip catalyst. Based on the relationship, the flow rate of ammonia that can be oxidized by the NH ₃ slip catalyst is calculated. Therefore, the NH ₃ flow rate calculation means can calculate the flow rate of oxidizable ammonia in the NH ₃ slip catalyst in consideration of the actual temperature condition, so that the exhaust gas flow rate control means determines the flow rate of the exhaust gas guided to the NH ₃ slip catalyst. It can be adjusted appropriately.

Further, in the exhaust purification apparatus according to the present invention, in the above invention, the NOx purification means has NH ₃ flow rate measurement means for measuring a flow rate of ammonia flowing in the exhaust pipe, and the exhaust gas flow rate control means includes: When the flow rate of ammonia measured by the NH ₃ flow rate measurement means exceeds the flow rate of ammonia that can be oxidized by the NH ₃ slip catalyst calculated by the NH ₃ flow rate calculation means, the NH ₃ slip catalyst is transferred to the NH ₃ slip catalyst. The flow rate of the exhaust gas to be led is controlled, and the flow rate of ammonia measured by the NH ₃ flow rate measurement unit exceeds the flow rate of ammonia that can be oxidized by the NH ₃ slip catalyst calculated by the NH ₃ flow rate calculation unit. If not, the flow rate of the exhaust gas led to the NH ₃ slip catalyst is not controlled.

According to the present invention configured as described above, when the flow rate of ammonia measured by the NH ₃ flow rate measurement unit exceeds the flow rate of ammonia that can be oxidized by the NH ₃ slip catalyst calculated by the NH ₃ flow rate calculation unit, the exhaust gas flow rate The control of the exhaust gas flow rate by the control unit is started, and the ammonia flow rate measured by the NH ₃ flow rate measurement unit does not exceed the ammonia flow rate that can be oxidized by the NH ₃ slip catalyst calculated by the NH ₃ flow rate calculation unit. since the control by the exhaust gas flow rate control means is continued until it is possible to suppress the flow rate of ammonia introduced into NH ₃ slip catalyst NH ₃ reliably below the flow rate of the oxidizable ammonia slip catalyst.

In the exhaust emission control device according to the present invention, the exhaust gas flow rate control means in the invention includes a diversion means for diverting the exhaust gas led from the NOx catalyst to the upstream side of the NOx catalyst and returning it. It is characterized by. With this configuration, after the nitrogen oxides contained in the exhaust gas introduced from the engine are reduced and processed in the NOx catalyst, excess ammonia that has not reacted and cannot be oxidized by the NH ₃ slip catalyst. By exhausting the exhaust gas containing ammonia to the upstream side of the NOx catalyst by the diversion means, the NOx catalyst can again process the nitrogen oxides in the exhaust gas using this excess ammonia.

Further, in the exhaust purification apparatus according to the present invention, in the above invention, the flow dividing means has one end connected between the NOx catalyst and the NH ₃ slip catalyst in the exhaust pipe, and the other end of the exhaust pipe. Among them, a branch pipe connected to the upstream side of the NOx catalyst, and a flow adjustment that is provided at the one end of the branch pipe so as to be openable and closable and adjusts the flow rate of the exhaust gas distributed to the branch pipe and the NH ₃ slip catalyst. And a board. With this configuration, the NOx catalyst among the exhaust gas that has passed through the NOx catalyst is changed by changing the degree of opening and closing of one end of the branch pipe by the flow adjustment plate according to the flow rate of the exhaust gas calculated by the exhaust gas flow rate calculation means. It is possible to simultaneously adjust both the flow rate of the exhaust gas returned to the upstream side and the flow rate of the exhaust gas led to the NH ₃ slip catalyst.

The exhaust purification apparatus of the present invention includes NOx purification means that reduces and purifies nitrogen oxides contained in exhaust gas discharged from the engine, and this NOx purification means has a flow rate of ammonia that can be oxidized by an NH ₃ slip catalyst. The NH ₃ flow rate calculation means for calculating the flow rate of ammonia, the relationship between the flow rate of ammonia that can be oxidized by the NH ₃ slip catalyst and the flow rate of exhaust gas containing ammonia at this flow rate is preset, and the ammonia calculated by the NH ₃ flow rate calculation means The exhaust gas flow rate calculating means for calculating the flow rate of the exhaust gas containing ammonia according to the flow rate of the exhaust gas, and the flow rate of the exhaust gas guided to the NH ₃ slip catalyst according to the exhaust gas flow rate calculated by the exhaust gas flow rate calculating means And an exhaust gas flow rate control means for controlling. Therefore, the exhaust gas flow rate control means controls the flow rate of the exhaust gas guided to the NH ₃ slip catalyst in accordance with the exhaust gas flow rate calculated by the NH ₃ flow rate calculation means and the exhaust gas flow rate calculation means. load fluctuation is large, the rotational speed is as emissions of exhaust gas of the engine is rapidly changed by operating in a non-steady state, the processing capacity in the NH ₃ slip catalyst the amount of ammonia introduced to the NH ₃ slip catalyst It is possible to quickly respond within the range. In this way, even when the engine load fluctuation is large and the engine speed is operating in an unsteady state, the occurrence of ammonia slip can be effectively suppressed, the adaptive capacity is higher than before, and the environment is excellent. An exhaust emission control device can be provided.

