JP2017160789A - Diesel engine system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a diesel engine system capable of promoting filter continuous regeneration processing.SOLUTION: A diesel engine system 1, 1a includes: a diesel oxidation catalyst 21; a filter 22; a nitrogen dioxide generation accumulation section 50 for, when exhaust gas is introduced, oxidizing nitrogen monoxide in the introduced exhaust gas to convert the nitrogen monoxide to nitrogen dioxide and accumulating the nitrogen dioxide; and a nitrogen dioxide introduction mechanism 60 for actuating an exhaust brake if an exhaust brake request is made, introducing exhaust gas downstream of the filter to the nitrogen dioxide generation accumulation section and introducing the nitrogen dioxide in the nitrogen dioxide generation accumulation section to exhaust gas upstream of the filter, when a temperature of exhaust gas flowing into the filter is equal to or higher than a predetermined temperature that allows execution of filter continuous regeneration processing for burning PMs in the filter by using the nitrogen dioxide.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a diesel engine system, and more particularly to a diesel engine system having a diesel oxidation catalyst and a filter.

  2. Description of the Related Art Conventionally, a diesel engine system including a filter that collects PM (Particulate Matter) such as soot contained in exhaust gas of a diesel engine is known (see, for example, Patent Document 1). In such a diesel engine system, when a large amount of PM in the exhaust gas accumulates on the filter, the filter is clogged and the collecting performance of the filter decreases.

Therefore, conventionally, the catalytic action of the diesel oxidation catalyst arranged upstream of the filter is used to change the nitrogen monoxide (NO) in the exhaust gas to nitrogen dioxide (NO ₂ ), and this nitrogen dioxide changes the PM of the filter. A filter continuous regeneration process is performed in which a filter is regenerated by burning it and discharging it as carbon dioxide (CO ₂ ).

JP 2004-108194 A

  However, in the prior art, it is difficult to promote the above-described continuous filter regeneration process.

  This invention is made | formed in view of the above, The objective is to provide the diesel engine system which can promote a filter continuous regeneration process.

  In order to achieve the above object, a diesel engine system according to the present invention includes a diesel oxidation catalyst disposed in an exhaust passage of the diesel engine and a filter disposed downstream of the diesel oxidation catalyst. In the case where the exhaust gas is introduced, the nitrogen dioxide generating and accumulating unit that oxidizes and accumulates nitrogen monoxide in the introduced exhaust gas to form nitrogen dioxide, and the temperature of the exhaust gas flowing into the filter is reduced by the nitrogen dioxide. When the exhaust temperature is higher than a predetermined temperature at which the continuous regeneration process for burning the PM of the filter can be performed, and the exhaust brake is requested, the exhaust brake is activated and the exhaust gas downstream of the filter is generated and accumulated in the nitrogen dioxide. The nitrogen dioxide in the nitrogen dioxide production and accumulation unit is introduced into the filter. And nitrogen dioxide introduction mechanism for introducing into the remote upstream exhaust, characterized in that it comprises a.

  According to the diesel engine system of the present invention, when the temperature of the exhaust gas flowing into the filter is equal to or higher than a predetermined temperature at which the continuous filter regeneration process can be performed, and when there is an exhaust brake request, the exhaust brake is operated, In the nitrogen generating and accumulating section, it is possible to oxidize and store nitrogen monoxide contained in the exhaust gas as nitrogen dioxide, and to introduce the accumulated nitrogen dioxide into the exhaust gas upstream of the filter. Thereby, since the amount of nitrogen dioxide introduced into the filter can be increased, the filter continuous regeneration process can be promoted.

  Further, according to the diesel engine system of the present invention, the filter continuous regeneration process can be promoted in this way, so the frequency of the filter forced regeneration process for forcibly supplying fuel to the exhaust passage upstream of the filter is reduced. Can be made. Thereby, the deterioration of the fuel consumption and the thermal deterioration of the filter due to frequent filter forced regeneration processing can be suppressed.

