JP2017040239A - Exhaust emission control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control device enabling improvement of NOx elimination performance.SOLUTION: An exhaust emission control device 30 include: a first addition valve 38 for adding fuel to exhaust gas; a first selective reduction type catalyst 39 for reducing NOx by using the fuel in the exhaust gas as a reduction agent; a second addition valve 44 for adding fuel to exhaust gas; a second selective reduction type catalyst 45 having a higher temperature activation region compared to the first selective reduction type catalyst 39 and the second selective reduction type catalyst 45 for reducing NOx by using the fuel in the exhaust gas as a reduction agent and generating NHby the reduction of NOx; and a third selective reduction type catalyst 47 for reducing NOx by using NHgenerated by the second selective reduction type catalyst 45 as a reduction agent.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an exhaust gas purification device that purifies nitrogen oxides in engine exhaust gas, and relates to an exhaust gas purification device that purifies nitrogen oxides using engine fuel as a reducing agent.

  Conventionally, as an exhaust purification device for a diesel engine, an HC-SCR catalyst that selectively reduces nitrogen oxides (hereinafter referred to as NOx) using a fuel of an engine mainly composed of hydrocarbon (HC) as a reducing agent. Some use (Carbon Carbon-Selective Catalytic Reduction). For example, Patent Document 1 discloses an exhaust purification device in which HC-SCR catalysts having different activation temperature ranges are arranged in series and fuel is added to each HC-SCR catalyst. According to this exhaust purification device, NOx can be reduced by the HC-SCR catalyst in a wide temperature range.

JP 2012-92690 A

  However, from the viewpoint of environmental protection and the like, the exhaust purification device is required to further improve the NOx purification performance. An object of the present invention is to provide an exhaust purification device that can improve NOx purification performance.

An exhaust emission control device that solves the above-mentioned problem is located downstream of the first addition valve that adds fuel to the exhaust gas flowing through the exhaust passage, and uses NOx using the fuel in the exhaust gas as a reducing agent. A first selective reduction catalyst that reduces the amount of gas, a second addition valve that is located downstream of the first selective reduction catalyst, adds fuel to exhaust gas, and is located downstream of the second addition valve, a high temperature activity range than 1 selective reduction catalyst second selective reduction catalyst, the second for generating NH ₃ by the reduction of NOx with reducing NOx using the fuel in the exhaust gas as a reducing agent A selective reduction type catalyst, a third selective reduction type catalyst located downstream of the second selective reduction type catalyst and reducing NOx using NH ₃ produced by the second selective reduction type catalyst as a reducing agent; The first addition amount, which is the amount of fuel added by the first addition valve, and the previous And a control unit for controlling the second amount is the addition amount of the fuel by the second addition valve.

According to the above configuration, the exhaust gas to which fuel is added by the first addition valve flows into the first selective reduction catalyst, and NOx is reduced using the fuel as a reducing agent. Further, the exhaust gas to which fuel is added by the second addition valve is reduced to NOx while NOx is reduced using the fuel as a reducing agent in the second selective reduction catalyst having a higher activation temperature range than the first selective reduction catalyst. (Hereinafter referred to as NH ₃ ) is generated. In the third selective reduction catalyst, NOx is reduced using NH ₃ produced by the second selective reduction catalyst as a reducing agent. According to such a configuration, the NOx purification performance can be enhanced.

  In the exhaust emission control device, the control unit obtains the temperature of the first selective reduction catalyst and the temperature of the second selective reduction catalyst, and a first NOx amount flowing into the first selective reduction catalyst; The second NOx amount flowing into the second selective reduction catalyst is calculated, and when the first selective reduction catalyst is in an active state, the first addition amount is increased as the first NOx amount is increased. It is preferable to increase the second addition amount as the amount of the second NOx increases when the two-selective reduction catalyst is in an active state.

  According to the above configuration, the addition amount of the first addition valve is increased or decreased according to the first NOx amount flowing into the first selective reduction catalyst, and the second addition according to the second NOx amount flowing into the second selective reduction catalyst. The amount of valve added is increased or decreased. As a result, the NOx purification performance can be improved while suppressing the fuel consumption for the purpose of NOx purification.

The exhaust purification apparatus preferably further includes a filter that traps particulate matter in the exhaust gas, and the first selective reduction catalyst includes a catalyst layer that forms a surface layer of the filter.
According to the above configuration, when the filter and the first selective reduction catalyst are mounted on the exhaust purification device, the volume occupied by the exhaust purification device can be reduced.

  In the exhaust emission control device, the control unit calculates an accumulation amount of particulate matter in the filter, and when the accumulation amount exceeds an upper limit value, regenerates the filter by adding fuel from the first addition valve. It is preferable to execute a regeneration process and a recovery process for recovering sulfur poisoning of the second selective catalytic reduction catalyst by adding fuel from the second addition valve during the regeneration process.

