JP2004308526A - Exhaust emission cleaning device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission cleaning device for an internal combustion engine adding an accurate amount of a reducing agent by reflecting a learning value in feedback control in case of adding fuel as the reducing agent to an exhaust system only in the case of the same cylinder combustion state as learning period. <P>SOLUTION: Provided are the exhaust emission cleaning device is arranged in the exhaust system, and provided with a fuel adding means adding fuel to the exhaust emission cleaning device, and a first air-fuel ratio detecting means detecting an air-fuel ratio in the downstream side of the exhaust emission cleaning device. A feedback value is found out so that the air-fuel ratio detected by the first air-fuel ratio detecting means is set to a target air-fuel ratio, memorized as the learning value, and reflected to a fuel adding amount from the next time. Further, the device has a second air-fuel ratio detecting means detecting the air-fuel ratio of exhaust gas discharged from the cylinder. The fuel amount added from the fuel adding means is determined by applying the learning value memorized corresponding to the air-fuel ratio detected by the second air-fuel ratio detecting means. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an exhaust gas purification device for an internal combustion engine.
[0002]
[Prior art]
In an internal combustion engine, such as a diesel engine or a lean-burn gasoline engine, which operates by burning an air-fuel mixture in an oxygen-excess state, an exhaust purification device is used to purify nitrogen oxides (hereinafter referred to as NOx) in exhaust gas. A NOx absorbent is provided in the exhaust passage.
[0003]
Such a NOx absorbent absorbs NOx in the inflow exhaust when the air-fuel ratio of the inflow exhaust is high, and absorbs the NOx in the exhaust when the air-fuel ratio of the inflow exhaust is low, as represented by the NOx storage reduction catalyst. When the NOx absorbent is disposed in the exhaust passage, NOx discharged from the internal combustion engine is absorbed by the NOx absorbent, and is appropriately reduced by adding fuel to the exhaust gas. Released in the atmosphere.
[0004]
Further, the fuel of the internal combustion engine usually contains sulfur and the like. At the time of combustion of the engine, not only NOx but also sulfur oxides (hereinafter referred to as SOx) such as SO ₂ and SO ₃ are generated at the same time. This SOx is also absorbed by the NOx absorbent similarly to NOx, but becomes a chemically stable sulfate (BaSO ₄ ) over time and is accumulated in the NOx absorbent.
[0005]
For this reason, SOx poisoning occurs in which the original function of the NOx absorbent that absorbs NOx is impaired, so that the SOx absorbed by the NOx absorbent needs to be released from the NOx absorbent at a predetermined timing.
[0006]
A device for adding a fuel as a reducing agent to exhaust gas for such a purpose is known. For example, a NOx absorbing material is provided in an exhaust passage of an internal combustion engine and a reducing agent is supplied upstream of the NOx absorbing material. There is an exhaust gas purifying apparatus including an agent supply unit and a reducing agent supply amount correcting unit that corrects the amount of the reducing agent to be supplied by the reducing agent supplying unit based on the air-fuel ratio of the exhaust gas flowing out through the NOx absorbent (for example, Patent Document 1).
[0007]
In such a reducing agent supply amount correcting means of the exhaust gas purification device, the reducing agent supply amount supplied by the reducing agent supply means is reduced under a predetermined condition based on the air-fuel ratio downstream of the NOx absorbent. The amount of fuel added from the fuel addition nozzle is determined by performing so-called feedback control that converges on the supply amount of the agent.
[0008]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 2002-188430
[Problems to be solved by the invention]
However, there are cases where the temperature of the catalyst cannot be accurately controlled even when the above-described feedback control is performed. By focusing on the change in the combustion air-fuel ratio in the cylinder of the internal combustion engine, it was found that by considering the change in the air-fuel ratio in the cylinder, it is possible to more accurately control the required amount of fuel added to the exhaust gas. Was.
[0010]
The present invention has been made in view of the above circumstances, and reflects a learning value in feedback control when adding fuel as a reducing agent to an exhaust system only in the case of a similar in-cylinder combustion state at the time of learning. Accordingly, it is an object of the present invention to provide an exhaust gas purifying apparatus for an internal combustion engine, in which an accurate amount of a reducing agent can be added.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, the present invention stores a feedback learning value of air-fuel ratio control by fuel addition corresponding to an air-fuel ratio in a cylinder serving as a base when adding fuel to exhaust gas. When the base air-fuel ratio is the same or similar, the learned value is applied.
