JP6469457B2 - Exhaust purification equipment - Google Patents

Description

  The present invention relates to an exhaust purification device that purifies nitrogen oxides contained in engine exhaust gas, and relates to an exhaust 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 problems is located downstream of a burner that can raise the temperature of exhaust gas flowing through an exhaust passage, a first addition valve that adds fuel to the exhaust gas, and the burner and the first addition valve. , A filter that traps particulate matter contained in exhaust gas, which reduces NOx using an oxidation catalyst that oxidizes nitrogen monoxide in the exhaust gas to convert it into nitrogen dioxide and fuel in the exhaust gas as a reducing agent A first selective reduction type catalyst, wherein the oxidation catalyst is formed on the upstream side of the first selective reduction type catalyst, and is located downstream of the filter and adds fuel to the exhaust gas. An addition valve and 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, using fuel in exhaust gas as a reducing agent NOx is reduced and N said second selective reduction catalyst to produce a NH ₃ by reduction of x, the second is located downstream of the selective reduction catalyst, NOx and NH ₃ to the second selective reduction catalyst is produced using a reducing agent And a controller that controls the burner to a combustion state when at least one of the oxidation catalyst and the first selective reduction catalyst is in an inactive state.

According to the above configuration, the temperature of the oxidation catalyst and the first selective catalyst is promoted by controlling the burner to the combustion state when at least one of the oxidation catalyst and the first selective reduction catalyst is in an inactive state. The Thereby, reduction of NOx by the first selective reduction catalyst can be realized at an early stage. Further, when the burner is in the combustion state, the temperature increase of the second and third selective reduction catalysts is also promoted, so that NOx by the second selective reduction catalyst using the fuel added by the second addition valve as a reducing agent. And reduction of NOx by the third selective reduction catalyst using NH ₃ produced by the second selective reduction catalyst as a reducing agent can be realized at an early stage. In addition, since part of nitrogen monoxide (hereinafter referred to as NO) in the exhaust gas is converted into nitrogen dioxide (hereinafter referred to as NO ₂ ) in the oxidation catalyst, the particulate matter of the filter is continuously removed with this NO _2. It can be oxidized. This makes it easier for the first selective reduction catalyst to be maintained in a clean state, so that the opportunity for contact between the first selective reduction catalyst and NOx in the exhaust gas increases, and NOx is reduced by the first selective reduction catalyst. Is done efficiently. As a result, the NOx purification performance can be improved.

In the exhaust emission control device, it is preferable that the control unit controls the burner to a combustion state when the second selective reduction catalyst is in an inactive state.
According to the above configuration, for example, even when the oxidation catalyst and the first selective reduction catalyst are in an active state, the burner is controlled to be in a combustion state when the second selective reduction catalyst is in an inactive state. As a result, the temperature increase of the second selective reduction catalyst is promoted, and NOx reduction by the second selective reduction catalyst can be realized at an early stage.

In the exhaust emission control device, it is preferable that the control unit controls the burner to a combustion state when the third selective reduction catalyst is in an inactive state.
According to the above configuration, for example, even when the first selective reduction catalyst and the second selective reduction catalyst are in an active state, the burner is controlled to be in a combustion state when the third selective reduction catalyst is in an inactive state. As a result, the temperature increase of the third selective reduction catalyst is promoted, and NOx reduction by the third selective reduction catalyst can be realized at an early stage.

  In the above exhaust purification apparatus, the burner includes the first addition valve and an ignition unit that ignites the fuel added by the first addition valve, and the control unit includes the oxidation catalyst and the first selective reduction catalyst. When the fuel is in an active state, the burner may be controlled to an addition state in which the fuel added by the first addition valve is not combusted.

  According to the above configuration, the fuel can be supplied to the burner and the fuel can be added to the exhaust gas by the first addition valve. Thereby, the configuration for supplying fuel to the burner and the configuration for adding fuel to the exhaust gas are made common, and the configuration of the exhaust emission control device can be simplified.

In the exhaust emission control device, the third selective reduction catalyst is a laminated structure, and an HC catalyst layer that reduces NOx using fuel as a reducing agent, and the third selective reduction catalyst laminated on the HC catalyst layer. It is preferable to provide a surface layer of the type catalyst, and an NH ₃ catalyst layer that reduces NOx using NH ₃ produced by the second selective reduction catalyst as a reducing agent.

According to the above configuration, in the third selective reduction catalyst, NOx can be reduced using the remaining fuel in the exhaust gas as the reducing agent in addition to NH ₃ produced by the second selective reduction catalyst.

