JP2015086714A - Exhaust purification device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To curb emission of ammonia into the atmosphere and generation of nitrogen monoxide without deteriorating NOpurification performance of an SCR catalyst.SOLUTION: An exhaust purification device comprises: an SCR catalyst 15 which is arranged on an exhaust passage 4 of an engine and selectively reduces NOin exhaust; a reduction agent supply device 17 which supplies urea water to the exhaust passage at an upstream side of the SCR catalyst; exhaust temperature increase control means which performs exhaust temperature increase control when an amount of a urea derived deposit in the exhaust passage reaches a predetermined amount; a temperature sensor 23 which detects a temperature of the exhaust at the upstream side of the SCR catalyst; desorption amount estimation means which estimates a desorption amount of ammonia desorbed from the urea derived deposit on the basis of the temperature of the exhaust detected by the temperature sensor; a NOsensor 24 which detects a concentration of the NOat the upstream side of the SCR catalyst; and NOemission amount control means which controls an amount of NOemission so that the concentration of the NOin the exhaust passage becomes a target concentration on the basis of the concentration of the NOdetected by the NOsensor and the desorption amount of the ammonia estimated by the desorption amount estimation means.

Description

  The present invention relates to an exhaust gas purification device for an internal combustion engine, and is particularly suitable as an exhaust gas purification device for a diesel engine in a construction machine including a diesel engine, a variable displacement hydraulic pump, and an exhaust gas purification device.

Work vehicles such as hydraulic excavators and cranes are equipped with a diesel engine as a drive source (power source). The amount of particulate matter (hereinafter referred to as PM) discharged from this diesel engine is NO _X Regulations have been strengthened year by year along with CO, HC, etc.
The exhaust gas purification device for purifying NO X _(nitrogen oxides) contained in exhaust gas of the engine, the ammonia produced by supplying urea water as a reducing agent into the exhaust gas, reduce NO _X in the exhaust gas 2. Description of the Related Art An exhaust gas purification apparatus equipped with an ammonia selective reduction type NO _X catalyst (Selective Catalytic Reduction) (hereinafter also simply referred to as an SCR catalyst) is used.

This exhaust purification device injects and supplies a liquid reducing agent or a precursor thereof at a flow rate corresponding to the operating state of the engine to the upstream side of the exhaust of the SCR catalyst disposed in the engine exhaust pipe, and NO _X is supplied on the SCR catalyst. By performing a selective reduction reaction, NO _X is purified to a harmless component.

  In such an exhaust purification device, urea water is generally supplied into the exhaust gas, and urea water is injected into the exhaust gas using a urea water injection valve or the like. If the state where the exhaust temperature from the engine is low continues, a part of the sprayed mist-like urea water is liquefied by colliding with the wall surface in the exhaust passage and adheres to the exhaust passage. The urea water adhering to the exhaust passage or the like is vaporized and deposited as solid urea crystals or the like on the wall surface in the exhaust passage to become urea-derived deposits.

  If the generation of urea-derived deposits continues in this way, there is a risk of causing problems such as an increase in exhaust flow resistance in the exhaust passage and a blockage of the exhaust passage. Further, when the exhaust temperature becomes high, urea-derived substances accumulated in a large amount in the exhaust passage are converted into ammonia at a stretch, and more ammonia than necessary is supplied to the SCR catalyst. In addition, there is a problem that ammonia is released into the atmosphere, that is, ammonia slip occurs.

Further, surplus ammonia causes a chemical reaction as shown in the following formula on the ammonia oxidation catalyst in the subsequent stage, and there is a problem that nitrous oxide (N ₂ 0), which is a greenhouse gas, is generated.
4NH ₃ +40 ₂ → 2N ₂ 0 + 6H ₂ 0
4NH ₃ + 4NO + 30 ₂ → 4N ₂ 0 + 6H ₂ 0

From the above, at a stage where the urea-derived material has accumulated to some extent in the exhaust passage, the temperature of the exhaust gas flowing in the exhaust passage is temporarily raised to gasify the urea-derived material that has accumulated. It is possible to remove it.
As this kind of prior art, there is one described in Japanese Patent No. 4986973 (Patent Document 1). According to the method disclosed in Patent Document 1, when the urea-derived material is accumulated in the exhaust passage and it is determined that the urea-derived material has reached the set accumulation limit value, the exhaust temperature in the exhaust passage is the target temperature. Control means for performing exhaust gas temperature raising control is provided.

And since this control means raises exhaust gas temperature to the comparatively low target temperature at the beginning of control, it suppresses that the urea-derived deposit is gasified at a stretch and is converted into ammonia, and prevents the occurrence of ammonia slip. I have to.
In addition, since the ammonia slip is less likely to occur as the deposition amount of the urea-derived deposit decreases, the control means quickly increases the target temperature by increasing the target temperature as the deposition amount decreases. Things are removed from the exhaust passage.

  In various operating states of the engine, the supply amount per unit time of ammonia that can be supplied to the SCR catalyst without causing ammonia slip is obtained, and the per unit time from the urea-derived deposit corresponding to the supply amount of ammonia. The exhaust temperature capable of maintaining the ammonia production amount is set as the target temperature.