[0012]
That is, an exhaust purification device installed in the exhaust system,
Fuel addition means for adding fuel to the exhaust gas purification device;
First air-fuel ratio detection means for detecting an air-fuel ratio downstream of the exhaust gas purification device,
In the internal combustion engine, a feedback value is obtained so that the air-fuel ratio detected by the first air-fuel ratio detection means becomes a target air-fuel ratio, and this feedback value is stored as a learning value and reflected in a fuel addition amount for the next and subsequent times.
A second air-fuel ratio detecting means for detecting an air-fuel ratio of the exhaust gas discharged from the cylinder; and applying a learning value stored in correspondence with the air-fuel ratio detected by the second air-fuel ratio detecting means. Determining the amount of fuel added from the fuel adding means.
[0013]
In this way, even when the combustion state of the internal combustion engine changes and the air-fuel ratio in the base cylinder changes, a learning value suitable for the combustion state is always selected during feedback control of fuel addition to the exhaust system. Since it is applied and applied, more accurate fuel addition can be performed.
[0014]
In this case, it is preferable to divide the air-fuel ratio in the cylinder into a plurality of stages according to values, and to apply a learning value corresponding to the stage to which the value of the air-fuel ratio at the time of adding the fuel belongs.
[0015]
The air-fuel ratio may be determined by dividing the air-fuel ratio into any number of stages. However, it is generally preferable to divide the air-fuel ratio into two to four stages.
[0016]
It is preferable that the learning value is reflected only when it is determined that the air-fuel ratio in the cylinder belongs to a predetermined corresponding stage at the next fuel addition.
[0017]
Further, the present invention can be applied to the case where the fuel addition is performed by the SOx poisoning recovery control of the catalyst installed in the exhaust system.
[0018]
According to the present invention, at the time of feedback control of fuel addition to the exhaust system, a learning value suitable for the combustion state of the internal combustion engine is selected and applied. Therefore, due to the difference between the learned value of the air-fuel ratio when the fuel in the cylinder is lean and the learned value of the air-fuel ratio when the fuel is rich, the overheating of the catalyst which may occur when the same learned value is applied. Can be prevented. Particularly, in the SOx poisoning recovery control, an increase in the amount of fuel added more than necessary and an increase in the catalyst temperature are suppressed.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, specific embodiments of the exhaust gas purification apparatus according to the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine 1 to which an exhaust purification device according to the present embodiment is applied, and an intake and exhaust system thereof.
[0020]
The internal combustion engine 1 shown in FIG. 1 is a water-cooled four-cycle diesel engine having four cylinders 2.
[0021]
The internal combustion engine 1 includes a fuel injection valve 3 for directly injecting fuel into a combustion chamber of each cylinder 2. Each fuel injection valve 3 is connected to a pressure accumulation chamber (common rail) 4 for accumulating fuel up to a predetermined pressure.
[0022]
The common rail 4 communicates with a fuel pump 6 via a fuel supply pipe 5. Fuel discharged from the fuel pump 6 is accumulated to a predetermined pressure by the common rail 4 and distributed to the fuel injection valve 3 of each cylinder 2. Is done.
[0023]
An intake branch pipe 8 is connected to the internal combustion engine 1, and each branch pipe of the intake branch pipe 8 communicates with a combustion chamber of each cylinder 2 via an intake port (not shown).
[0024]
The intake branch pipe 8 is connected to the intake pipe 9, and an intake throttle valve 13 for adjusting the flow rate of intake air flowing through the intake pipe 9 is provided at a position located immediately upstream of the intake branch pipe 8. .
[0025]
The intake pipe 9 located between the air flow meter 11 and the intake throttle valve 13 installed upstream of the intake pipe 9 is provided with a centrifugal supercharger (turbocharger) 15 that operates using the energy of exhaust gas as a driving source. A compressor housing 15a is provided.
