JP2018096210A - Exhaust emission control system and its controlling method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control system capable of improving fuel consumption by reducing a frequency of forcible regeneration due to injection of fuel, and its controlling method.SOLUTION: In an exhaust emission control system 20, an injection valve 21 for a pipeline, an oxidation catalyst device 22, and a collecting filter 23 are arranged in an exhaust passage 15 of an engine 10. The system comprises a first temperature sensor 31 and a control device 30. In regenerating a filter, when exhaust gas temperature Tx is lower than a lower limit value Td of a temperature zone suitable for continuous regeneration, the control device 30 makes the injection valve 21 for the pipeline perform intermittent injection for repeating an injection period Δt1 and a stopping period Δt2 since filter regeneration start till finish, so as to maintain the exhaust gas temperature Tx to a temperature zone (Td to Tu) suitable for continuous regeneration.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an exhaust gas purification system and a control method thereof, and more particularly to an exhaust gas purification system and a control method thereof that improve fuel efficiency.

  In general, forced regeneration is known as a method for regenerating a collection filter by removing the collected particulate matter. In forced regeneration, fuel is injected into the oxidation catalyst device to oxidize it, and the exhaust gas temperature is raised by utilizing the oxidation reaction heat generated by the oxidation, and the particulate matter collected by the collection filter The substance is removed by incineration.

  In this regard, an exhaust gas purification system that periodically (intermittently) supplies fuel to the oxidation catalyst device during forced regeneration has been proposed (see, for example, Patent Document 1). However, such forced regeneration can regenerate the collection filter, but it is necessary to raise the temperature of the exhaust gas to a high temperature of 500 degrees or more. Therefore, when the frequency of forced regeneration increases, there is a problem that fuel consumption required for regeneration of the collection filter increases and fuel consumption deteriorates.

JP 2005-98184 A

  By the way, as a method of removing the particulate matter collected by the collection filter, continuous regeneration is known in addition to the forced regeneration described above. In the continuous regeneration, the particulate matter collected by the collection filter is decomposed and removed by utilizing the oxidative decomposition ability of nitrogen dioxide generated by oxidation in the oxidation catalyst device.

  The oxidation removal rate of particulate matter during continuous regeneration depends on the exhaust gas temperature and the concentration of nitrogen dioxide in the collection filter. The higher the exhaust gas temperature, the more the oxidation reaction between nitrogen dioxide and particulate matter is promoted, while the nitrogen dioxide returns to nitric oxide at a higher temperature. Therefore, in order to effectively carry out the continuous regeneration, generation of nitrogen dioxide in the oxidation catalyst device while maintaining the exhaust gas temperature in the collection filter at a temperature suitable for continuous regeneration (for example, 250 to 500 degrees). The amount needs to be increased.

  However, in an environment where high concentration fuel coexists, there is a problem that the production of nitrogen dioxide in the oxidation catalyst device is hindered. That is, maintaining the exhaust gas temperature for the purpose of effective continuous regeneration and increasing the concentration of nitrogen dioxide are contradictory, and it has been difficult to achieve both.

  An object of the present invention is to provide an exhaust gas purification system that can reduce the frequency of forced regeneration and improve fuel efficiency, and a control method therefor.

The exhaust gas purification system of the present invention that achieves the above object adds fuel to the exhaust gas in order from the upstream side to the downstream side with respect to the exhaust gas flow into the exhaust passage through which the exhaust gas discharged from the engine passes. In an exhaust gas purification system in which a fuel addition device, an oxidation catalyst device that oxidizes fuel and nitrogen oxides contained in exhaust gas, and a collection filter that collects particulate matter contained in exhaust gas are arranged A particulate matter collected by the collection filter, comprising: a temperature acquisition device for acquiring an exhaust gas temperature in the collection filter; and a control device connected to the temperature acquisition device and the fuel addition device. In the case of performing filter regeneration to remove the particulate matter, the exhaust gas temperature acquired by the temperature acquisition device is converted to particulate matter collected by the collection filter with nitrogen dioxide. When the control device falls below a lower limit value of a temperature range suitable for continuous regeneration to be removed, an injection period during which fuel is injected and a stop period during which fuel injection is stopped from the start to the end of the filter regeneration. In this configuration, the fuel adding device is made to perform intermittent injection repeatedly to maintain the acquired exhaust gas temperature in a temperature range suitable for the continuous regeneration.

