JP2004346795A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device for an internal combustion engine capable of suppressing worsening of fuel economy and sufficiently recovering NOx purifying performance by efficiently purging sulfur in a short time while preventing the thermal degradation of a catalyst. <P>SOLUTION: This exhaust emission control device for the internal combustion engine has an NOx storage catalyst 16 interposed in an exhaust pipe 7 to absorb NOx in exhaust gas in a lean gas state with high oxygen concentration while releasing/reducing the NOx in a rich gas state with low oxygen concentration and high reducing agent concentration. The exhaust emission control device is provided with a passage changeover means comprising pipelines 7a-7d, rotary valves 22a, 22b, and the like capable of changing an exhaust gas passage with respect to the NOx storage catalyst 16 over to normal or reverse flow; a start timing determining means for determining the start timing of sulfur purge control for desorbing SOx poisoning the NOx storage catalyst 16; and an electronic control unit 30 for operating the passage changeover means to make exhaust gas flow backward to the NOx storage catalyst 16 when the start timing determining means determines the start timing of sulfur purge control. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an exhaust purification device for an internal combustion engine in which a NOx storage catalyst is interposed in an exhaust passage.
[0002]
[Prior Art and Problems to be Solved by the Invention]
2. Description of the Related Art In recent years, lean-burn internal combustion engines in which the internal combustion engine is operated at a lean air-fuel ratio to improve fuel efficiency and the like have been put to practical use. This lean-burn internal combustion engine has a problem in that when operated at a lean air-fuel ratio, the three-way catalyst cannot sufficiently purify nitrogen oxides (NOx) in exhaust gas due to its purification characteristics. A NOx storage (type) catalyst that stores NOx in exhaust gas therein and releases and reduces NOx stored during operation at a stoichiometric or rich air-fuel ratio is employed.
[0003]
The NOx storage catalyst, NOx in exhaust gas in an excess oxygen state of the internal combustion engine (lean state) occluded as nitrate (X-NO _3), occluded NOx with a reducing agent carbon monoxide (CO), etc. This is a catalyst having the property of releasing in an excess state (rich gas state) and reducing it to nitrogen (N ₂ ) (carbonate X-CO ₃ is generated at the same time). By the way, the fuel contains a sulfur (S) component, and the S component reacts with oxygen in the lean gas state to form a sulfur oxide (SOx), and this SOx is stored as a sulfate in the form of NOx as well as NOx. Occluded by the catalyst.
[0004]
When the sulfur component is occluded in the NOx storage catalyst in this manner, the NOx is not stored, so that the performance of the NOx storage catalyst is reduced. When the sulfur component ratio is increased, the NOx storage catalyst does not function as a NOx storage catalyst. Therefore, in order to maintain the performance of the NOx storage catalyst, it is necessary to periodically release (S purge) the stored (poisoned) SOx.
[0005]
It is said that the S purge is established under a high temperature rich gas condition. However, since it is difficult to achieve high-temperature rich gas conditions only by engine combustion, fuel injection (addition of light oil) to the exhaust pipe is performed to cause a combustion reaction on the NOx storage catalyst, and the reaction heat causes NOx storage. It is realistic to raise the temperature of the catalyst.
[0006]
Here, as a result of a detailed investigation of the state of S poisoning of the NOx storage catalyst by the present inventors, S was determined as shown in FIG. 4 irrespective of the SOx concentration in the exhaust gas (S concentration in the used fuel). It was found that a large amount was accumulated upstream of the exhaust gas on the NOx storage catalyst. 4 (a) is a short-time S poisoning, and FIG. 4 (b) is a long-time S poisoning. The NOx storage catalyst is divided into six equal parts from the upstream side, and the S concentration contained in each is divided. Was subjected to quantitative analysis. On the other hand, it has been found that when the heat of catalytic reaction due to the addition of light oil is used as an assist in enriching at a high temperature, the temperature tends to increase more in the downstream than in the upstream as shown in FIG.