Japanese Patent No. 4986973

However, in the thing of the said patent document 1, since the said control means raises exhaust gas temperature to the comparatively low target temperature at the beginning of control, it suppresses that urea origin deposits are gasified at a stretch and converted into ammonia. In addition, ammonia slip can be prevented from occurring. However, those of Patent Document 1, since the NO _X emissions in many engine operating region, the adsorption amount of ammonia to the selective reduction type NO _X catalyst (SCR catalyst) will be excessively decreased, the SCR catalyst We have the problem that a possibility is also greatly reduced of the NO _X purification performance.

An object of the present invention is an internal combustion engine that can suppress the release of ammonia into the atmosphere and the generation of nitrous oxide (N ₂ 0) as a greenhouse gas without deteriorating the NO _X purification performance of the selective reduction type NO _X catalyst. It is to obtain an exhaust gas purification device.

In order to achieve the above object, the present invention provides a selective reduction type NO _X catalyst that is disposed in an exhaust passage of an engine and selectively reduces NO _X in exhaust using ammonia generated by supplying urea water as a reducing agent. A reducing agent supply device for supplying urea water into the exhaust passage on the upstream side of the selective reduction type NO _X catalyst, and when the amount of urea-derived material deposited in the exhaust passage reaches a predetermined amount, In an exhaust gas purification apparatus for an internal combustion engine, comprising an exhaust gas temperature raising control means for performing an exhaust gas temperature raising control so that the exhaust gas temperature in the exhaust passage becomes a target temperature, than the selective reduction type NO _X catalyst in the exhaust passage. Based on the temperature sensor that detects the exhaust gas temperature on the upstream side and the temperature of the exhaust gas detected by this temperature sensor, the unit time of ammonia that gasifies and separates from the urea-derived deposits accumulated in the exhaust passage A withdrawal amount estimating means for estimating the Rino withdrawal amount, the NO _X sensor for detecting the concentration of NO _X upstream of the selective reduction type NO _X catalyst in the exhaust passage, NO _X detected by the NO _X sensor Based on the concentration and the ammonia release amount per unit time estimated by the release amount estimation means, the NO _X emission amount into the exhaust passage is adjusted so that the NO _X concentration in the exhaust passage becomes the target concentration. It is characterized by comprising NO _X emission amount adjusting means for controlling.

Further, the present invention provides an exhaust gas purification apparatus for an internal combustion engine, wherein an EGR passage for returning a part of the exhaust gas flowing through the exhaust passage to the intake passage of the internal combustion engine as EGR (exhaust gas recirculation) gas; , and a EGR valve which controls an amount of the EGR gas provided in the EGR passage, the NO _X emission adjusting means, the opening degree of the EGR valve increases or decreases from the opening at the time of normal control NO _The amount of ammonia released per unit time estimated by the above-mentioned amount-of-leaving amount estimation means and the amount of NO _X emissions per unit time estimated from the NO _X concentration detected by the NO _X sensor are adjusted. The opening degree of the EGR valve is determined based on the comparison result.

  Furthermore, the present invention provides the exhaust gas purification apparatus for an internal combustion engine, wherein when the exhaust gas temperature raising control means is executing exhaust gas temperature raising control, urea water is supplied from the reducing agent supply device into the exhaust passage. It is characterized by stopping.

  In the exhaust gas purification apparatus for an internal combustion engine according to the present invention, an oxidation catalyst is provided in the exhaust passage on the upstream side of the reducing agent supply device, and the exhaust temperature raising control means is configured to enter the exhaust gas flowing into the oxidation catalyst. The exhaust gas temperature raising control is performed by controlling the fuel supply amount.

According to the exhaust gas purification apparatus for an internal combustion engine of the present invention, ammonia is released into the atmosphere without deteriorating the NO _x purification performance of the selective reduction type NO _x catalyst, and nitrous oxide (N ₂ 0) of a greenhouse gas. An effect of obtaining an exhaust gas purification apparatus for an internal combustion engine that can suppress the occurrence of the above is obtained.

1 is an overall configuration diagram showing Embodiment 1 of an exhaust gas purification apparatus for an internal combustion engine according to the present invention. 2 is a flowchart for explaining exhaust temperature raising control executed by an ECU shown in FIG. 1. 3 is a flowchart for explaining NO _X emission amount adjustment control executed by an ECU shown in FIG. 1. It is a diagram explaining the relationship between exhaust gas temperature and the amount of separation of ammonia per unit time.

  Hereinafter, specific examples of the present invention will be described with reference to the drawings.

  FIG. 1 is an overall configuration diagram showing a first embodiment of an exhaust emission control device for an internal combustion engine according to the present invention. In the present embodiment, the present invention is applied to an exhaust purification device of an internal combustion engine (diesel engine in this embodiment) used in a construction machine such as a diesel engine, a variable displacement hydraulic pump, and a hydraulic excavator provided with an exhaust purification device. An example will be described.

An exhaust gas purification apparatus in a diesel engine as an internal combustion engine used in construction machinery includes an exhaust gas purification apparatus that uses an aqueous urea solution as a liquid reducing agent and purifies NO _X contained in engine exhaust gas by a catalytic reduction reaction. Yes.