1 is a side view showing a hydraulic excavator provided with an exhaust purification apparatus according to the present invention. It is a figure which shows the structure of one Embodiment of the exhaust gas purification apparatus which concerns on this invention. FIG. 3 is a diagram for explaining a main part of the present embodiment shown in FIG. 2, (a) a diagram showing a state in which a flow adjusting plate closes a branch pipe, and (b) a diagram in which the flow regulating plate opens the branch pipe. It is a figure which shows a state. It is a flowchart explaining operation | movement of this embodiment. NH ₃ is a diagram showing the relationship between the flow rate of the oxidizable ammonia slip catalyst and the flow rate of the exhaust gas. It is a diagram showing the relationship between the flow rate of the oxidizable ammonia at a temperature and NH ₃ slip catalyst in the exhaust gas.

  EMBODIMENT OF THE INVENTION Hereinafter, the form for implementing the exhaust gas purification apparatus which concerns on this invention is demonstrated based on figures.

  One embodiment of an exhaust emission control device according to the present invention is provided in a hydraulic excavator 41 as shown in FIG. 1, for example. This hydraulic excavator 41 is disposed on the traveling body 42, on the upper side of the traveling body 42, and has a revolving body 43 having a revolving frame 43a, and a front work machine that is attached to the front of the revolving body 43 and rotates in the vertical direction. 44. The revolving structure 43 includes a cab 47 disposed at the front, a counterweight 46 disposed at the rear, an engine room 45 disposed between the cab 47 and the counterweight 46, and an upper side of the engine room 45. And a vehicle body cover 48 that closes the engine room 45 so as to be openable and closable.

  Further, as shown in FIGS. 1 and 2, the revolving structure 43 includes an engine 1 housed in an engine room 45, and an exhaust pipe 10 for exhausting exhaust gas guided from the engine 1. In the embodiment, harmful substances such as carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NOx), and soot in the exhaust gas flowing through the exhaust pipe 10 are treated. The body cover 48 described above is provided with a tail pipe 50 that is connected to the exhaust pipe 10 inside the revolving structure 43 and discharges the exhaust gas flowing through the exhaust pipe 10 to the outside.

  The revolving structure 43 is provided in a fuel injection pump (not shown) for injecting fuel, a common rail (not shown) that is connected to the engine 1 and stores fuel supplied from the fuel injection pump at a high pressure, and each cylinder of the engine 1. And an injector (not shown) to which high-pressure fuel is supplied, and fuel is injected from the injector into each cylinder of the engine 1. The revolving structure 43 has one end that sucks outside air into the inside and the other end that is connected to the engine 1 and is provided in the middle of the intake pipe 3. An air cleaner 5 that cleans the air and a turbocharger 4 that is provided between the intake pipe 2 and the intake pipe 3 and that is disposed on the downstream side of the air cleaner 5 and increases the thermal efficiency of the engine 1 are provided.

  The turbocharger 4 is composed of, for example, a compressor 4 a that supercharges air that has passed through an air cleaner 5, and a turbine 4 b that is connected to the other end of the intake pipe 3 and provided upstream of the exhaust pipe 10. Yes. Therefore, the rotating shaft of the turbine 4b is connected to the rotating shaft of the compressor 4a, and the turbine 4b rotates by receiving the exhaust gas flowing through the exhaust pipe 10, and the compressor 4a is driven by this rotational force. ing.

  On the other hand, the intake pipe 2 has one end connected to the compressor 4 a of the turbocharger 4 and the other end connected to the engine 1. The intake pipe 2 is provided with an intercooler 6 that cools the air supercharged by the compressor 4 a and between the intercooler 6 and the engine 1. The air cooled by the intercooler 6 is sent to the engine 1. And an intake control valve 7 for controlling the flow rate of air.