[0026]
On the other hand, an exhaust branch pipe 18 is connected to the internal combustion engine 1, and each branch pipe of the exhaust branch pipe 18 communicates with the combustion chamber of each cylinder 2 via an exhaust port 1b.
[0027]
The exhaust branch pipe 18 is connected to a turbine housing 15 b of the centrifugal supercharger 15. The turbine housing 15b is connected to an exhaust pipe 19, which communicates downstream with the atmosphere.
[0028]
A storage-reduction type NOx catalyst 20 (hereinafter simply referred to as a NOx catalyst) including a NOx holding material is provided in the exhaust pipe 19. The NOx catalyst 20 is formed of a porous material such as cordierite, for example, using alumina as a carrier and, on the carrier, potassium (K), sodium (Na), lithium (Li), cesium (Cs), or the like. And at least one selected from alkaline earths such as barium (Ba) or calcium (Ca), rare earths such as lanthanum (La) or yttrium (Y), and a noble metal such as platinum (Pt). Is carried. In the present embodiment, barium (Ba) and platinum (Pt) are supported on a carrier made of alumina, and a transition metal such as ceria (CeO ₂ ) having an oxygen storage (O ₂ storage) ability is used. Has been added.
[0029]
The NOx catalyst 20 holds the NOx in the exhaust gas when the oxygen concentration of the exhaust gas flowing into the NOx catalyst 20 is high, and holds the NOx when the oxygen concentration of the exhaust gas flowing into the NOx catalyst 20 decreases. The released NOx is released. At that time, if reducing components such as hydrocarbons (HC) and carbon monoxide (CO) are present in the exhaust gas, NOx released from the NOx catalyst 20 is reduced. Further, a transition metal such as ceria (CeO ₂ ) has the ability to temporarily hold oxygen according to the characteristics of exhaust gas and release it as activated oxygen.
[0030]
An exhaust temperature sensor 24 that outputs an electric signal corresponding to the temperature of exhaust flowing through the exhaust pipe 19 is attached to the exhaust pipe 19 upstream of the NOx catalyst 20. Further, an NOx sensor 23 that outputs an electric signal corresponding to the NOx concentration in the exhaust flowing through the exhaust pipe 19 and an electric signal corresponding to the air-fuel ratio of the exhaust are output to the exhaust pipe 19 downstream of the NOx catalyst 20. The air-fuel ratio sensor 22 is mounted.
[0031]
By the way, when the internal combustion engine 1 is performing the lean burn operation, the air-fuel ratio of the exhaust gas discharged from the internal combustion engine 1 becomes a lean atmosphere and the oxygen concentration in the exhaust gas becomes high, so that the NOx contained in the exhaust gas is reduced by the NOx catalyst 20. However, if the lean burn operation of the internal combustion engine 1 is continued for a long time, the NOx holding capacity of the NOx catalyst 20 is saturated, and NOx in the exhaust gas is not held by the NOx catalyst 20 but is held in the atmosphere. It is released inside.
[0032]
In particular, in a diesel engine such as the internal combustion engine 1, a mixture having a lean air-fuel ratio is burned in most of the operating region, and the air-fuel ratio of the exhaust gas becomes a lean air-fuel ratio in most of the operating region. The NOx holding capacity of the catalyst 20 is likely to be saturated.
[0033]
Note that the lean air-fuel ratio here is, for example, in the range of 20 to 50 in a diesel engine, and means a region in which NOx cannot be purified by a three-way catalyst. Therefore, when the internal combustion engine 1 is performing the lean burn operation, the oxygen concentration in the exhaust gas flowing into the NOx catalyst 20 is reduced and the fuel concentration is increased before the NOx holding capacity of the NOx catalyst 20 is saturated, and the NOx catalyst is increased. It is necessary to reduce the NOx held in 20.
[0034]
As a method of reducing the oxygen concentration in this way, the amount of EGR gas is further increased after adding the fuel in the exhaust gas or increasing the amount of recirculated EGR gas to increase the amount of generated soot to a maximum. Low-temperature combustion (see Japanese Patent No. 3116876), a secondary injection method for injecting fuel again during an expansion stroke or an exhaust stroke after a main injection for injecting fuel for engine output, and the like can be considered. In the fuel addition in the exhaust, a fuel supply mechanism for adding a fuel (light oil) as a reducing agent to the exhaust flowing through the exhaust pipe 19 upstream of the NOx catalyst 20 is provided, and the fuel is added from the fuel supply mechanism to the exhaust. Thus, the oxygen concentration of the exhaust gas flowing into the NOx catalyst 20 can be reduced and the fuel concentration can be increased.
