JP5332664B2 - Engine exhaust purification system - Google Patents

Description

  The present invention relates to an exhaust purification device that purifies exhaust exhausted from an engine.

  Conventionally, a diesel particulate filter (Diesel Particulate Filter; hereinafter referred to as “DPF”) that collects particulate matter (Particulate Matter; hereinafter referred to as “PM”) contained in diesel engine exhaust and purifies the exhaust is provided. Exhaust gas purification apparatuses are known (for example, Patent Document 1).

Japanese Patent Laid-Open No. 9-53442

  In an exhaust purification device equipped with a DPF, when a predetermined amount of PM is deposited on the DPF, the exhaust temperature is raised, and the DPF temperature is maintained at about 600 ° C. at which the PM starts to self-ignite, thereby forcing the DPF function. DPF forced regeneration control for performing regeneration is performed. However, in the exhaust gas purification apparatus provided with the NOx catalytic converter in the exhaust passage downstream of the DPF as in Patent Document 1, the NOx catalyst of the NOx catalytic converter is likely to be thermally deteriorated due to the thermal load by the DPF forced regeneration control. There is a problem.

  Therefore, the present invention has been made paying attention to such problems, and an object thereof is to provide an engine exhaust purification device capable of purifying exhaust gas while suppressing thermal deterioration of the NOx catalyst. To do.

The present invention solves the above problems by the following means .

The present invention is an engine exhaust purification device that includes a filter that collects particulate matter in exhaust gas, and is provided in an exhaust passage upstream of the filter to collect and desorb NOx in accordance with the air-fuel ratio. , a NOx catalytic converter having NOx catalyst for purifying the temperature of the filter, the filter temperature determination means for determining whether the particulate matter deposited in the filter is in the combustion temperature range for burning by NO ₂ in NOx And determining whether the amount of particulate matter deposited on the filter is larger than a first predetermined value which is a deposition limit amount and larger than a second predetermined value set smaller than the first predetermined value. a deposition amount determining means for, as the particulate matter deposited on the filter by NO ₂ in NOx is burned, the air-fuel to control the air-fuel ratio to the desorption air to desorb the NOx NOx catalyst is collected Control means and filter forced regeneration means for burning particulate matter deposited on the filter by raising the exhaust gas temperature, the filter temperature is within the combustion temperature range, and the accumulation amount is less than the second predetermined value. If it is larger, the air-fuel ratio control means controls the air-fuel ratio to the desorption air-fuel ratio, the particulate matter deposited on the filter is combusted, the filter temperature is not within the combustion temperature range, and the deposition amount is greater than the first predetermined value. When it is large, the exhaust gas temperature is raised by the filter forced regeneration means, and the particulate matter deposited on the filter is burned .

According to the present invention, particulate matter deposited on the filter is burned by NO _{2 in} NOx desorbed from the NOx catalyst, so the frequency of filter forced regeneration control for raising the filter temperature and burning particulate matter is reduced. be able to. This makes it possible to purify the exhaust gas while suppressing thermal deterioration of the NOx catalyst.

It is a schematic block diagram of the exhaust emission control device of the diesel engine for vehicles. And DPF temperature is a diagram showing the relationship between the oxidation rate of the PM by NO _2. It is a flowchart explaining the main routine which a controller performs.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a schematic configuration diagram of an exhaust emission control device 100 for a vehicle diesel engine.

  Referring to FIG. 1, the exhaust purification device 100 includes an engine 10, an intake passage 20 through which fresh air from the outside flows into the engine 10, an exhaust passage 30 through which exhaust from the engine 10 flows outside, and a controller 40. .

  An intake throttle valve 21 is provided in the intake passage 20.

  The intake throttle valve 21 adjusts the amount of intake air supplied to the engine 10 by changing the intake flow area of the intake passage 20. The intake air that has passed through the intake throttle valve 21 is distributed to each cylinder of the engine 10 via an intake collector.

  The engine 10 includes an injector 11 for each cylinder.

  The injector 11 is provided so as to face the combustion chamber of each cylinder of the engine 10 and injects fuel into the combustion chamber. The injected fuel is combusted by intake air that has been highly compressed in the combustion chamber and has reached a high temperature. Exhaust gas generated by the combustion is discharged from the engine 10 to the exhaust passage 30.