  Here, the engine 1 is connected to an intake pipe 2 and is connected to an intake manifold 8 that evenly distributes air sent from the intake pipe 2 to each cylinder, and an exhaust pipe 10, and exhaust gas discharged from the engine 1 An exhaust manifold 9 to be joined to the pipe line, and the intake manifold 8 and the exhaust manifold 9 are connected to each other, and a part of the exhaust gas discharged after combustion of the fuel is taken out and re-intaked from the exhaust side to the intake side. A passage 12 and an EGR valve 11 provided in the EGR passage 12 are provided.

  In the present embodiment, the swing body 43 controls the opening / closing operation of the intake control valve 7 described above, and controls an electronic control unit (ECU) 30 that controls the operation of various means described later, and the exhaust discharged from the engine 1. PM purification means 15 for processing harmful particulate matter (PM) contained in the gas, and an exhaust throttle valve 13 for raising the temperature of the exhaust gas so as to ensure the activity of a catalyst described later in the PM purification means 15; And NOx purification means 17 for reducing and purifying nitrogen oxides contained in the exhaust gas flowing through the exhaust pipe 10.

  The exhaust throttle valve 13, the PM purification unit 15, and the NOx purification unit 17 are provided in this order in the exhaust pipe 10 from the upstream side to the downstream side of the exhaust pipe 10. That is, one end of the exhaust pipe 10 is connected to the engine 1, and the other end is connected to the tail pipe 50 via the turbine 4 b of the turbocharger 4, the exhaust throttle valve 13, the PM purification means 15, and the NOx purification means 17. It is connected.

  The PM purification means 15 includes, for example, a particulate filter (PF) 19 that collects particulate particulate matter (PM) contained in exhaust gas, and a pre-stage oxidation provided upstream of the particulate filter 19. And a catalyst 18. The particulate filter 19 described above is composed of a porous body with an oxidation catalyst such as platinum, for example, and the particulate matter component is mainly composed of soot such as solid carbon.

  Accordingly, when the exhaust gas discharged from the engine 1 flows through the exhaust pipe 10 and is guided in the order of the turbine 4b, the exhaust throttle valve 13, and the PM purification means 15, and passes through the particulate filter 19 of the PM purification means 15. In addition, particulate matter contained in the exhaust gas is trapped in the wall of the porous body.

  When the particulate matter continues to be trapped by the particulate filter 19 for a long period of time, the particulate matter accumulates in the walls of the porous body and the particulate filter 19 gradually becomes clogged, and the exhaust gas of the engine 1 Therefore, it is necessary to remove particulate matter collected by the particulate filter 19 as appropriate. For this reason, the PM purification means 15 is provided with a regeneration processing means (not shown) for performing a regeneration process for burning and removing the particulate matter collected by the particulate filter 19.

  The regeneration processing by the regeneration processing means is performed by, for example, performing sub-injection (pilot injection, post-injection) in which fuel is injected into the combustion chamber of the engine 1 while being advanced or retarded with respect to the main injection of the engine 1 to The particulate filter contains a hydrocarbon or carbon monoxide, and the unburned components are burned in the pre-stage oxidation catalyst 18 so that the exhaust temperature rises, and the particulate filter located downstream of the pre-stage oxidation catalyst 18. In 19, a combustion temperature of about 600 ° C. is obtained, and soot is burned by this combustion temperature.

On the other hand, the NOx purification means 17 promotes the reaction between NH ₃ supply means, which will be described later, for supplying ammonia into the exhaust pipe 10, for example, and ammonia supplied by the NH ₃ supply means and nitrogen oxides in the exhaust gas. The NOx catalyst 20 and at least a downstream side of the NOx catalyst 20 and an NH ₃ slip catalyst (second-stage oxidation catalyst) 21 that oxidizes ammonia in the exhaust gas led from the NOx catalyst 20 are configured.

The NH ₃ supply means described above is disposed between, for example, a urea water tank (not shown) that stores urea water, and the PM purification means 15 and the NOx catalyst 20 in the exhaust pipe 10, and urea supplied from the urea water tank. And an injection means 23 for injecting water into the exhaust pipe 10. The urea water injected by the injection means 23 is hydrolyzed by the heat of the exhaust gas, so that ammonia is generated in the exhaust pipe 10.

In the present embodiment, the exhaust pipe 10 is located upstream and downstream of the NOx catalyst 20, that is, between the PM purification means 15 and the NOx catalyst 20, and between the NH ₃ slip catalyst 21 and the NOx catalyst 20. NOx concentration measuring means 22 and 24 for measuring the concentration of nitrogen oxides are respectively provided. These NOx concentration measuring means 22, 24 are connected to the electronic control unit 30, and information on the measured concentration is transmitted to the electronic control unit 30.