[0007]
Therefore, if S purge is performed by adding light oil so that the temperature of the NOx storage catalyst is not deteriorated by heat, the upstream S component cannot be sufficiently removed. If the temperature is controlled so that the upstream S component can be removed, the downstream side is excessively heated. There is a problem that the possibility of heat deterioration due to heating increases.
[0008]
Therefore, the present inventors have paid attention to the fact that the S purge can be performed efficiently by reversing the exhaust gas flow path for the NOx storage catalyst (forward / backward switching) during the S purge.
[0009]
A technique for reversing the exhaust gas flow path with respect to the catalyst is disclosed in Japanese Patent Application Laid-Open Publication No. H11-163873, which reverses the flow of exhaust gas passing through the particulate filter under a predetermined condition. The fine particles are dispersed and collected on both surfaces of the wall, and do not reverse the flow of the exhaust gas during the S purge. Therefore, the technique disclosed in Patent Document 1 does not perform the S purge control according to the temperature distribution of the catalyst, so that the S purge cannot be performed efficiently.
[0010]
[Patent Document 1]
JP 2002-97926 A
Therefore, an object of the present invention is to provide an exhaust gas purifying apparatus for an internal combustion engine that can efficiently perform S purge in a short time while preventing thermal deterioration of a catalyst, thereby sufficiently recovering NOx purification performance and suppressing deterioration of fuel efficiency. Is to do.
[0012]
[Means for Solving the Problems]
To achieve the above object, an exhaust gas purification device for an internal combustion engine according to claim 1 of the present invention is an exhaust gas purification device for an internal combustion engine in which a NOx storage catalyst is interposed in an exhaust passage.
Flow path switching means capable of switching an exhaust gas flow path for the NOx storage catalyst between forward and reverse flow;
Start time determination means for determining a start time of S purge control for desorbing poisoned SOx by the NOx storage catalyst;
Control means for operating the flow path switching means to cause the exhaust gas to flow backward to the NOx storage catalyst when the start time determination means determines that it is the start time of the S purge control;
It is characterized by having. Thus, the S purge can be efficiently performed in a short time while preventing thermal deterioration.
[0013]
The exhaust gas purifying apparatus for an internal combustion engine according to claim 2 of the present invention, wherein the control means includes an S purge possibility determining means for determining whether or not the operating state of the engine is an operating state capable of performing the S purge. When the timing determining means determines that it is the start time of the S purge control, and the S purge possibility determining means determines that the S purge is possible, the flow switching means is operated by the flow switching control means. The exhaust gas is caused to flow back to the NOx storage catalyst. Thus, it is determined whether or not the operating state allows the S purge, and the S purge control is performed only in the operating state where the S purge can be performed. Therefore, unnecessary rich operation is not performed, and deterioration of fuel efficiency can be suppressed. At the same time, the sulfate can be properly and reliably eliminated.
[0014]
In the exhaust gas purifying apparatus for an internal combustion engine according to claim 3 of the present invention, when the S purge possibility determining means determines that the S purge is not possible during the execution of the S purge control, The purge control is interrupted to switch the exhaust gas flow path to the normal flow, and the S purge control is restarted when it is determined that the operation state of the engine has returned to the operation state in which the S purge can be performed during the suspension of the S purge control. Then, the exhaust gas flow path is switched to the reverse flow. As a result, useless rich operation is not performed, and deterioration of fuel efficiency and deterioration of exhaust gas properties can be suppressed.
[0015]
According to a fourth aspect of the present invention, in the exhaust gas purifying apparatus for an internal combustion engine, the control unit includes a target S purge amount setting unit that sets a target S purge amount. When the purge control is restarted, a value obtained by subtracting the S purge amount at the time when the S purge control is interrupted from the target S purge amount set by the target S purge amount setting means is set as a new target S purge amount. It is characterized by the following. As a result, the S purge control can be performed quickly without waste, and deterioration of fuel efficiency is further suppressed.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an exhaust gas purifying apparatus for an internal combustion engine according to the present invention will be described in detail with reference to the drawings by using embodiments.
