JP6809181B2 - Exhaust gas purification system and its control method - Google Patents

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 for improving fuel efficiency and a control method thereof.

As a method of removing the collected particulate matter and regenerating the collection filter, forced regeneration is generally known. In forced regeneration, fuel is injected and supplied to the oxidation catalyst device to oxidize it, and the heat of the oxidation reaction generated by the oxidation is used to raise the exhaust gas temperature and collect it in the form of particles collected by a collection filter. The substance is incinerated and removed.

In this regard, an exhaust gas purification system having a plurality of oxidation catalyst devices has been proposed (see, for example, Patent Documents 1 and 2). However, in the forced regeneration in such an exhaust gas purification system, while the collection filter can be regenerated, it is necessary to raise the temperature of the exhaust gas to a high temperature of 500 degrees or higher. Therefore, when the frequency of forced regeneration increases, the fuel consumption required for regeneration of the collection filter becomes large, and there is a problem that fuel consumption deteriorates.

Japanese Unexamined Patent Publication No. 2006-266142 JP-A-2010-127125

By the way, as a method for removing the particulate matter collected by the collection filter, continuous regeneration is known in addition to the above-mentioned forced regeneration. In continuous regeneration, 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 in 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 faster the oxidation reaction between nitrogen dioxide and particulate matter, while nitrogen dioxide returns to nitric oxide at higher temperatures. Therefore, in order to effectively carry out continuous regeneration, the production of nitrogen dioxide in the oxidation catalyst device is performed while maintaining the exhaust gas temperature in the collection filter at a temperature suitable for continuous regeneration (for example, 250 ° C to 500 ° C). You need to increase the amount.

However, in an environment where a high concentration of fuel coexists, there is a problem that the production of nitrogen dioxide in the oxidation catalyst device is inhibited. 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 is difficult to achieve both.

An object of the present invention is to provide an exhaust gas purification system capable of reducing the frequency of forced regeneration and improving fuel efficiency, and a control method thereof.

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 flow of the exhaust gas 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 for exhaust gas, an oxidation catalyst device for oxidizing fuel and nitrogen oxides contained in exhaust gas, and a collection filter for collecting particulate matter contained in exhaust gas are arranged. A temperature acquisition device for acquiring the exhaust gas temperature in the collection filter, a control device connected to the temperature acquisition device and the fuel addition device, and the oxidation catalyst device include a temperature raising unit and a generation unit. The exhaust gas flow is provided with a branch portion that branches the exhaust gas flow into a plurality of parts on the upstream side of the oxidation catalyst device, and fuel is added from the fuel addition device by this branch portion. Filter regeneration that guides the exhaust gas to the temperature rising section and guides the exhaust gas to which no fuel is added from the fuel addition device to the generation section, and removes the particulate matter collected by the collection filter. When the exhaust gas temperature acquired by the temperature acquisition device falls below the lower limit of the temperature range suitable for continuous regeneration in which the particulate matter collected by the collection filter is decomposed and removed by nitrogen dioxide. The control device is characterized in that the fuel addition device is injected with fuel from the start to the end of the filter regeneration to maintain the acquired exhaust gas temperature in a temperature range suitable for the continuous regeneration. Is to be.
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 flow of the exhaust gas 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 for exhaust gas, an oxidation catalyst device for oxidizing fuel and nitrogen oxides contained in exhaust gas, and a collection filter for collecting particulate matter contained in exhaust gas are arranged. The oxidation catalyst device has a temperature rise section and a generation section, and is provided with a branch section that branches the exhaust gas flow into a plurality of parts upstream of the oxidation catalyst device with respect to the exhaust gas flow. The unit is configured to guide the exhaust gas to which fuel is added from the fuel addition device to the temperature raising section and to guide the exhaust gas to which no fuel is added from the fuel addition device to the generation section. The exhaust passage is composed of a branch pipe that branches into a plurality of passages, the fuel addition device and the temperature raising unit are arranged in one of the passages branched by the branch pipe, and the generation unit is in the other passage. Is characterized by being arranged.