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 a perspective view which shows typically an example of the perspective structure of a filter, Comprising: It is a figure which exposes and shows a part of filter body. 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 flowchart which shows an example of the process which selects the operating state of a burner. It is a graph which shows an example of the result of having compared the purification performance of NOx. It is a graph which shows an example of the result of having compared the catalyst size. It is a flowchart which shows the other example of the process which selects the operating state of a burner.

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). The cylinder block 11 of the engine 10 is formed with six cylinders 12 arranged in a row. 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 is provided in the EGR passage 25, and an EGR valve 27 capable of changing the flow path cross-sectional area of the EGR passage 25 is provided on the intake passage 16 side of the EGR cooler 26. 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 burner 31 that can raise the temperature of the exhaust gas. The burner 31 has a first addition part 32 for adding fuel to the exhaust gas flowing in the exhaust passage 20 and an ignition part 33 for igniting the fuel added to 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 ignition unit 33 is, for example, a spark plug or a glow plug, and is driven by power supplied from a power supply device (not shown) to ignite the fuel added by the first addition unit 32. The ignited fuel burns with oxygen remaining in the exhaust gas as an oxidant. The addition of fuel by the first addition unit 32 and the driving of the ignition unit 33 are controlled by a control device 70 described later. The control device 70 controls the operation state of the burner 31 to any one of the stop state, the combustion state, and the addition state through the control of the first addition unit 32 and the ignition unit 33. The stop state is a state in which the first addition unit 32 does not add fuel. The combustion state is a state where the fuel added by the first addition unit 32 burns, and the addition state is a state where the fuel added by the first addition unit 32 does not burn.

  The burner 31 may include an air supply unit that can supply air to the fuel added by the first addition unit 32. According to such a configuration, the degree of freedom regarding the amount of fuel that can be added by the first addition unit 32 is improved while suppressing the amount of unburned fuel generated in the burner 31.

  The exhaust purification device 30 includes a filter 40 downstream of the burner 31 in the exhaust passage 20. The filter 40 has a filter function for capturing particulate matter (PM) in exhaust gas, an oxidation function for oxidizing fuel and NO in the exhaust gas, and NOx using the fuel in the exhaust gas as a reducing agent. NOx reduction function for reducing When the filter 40 is heated to a regeneration temperature Tfr (for example, 600 ° C.) by the burner 31, the particulate matter is incinerated to regenerate the filter function.

As shown in FIG. 2, the filter 40 includes, for example, a filter body 40a that is a wall flow filter made of ceramic or stainless steel having excellent heat resistance, and an oxidation catalyst 40b that is a catalyst layer coated on the filter body 40a. And a first selective reduction catalyst 40c. Oxidation catalyst 40b is formed on the upstream side of the first selective reduction catalyst 40c, converts NO in the exhaust gas as well as oxidizing fuel in the exhaust gas to the NO ₂ oxidation. The first selective reduction catalyst 40c is formed in a portion other than the oxidation catalyst 40b, and uses the fuel that has passed through the oxidation catalyst 40b as a reducing agent to reduce NOx in the exhaust gas.

  The oxidation catalyst 40b has a particulate catalyst carrier and a catalyst metal supported on the catalyst carrier. The material for forming the catalyst carrier is, for example, zeolite or alumina. The catalytic metal is at least one of platinum-based elements such as platinum, palladium, and rhodium. When the catalyst carrier is zeolite, the oxidation catalyst 40b is composed of zeolite particles in which catalytic metal ions are substituted with zeolite cations. When the catalyst carrier is alumina, the oxidation catalyst 40b is composed of γ-alumina particles supporting a catalyst metal or θ-alumina particles supporting a catalyst metal. The oxidation catalyst 40b contains 1 g to 6 g of catalyst metal per liter so that the oxidation reaction of fuel and NO in the exhaust gas has priority over the reduction reaction of NOx using the fuel in the exhaust gas as a reducing agent. Configured as follows. Further, the oxidation catalyst 40b has a temperature range in which the oxidation catalyst temperature Tox, which is the temperature, is equal to or higher than the lower limit oxidation temperature ToxL (for example, 150 ° C.) and lower than the upper limit oxidation temperature ToxH (for example, 350 ° C.).