According to the above configuration, the first selective reduction catalyst and the second selective reduction catalyst are easily maintained in a clean state. As a result, the NOx purification performance can be improved.
Further, in order to recover the sulfur poisoning of the second selective reduction catalyst, it is necessary to raise the temperature of the second selective reduction catalyst. Further, in the second selective reduction catalyst, a fuel oxidation reaction occurs in parallel with the NOx reduction reaction using the fuel as a reducing agent. Therefore, the temperature of the second selective reduction catalyst increases due to the inflow of fuel.

  According to the above configuration, since the recovery process is performed during the regeneration process, the exhaust gas flowing into the second selective catalytic reduction catalyst is the exhaust gas whose temperature has increased with the regeneration process of the filter. That is, the exhaust gas whose temperature has been raised by the regeneration process of the filter can be used for raising the temperature of the second selective reduction catalyst. As a result, the temperature of the second selective reduction catalyst in the recovery process can be efficiently increased.

  In the exhaust purification apparatus, the control unit may calculate a sulfur poisoning amount in the second selective reduction catalyst, and execute the recovery process on condition that the poisoning amount exceeds a threshold value. preferable.

  According to the above configuration, the recovery process is performed on the condition that the poisoning amount of sulfur in the second selective reduction catalyst exceeds the threshold value. Thereby, since execution of an excessive recovery process is suppressed, the amount of fuel consumption required for exhaust gas purification can be suppressed.

It is a schematic structure figure showing the schematic structure of the engine system carrying the exhaust gas purification device of one embodiment. It is sectional drawing which shows the cross-section near the surface of a 3rd selective reduction catalyst. The structure of the HC catalyst layer and NH ₃ catalyst layer is a diagram schematically illustrating. It is a block diagram which shows an example of a structure of a control apparatus. It is a timing chart about the implementation time of reproduction processing and recovery processing. It is a graph which shows an example of the result of having compared NOx purification rate.

An embodiment of an exhaust emission control device will be described with reference to FIGS. First, an overall configuration of an engine system equipped with an exhaust emission control device will be described with reference to FIG.
As shown in FIG. 1, the engine system includes a diesel engine 10 (hereinafter referred to as an engine 10). A plurality of cylinders 12 are formed in the cylinder block 11 of the engine 10. Fuel is injected into each cylinder 12 from an injector 13. Connected to the cylinder block 11 are an intake manifold 14 for supplying intake air to each cylinder 12 and an exhaust manifold 15 into which exhaust gas from each cylinder 12 flows.

  In the intake passage 16 connected to the intake manifold 14, an air cleaner (not shown), a compressor 18 constituting a turbocharger 17, and an intercooler 19 are provided in order from the upstream side. The exhaust passage 20 connected to the exhaust manifold 15 is provided with a turbine 22 that is connected to the compressor 18 via a connecting shaft and constitutes the turbocharger 17.

  The engine system includes an EGR passage 25 that connects the exhaust manifold 15 and the intake passage 16. An EGR cooler 26 and an EGR valve 27 are provided in the EGR passage 25. When the EGR valve 27 is in an open state, a part of the exhaust gas is introduced into the intake passage 16 through the EGR passage 25 as EGR gas. The cylinder 12 is supplied with a working gas that is a mixed gas of exhaust gas and intake air.

  In the cylinder 12, an air-fuel mixture of the working gas and the fuel injected by the injector 13 burns. The exhaust gas from the cylinder 12 flows into the exhaust passage 20 through the exhaust manifold 15, passes through the turbine 22, and then flows into the exhaust purification device 30.

  The exhaust purification device 30 includes a first oxidation catalyst 31 (ATC: After Turbo Catalyst) in the exhaust passage 20 through which exhaust gas flows. The first oxidation catalyst 31 oxidizes the fuel in the exhaust gas and raises the temperature of the exhaust gas.

  The first oxidation catalyst 31 has a monolithic carrier made of ceramic or metal, and a catalyst layer coated on the monolithic carrier. The catalyst layer has, for example, a particulate catalyst support made of zeolite or alumina, and a catalyst metal supported on the catalyst support. The catalytic metal is at least one of platinum-based elements such as platinum, palladium, and rhodium. The first oxidation catalyst 31 has a temperature range in which the first oxidation catalyst temperature, which is the temperature, is equal to or higher than the first oxidation lower limit temperature and equal to or lower than the first oxidation upper limit temperature in the active temperature range.

  The exhaust purification device 30 includes a first addition unit 32 that adds fuel to the exhaust gas downstream of the first oxidation catalyst 31 in the exhaust passage 20. The first addition unit 32 includes a first fuel passage 35 connected to a fuel tank 34 that stores fuel as a reducing agent. The fuel tank 34 may be a fuel tank that stores fuel injected by the injector 13, or may be a fuel tank that is provided separately from the fuel tank. The first addition unit 32 includes a pump 36 and a first adjustment valve 37 in the first fuel passage 35. The pump 36 is a pump that uses, for example, an engine as a power source, and pumps the fuel in the fuel tank 34 to the first adjustment valve 37 at a predetermined pressure. The first adjustment valve 37 is a valve that can change the cross-sectional area of the first fuel passage 35 and adjusts the amount of fuel that passes through the first adjustment valve 37. The first addition unit 32 includes a first addition valve 38 located in the exhaust passage 20. The first addition unit 32 adds fuel to the exhaust gas from the first addition valve 38 when the first adjustment valve 37 is open, and the first addition valve 38 when the first adjustment valve 37 is closed. Do not add fuel to the exhaust gas. The addition of fuel by the first addition unit 32 is controlled by a control device 70 described later. The first addition valve 38 may be a fuel injection valve in which the function of the first adjustment valve 37 is built.