  This exhaust purification device will be described with reference to FIG. In FIG. 1, 1 is a 4-cylinder diesel engine (hereinafter also simply referred to as an engine), and 2 is a fuel injection valve (injector) for injecting high-pressure fuel into each cylinder. 3 is an intake passage, 4 is an exhaust passage, a compressor 5 a of a turbocharger 5 is provided in the intake passage 3, and a turbine 5 b of the turbocharger 5 is provided in the exhaust passage 4. The rotating shaft of the turbine 5b is connected to the rotating shaft of the compressor 5a, and is configured to drive the compressor 5a when the turbine 5b is rotated by exhaust flowing in the exhaust passage 4. .

The air sucked from the intake passage 3 flows into the compressor 5a of the turbocharger 5, and the air pressurized by the compressor 5a enters the intake manifold 8 via the intercooler 6 and the intake control valve 7, From here, it is introduced into each cylinder of the engine 1. Further, the exhaust gas discharged from each cylinder of the engine 1 flows into the exhaust passage 4 from the exhaust manifold 9, passes through the turbine 5b of the turbocharger 5, and then flows into the first exhaust aftertreatment device 12. Has been. The first exhaust aftertreatment device 12 is provided with an oxidation catalyst 13, which oxidizes nitrogen monoxide (NO) in the exhaust to generate nitrogen dioxide (NO ₂ ).

  A second exhaust aftertreatment device 14 is provided on the downstream side of the first exhaust aftertreatment device 12 via an exhaust passage 4a. This second exhaust aftertreatment device 14 is provided with an ammonia selective reduction type NOx catalyst (SCR catalyst) 15 that purifies exhaust by selectively reducing nitrogen oxide (NOx) in the exhaust using ammonia as a reducing agent. In addition, an ammonia oxidation catalyst 16 for oxidizing and removing ammonia flowing out from the SCR catalyst 15 is provided on the downstream side of the SCR catalyst 15.

  The SCR catalyst 15 may be any catalyst as long as it is normally used for denitration, for example, a catalyst in which denitration active components such as vanadium and tungsten are carried on titanium oxide, copper, iron, cerium and the like. Suitable is a catalyst in which a zeolite obtained by ion-exchange of a transition metal is supported on a cordierite honeycomb structure or the like.

  A reducing agent for injecting and supplying a reducing agent (urea water) into the exhaust passage 4a between the first exhaust aftertreatment device 12 and the second exhaust aftertreatment device 14 in the exhaust in the exhaust passage 4a. An injection nozzle 17a of the supply device 17 is provided. Reference numeral 18 denotes a reducing agent tank (urea water tank) in which urea water is stored. The urea aqueous solution in the reducing agent tank 18 is supplied to the injection nozzle 17a via the pump 17b, the reducing agent control valve 17c, and the reducing agent supply pipe 17d. The urea water is jetted from the jet nozzle 17a into the exhaust gas in the exhaust passage 4a. The reducing agent supply device 17 includes the injection nozzle 17a, a pump 17b, a reducing agent control valve 17c, a reducing agent supply pipe 17d, a reducing agent flow rate sensor 17e, and the like.

The reducing agent tank 18 is provided with a reducing agent concentration sensor 19 for detecting the concentration of the reducing agent and a liquid level sensor 20 for detecting the remaining amount of the reducing agent (urea aqueous solution).
The atomized urea water sprayed from the reducing agent supply device 17 is hydrolyzed by the heat of the exhaust to become ammonia, and is supplied to the SCR catalyst 15. The SCR catalyst 15 by promoting the denitration reaction with NOx in the exhaust and supplied ammonia, and reduces and purifies NOx to harmless N _2.
At this time, when ammonia flows out of the SCR catalyst 15 without reacting with NOx, the ammonia is oxidized and removed by the ammonia oxidation catalyst 16 disposed on the downstream side. .

  A temperature sensor 21 for detecting the temperature of the exhaust is provided upstream of the oxidation catalyst 13 provided in the first exhaust aftertreatment device 12, and the oxidation catalyst 13 is also provided downstream of the oxidation catalyst 13. A temperature sensor 22 is provided for detecting the temperature of the exhaust gas after passing. A temperature sensor 23 for detecting the exhaust temperature is also provided in the exhaust passage 4a upstream of the SCR catalyst 15 provided in the second exhaust aftertreatment device 14. Further, the exhaust passage 4a upstream of the SCR catalyst 15 is provided with a NOx sensor 24 for measuring the NOx concentration in the exhaust flowing through the exhaust passage 4a. A NOx sensor 25 is also provided on the downstream side of the oxidation catalyst 16 provided in the apparatus so as to measure the NOx concentration in the exhaust discharged to the atmosphere.

  Further, an exhaust gas recirculation passage, that is, an EGR passage 10 is provided so as to connect the exhaust manifold 9 and the intake manifold 8, and an EGR valve 11 is provided in the EGR passage 10. During operation of the engine 1, a part of the exhaust gas is recirculated as EGR gas from the exhaust manifold 9 side to the intake manifold 8 side according to the opening degree of the EGR valve 11.