[0035]
As shown in FIG. 1, the fuel supply mechanism is mounted so that its injection hole faces the exhaust branch pipe 18, and the fuel supply mechanism opens a valve from a signal from an ECU 35 described later to inject fuel, and A fuel supply passage 29 for guiding the fuel discharged from the fuel pump 6 to the fuel addition valve 28;
[0036]
In such a fuel supply mechanism, high-pressure fuel discharged from the fuel pump 6 is applied to the fuel addition valve 28 via the fuel supply path 29. Then, the fuel addition valve 28 is opened by a signal from the ECU 35 and fuel as a reducing agent is injected into the exhaust branch pipe 18.
[0037]
The fuel injected from the fuel addition valve 28 into the exhaust branch pipe 18 reduces the oxygen concentration of the exhaust gas flowing from the upstream of the exhaust branch pipe 18, reaches the NOx catalyst 20, and is retained by the NOx catalyst 20. NOx will be reduced.
[0038]
Thereafter, the fuel addition valve 28 is closed by a signal from the ECU 35, and the addition of fuel into the exhaust branch pipe 18 is stopped.
[0039]
Further, the internal combustion engine 1 is provided with a crank position sensor 33 that outputs an electric signal corresponding to the rotational position of the crankshaft.
[0040]
The internal combustion engine 1 configured as described above is provided with an electronic control unit (ECU: Electronic Control Unit) 35 for controlling the internal combustion engine 1. The ECU 35 is a unit that controls the operating state of the internal combustion engine 1 according to the operating conditions of the internal combustion engine 1 and the driver's requirements.
[0041]
The ECU 35 includes a ROM (Read Only Memory) 352, a RAM (Random Access Memory) 353, a CPU (Central Control Unit) 351, an input port 356, and an output port 357 connected to each other by a bidirectional bus 350.
[0042]
The input port 356 of the ECU 35 has an A / A corresponding to an output signal of the various sensors described above, an accelerator opening sensor 36 for detecting an amount of depression of an accelerator pedal, a crank angle sensor 33 for detecting a rotation speed of a crankshaft, and the like. It is input via the D converter 355 or directly.
[0043]
On the other hand, the output port 357 is connected to the fuel injection valve 3, the fuel addition valve 28, and the like.
[0044]
Further, on a ROM (read only memory) 352, a control map created based on various preliminary experiments is provided corresponding to each device. The CPU 351 compares output signals of various sensors input to the input port 356 with a control map developed on the ROM 352, and outputs various control signals based on values calculated in the control map to various devices via the output port 357. Output to The RAM 353 records output signals from various sensors input to the input port 356, control signals output to the output port 367, and the like as an operation history of the internal combustion engine. Then, upon receiving a request from the CPU 351, the CPU 351 inputs and outputs various signals to and from the CPU 351.
[0045]
The ECU 35 calculates a “target required torque” required for the current engine operation based on the output signals of the crank angle sensor 33 and the accelerator opening sensor 36 and the like, and obtains the target required torque by using the fuel injection valve 3 or the fuel pump 3. The control signal output to 6 is updated as needed to correct the fuel supply amount in the fuel supply system. Further, based on the output values from the various sensors, the control of the supply of fuel in the exhaust gas purification device described later is also executed at the same time.
[0046]
By setting the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 20 to the target rich air-fuel ratio in a spike manner, it is possible to reduce the NOx held in the NOx catalyst 20. However, in the NOx catalyst 20, SOx is absorbed by the same mechanism as that for holding NOx. However, once held SOx is less likely to be released than NOx, and NOx is released in a reducing atmosphere having a reduced oxygen concentration. Even if it does, SOx will not accumulate and will gradually accumulate in the NOx catalyst 20. Such sulfur poisoning (hereinafter referred to as SOx poisoning) causes a decrease in the NOx purification rate of the NOx catalyst 20. Therefore, it is necessary to perform a poisoning recovery process for releasing SOx from the NOx catalyst 20 at an appropriate time. Such SOx poisoning recovery control is executed by the ECU 35.