  In the above configuration, the nitrogen dioxide introduction mechanism includes an upstream exhaust brake valve disposed in the exhaust passage upstream of the diesel oxidation catalyst, and a downstream side disposed in the exhaust passage downstream of the filter. An exhaust brake valve, a first passage for introducing exhaust gas downstream from the filter and upstream from the downstream exhaust brake valve into the nitrogen dioxide generation and accumulation unit, and nitrogen dioxide in the nitrogen dioxide generation and accumulation unit A second passage introduced into the exhaust upstream of the filter and downstream of the upstream exhaust brake valve; a first valve for opening and closing the first passage; and a second valve for opening and closing the second passage; A control device for controlling the upstream brake valve, the downstream brake valve, the first valve, and the second valve. The control device opens the upstream side exhaust brake valve and the first valve when the exhaust brake request is present when the temperature of the exhaust gas flowing into the filter is equal to or higher than the predetermined temperature, and the downstream side A first control process for closing the side exhaust brake valve and the second valve is executed, and after the first control process, the upstream side exhaust brake valve and the first valve are closed, and the downstream side exhaust brake is closed. A second control process for opening the valve and the second valve may be executed.

  According to this configuration, when there is an exhaust brake request when the temperature of the exhaust gas flowing into the filter is equal to or higher than a predetermined temperature, the exhaust brake is operated by closing the downstream exhaust brake valve in the first control process. In addition, in the second control process, the exhaust brake can be operated by closing the upstream exhaust brake valve. In addition, by executing the first control process, it is possible to introduce exhaust gas downstream from the filter into the nitrogen dioxide generation and accumulation unit via the first passage, and by executing the second control process, Nitrogen dioxide in the nitrogen dioxide generating and accumulating section can be introduced into the exhaust gas upstream of the filter through the second passage. Thereby, since the amount of nitrogen dioxide introduced into the filter can be increased, the filter continuous regeneration process can be promoted.

  The said structure can be set as the structure further equipped with the urea SCR system in the said exhaust passage of the downstream rather than the said downstream exhaust brake valve. According to this configuration, the urea SCR system can reduce NOx in the exhaust downstream of the downstream exhaust brake valve.

  Further, since the regeneration of the filter is effectively achieved by the nitrogen dioxide generation and accumulation section and the nitrogen dioxide introduction mechanism, the urea aqueous solution in the urea SCR system is compared with the case where such a member is not provided. Consumption can be reduced.

  Further, since the amount of nitrogen dioxide introduced into the filter is increased by the nitrogen dioxide generation and accumulation unit and the nitrogen dioxide introduction mechanism, the amount of nitrogen dioxide that passes through (slips) this filter and is supplied to the urea SCR system is reduced. It can be increased to facilitate a fast FASTSCR reaction. Thereby, the reduction rate of NOx can be promoted.

According to the present invention, the continuous filter regeneration process can be promoted. Further, according to the present invention, since the filter continuous regeneration process can be promoted in this way, the frequency of executing the filter forced regeneration process can also be reduced. Thereby, the deterioration of the fuel consumption and the thermal deterioration of the filter due to frequent filter forced regeneration processing can be suppressed.

1 is a schematic diagram schematically showing the overall configuration of a diesel engine system according to Embodiment 1. FIG. It is an example of the flowchart of the 1st control processing and 2nd control processing by a control apparatus. FIG. 3 is a schematic diagram schematically showing an overall configuration of a diesel engine system according to a second embodiment.

(Embodiment 1)
Hereinafter, a diesel engine system 1 according to Embodiment 1 of the present invention will be described with reference to the drawings. Regarding the drawings, the dimensions are changed from the actual product so that the configuration is easy to understand, and the ratio of the thickness, width, length, etc. of each member and each component does not necessarily match the actual product ratio. Not necessarily.

  FIG. 1 is a schematic diagram schematically showing an overall configuration of a diesel engine system 1 according to the present embodiment. Although the specific kind of vehicle in which this diesel engine system 1 is mounted is not particularly limited, a large vehicle such as a bus or a truck is used in the present embodiment. The diesel engine system 1 includes a diesel engine 2, an exhaust passage 3, a turbocharger 4, a control device 7, and an exhaust treatment system 10.

  The fuel injection amount and fuel injection timing of the diesel engine 2 are controlled by the control device 7. The control device 7 according to the present embodiment serves not only as a control device for the diesel engine 2 but also as a control device for the exhaust treatment system 10. Such a control device 7 includes a microcomputer having a CPU that executes various control processes, arithmetic processes, and the like, and a ROM, a RAM, and the like that function as a storage unit that stores various information used for the operation of the CPU. ing. In addition, the diesel engine system 1 can be configured to include a control device dedicated to the exhaust treatment system 10 separately from the control device of the diesel engine 2.