  Reference numeral 26 denotes a common rail common to the cylinders of the engine 1, and high-pressure fuel (light oil) stored in the common rail 26 is supplied to the fuel injection valves 2 provided in the cylinders. 2 is injected into each cylinder.

  The urea aqueous solution stored in the reducing agent tank 18 is supplied from the injection nozzle 17a to the exhaust passage 4a via the reducing agent supply device 17, and the reducing agent control valve of the reducing agent supply device 17 is supplied. 17c is controlled by a reducing agent injection control unit (hereinafter referred to as DCU) 30 to supply an aqueous urea solution corresponding to the engine operating state to the injection nozzle 17a intermittently. Detection signals from the reducing agent concentration sensor 19 and the reducing agent liquid level sensor 20 are input to the DCU 30.

The aqueous urea solution injected and supplied from the injection nozzle 17a is hydrolyzed by the heat of the exhaust and the water vapor in the exhaust, thereby generating ammonia. The generated ammonia reacts with NO _X in the exhaust gas in the SCR catalyst 15 to be purified into water and harmless gas. Further, since the ammonia that has passed through the SCR catalyst 15 is oxidized by the ammonia oxidation catalyst 16 disposed on the downstream side thereof, it is possible to prevent ammonia that emits a strange odor from being released into the atmosphere.

  31 is an ECU (engine control unit) for performing comprehensive control including operation control of the engine 1, an arithmetic unit (CPU) for executing various procedures, and a storage unit (memory for storing various set values in advance) ), A controller unit including a timer counter, an input / output device, and the like, which calculate various control amounts and control various devices based on the control amounts.

  In addition to the exhaust gas temperature sensors 21 to 23 and the NOx sensors 24 and 25 described above, a rotation sensor for detecting the rotation speed Ne of the engine and an engine cooling are collected on the input side of the ECU 31 in order to collect information necessary for various controls. Various sensors such as a water temperature sensor for detecting the water temperature are connected. Various devices such as the fuel injection valve 2, the intake control valve 7, and the EGR valve 11 of each cylinder that are controlled based on the calculated control amount are connected to the output side of the ECU 31.

  The DCU 30 is a control device for performing reducing agent injection control, and is configured by a controller unit similar to the ECU 31. Various sensors such as the reducing agent concentration sensor 19 and the liquid level sensor 20 are connected to the input side of the DCU 30 as described above. Further, various devices such as the reducing agent control valve 17c that is controlled based on the calculated control amount are connected to the output side of the DCU 30.

  The DCU 30 and the ECU 31 are connected by CAN communication, and information on the engine side (for example, detection signals of a NOx sensor, a temperature sensor, and a rotation sensor) is provided to the DCU 30 through the ECU 31. Further, for example, information regarding the reduction catalyst such as the remaining amount of the reducing agent, the amount of reducing agent injected, and the concentration of the reducing agent is also provided to the ECU 31 through the DCU 30. Accordingly, these pieces of information can be mutually used through the CAN.

CAN is an abbreviation for Controller Area Network and refers to serial communication for real-time applications used for in-vehicle multiplex communication.
And ECU31 cooperates with DCU30 mutually connected via CAN, and controls the fuel injection valve 2, the intake control valve 7, the EGR valve 11, etc. which were attached to the engine 1, respectively.

  The DCU 30 executes a control program stored in a ROM (Read Only Memory) or the like, thereby electronically controlling the reducing agent supply device 17 in accordance with the exhaust temperature, the rotational speed of the engine, and the load. Here, as the engine load, for example, a state quantity closely related to torque, such as a fuel injection flow rate, an intake flow rate, a supercharging pressure, a pump pressure, and a pump flow rate, can be applied. Further, the rotational speed and load of the engine 1 are not limited to the configuration read from the ECU 31 and may be directly detected by a known sensor.

  In this embodiment, when a certain amount of urea is accumulated in the exhaust passage 4a and reaches a predetermined amount, the inlet side temperature Tg of the SCR catalyst 15 detected by the exhaust temperature sensor 23 is raised. Exhaust temperature rise control is executed, thereby removing urea-derived substances accumulated in the exhaust passage 4a.

This exhaust temperature increase control (exhaust temperature increase control means) will be described.
In this embodiment, the oxidation catalyst 13 is provided in the exhaust passage 4 on the upstream side of the reducing agent supply device 17. Further, the fuel is supplied to the exhaust gas flowing into the oxidation catalyst 13. Yes. For example, when fuel is supplied to the engine 1 by fuel injection into each cylinder, fuel is supplied into the exhaust by performing additional injection (post injection) at a timing that does not contribute to the generation of power. can do. According to this method, it is not necessary to provide a new device for supplying fuel into the exhaust gas. Alternatively, a special fuel injection valve (injector) may be provided, and fuel may be supplied into the exhaust gas by injecting fuel into the exhaust passage 4 upstream of the oxidation catalyst 13. good.

  By supplying the fuel into the exhaust gas in this way, the fuel is oxidized by the oxidation catalyst 13, thereby controlling the exhaust temperature to rise to the target temperature. In this embodiment, since the exhaust gas temperature raising control is performed in this way, the exhaust temperature can be easily set to the target temperature, and the exhaust gas that has been raised to the target temperature is exhausted downstream from the reducing agent supply device 17. It can be made to flow into the passage 4a.