The control method of the exhaust gas purification system of the present invention that achieves the above object is to use the exhaust gas in 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 for adding fuel, an oxidation catalyst device for oxidizing fuel and nitrogen oxides contained in exhaust gas, and a collection filter for collecting particulate matter contained in exhaust gas are arranged. In the control method of the exhaust gas purification system in which the oxidation catalyst device has a temperature raising unit and a generation unit, when the filter regeneration for removing the particulate matter collected by the collection filter is performed, the collection is performed. When the exhaust gas temperature in the filter is acquired and the acquired exhaust gas temperature falls below the lower limit of the temperature range suitable for continuous regeneration in which the particulate matter collected by the collection filter is oxidatively decomposed by nitrogen dioxide. Regarding the flow of exhaust gas, the flow of exhaust gas is branched into a plurality of parts on the upstream side of the oxidation catalyst device, and the exhaust gas to which fuel is added from the fuel addition device is guided to the temperature rising section and the fuel addition is performed. This method is characterized in that the exhaust gas to which no fuel is added is guided from the apparatus to the generation unit, and the acquired exhaust gas temperature is maintained in a temperature range suitable for the continuous regeneration.

According to the present invention, the flow of the exhaust gas is branched on the upstream side of the oxidation catalyst device to guide the exhaust gas to which the fuel has been added from the fuel addition device to the temperature rising section, and the fuel is added from the fuel addition device. By guiding the exhaust gas that has not been produced to the generation unit, an environment in which high-concentration fuel coexists in the oxidation catalyst device and an environment in which fuel does not coexist are created at the same time. Therefore, in the temperature rising section in an environment where high-concentration fuel coexists, the temperature of the exhaust gas can be raised by utilizing the heat of oxidation reaction generated by the oxidation of the fuel in the oxidation catalyst device. Further, in the production unit in an environment where a high concentration fuel does not coexist in the oxidation catalyst device, the amount of nitrogen dioxide produced can be increased to increase the concentration of nitrogen dioxide contained in the exhaust gas.

As a result, by maintaining the exhaust gas temperature at a temperature suitable for continuous regeneration and increasing the nitrogen dioxide concentration, it is advantageous to improve the oxidation removal rate of particulate matter by continuous regeneration, and it is continuous instead of forced regeneration. Regeneration can be used. Along with this, the frequency of forced regeneration can be reduced, the fuel consumption required for regeneration of the collection filter can be reduced, and fuel efficiency can be improved.

It is a block diagram which illustrates the engine which mounted the 1st Embodiment of the exhaust gas purification system of this invention. It is a perspective view which illustrates the branch part of FIG. 1, a fuel addition device, an oxidation catalyst device, and a collection filter. It is a flow chart which illustrates the control method of the exhaust gas purification system of FIG. It is a relational figure which illustrates the relationship of the exhaust gas temperature and the concentration of nitrogen dioxide with respect to the decomposition rate of the particulate matter in the collection filter of FIG. FIG. 5 is a relationship diagram illustrating the relationship between the exhaust gas temperature and the fuel concentration with respect to the nitrogen dioxide production rate in the oxidation catalyst device of FIG. It is a perspective view which illustrates the 2nd Embodiment of the exhaust gas purification system of this invention. It is a block diagram which illustrates the 3rd Embodiment of the exhaust gas purification system of this invention. It is a block diagram which illustrates the 4th Embodiment of the exhaust gas purification system of this invention. It is a block diagram which illustrates the 5th Embodiment of the exhaust gas purification system of this invention.

Hereinafter, embodiments of the exhaust gas purification system of the present invention and its control method will be described.

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

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

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, a pipe injection valve 21, an oxidation catalyst device 22, a collection filter 23, and a 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 at a position 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 that adds the fuel.

The oxidation catalyst device 22 is a columnar porous structure, which is partitioned by a porous partition wall made of ceramics and penetrates from an inlet where the exhaust gas G1 flows in to an outlet where the exhaust gas G1 flows out. A plurality of ventilation holes (cells) serving as roads are formed. The oxidation catalyst device 22 carries an oxidation catalyst that oxidizes hydrocarbons, carbon monoxide, and nitric oxide contained in the exhaust gas G1 on its porous partition wall. Examples of the oxidation catalyst include precious metals such as platinum (Pt), rhodium (Rh), and palladium (Pd).