  Further, the control method of the exhaust gas purification system of the present invention that achieves the above-described object is directed to the exhaust passage through which the exhaust gas discharged from the engine passes in order from the upstream side to the downstream side with respect to the flow of the exhaust gas. A fuel addition device that adds fuel to the gas, an oxidation catalyst device that oxidizes fuel and nitrogen oxides contained in the exhaust gas, and a collection filter that collects particulate matter contained in the exhaust gas are arranged. In the control method of the exhaust gas purification system, when performing filter regeneration to remove the particulate matter collected by the collection filter, the exhaust gas temperature in the collection filter is acquired, and the acquired exhaust gas temperature is When the particulate matter collected by the collection filter falls below the lower limit of the temperature range suitable for continuous regeneration in which oxidative decomposition is performed with nitrogen dioxide, the filter regeneration is started. From the end to the end, the fuel addition device is made to perform intermittent injection that repeats an injection period in which fuel is injected and a stop period in which fuel injection is stopped, and the acquired exhaust gas temperature is suitable for the continuous regeneration. It is a method characterized by maintaining the temperature zone.

  According to the present invention, fuel is added to exhaust gas by intermittent injection from the fuel addition device, and an environment where high concentration fuel coexists in the oxidation catalyst device and an environment where fuel does not coexist in the oxidation catalyst device are intentional. It produces alternately. Therefore, in an environment where high-concentration fuel coexists, the temperature of the exhaust gas can be increased using the oxidation reaction heat generated by the oxidation of the fuel in the oxidation catalyst device. Also, in an environment where high-concentration fuel does not coexist in the oxidation catalyst device, the exhaust gas temperature decreases, while the amount of nitrogen dioxide generated in the oxidation catalyst device is increased to increase the nitrogen dioxide contained in the exhaust gas. Can be a concentration.

  As a result, maintaining the exhaust gas temperature at a temperature suitable for continuous regeneration and increasing the concentration of nitrogen dioxide is advantageous for improving the oxidation removal rate of particulate matter by continuous regeneration, and is continuous instead of forced regeneration. It becomes possible to use reproduction. Along with this, the frequency of forced regeneration can be reduced, the amount of fuel consumption required for regeneration of the collection filter can be reduced, and fuel consumption can be improved.

It is a block diagram which illustrates the engine carrying 1st embodiment of the exhaust-gas purification system of this invention. It is a flowchart which illustrates a part of control method of the exhaust gas purification system of FIG. It is a flowchart which illustrates a part of control method of the exhaust gas purification system of FIG. FIG. 2 is a relationship diagram illustrating the relationship between elapsed time, fuel injection amount, exhaust gas temperature, and nitrogen dioxide in the exhaust gas purification system of FIG. 1. FIG. 2 is a relationship diagram illustrating the relationship between exhaust gas temperature and nitrogen dioxide concentration with respect to the decomposition rate of particulate matter in the collection filter of FIG. 1. FIG. 2 is a relationship diagram illustrating the relationship between exhaust gas temperature and fuel concentration with respect to the production rate of nitrogen dioxide in the oxidation catalyst device of FIG. 1. It is a block diagram which illustrates the engine carrying 2nd embodiment of the exhaust gas purification system of this invention. It is a flowchart which illustrates a part of control method of the exhaust-gas purification system of FIG.

  Embodiments of an exhaust gas purification system and a control method thereof according to the present invention will be described below.

  As illustrated in FIG. 1, the exhaust gas purification system 20 of the first embodiment is a system that is provided in the engine 10 and purifies the exhaust gas G1.

  The engine 10 includes an engine body 13 having a plurality of cylinders 11 and cylinder injection valves 12 arranged in series, and an exhaust passage through which exhaust gas G1 generated by fuel combustion is discharged via an exhaust manifold 14. 15 and an exhaust gas purification system 20.

  The exhaust gas purification system 20 is arranged in the exhaust passage 15 in order from the upstream side to the downstream side with respect to the flow of the exhaust gas G1, and the piping injection valve 21, the oxidation catalyst device 22, the collection filter 23, the reducing agent injection. It has a valve 24, a selective reduction catalyst device 25, and an ammonia catalyst device 26.

  The piping injection valve 21 is inserted in the middle of the exhaust passage 15 interposed between the exhaust manifold 14 and the oxidation catalyst device 22 with the injection port directed in the flow direction of the exhaust gas G1. The pipe injection valve 21 is supplied with the same fuel as the fuel injected from the cylinder injection valve 12 into the cylinder 11 from the fuel supply system including the fuel tank 27a and the fuel pump 27b, and is supplied to the exhaust gas G1. It functions as a fuel addition device for adding the fuel.

  The oxidation catalyst device 22 is a cylindrical porous structure, and is partitioned by a porous partition made of ceramics. The oxidation catalyst device 22 penetrates from the inlet through which the exhaust gas G1 flows into the outlet through which the exhaust gas G1 flows. A plurality of ventilation holes (cells) serving as paths are formed. The oxidation catalyst device 22 carries an oxidation catalyst for oxidizing hydrocarbons, carbon monoxide, and nitrogen monoxide contained in the exhaust gas G1 in its porous partition wall. Examples of the oxidation catalyst include noble metals such as platinum (Pt), rhodium (Rh) and palladium (Pd).