  In the exhaust passage 30, an oxidation catalytic converter 31, a NOx catalytic converter 32, and a DPF 33 are provided in order from the upstream.

The oxidation catalyst converter 31 carries an oxidation catalyst on a cordierite monolith carrier. When the exhaust air / fuel ratio is leaner than the stoichiometric air / fuel ratio (stoichiometric), the oxidation catalyst of the oxidation catalytic converter 31 oxidizes nitrogen monoxide (NO) contained in the exhaust to generate nitrogen dioxide (NO ₂ ).

The NOx catalytic converter 32 carries a NOx catalyst on a monolith carrier made of cordierite. NOx catalyst NOx catalytic converter 32, the exhaust air-fuel ratio is trapped NOx in ₂ such NO in the exhaust during lean of stoichiometry, exhaust air-fuel ratio is desorption of NOx when the stoichiometric or rich, reduced.

  The DPF 33 is a cordierite porous honeycomb structure, and the flow path through which the exhaust flows is partitioned into a lattice shape by a porous thin wall. The inlet of each flow path is alternately sealed, and the flow path where the inlet is not sealed is sealed at the outlet. Therefore, when the PM contained in the exhaust gas flowing into the DPF 33 passes through the porous thin wall, Collected on the surface. Therefore, the DPF 33 collects PM contained in the exhaust discharged from the engine 10 and flows the exhaust from which the PM is removed downstream.

  The controller 40 includes a microcomputer that includes a central processing unit (CPU), a read-only memory (ROM), a random access memory (RAM), and an input / output interface (I / O interface).

  The controller 40 includes a crank angle sensor 41 that detects the engine rotation speed, an accelerator pedal sensor 42 that detects the amount of depression of the accelerator pedal, a temperature sensor 43 that detects the exhaust temperature on the inlet side of the DPF 33, and an inlet side of the DPF 33 The detection data from the pressure sensor 44 for detecting the exhaust pressure of each is input as a signal.

  The controller 40 calculates the NOx accumulation amount in the NOx catalytic converter 32 and the PM accumulation amount in the DPF 33 based on these input signals, and performs regeneration control of the NOx catalyst and the DPF 33.

  By the way, in the exhaust emission control device provided with the DPF, when a predetermined amount of PM is deposited on the DPF, the DPF temperature is set to 600 ° C. or more, and the DPF forced regeneration control is executed to burn and remove the PM. Therefore, there is a problem that the NOx catalyst is likely to be thermally deteriorated due to the heat load by the DPF forced regeneration control.

In the exhaust purification apparatus 100 of the present embodiment, in addition to performing DPF forced regeneration control, PM deposited on the DPF 33 is oxidized and removed using NO ₂ stored in the NOx catalyst of the NOx catalytic converter 32. Regeneration control DPF33 by NO ₂ in NOx is, DPF temperature is performed at a low temperature than at DPF forced regeneration, 2NO and soot (C) is the main component of NO ₂ and _{PM 2 + 2C → N 2 +} 2CO 2 In this way, PM deposited on the DPF 33 is burned.

FIG. 2 is a graph showing the relationship between the DPF temperature and the oxidation rate of PM by NO ₂ .

As shown in FIG. 2, when the DPF temperature is higher than 300 ° C., the PM soot deposited on the DPF 33 is easily oxidized and removed by NO ₂ , and the oxidation rate becomes maximum when the DPF temperature is about 400 ° C. In the diesel engine 10, the DPF temperature does not exceed 400 ° C. unless control is performed to increase the exhaust temperature. Therefore, the NOx stored in the NOx catalyst when the DPF temperature is in the range of 300 ° C. to 400 ° C. ₂ is used to burn the PM deposited on the DPF 33. As described above, in the exhaust purification apparatus 100, the frequency of the DPF forced regeneration control is reduced by regenerating the DPF 33 with NO ₂ in NOx, thereby suppressing the thermal deterioration of the NOx catalyst.

  Next, the NOx catalyst and DPF 33 regeneration control performed by the controller 40 will be described with reference to FIG.

  FIG. 3 is a flowchart for explaining a main routine executed by the controller 40. This main routine is repeatedly executed at regular intervals, for example, 10 ms during the operation of the engine 100.