  The exhaust purification device 30 includes a first selective reduction catalyst 39 downstream of the first addition valve 38 in the exhaust passage 20. The first selective reduction catalyst 39 includes a second oxidation catalyst 39c and a third oxidation catalyst 40c that are located in the first muffler portion 20A that is the diameter-expanded portion of the exhaust passage 20. The second oxidation catalyst 39c has the strongest oxidizing power among the exhaust purification devices 30, and has a function of oxidizing the fuel in the exhaust gas to raise the temperature of the exhaust gas, and using the fuel in the exhaust gas as a reducing agent. And a NOx reduction function for reducing NOx. The second oxidation catalyst 39c has a monolithic carrier made of ceramic or metal and a catalyst layer coated on the monolithic carrier. The catalyst layer has, for example, a particulate catalyst support made of zeolite or alumina, and a catalyst metal supported on the catalyst support. The catalytic metal is at least one of platinum-based elements such as platinum, palladium, and rhodium. The second oxidation catalyst 39c has a temperature range in which the temperature of the second oxidation catalyst, which is the temperature, is equal to or higher than the second oxidation lower limit temperature (eg, 150 ° C.) and lower than the second oxidation upper limit temperature (eg, 350 ° C.). Have.

  The exhaust purification device 30 includes a filter 40 (DPF: Diesel Particulate Filter) downstream of the second oxidation catalyst 39c in the first muffler unit 20A. The filter 40 has a filter function for capturing particulate matter (hereinafter referred to as PM (Particulate Matter)) in the exhaust gas, and a NOx reduction function for reducing NOx using the fuel in the exhaust gas as a reducing agent. When the filter 40 is heated to a regeneration temperature Tfr (for example, 600 ° C.), PM is incinerated to regenerate the filter function.

  The filter 40 is composed of, for example, a filter body that is a wall flow filter made of ceramic or stainless steel having excellent heat resistance, and a third oxidation catalyst 40c that is a catalyst layer coated on the filter body. The third oxidation catalyst 40c has a higher function as a selective reduction catalyst than the second oxidation catalyst 39c, and uses the fuel in the exhaust gas as a reducing agent to reduce NOx in the exhaust gas.

  The third oxidation catalyst 40c is composed of, for example, a particulate catalyst support made of zeolite or alumina, and a catalyst metal supported on the catalyst support. The catalyst metal is at least one of platinum-based elements such as platinum, palladium, and rhodium. Further, the third oxidation catalyst 40c has a third oxidation catalyst temperature, which is the temperature, equal to or higher than the third oxidation lower limit temperature (eg, 200 ° C.) and lower than the third oxidation upper limit temperature (eg, 300 ° C.) as an active temperature range. . That is, the first selective reduction catalyst 39 has a first upper limit temperature (for example, 300 ° C.) that is equal to or higher than the first lower limit temperature (for example, 200 ° C.) at which both the second oxidation catalyst 39c and the third oxidation catalyst 40c are activated. ) It has the following temperature range as the active temperature range.

  The exhaust purification device 30 includes a second addition unit 41 that adds fuel to the exhaust gas flowing through the exhaust passage 20 downstream of the filter 40 in the exhaust passage 20. The second addition unit 41 includes a second fuel passage 42 connected between the pump 36 and the first adjustment valve 37 in the first fuel passage 35. The second addition unit 41 includes a second adjustment valve 43 that can change the flow path cross-sectional area of the second fuel passage 42. A predetermined pressure of fuel is pumped to the second regulating valve 43 by a pump 36 provided in the first fuel passage 35. The second addition unit 41 includes a second addition valve 44 that adds the fuel that has passed through the second adjustment valve 43 to the exhaust gas. That is, the second addition unit 41 adds fuel to the exhaust gas from the second addition valve 44 when the second adjustment valve 43 is in the open state, and the second addition portion 41 when the second adjustment valve 43 is in the closed state. No fuel is added from the valve 44 to the exhaust gas. The addition of fuel by the second addition unit 41 is controlled by a control device 70 described later. The second addition valve 44 may be a fuel injection valve in which the function of the second adjustment valve 43 is built.