  The exhaust passage 3 is a passage through which exhaust discharged from each cylinder of the diesel engine 2 passes. The turbocharger 4 includes a turbine 5 and a compressor 6 connected to the turbine 5. The turbine 5 is disposed in the middle of the exhaust passage 3 on the downstream side of the exhaust manifold, and rotates by receiving the exhaust force. The compressor 6 is disposed in the middle of the passage upstream of the intake manifold of the intake passage (not shown). When the turbine 5 receives the force of the exhaust gas and rotates, the compressor 6 connected to the turbine 5 rotates to supercharge the intake air.

  The exhaust treatment system 10 is a system for treating the exhaust of the diesel engine 2. The exhaust treatment system 10 includes an exhaust treatment device 20, a fuel addition valve 30, a temperature sensor 40, a nitrogen dioxide generation and accumulation unit 50, and a nitrogen dioxide introduction mechanism 60. The exhaust treatment device 20 includes a DOC (Diesel Oxidation Catalyst) 21 as a diesel oxidation catalyst and a filter 22 capable of collecting PM such as soot contained in the exhaust of the diesel engine 2. The DOC 21 and the filter 22 are disposed in a portion of the exhaust passage 3 on the downstream side of the turbine 5. The filter 22 is disposed downstream of the DOC 21 with a predetermined interval between the filter 22 and the DOC 21. As this filter 22, for example, a diesel particulate filter can be used.

The DOC 21 has a configuration in which a noble metal catalyst such as platinum (Pt) or palladium (Pd) is supported on a filter through which exhaust gas can pass. The DOC 21 promotes an oxidation reaction that changes nitrogen monoxide (NO) in the exhaust gas to nitrogen dioxide (NO ₂ ) by the oxidation catalytic action of the noble metal catalyst. When the exhaust gas temperature becomes equal to or higher than the predetermined temperature, the nitrogen dioxide generated in the DOC 21 can burn the PM of the filter 22 and discharge it as carbon dioxide (CO ₂ ) (this is referred to as “filter continuous regeneration process”). ").

  The fuel addition valve 30 is disposed in the exhaust passage 3 upstream from the DOC 21 and downstream from the turbine 5, and adds fuel to the exhaust passage 3 in response to an instruction from the control device 7. When the predetermined condition is satisfied, the control device 7 performs a process of adding fuel from the fuel addition valve 30 into the exhaust passage 3 (referred to as “filter forced regeneration process”).

  Specifically, the fuel added from the fuel addition valve 30 in the forced filter regeneration process is oxidized (combusted) in the DOC 21. The temperature of the exhaust is raised by the reaction heat at this time. Then, by forcibly raising the temperature of the filter 22 by the exhaust gas that has reached a high temperature, the combustion of the PM deposited on the filter 22 can be promoted, and the regeneration of the filter 22 can be forcibly aimed.

  The conditions for starting the execution of the forced filter regeneration process are not particularly limited, and various conditions for which it is desired to perform the forced filter regeneration process (for example, the previous forced filter regeneration process is executed). Or when the pressure difference between the front and rear of the filter 22 reaches a predetermined value as the amount of soot accumulated on the filter 22 increases. . This condition may be stored in advance in a storage unit (for example, ROM) of the control device 7 (that is, it may be set in advance). Note that the control device 7 according to the present embodiment lights the warning lamp on the driver's seat of the vehicle when the conditions for starting the execution of the forced filter regeneration process are satisfied, so that the driver can Is notified. When the driver who has received this notification turns on the driver's seat switch, the execution of the forced filter regeneration process is started.

  The temperature sensor 40 detects the temperature of the exhaust gas flowing into the filter 22, that is, the exhaust gas temperature upstream of the filter 22, and transmits the detection result to the control device 7. In addition to the temperature sensor 40 illustrated in FIG. 1, the diesel engine system 1 detects various information used for the operation of the diesel engine system 1, such as a crank position sensor, an intake air amount sensor, an accelerator position sensor, and the like. Various sensors are provided.

  Next, the nitrogen dioxide generation / accumulation unit 50 and the nitrogen dioxide introduction mechanism 60 will be described. The nitrogen dioxide generation / accumulation unit 50 is a part that oxidizes nitrogen monoxide in the introduced exhaust gas to accumulate it as nitrogen dioxide when the exhaust gas is introduced. As long as it has such a function, the specific configuration of the nitrogen dioxide generation and accumulation unit 50 is not particularly limited, but in the present embodiment, as an example, a NO oxidation catalyst 51 and a pressure accumulation tank 52 are provided. ing.