The collection filter 23 is a columnar porous structure, and a plurality of ventilation holes are formed by a porous partition wall made of ceramics like the oxidation catalyst device 22. Unlike the oxidation catalyst device 22, the collection filter 23 has its ventilation holes blocked 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 stomata are alternately blocked.

The reducing agent injection valve 24 is inserted at an intermediate position of the exhaust passage 15 interposed between the collection filter 23 and the selective reduction catalyst device 25, with the injection port directed toward the flow direction of the exhaust gas G1. In the reducing agent injection valve 24, urea water is supplied from a urea water supply system including a urea water tank 28a and a urea water pump 28b, and urea water is added to the exhaust gas G1 as a reducing agent. The urea water supply system is provided with a cooling water pipe 29 through which the cooling water flows after cooling the engine body 13, and the cooling water warms the urea water tank 28a, the pipe through which the urea water flows, and the like. There is.

The selective reduction catalyst device 25 is a columnar porous structure, and similarly to the oxidation catalyst device 22, a plurality of ventilation holes are formed by a porous partition wall made of ceramics. Unlike the oxidation catalyst device 22, the selective reduction catalyst device 25 carries a selective reduction catalyst that reduces the nitrogen oxides contained in the exhaust gas G1 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 oxidatively decomposing ammonia or a function of adsorbing ammonia.

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

In the exhaust gas purification system 20, it is necessary to periodically remove the particulate matter collected by the collection filter 23. Forced regeneration and continuous regeneration can be exemplified as methods for removing the collected particulate matter.

In the forced regeneration, the exhaust gas temperature Tx in the collection filter 23 is raised to a temperature Ta suitable for forced regeneration (hereinafter referred to as the forced regeneration temperature Ta) or higher, and the particles are collected in the collection filter 23. The substance is burned and removed by 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, fuel is injected from the pipe injection valve 21, hydrocarbons are oxidized by the oxidation catalyst device 22, and the oxidation reaction generated by the oxidation is performed. 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 produced in the oxidation catalyst device 22 is increased to increase the amount of nitrogen dioxide contained in the exhaust gas G1. The concentration needs to be high.

The temperature range (Td to Tu) suitable for continuous reproduction is in the 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 a temperature equal to or lower than the forced regeneration temperature Ta, and is set to a temperature at which nitrogen dioxide can stably exist. As the temperature zone, the lower limit value Td is preferably set to 250 degrees and the upper limit value is set to 500 degrees, and the lower limit value Td is more preferably 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, when the engine 10 has a high rotation speed and a high load, when the exhaust gas temperature Tx reaches the forced regeneration temperature Ta, forced regeneration occurs spontaneously. Further, when the engine 10 has a high rotation 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, the forced regeneration and the continuous regeneration indicate a case where fuel is intentionally injected from the piping injection valve 21 by the control device 30.

If the frequency of forced regeneration by injecting fuel increases, fuel efficiency may deteriorate. Therefore, the exhaust gas purification system 20 of this embodiment intentionally creates an environment in which continuous regeneration occurs, thereby reducing the frequency of forced regeneration.

Specifically, in the exhaust gas purification system 20, the oxidation catalyst device 22 has a temperature raising unit 22a and a generation unit 22b, and includes a branching unit 40 on the upstream side of the oxidation catalyst device 22. Then, the exhaust gas purification system 20 branches the flow of the exhaust gas G1 by the branch portion 40, guides the exhaust gas to which the fuel is added to the temperature raising unit 22a, and generates the exhaust gas to which the fuel is not added. It is configured to lead to the portion 22b.

Further, 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 piping injection valve 21 to inject the exhaust gas temperature. It is configured to maintain Tx in a temperature range (Td to Tu) suitable for continuous reproduction.

As illustrated in FIG. 2, in the temperature raising unit 22a and the generation unit 22b, one columnar oxidation catalyst device 22 is divided in the xz plane and formed in a semicircular shape, and the flow direction of the exhaust gas G1. They are arranged in parallel in the y direction, which intersects the x direction.