  The collection filter 23 is a cylindrical porous structure, and a plurality of ventilation holes are formed by porous partition walls made of ceramics as in the oxidation catalyst device 22. Unlike the oxidation catalyst device 22, the collection filter 23 has a vent hole that is closed at either the inlet or the outlet by a sealing member, and the inlet and outlet of the collection filter 23 are adjacent to each other. The pores are alternately blocked.

  The reducing agent injection valve 24 is inserted in the middle position of the exhaust passage 15 interposed between the collection filter 23 and the selective reduction catalyst device 25 with the injection port directed in the flow direction of the exhaust gas G1. The reducing agent injection valve 24 is supplied with urea water from a urea water supply system including a urea water tank 28a and a urea water pump 28b, and adds urea water as a reducing agent to the exhaust gas G1. The urea water supply system is provided with a cooling water pipe 29 through which the cooling water after cooling the engine body 13 flows, and the urea water tank 28a and the pipe through which the urea water flows are heated by the cooling water. Yes.

The selective reduction catalyst device 25 is a cylindrical porous structure, and a plurality of ventilation holes are formed by porous partition walls made of ceramics as in the oxidation catalyst device 22. Unlike the oxidation catalyst device 22, the selective reduction catalyst device 25 carries a selective reduction catalyst that reduces nitrogen oxides contained in the exhaust gas G <b> 1 on its porous partition wall. Examples of the selective reduction catalyst include vanadium and zeolite.

  The ammonia catalyst device 26 is a device that removes ammonia contained in the exhaust gas G1 after passing through the selective reduction catalyst device 25, and has a function of oxidizing and decomposing ammonia or a function of adsorbing ammonia.

  In the exhaust gas purification system 20, the purification target component contained in the exhaust gas G1 is purified by passing the exhaust gas G1 through each device. Specifically, the oxidation catalyst device 22 oxidizes hydrocarbons, carbon oxides, and nitrogen oxides contained in the exhaust gas G1. Next, the particulate matter contained in the exhaust gas G1 is collected by the collection filter 23. Next, nitrogen oxides contained in the exhaust gas G1 are reduced by the selective reduction catalyst device 25 by a reduction reaction by ammonia generated by hydrolysis of urea water injected from the reducing agent injection valve 24. Next, ammonia contained in the exhaust gas G1 is removed by the ammonia catalyst device 26.

  In the exhaust gas purification system 20, it is necessary to periodically remove the particulate matter collected by the collection filter 23. Examples of the method for removing the collected particulate matter include forced regeneration and continuous regeneration.

  In forced regeneration, the temperature of the exhaust gas Tx in the collection filter 23 is raised to a temperature Ta suitable for forced regeneration (hereinafter, referred to as forced regeneration temperature Ta), and the particles collected by the collection filter 23 are collected. Substances are burned away with oxygen. As the forced regeneration temperature Ta, for example, a high temperature of 500 degrees or more can be exemplified. In this embodiment, when the exhaust gas temperature Tx is lower than the forced regeneration temperature Ta, the fuel is injected from the piping injection valve 21 to oxidize hydrocarbons by the oxidation catalyst device 22 and the oxidation reaction caused by the oxidation. The temperature of the exhaust gas G1 is raised by using heat.

  In the continuous regeneration, the particulate matter collected by the collection filter 23 is decomposed and removed by utilizing the oxidative decomposition ability of nitrogen dioxide generated by oxidation in the oxidation catalyst device 22. In the continuous regeneration, the exhaust gas temperature Tx is maintained in a temperature range (Td to Tu) suitable for continuous regeneration, and the amount of nitrogen dioxide generated in the oxidation catalyst device 22 is increased, so that the nitrogen dioxide contained in the exhaust gas G1 is increased. The concentration needs to be high.

  The temperature range (Td to Tu) suitable for continuous regeneration is a range from the lower limit value Td to the upper limit value Tu. The lower limit value Td is set to a value at which the oxidation catalyst device 22 is activated and nitrogen dioxide and particulate matter can undergo an oxidation reaction. The upper limit value Tu is set to a temperature at which nitrogen dioxide can stably exist at a temperature equal to or lower than the forced regeneration temperature Ta. As the temperature zone, the lower limit value Td is preferably set to 250 degrees (° C.) and the upper limit value is preferably set to 500 degrees, more preferably the lower limit value Td is set to 300 degrees and the upper limit value Tu is set to 400 degrees.