The oxidation catalyst 40b is formed in the range of the length Lb from the upstream end of the filter 40 having the full length L. This length Lb is preferably set to a smaller value in the range of 10% or more of the total length L and 90% or less of the total length L. By setting the length Lb to 10% or more of the total length L, the temperature rise of the particulate matter accompanying the oxidation of the fuel, and the oxidation of the particulate matter by NO ₂ converted from NO, thereby the particulate matter It becomes easy to start combustion. That is, the regeneration of the filter 40 during the operation of the engine 10 is easily performed continuously. Further, when the length Lb is set to 90% or less of the total length L, the NOx purification action in the first selective reduction catalyst 40c can be reliably obtained. Further, by reducing the length Lb, more fuel is supplied to the first selective reduction catalyst 40c, and the NOx purification performance of the first selective reduction catalyst 40c can be improved. In addition, the cost of the filter 40 can be reduced by reducing the amount of catalyst metal used.

  The first selective reduction catalyst 40c has a particulate catalyst carrier and a catalyst metal supported on the catalyst carrier. The material for forming the catalyst carrier is, for example, zeolite or alumina. The catalyst metal is at least one of platinum-based elements such as platinum, palladium, and rhodium. When the catalyst carrier is zeolite, the first selective reduction catalyst 40c is composed of zeolite particles in which catalytic metal ions are substituted with zeolite cations. When the catalyst carrier is alumina, the first selective reduction catalyst 40c is composed of γ-alumina particles supporting a catalyst metal or θ-alumina particles supporting a catalyst metal. The first selective reduction catalyst 40c has a catalyst metal of 0 per liter so that the NOx reduction reaction using the fuel in the exhaust gas as a reducing agent takes precedence over the oxidation reaction of the fuel and NO in the exhaust gas. It is comprised so that it may contain. The first selective reduction catalyst 40c has a temperature range in which the first catalyst temperature Tc1, which is the temperature, is equal to or higher than the first lower limit temperature Tc1L (eg, 200 ° C.) and lower than the first upper limit temperature Tc1H (eg, 300 ° C.). It has as an active temperature range.

  That is, the filter 40 includes an oxidation catalyst 40b and a first selective reduction catalyst 40c made of the same type of catalytic metal, and the oxidation catalyst 40b has a concentration of catalytic metal higher than that of the first selective reduction catalyst 40c. Is the high part. In the filter 40, since the oxidation catalyst 40b and the first selective reduction catalyst 40c have a stronger oxidizing power than the second selective reduction catalyst 45 described later, most of the fuel in the exhaust gas is consumed. Note that the filter 40 may be configured by further coating the oxidation catalyst 40b on the filter body 40a that is entirely coated with the first selective reduction catalyst 40c. The filter 40 may be configured by coating the filter main body 40a with the oxidation catalyst 40b and the first selective reduction catalyst 40c in different regions.

  The exhaust purification device 30 includes a second addition unit 41 that adds fuel to the exhaust gas flowing in 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 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 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. When the catalyst layer contains silver alumina, the second selective reduction catalyst 45 is formed by coating, for example, γ-alumina particles supporting silver or θ-alumina particles supporting silver on a monolith support. Composed. When the catalyst layer contains silver zeolite, the second selective reduction catalyst 45 is configured, for example, by coating a monolithic carrier with zeolite particles in which silver ions are replaced with cations contained in the zeolite. The second selective reduction catalyst 45 has a relatively high temperature range in which the second catalyst temperature Tc2 as the temperature is equal to or higher than the second lower limit temperature Tc2L (for example, 200 ° C.) and equal to or lower than the second upper limit temperature Tc2H (for example, 650 ° C.). As an active temperature range, and NH ₃ is generated in a reaction for 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 exhaust passage 20.
As shown in FIG. 3, the third selective reduction catalyst 47 includes a monolithic carrier 48 made of ceramic or metal, an HC catalyst layer 49 laminated on the surface of the monolithic carrier 48, and an NH laminated 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. ZSM-5 type zeolite or beta type zeolite can be applied to this zeolite. The pore diameter of the ZSM-5 type zeolite and the beta type zeolite is, for example, 5 to 8 mm, which is larger than the molecular diameter of the hydrocarbon contained in the fuel. That is, ZSM-5 type zeolite and beta type zeolite are porous materials 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. As this zeolite, a zeolite having a chabazite structure is applicable, for example, a SAPO-34 type zeolite is applicable. SAPO is a silicoaluminophosphate. The pore diameter of the SAPO-34 type zeolite is, for example, _{3 to 4} mm, which is smaller than the molecular diameter of the hydrocarbon contained in the fuel and larger than the molecular diameter of NH ₃ . In other words, the SAPO-34 type zeolite is a porous material having pores that refuse to enter hydrocarbons but allow NH ₃ to enter. 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 temperature range in which the third catalyst temperature Tc3, which is the temperature, is equal to or higher than the third lower limit temperature Tc3L (eg, 200 ° C.) and lower than the third upper limit temperature Tc3H (eg, 600 ° C.). Have as a zone.

