JP4780335B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust emission control device for an internal combustion engine, and more particularly to a technique for injecting a reducing agent into an exhaust passage and supplying the reducing agent to an exhaust purification catalyst.

A NOx (nitrogen oxide) storage catalyst is known as a device for purifying exhaust gas from a diesel engine.
The NOx storage catalyst stores NOx in the exhaust gas in a lean atmosphere. A method of regenerating a NOx storage catalyst is known in which NOx stored in the NOx storage catalyst is reduced, detoxified and released by supplying a reducing agent such as fuel to the NOx storage catalyst. As a device for supplying fuel or the like to the NOx storage catalyst, a method (purge process) in which a fuel injection valve is provided upstream of the NOx storage catalyst and fuel is directly injected into the exhaust passage is known.

Here, the fuel injection amount from the fuel injection valve provided in the exhaust passage is normally set based on the operating state such as the engine speed. However, there is a case where an error occurs in the actual fuel injection amount with respect to the target fuel injection amount set from the operating state of the engine due to clogging of the injection hole of the fuel injection valve due to soot in the exhaust gas or deterioration with time. Therefore, air-fuel ratio detection means is further provided in the exhaust passage downstream of the fuel injection valve, and the actual air-fuel ratio of the exhaust detected by this air-fuel ratio sensor is fed back, thereby bringing the actual air-fuel ratio of the exhaust closer to the target air-fuel ratio. At the same time, a method is known in which the feedback amount at the end of fuel injection into the exhaust passage is stored as a learned value and used in the subsequent purge process (Patent Document 1). Furthermore, in this patent document 1, in order to prevent the learning accuracy from being lowered due to the O ₂ storage function in the NOx storage catalyst, after waiting for the O ₂ storage to disappear after injecting fuel into the exhaust passage. Do learning.
JP 2004-316604 A

However, in Patent Document 1 described above, learning opportunities are limited to the purge process, and learning is performed after the O ₂ storage is eliminated. Therefore, it is difficult to secure the learning frequency, and there is a possibility that the learning accuracy cannot be ensured as expected. is there.
The present invention has been made to solve such problems, and the object of the present invention is to learn while avoiding a decrease in the learning accuracy of the fuel injection amount caused by the O ₂ storage function in the catalyst. An object of the present invention is to provide an exhaust emission control device for an internal combustion engine that can ensure a sufficient frequency.

In order to achieve the above object, an invention according to claim 1 is provided in an exhaust passage of an internal combustion engine, provided in a purification catalyst for purifying exhaust, an exhaust passage upstream of the purification catalyst, and a fuel in the exhaust passage. When the internal combustion engine is in a steady operation state, the fuel injection valve in the exhaust passage for injecting the air, the air-fuel ratio detection means for detecting the exhaust air-fuel ratio provided in the exhaust passage downstream of the fuel injection valve in the exhaust passage, The fuel is injected from the fuel injection valve in the exhaust passage within a range where the exhaust air / fuel ratio becomes lean, and the actual fuel injection from the fuel injection valve in the exhaust passage is based on the actual value of the exhaust air / fuel ratio detected by the air / fuel ratio detection means. Learning means for calculating the amount and learning the relationship between the actual fuel injection amount and the target fuel injection amount in the fuel injection valve in the exhaust passage, a filter provided in the exhaust passage and collecting particulate matter in the exhaust, Control the fuel injection valve in the exhaust passage And a filter regeneration means for regenerating the filter by injecting fuel into the exhaust passage and burning the particulate matter collected by the filter to regenerate the filter. The learning means is a fuel in the exhaust passage during filter regeneration by the filter regeneration means. The relationship between the actual fuel injection amount from the injection valve and the target fuel injection amount is learned. It should be noted that when the air-fuel ratio sensor is located downstream of the filter, it is desirable that the learning be performed in the latter half of the filter regeneration or immediately after the regeneration is completed, where the influence of particulate matter combustion on the air-fuel ratio is small.