Further, in this embodiment, when the exhaust temperature raising control means for performing the exhaust temperature raising control in the exhaust passage 4 is executing the exhaust temperature raising control, the reducing agent supply device 17 enters the exhaust passage 4a. The supply of the reducing agent (urea water) is stopped.
With this configuration, when the exhaust gas temperature raising control is being performed, urea water is not supplied from the reducing agent supply device 17, so the amount of ammonia supplied to the SCR catalyst 15 is urea. Only the ammonia desorption amount from the origin deposit (the desorption amount per unit time of ammonia that is gasified and desorbed from the urea-derived deposit) can be controlled more easily.

Further, in this embodiment, in addition to the exhaust gas Atsushi Nobori control, depending on the departure amount of urea-derived deposits, thereby controlling so as to correct NO _X emissions were accordingly. That is, the so concentration of NO _X in the exhaust passage becomes equal to the target density, comprising a NO _X emission amount adjusting means for adjusting the NO _X emissions the to the exhaust passage during the release and greenhouse ammonia into the atmosphere Control is performed to suppress the generation of nitrous oxide (N ₂ 0), which is a gas.
For the NO _X emission adjusting means for performing the control for adjusting the NO _X emissions (NO _X emissions adjustment control) will be described.

In this embodiment, as described above, an EGR passage (exhaust gas recirculation passage) 10 is provided so as to connect the exhaust manifold (exhaust passage) 9 and the intake manifold (intake passage) 8, thereby The portion is recirculated to the intake side of the engine 1 as EGR (exhaust gas recirculation) gas. The EGR passage 10 is provided with an EGR valve 11. The NO _X emissions adjusting means, the opening degree of the EGR valve 11, by increasing or decreasing from the opening at the time of normal control, and adjusts the NO _X emissions.

This will be described in more detail.
In this embodiment, a temperature sensor 23 that detects the exhaust temperature upstream of the SCR catalyst in the exhaust passage 4a, and the temperature of the exhaust gas detected by the temperature sensor 23 is accumulated in the exhaust passage 4a. There is provided a desorption amount estimating means for estimating the desorption amount per unit time of ammonia that is gasified from the urea-derived deposit. Further, a NO _X sensor 24 for detecting the NO _X concentration upstream of the SCR catalyst 15 in the exhaust passage 4a is provided.

The NO _X emission amount adjusting means is based on the NO _X concentration detected by the NO _X sensor 24 and the ammonia release amount per unit time estimated by the release amount estimation means. as concentration of NO _X in is the target concentration, and controls the NO _X emissions the into the exhaust passage 4, 4a.

That is, the amount of ammonia released per unit time estimated by the amount-of-detachment estimation means for estimating the amount of ammonia released from the urea-derived deposit deposited in the exhaust passage 4a per unit time, and the NO _X The NO _X emission amount per unit time estimated from the NO _X concentration detected by the sensor 24 is converted into the number of moles (grams are converted into moles) and compared, and based on the comparison result, the EGR valve 11 The opening correction amount is determined.

Incidentally, the adjustment of the NO _X emissions control of the opening degree of the EGR valve 11 is described in detail in the description of FIG. 3 to be described later.
Further, in the example shown in FIG. 1, an EGR passage 10 is provided so as to connect the exhaust manifold 9 and the intake manifold 8. The EGR passage 10 connects the exhaust side and the intake side of the engine 1. For example, the exhaust passage 4 and the intake side of the engine 1 may be connected.

By controlling the EGR valve 11 in this way, the fit to the withdrawal amount of the urea-derived deposit by the exhaust Atsushi Nobori control can be increased or decreased to an appropriate amount of NO _X release and greenhouses ammonia into the atmosphere Generation of nitrous oxide (N ₂ 0) as an effect gas can be suppressed.
Further, the NO _X emission amount adjustment control by the EGR valve 11 has good responsiveness, and can quickly increase or decrease the NO _X emission amount without greatly impairing drivability.

Hereinafter, a specific control example of the exhaust gas purification apparatus for an internal combustion engine of the present embodiment will be described with reference to FIG. FIG. 2 is a flowchart for explaining the exhaust gas temperature raising control executed by the ECU 31 shown in FIG.
The ECU 31 executes exhaust gas temperature raising control according to the flowchart shown in FIG. 2 in order to remove urea-derived deposits in accordance with the deposition state of urea-derived deposits in the exhaust pipe 4a. The exhaust gas temperature raising control is started when the engine 1 is started, and is ended when the engine 1 is stopped.

  When the driver rotates the key switch to the start position, the ECU 31 issues a start signal to start the engine 1 (step S1). After that, the key switch automatically returns to the ON position. When the driver depresses the accelerator at that position and changes from the low speed Lo to the high speed Hi, the ECU 31 generates an accelerator signal and changes the set value of the governor. To control the engine speed.

  When this control is started, the ECU 31 determines whether or not the value of the flag F is 1 in step S2. The value of the flag F is determined based on the determination described later, whether or not the amount of urea-derived deposits in the exhaust passage 4 has reached its limit, that is, exhaust gas temperature raising control is required to remove the urea-derived deposits. If the value of the flag F is 1, it indicates that the amount of urea-derived material has reached its limit. The initial value of the flag F is 0.