  Note that forced regeneration and continuous regeneration may occur spontaneously depending on the operating state of the engine 10. For example, forced regeneration occurs spontaneously when the exhaust gas temperature Tx reaches the forced regeneration temperature Ta when the engine 10 is at a high speed and a high load. Further, even when the engine 10 is at a high speed and a high load, the exhaust gas temperature Tx is in a temperature range (Td to Tu) suitable for continuous regeneration, and continuous regeneration is performed in an environment where the exhaust gas G1 contains nitrogen dioxide. May occur. In this embodiment, forced regeneration and continuous regeneration indicate a case where the control device 30 intentionally injects fuel from the piping injection valve 21.

  If the frequency of forced regeneration by fuel injection increases, the fuel consumption may deteriorate. Therefore, the exhaust gas purification system 20 of this embodiment reduces the frequency of performing this forced regeneration by creating an environment where intentional continuous regeneration occurs. Specifically, the exhaust gas purification system 20 includes a control device 30 and various sensors, and when the collection filter 23 is regenerated, the control device 30 causes the injection valve 21 for piping to perform intermittent injection, The exhaust gas temperature Tx is maintained in a temperature range (Td to Tu) suitable for continuous regeneration.

  The control device 30 is connected to the piping injection valve 21, the reducing agent injection valve 24, the first temperature sensor 31, the differential pressure sensor 32, the second temperature sensor 33, the NOx sensor 34, and the third temperature sensor 35. The control device 30 has a function of adjusting the fuel injection of the piping injection valve 21 and the urea water injection of the reducing agent injection valve 24 based on values acquired by various sensors. Specifically, the control device 30 is hardware configured by a CPU that performs various information processing, an internal storage device that can read and write programs and information processing results used for performing the various information processing, and various interfaces. is there.

  The first temperature sensor 31 functions as a temperature acquisition device that acquires the exhaust gas temperature Tx in the collection filter 23, and is composed of temperature sensors arranged at the inlet and the outlet of the collection filter 23. . The first temperature sensor 31 acquires the temperature of the exhaust gas G1 that passes through the inlet of the collection filter 23 and the temperature of the exhaust gas G1 that passes through the outlet, and outputs the average value of the acquired temperatures as the exhaust gas temperature Tx. ing. The temperature acquisition device may be a sensor that acquires only the temperature of the exhaust gas G1 that passes through the inlet of the collection filter 23, or a sensor that acquires only the temperature of the exhaust gas G1 that passes through the outlet of the collection filter 23. Good. Further, instead of a sensor that directly acquires the exhaust gas temperature Tx, the rotational speed of the engine 10 and the amount of fuel injected from the cylinder injection valve 12 and combusted inside the cylinder 11, or the oxidation in the oxidation catalyst device 22. An apparatus that models and predicts the exhaust gas temperature Tx based on a reaction or the like may be used.

  The differential pressure sensor 32 functions as a device that acquires a value that can estimate the amount of particulate matter deposited on the collection filter 23. Specifically, the differential pressure sensor 32 acquires the differential pressure before and after the collection filter 23. Yes.

  The second temperature sensor 33 functions as a device that acquires a value by which the purification state in the selective reduction catalyst device 25 can be estimated, and specifically acquires the exhaust gas temperature in the selective reduction catalyst device 25. .

  The NOx sensor 34 functions as a device that acquires the concentration of nitrogen oxides contained in the exhaust gas G1 after passing through the selective reduction catalyst device 25. The control device 30 adjusts the amount of urea water injected from the reducing agent injection valve 24 based on the value acquired by the NOx sensor 34.

  The third temperature sensor 35 functions as a device that acquires a value capable of estimating the purification state in the selective reduction catalyst device 25, and specifically acquires the urea water temperature in the urea water supply system.

  In the intermittent injection, between the start of regeneration of the collection filter 23 and the end thereof, the injection period Δt1 during which fuel is injected from the piping injection valve 21 and the fuel injection of the piping injection valve 21 are stopped. This is an injection mode in which the stop periods Δt2 are alternately continued. Specifically, in the intermittent injection of this embodiment, when the exhaust gas temperature Tx falls to the lower limit value Td, fuel is injected from the piping injection valve 21, and the exhaust gas temperature Tx rises to the upper limit value Tu. This is an injection mode in which the fuel injection from the piping injection valve 21 is stopped.

  Next, a control method of the exhaust gas purification system 20 will be described. This control method is performed every predetermined period from when the control device 30 and various sensors are activated to when they are stopped.

  The control device 30 acquires parameters via various sensors (S110). The parameter is a parameter required for judging the regeneration of the collection filter 23. In this embodiment, the parameters are values that can estimate the exhaust gas temperature Tx acquired by various sensors, the amount of particulate matter deposited on the collection filter 23, and the value that can estimate the purification state in the selective reduction catalyst device 25. It is. Specifically, the value by which the accumulation amount can be estimated is the differential pressure before and after the collection filter 23 acquired by the differential pressure sensor 32. Values that can estimate the purification state are the exhaust gas temperature in the selective reduction catalyst device 25 acquired by the second temperature sensor 33, the urea water temperature in the urea water supply system acquired by the third temperature sensor 35, and the like.