As shown in FIG. 4, 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

  The exhaust purification device 30 includes an intake air amount sensor 55 that detects an intake air amount Qa upstream of the compressor 18 in the intake passage 16. The exhaust purification device 30 includes a first temperature sensor 56 that detects the first exhaust temperature Te1 between the burner 31 and the filter 40, and a second exhaust temperature between the second addition valve 44 and the second selective reduction catalyst 45. A second temperature sensor 57 for detecting Te2, a third temperature sensor 58 for detecting the third exhaust temperature Te3 downstream of the third selective reduction catalyst 47, and an engine speed sensor 59 for detecting the engine speed Ne are provided. . Various sensors output a signal indicating each detected value to the control device 70. Further, a signal indicating the fuel injection amount Qf is input to the control device 70 from an injection control unit 60 that controls fuel injection from the injector 13.

  The control device 70 is a microcomputer having a CPU, a ROM in which various data such as various control programs and activation temperatures of each catalyst are stored, and a RAM in which various calculation results and various data are temporarily stored. It is composed around. The control device 70 acquires various information based on signals from various sensors and the like. The control device 70 controls the operating state of the burner 31 by controlling the first regulating valve 37 and the ignition unit 33 based on the various information acquired and the various control programs and various data stored in the ROM. The addition of fuel by the second addition unit 41 is controlled by controlling the second adjustment valve 43. Note that the control device 70 treats the intake air amount Qa as the exhaust flow rate Qe, which is the exhaust gas flow rate.

  As described above, the burner 31 has a stop state, a combustion state, and an addition state. The control device 70 controls the operating state of the burner 31 by controlling the first regulating valve 37 and the ignition unit 33 as follows.

  When the burner 31 is in the stop state, the control device 70 controls the first adjustment valve 37 to be closed. When controlling the burner 31 from the stop state to the combustion state, the control device 70 supplies power to the ignition unit 33 for a predetermined time and controls the first adjustment valve 37 from the closed state to the open state. Thereafter, the control device 70 keeps the burner 31 in the combustion state by continuously controlling the first regulating valve 37 to the open state. When controlling the burner 31 from the stop state to the addition state, the control device 70 controls the first adjustment valve 37 from the closed state to the open state without supplying power to the ignition unit 33. Thereafter, the control device 70 keeps the burner 31 in the added state by continuing to control the first regulating valve 37 to the open state.

  When controlling the burner 31 from the addition state to the combustion state, the control device 70 supplies power to the ignition unit 33 for a predetermined time and maintains the first adjustment valve 37 in the open state. When controlling the burner 31 from the combustion state to the addition state, the control device 70 does not supply power to the ignition unit 33, for example, by controlling the first adjustment valve 37 to a closed state for a predetermined time, thereby burning the fuel. Then, the first adjustment valve 37 is again controlled to open.

  The control device 70 controls the operating state of the burner 31 and executes normal processing for controlling the addition of fuel by the second addition unit 41. The control device 70 acquires the intake air amount Qa (exhaust flow rate Qe), the first exhaust temperature Te1, the second exhaust temperature Te2, the third exhaust temperature Te3, the engine speed Ne, and the fuel injection amount Qf. The controller 70 calculates the oxidation catalyst temperature Tox and the first catalyst temperature Tc1. The control device 70 substitutes, for example, the exhaust flow rate Qe, the first exhaust temperature Te1, the second exhaust temperature Te2, and the like into the arithmetic expression for obtaining the oxidation catalyst temperature Tox and the arithmetic expression for obtaining the first catalyst temperature Tc1. Thus, the oxidation catalyst temperature Tox and the first catalyst temperature Tc1 are calculated. These arithmetic expressions are set based on, for example, the mass and heat capacity of each of the filter body 40a, the oxidation catalyst 40b, and the first selective reduction catalyst 40c. The control device 70 calculates the second catalyst temperature Tc2 and the third catalyst temperature Tc3. The control device 70 includes, for example, an exhaust flow rate Qe, a second exhaust temperature Te2, and a third exhaust temperature Te3 in an arithmetic expression for obtaining the second catalyst temperature Tc2 and an arithmetic expression for obtaining the third catalyst temperature Tc3. The second catalyst temperature Tc2 and the third catalyst temperature Tc3 are calculated by substituting etc. These arithmetic expressions are set based on the mass and heat capacity of each of the second selective reduction catalyst 45 and the third selective reduction catalyst 47, for example.