  In step S101, the controller 40 determines whether or not the NOx accumulation amount in the NOx catalyst of the NOx catalytic converter 32 is larger than a predetermined value NOX.

  The NOx accumulation amount is calculated by integrating the NOx amount obtained from the detection value of the crank angle sensor 41 and the detection value of the accelerator pedal sensor 42.

  When the NOx accumulation amount is larger than the predetermined value NOX, the controller 40 executes the process of step S102. In other cases, the controller 40 ends the process.

  In step S102, the controller 40 determines whether or not the DPF temperature is within a range of 300 ° C to 400 ° C. In the present embodiment, the exhaust temperature on the DPF inlet side detected by the temperature sensor 43 is estimated as the DPF temperature.

  When the DPF temperature is within the range of 300 ° C. to 400 ° C., the controller 40 executes the process of step S103, and otherwise executes the process of step S106.

  In step S103, the controller 40 determines whether or not the PM accumulation amount in the DPF 33 is larger than a predetermined value PM1.

  The PM accumulation amount is calculated based on the exhaust pressure on the DPF inlet side detected by the pressure sensor 44.

  The controller 40 executes the process of step S104 when the PM accumulation amount in the DPF 33 is larger than the predetermined value PM1, and otherwise executes the process of step S105.

  In step S104, the controller 40 performs NOx desorption control and ends the process.

  In the NOx desorption control, the exhaust air / fuel ratio is stoichiometric, more specifically, the excess air ratio λ is set to about 1.0. This exhaust air-fuel ratio is an air-fuel ratio at which NOx is removed from the NOx catalyst. The exhaust air / fuel ratio is controlled by adjusting the opening of the intake throttle valve 21 and the fuel injection amount from the injector 11.

  Note that the exhaust air-fuel ratio in the NOx desorption control is substantially the same as stoichiometric, but may be slightly richer.

By controlling the exhaust air / fuel ratio as described above, NOx stored in the NOx catalyst of the NOx catalytic converter 32 is desorbed. Most of the desorbed NOx flows into the DPF 33 without being purified by the NOx catalyst. At this time, since the DPF temperature is about 300 ° C. to 400 ° C., PM soot accumulated on the DPF 33 is burned and removed by NO ₂ in NOx. Thereby, the NOx catalyst of the NOx catalytic converter 32 can be regenerated and the DPF 33 can also be regenerated.

  When the PM accumulation amount is smaller than PM1, in step S105, the controller 40 performs NOx purification control and ends the process.

  In the NOx purification control, the exhaust air-fuel ratio is richer than stoichiometric, more specifically, the excess air ratio λ is controlled to about 0.8, so that NOx stored in the NOx catalyst of the NOx catalytic converter 32 is removed. The desorbed and desorbed NOx is reduced and purified by hydrocarbon (HC) and carbon monoxide (CO) in the exhaust gas. As a result, the NOx catalyst of the NOx catalyst converter 32 can be regenerated.

  If the exhaust air-fuel ratio is made richer than the stoichiometric ratio, the amount of PM contained in the exhaust increases. However, since the NOx purification control is performed when the PM accumulation amount is smaller than the predetermined value PM1, even if the PM amount in the exhaust increases. In the DPF 33, PM is not excessively deposited.

  On the other hand, when the DPF temperature is not within the range of 300 ° C. to 400 ° C., in step S106, the controller 40 determines whether or not the PM accumulation amount in the DPF 33 is larger than the predetermined value PM2. The predetermined value PM2 is a value larger than the predetermined value PM1 in step S103, and is a PM accumulation amount limit value.

  When the PM accumulation amount in the DPF 33 is larger than the predetermined value PM2, it is necessary to regenerate the DPF as soon as possible, so the controller 40 performs DPF forced regeneration control in step S107. In other cases, the controller 40 executes the process of step S105.

  In step S107, the controller 40 performs DPF forced regeneration control and ends the process.

  In the DPF forced regeneration control, the main fuel injection timing is retarded or post fuel injection is performed after the main fuel injection, the exhaust temperature is increased, the DPF temperature is maintained at about 600 ° C., and the DPF 33 is accumulated. Burn PM.