The exhaust purification device 30 includes a second selective reduction catalyst 45 that reduces NOx using the fuel in the exhaust gas as a reducing agent downstream of the second addition valve 44 in the exhaust passage 20. The second selective reduction catalyst 45 is located in the second muffler part 20B, which is the next enlarged diameter part of the first muffler part 20A. The second selective reduction catalyst 45 has a monolith support made of ceramic or metal and a catalyst layer coated on the monolith support. The catalyst layer contains silver alumina or silver zeolite. The second selective reduction catalyst 45 has a relatively high temperature range in which the second catalyst temperature, which is the temperature, is equal to or higher than the second lower limit temperature (eg, 200 ° C.) and lower than the second upper limit temperature (eg, 650 ° C.). As a region, NH ₃ is produced in the reaction of reducing NOx. Further, in the second selective reduction catalyst 45 having the above-described configuration, the reduction reaction of NOx by the fuel proceeds in preference to the oxidation reaction of the fuel, so that part of the fuel passes without reacting. Therefore, it is possible to use the passed fuel as a reducing agent for the subsequent catalyst.

The exhaust purification device 30 includes a third selective reduction catalyst 47 downstream of the second selective reduction catalyst 45 in the second muffler portion 20B.
As shown in FIG. 2, the third selective reduction catalyst 47 includes a monolith support 48 made of ceramic or metal, an HC catalyst layer 49 stacked on the surface of the monolith support 48, and an NH stacked on the HC catalyst layer 49. ₃ catalyst layers 50.

  The HC catalyst layer 49 reduces NOx by using the fuel in the exhaust gas as a reducing agent. The HC catalyst layer 49 includes a particulate catalyst carrier and copper supported on the catalyst carrier. The material for forming the catalyst carrier is zeolite having a porous structure. This zeolite is a porous material having pores into which hydrocarbons can enter. The HC catalyst layer 49 is configured by coating a monolithic carrier with a particulate catalyst carrier supporting copper.

The NH ₃ catalyst layer 50 reduces NOx using NH ₃ generated in the second selective reduction catalyst 45 as a reducing agent. The NH ₃ catalyst layer 50 includes a particulate catalyst carrier and copper supported on the catalyst carrier. The material for forming the catalyst carrier is zeolite having a porous structure. This zeolite is a porous material that has pores that reject the ingress of hydrocarbons while allowing the ingress of NH ₃ . The NH ₃ catalyst layer 50 is configured by coating a particulate catalyst carrier supporting copper on a monolith carrier on which the HC catalyst layer 49 is formed. The third selective reduction catalyst 47 has a third catalyst temperature, which is the temperature, equal to or higher than the third lower limit temperature (eg, 200 ° C.) and lower than the third upper limit temperature (eg, 600 ° C.) in the active temperature range.

As shown in FIG. 3, in the third selective reduction catalyst 47, NH ₃ (ammonia) enters the holes 51 h of the catalyst carrier 51 constituting the NH ₃ catalyst layer 50, while HC (hydrocarbon) is introduced into the catalyst carrier 51. It does not enter the hole 51h. Therefore, HC reaches the HC catalyst layer 49 through the gaps 52 between the particles of the catalyst carrier 51. Then, the HC that has reached the HC catalyst layer 49 enters the holes 53 h of the catalyst carrier 53 constituting the HC catalyst layer 49. Thereby, in the NH ₃ catalyst layer 50, NOx is reduced using NH ₃ entering the hole 51h as a reducing agent, and in the HC catalyst layer 49, NOx is reduced using HC entering the hole 53h as a reducing agent. The

As shown in FIG. 1, the exhaust purification device 30 includes a fourth oxidation catalyst 54 downstream of the third selective reduction catalyst 47 in the second muffler portion 20B. The fourth oxidation catalyst 54 oxidizes the fuel and NH ₃ that have passed through the third selective reduction catalyst 47. The fourth oxidation catalyst 54 has a monolithic carrier made of ceramic or metal, and a catalyst layer coated on the monolithic carrier. The catalyst layer has, for example, a particulate catalyst support made of zeolite or alumina, and a catalyst metal supported on the catalyst support. The catalytic metal is at least one of platinum-based elements such as platinum, palladium, and rhodium.

  The exhaust purification device 30 includes various sensors. The exhaust purification device 30 includes an intake air amount sensor 55 that detects an intake air amount upstream of the compressor 18 in the intake passage 16. The exhaust purification device 30 includes temperature sensors that detect the temperature of exhaust gas at various locations in the exhaust passage 20. The temperature sensor 56 is located between the first oxidation catalyst 31 and the first addition valve 38 and detects the ATC exhaust temperature that is the temperature of the exhaust gas that has passed through the first oxidation catalyst 31. The temperature sensor 57 is located between the first addition valve 38 and the second oxidation catalyst 39c, and detects the first exhaust temperature, which is the temperature of the exhaust gas flowing into the second oxidation catalyst 39c. The temperature sensor 58 is located between the second oxidation catalyst 39c and the filter 40, and detects an inflow temperature that is the temperature of the exhaust gas flowing into the filter 40. The temperature sensor 59 is located between the filter 40 and the second addition valve 44 and detects an outflow temperature that is the temperature of the exhaust gas that has passed through the filter 40. The temperature sensor 60 is located between the second addition valve 44 and the second selective reduction catalyst 45 and detects a second exhaust temperature that is the temperature of the exhaust gas flowing into the second selective reduction catalyst 45. The temperature sensor 61 is located downstream of the fourth oxidation catalyst 54 and detects a third exhaust temperature that is the temperature of the exhaust gas that has passed through the fourth oxidation catalyst 54.