  As a means for determining whether or not the amount of the urea-derived material has reached the limit, for example, the pressure sensor detects the pressure upstream of the position of the injection nozzle 17a of the reducing agent supply device 17 in the exhaust passages 4 and 4a. It can be determined by detecting with (not shown). That is, the urea-derived material accumulates mainly on the inner surface (exhaust pipe inner surface) of the exhaust passage 4a between the injection nozzle 17a and the SCR catalyst 15, and the urea-derived material accumulates on this portion. As the flow resistance increases, the pressure on the upstream side increases, so by detecting the pressure in this part, it is possible to determine whether the amount of urea-derived material has reached its limit. it can.

  In addition to the above, as a means for determining whether or not the accumulated amount of the urea-derived material has reached the limit, for example, if a pressure sensor is also provided downstream of the ammonia oxidation catalyst 16, for example, upstream of the injection nozzle 17a. The differential pressure ΔP is obtained by the pressure sensor on the side and the pressure sensor on the downstream side of the ammonia oxidation catalyst 16, and when the differential pressure ΔP is equal to or greater than a predetermined value, the accumulation amount of urea-derived material has reached the limit. It can also be determined.

In addition to the above-described determination means, the time when the operation region of the engine 1 is in the operation region where urea-derived material is accumulated is counted, and this time-measurement time becomes the deposition limit of the urea-derived material. When the limit determination time is reached, it may be determined that the amount of urea-derived material accumulated in the exhaust passage has increased to reach the limit.
By such determination means, it is determined whether or not the amount of accumulated urea-derived material has reached the limit. If it is determined that the limit has been reached, the value of the flag F is set to 1.

Since the initial value of the flag F is 0, in this case (F = 0), it is determined in step S2 that the value of the flag F is not 1, and the process proceeds to step S3. In step S <b> 3, it is determined whether or not a condition capable of supplying urea water is satisfied and a state in which ammonia supply to the SCR catalyst 15 is required is reached.
Specifically, based on the exhaust temperature detected by the exhaust temperature sensor 23, it is determined whether or not the SCR catalyst 15 is activated. When it is determined that the SCR catalyst 15 is activated, urea water is supplied. It is determined that the supplyable condition is satisfied and the supply of ammonia to the SCR catalyst 15 is necessary.

If it is determined in step S3 that the urea water supply condition is satisfied, the process proceeds to step S4, the urea water injection from the injection nozzle 17a is permitted, and the urea water is injected into the exhaust passage 4a.
On the other hand, if it is determined in step S3 that the urea water supply condition is not satisfied, the current control cycle is terminated.

  If it is determined in step S2 that the flag value F has reached 1, control is performed to increase the temperature of the exhaust gas flowing through the exhaust passage 4 (exhaust temperature rise control), thereby deriving from the urea accumulated in the exhaust passage 4a. It dissolves and removes things, and suppresses engine performance degradation. That is, the process proceeds to step S5, where the ECU 31 is in an operation state in which the engine 1 can raise the temperature of the exhaust based on the main injection amount from the fuel injection valve 2, the rotational speed of the engine 1 detected by the rotation sensor, and the like. Determine whether or not. When it is determined that the engine 1 is not in an operation state in which the exhaust gas temperature can be raised, the ECU 31 stops the exhaust gas temperature raising control and ends the control cycle. That is, the exhaust gas temperature raising control is not performed unless the engine 1 is in an operation state in which the exhaust gas temperature raising control can be executed.

  If it is determined in step S5 that the engine 1 is in an operation state in which the exhaust gas temperature raising control is possible, the ECU 31 advances the process to step S6, executes the exhaust gas temperature raising control, and performs the processes after step S6. At this time, since the value of the flag F is 1, the reducing agent supply valve 17c of the reducing agent supply device 17 is closed, and the injection of urea water into the exhaust passage 4a is stopped. That is, the exhaust gas temperature raising control is executed without supplying urea water to the exhaust passage 4a.

When the exhaust gas temperature raising control is executed, the process proceeds to step S7 in a state where the exhaust gas temperature has been continued, the exhaust gas temperature raising control completion determination timer A is started, and then the process proceeds to step S8.
In step S8, the separation amount per unit time at the target temperature when the exhaust gas is heated is read from the urea-derived deposit separation amount map in the preset engine operating condition. As shown in FIG. 4, the urea-derived deposit detachment amount map is obtained in advance by experiment or the like for each model to determine the urea-derived deposit detachment amount per unit time with respect to the exhaust temperature of the engine 1, using the exhaust temperature as a parameter. Such a urea-derived deposit detachment amount map is stored in the storage unit of the ECU 31.