  Then, the electronic control unit 30 calculates the amount of urea water necessary for treating nitrogen oxides based on the concentration of nitrogen oxides measured by the NOx concentration measuring means 22, and the calculated urea water is exhausted from the exhaust pipe. The injection of the injection means 23 is controlled so as to be supplied into the inside 10. Further, the electronic control unit 30 calculates the amount of urea water that is insufficient to actually treat nitrogen oxides based on the concentration of nitrogen oxides measured by the NOx concentration measuring unit 24, and injects from the injection unit 23. The supplied amount of urea water is corrected. Note that the NOx concentration measuring means 22 is arranged on the upstream side of the injection device 23.

In the present embodiment, the NOx purification means 17 includes an NH ₃ flow rate calculating means for calculating the flow rate of ammonia that can be oxidized by the NH ₃ slip catalyst 21, an ammonia flow rate that can be oxidized by the NH ₃ slip catalyst 21, and ammonia at this flow rate. The first function generating means (exhaust gas flow rate calculating means) for calculating the flow rate of exhaust gas containing ammonia corresponding to the ammonia flow rate calculated by the NH ₃ flow rate calculating means is preset. ) And an exhaust gas flow rate control means for controlling the flow rate of the exhaust gas guided to the NH ₃ slip catalyst 21 in accordance with the flow rate of the exhaust gas calculated by the first function generating means, and these NH ₃ flow rates The calculation means, the first function generation means, and the exhaust gas flow rate control means are stored in the electronic control unit 30.

Further, the exhaust gas flow rate control means includes a diversion means 26 for diverting the exhaust gas guided from the NOx catalyst 20 to the upstream side of the NOx catalyst 20 and returning it, for example, as shown in FIGS. The branching means 26 has one end connected between the NOx catalyst 20 and the NH ₃ slip catalyst 21 in the exhaust pipe 10 and the other end connected to the upstream side of the NOx catalyst 20 in the exhaust pipe 10. 31 and a flow adjusting plate 33 that is provided at one end of the branch pipe 31 so as to be openable and closable and adjusts the flow rate of the exhaust gas distributed to the branch pipe 31 and the NH ₃ slip catalyst 21 according to the angle.

  In the present embodiment, the other end of the branch pipe 31 is connected between the air cleaner 5 of the intake pipe 3 and the compressor 4 a of the turbocharger 4. Further, the diverting means 26 is a support member 32 that is rotatably supported so that the opening / closing angle of the flow adjusting plate 33 is adjusted, and a drive that drives the supporting member 32 to control the opening / closing angle of the flow adjusting plate 33. A device 35, and a stopper 35 that seals the exhaust gas so as not to leak into the branch pipe 31 when the flow adjusting plate 33 is closed, while mitigating the impact received by the flow adjusting plate 33 when the flow adjusting plate 33 is closed. And an exhaust gas flow rate measuring means 27 for measuring the flow rate of the exhaust gas flowing into the branch pipe 31.

  The driving device 34 and the exhaust gas flow rate measuring means 27 are connected to the electronic control unit 30, respectively, and the information on the exhaust gas flow rate measured by the exhaust gas flow rate measuring means 27 is transmitted to the electronic control unit 30. ing. The exhaust gas flow rate control means drives the drive device 34 to rotate the flow adjustment plate 33 and feeds back the flow adjustment plate 33 according to the exhaust gas flow rate measured by the exhaust gas flow rate measurement means 27. The angle for rotating the lens is corrected.

Here, the relationship preset by the first function generating means is such that, for example, as shown in FIG. 5, the flow rate of exhaust gas containing ammonia at this flow rate is proportional to the flow rate of ammonia that can be oxidized by the NH ₃ slip catalyst 21. It is supposed to be. Further, the NH ₃ flow rate calculating means described above can be oxidized by the temperature measuring means for measuring the temperature of the exhaust gas passing through the NH ₃ slip catalyst 21, and the temperature measured by the temperature measuring means and the NH ₃ slip catalyst 21. A relationship with the flow rate of ammonia is set in advance, and second function generating means (ammonia temperature flow rate calculating means) for calculating the flow rate of ammonia according to the temperature measured by the temperature measuring means is included.