  The control device 70 calculates the particulate matter deposition amount Mf in the filter 40 separately from the normal processing. When the calculated deposition amount Mf exceeds the upper limit value, the normal processing is forcibly terminated and the filter function of the filter 40 is performed. The playback process for playing back is executed. For example, the control device 70 calculates the deposition amount Mf based on the pressure loss or the like in the filter 40. In the regeneration process, the control device 70 raises the first catalyst temperature Tc1 to the regeneration temperature Tfr by controlling the burner 31 to the combustion state. The control device 70 calculates the accumulation amount Mf even when the burner 31 is in the combustion state. When the accumulation amount Mf falls below the lower limit value, the regeneration process is terminated and the normal process is resumed.

The operation of the exhaust emission control device 30 will be described with reference to FIG.
As shown in FIG. 5, in the normal process, the control device 70 acquires various information based on signals from various sensors (step S11). The control device 70 calculates various catalyst temperatures Tox, Tc1, Tc2, and Tc3 according to the above-described processing based on the information acquired in step S11 and various arithmetic expressions stored in the ROM. (Step S12).

  Next, the control device 70 determines whether at least one of the oxidation catalyst 40b and the first selective reduction catalyst 40c is in an inactive state as the first condition (step S13). When the oxidation catalyst temperature Tox is less than the oxidation lower limit temperature ToxL or the first catalyst temperature Tc1 is less than the first lower limit temperature Tc1L, that is, when the first condition is satisfied (step S13: YES), the control device 70 It is determined whether or not the combustion permission condition is satisfied based on the operating state (step S14). For example, when the operating state of the engine 10 does not correspond to either the high load state in which the fuel injection amount Qf is greater than a predetermined amount or the high rotation state in which the engine rotational speed Ne is greater than the predetermined rotational speed, the control device 70 It is determined that the combustion permission condition is satisfied.

  When the combustion permission condition is satisfied (step S14: YES), the control device 70 selects the combustion state (step S15), controls the burner 31 to the combustion state, and controls the second adjustment valve 43 to the closed state. When the combustion permission condition is not satisfied (step S14: NO), the control device 70 selects the stopped state (step S16), controls the burner 31 to the stopped state, and controls the second adjustment valve 43 to the closed state. In the combustion state, the control device 70 calculates the fuel addition amount based on, for example, the intake air amount Qa, the engine speed Ne, the fuel injection amount Qf, and the like, and the calculated fuel addition amount is supplied from the first addition valve 38. The first regulating valve 37 is controlled to be added. At this time, as the exhaust gas is heated by the burner 31, the filter 40 having the oxidation catalyst 40b and the first selective reduction catalyst 40c, the second selective reduction catalyst 45, and the third selective reduction catalyst 47 The temperature is raised. Thereby, the reduction of NOx can be realized at an early stage in each of the first to third selective reduction catalysts 40c, 45, 47.

  Note that, in a high load state, the exhaust gas temperature is high, so the exhaust gas temperature rise effect by the burner 31 is small. Further, in a high rotation state, the burner 31 is likely to misfire due to a large exhaust flow rate Qe. Therefore, the fuel consumption in the burner 31 can be suppressed by controlling the burner 31 to the stop state in the high load state and the high rotation state.

  On the other hand, when the first condition is not satisfied (step S13: NO), the control device 70 determines whether the second selective reduction catalyst 45 is in an inactive state as the second condition (step S17). When the second catalyst temperature Tc2 is lower than the second lower limit temperature Tc2L, that is, when the second condition is satisfied (step S17: YES), the control device 70 determines whether or not the combustion state ( Step S15) or a stopped state (Step S16) is selected. The control device 70 controls the burner 31 to the selected operating state and controls the second adjustment valve 43 to the closed state. By controlling the burner 31 to the combustion state, the temperature increase of the second selective reduction catalyst 45 is promoted, and NOx reduction by the second selective reduction catalyst 45 can be realized at an early stage.

  On the other hand, when the second condition is not satisfied (step S17: NO), the control device 70 determines whether the third selective reduction catalyst 47 is in an inactive state as a third condition (step S18). When the third catalyst temperature Tc3 is lower than the third lower limit temperature Tc3L, that is, when the third condition is satisfied (step S18: YES), the control device 70 determines the combustion state (step S18: YES) according to the success or failure of the combustion permission condition in step S14. Step S15) or a stopped state (Step S16) is selected. The control device 70 controls the burner 31 to the selected operating state and controls the second adjustment valve 43 to the closed state. By controlling the burner 31 to the combustion state, the temperature increase of the third selective reduction catalyst 47 is promoted, and NOx reduction by the third selective reduction catalyst 47 can be realized at an early stage. When the third condition is not satisfied (step S18: NO), that is, when the respective catalysts 40b, 40c, 45, and 47 are in the active state, the control device 70 controls the burner 31 to the addition state (step S19). At the same time, the second adjustment valve 43 is controlled to be in an open state, and fuel is added to the exhaust gas from the second addition valve 44.