[0047]
The mechanism of SOx poisoning described above is roughly as follows.
[0048]
When the fuel is burned in the internal combustion engine 1, SOx such as sulfur dioxide (SO ₂ ) and sulfur trioxide (SO ₃ ) is generated. When the oxygen concentration of the exhaust gas flowing into the NOx catalyst 20 is high, SOx such as sulfur dioxide (SO ₂ ) or sulfur trioxide (SO ₃ ) in the inflowing exhaust gas is oxidized on the surface of platinum (Pt), and sulfate ions ( SO ₄ ²⁻ ) is held in the NOx catalyst 20.
[0049]
Further, the sulfate ions (SO ₄ ²⁻ ) absorbed by the NOx catalyst 20 combine with barium oxide (BaO) to form sulfate (BaSO ₄ ). This sulfate (BaSO ₄ ) is stable compared to barium nitrate (Ba (NO ₃ ) ₂ ) and is not easily decomposed. Even if the oxygen concentration of the exhaust gas flowing into the NOx catalyst 20 becomes low, it is not decomposed. , Remain in the NOx catalyst 20.
[0050]
In this way, when the amount of sulfate (BaSO ₄ ) in the NOx catalyst 20 increases, the amount of barium oxide (BaO) that can contribute to the retention of NOx decreases accordingly. The holding capacity is reduced, and SOx poisoning occurs.
[0051]
A method for eliminating SOx poisoning of the NOx catalyst 20 is to raise the ambient temperature of the NOx catalyst 20 to a high temperature range of about 600 to 650 ° C. and lower the oxygen concentration of the exhaust gas flowing into the NOx catalyst 20. , barium sulfate absorbed in the NOx catalyst 20 (BaSO ₄₎ SO ₃ ^- then pyrolyzed, then SO ₃ ^{- -} and SO ₄ and SO ₄ ^- hydrocarbons in the exhaust gas (HC) and carbon monoxide ( CO) is reacted gaseous by SO ₂ ^- a method of reducing can be exemplified.
[0052]
In this embodiment, the ECU 35 oxidizes those unburned fuel components in the NOx catalyst 20 by adding fuel to the exhaust gas from the fuel addition valve 28, and heats the NOx catalyst 20 by the heat generated during the oxidation. Increase bed temperature. At the same time, fuel may be secondarily injected from the fuel injection valve 3 during the expansion stroke or the exhaust stroke of each cylinder.
[0053]
By the above-described fuel addition, the bed temperature of the NOx catalyst 20 rises from 600 ° C. to a high temperature range of about 650 ° C. After that, the ECU 35 injects fuel from the fuel addition valve 28 so as to continuously reduce the oxygen concentration of the exhaust gas flowing into the NOx catalyst 20.
[0054]
When the above-mentioned poisoning recovery process is executed, the oxygen concentration of the exhaust gas flowing into the NOx catalyst 20 becomes low under the condition that the bed temperature of the NOx catalyst 20 is high, so that the barium sulfate ( BaSO ₄₎ is SO ₃ ^- and SO ₄ ^- are thermally decomposed, they SO ₃ ^- and SO ₄ ^- are reduced by reaction with hydrocarbons (HC) and carbon monoxide in the exhaust gas (CO), NOx Te following SOx poisoning of the catalyst 20 will be recovered.
[0055]
In the SOx poisoning recovery control, a so-called rich spike is executed to lower the oxygen concentration of the exhaust gas. Further, one rich spike is formed by a plurality of fuel injections so that the air-fuel ratio does not become excessively rich.
[0056]
Here, if a large amount of fuel is injected at once, there is a possibility that the air-fuel ratio becomes excessively rich, and a part of the fuel that cannot be completely reacted by the NOx catalyst 20 may flow downstream. Therefore, in the present embodiment, a small amount of fuel is divided into a plurality of times and injected intermittently to form a rich atmosphere while suppressing over-rich.