The invention of claim 2 is provided in an exhaust passage of an internal combustion engine, and stores nitrogen oxides in exhaust under a lean air-fuel ratio atmosphere, and reduces the stored nitrogen oxides under stoichiometric or rich air-fuel ratio atmosphere. A nitrogen oxide storage catalyst to be removed; a fuel injection valve in the exhaust passage which is provided in an exhaust passage upstream of the nitrogen oxide storage catalyst and injects fuel into the exhaust passage; and a downstream side of the fuel injection valve in the exhaust passage. An air-fuel ratio detecting means provided in the exhaust passage for detecting the exhaust air-fuel ratio and when the internal combustion engine is in a steady operation state, fuel is injected from the fuel injection valve in the exhaust passage within a range where the exhaust air-fuel ratio becomes lean. The actual fuel injection amount from the fuel injection valve in the exhaust passage is calculated based on the measured value of the exhaust air / fuel ratio detected by the air / fuel ratio detection means, and the actual fuel injection amount and the target fuel injection in the fuel injection valve in the exhaust passage are calculated. Relationship with quantity And learning means for learning, so that nitrogen oxides occluded in the nitrogen oxide storage catalyst or sulfur oxides are reduced and removed, and controls the exhaust passage fuel injection valve, as a reducing agent to the nitrogen oxides storage catalyst Purge processing means for supplying the fuel , and the learning means temporarily increases or decreases the target fuel injection amount within the range in which the exhaust air-fuel ratio becomes lean during the purge processing by the purge processing means, The relationship between the actual fuel injection amount from the injection valve and the target fuel injection amount is learned.

According to a third aspect of the present invention, in the second aspect , the purge processing means intermittently injects the target fuel injection amount at which the exhaust air-fuel ratio becomes rich into the fuel injection valve in the exhaust passage a plurality of times, and the learning means includes: Learning the relationship between the actual fuel injection amount from the fuel injection valve in the exhaust passage and the target fuel injection amount by setting at least one target fuel injection amount of the fuel to be injected a plurality of times within a range in which the exhaust air-fuel ratio becomes lean. It is characterized by that.

  Preferably, the injection timing for leaning the exhaust air-fuel ratio is good in the second half of the purge process where the temperature in the exhaust pipe is high.

According to the exhaust gas purification apparatus for an internal combustion engine of claim 1 of the present invention, the fuel is injected into the exhaust passage within a range where the exhaust air-fuel ratio becomes lean, and the relationship between the target fuel injection amount and the actual fuel injection amount is learned. Therefore, even if the purification catalyst has an O ₂ storage function, learning can be performed without being affected by this. Therefore, the learning frequency can be increased and the learning effect can be sufficiently obtained. And the precision of subsequent fuel injection amount control can be improved from this learning result, for example.

In particular, since the relationship between the actual fuel injection amount from the fuel injection valve in the exhaust passage and the target fuel injection amount is learned at the time of filter regeneration, the learning opportunities can be increased compared with the case where learning is performed during the purge process. Also, by learning while the temperature in the exhaust pipe is rising due to filter regeneration, it is possible to burn all the fuel injected from the fuel injection valve in the exhaust passage during this learning, and to detect the air-fuel ratio at the time of learning Accuracy can be improved. When the air-fuel ratio sensor is provided on the downstream side of the filter, the exhaust air-fuel ratio can be correctly detected by setting the learning timing to the latter half of the filter regeneration where the influence of particulate matter combustion on the air-fuel ratio is small or immediately after the regeneration is completed.

According to the exhaust gas purification apparatus for an internal combustion engine according to claims 2 and 3 of the present invention, the purification catalyst occludes nitrogen oxide in the exhaust under a lean air-fuel ratio atmosphere, and the occluded nitrogen oxide is stoichiometric or A nitrogen oxide storage catalyst that reduces and removes under a rich air-fuel ratio atmosphere, and temporarily reduces the fuel injection amount during the purge process of nitrogen oxide or sulfur oxide within the range where the exhaust air-fuel ratio becomes lean Since the relationship between the actual fuel injection amount from the fuel injection valve in the exhaust passage and the target fuel injection amount is learned, the temperature in the exhaust pipe rises compared to when learning during the nitrogen oxide purge process. Therefore, the fuel injected from the fuel injection valve in the exhaust passage can be burned more completely, and the air-fuel ratio detection accuracy during learning can be improved.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram of an exhaust system of an engine (internal combustion engine) 1 to which an exhaust emission control device of the present invention is applied.
The engine 1 is a diesel engine, and an exhaust catalyst 2 is provided with an oxidation catalyst 3, a NOx storage catalyst 4, and a DPF (filter) 5 in that order from the upstream side. The oxidation catalyst 3 is formed by supporting a catalytic noble metal such as platinum (Pt), palladium (Pd), rhodium (Rh) on a porous wall forming a passage, and oxidizes CO and HC in exhaust gas. together is converted to CO ₂ and _{H 2} O Te has a function of NO in the exhaust is oxidized to generate NO _2.