The temperature measuring means is provided between the NOx catalyst 20 and the NH ₃ slip catalyst 21 in the exhaust pipe 10, for example, and is detected by the temperature sensor 28 disposed in the vicinity of the NH ₃ slip catalyst 21. Temperature prediction means for predicting the temperature inside the NH ₃ slip catalyst 21 from the measured temperature. The temperature sensor 28 is connected to the electronic control unit 30, and temperature information detected by the temperature sensor 28 is transmitted to the electronic control unit 30. Further, the relationship preset by the second function generating means is that, for example, as shown in FIG. 6, the flow rate of ammonia that can be oxidized by the NH ₃ slip catalyst 21 increases as the temperature of the exhaust gas rises. The rate of increase in the flow rate of the exhaust gas becomes slower as the temperature of the exhaust gas becomes higher.

Further, the NOx purification unit 17 includes, for example, an NH ₃ flow rate measuring unit 25 that is provided between the NOx catalyst 20 and the diversion unit 26 in the exhaust pipe 10 and measures the flow rate of ammonia flowing through the exhaust pipe 10. ing. The NH ₃ flow rate measuring means 25 is connected to the electronic control unit 30, and information on the ammonia flow rate measured by the NH ₃ flow rate measuring means 25 is transmitted to the electronic control unit 30.

The exhaust gas flow rate control means is configured such that the ammonia flow rate measured by the NH ₃ flow rate measurement means 25 exceeds the ammonia flow rate that can be oxidized by the NH ₃ slip catalyst 21 calculated by the NH ₃ flow rate calculation means. Further, as shown in FIG. 3B, the flow rate of the exhaust gas guided to the NH ₃ slip catalyst 21 is controlled, and the ammonia flow rate measured by the NH ₃ flow rate measuring means 25 is calculated by the NH ₃ flow rate calculating means. In addition, when the flow rate of ammonia that can be oxidized by the NH ₃ slip catalyst 21 is not exceeded, the flow rate of the exhaust gas guided to the NH ₃ slip catalyst 21 is not controlled as shown in FIG.

  Next, the operation of the present embodiment will be described based on the flowchart of FIG.

  FIG. 4 is a flowchart for explaining the operation of this embodiment.

  In the present embodiment, as shown in FIG. 4, when the engine 1 of the excavator 41 is started (step (hereinafter referred to as S) 1), exhaust gas is discharged from the engine 1 into the exhaust pipe 10. At this time, since the exhaust gas passes through the PM purification means 15 and the NOx purification means 17 in this order, the concentration of nitrogen oxides in the exhaust gas in which the NOx concentration measurement means 22 circulates between the PM purification means 15 and the NOx catalyst 20. (S2), and the electronic control unit 30 calculates the amount of urea water necessary to treat the nitrogen oxides based on the measured nitrogen oxide concentration (S3).

  Next, the electronic control unit 30 controls the injection means 23 so that the urea water calculated in step S3 is supplied into the exhaust pipe 10, and the urea water is injected from the injection means 23 (S4). Then, the NOx concentration measuring means 24 measures the concentration of nitrogen oxide in the exhaust gas flowing between the diverting means 26 and the NOx catalyst 20 (S5), and the electronic control unit 30 determines the measured nitrogen oxide concentration. Based on the concentration, the amount of urea water that is insufficient to actually treat nitrogen oxides is calculated.

  At this time, the electronic control unit 30 determines whether or not the concentration of nitrogen oxides measured by the NOx concentration measuring means 24 is larger than, for example, a predetermined value a (ppm) (S6). When the electronic control unit 30 determines that the concentration of nitrogen oxides measured by the NOx concentration measuring unit 24 is larger than the predetermined value a (ppm), the supply amount of urea water injected from the injection unit 23 is corrected. (S7).

On the other hand, when the electronic control unit 30 determines in step S6 that the concentration of nitrogen oxides measured by the NOx concentration measuring unit 24 is not larger than the predetermined value a (ppm), and from the injection unit 23 in step S7. After the supply amount of injected urea water is corrected, the NH ₃ flow rate measuring means 25 measures the flow rate of ammonia flowing between the NOx catalyst 20 and the diversion means 26 in the exhaust pipe 10 (S8), The electronic control unit 30 determines whether or not the measured ammonia flow rate is larger than, for example, a predetermined value b (S9).

When the electronic control unit 30 determines that the ammonia flow rate measured by the NH ₃ flow rate measuring means 25 is not greater than the predetermined value b, the electronic control unit 30 returns to the operation of step S2. On the other hand, when the electronic control unit 30 determines in step S9 that the ammonia flow rate measured by the NH ₃ flow rate measuring means 25 is larger than the predetermined value b, the temperature sensor 28 is connected to the NOx catalyst 20 in the exhaust pipe 10. The temperature of the exhaust gas flowing between the NH ₃ slip catalyst 21 is detected, and the temperature inside the NH ₃ slip catalyst 21 is predicted from the temperature detected by the temperature prediction means (S10).