  Next, the control device 30 determines whether or not the exhaust gas temperature Tx is below a lower limit value Td of a temperature range suitable for continuous regeneration (S120). When the exhaust gas temperature Tx is equal to or higher than the lower limit value Td, spontaneous continuous regeneration or forced regeneration occurs. Therefore, when the fuel is not injected from the piping injection valve 21 and the exhaust gas temperature Tx is lower than the lower limit value Td, the control returns to the start without performing the control of injecting the fuel from the piping injection valve 21. .

  Next, the control device 30 determines whether or not the collection filter 23 needs to be regenerated as the condition A (S130). Specifically, in this step, it is determined whether or not the differential pressure before and after the collection filter 23 acquired by the differential pressure sensor 32 exceeds a first threshold value. This first threshold value is set to a value that can determine that the fuel consumption deteriorates due to the pressure loss in the collection filter 23 that increases as particulate matter accumulates on the collection filter 23.

  Next, when the condition A is satisfied (YES), the control device 30 determines whether or not forced regeneration is necessary in the regeneration of the collection filter 23 as the condition B (S140). Specifically, in this step, it is determined whether or not the differential pressure before and after the collection filter 23 acquired by the differential pressure sensor 32 exceeds a second threshold value. The second threshold value is set to a value that can determine that particulate matter has accumulated on the collection filter 23 more than the state of the first threshold value.

  As conditions A and B, it suffices to determine whether or not the regeneration of the collection filter 23 is necessary and whether or not forced regeneration is necessary for regeneration, that is, the amount of particulate matter deposited can be determined. For example, a PM sensor that measures particulate matter contained in the exhaust gas G1 may be used. Alternatively, the amount of particulate matter deposited may be modeled from the rotational speed of the engine 10 or the fuel injection amount.

  When the exhaust gas temperature Tx falls below the lower limit value Td (S120: YES), the condition A is satisfied (S130: YES), and the condition B is satisfied (S140: YES), the control device 30 performs forced regeneration (S150). ). As described above, in the forced regeneration, the exhaust gas temperature Tx is forcibly regenerated by adjusting the injection amount of fuel injected from the piping injection valve 21 based on the exhaust gas temperature Tx acquired by the first temperature sensor 31. The temperature is raised to a temperature suitable for (for example, 500 ° C. or more).

  On the other hand, when the exhaust gas temperature Tx falls below the lower limit value Td (S120: YES), the condition A is satisfied (S130: YES), and the condition B is not satisfied (S140: NO), the control device 30 performs continuous regeneration. . Specifically, in the situation where the regeneration of the collection filter 23 is not necessary, the situation where the forced regeneration is not necessary, that is, the situation where regeneration is necessary but the amount of accumulated particulate matter is relatively small, The control device 30 performs continuous reproduction.

  Next, the control device 30 determines whether or not to end the regeneration of the collection filter 23 as the condition C (S160). Specifically, in this step, it is determined whether or not the differential pressure before and after the collection filter 23 exceeds a third threshold value. The third threshold value is set to a value lower than the first threshold value in the condition A, and is set to a value that can determine that the collection filter 23 has been regenerated.

  Thus, when the collection filter 23 is regenerated, the process returns to the start.

  As illustrated in FIG. 3, when performing continuous regeneration, the control device 30 stops the injection period Δt1 during which fuel is injected into the piping injection valve 21 and fuel injection from the start to the end of filter regeneration. The intermittent injection that repeats the stop period Δt2 is performed.

  Specifically, the control device 30 determines whether or not the exhaust gas temperature Tx is equal to or lower than the lower limit value Td (S210). When it is determined that the exhaust gas temperature Tx has become equal to or lower than the lower limit value Td, the control device 30 issues an instruction to inject fuel into the piping injection valve 21, and the piping injection valve 21 injects fuel (S220). The fuel injection amount Qx at this time may be adjusted based on the exhaust gas temperature discharged from the engine body 13. For example, map data indicating the relationship between the injection amount Qx that can be increased from the lower limit value Td to the upper limit value Tu and the exhaust gas temperature exhausted from the engine body 13 is created in advance by experiments and tests. Adjust based on.

  The control device 30 determines whether or not the exhaust gas temperature Tx is equal to or higher than the upper limit value Tu (S230). When it is determined that the exhaust gas temperature Tx has become equal to or higher than the upper limit value Tu, the control device 30 instructs the piping injection valve 21 to stop fuel injection, and the piping injection valve 21 stops fuel injection (S240). ).

  When the exhaust gas temperature Tx exceeds the lower limit value Td and falls below the upper limit value Tu, the control device 30 maintains the injection state of the pipe injection valve 21 without giving an instruction to the pipe injection valve 21 (S250). ).