The branch portion 40 is arranged on the upstream side of the oxidation catalyst device 22 with respect to the flow of the exhaust gas G1, and is composed of a partition member that branches the flow of the exhaust gas G1 into two exhaust gases G2 and G3. In this embodiment, the branch portion 40 is composed of a plate perpendicular to the inlet end face of the oxidation catalyst device 22. The branch portion 40 is erected from the downstream side to the upstream side with respect to the flow of the exhaust gas G1 from the inlet end face, and divides the inside of the exhaust passage 15 on the upstream side of the oxidation catalyst device 22 into two left and right.

When the inside of the exhaust passage 15 is partitioned by the branch portion 40, the exhaust gas G1 flowing through the exhaust passage 15 branches into two exhaust gases G2 and G3 between the tip portion of the branch portion 40 and the outlet of the oxidation catalyst device 22. To do. A piping injection valve 21 and a temperature raising unit 22a are arranged in the flow path of one of the branched exhaust gas G2, and a generation unit 22b is arranged in the flow path of the other exhaust gas G3.

The piping injection valve 21 may be arranged so as to add fuel to the exhaust gas G2 that passes through one of the branched flow paths partitioned by the branch portion 40 in the exhaust passage 15, and the exhaust gas G2 may be arranged. It may be arranged upstream from the flow path. When the piping injection valve 21 is arranged upstream of the flow path of the exhaust gas G2, the injection port is set to the exhaust gas G2 so that the fuel injected from the piping injection valve 21 does not enter the flow path of the exhaust gas G3. It is preferable to direct it to the flow path of.

Further, most of the exhaust gases G2 and G3 flowing into the oxidation catalyst device 22 flow along the ventilation holes, but the exhaust gases G2 and G3 may be mixed at the internal boundary portion of the oxidation catalyst device 22.

The control device 30 is connected to a piping injection valve 21, a reducing agent injection valve 24, a first temperature sensor 31, a differential pressure sensor 32, a second temperature sensor 33, a NOx sensor 34, and a 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 the values acquired by various sensors. Specifically, the control device 30 is hardware composed of 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 for acquiring 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, respectively. .. The first temperature sensor 31 acquires the temperature of the exhaust gas G1 passing through the inlet of the collection filter 23 and the temperature of the exhaust gas G1 passing 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 the sensor that directly acquires the exhaust gas temperature Tx, the rotation speed of the engine 10, the amount of fuel injected from the cylinder injection valve 12 and burned inside the cylinder 11, and the oxidation in the oxidation catalyst device 22. An apparatus for modeling and predicting the exhaust gas temperature Tx based on a reaction or the like may be used.

The differential pressure sensor 32 functions as a device for acquiring an estimateable value of 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. There is.

The second temperature sensor 33 functions as a device for acquiring an estimateable value of the purification state in the selective reduction catalyst device 25, and specifically, acquires the exhaust gas temperature in the selective reduction catalyst device 25. ..

The NOx sensor 34 functions as a device for acquiring 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 injection 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 for acquiring an estimateable value of the purification state in the selective reduction catalyst device 25, and specifically, acquires the urea water temperature in the urea water supply system.

Next, a control method of the exhaust gas purification system 20 will be described. This control method is performed at predetermined intervals from the start to the stop of the control device 30 and various sensors.

The control device 30 acquires parameters via various sensors (S110). The parameter is a parameter required for the reproduction determination of the collection filter 23. In this embodiment, the parameters are the exhaust gas temperature Tx acquired by various sensors, a value capable of estimating the amount of particulate matter deposited on the collection filter 23, and a value capable of estimating the purification state in the selective reduction catalyst device 25. Is. Specifically, the value at which the accumulated 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 purified 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 the lower limit value Td of the temperature zone suitable for continuous reproduction (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, if the exhaust gas temperature Tx is below the lower limit value Td without injecting fuel from the piping injection valve 21, the process returns to the start without controlling the injection of 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 the first threshold value. This first threshold value is set to a value at which it can be determined that the fuel consumption is deteriorated due to the pressure loss in the collection filter 23, which increases due to the accumulation of particulate matter 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 for 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 the second threshold value. This second threshold value is set to a value at which it can be determined that particulate matter is deposited on the collection filter 23 rather than the state of the first threshold value.