Next, the second function generating means of the NH ₃ flow rate calculating means calculates the flow rate of ammonia that can be oxidized by the NH ₃ slip catalyst 21 according to the temperature predicted in step S10 (S11). Then, the exhaust gas flow rate control means determines whether or not the ammonia flow rate measured in step S8 is larger than the ammonia flow rate calculated in step S11 (S12).

  At this time, if the exhaust gas flow rate control means determines that the ammonia flow rate measured in step S8 is not larger than the ammonia flow rate calculated in step S11, the exhaust gas flow rate control means drives the drive device 34 to move the flow adjustment plate 33. Do not control to rotate. On the other hand, when the exhaust gas flow rate control unit determines in step S12 that the ammonia flow rate measured in step S8 is larger than the ammonia flow rate calculated in step S11, the first function generation unit calculates in step S11. The flow rate of the exhaust gas containing ammonia at this flow rate is calculated according to the flow rate of the ammonia (S13).

Thereafter, the exhaust gas flow rate control means calculates an angle for rotating the flow adjusting plate 33 based on the exhaust gas flow rate calculated in step S13 (S14). That is, this angle is determined so that the exhaust gas having the flow rate calculated in step S13 is diverted to the NH ₃ slip catalyst 21. Then, the exhaust gas flow rate control means drives the drive device 34 to rotate the flow adjustment plate 33 by the calculated angle (S15).

  In the present embodiment, the above-described steps S2 to S2 are performed until the engine 1 is in an idle state, for example, until the state where the rotation speed of the engine 1 is 1000 (rpm) continues for 600 seconds (S16), that is, while the excavator 41 is working. The series of operations in S15 is repeated. Further, even when the state where the rotation speed of the engine 1 is 1000 (rpm) continues for 600 seconds (S16), if the engine 1 is not stopped (S17), a series of operations of steps S2 to S15 are repeated. On the other hand, when the rotation speed of the engine 1 is 1000 (rpm) continues for 600 seconds (S16) and the engine 1 is stopped (S17), the operation of the present embodiment is terminated.

According to the present embodiment configured as described above, even if the exhaust speed of the engine 1 suddenly increases during the operation of the excavator 41 and the exhaust gas discharged from the engine 1 increases, the procedure is continued. In step S11 and step S13, the flow rate of exhaust gas containing ammonia at a flow rate that can be oxidized by the NH ₃ slip catalyst 21 is calculated by the NH ₃ flow rate calculation unit and the first function generation unit, and the exhaust gas flow rate control unit calculates the exhaust gas. By rotating the flow adjusting plate 33 in accordance with the flow rate of the exhaust gas, the exhaust gas that has passed through the NOx catalyst 20 is distributed to the branch pipe 31 and the NH ₃ slip catalyst 21, and the amount of ammonia that is guided to the NH ₃ slip catalyst 21 is reduced. Can be suppressed. Thereby, the amount of ammonia in the exhaust gas guided to the NH ₃ slip catalyst 21 does not become excessive, and the ammonia can be sufficiently oxidized by the NH ₃ slip catalyst 21 and processed.

Therefore, in the present embodiment, by directly adjusting the flow rate of the exhaust gas guided to the NH ₃ slip catalyst 21 by the exhaust gas flow rate control means by the flow adjustment plate 33, the load fluctuation of the engine 1 is large and the rotational speed is unsteady. also emissions of exhaust gas of the engine 1 is operating in a state is increased or decreased, can quickly be made to correspond to a range of processing capacity the amount of ammonia introduced to the NH ₃ slip catalyst 21 in NH ₃ slip catalyst 21 . Thus, even when the load fluctuation of the engine 1 is large and the rotational speed operates in an unsteady state, the occurrence of ammonia slip can be effectively suppressed. As a result, it is possible to provide an exhaust purification device having high adaptability and excellent environmental performance. In this embodiment, since the supply amount of urea water injected from the injection unit 23 is also corrected according to the concentration of nitrogen oxides measured by the NOx concentration measurement unit 24 in step S7, the ammonia slip Generation | occurrence | production can be suppressed further.