[0057]
In the SOx poisoning recovery control, the above-described fuel addition is performed such that the air-fuel ratio of exhaust gas (target air-fuel ratio) that can release SOx accumulated from the NOx catalyst 20 is obtained. At this time, the value of the air-fuel ratio sensor 22 is fed back so that the value of the air-fuel ratio sensor 22 downstream of the NOx catalyst 20 becomes the target air-fuel ratio, and the amount of fuel added to the exhaust gas from the fuel addition valve 28 is controlled. The fuel amount at this time is reflected as a learning value in the fuel amount at the time of the next fuel addition. That is, the fuel addition amount is calculated from the base fuel addition amount and the learning value.
[0058]
In the exhaust gas purifying apparatus shown in the present embodiment, an air-fuel ratio sensor 22 is attached to an exhaust pipe 19 arranged downstream of the NOx catalyst 20, and a value detected by the air-fuel ratio sensor 22 is fed back to a fuel supply amount. Fuel supply.
[0059]
However, assuming that the learning value when the combustion air-fuel ratio in the cylinder is lean (for example, about A / F25) is applied as it is when the combustion air-fuel ratio is rich (for example, about A / F18), The air-fuel ratio of the fuel-added exhaust gas may be richer than the target value because the air-fuel ratio is rich. Therefore, in such feedback control, the bed temperature of the NOx catalyst 20 may be excessively increased, and in such a case, the NOx catalyst 20 may be thermally deteriorated.
[0060]
In the present embodiment, instead of applying the same learning value in all cases, the learning value to be stored is changed depending on the combustion state in the cylinder, and these stored learning values are reflected only when the combustion state is the same. I tried to make it. According to such control, an optimal fuel amount according to the combustion state is added.
[0061]
Next, the SOx poisoning recovery control performed by the ECU 35 will be described based on a flowchart shown in FIG.
[0062]
This flowchart shows the “SOx poisoning recovery control routine” executed for the purpose of SOx poisoning recovery, but can also be applied when supplying fuel for promoting the NOx releasing action.
[0063]
First, in step S101, the ECU 35 stores the output signals of various sensors on the RAM 353 in order to collect the operation history from the start of the engine operation. For example, the elapsed time from the start of the engine operation, the amount of fuel supplied to each cylinder 2 to satisfy the target required torque, the amount of air drawn into each cylinder 2, the elapsed time since the last fuel supply, the vehicle It is an integrated value of the number of traveling distances, an exhaust gas temperature, and the like. The collected operation history is read out to the CPU 351, and it is determined in the CPU 351 whether or not the SOx poisoning recovery control condition, that is, the fuel supply execution condition is satisfied. The SOx poisoning recovery control condition is whether or not the amount of SOx absorbed by the NOx catalyst 20 is equal to or more than a predetermined amount. When this condition is not satisfied, the execution of this processing routine is temporarily terminated.
[0064]
When the above condition is satisfied, the process proceeds to step S102, and the ECU 35 determines which range the air-fuel ratio of the in-cylinder combustion is in. Here, it is determined whether or not the range is (1) 18 <cylinder air-fuel ratio <20, (2) 20 <cylinder air-fuel ratio <25, (3) 25 <cylinder air-fuel ratio <30. If it does not belong to any of these ranges, the execution of this processing routine is temporarily terminated.
[0065]
On the other hand, when the air-fuel ratio of the in-cylinder combustion belongs to any range, the process proceeds to step S103, and the basic supply amount of the added fuel is calculated. In step S103, the base addition of fuel used for recovery of SOx poisoning is performed using the air-fuel ratio of the air-fuel mixture currently being used for engine operation and the amount of SOx absorption calculated in step 102 as parameters. The amount is calculated based on a base addition amount calculation map prepared on the ROM 352 in advance. The basic supply amount calculation map is created based on various preliminary experiments.
[0066]
Next, depending on whether the in-cylinder air-fuel ratio belongs to any of (1) to (3) determined in step S102, learning values to be applied are processed according to different flows.