  As described above, in the exhaust purification device 100 of the present embodiment, the following effects can be obtained.

In the exhaust purification apparatus 100, the NOx catalytic converter is provided in the exhaust passage 30 upstream of the DPF 33, and NOx desorption control is performed when the DPF temperature is from 300 ° C to 400 ° C. The PM soot deposited on the DPF 33 is burned by NO ₂ . Since the DPF 33 is regenerated using NO ₂ desorbed from the NOx catalyst, the frequency of the DPF forced regeneration control that needs to raise the exhaust gas temperature can be reduced. Therefore, the exhaust purification device 100 can purify the exhaust while suppressing thermal deterioration of the NOx catalyst.

  In the DPF forced regeneration control, post fuel injection is performed separately from the main fuel injection to raise the exhaust temperature. However, if the frequency of the DPF forced regeneration control is reduced, the number of post fuel injections is also reduced. Is suppressed and fuel efficiency is improved.

  Note that the present invention is not limited to the above-described embodiment, and it is obvious that various modifications can be made within the scope of the technical idea.

  In this embodiment, the exhaust temperature on the DPF inlet side detected by the temperature sensor 43 is the DPF temperature. However, a temperature sensor may be installed in the DPF 33 to directly detect the DPF temperature.

  In the present embodiment, the PM accumulation amount is calculated based on the exhaust pressure on the DPF inlet side detected by the pressure sensor 44, but is obtained from the detection value of the crank angle sensor 41 and the detection value of the accelerator pedal sensor 42. The PM accumulation amount may be calculated by integrating the PM amount.

100 Exhaust Purification Device 10 Engine 11 Injector 20 Intake Passage 21 Intake Throttle Valve 30 Exhaust Passage 31 Oxidation Catalytic Converter 32 NOx Catalytic Converter 33 Diesel Particulate Filter (Filter)
40 controller (air-fuel ratio control means)

Claims (4)

An exhaust purification device for an engine comprising a filter for collecting particulate matter in exhaust gas,
A NOx catalytic converter provided in an exhaust passage upstream of the filter and having a NOx catalyst for collecting, desorbing and purifying NOx according to the air-fuel ratio;
Filter temperature determining means for determining whether the temperature of the filter is within a combustion temperature range in which particulate matter deposited on the filter by NO ₂ in NOx burns;
It is determined whether the amount of particulate matter deposited on the filter is larger than a first predetermined value that is a deposition limit amount and larger than a second predetermined value that is set smaller than the first predetermined value. A deposit amount judging means for
As the particulate matter deposited on the filter by NO ₂ in NOx is burned, the air-fuel ratio control means for controlling the air-fuel ratio to the desorption air-fuel ratio the NOx catalyst desorbs NOx was collected,
Filter forced regeneration means for burning particulate matter deposited on the filter by raising the exhaust temperature,
Particles deposited on the filter by controlling the air-fuel ratio to the desorption air-fuel ratio by the air-fuel ratio control means when the filter temperature is in the combustion temperature range and the accumulation amount is larger than a second predetermined value. Burning the substance,
When the filter temperature is not within the combustion temperature range and the accumulation amount is larger than a first predetermined value, the exhaust temperature is raised by the filter forced regeneration means, and particulate matter deposited on the filter is burned.
An exhaust emission control device for an engine. The air-fuel ratio control means desorbs the NOx collected by the NOx catalyst by controlling the desorption air-fuel ratio so that it is slightly richer than the stoichiometric air-fuel ratio or the stoichiometric air-fuel ratio.
The engine exhaust gas purification apparatus according to claim 1. The air-fuel ratio control means is configured such that the filter temperature is within the combustion temperature range and the accumulation amount is smaller than a second predetermined value, and the filter temperature is not within the combustion temperature range and the accumulation amount is the first. When the air-fuel ratio is smaller than a predetermined value, the air-fuel ratio is controlled to be a purification air-fuel ratio richer than the desorption air-fuel ratio, and NOx trapped in the NOx catalyst is desorbed and purified;
The exhaust emission control device for an engine according to claim 1 or 2. The combustion temperature range is the temperature range of 400 ° C. from 300 ° C., an exhaust purifying apparatus for an engine according to any one of claims 1 to 3, wherein the.

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