In this embodiment, the temperature inside the NH ₃ slip catalyst 21 is predicted by the temperature sensor 28 and the temperature predicting unit in step S10, and the second function generating unit sets the predicted temperature and the preset temperature shown in FIG. By calculating the flow rate of ammonia that can be oxidized by the NH ₃ slip catalyst 21 based on the relationship, the actual temperature of the NH ₃ slip catalyst 21 can be reflected in the calculation of the ammonia flow rate. The flow rate of the exhaust gas guided to the NH ₃ slip catalyst 21 can be adjusted appropriately. Thereby, the accuracy of the exhaust gas flow rate control means for the distribution of the exhaust gas to the branch pipe 31 and the NH ₃ slip catalyst 21 can be improved. In particular, as shown in FIG. 6, the lower the exhaust gas temperature, the larger the rate of change of the flow rate of ammonia that can be oxidized by the NH ₃ slip catalyst 21 with respect to the exhaust gas temperature. _{When the three-} slip catalyst 21 is not sufficiently warmed, the exhaust gas flow rate control means can effectively control the exhaust gas flow rate.

Further, in the present embodiment, the ammonia flow rate measured by the NH ₃ flow rate measurement unit 25 in step S8 is the ammonia flow rate that can be oxidized by the NH ₃ slip catalyst 21 calculated by the NH ₃ flow rate calculation unit in step S11. If exceeded, control for driving the drive device 34 to rotate the flow adjusting plate 33 in steps S13 to S15 is started, and the flow rate of ammonia measured by the NH ₃ flow rate measuring means 25 in step S8 is changed to NH in step S11. _{Since the} control of rotating the flow adjusting plate 33 is continued until the flow rate of ammonia that can be oxidized by the NH ₃ slip catalyst 21 calculated by the ₃ flow rate calculation means is not exceeded, the flow rate of ammonia guided to the NH ₃ slip catalyst 21 Can be reliably suppressed below the flow rate of ammonia that can be oxidized by the NH ₃ slip catalyst 21. After the engine 1 is started in step S1, the ammonia flow rate measured by the NH ₃ flow rate measuring means 25 in step S8 can be oxidized by the NH ₃ slip catalyst 21 calculated by the NH ₃ flow rate calculating means in step S11. does not exceed the flow rate of ammonia, since one end of the branch pipe 31 is maintained in a state of being closed by a flow control plate 33, for example, the flow rate of the exhaust gas guided to the NH ₃ slip catalyst 21 by the vibration of the hydraulic excavator 41 Unnecessary restrictions can be prevented.

Further, in the present embodiment, the exhaust gas flow rate control means reduces the nitrogen oxide contained in the exhaust gas led from the engine 1 by the NOx catalyst 20 and then treats the excess ammonia without reacting. Of this, the exhaust gas containing excess ammonia that cannot be oxidized by the NH ₃ slip catalyst 21 is diverted from the branch pipe 31 of the diverting means 26 to the intake pipe 3 upstream of the NOx catalyst 20 and returned to the exhaust gas. The NOx catalyst 20 can react with nitrogen oxides contained in the exhaust gas again. As a result, nitrogen oxides in the exhaust gas can be efficiently processed, and surplus ammonia that has not reacted in the NOx catalyst 20 can be effectively utilized.

Further, in this embodiment, since the flow adjusting plate 33 provided at one end of the branch pipe 31 is rotatably supported by the support member 32, the exhaust gas flow rate control means drives the drive device 34 to flow. By rotating the adjustment plate 33 by the angle calculated in step S <b> 14, the flow rate of the exhaust gas that flows to the branch pipe 31 among the exhaust gas that has passed through the NOx catalyst 20 and the flow rate of the exhaust gas that leads to the NH ₃ slip catalyst 21. Both of them can be adjusted simultaneously. In addition, since the support member 32 is provided on the downstream side of the portion where the branch pipe 31 and the exhaust pipe 10 are connected, when the flow adjusting plate 33 rotates around the support member 32, NOx The exhaust gas that has passed through the catalyst 20 can be easily guided into the branch pipe 31.

  In the present embodiment described above, the diverting means 26 is provided on the downstream side of the portion where the branch pipe 31 and the exhaust pipe 10 are connected, and includes a support member 32 that rotatably supports the flow adjusting plate 33. The case where one end of the branch pipe 31 is opened and closed by rotating the flow adjustment plate 33 with the drive device 34 has been described. However, the present invention is not limited to this case. For example, the flow adjustment plate 33 is provided at one end of the branch pipe 31. A slide support means for slidably supporting may be provided, and one end of the branch pipe 31 may be opened and closed by sliding the flow adjusting plate 33 with the driving device 34.