  The NOx storage catalyst 4 is configured, for example, by supporting a NOx storage agent such as barium (Ba) or potassium (K) on a support containing a noble metal such as platinum (Pt) or palladium (Pd). While trapping NOx under an air-fuel ratio atmosphere (oxidizing atmosphere), it has the function of releasing the trapped NOx under a rich air-fuel ratio atmosphere (reducing atmosphere) and reducing it by reacting with HC and CO in the exhaust. is doing.

The DPF 5 has a function of, for example, alternately closing the upstream side and the downstream side of the honeycomb carrier passage with plugs to collect PM in the exhaust gas, and further, on the porous wall forming the passage. It is formed by supporting a catalytic noble metal such as platinum (Pt), palladium (Pd), rhodium (Rh).
An exhaust pipe fuel injection valve (exhaust passage fuel injection valve) 6 is installed upstream of the oxidation catalyst 3. Fuel is supplied to the exhaust pipe fuel injection valve 6 from a fuel tank (not shown) by a fuel pump driven by the engine 1. The exhaust pipe fuel injection valve 6 has a function of injecting the supplied fuel into the exhaust pipe 2.

  The exhaust pipe 2 includes a first temperature sensor 7 on the upstream side of the oxidation catalyst 3, a second temperature sensor 8 between the oxidation catalyst 3 and the NOx storage catalyst 4, and a third temperature sensor 9 on the NOx storage catalyst 4. The fourth temperature sensor 10 is provided on the downstream side of the DPF 5. The first temperature sensor 7 is the temperature of the exhaust gas flowing into the oxidation catalyst 3, the second temperature sensor 8 is the temperature of the exhaust gas flowing into the NOx storage catalyst 4, and the third temperature sensor 9 is the catalyst of the NOx storage catalyst 4. The fourth temperature sensor 10 has a function of detecting the temperature of the exhaust gas flowing out from the DPF 5. In addition, the exhaust pipe 2 is provided with an air-fuel ratio sensor (air-fuel ratio detection means) 11 for detecting the air-fuel ratio of the exhaust gas on the downstream side of the DPF 5 and for detecting the differential pressure between the upstream side and the downstream side of the DPF 5. A pressure sensor 12 is provided.

The ECU 20 is a control device for performing comprehensive control including operation control of the engine 1, and includes an input / output device, a storage device (ROM, RAM, nonvolatile RAM, etc.), a central processing unit (CPU), and the like. It consists of
On the input side of the ECU 20, in addition to the first to fourth temperature sensors 7 to 10, the air-fuel ratio sensor 11, and the differential pressure sensor 12, an air flow sensor that detects the intake flow rate of the engine 1, and a crank angle that detects the crank angle A sensor, an accelerator position sensor for detecting the depression amount of the accelerator pedal, and the like are connected, and detection information from these sensors is input.

  On the other hand, the output side of the ECU 20 is connected to various output devices such as a fuel injection valve for injecting fuel into the combustion chamber of the engine 1 and an intake throttle valve (not shown) in addition to the above-described fuel injection valve 6 in the exhaust pipe. . The ECU 20 calculates a fuel injection amount, a fuel injection timing, and the like into the combustion chamber based on detection information from various sensors, and outputs them to various output devices, so that a fuel injection valve and an intake throttle valve can be output at appropriate timing. Control etc.

By the way, by disposing the oxidation catalyst 3 upstream of the DPF 5 as described above, NO ₂ is discharged from the oxidation catalyst 3 in the rich air-fuel ratio atmosphere, passes through the NOx storage catalyst 4, flows into the DPF 5, and flows into the DPF 5 It reacts with soot, which is a carbon component in the PM collected and deposited, and oxidizes it. The oxidized soot becomes CO _{2 and} is removed from the DPF ₅ , and the DPF 5 is continuously regenerated.

  In the above-described continuous regeneration, the DPF 5 may not be sufficiently regenerated depending on the operating condition of the engine 1. Therefore, in the present embodiment, the PM accumulation amount in the DPF 5 is estimated based on the differential pressure detected by the differential pressure sensor 12 and the exhaust gas flow rate, and the forced regeneration is performed when the estimated amount exceeds the allowable amount. To implement. The forced regeneration is executed by the ECU 20 controlling the fuel injection valve 6 in the exhaust pipe and supplying fuel into the exhaust pipe 2. The fuel supplied into the exhaust pipe 2 flows into the oxidation catalyst 3 and is oxidized by the oxidation catalyst 3, thereby raising the exhaust temperature. Thereby, PM deposited on the DPF 5 is burned to regenerate the DPF 5 (filter regeneration means).