Next, in step S9, the amount of ammonia (NH ₃ ) in the exhaust gas is calculated on the assumption that all the urea-derived substances gasified and separated by the exhaust gas temperature raising control are converted into ammonia.
In the next step S _<b> 10, the NO _X amount (NO _X mass) in the exhaust gas is calculated from the detected value of the NO _X sensor 24. Specifically, as shown in the following equation (1), the NO _X concentration (NO _{X conc} ) detected from the NO _X sensor 24 is multiplied by the exhaust gas flow rate (Q _out ).
NO _{X mass} = NO x _conc × Q _out (1)

In the same operating condition, the exhaust gas flowing through the exhaust passage 4 is expressed by the following equation (2) by adjusting the opening degree of the EGR valve 11 and increasing or decreasing the exhaust circulation amount Q _EGR flowing through the EGR passage 10. The flow rate Q _out can also be controlled.
_{Q out = Q IN - Q EGR} ... (2)

In step S11, whether or not “NH ₃ / N0 _X molar ratio” is around 1 by converting the calculated amount of ammonia (NH ₃ ) and NO _X amount (NO _Xmass ) in the exhaust gas into moles. Determine. That is, if the allowable range is α, the condition that “NH ₃ / N0 _X molar ratio” is near 1 is satisfied when the following expression (3) is satisfied, and therefore, the NO _X amount adjustment control is executed. Without proceeding to step S13. Further, when the following expression (4) is satisfied, the condition that the “NH ₃ / N0 _X molar ratio” is around 1 is not satisfied, so the routine proceeds to step S12 and the NO _X amount adjustment control is executed.
| 1-NH ₃ / NOX | ≦ α (3)
| 1-NH ₃ / NOX |> α (4)

In step S13, it is determined whether or not the value of the exhaust gas temperature raising control completion determination timer A has reached the completion determination time A0. When the completion determination time A0 is reached, the value of the flag F is set to 0 (step S14), and the exhaust gas temperature raising control is ended (step S15). At this time, it can be considered that all the urea-derived deposits in the exhaust passage 4a have disappeared.
In response to the value of the flag F becoming 0, in step S16, the exhaust gas temperature increase control completion determination timer A is reset (A = 0) in preparation for the next timing process. In step S17, the urea water supply from the reducing agent supply device 17 is permitted, and the urea water injection from the injection nozzle 17a to the exhaust passage 4a is resumed.

FIG. 3 is a flowchart for explaining the NO _X emission amount adjustment control executed by the ECU 31 shown in FIG. With reference to FIG. 3, the control for increasing or decreasing the NO _X amount by the NO _X emission amount adjustment control will be described.
As described above, the ECU 31 performs exhaust gas temperature raising control in order to remove urea-derived deposits in accordance with the deposition state of urea-derived deposits in the exhaust passage 4a. In parallel with the exhaust temperature raising control, the NO _X amount adjustment control in the exhaust discharged from the engine 1 is executed according to the flowchart shown in FIG.

First, when control is started (step S21), the ECU 31 determines in step S22 whether the “NH ₃ / N0 _X molar ratio” is around 1. When it is determined that the “NH ₃ / NO _X molar ratio” is near 1, the control cycle is ended and the NO _X amount adjustment control is not performed. On the other hand, if it is determined in step S22 that the “NH ₃ / N0 _X molar ratio” is not near 1, the ECU 31 advances the process to step S23 and executes NOX amount adjustment control.

First, in step S24, it is determined whether or not “NH ₃ / NO _X molar ratio> 1 + α”. If it is determined that Yes, the proportion of the NO _X is too small relative to NH _3, to perform the NO _X increasing control (step S25). On the other hand, if it is determined NO in step S24, the ratio of the NO _X is too large relative to NH _3, it performs NO _X reduction control (step S26).

In the present embodiment, the NO _X emission amount adjustment control is executed in this way. As the control for increasing the NO _X amount, the EGR valve 11 is closed, the fuel injection timing is advanced, and the fuel injection pressure is increased. In step S25, all these controls or a part of pre-selected controls are executed. Wherein each control to increase the amount of NO _X is intended to increase the amount of NO _X in the exhaust gas by improving the combustion conditions. In other words, the closing of the EGR valve 11 improves the combustion state by stopping the return of the inert exhaust gas to the intake side, and the advance of the fuel injection timing and the increase in the injection pressure also improve the combustion state. it is those, in which _the amount of NO _X in the exhaust gas by these factors is increased.
On the other hand, the control for reducing the amount of NO _X, the valve opening of the EGR valve 11, retarding the fuel injection timing, the control is set such as reduction in fuel injection pressure, the step S26 in the control of all these Alternatively, some control selected in advance is executed.

As described above, according to this embodiment, since the adjustment to the appropriate amount of NO _X in accordance with the withdrawal amount of the urea-derived deposit by the exhaust Atsushi Nobori control, release and ammonia into the atmosphere, greenhouse gases effect that can be obtained to suppress the occurrence of nitrous oxide (N 2 ₀₎ is.

Incidentally, the NO _X emission adjustment control is used for adjusting the NO _X emissions by correcting the opening degree of the EGR valve 11, NO _X emissions adjustment control by the EGR valve 11 is responsive can be well, also or rapidly increased NO _X emissions without significantly impairing the drivability, or reduced.

Further, in this embodiment, the estimated amount of released urea-derived deposits and NO _X emission estimated from the NO _X concentration are converted into moles and compared, and based on the deviation, the EGR valve 11 The opening correction amount is determined. Therefore, it can be increased or decreased to an appropriate amount of NO _X in accordance with the amount of urea-derived deposits released by exhaust gas temperature raising control, and the release of ammonia into the atmosphere and the nitrous oxide (N ₂ 0) of greenhouse gases. Can be suppressed.