(When the air-fuel ratio is in the range of (1))
When the in-cylinder air-fuel ratio is in the range of (1), the process proceeds to step S104 shown in FIG. In step S104, conditions for adding a fuel as a reducing agent are determined. The addition amount A at this time is obtained by multiplying the base addition amount by a learning value Gmm ³ fed back during the previous fuel addition. That is, to perform the increase correction of the basic supply amount, the correction supply amount of the fuel to be increased is calculated according to the difference between the air-fuel ratio detected by the air-fuel ratio sensor 22 and the target air-fuel ratio.
[0067]
On the other hand, when the reduction correction of the basic supply amount is performed, similarly, the correction supply amount of the fuel to be reduced is calculated according to the difference between the air-fuel ratio detected by the air-fuel ratio sensor 22 and a predetermined air-fuel ratio. .
[0068]
Further, the fuel addition interval Bms, the addition time Csec, and the addition suspension time Dsec are determined based on the addition amount A. These are determined in consideration of whether or not the catalyst temperature of the NOx catalyst 20 has reached a high temperature range where SOx can be thermally decomposed, whether or not the exhaust gas temperature is equal to or lower than a predetermined upper limit, and the like. Normally, when the fuel addition amount A is large, the fuel addition interval Bms is short, the addition time Csec is long, and the addition suspension time Dsec is set short. Conversely, if the addition amount is small, the fuel addition interval Bms is short, the addition time Csec is short, and the addition pause time Dsec is long.
[0069]
Next, the process proceeds to step S105, and it is determined whether a condition for determining the addition of fuel into exhaust gas is satisfied. The conditions include whether the internal combustion engine 1 is in an operating state suitable for SOx poisoning recovery, and whether the temperature of the NOx catalyst 20 is in a high temperature range (for example, in the range of 550 to 700 ° C.) in which SOx can be thermally decomposed. Further, conditions such as whether the air-fuel ratio of the exhaust gas is smaller than the stoichiometric ratio, whether the supply of the fuel for promoting the NOx absorption / release operation is in an execution state, and the like can be exemplified. When these conditions are not satisfied, the execution of this processing routine is temporarily terminated.
[0070]
If an affirmative determination is made in step S105, the process proceeds to step S106, and fuel addition is performed.
[0071]
Next, in step S107, the actual air-fuel ratio downstream of the NOx catalyst 20 is detected by the air-fuel ratio sensor 22 and the difference E between the actual air-fuel ratio and the target air-fuel ratio is detected in order to start correction of the basic supply amount, that is, feedback control. Is calculated.
[0072]
Based on this difference E, F is obtained from a one-dimensional map with F (coefficient), and the addition amount is calculated.
[0073]
Subsequently, the process proceeds to step S108, where the learning value G is calculated based on the F. The learning value G thus calculated is reflected in the next fuel addition, and converges on the target air-fuel ratio by such repetition.
(When the air-fuel ratio is in the range of (2))
If the in-cylinder air-fuel ratio is in the range of (2), the process proceeds to step S110 shown in FIG.
In step S110, conditions for fuel addition are determined. The addition amount A at this time is obtained by multiplying the base addition amount by a learning value Hmm ³ fed back during the previous fuel addition.
[0074]
Steps from step S111 to step S115 are the same as those in the above-described case where the air-fuel ratio is (1), and will not be described.
(When the air-fuel ratio is in the range of (3))
When the air-fuel ratio in the cylinder is in the range of (3), the process proceeds to step S116 shown in FIG.
In step S116, conditions for fuel addition are determined. The addition amount A at this time is obtained by multiplying the base addition amount by a learning value Imm ³ fed back during the previous fuel addition.
[0075]
The steps from step S117 to step S121 are the same as those in the case where the air-fuel ratio is (1), and thus will not be described.
[0076]
In the present embodiment, when supplying fuel, fuel is supplied to the exhaust passage. However, sub-injection into a combustion chamber that does not contribute to engine combustion, or air-fuel mixture supplied for engine combustion is performed. Fuel may be supplied to the NOx catalyst by performing air-fuel ratio control or the like in which the fuel ratio is set to a low value in advance. In either case, the air-fuel ratio downstream of the NOx catalyst is fed back to determine the fuel supply amount.
[0077]
The configuration of the fuel supply device described above is merely an embodiment of the present invention, and details thereof may be changed as desired. For example, the fuel addition valve 28, which is a mechanical open / close valve, can be an electromagnetic valve. Further, a change may be made such that the fuel supply device is configured to be completely independent of the fuel supply system.