As conditions A and B, it suffices if it is possible to determine whether or not the collection filter 23 needs to be regenerated and whether or not forced regeneration is necessary for regeneration, that is, it is sufficient to determine the amount of particulate matter deposited, instead of the differential pressure sensor 32. For example, a PM sensor that measures particulate matter contained in the exhaust gas G1 may be used. Further, the accumulated amount of particulate matter may be modeled from the rotation speed of the engine 10 and the fuel injection amount.

When the exhaust gas temperature Tx is 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 the fuel injected from the piping injection valve 21 based on the exhaust gas temperature Tx acquired by the first temperature sensor 31. The temperature has been raised to a temperature suitable for (for example, 500 degrees or more).

On the other hand, when the exhaust gas temperature Tx is lower than 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. .. As described above, in the continuous regeneration, the exhaust gas temperature Tx is continuously regenerated by adjusting the injection amount of the 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 range (Td to Tu) suitable for.

Next, the control device 30 determines whether or not to end the reproduction 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 the third threshold value. This third threshold value is set to a value lower than the first threshold value under the condition A, and is set to a value at which it can be determined that the collection filter 23 has been regenerated.

In this way, when the collection filter 23 is regenerated, the process returns to the start.

As described above, in the exhaust gas purification system 20, when continuous regeneration is started, the branch portion 40 branches the flow of the exhaust gas G1 into two exhaust gases G2 and G3 on the upstream side of the oxidation catalyst device 22. Therefore, the exhaust gas G2 to which the fuel is added is guided from the pipe injection valve 21 to the temperature raising unit 22a, and the exhaust gas G3 to which the fuel is not added is guided to the generation unit 22b.

That is, an environment in which high-concentration fuel coexists in the oxidation catalyst device 22 and an environment in which fuel does not coexist are simultaneously created. Therefore, in the temperature raising unit 22a in an environment where high-concentration fuel coexists, the temperature of the exhaust gas G2 can be raised by utilizing the heat of oxidation reaction generated by the oxidation of the fuel. Further, in the generation unit 22b in an environment where high-concentration fuel does not coexist, the amount of nitrogen dioxide produced can be increased to increase the concentration of nitrogen dioxide contained in the exhaust gas G3.

As a result, by maintaining the exhaust gas temperature Tx in a temperature range (Td to Tu) suitable for continuous regeneration and increasing the nitrogen dioxide concentration, it becomes advantageous to improve the oxidation removal rate of particulate matter by continuous regeneration. , It becomes possible to use continuous playback instead of forced playback. Along with this, the frequency of forced regeneration by injecting fuel can be reduced, the fuel consumption required for regeneration of the collection filter 23 can be reduced, and fuel efficiency can be improved.

As illustrated in FIG. 4, 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 the particulate matter by continuous regeneration, it is necessary to maintain the exhaust gas temperature Tx high and increase the concentration of nitrogen dioxide.

As illustrated in FIG. 5, in an environment where a high concentration fuel coexists in the oxidation catalyst device 22, the concentration of nitrogen dioxide becomes lower than in an environment where a high concentration fuel does not coexist. 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 becomes low. In addition, when the exhaust gas temperature Tx exceeds the upper limit value Tu, the reaction of nitrogen dioxide returning to nitric oxide is promoted, so that the concentration of nitrogen dioxide becomes low.

As described above, maintaining the exhaust gas temperature for the purpose of effective continuous regeneration and increasing the concentration of nitrogen dioxide are contradictory. In this regard, the flow of the exhaust gas G1 is branched into two, the exhaust gas G2 and the G3, the exhaust gas G2 to which the fuel is added is guided to the temperature raising unit 22a, and the exhaust gas G3 to which the fuel is not added is generated. By guiding to the part 22b, it is possible to maintain the exhaust gas temperature and increase the concentration of nitrogen dioxide at the same time.

In the case of continuous regeneration, control may be performed to increase the 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 a control in which the injection amount and the injection timing of the fuel injected from the injector 12 are changed so that the cylinder 11 burns in a high temperature state and a high oxygen state.