  Further, the engine 1 is provided with a NOx purge function for discharging NOx stored in the NOx storage catalyst 4. In the NOx purge, the ECU 20 controls the fuel injection valve 6 in the exhaust pipe 6 based on the detection information from the various sensors described above, that is, the operating state of the engine 1 to inject fuel into the exhaust pipe 2, and the NOx storage catalyst 4 This is executed by enriching the air-fuel ratio of the exhaust gas flowing into the engine. The fuel injection of the exhaust pipe fuel injection valve 6 is intermittently performed a plurality of times, and the exhaust air-fuel ratio fluctuates periodically when the fuel injection is rich and lean when the fuel injection is stopped. Further, since SOx resulting from oxidation of the sulfur component in the fuel is also deposited on the NOx storage catalyst 4 as a sulfate, the engine 1 has an S purge function in order to remove the accumulated sulfur component from the NOx storage catalyst 4. Is also provided. This S purge is also executed by controlling the fuel injection valve 6 in the exhaust pipe by the ECU 20 to inject fuel into the exhaust pipe 2, controlling the exhaust flowing into the NOx storage catalyst 4 to a high temperature and enriching the air-fuel ratio. (Purge processing means).

In the exhaust emission control device according to the present invention, the ECU 20 temporarily performs fuel injection in the exhaust pipe during steady operation, and calculates the actual fuel injection amount from the fuel injection valve 6 in the exhaust pipe based on the change in the exhaust air-fuel ratio at this time. An exhaust pipe injection amount learning that learns the relationship between the actual fuel injection amount and the target fuel injection amount is performed (learning means).
FIG. 2 is a flowchart showing a control procedure of the exhaust pipe injection amount learning control. This routine is repeatedly executed when the engine is operating.

First, in step S10, it is determined whether or not the engine 1 is in a steady operation state, that is, whether or not the air-fuel ratio of the exhaust discharged from the engine 1 is constant. Specifically, it is determined whether or not the rotational speed and load of the engine 1 are stable at a substantially constant level. When it is in a steady operation state, the process proceeds to step S12.
In step S12, a control signal for injecting fuel of the target fuel injection amount Qft into the exhaust pipe 2 is output to the fuel injection valve 6 in the exhaust pipe. The target fuel injection amount Qt may be set as appropriate within a range that remains lean even when the exhaust air-fuel ratio decreases due to fuel injection from the exhaust pipe fuel injection valve 6. Then, the process proceeds to step S14.

In step S14, the exhaust air / fuel ratio A / Frich is input from the air / fuel ratio sensor 11 and stored in the storage device. Then, the process proceeds to step S16.
In step S16, the fuel injection from the exhaust pipe fuel injection valve 6 is stopped. Then, the process proceeds to step S18.
In step S18, the exhaust air / fuel ratio A / Flean is input from the air / fuel ratio sensor 11 and stored in the storage device. Then, the process proceeds to step S20.

In step S20, using the intake air amount Qair detected by the air flow meter, the fuel density B, and the exhaust air / fuel ratios A / Frich and A / Flean input in steps S12 and S16 and stored in the storage device, the following (1) The actual fuel injection amount Qfr is calculated by the equation.
Qfr = Qair / (A / Frich) / B-Qair / (A / Flean) / B (1)
Then, the process proceeds to step S20.

In step S20, the correction coefficient Cf is calculated by the following equation (2) using the target fuel injection amount Qft set in step S12 and the actual fuel injection amount Qfr calculated in step S18.
Cf = Qft / Qfr (2)
The correction coefficient Cf is stored in the storage device and learned as the relationship between the target fuel injection amount Qft and the actual fuel injection amount Qfr. Then, this routine is returned.

On the other hand, if it is determined in step S10 that the vehicle is not in a steady operation state, this routine is returned.
FIG. 3 is a time chart showing the transition of the exhaust air / fuel ratio during the exhaust pipe injection amount learning control in the present embodiment.
As shown in FIG. 3, in the present embodiment, the exhaust air-fuel ratio fluctuates up and down by turning on and off the fuel injection from the fuel injection valve 6 in the exhaust pipe during the exhaust pipe injection amount learning control. Further, even during fuel injection, the exhaust air-fuel ratio remains within the lean range.