Further, in the present embodiment, the exhaust gas temperature raising control is performed by supplying fuel into the exhaust gas and oxidizing with the oxidation catalyst 13, so that the exhaust gas temperature raising control can be executed relatively easily. For example, when fuel is supplied to the engine 1 by fuel injection into the cylinder, fuel can be supplied into the exhaust by additionally injecting fuel at a timing that does not contribute to the generation of power. According to this method, there is an advantage that it is not necessary to provide a new device for supplying fuel into the exhaust gas.
Further, in the above-described embodiment, when the exhaust gas temperature raising control is being executed, the urea water is not supplied from the reducing agent supply device 17, so that ammonia slip can be prevented more reliably. be able to.

In addition, this invention is not limited to an above-described Example, Various modifications are included. For example, although the engine (internal combustion engine) 1 has been described as a diesel engine in the above embodiment, the present invention can be similarly applied to other types of internal combustion engines such as a gasoline engine. Further, the present invention has been described as an exhaust purification device in a construction machine such as a hydraulic excavator. However, the present invention can be similarly applied to a general vehicle such as a truck.
Further, the above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described.

1: Engine (diesel engine), 2: Fuel injection valve (injector),
3: Intake passage, 4, 4a: Exhaust passage,
5: Turbocharger, 5a: Compressor, 5b: Turbine,
6: Intercooler, 7: Intake control valve, 8: Intake manifold (intake passage),
9: Exhaust manifold (exhaust passage),
10: EGR passage (exhaust gas recirculation passage), 11: EGR valve,
12: first exhaust aftertreatment device, 13: oxidation catalyst,
14: second exhaust aftertreatment device, 15: selective reduction type NO _X catalyst (SCR catalyst),
16: Ammonia oxidation catalyst,
17: reducing agent supply device, 17a: injection nozzle, 17b: pump, 17c: reducing agent control valve,
17d: reducing agent supply pipe, 17e: reducing agent flow rate sensor,
18: reducing agent tank (urea water tank), 19: reducing agent concentration sensor, 20: liquid level sensor,
21-23: temperature sensor, 24, 25: NO _X sensor, 26: common rail,
30: Reducing agent injection control unit (DCU),
31: Engine control unit (ECU).

Claims (4)

A selective reduction type NO _X catalyst that is disposed in the exhaust passage of the engine and selectively reduces NO _X in the exhaust gas using ammonia generated by supplying urea water as a reducing agent;
A reducing agent supply device for supplying urea water into the exhaust passage on the upstream side of the selective reduction type NO _X catalyst;
An internal combustion engine comprising exhaust temperature raising control means for performing exhaust gas temperature raising control so that the exhaust temperature in the exhaust passage becomes a target temperature when the amount of urea-derived material accumulated in the exhaust passage reaches a predetermined amount In an engine exhaust gas purification device,
A temperature sensor for detecting the upstream side of the exhaust gas temperature than the selective reduction type NO _X catalyst in the exhaust passage,
Based on the temperature of the exhaust gas detected by this temperature sensor, a desorption amount estimation means for estimating the desorption amount per unit time of ammonia gasified from the urea-derived deposit accumulated in the exhaust passage, and
And NO _X sensor for detecting the concentration of NO _X upstream of the selective reduction type NO _X catalyst in the exhaust passage,
Based on the NO _X concentration detected by the NO _X sensor and the ammonia desorption amount per unit time estimated by the desorption amount estimating means, the NO _X concentration in the exhaust passage becomes the target concentration so as to become the target concentration. exhaust purification system of an internal combustion engine, characterized in that it comprises a NO _X emission amount adjusting means for controlling NO _X emissions into the exhaust passage in. The exhaust gas purification apparatus for an internal combustion engine according to claim 1,
An EGR passage for returning a part of the exhaust gas flowing through the exhaust passage as an EGR (exhaust gas recirculation) gas to the intake passage of the internal combustion engine, and an EGR provided in the EGR passage for controlling the amount of the EGR gas With a valve,
The NO _X emissions adjusting means, the opening degree of the EGR valve increases or decreases from the opening at the time of normal control to adjust the NO _X emissions, the withdrawal amount per unit time of the ammonia estimated by the estimating means internal combustion amount of withdrawal and on the basis of the comparison result between the NO _X emissions per unit time is estimated from the detected NO _X concentration with NO _X sensor, and determines the opening degree of the EGR valve Engine exhaust purification system.   2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein when the exhaust gas temperature raising control means is executing exhaust gas temperature raising control, the supply of urea water from the reducing agent supply device to the exhaust passage is stopped. An exhaust emission control device for an internal combustion engine.   2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein an oxidation catalyst is provided in the exhaust passage on the upstream side of the reducing agent supply device, and the exhaust temperature raising control unit is configured to supply exhaust gas flowing into the oxidation catalyst. An exhaust gas purification apparatus for an internal combustion engine, characterized in that exhaust gas temperature raising control is performed by controlling a fuel supply amount.

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