In addition, when controlling to increase the emission amount, it is necessary to deal with nitrogen dioxide which has not completely reacted by the collection filter 23. Therefore, when the nitrogen oxide can be reduced in the selective reduction catalyst device 25, continuous regeneration may be performed. The state in which nitrogen oxides can be reduced by the selective reduction catalyst device 25 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. It is maintained at a temperature at which it can be hydrolyzed to ammonia. Further, the urea water temperature acquired by the third temperature sensor 35 is in a state where 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 the threshold value, and whether or not urea water can be injected from the reducing agent injection valve 24. In addition to this, it suffices if it is possible to determine whether or not the purified 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 a urea water pump. The temperature of the piping around 28b may be used. By doing so, it is possible to prevent the nitrogen dioxide that has passed through the collection filter 23 without reacting with the particulate matter from being reduced by the selective reduction catalyst device 25 and discharged to the outside. Further, the determination as to whether or not the nitrogen oxide can be reduced in the selective reduction catalyst device 25 may be added to the flow shown in FIG.

As illustrated in FIG. 6, in the exhaust gas purification system 20 of the second embodiment, the shape of the branch portion 40 is different from that of the first embodiment. In this embodiment, the branch portion 40 is formed in a tubular shape, and its axial direction is directed to the direction in which the exhaust gas G1 flows. The branch portion 40 divides the inside of the exhaust passage 15 on the upstream side of the oxidation catalyst device 22 into two inside and outside.

A piping injection valve 21 and a temperature rising portion 22a are arranged in the flow path of the exhaust gas G2 formed inside the branch portion 40, and the flow path of the exhaust gas G3 formed outside the branch portion 40. 22b is arranged in the generation unit 22b. In this embodiment, the temperature rising section 22a is formed in a columnar shape, and the generating section 22b is formed in a circular ring columnar shape.

As described above, the branch portion 40 may be configured so as to be able to partition the inside of the exhaust passage 15, and the shape of the partition member is not limited. Further, the exhaust gas branched by the branching portion 40 may be at least two or more, and for example, the oxidation catalyst device 22 may be divided into four parts, left, right, upper and lower.

If the temperature raising unit 22a is covered with the generation unit 22b as in the second embodiment, it is advantageous for the temperature of the generation unit 22b to rise. Further, even if the oxidation catalyst device 22 is divided into four parts, left and right, upper and lower, and the exhaust gases G2 and G3 are passed alternately in the circumferential direction, it is advantageous for the temperature of the generation unit 22b to rise as in the second embodiment.

As illustrated in FIG. 7, the exhaust gas purification system 20 of the third embodiment has a branch portion 40 different from that of the above-described embodiment. In this embodiment, the branch portion 40 is composed of a branch pipe that branches the exhaust passage 15 into two passages.

The oxidation catalyst device 22 is composed of two members, a first member and a second member, and the first member functions as a temperature raising unit 22a and the second member functions as a generation unit 22b.

The first member and the second member are columnar porous structures, which are partitioned by a porous partition wall made of ceramics to form a plurality of vent holes (cells). An oxidation catalyst is supported on the partition wall. The oxidation catalyst supported on the first member is preferably a catalyst suitable for the oxidation of hydrocarbons, and the oxidation catalyst supported on the second member is preferably a catalyst suitable for the oxidation of nitrogen oxides.

The branch portion 40 is a pipe that is arranged upstream of the oxidation catalyst device 22 with respect to the flow of the exhaust gas G1 and branches the exhaust passage 15 into two passages. When the exhaust passage 15 is branched into two passages by the branch portion 40 and then merged, the exhaust gas G1 branches into two exhaust gases G2 and G3 between the time when the exhaust gas G1 branches at the branch pipe 29a and the time when the exhaust gas G1 merges at the merge pipe 29b. To do. A piping injection valve 21 and a temperature raising unit 22a are arranged in the passage of one of the branched exhaust gas G2, and a generation unit 22b is arranged in the passage of the other exhaust gas G3. The branch portion 40 may be configured so that the exhaust passage 15 can be branched into a plurality of passages, and the number of branches of the branch pipe is not limited.

When the branch portion 40 is composed of a branch pipe, a confluence portion 41 is provided on the downstream side of the flow of the exhaust gas G1 with respect to the oxidation catalyst device 22. The merging portion 41 is a pipe that joins the passage branched by the branch portion 40 into one exhaust passage 15.