[0017]
[Example]
FIG. 1 is a schematic configuration diagram in which an exhaust gas purification device for an internal combustion engine of the present invention is applied to a compression ignition type internal combustion engine (diesel engine), FIG. 2 is an explanatory diagram of the operation of a flow path switching unit, and FIG. It is a flowchart.
[0018]
As shown in FIG. 1, each cylinder of the engine body 1 is supplied with intake air from an air cleaner (not shown) via an intake pipe 2 and an intake manifold 3, and is not shown via a common rail 4 and a fuel injection valve 5. Fuel is supplied from a fuel pump. The fuel injection valve 5 is of an electronic control type whose injection amount and injection timing are controlled by an electronic control unit (ECU) 30, which will be described later. Wiring in the drawing is omitted to avoid complication. On the other hand, the exhaust gas discharged from each cylinder of the engine body 1 is discharged to the atmosphere via an exhaust manifold 6 as an exhaust passage and an exhaust pipe 7.
[0019]
A turbocharger 8 is provided between the intake pipe 2 and the exhaust pipe 7, and the intake air is pressurized by a compressor that rotates integrally with a turbine rotated by the exhaust gas and supplied to each cylinder of the engine body 1. It has become. At this time, the pressurized air is cooled by the intercooler 9 interposed in the intake pipe 2, so that the efficiency of charging each cylinder of the engine body 1 is increased.
[0020]
The intake pipe 2 is provided with an air flow sensor 10 located upstream of the turbocharger 8 for detecting the amount of intake air, and an intake throttle valve 11 located downstream of the intercooler 9. The output signal of the airflow sensor 10 is input to the ECU 30, and the opening and closing of the intake throttle valve 11 is controlled by the ECU 30 via an actuator (not shown).
[0021]
The intake manifold 3 and the exhaust manifold 6 are connected by an EGR (exhaust gas recirculation) passage 12, and are controlled at predetermined times by an EGR valve 14 controlled to be opened and closed by an actuator 13 by the ECU 30 according to an engine operating state. A fixed amount of EGR is performed to suppress the generation of NOx as much as possible. The EGR passage 12 is provided with an EGR cooler 15 for cooling the EGR gas.
[0022]
Then, a NOx storage catalyst 16 is interposed in the exhaust pipe 7. The NOx storage catalyst 16 has a characteristic of absorbing NOx in exhaust gas in a lean gas state having a high oxygen concentration, and releasing and reducing this NOx in a rich gas state having a low oxygen concentration and a high concentration of a reducing agent such as HC or CO. .
[0023]
Rotary valves 22a and 22b and flow paths 7c and 7d as flow switching means are provided between the flow path 7a of the exhaust pipe 7 upstream of the NOx storage catalyst 16 and the flow path 7b downstream of the NOx storage catalyst 16. The exhaust gas passage for the NOx storage catalyst 16 can be switched between forward and reverse flows.
[0024]
In other words, the rotary valves 22a and 22b are controlled by the ECU 30 as control means for causing the exhaust gas to flow backward to the NOx storage catalyst 16, and as shown in FIG. The exhaust gas flows through the pipe 7a → the NOx storage catalyst 16 → the pipe 7b (see FIG. 2A). During the S purge control, the pipe 7c → the pipe 7d → the NOx storage catalyst 16 → the pipe 7a → The switching is controlled so as to flow through the pipe 7d (see FIG. 2B).
[0025]
The exhaust pipe 7 immediately before the rotary valve 22a and the exhaust pipe 7 immediately after the rotary valve 22b are provided with temperature sensors (catalyst front and rear temperature sensors) 17a and 17b for detecting the temperature of the exhaust gas. Is provided with an oxygen sensor (catalyst outlet oxygen sensor) 18 for detecting the oxygen concentration in the exhaust gas. The output signals of these sensors 17a, 17b, 18 are input to the ECU 30.