  The exhaust purification device 30 includes NOx sensors 62 and 63 that detect the NOx concentration of the exhaust gas. The NOx sensor 62 is located between the filter 40 and the second addition valve 44 and detects an intermediate concentration that is the NOx concentration of the exhaust gas that has passed through the filter 40. The NOx sensor 63 is located downstream of the fourth oxidation catalyst 54 and detects the exhaust concentration that is the NOx concentration of the exhaust gas that has passed through the fourth oxidation catalyst 54.

  The exhaust purification device 30 includes pressure sensors 64 and 65 that detect the pressure of the exhaust gas. The pressure sensor 64 is located between the second oxidation catalyst 39c and the filter 40, and detects the inflow pressure that is the pressure of the exhaust gas flowing into the filter 40. The pressure sensor 65 is located between the filter 40 and the second addition valve 44 and detects the outflow pressure that is the pressure of the exhaust gas that has passed through the filter 40.

  The exhaust purification device 30 also includes an engine speed sensor 66 that detects the engine speed and an accelerator position sensor 67 that detects the accelerator position. The various sensors output signals indicating the detected values to the control device 70 that performs overall control of the engine system.

  As shown in FIG. 4, the control device 70 temporarily stores a CPU, a ROM that stores various data such as various control programs and activation temperatures of each catalyst, and calculation results and various data in various calculations. It is mainly composed of a microcomputer having a RAM. Based on various information acquired based on signals from various sensors and various control programs and various data stored in the ROM, the control device 70 injects fuel by the injector 13, adds fuel by the first addition valve 38, The addition of fuel by the second addition valve 44 is controlled. The control device 70 treats the intake air amount as an exhaust flow rate that is a flow rate of the exhaust gas.

  The control device 70 controls fuel injection by the injector 13. The control device 70 calculates the main injection amount based on the engine speed, the accelerator opening, and the like, and controls the injector 13 so that the main injection amount of fuel is injected into the cylinder 12. In addition, the control device 70 performs post-injection in which fuel is injected from the injector 13 during the expansion process of the combustion cycle in the regeneration process of the filter 40. The post injection amount is, for example, an amount that can be oxidized by the first oxidation catalyst 31 based on the ATC exhaust temperature, and is selected from an injection table that associates the ATC exhaust temperature with the post injection amount.

  The control device 70 executes normal processing for NOx purification. In the normal processing, the control device 70 acquires the exhaust flow rate, the first exhaust temperature, the second exhaust temperature, and the engine speed, and adds the fuel by the first addition unit 32 and the fuel addition by the second addition unit 41. And control.

  The control device 70 acquires the first exhaust temperature from the temperature sensor 57 as a first temperature acquisition unit, and adds fuel from the first addition valve 38 when the first exhaust temperature is equal to or higher than the first addition temperature. The first addition temperature is a first exhaust temperature at which it is determined that the second oxidation catalyst 39c and the third oxidation catalyst 40c are in an active state. The control device 70 functions as a first NOx amount calculation unit, and is a NOx amount that flows into the third oxidation catalyst 40c from the engine model in which the engine speed, the main injection amount, the intake air amount and the like are set as parameters. The amount of 1NOx is calculated. Based on the first NOx amount and the first exhaust temperature, the control device 70 determines the amount of fuel added by the first addition valve 38 so that the reduction amount of NOx in the second oxidation catalyst 39c and the third oxidation catalyst 40c is maximized. A certain first addition amount is calculated. That is, the first addition amount increases as the first NOx amount increases.

  The control device 70 acquires the second exhaust temperature from the temperature sensor 60 as a second temperature acquisition unit, and adds fuel from the second addition valve 44 when the second exhaust temperature is equal to or higher than the second addition temperature. The second addition temperature is a second exhaust temperature at which the second and third selective reduction catalysts 45 and 47 are determined to be in an active state. The control device 70 functions as a second NOx amount calculation unit, and calculates a second NOx amount that is NOx flowing into the second selective reduction catalyst 45 based on the exhaust gas flow rate and the intermediate concentration. Based on the second NOx amount and the second exhaust temperature, the control device 70 uses the second addition valve 44 so that the amount of NOx reduction in the second selective reduction catalyst 45 and the third selective reduction catalyst 47 is maximized. A second addition amount that is an addition amount of fuel is calculated. That is, the second addition amount increases as the second NOx amount increases.

  The control device 70 executes a regeneration process for regenerating the filter function of the filter 40. The control device 70 calculates the PM accumulation amount Mf in the filter 40, and performs normal processing on the condition that the first exhaust temperature is equal to or higher than the first addition temperature and the accumulation amount Mf exceeds the upper limit value Mf1. Forcibly end and start the playback process. The control device 70 calculates the deposition amount Mf based on the pressure loss at the filter 40 based on the exhaust gas flow rate, the inflow pressure and the outflow pressure.