The exhaust gas to which fuel is added by the first addition valve 38 flows into the filter 40. In the filter 40, the particulate matter is trapped in the exhaust gas 40, part of the fuel is oxidized by the oxidation catalyst 40b, and part of NO is oxidized and converted to NO ₂ . At this time, when the particulate matter captured by the filter 40 begins to burn using NO ₂ as an oxidizing agent, the combustion is propagated to other particulate matter, so that the filter function of the filter 40 is regenerated. Combustion of particulate matter using NO ₂ as an oxidizing agent is started at a combustion start temperature Tf1 (for example, 300 ° C.) lower than the regeneration temperature Tfr. In the filter 40, the NOx is reduced in the exhaust gas by the first selective reduction catalyst 40c using the fuel that has passed through the oxidation catalyst 40b as a reducing agent.

The exhaust gas that has passed through the filter 40 is added with fuel by the second addition valve 44 and then flows into the second selective reduction catalyst 45. In the second selective reduction catalyst 45, the exhaust gas uses the fuel added by the second addition valve 44 as a reducing agent to reduce NOx and take in NH ₃ generated by the reduction reaction. In the second selective reduction catalyst 45, the NOx reduction reaction by the fuel is prioritized over the fuel oxidation reaction, and therefore some fuel does not react. That is, the exhaust gas that has passed through the second selective reduction catalyst 45 contains the fuel that has not reacted in the second selective reduction catalyst 45 and NH ₃ that is generated by the reduction reaction of NOx. It flows into the mold catalyst 47. In the third selective reduction catalyst 47, the exhaust gas is reduced in NOx using the fuel that has not reacted in the second selective reduction catalyst 45 and NH ₃ produced in the second selective reduction catalyst 45 as a reducing agent. Is done.

  Note that when the accumulation amount Mf exceeds the upper limit value during execution of the normal process, the control device 70 forcibly ends the normal process and executes the regeneration process of the filter 40. During the regeneration process, the control device 70 performs fuel addition by the second addition unit 41 when the second and third selective reduction catalysts 45 and 47 are in the active state. When the reproduction process ends, the control device 70 resumes the normal process.

FIG. 6 is a graph showing an example of a result of comparison of NOx purification performance when the engine 10 is operated in the WHTC mode. The embodiment is the exhaust purification device 30 described above. Further, in the comparative example, in order from the upstream side of the exhaust passage, the first fuel addition valve, the low temperature HC-SCR catalyst including an oxidation catalyst function for oxidizing fuel and NO, the filter having only the filter function, and the second fuel addition valve , An exhaust purification device in which a high-temperature HC-SCR catalyst and an NH ₃ -SCR catalyst using NH ₃ as a reducing agent are arranged. As shown in FIG. 6, in the exhaust purification device 30 of the example, it was confirmed that the purification performance was improved by about 10% compared to the exhaust purification device of the comparative example.

FIG. 7 is a graph comparing the catalyst size, which is the total volume of the catalyst, in the comparative example and the example described above. In the comparative example, the catalyst size is the sum of the volumes of the low temperature type HC-SCR catalyst, the high temperature type HC-SCR catalyst, and the NH ₃ -SCR catalyst. In the embodiment, the total volume of each of the oxidation catalyst 40b, the first selective reduction catalyst 40c, the second selective reduction catalyst 45, and the third selective reduction catalyst 47 is shown. As shown in FIG. 7, in the example, it was confirmed that the catalyst size was reduced by about 10% compared to the comparative example, although the NOx purification rate was improved by about 10% as shown in FIG.

According to the exhaust purification device 30 of the above embodiment, the effects listed below can be obtained.
(1) The burner 31 is controlled to a combustion state when at least one of the oxidation catalyst 40b and the first selective reduction catalyst 40c is in an inactive state. As a result, the temperature increase of the oxidation catalyst 40b, the first selective reduction catalyst 40c, the second selective reduction catalyst 45, and the third selective reduction catalyst 47 is promoted, and NOx reduction using fuel as a reducing agent is promoted. It is feasible early. Further, if the burner 31 is controlled to be in the addition state when the oxidation catalyst 40b is in the inactive state, there is a possibility that the fuel is excessively supplied to the first selective reduction catalyst 40c. In this regard, with the above-described configuration, it is possible to suppress wasteful fuel consumption by suppressing excessive supply of fuel to the first selective reduction catalyst 40c.