[0026]
The exhaust pipe 7 is provided with an exhaust throttle valve 19 and an oxygen sensor (engine outlet oxygen sensor) 20 for detecting the oxygen concentration in the exhaust gas which are located downstream of the turbocharger 8 in order toward the downstream side. The exhaust throttle valve 19 is controlled to open and close by an ECU 30 via an actuator (not shown), and an output signal of the oxygen sensor 20 is input to the ECU 30.
[0027]
Further, a fuel injection valve 21 whose injection amount and injection timing are controlled by the ECU 30 is provided in the exhaust pipe 7 located upstream of the NOx storage catalyst 16 and downstream of the oxygen sensor 20.
[0028]
The ECU 30 includes a microcomputer (CPU), a memory, and an interface as an input / output signal processing circuit. The input side of the ECU 30 is connected to the air flow sensor 10, the temperature sensors 17a and 17b, and the oxygen sensors 18 and 20, and detects a rotation sensor (not shown) for detecting an engine speed and a vehicle speed. A vehicle speed sensor, an accelerator opening sensor for detecting an accelerator pedal opening, and the like are connected to each other, and engine operation information from these sensors and the like is input. On the other hand, the fuel injection valves 5 and 21, the intake throttle valve 11, the EGR valve 14, the exhaust throttle valve 19, the rotary valves 22a and 22b, and the like are connected to the output side of the ECU 30.
[0029]
The ECU 30 controls the injection amount and the injection timing of the fuel injection valve 5 based on the engine operation information from the above-described sensors and the like, and controls the opening and closing of the EGR valve 14 according to the engine operation state to control the PM and NOx. Is suppressed as much as possible.
[0030]
Further, when the exhaust gas is enriched only by in-cylinder combustion, the ECU 30 controls the opening and closing of the fuel injection valve 21 by controlling the opening and closing of the fuel injection valve 21 because there are many problems such as generation of smoke and torque fluctuation particularly in a high load region. By injecting (adding) fuel (light oil) from the injection valve 21 to the exhaust pipe 7, the exhaust gas is enriched, and the NOx storage catalyst 16 purifies NOx.
[0031]
Further, in order to desorb the SOx poisoned by the NOx storage catalyst 16, the ECU 30 determines when the poisoning amount (hereinafter referred to as the S accumulation amount) reaches a predetermined value (determines the start time of the S purge control). The fuel injection valve 21 injects fuel to make a rich gas state, and switches the rotary valves 22a and 22b to cause exhaust gas to flow back to the NOx storage catalyst 16 to perform S purge control. Has become.
[0032]
The S purge control will be described in detail with reference to the flowchart of FIG.
First, in step P1, it is determined whether or not the S accumulation amount calculated from the integrated value of the fuel consumption amount of the engine body 1 has reached a predetermined amount for starting the S purge (start timing determination means). In step P2, an S purge target amount is set according to the S accumulation amount (target S purge amount setting means). On the other hand, if NO, the calculation of the S accumulation amount from the integrated value of the fuel consumption amount is continued in Step P3.
[0033]
After step P2, at step P4, the operating state of the engine body 1 (torque, rotation, vehicle speed, accelerator opening, exhaust temperature (detected by the catalyst front-rear temperature sensors 17a, 17b), λ (excess air ratio, engine outlet It is determined whether or not the operating state is such that the exhaust gas temperature (the temperature of the NOx storage catalyst 16) can be increased, such as in a high load region, where S purging is possible (S purging possible determining means). For example, in step P5, the target fuel (light oil) addition amount to the exhaust pipe 7 is calculated based on the addition amount map determined by the exhaust temperature (the temperature of the NOx storage catalyst 16) and λ. On the other hand, if the answer is NO, the process waits until the operation state in which S purge can be performed.
[0034]
After step P5, fuel injection (light oil addition) is started from the fuel injection valve 21 in step P6 to shift to a rich gas state in which the oxygen concentration is low and the reducing agent concentration is high, and the rotary valves 22a and 22b are switched. The flow path is switched so that the exhaust gas flows backward to the NOx storage catalyst 16, and then, in step P7, it is determined whether or not the exhaust gas is in a rich state (rich gas state) based on a signal from the catalyst outlet oxygen sensor 18.