  As described above, in the continuous regeneration, the injection period Δt1 in which the fuel is injected from the piping injection valve 21 until the condition C is satisfied, that is, until the regeneration of the collection filter 23 is started and ended. And intermittent injection, which is an injection mode in which the stop period Δt2 in which the fuel injection of the piping injection valve 21 stops, is alternately continued.

  As illustrated in FIG. 4, when continuous regeneration is started at time t0, from time t0 to time t1, the piping injection valve 21 injects fuel and raises the exhaust gas temperature Tx to the upper limit value Tu. To do. During this period, since the high-concentration fuel coexists in the oxidation catalyst device 22, the amount of nitrogen dioxide produced does not increase, and the nitrogen dioxide concentration is maintained at a low concentration Cd.

  Next, when the exhaust gas temperature Tx reaches the upper limit value Tu at time t1, in the stop period Δt2 from time t1 to time t2, the pipe injection valve 21 stops fuel injection, and the exhaust gas temperature Tx is set to the lower limit value. The temperature is lowered to Td.

  During this stop period Δt2, since the fuel is not coexisting with the oxidation catalyst device 22, the oxidation reaction of nitrogen monoxide in the oxidation catalyst device 22 is promoted to increase the amount of nitrogen dioxide generated, and the exhaust gas G1 The concentration of nitrogen dioxide contained in is increased from a low concentration Cd to a high concentration Cu. Therefore, during the stop period Δt2, the oxidative decomposition rate of the particulate matter by nitrogen dioxide is increased in the collection filter 23, and the particulate matter is removed.

  Next, when the exhaust gas temperature Tx reaches the lower limit value Td at time t2, in the injection period Δt1 from time t2 to time t3, the pipe injection valve 21 injects fuel, and the exhaust gas temperature Tx reaches the upper limit value Tu. Raise the temperature. During the injection period Δt1, since the high concentration fuel coexists in the oxidation catalyst device 22, the amount of generated nitrogen dioxide does not increase and the concentration of nitrogen dioxide is maintained at the low concentration Cd.

  In this way, by performing intermittent injection in which the injection period Δt1 and the stop period Δt2 are repeated until the continuous regeneration is completed, an environment in which high concentration fuel coexists in the oxidation catalyst device 22 and an environment in which fuel does not coexist are established. The two environments are intentionally created alternately.

  Therefore, in an environment where high-concentration fuel coexists, the exhaust gas temperature Tx can be raised using the oxidation reaction heat generated by the oxidation of the fuel in the oxidation catalyst device 22. Further, in an environment where high-concentration fuel does not coexist in the oxidation catalyst device 22, the exhaust gas temperature Tx decreases, while the amount of nitrogen dioxide generated in the oxidation catalyst device 22 is increased to be contained in the exhaust gas G 1. Nitrogen can be concentrated.

  As a result, the exhaust gas temperature Tx is maintained in a temperature range (Td to Tu) suitable for continuous regeneration and the nitrogen dioxide concentration is increased, thereby improving the particulate matter oxidation removal rate in the collection filter 23 by continuous regeneration. And it is possible to use continuous regeneration instead of forced regeneration. Along with this, the frequency of forced regeneration by fuel injection can be reduced, the amount of fuel consumption required for regeneration of the collection filter 23 can be reduced, and fuel consumption can be improved.

  As illustrated in FIG. 5, the higher the exhaust gas temperature Tx, the faster the oxidative decomposition rate of the particulate matter. Further, the higher the concentration of nitrogen dioxide, the faster the oxidative decomposition rate of the particulate matter. That is, in order to effectively remove particulate matter by continuous regeneration, it is necessary to keep the exhaust gas temperature Tx high and to increase the concentration of nitrogen dioxide.

  As illustrated in FIG. 6, in an environment where high concentration fuel coexists in the oxidation catalyst device 22, the concentration of nitrogen dioxide becomes lower than in an environment where high concentration fuel does not coexist. Further, when the exhaust gas temperature Tx is lower than the lower limit value Td, the oxidation catalyst device 22 is not activated, so that the concentration of nitrogen dioxide is reduced. In addition, when the exhaust gas temperature Tx exceeds the upper limit value Tu, the reaction of returning nitrogen dioxide to nitrogen monoxide is promoted, so that the concentration of nitrogen dioxide decreases.

  Thus, maintaining the exhaust gas temperature for the purpose of effective continuous regeneration is contrary to increasing the concentration of nitrogen dioxide. In this regard, the exhaust gas purification system 20 maintains the exhaust gas temperature by causing the pipe injection valve 21 to perform intermittent injection and maintaining the exhaust gas temperature Tx in a temperature range (Td to Tu) suitable for continuous regeneration. And a high concentration of nitrogen dioxide can be achieved.