[0078]
In the above-described embodiment, the air-fuel ratio sensor 22 is used to detect the air-fuel ratio downstream of the NOx catalyst 20, but an oxygen (O ₂ ) sensor may be used instead of the air-fuel ratio sensor 22.
[0079]
Further, in the present embodiment, an example in which the present invention is applied to a diesel engine is described, but the present invention is of course also useful for a gasoline engine.
[0080]
As described above, in the present control, three stages are set based on the value of the air-fuel ratio in the cylinder of the internal combustion engine, and the learning value is obtained for each stage, so that the next time the fuel is added in the cylinder, It is determined to which stage the air-fuel ratio belongs, and the corresponding learning value is applied. Therefore, during feedback control of fuel addition during execution of SOx poisoning recovery control of the NOx catalyst, a learning value suitable for the combustion state of the internal combustion engine is selected, an appropriate value is reflected in fuel addition, and convergence to the target value is achieved. Becomes easier.
[0081]
【The invention's effect】
As described above, according to the present invention, when performing feedback control of fuel addition to the exhaust system, a learning value suitable for the combustion state of the internal combustion engine is selected and applied, so that the accuracy of feedback control is improved.
[0082]
Further, in the SOx poisoning recovery control, it is possible to prevent the amount of fuel to be added from being increased more than necessary and the catalyst temperature from rising, and the catalyst from being overheated.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an internal combustion engine according to an embodiment of the present invention.
FIG. 2 is a diagram showing a schematic configuration of an ECU.
FIG. 3 is a flowchart illustrating an execution flow of SOx poisoning recovery control.
FIG. 4 is a flowchart showing an execution flow of SOx poisoning recovery control when the air-fuel ratio is in the region of (1) in FIG.
FIG. 5 is a flowchart showing an execution flow of SOx poisoning recovery control when the air-fuel ratio is in a region of (2) in FIG. 3;
FIG. 6 is a flowchart showing an execution flow of SOx poisoning recovery control when the air-fuel ratio is in the area of (3) in FIG. 3;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 ... Cylinder 3 ... Fuel injection valve 4 ... Common rail 5 ... Fuel supply pipe 6 ... Fuel pump 8 ... Intake branch pipe 9 ... Intake pipe 18 Exhaust branch pipe 19 Exhaust pipe 20 NOx catalyst 22 Air-fuel ratio sensor 23 NOx sensor 24 Exhaust temperature sensor 28 Fuel addition valve 29 ... Fuel supply path 33 ... Crank position sensor 35 ... ECU
36 ・ ・ ・ Accelerator opening sensor

Claims (4)

An exhaust purification device installed in the exhaust system;
Fuel addition means for adding fuel to the exhaust gas purification device;
First air-fuel ratio detection means for detecting an air-fuel ratio downstream of the exhaust purification device,
In the internal combustion engine, a feedback value is obtained so that the air-fuel ratio detected by the first air-fuel ratio detection means becomes a target air-fuel ratio, and this feedback value is stored as a learning value and reflected in a fuel addition amount for the next and subsequent times.
A second air-fuel ratio detecting means for detecting an air-fuel ratio of the exhaust gas discharged from the cylinder; and applying a learning value stored in correspondence with the air-fuel ratio detected by the second air-fuel ratio detecting means. And determining the amount of fuel added from the fuel addition means. 2. The internal combustion engine according to claim 1, wherein the air-fuel ratio in the cylinder is divided into a plurality of stages according to the value, and a learning value corresponding to the stage to which the value of the air-fuel ratio at the time of adding the fuel belongs is applied. Exhaust gas purification device. 3. The exhaust system according to claim 1, wherein the learning value is reflected only when it is determined that the air-fuel ratio in the cylinder belongs to a predetermined corresponding stage at the next fuel addition. Purification device. The internal combustion engine according to any one of claims 1 to 3, wherein the exhaust gas purification device is an occlusion reduction type NOx catalyst, and the fuel addition is performed in SOx poisoning recovery control of the occlusion reduction type NOx catalyst. Engine exhaust purification device.

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