  The NO oxidation catalyst 51 is a catalyst that promotes an oxidation reaction that oxidizes nitrogen monoxide in exhaust gas that has been introduced through a first passage 63, which will be described later, to change it into nitrogen dioxide. The specific configuration of the NO oxidation catalyst 51 is not particularly limited. For example, a noble metal catalyst that can promote such an oxidation reaction can be used.

  The pressure accumulation tank 52 is connected to the downstream side of the NO oxidation catalyst 51 and is a tank that accumulates nitrogen dioxide that has passed through the NO oxidation catalyst 51.

The nitrogen dioxide introduction mechanism 60 has an exhaust brake request when the temperature of the exhaust gas flowing into the filter 22 is equal to or higher than a predetermined temperature at which continuous filter regeneration processing (regeneration processing in which PM of the filter 22 is combusted by nitrogen dioxide) can be performed. In this case, the exhaust brake is operated, the exhaust gas downstream of the filter 22 is introduced into the nitrogen dioxide generation / accumulation unit 50, and the nitrogen dioxide of the nitrogen dioxide generation / accumulation unit 50 is introduced into the exhaust gas upstream of the filter 22. It is a mechanism to make. The specific configuration of the nitrogen dioxide introduction mechanism 60 is not particularly limited as long as it has such a function, but in the present embodiment, as an example, the upstream side exhaust brake valve 61, the downstream side exhaust brake, and the like. A valve 62, a first passage 63, a second passage 64, a first valve 65, and a second valve 66 are provided, and these valves (upstream exhaust brake valve 61, downstream exhaust brake valve 62, first valve 65, and A control device 7 for controlling the second valve 66) is also included in the components. Details of these members will be described below.

  The upstream exhaust brake valve 61 is disposed in the exhaust passage 3 upstream of the DOC 21 and downstream of the turbine 5. Note that, as an example, the upstream side exhaust brake valve 61 according to the present embodiment is disposed further downstream than the fuel addition valve 30, but is not limited to this configuration. The downstream exhaust brake valve 62 is disposed in the exhaust passage 3 on the downstream side of the filter 22. When the upstream side exhaust brake valve 61 and the downstream side exhaust brake valve 62 are closed in response to an instruction from the control device 7, the exhaust brake is activated (that is, the exhaust brake is applied).

  The first passage 63 is a passage that introduces the exhaust gas in the exhaust passage 3 downstream of the filter 22 and upstream of the downstream exhaust brake valve 62 into the NO oxidation catalyst 51 of the nitrogen dioxide generation and accumulation unit 50. is there.

  The second passage 64 is a passage for introducing nitrogen dioxide in the nitrogen dioxide generation and accumulation unit 50, specifically, into the exhaust gas upstream of the filter 22 and downstream of the upstream exhaust brake valve 61. . Specifically, the second passage 64 according to the present embodiment communicates the outlet of the pressure accumulation tank 52 and a portion between the DOC 21 and the filter 22 of the exhaust treatment device 20. Thus, the second passage 64 introduces the nitrogen dioxide in the pressure accumulation tank 52 into the exhaust gas upstream of the filter 22 and downstream of the DOC 21. However, the introduction destination of nitrogen dioxide in the second passage 64 is not limited to this. For example, in the second passage 64, the nitrogen dioxide in the accumulator tank 52 is more upstream than the DOC 21 and more upstream than the upstream exhaust brake valve 61. Alternatively, the exhaust gas may be introduced into the exhaust gas in the downstream exhaust passage 3.

  The first valve 65 is disposed in the first passage 63 and opens and closes the first passage 63 in response to an instruction from the control device 7. The second valve 66 is disposed in the second passage 64 and is a valve that opens and closes the second passage 64 in response to an instruction from the control device 7.

  The control device 7 opens the upstream side exhaust brake valve 61 and the first valve 65 when there is an exhaust brake request when the temperature of the exhaust gas flowing into the filter 22 is equal to or higher than a predetermined temperature at which continuous filter regeneration processing can be performed. A first control process is performed to close the downstream exhaust brake valve 62 and the second valve 66, and after the execution of the first control process, the upstream exhaust brake valve 61 and the first valve 65 are closed. Then, a second control process for opening the downstream exhaust brake valve 62 and the second valve 66 is executed.