(2) The particulate matter captured by the filter 40 starts combustion at the combustion start temperature Tf1 lower than the regeneration temperature Tfr using NO ₂ generated by the oxidation catalyst 40b as an oxidant. Therefore, it is possible to continuously regenerate the filter function of the filter 40 during operation of the engine 10 without raising the temperature of the filter 40 to the regeneration temperature Tfr. As a result, the first selective reduction catalyst 40c is easily maintained in a clean state, thereby increasing the chance of contact between the first selective reduction catalyst 40c and NOx in the exhaust gas. Reduction of NOx is performed efficiently. In addition, the thermal load on the filter 40 due to regeneration of the filter function is reduced, and the frequency of regeneration processing by the burner 31 is reduced, so that the fuel consumption in the burner 31 is also reduced.

(3) The NOx purification performance is improved by the above (1) and (2).
(4) According to the exhaust purification device 30 described above, the catalyst size can be reduced while improving the NOx purification performance.

(5) The burner 31 is controlled to the combustion state when the combustion permission condition is satisfied. Therefore, the temperature of each catalyst can be efficiently increased by the burner 31.
(6) When the burner 31 is in the added state, a part of the fuel in the exhaust gas is oxidized in the oxidation catalyst 40b, so that the temperature drop of the oxidation catalyst 40b and the first selective reduction catalyst 40c is suppressed. As a result, the oxidation catalyst 40b and the first selective reduction catalyst 40c are easily maintained in the active state.

  (7) When the second selective reduction catalyst 45 is in the inactive state, the burner 31 is controlled to the combustion state. Thereby, the temperature increase of the second selective reduction catalyst 45 is promoted, and NOx reduction by the second selective reduction catalyst 45 can be realized at an early stage.

  (8) When the third selective reduction catalyst 47 is in an inactive state, the burner 31 is controlled to be in a combustion state. Accordingly, the temperature increase of the third selective reduction catalyst is promoted, and NOx reduction by the third selective reduction catalyst can be realized at an early stage.

  (9) By controlling the burner 31 to the addition state, the first supply valve 38 can be configured to supply fuel to the burner 31 and to add fuel to the exhaust gas flowing into the filter 40. As a result, the configuration of the exhaust purification device 30 can be simplified.

(10) The third selective reduction catalyst 47 includes an HC catalyst layer 49 and an NH ₃ catalyst layer 50. Thus, the third selective reduction catalyst 47 can reduce NOx using the fuel that has passed through the second selective reduction catalyst 45 and NH ₃ produced by the second selective reduction catalyst 45.

(11) If fuel is added from the second addition valve 44 when the second selective reduction catalyst 45 is in an active state and the third selective reduction catalyst 47 is in an inactive state, the second selection There is a possibility that NH ₃ produced by the reduction catalyst 45 may pass through the third selective reduction catalyst 47 without reacting. In this regard, according to the above configuration, the fuel is added by the second addition valve 44 after both the second and third selective reduction catalysts 45 and 47 reach the active state. As a result, the NH ₃ produced by the second selective reduction catalyst 45 is suppressed from being discharged to the outside air.

In addition, the said embodiment can also be suitably changed and implemented as follows.
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 exhaust purification device 30 may have a configuration in which fuel as a reducing agent is separately added to the exhaust gas between the burner 31 and the filter 40. In such a case, the burner 31 is not controlled in the added state, but is controlled in the stopped state or the combustion state.

  The control device 70, when the oxidation catalyst 40b, the first selective reduction catalyst 40c, and the second selective reduction catalyst 45 are in an active state and the third selective reduction catalyst 47 is in an inactive state, While controlling the burner 31 to the addition state, the fuel may be added to the exhaust gas from the second addition valve 44. At this time, the NOx emission amount is suppressed by the amount of NOx reduced by the first selective reduction catalyst 40c and NOx reduced by the second selective reduction catalyst 45c.

  As shown in FIG. 8, when the oxidation catalyst 40b and the first selective reduction catalyst 40c are in the active state, the control device 70 determines whether the burner is in the state of the second and third selective reduction catalysts 45 and 47. You may control 31 to an addition state. In this case, after acquiring various information (step S21) and calculating various catalyst temperatures (step S22), the control device 70 determines whether or not the first condition is satisfied (step S23). When the first condition is satisfied (step S23: YES), the control device 70 determines whether or not the fuel permission condition is satisfied (step S24), and the burner 31 is in the combustion state (step S25) or is stopped. (Step S26). On the other hand, when the first condition is not satisfied (step S23: NO), the control device 70 controls the burner 31 to the addition state (step S27). According to such a configuration, the temperature of the exhaust gas flowing into the second and third selective reduction catalysts 45 and 47 is increased by the oxidation of fuel in the oxidation catalyst 40b, and NOx is reduced by the first selective reduction catalyst 40c. This reduces the amount of NOx emissions.