  When performing continuous regeneration, control may be performed to increase the emission amount of nitrogen oxides contained in the exhaust gas G1 discharged from the engine body 13. Examples of the control for increasing the discharge amount include control for changing the injection amount and injection timing of the fuel injected from the injector 12 so that the cylinder 11 burns in a high temperature state and a high oxygen state.

In addition, when performing control which increases discharge | emission amount, it is necessary to cope with the nitrogen dioxide which did not react with the collection filter 23 completely. Therefore, continuous regeneration may be performed when the selective reduction catalyst device 25 is capable of reducing nitrogen oxides. The state in which the selective reduction catalyst device 25 can reduce nitrogen oxides means that the exhaust gas temperature in the selective reduction catalyst device 25 acquired by the second temperature sensor 33 is the urea water injected from the reducing agent injection valve 24. The temperature is maintained at a temperature capable of hydrolyzing to ammonia. Further, the urea water temperature acquired by the third temperature sensor 35 is in a state where the urea water becomes a temperature at which the urea water is thawed, and the urea water can be injected from the reducing agent injection valve 24. Specifically, it is determined whether or not the temperature acquired by the second temperature sensor 33 is equal to or higher than a threshold value, or whether or not urea water can be injected from the reducing agent injection valve 24. In addition to this, it is only necessary to determine whether the purification state in the selective reduction catalyst device 25 is a state in which nitrogen oxides can be reduced. For example, the concentration of nitrogen oxides acquired by the NOx sensor 34 can be used, or the urea water pump The temperature of the piping around 28b may be used. By doing in this way, it is possible to reduce the nitrogen dioxide that has passed through the collection filter 23 without reacting with the particulate matter by the selective reduction catalyst device 25 and prevent the nitrogen dioxide from being discharged to the outside. it can. Moreover, you may add to the flow shown in FIG. 2 whether the selective reduction catalyst apparatus 25 is a state which can reduce | restore nitrogen oxides.

  As illustrated in FIG. 7, the exhaust gas purification system 20 of the second embodiment includes a timer 36 with respect to the first embodiment, and controls intermittent injection based on the count of the timer 36.

  The timer 36 is a device that counts the injection period Δt1 and the stop period Δt2 alternately and continuously. Note that the control device 30 may have a functional element that functions as the timer 36.

  The injection period Δt1 is a period in which the exhaust gas temperature Tx rises from the lower limit value Td to the upper limit value Tu, and is set based on the fuel injection amount Qx injected from the piping injection valve 21. For example, map data indicating the relationship between the injection period Δt1 and the injection amount Qx may be created in advance by experiments or tests, and the injection period Δt1 may be set based on the map data.

  The stop period Δt2 is a period during which the exhaust gas temperature Tx falls from the upper limit value Tu to the lower limit value Td, and is set based on the exhaust gas temperature discharged from the engine body 13. For example, map data indicating the relationship between the stop period Δt2 and the exhaust gas temperature may be created in advance by experiments or tests, and the stop period Δt2 may be set based on the map data.

  The stop period Δt2 is desirably set longer than the injection period Δt1. Thus, by making the stop period Δt2 long, it is advantageous for increasing the amount of nitrogen dioxide generated in the oxidation catalyst device 22.

  As illustrated in FIG. 8, when performing continuous regeneration, the control device 30 raises the exhaust gas temperature Tx to the lower limit value Td (S230, S310). Next, when the exhaust gas temperature Tx is equal to or higher than the lower limit value Td, fuel injection and fuel injection stop are determined based on whether the flag is “0” or “1” (S320).

  When the flag is “0”, the control device 30 injects fuel from the piping injection valve 21 while the timer 36 counts the injection period Δt1 and sets the flag to “1” (S230, S330, S340, S350). When the flag is “1”, the control device 30 stops the fuel injection from the piping injection valve 21 and sets the flag to “0” while the timer 36 counts the stop period Δt2. (S240, S330, S360, S370). Repeat until the above condition C is satisfied.

  As described above, even if based on the count of the timer 36 instead of the exhaust gas temperature Tx, by performing intermittent injection in which the injection period Δt1 and the stop period Δt2 are repeated, an environment in which high-concentration fuel coexists in the oxidation catalyst device 22 is obtained. And the environment where fuel does not coexist can be intentionally created alternately.

  In the above-described embodiment, the example in which the pipe injection valve 21 is used as the fuel addition device for adding fuel to the exhaust gas G1 has been described. However, instead of the pipe injection valve 21, the cylinder injection valve 12 is used. Also good. When the cylinder injection valve 12 is used as a fuel addition device, fuel is added from the cylinder injection valve 12 to the exhaust gas G1 by post injection. As described above, the fuel adding device only needs to be able to add fuel until the exhaust gas G1 reaches the oxidation catalyst device 22. For example, the piping injection valve 21 may be provided at each port of the exhaust manifold 14. .