By the above control, when the temperature of the exhaust gas flowing into the filter 22 is equal to or higher than a predetermined temperature and when there is an exhaust brake request, the exhaust brake is operated by closing the downstream exhaust brake valve 62 in the first control process. In addition, the exhaust brake can be operated by closing the upstream exhaust brake valve 61 in the second control process. Further, by executing the first control process, the exhaust gas downstream from the filter 22 can be introduced into the nitrogen dioxide generation and accumulation unit 50 via the first passage 63, and the second control process is executed. As a result, the nitrogen dioxide in the nitrogen dioxide generation and accumulation unit 50 can be introduced into the exhaust gas upstream of the filter 22 via the second passage 64.

  Details of the control of the control device 7 described above will be described with reference to a flowchart. FIG. 2 is an example of a flowchart of the first control process and the second control process performed by the control device 7. Specifically, the control unit (CPU) of the control device 7 repeatedly executes the flowchart of FIG. 2 at a predetermined cycle. First, the control device 7 determines whether or not the temperature of the exhaust gas flowing into the filter 22 (exhaust temperature) is equal to or higher than a predetermined temperature (step S10). This predetermined temperature is a temperature at which the continuous filter regeneration process can be performed (specifically, nitrogen monoxide in the exhaust gas is changed to nitrogen dioxide, and the PM of the filter 22 is burned by this nitrogen dioxide to change to carbon dioxide. The specific value is not particularly limited. The specific value of the predetermined temperature is obtained in advance by experiments, simulations, and the like, and is stored in advance in a storage unit (for example, ROM) of the control device 7.

  Further, the control device 7 acquires the temperature of the exhaust gas flowing into the filter 22 described above based on the detection result of the temperature sensor 40. However, the method for acquiring the exhaust temperature by the control device 7 is not limited to the method using the temperature sensor 40, and for example, the control device 7 uses an index (for example, diesel engine 2) having a correlation with the exhaust temperature. The exhaust temperature may be estimated on the basis of the load or the like.

  When it determines with NO by step S10, the control apparatus 7 performs a flowchart from a start (return). On the other hand, when it determines with YES by step S10, the control apparatus 7 determines whether there exists an exhaust brake request | requirement (step S20). Specifically, an exhaust brake switch for operating the exhaust brake is arranged in the driver seat of the vehicle according to the present embodiment, and when the driver desires to operate the exhaust brake, the exhaust brake switch is turned on. To do. Then, the control device 7 determines that there is an exhaust brake request (YES) when the exhaust brake switch is turned ON and the depression amount of the accelerator pedal becomes zero. In addition, the control apparatus 7 acquires the depression amount of this accelerator pedal based on the detection result of an accelerator pedal position sensor (not shown).

  When it determines with NO by step S20, the control apparatus 7 performs a flowchart from a start (return). On the other hand, when it determines with YES by step S20, the control apparatus 7 performs the 1st control process mentioned above (step S30). Specifically, the control device 7 opens the upstream side exhaust brake valve 61 and the first valve 65 and closes the downstream side exhaust brake valve 62 and the second valve 66. By executing the first control process, the exhaust brake is operated, and the exhaust gas downstream of the filter 22 can be introduced into the nitrogen dioxide generation and accumulation unit 50 through the first passage 63. Thereby, nitrogen dioxide is accumulated in the pressure accumulation tank 52.

  In addition, the execution period of step S30 is not specifically limited, An appropriate period is calculated | required beforehand by performing experiment, simulation, etc., and is memorize | stored in the memory | storage part (for example, ROM etc.) of the control apparatus 7. That is, the control device 7 according to the present embodiment executes step S30 for a predetermined period stored in advance in the storage unit, and then executes step S40 described later. Note that the longer the execution period of step S30, the more the amount of nitrogen dioxide accumulated in the pressure accumulation tank 52 can be increased.

In step S40, the control device 7 executes the second control process described above. Specifically, the control device 7 closes the upstream exhaust brake valve 61 and the first valve 65 and opens the downstream exhaust brake valve 62 and the second valve 66. By executing the second control process, the upstream side exhaust brake valve 61 is closed, so that the exhaust brake can be operated continuously. Further, since the first valve 65 is closed and the downstream exhaust brake valve 62 and the second valve 66 are opened, the nitrogen dioxide in the pressure accumulation tank 52 of the nitrogen dioxide generation and accumulation unit 50 is filtered through the second passage 64. The exhaust gas can be introduced into the exhaust gas upstream of the exhaust gas 22.