  In the regeneration process, the control device 70 performs post injection by the injector 13 and addition of fuel by the first addition valve 38. The fuel by the post injection is oxidized by the first oxidation catalyst 31, and the fuel added by the first addition valve 38 is oxidized by the second oxidation catalyst 39c. That is, the exhaust gas whose temperature has been increased stepwise flows into the filter 40. The control device 70 calculates the amounts of various fuels so that the inflow temperature becomes a target value indicating the regeneration temperature Tfr of the filter 40.

  In the regeneration process, the control device 70 calculates the PM combustion amount Gpm. The control device 70 calculates the average temperature of the filter 40 based on the exhaust flow rate, the temperature difference between the inflow temperature and the outflow temperature, and the like. The control device 70 calculates the PM combustion amount Gpm based on the average temperature and the PM combustion speed. When the combustion amount Gpm reaches the accumulation amount Mf, the control device 70 ends the regeneration process and resumes the normal process. Note that if the first exhaust temperature falls below the first addition temperature during the regeneration process, the control device 70 stops the regeneration process and resumes the normal process.

  Here, in a diesel engine, sulfur oxide (SOx) is generated with combustion of fuel or lubricating oil. Sulfur oxide flows into the exhaust purification device 30 together with the exhaust gas and adheres to various catalysts. The catalyst performance of various catalysts deteriorates due to the adhesion of sulfur oxides, that is, sulfur poisoning. Therefore, it is preferable that the catalyst is periodically recovered from sulfur poisoning. In particular, the second selective reduction catalyst 45 is easily affected by sulfur poisoning. This is because, in the first and second oxidation catalysts 31, 39c and the filter 40, sulfur oxides are easily removed by the temperature rise accompanying the regeneration process, and the exhaust gas that has passed through the filter 40 is the second choice. Based on these, it flows into the reduced catalyst 45. The control device 70 executes a recovery process for recovering sulfur poisoning in the second selective reduction catalyst 45 and raises the temperature of the second selective reduction catalyst 45 to a recovery temperature Tsr at which sulfur oxides are removed.

  In the second selective reduction catalyst 45, a fuel oxidation reaction also occurs in parallel with the NOx reduction reaction using the fuel as a reducing agent. Therefore, the temperature of the second selective reduction catalyst 45 is increased by the supply of fuel. However, it is difficult to raise the temperature of the second selective reduction catalyst 45 to the recovery temperature Tsr only by the oxidation reaction of fuel. Therefore, the control device 70 performs a recovery process during the regeneration process of the filter 40. That is, the control device 70 executes the recovery process when the accumulation amount Mf of the filter 40 exceeds the upper limit value Mf1 in a state where the poisoning amount Ms exceeds the threshold value Ms1.

  The control device 70 calculates the poisoning amount Ms of the second selective reduction catalyst 45 based on, for example, the integrated value of the main injection amount from the previous recovery process. Then, when the poisoning amount Ms exceeds a predetermined threshold value Ms1, the control device 70 executes the recovery process together with the regeneration process of the filter 40. The threshold value Ms1 is a value at which the second selective reduction catalyst 45 is sufficiently recovered from sulfur poisoning by executing the recovery process together with the regeneration process of the filter 40.

  In the recovery process, the controller 70 adds the second addition valve 44 so that the temperature of the second selective catalytic reduction catalyst 45 reaches the recovery temperature Tsr based on, for example, the temperature difference between the recovery temperature Tsr and the second exhaust temperature. Calculate the quantity. The control device 70 controls the second adjustment valve 43 so that the calculated addition amount of fuel is added from the second addition valve 44. And the control apparatus 70 complete | finishes a recovery process with the completion | finish of a reproduction | regeneration process, and resumes a normal process.

  That is, as shown in FIG. 5, the control device 70 starts the calculation of the deposition amount Mf and the calculation of the poisoning amount Ms from time t1 when the engine is started. The control device 70 executes the regeneration process several times until the poisoning amount Ms exceeds the threshold value Ms1. The control device 70 executes the regeneration process and the recovery process at time t6 when the deposition amount Mf exceeds the upper limit value Mf1 while the poisoning amount Ms exceeds the threshold value Ms1. Thereby, the filter function of the filter 40 is regenerated and the sulfur poisoning of the second selective reduction catalyst 45 is recovered.

The operation of the exhaust emission control device 30 will be described with reference to FIG.
According to the exhaust purification device 30 described above, the exhaust gas to which fuel has been added by the first addition valve 38 is reduced by the second oxidation catalyst 39c and the third oxidation catalyst 40c by the NOx in the exhaust gas using the fuel as a reducing agent. The Further, the exhaust gas to which the fuel is added by the second addition valve 44 is reduced in NOx while reducing NOx using the fuel as a reducing agent in the second selective reduction catalyst 45 having an activation temperature range higher than that of the third oxidation catalyst 40c. ₃ is generated. In the third selective reduction catalyst 47, NOx is reduced using the fuel that has passed through the second selective reduction catalyst 45 and NH ₃ produced in the second selective reduction catalyst 45 as a reducing agent. According to such a configuration, the NOx purification performance can be enhanced.