DESCRIPTION OF SYMBOLS 1 Engine 2, 3 Intake pipe 4 Turbocharger 4a Compressor 4b Turbine 5 Air cleaner 6 Intercooler 7 Intake control valve 8 Intake manifold 9 Exhaust manifold 10 Exhaust pipe 11 EGR valve 12 EGR passage 13 Exhaust throttle valve 15 PM purification means 17 NOx purification means 18 Pre-stage oxidation catalyst 19 Particulate filter 20 NOx catalyst 21 NH ₃ slip catalyst (post-stage oxidation catalyst)
22, 24 NOx concentration measuring means 23 Injection means 25 NH ₃ flow rate measuring means 26 Splitting means 27 Exhaust gas flow rate measuring means 28 Temperature sensor 30 Electronic control unit 31 Branch pipe 32 Support member 33 Flow adjusting plate 34 Drive device 35 Stopper 41 Hydraulic excavator 42 traveling body 43 revolving body 44 front work machine 50 tail pipe

Claims (5)

An exhaust pipe for exhausting exhaust gas led from the engine, and NOx purification means provided in the exhaust pipe for reducing and purifying nitrogen oxides contained in the exhaust gas flowing through the exhaust pipe. The purifying means includes NH ₃ supply means for supplying ammonia into the exhaust pipe, a NOx catalyst for promoting the reaction between ammonia supplied by the NH ₃ supply means and nitrogen oxides in the exhaust gas, and the NOx catalyst. Is also provided on the downstream side, and an exhaust gas purification apparatus comprising at least an NH ₃ slip catalyst that oxidizes ammonia in the exhaust gas led from the NOx catalyst,
The NOx purification means includes
NH ₃ flow rate calculating means for calculating a flow rate of ammonia that can be oxidized by the NH ₃ slip catalyst;
The relationship between the flow rate of ammonia that can be oxidized by the NH ₃ slip catalyst and the flow rate of exhaust gas containing ammonia at this flow rate is set in advance, and includes ammonia corresponding to the flow rate of ammonia calculated by the NH ₃ flow rate calculation means. Exhaust gas flow rate calculating means for calculating the flow rate of exhaust gas;
An exhaust gas purification apparatus comprising exhaust gas flow rate control means for controlling the flow rate of exhaust gas guided to the NH ₃ slip catalyst in accordance with the exhaust gas flow rate calculated by the exhaust gas flow rate calculation means. The exhaust emission control device according to claim 1,
The NH ₃ flow rate calculating means includes:
Temperature measuring means for measuring the temperature of the exhaust gas passing through the NH ₃ slip catalyst;
An ammonia temperature at which the relationship between the temperature measured by the temperature measuring means and the flow rate of ammonia that can be oxidized by the NH ₃ slip catalyst is preset, and the ammonia flow rate is calculated according to the temperature measured by the temperature measuring means. An exhaust gas purification apparatus comprising: a flow rate calculating means. The exhaust emission control device according to claim 1 or 2,
The NOx purification means includes
NH ₃ flow rate measuring means for measuring the flow rate of ammonia flowing in the exhaust pipe,
The exhaust gas flow rate control means includes
When the flow rate of ammonia measured by the NH ₃ flow rate measurement means exceeds the flow rate of ammonia that can be oxidized by the NH ₃ slip catalyst calculated by the NH ₃ flow rate calculation means, the NH ₃ slip catalyst is transferred to the NH ₃ slip catalyst. The flow rate of the exhaust gas to be led is controlled, and the flow rate of ammonia measured by the NH ₃ flow rate measurement unit exceeds the flow rate of ammonia that can be oxidized by the NH ₃ slip catalyst calculated by the NH ₃ flow rate calculation unit. If not, the exhaust gas purification apparatus is characterized in that the flow rate of the exhaust gas led to the NH ₃ slip catalyst is not controlled. The exhaust emission control device according to any one of claims 1 to 3,
The exhaust gas flow control means includes a diversion means for diverting the exhaust gas guided from the NOx catalyst to an upstream side of the NOx catalyst and returning it. The exhaust emission control device according to claim 4,
The diversion means is
One end of the exhaust pipe is connected between the NOx catalyst and the NH ₃ slip catalyst, and the other end of the exhaust pipe is connected to the upstream side of the NOx catalyst;
An exhaust purification apparatus comprising: a flow adjusting plate that is provided at the one end of the branch pipe so as to be openable and closable and adjusts the flow rate of the exhaust gas distributed to the branch pipe and the NH ₃ slip catalyst.

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