As described above, the branch portion 40 is composed of a branch pipe, and the oxidation catalyst device 22 is physically divided into two members, a first member that functions as a temperature raising unit 22a and a second member that functions as a generation unit 22b. By separating them, it is advantageous to create an environment in which high-concentration fuels coexist more reliably and an environment in which fuels do not coexist at the same time. Further, by dividing the oxidation catalyst device 22 by function, it becomes possible to use an oxidation catalyst suitable for the temperature raising unit 22a and an oxidation catalyst suitable for the generation unit 22b, so that continuous regeneration can be performed more effectively. it can.

As illustrated in FIG. 8, in the exhaust gas purification system 20 of the fourth embodiment, the piping injection valve 21 is arranged in all the passages branched by the branch portion 40 with respect to the third embodiment. Is different.

In the exhaust gas purification system 20, the control device 30 causes each piping injection valve 21 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 one of the pipes. When fuel is injected into the injection valve 21, the other piping injection valve 21 is configured to stop the injection of fuel.

A piping injection valve 21 is provided as a fuel addition device for each of the flow paths branched by the branching portion 40 in this way, and intermittent injection is performed to provide the temperature raising section 22a and the generating section 22b of the oxidation catalyst device 22. Can be replaced alternately. This is advantageous for maintaining the exhaust gas temperature Tx in a temperature range suitable for continuous regeneration and at a temperature equal to or higher than the lower limit value Td at which the generation unit 22b is activated.

As illustrated in FIG. 9, the exhaust gas purification system 20 of the fifth embodiment uses the cylinder injection valve 12 instead of the piping injection valve 21 as the fuel addition device and branches as compared with the third embodiment. Part 40 is different. In this embodiment, the branch portion 40 is composed of two exhaust manifolds and two passages.

When the cylinder injection valve 12 is used as the fuel addition device, fuel is added to the exhaust gas G1 from the cylinder injection valve 12 by post injection. That is, in this embodiment, two of the cylinder injection valves 12 that inject fuel into the cylinder 11 function as a fuel addition device by performing post injection, and the remaining two are configured not to perform post injection. Has been done.

In the branch portion 40, the exhaust manifold is divided into two, and among the ports, the passage through which the exhaust gas G2 to which fuel is added by post injection passes and the exhaust gas G3 to which no fuel is added pass. Branch to the aisle.

As described above, as the fuel addition device, it is sufficient that the fuel can be added until the exhaust gas G1 reaches the oxidation catalyst device 22. For example, the piping injection valve 21 is installed on the exhaust manifold 14 on the upstream side of the temperature raising unit 22a. It may be provided in each port of.

In the above-described embodiment, when the exhaust gas temperature Tx is raised, after injection from the cylinder injection valve 12 at the timing when the piping injection valve 21 injects the fuel in addition to the fuel injection from the piping injection valve 21. The injection may be performed.

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

In the above-described embodiment, an example of switching between forced regeneration and continuous regeneration according to conditions has been described, but if the collection filter 23 can be regenerated by sufficiently removing particulate matter by continuous regeneration, forced regeneration It may be configured not to perform. That is, setting the second threshold value to a larger value is advantageous in reducing the frequency of forced reproduction.

When the branch portion 40 is composed of a partition member, the branch portion 40 may be configured to extend from the tip end to the end of the oxidation catalyst device 22 to partition the inside of the oxidation catalyst device 22. Further, when the branch portion 40 is composed of a branch pipe, the oxidation catalyst device 22 may be used as one member, and the two passages branched by the branch pipe may be connected to the inlet of the oxidation catalyst device 22. Good.