[0035]
If it is possible in step P7, it is determined in step P8 whether the S purge operation can be continued based on the operating state (torque, rotation, vehicle speed, accelerator opening) of the engine body 1. If NO in step P7, the amount of fuel injection from the fuel injection valve 21 is corrected (increased) in step P9.
[0036]
During this time, the S purge amount is stored. This S purge amount is calculated based on a SOx desorption amount map determined by the temperature of the NOx storage catalyst 16 estimated (calculated) from the exhaust gas temperature detected by the before and after catalyst temperature sensors 17a and 17b. The stored S purge amount is deducted from the S purge target amount when the present S purge control is re-executed after the interruption in step P8.
[0037]
If it is possible in the step P8, the S purge control is continued until the set S purge target amount is achieved in the step P10. When the S purge target amount is achieved, the rotary valves 22a and 22b are switched in the step P12. Then, the exhaust gas flow path is returned to the normal (forward) flow of the exhaust gas to the NOx storage catalyst 16, and the S purge control ends.
[0038]
On the other hand, if NO in step P8, the fuel injection from the fuel injection valve 21 is stopped in step P11, and the rotary valves 22a and 22b are switched to allow the exhaust gas to flow forward (forward) to the NOx storage catalyst 16. The exhaust gas flow path is returned to its original state, and the process returns to step P4 and waits until an operation state in which S purge can be performed.
[0039]
As described above, in the present embodiment, when the S purge control is performed, the rotary valves 22 a and 22 b are switched to switch the flow path so that the exhaust gas flows back to the NOx storage catalyst 16. Efficient S purge according to the distribution and the temperature distribution can be performed. That is, the reaction heat due to the addition of light oil flows to the portion where the amount of S deposited is large, and the progress of the S purge is accelerated. Further, since the temperature rise more than necessary can be avoided, it is possible to minimize the progress of the deterioration of the NOx storage catalyst 16 due to heat. As a result, it is possible to sufficiently recover the NOx purification performance and to suppress deterioration in fuel efficiency.
[0040]
Further, when the S purge control is interrupted, the S purge amount is stored, and when the S purge control is performed again, the stored S purge amount is subtracted from the S purge target amount. Purge control can be performed, and fuel economy deterioration is further suppressed.
[0041]
It is needless to say that the present invention is not limited to the above embodiments, and various changes can be made without departing from the scope of the present invention. For example, the channel switching means may have various structures. Further, the exhaust gas purification device for an internal combustion engine of the present invention can be applied to a spark ignition type internal combustion engine (gasoline engine). In this case, the exhaust gas can be enriched by in-cylinder combustion.
[0042]
【The invention's effect】
As described above, according to the first aspect of the present invention, in an exhaust gas purification apparatus for an internal combustion engine in which a NOx storage catalyst is provided in an exhaust passage, a flow path for switching the exhaust gas flow path for the NOx storage catalyst between forward and reverse flows. Switching means, start time determining means for determining the start time of S purge control for desorbing SOx poisoned by the NOx storage catalyst, and determining that the start time determining means is the start time of S purge control. Control means for activating the flow path switching means to cause the exhaust gas to flow back to the NOx storage catalyst, so that the S purge can be efficiently performed in a short time while preventing thermal deterioration, and the NOx purification performance Can be sufficiently recovered, and deterioration of fuel efficiency can be suppressed.
[0043]
According to the second aspect of the present invention, the control unit includes an S purge possibility determination unit that determines whether the operation state of the engine is an operation state in which the S purge is possible. Is determined to be a start time, and when the S purge possibility determination means determines that the S purge is possible, the flow path switching means is operated by the flow path switching control means so that the NOx storage catalyst is controlled. Since the exhaust gas is caused to flow backward, it is determined whether or not the operating state allows the S purge, and the S purge control is performed only in the operating state where the S purge can be performed. The deterioration can be suppressed, and the sulfate can be properly and reliably desorbed.