  FIG. 6 is a graph showing an example of the result of comparing the NOx purification performance when the engine 10 is operated in the test cycle of WHTC, WHSC, and WNTE. The embodiment is the exhaust purification device 30 described above. In the comparative example, the first oxidation catalyst 31, the first addition valve 38, the second oxidation catalyst 39c, the filter 40 including the third oxidation catalyst 40c, the fourth oxidation catalyst 54, and the like are arranged in order from the upstream side of the exhaust passage. Exhaust gas purification device. As shown in FIG. 6, in the exhaust purification device 30 of the example, it was confirmed that the NOx purification performance was improved as compared with the exhaust purification device of the comparative example.

According to the exhaust purification device 30 of the above embodiment, the effects listed below can be obtained.
(1) According to the exhaust purification device 30, NOx purification performance can be enhanced.
(2) The control device 70 calculates the first addition amount that is the amount of fuel added by the first addition valve 38 so that the NOx reduction amount in the second oxidation catalyst 39c and the third oxidation catalyst 40c is maximized. Further, the control device 70 calculates the second addition amount that is the amount of fuel added by the second addition valve 44 so that the NOx reduction amount in the second selective reduction catalyst 45 and the third selective reduction catalyst 47 is maximized. To do. Thereby, the NOx purification performance can be improved while suppressing the fuel consumption for the purpose of NOx purification.

  (3) Since the third oxidation catalyst 40c is a catalyst layer constituting the surface layer of the filter 40, the volume occupied by the exhaust purification device 30 can be reduced when the filter and the third oxidation catalyst are mounted.

  (4) By performing the recovery process during the regeneration process, the exhaust gas whose temperature has been raised by the combustion of PM flows into the second selective reduction catalyst 45. That is, the exhaust gas whose temperature has been raised by the regeneration process of the filter 40 can be used for raising the temperature of the second selective reduction catalyst 45. As a result, the temperature of the second selective reduction catalyst 45 in the recovery process can be efficiently increased.

  (5) In addition, the recovery process is executed when the poisoning amount Ms in the second selective reduction catalyst 45 exceeds the threshold value Ms1. Thereby, since execution of an excessive recovery process is suppressed, the fuel consumption accompanying a recovery process can be suppressed.

  (6) The exhaust purification device 30 includes a first oxidation catalyst 31 and a second oxidation catalyst 39c, and performs post-injection by the injector 13 and addition of fuel by the first addition valve 38 in the regeneration process of the filter 40. Thereby, the temperature of the exhaust gas flowing into the filter 40 can be efficiently raised. As a result, the time required for the reproduction process can be shortened.

  (7) Further, since the second oxidation catalyst 39c located immediately before the filter 40 has the strongest oxidizing power, the exhaust gas flowing into the filter 40 can be effectively heated in the regeneration process of the filter 40. it can. Further, it is possible to suppress the temperature drop of the exhaust gas until it flows into the filter 40. As a result, the time required for the reproduction process can be shortened.

(8) The exhaust purification device 30 includes a fourth oxidation catalyst 54 downstream of the third selective reduction catalyst 47. As a result, the fuel and NH ₃ that have passed through the third selective reduction catalyst 47 are oxidized. As a result, the degree of freedom for the first addition amount and the second addition amount is improved.

In addition, the said embodiment can also be suitably changed and implemented as follows.
The controller 70 is not limited to when the poisoning amount Ms exceeds the threshold value Ms1, and may execute the recovery process every time the regeneration process is performed. According to this, it becomes easy to maintain the state with little sulfur poisoning about the 2nd selective reduction catalyst 45, and the purification | cleaning performance of NOx is further improved.

  -The execution of the recovery process is not limited to the execution of the reproduction process. In this case, it is preferable that the exhaust purification device 30 is equipped with a heating unit that raises the temperature of the second selective reduction catalyst 45, such as an electric heater. Further, the control device 70 may not perform the recovery process.

  The exhaust purification device 30 may include the third oxidation catalyst 40c and the filter 40 separately. At this time, the third oxidation catalyst 40c may be positioned downstream of the filter 40 in order to suppress the adhesion of PM to the third oxidation catalyst 40c. Further, the exhaust purification device 30 does not have to be regenerated and does not have to include a filter.

The first addition amount may be a constant amount regardless of the first NOx amount. Further, the second addition amount may be a constant amount regardless of the second NOx amount.
The third selective reduction catalyst 47 only needs to have a function of reducing NOx using NH ₃ produced by the second selective reduction catalyst 45 as a reducing agent, and only the NH ₃ catalyst layer 50 is used as a catalyst layer. You may have as.