10 Engine 15 Exhaust passage 20 Exhaust gas purification system 21 Piping injection valve 22 Oxidation catalyst device 22a Temperature rise section 22b Generation section 23 Collection filter 40 Branch section G2 Exhaust gas with fuel added G3 Exhaust gas without fuel

Claims (5)

A fuel addition device that adds fuel to the exhaust gas in order from the upstream side to the downstream side with respect to the flow of the exhaust gas, and the fuel and nitrogen oxidation contained in the exhaust gas into the exhaust passage through which the exhaust gas discharged from the engine passes. In an exhaust gas purification system in which an oxidation catalyst device that oxidizes an object and a collection filter that collects particulate matter contained in the exhaust gas are arranged.
A temperature acquisition device for acquiring the exhaust gas temperature in the collection filter, a temperature acquisition device, and a control device connected to the fuel addition device are provided.
The oxidation catalyst device has a temperature raising unit and a generating unit.
With respect to the flow of exhaust gas, a branch portion is provided on the upstream side of the oxidation catalyst device to branch the flow of exhaust gas into a plurality of branches, and the branch portion raises the temperature of the exhaust gas to which fuel is added from the fuel addition device. In addition to guiding to the unit, the exhaust gas to which fuel has not been added from the fuel addition device is guided to the generation unit .
When the filter is regenerated to remove the particulate matter collected by the collection filter, the exhaust gas temperature acquired by the temperature acquisition device uses nitrogen dioxide to collect the particulate matter collected by the collection filter. When the temperature falls below the lower limit of the temperature range suitable for continuous regeneration to be decomposed and removed, the control device injects fuel into the fuel addition device from the start to the end of the filter regeneration to obtain the obtained exhaust gas temperature. An exhaust gas purification system characterized in that it is configured to maintain a temperature range suitable for continuous regeneration . The branch portion is composed of a partition member that partitions the inside of the exhaust passage into a plurality of parts, and the fuel addition device and the temperature riser portion are arranged in one of the flow paths that is partitioned and branched by the partition member. The exhaust gas purification system according to claim 1, wherein the generation unit is arranged in the other flow path. The branch portion is composed of a branch pipe that branches the exhaust passage into a plurality of passages, and the fuel addition device and the temperature riser portion are arranged in one passage branched by the branch pipe, and the other passage. The exhaust gas purification system according to claim 1, wherein the generation unit is arranged in the air. A fuel addition device that adds fuel to the exhaust gas in order from the upstream side to the downstream side with respect to the flow of the exhaust gas, and the fuel and nitrogen oxidation contained in the exhaust gas into the exhaust passage through which the exhaust gas discharged from the engine passes. In an exhaust gas purification system in which an oxidation catalyst device that oxidizes an object and a collection filter that collects particulate matter contained in the exhaust gas are arranged.
The oxidation catalyst device has a temperature raising unit and a generating unit.
With respect to the flow of exhaust gas, a branch portion is provided on the upstream side of the oxidation catalyst device to branch the flow of exhaust gas into a plurality of branches, and the branch portion raises the temperature of the exhaust gas to which fuel is added from the fuel addition device. In addition to guiding to the unit, the exhaust gas to which fuel has not been added from the fuel addition device is guided to the generation unit .
The branch portion is composed of a branch pipe that branches the exhaust passage into a plurality of passages, and the fuel addition device and the temperature riser portion are arranged in one passage branched by the branch pipe, and the other passage. An exhaust gas purification system characterized in that the generation unit is arranged in the air. A fuel addition device that adds fuel to the exhaust gas in order from the upstream side to the downstream side with respect to the flow of the exhaust gas, and the fuel and nitrogen oxidation contained in the exhaust gas into the exhaust passage through which the exhaust gas discharged from the engine passes. An exhaust gas in which an oxidation catalyst device for oxidizing an object and a collection filter for collecting particulate matter contained in the exhaust gas are arranged, and the oxidation catalyst device has a temperature raising unit and a generation unit. In the control method of the purification system
When performing filter regeneration for removing particulate matter collected by the collection filter, the exhaust gas temperature in the collection filter is acquired.
When the acquired exhaust gas temperature falls below the lower limit of the temperature range suitable for continuous regeneration in which the particulate matter collected by the collection filter is oxidatively decomposed by nitrogen dioxide.
Regarding the flow of exhaust gas, the flow of exhaust gas is branched into a plurality of parts on the upstream side of the oxidation catalyst device, and the exhaust gas to which fuel is added from the fuel addition device is guided to the temperature riser and the fuel addition is performed. A control method for an exhaust gas purification system, which comprises guiding an exhaust gas to which no fuel is added from an apparatus to the generation unit and maintaining the acquired exhaust gas temperature in a temperature range suitable for the continuous regeneration.