[0044]
According to the third aspect of the present invention, when the S purge possibility determination means determines that the S purge is not possible during the execution of the S purge control, the control means suspends the S purge control and exhausts the gas. The gas flow path is switched to the normal flow, and when it is determined that the operation state of the engine has returned to the operation state in which the S purge can be performed during the suspension of the S purge control, the S purge control is restarted to change the exhaust gas flow path. Since the flow is switched to the reverse flow, useless rich operation is not performed, and deterioration in fuel efficiency and deterioration in exhaust gas properties can be suppressed.
[0045]
According to the invention of claim 4, the control means includes a target S purge amount setting means for setting a target S purge amount. When the S purge control is interrupted and the S purge control is thereafter resumed, , The value obtained by subtracting the S purge amount at the time point when the S purge control is interrupted from the target S purge amount set by the target S purge amount setting means is set as a new target S purge amount, so that the S Purge control can be performed, and fuel consumption deterioration is further suppressed.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram in which an exhaust gas purification device for an internal combustion engine of the present invention is applied to a compression ignition type internal combustion engine (diesel engine).
FIG. 2 is an explanatory diagram of an operation of a flow path switching unit.
FIG. 3 is a flowchart of S purge control.
FIG. 4 is a graph showing a sulfur distribution in a catalyst after sulfur poisoning.
FIG. 5 is a graph showing a temperature distribution in a catalyst when gas oil is added.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Engine main body, 2 intake pipes, 3 intake manifolds, 4 common rails, 5 fuel injection valves, 6 exhaust manifolds, 7 exhaust pipes, 7a to 7d pipes, 8 turbochargers, 9 intercoolers, 10 air flow sensors, 11 intake throttles Valve, 12 EGR passage, 13 actuator, 14 EGR valve, 15 EGR cooler, 16 NOx storage catalyst, 17a, 17b temperature sensor, 18 oxygen sensor (catalyst outlet oxygen sensor), 19 exhaust throttle valve, 20 oxygen sensor (engine outlet oxygen) Sensor), 21 fuel injection valve, 22a, 22b rotary valve, 30 electronic control unit (ECU)

Claims (4)

The exhaust gas of the internal combustion engine is provided with an NOx storage catalyst in the exhaust passage, in which a NOx in the exhaust gas is absorbed in a lean gas state with a high oxygen concentration while releasing and reducing this NOx in a rich gas state with a low oxygen concentration and a high reducing agent concentration. In the purification device,
Flow path switching means capable of switching an exhaust gas flow path for the NOx storage catalyst between forward and reverse flow;
Start time determination means for determining a start time of S purge control for desorbing poisoned SOx by the NOx storage catalyst;
Control means for operating the flow path switching means to cause the exhaust gas to flow backward to the NOx storage catalyst when the start time determination means determines that it is the start time of the S purge control;
An exhaust gas purification device for an internal combustion engine, comprising: The control means includes an S purge possibility determining means for determining whether or not the operating state of the engine is an operating state in which the S purge can be performed, and the start time determining means determines that the start time of the S purge control has been reached. And, when the S purge possibility determining means determines that the S purge is possible, the flow path switching means is operated by the flow path switching control means to cause the exhaust gas to flow backward to the NOx storage catalyst. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1. The control means interrupts the S purge control and switches the exhaust gas flow path to a normal flow when the S purge possibility determination means determines that the S purge is not possible during the execution of the S purge control. When it is determined that the operation state of the engine has returned to the operation state in which the S purge can be performed while the S purge control is suspended, the S purge control is restarted to switch the exhaust gas flow path to the reverse flow. Item 3. An exhaust gas purification device for an internal combustion engine according to Item 2. The control means includes a target S purge amount setting means for setting a target S purge amount. When the S purge control is interrupted and the S purge control is resumed thereafter, the time when the S purge control is interrupted is set. 4. The exhaust gas purifying apparatus for an internal combustion engine according to claim 3, wherein a value obtained by subtracting the S purge amount from the target S purge amount set by the target S purge amount setting means is set as a new target S purge amount. .

Images