  Note that the control device 7 according to the present embodiment, when starting the execution of step S40, when the exhaust temperature falls below a predetermined temperature or when there is no exhaust brake request (for example, the driver turns off the exhaust brake switch). Or when the accelerator pedal depression amount is greater than zero), the execution of step S40 is terminated. Specifically, the control device 7 closes the first valve 65 and the second valve 66 and opens the upstream exhaust brake valve 61 and the downstream exhaust brake valve 62, thereby completing the execution of step S40. Let However, the specific conditions for terminating the execution of step S40 are not limited to this, and as another example, the control device 7 may start after the execution of step S40 after a predetermined period has elapsed. The execution of step S40 may be terminated. After step S40, the control device 7 executes the flowchart from the start (return).

  As described above, according to the present embodiment, when there is an exhaust brake request when the temperature of the exhaust gas flowing into the filter 22 is equal to or higher than a predetermined temperature at which the filter continuous regeneration process can be performed, step S30 and step S40 are performed. And the exhaust gas brake is operated, and the nitrogen dioxide generation and accumulation unit 50 oxidizes and accumulates nitrogen monoxide contained in the exhaust gas as nitrogen dioxide. The accumulated nitrogen dioxide is upstream of the filter 22. It can be introduced into the exhaust. Thereby, since the amount of nitrogen dioxide introduced into the filter 22 can be increased, the filter continuous regeneration process can be promoted.

  Further, according to the present embodiment, the filter continuous regeneration process can be promoted in this way, so that the frequency of executing the filter forced regeneration process (that is, the frequency of fuel addition by the fuel addition valve 30) can be reduced. . Thereby, the deterioration of the fuel consumption and the thermal deterioration of the filter 22 due to frequent filter forced regeneration processing can be suppressed.

(Embodiment 2)
FIG. 3 is a schematic diagram schematically showing an overall configuration of a diesel engine system 1a according to Embodiment 2 of the present invention. The diesel engine system 1a according to the present embodiment is different from the diesel engine system 1 shown in FIG. 1 in that an exhaust treatment system 10a is provided instead of the exhaust treatment system 10. The exhaust treatment system 10 a differs from the exhaust treatment system 10 in that it further includes a urea SCR system 70. Since the other configuration of the exhaust treatment system 10a is the same as that of the exhaust treatment system 10, description of the other configuration is omitted.

  The urea SCR system 70 is disposed in the exhaust passage 3 downstream of the downstream exhaust brake valve 62. Specifically, the urea SCR system 70 according to the present embodiment includes a urea aqueous solution injection valve (not shown) that injects the urea aqueous solution toward the exhaust passage 3 and exhausts downstream of the urea aqueous solution injection valve. The passage 3 is provided with a NOx selective reduction catalyst (not shown).

  The urea aqueous solution injection valve receives an instruction from the control device 7 and injects the urea aqueous solution into the exhaust gas. The timing at which the control device 7 injects the urea aqueous solution into the urea aqueous solution injection valve is not particularly limited as long as the diesel engine 2 is in operation, but the control device 7 according to the present embodiment is, for example, The urea aqueous solution is injected at least during execution of the second control process.

The NOx selective reduction catalyst is a catalyst that selectively reduces NOx in the exhaust gas using ammonia (NH ₃ ). In general, the NOx selective reduction catalyst is an SCR (Selective C).
sometimes referred to as an “atomic reduction” catalyst. The specific type of the NOx selective reduction catalyst is not particularly limited, and for example, a known NOx selective reduction catalyst such as a base metal oxide such as vanadium, molybdenum, tungsten, or a noble metal such as zeolite can be used. In this embodiment, vanadium is used as an example of the NOx selective reduction catalyst.

When the urea aqueous solution is injected from the urea aqueous solution injection valve, urea in the urea aqueous solution is hydrolyzed, and as a result, ammonia (NH ₃ ) is generated. This ammonia reduces NOx under the catalytic action of the NOx selective reduction catalyst. As a result, nitrogen and water are generated. In this way, the urea SCR system 70 attempts to reduce NOx in the exhaust.