  When the exhaust gas temperature Tx is increased, in addition to fuel injection from the pipe injection valve 21, after injection from the cylinder injection valve 12 may be performed at a timing at which the pipe injection valve 21 injects. .

  Further, when the engine 10 includes an EGR system that recirculates the exhaust gas G1 as EGR gas from the exhaust passage 15 to an intake passage (not shown), the amount of EGR gas that is recirculated may be reduced during continuous regeneration. In particular, it is preferable to reduce the amount of EGR gas that is recirculated during the stop period Δt2. This is advantageous for increasing the amount of nitrogen dioxide produced in the oxidation catalyst device 22.

  In the above-described embodiment, an example in which forced regeneration and continuous regeneration are switched according to conditions has been described. However, when the collection filter 23 can be regenerated by sufficiently removing particulate matter by continuous regeneration, forced regeneration is performed. You may comprise so that it may not perform. That is, setting the second threshold value to a larger value is advantageous for reducing the frequency of forced regeneration.

DESCRIPTION OF SYMBOLS 10 Engine 15 Exhaust passage 20 Exhaust gas purification system 21 Injection valve 22 for piping Oxidation catalyst device 23 Collection filter 30 Control device 31 First temperature sensor Td Lower limit value Tu Upper limit value Δt1 Injection period Δt2 Stop period

Claims (6)

A fuel addition device for adding fuel to the exhaust gas in order from the upstream side to the downstream side with respect to the flow of the exhaust gas in the exhaust passage through which the exhaust gas discharged from the engine passes, and the fuel and nitrogen oxidation contained in the exhaust gas In an exhaust gas purification system in which an oxidation catalyst device that oxidizes matter and a collection filter that collects particulate matter contained in exhaust gas are arranged,
A temperature acquisition device for acquiring the exhaust gas temperature in the collection filter, and a control device connected to the temperature acquisition device and the fuel addition device,
When performing filter regeneration to remove particulate matter collected by the collection filter, the exhaust gas temperature acquired by the temperature acquisition device is converted to nitrogen dioxide by collecting the particulate matter collected by the collection filter. When the temperature falls below the lower limit value of the temperature range suitable for continuous regeneration to be decomposed and removed, the control device causes an injection period during which fuel is injected and a stop period during which fuel injection is stopped from the start to the end of the filter regeneration. The exhaust gas purification system is configured to cause the fuel addition device to perform intermittent injection repeatedly to maintain the acquired exhaust gas temperature in a temperature range suitable for the continuous regeneration.   The exhaust gas purification system according to claim 1, wherein an upper limit value of a temperature zone suitable for the continuous regeneration is lower than a temperature suitable for forced regeneration in which particulate matter collected by the collection filter is removed by combustion with oxygen. .   When the control device causes the fuel addition device to inject fuel when the exhaust gas temperature acquired by the temperature acquisition device has decreased to the lower limit value, and when the exhaust gas temperature has increased to the upper limit value. The exhaust gas purification system according to claim 2, wherein the fuel injection from the fuel addition device is stopped. A timer for counting the injection period and the stop period alternately and continuously;
While the timer counts the injection period, the controller injects fuel from the fuel addition apparatus, and while the timer counts the stop period, from the fuel addition apparatus. The exhaust gas purification system according to claim 2, wherein the fuel injection is stopped.   The injection period is set to a time during which the exhaust gas temperature acquired by the temperature acquisition device rises from the lower limit value to the upper limit value, and the stop period is determined so that the exhaust gas temperature is higher than the upper limit value. The exhaust gas purification system according to claim 4, wherein the exhaust gas purification system is set to a time when it falls to a lower limit value. A fuel addition device for adding fuel to the exhaust gas in order from the upstream side to the downstream side with respect to the flow of the exhaust gas in the exhaust passage through which the exhaust gas discharged from the engine passes, and the fuel and nitrogen oxidation contained in the exhaust gas In a control method of an exhaust gas purification system in which an oxidation catalyst device that oxidizes matter and a collection filter that collects particulate matter contained in exhaust gas are arranged,
When performing filter regeneration to remove particulate matter collected by the collection filter, obtain the exhaust gas temperature in the collection filter,
When the obtained exhaust gas temperature is below the lower limit value of the temperature range suitable for continuous regeneration in which the particulate matter collected by the collection filter is oxidized and decomposed by nitrogen dioxide,
From the start to the end of the filter regeneration, the fuel addition device performs intermittent injection that repeats an injection period in which fuel is injected and a stop period in which fuel injection is stopped, and the acquired exhaust gas temperature is A control method for an exhaust gas purification system, characterized by maintaining a temperature range suitable for continuous regeneration.