  -The control apparatus 70 should just acquire the temperature of the 1st selective reduction catalyst 39 as a 1st temperature acquisition part. Therefore, the control device 70 calculates, for example, the average value of the inflow temperature and the outflow temperature as the temperature of the third oxidation catalyst 40 c, and uses the calculated temperature of the third oxidation catalyst 40 c as the temperature of the first selective reduction catalyst 39. Also good. Moreover, the control apparatus 70 should just acquire the temperature of the 2nd selective reduction catalyst 45 as a 2nd temperature acquisition part. For this reason, the control device 70, for example, a temperature gradient based on the second exhaust temperature and the third exhaust temperature, the heat capacity of the second selective reduction catalyst 45, the relative position of the second selective reduction catalyst 45 with respect to the temperature sensor 60, and the like. Based on this, the temperature of the second selective catalytic reduction catalyst 45 may be calculated.

  The first NOx amount is not limited to being calculated from the engine model. For example, a NOx sensor that detects the inflow concentration that is the NOx concentration of the exhaust gas flowing into the second oxidation catalyst 39c is installed in the exhaust passage 20, and this inflow It may be calculated based on the concentration and the exhaust flow rate.

  The second NOx amount is not limited to the calculation based on the detected value of the NOx sensor 62 and the exhaust gas flow rate. For example, the engine speed, the main injection amount, the intake air amount, and the first addition amount are set as parameters. It may be calculated from the model.

The exhaust purification device 30 may have a configuration in which the fourth oxidation catalyst 54 is omitted.
The activation temperature range of the first selective reduction catalyst 39 may be a temperature range in which at least one of the second oxidation catalyst 39c and the third oxidation catalyst 40c is in an active state. According to such a configuration, for example, when the second oxidation catalyst 39c is activated at a temperature lower than that of the third oxidation catalyst 40c, even if only the second oxidation catalyst 39c is in an active state, the fuel is supplied from the first addition valve 38. Added. At this time, in the second oxidation catalyst 39c, the reduction of NOx using the fuel as the reducing agent and the temperature increase of the exhaust gas due to the oxidation of the fuel are performed. The temperature increase of the third oxidation catalyst 40c can be promoted by the temperature increase of the exhaust gas by the second oxidation catalyst 39c.

DESCRIPTION OF SYMBOLS 10 ... Diesel engine, 13 ... Injector, 20 ... Exhaust passage, 20A ... 1st muffler part, 20B ... 2nd muffler part, 30 ... Exhaust gas purification device, 31 ... 1st oxidation catalyst, 32 ... 1st addition part, 37 ... First regulating valve, 38 ... first addition valve, 39 ... first selective reduction catalyst, 39c ... second oxidation catalyst, 40 ... filter, 40c ... third oxidation catalyst, 41 ... second addition section, 43 ... second Adjustment valve 44 ... second addition valve 45 ... second selective reduction catalyst 47 ... third selective reduction catalyst 49 ... HC catalyst layer 50 ... NH ₃ catalyst layer 54 ... fourth oxidation catalyst 55 ... Intake air amount sensor, 56, 57, 58, 59, 60, 61 ... temperature sensor, 62, 63 ... NOx sensor, 64, 65 ... pressure sensor, 70 ... control device.

Claims (5)

A first addition valve for adding fuel to the exhaust gas flowing through the exhaust passage;
A first selective reduction type catalyst that is located downstream of the first addition valve and reduces NOx using fuel in exhaust gas as a reducing agent;
A second addition valve located downstream of the first selective reduction catalyst and for adding fuel to the exhaust gas;
A second selective reduction catalyst located downstream of the second addition valve and having a temperature active region higher than that of the first selective reduction catalyst, wherein NOx is reduced using fuel in the exhaust gas as a reducing agent. And the second selective reduction catalyst that generates NH ₃ by reduction of NOx,
A third selective reduction catalyst that is located downstream of the second selective reduction catalyst and reduces NOx using NH ₃ produced by the second selective reduction catalyst as a reducing agent;
An exhaust emission control device comprising: a control unit that controls a first addition amount that is an addition amount of fuel by the first addition valve and a second addition amount that is an addition amount of fuel by the second addition valve. The controller is
The temperature of the first selective reduction catalyst and the temperature of the second selective reduction catalyst are acquired, and the first NOx amount flowing into the first selective reduction catalyst and the first selective reduction catalyst flowing into the second selective reduction catalyst are obtained. 2NOx amount is calculated,
When the first selective reduction catalyst is in an active state, the first addition amount increases as the first NOx amount increases, and when the second selective reduction catalyst is in an active state, the second NOx amount increases. The exhaust emission control device according to claim 1, wherein the second addition amount is increased. A filter for capturing particulate matter in the exhaust gas;
The exhaust emission control device according to claim 1 or 2, wherein the first selective reduction catalyst includes a catalyst layer constituting a surface layer of the filter. The control unit calculates the amount of particulate matter deposited on the filter, and performs regeneration processing to regenerate the filter by adding fuel from the first addition valve when the amount of deposition exceeds an upper limit value. The exhaust emission control device according to claim 3, wherein a recovery process for recovering sulfur poisoning of the second selective reduction catalyst is performed by adding fuel from the second addition valve during the regeneration process. 5. The exhaust gas purification according to claim 4, wherein the control unit calculates a sulfur poisoning amount in the second selective reduction catalyst, and executes the recovery process on the condition that the poisoning amount exceeds a threshold value. apparatus.