  According to the present embodiment, in addition to the operational effects of the first embodiment described above, the following operational effects can be achieved. Specifically, according to the present embodiment, the urea SCR system 70 can reduce NOx in the exhaust gas in the exhaust passage 3 downstream of the downstream exhaust brake valve 62. Further, the present embodiment also includes the nitrogen dioxide generation / accumulation unit 50 and the nitrogen dioxide introduction mechanism 60. Since these members effectively regenerate the filter 22, these members are not provided. Compared to the case, the consumption amount of the urea aqueous solution in the urea SCR system 70 can be reduced.

In addition, by supplying the urea aqueous solution of the urea SCR system 70, the following two types of reactions, the standard SCR reaction (Formula 1) and the FASTSCR reaction (Formula 2), can occur.

  When the standard SCR reaction (Formula 1) and the FASTSCR reaction (Formula 2) are compared, the FASTSCR reaction has a faster reaction rate. Therefore, the NOx in the exhaust can be processed faster when the FASTSCR reaction occurs.

  In this regard, according to the present embodiment, the nitrogen dioxide generation and accumulation unit 50 and the nitrogen dioxide introduction mechanism 60 are provided, and the amount of nitrogen dioxide introduced into the filter 22 by these members is increased. The amount of nitrogen dioxide that passes through (slips) and is supplied to the urea SCR system 70 can be increased to facilitate a FASTSCR reaction with a faster reaction rate than the standard SCR reaction. Thereby, the reduction rate of NOx can be promoted.

  Although the preferred embodiments of the present invention have been described above, the present invention is not limited to such specific embodiments, and various modifications and changes can be made within the scope of the gist of the present invention described in the claims. Is possible.

1, 1a Diesel engine system 2 Diesel engine 3 Exhaust passage 7 Control device 10, 10a Exhaust treatment system 21 DOC (diesel oxidation catalyst)
22 Filter 50 Nitrogen dioxide production accumulation part 51 NO oxidation catalyst 52 Pressure accumulation tank 60 Nitrogen dioxide introduction mechanism 61 Upstream exhaust brake valve 62 Downstream exhaust brake valve 63 First passage 64 Second passage 65 First valve 66 Second valve 70 Urea SCR system

Claims (3)

In a diesel engine system having a diesel oxidation catalyst disposed in an exhaust passage of a diesel engine and a filter disposed downstream of the diesel oxidation catalyst,
A nitrogen dioxide generating and accumulating unit that accumulates nitrogen monoxide by oxidizing nitric oxide in the introduced exhaust gas when the exhaust gas is introduced; and
When the temperature of the exhaust gas flowing into the filter is equal to or higher than a predetermined temperature at which the filter continuous regeneration process for burning the PM of the filter by nitrogen dioxide can be performed, and when there is an exhaust brake request, the exhaust brake is operated, A nitrogen dioxide introduction mechanism that introduces exhaust gas downstream of the filter into the nitrogen dioxide production and accumulation unit, and introduces nitrogen dioxide of the nitrogen dioxide production and accumulation unit into the exhaust gas upstream of the filter. Diesel engine system featuring. The nitrogen dioxide introduction mechanism is
An upstream exhaust brake valve disposed in the exhaust passage upstream from the diesel oxidation catalyst, and a downstream exhaust brake valve disposed in the exhaust passage downstream from the filter;
A first passage for introducing exhaust gas downstream of the filter and upstream of the downstream exhaust brake valve into the nitrogen dioxide generation and accumulation unit; and nitrogen dioxide in the nitrogen dioxide generation and accumulation unit upstream of the filter And a second passage to be introduced into the exhaust downstream of the upstream exhaust brake valve;
A first valve for opening and closing the first passage, and a second valve for opening and closing the second passage;
A control device for controlling the upstream brake valve, the downstream brake valve, the first valve, and the second valve;
The control device opens the upstream exhaust brake valve and the first valve when the exhaust brake request is present when the temperature of the exhaust gas flowing into the filter is equal to or higher than the predetermined temperature, and the downstream side A first control process for closing the exhaust brake valve and the second valve is executed. After the first control process, the upstream exhaust brake valve and the first valve are closed, and the downstream exhaust brake valve is closed. The diesel engine system according to claim 1, wherein the diesel engine system is configured to execute a second control process for opening the second valve.   The diesel engine system according to claim 1 or 2, further comprising a urea SCR system in the exhaust passage downstream of the downstream exhaust brake valve.

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