  When the control device 70 controls the burner 31 to the combustion state when the oxidation catalyst 40b and the first selective reduction catalyst 40c are in the active state, unburned fuel is included in the exhaust gas flowing into the filter 40. The burner 31 may be controlled in a rich combustion state in which the fuel is rich. According to such a configuration, NOx can be reduced by the first selective reduction catalyst 40c using the unburned fuel as a reducing agent.

  The control device 70 may not include the combustion permission condition as a condition for controlling the burner 31 to the combustion state. According to such a configuration, for example, the burner 31 is burned when the rapid heating of various catalysts is required even in a high load state or when the combustion state of the burner 31 is stable even in a high rotation state. The state can be controlled.

The exhaust purification device 30 may have a second oxidation catalyst that oxidizes the fuel remaining in the exhaust gas and NH ₃ downstream of the third selective reduction catalyst 47. According to such a configuration, the degree of freedom with respect to the amount of fuel added by the second addition unit 41 is improved in reducing NOx.

DESCRIPTION OF SYMBOLS 10 ... Diesel engine, 11 ... Cylinder block, 12 ... Cylinder, 13 ... Injector, 14 ... Intake manifold, 15 ... Exhaust manifold, 17 ... Intake passage, 17 ... Turbocharger, 18 ... Compressor, 19 ... Intercooler, 20 ... Exhaust passage , 22 ... turbine, 25 ... EGR passage, 26 ... EGR cooler, 27 ... EGR valve, 30 ... exhaust purification device, 31 ... burner, 32 ... first addition part, 33 ... ignition part, 34 ... fuel tank, 35 ... first 1 fuel passage, 36 ... pump, 37 ... first regulating valve, 38 ... first addition valve, 40 ... filter, 40a ... filter body, 40b ... oxidation catalyst, 40c ... first selective reduction catalyst, 41 ... second addition Part, 42 ... second fuel passage, 43 ... second regulating valve, 44 ... second addition valve, 45 ... second selective reduction The catalyst, 47 ... third selective reduction catalyst, 48 ... monolithic support, 49 ... HC catalyst layer, 50 ... NH ₃ catalyst layer, 51 ... catalyst supports, 51h ... hole, 52 ... gap, 53 ... catalyst supports, 53h ... hole , 55 ... intake air amount sensor, 56 ... first temperature sensor, 57 ... second temperature sensor, 58 ... third temperature sensor, 59 ... engine speed sensor, 60 ... injection control unit, 70 ... control device.

Claims (4)

A burner capable of raising the temperature of exhaust gas flowing through the exhaust passage;
A first addition valve for adding fuel to the exhaust gas;
An exhaust gas filter that is located downstream of the burner and the first addition valve and captures particulate matter contained in exhaust gas, which oxidizes nitrogen monoxide in the exhaust gas and converts it into nitrogen dioxide, and exhaust A first selective reduction catalyst that reduces NOx using fuel in gas as a reducing agent, and the oxidation catalyst is formed on the upstream side of the first selective reduction catalyst;
A second addition valve located downstream of the filter 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;
A controller that controls the burner to a combustion state when at least one of the oxidation catalyst and the first selective reduction catalyst is in an inactive state ;
The third selective reduction catalyst is a laminated structure,
An HC catalyst layer for reducing NOx using fuel as a reducing agent;
Said laminated on HC catalyst layer constitutes a surface layer of said third selective reduction catalyst, and a NH ₃ catalyst layer for reducing NOx with NH ₃ to the second selective reduction catalyst is generated in the reducing agent Exhaust purification device.   The exhaust emission control device according to claim 1, wherein the control unit controls the burner to a combustion state when the second selective reduction catalyst is in an inactive state.   The exhaust emission control device according to claim 2, wherein the control unit controls the burner to a combustion state when the third selective reduction catalyst is in an inactive state. The burner includes the first addition valve and an ignition part that ignites the fuel added by the first addition valve,
The control unit, when the oxidation catalyst and the first selective reduction catalyst are in an active state,
The exhaust emission control device according to any one of claims 1 to 3, wherein the burner is controlled to an addition state in which the fuel added by the first addition valve is not combusted.

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