  By the above control, the injection amount learning in the exhaust pipe is performed when the engine 1 is in a steady operation state. In this exhaust pipe injection amount learning, fuel is temporarily injected from the fuel injection valve 6 in the exhaust pipe, and the exhaust air / fuel ratio A / Frich at the time of fuel injection and the exhaust air / fuel ratio A / Flean at the time of fuel injection stop are detected. The actual fuel injection amount Qfr is calculated based on the deviation of the exhaust air / fuel ratio A / Frich and A / Flean. Further, the learning is performed by calculating the ratio between the actual fuel injection amount Qfr and the target fuel injection amount Qft as a correction coefficient.

  Then, the driving time of the fuel injection valve 6 in the exhaust pipe is corrected by using the correction coefficient Cf calculated as described above in the subsequent S purge or NOx purge processing. Accordingly, even when the fuel injection valve 6 in the exhaust pipe is clogged by soot in the exhaust or when the fuel injection valve 6 in the exhaust pipe has deteriorated over time, the fuel is accurately injected from the fuel injection valve 6 in the exhaust pipe. S purge or NOx purge can be performed with high accuracy.

In particular, in the present embodiment, when fuel is injected from the exhaust pipe fuel injection valve 6 during learning of the exhaust pipe injection quantity, the fuel injection quantity is set within a range where the exhaust air-fuel ratio remains lean. During the amount learning, the fuel is not affected by the O ₂ storage function of the NOx storage catalyst 4 and the injection amount learning in the exhaust pipe can be performed accurately, and the injection amount learning in the exhaust pipe is not limited to the NOx purge and S purge. It becomes possible and the learning frequency can be increased. Further, in the present embodiment, since the exhaust pipe injection amount learning is performed when the engine 1 is in a steady operation state, the exhaust pipe injection amount learning can be performed regardless of the injection accuracy of the fuel injection valve of the engine 1.

  It should be noted that this exhaust pipe injection amount learning may be performed during DPF regeneration. During DPF regeneration, even if fuel is injected from the exhaust pipe fuel injection valve 6 and the exhaust air / fuel ratio is lowered, the exhaust air / fuel ratio is often kept lean, so that it is possible to learn the injection quantity in the exhaust pipe. As the exhaust gas temperature rises due to DPF regeneration, the fuel injected at the time of learning the injection amount in the exhaust pipe is completely burned downstream of the air-fuel ratio sensor 11, and the air-fuel ratio detection accuracy can be improved. The exhaust air / fuel ratio can be detected correctly by setting the learning timing to the latter half of DPF regeneration or immediately after the end of regeneration, where the influence of particulate matter combustion on the air / fuel ratio is small.

Further, the exhaust pipe injection amount learning may be performed by setting the target fuel injection amount so that the exhaust air-fuel ratio becomes lean in at least one of the fuel injections intermittently performed a plurality of times during NOx purge or S purge. . In this case, the exhaust air-fuel ratio becomes lean in the injection interval performed a plurality of times, and the O ₂ storage function in the NOx storage catalyst 4 becomes saturated. Therefore, the injection amount learning in the exhaust pipe is not affected by the O ₂ storage function. Can be implemented accurately. Further, it is more preferable to perform the S purge in which the exhaust temperature becomes high. In particular, if the fuel injection targeting lean for learning the injection amount in the exhaust pipe is performed in the latter half of the S purge process in which the exhaust temperature is high and stable, the air-fuel ratio detection accuracy can be further improved.

1 is a schematic configuration diagram of an exhaust system of an internal combustion engine according to the present invention. It is a flowchart which shows the control procedure of the injection amount learning control in an exhaust pipe. 6 is a time chart showing the transition of the exhaust air-fuel ratio during exhaust pipe injection amount learning control.

Explanation of symbols

1 Engine 2 Exhaust pipe 3 Oxidation catalyst 4 NOx storage catalyst 5 DPF
6 Fuel injection valve in exhaust pipe 11 Air-fuel ratio sensor 20 ECU

Claims (3)

A purification catalyst that is provided in an exhaust passage of the internal combustion engine and purifies exhaust;
An exhaust passage fuel injection valve that is provided in an exhaust passage upstream of the purification catalyst and injects fuel into the exhaust passage;
An air-fuel ratio detecting means provided in an exhaust passage downstream of the fuel injection valve in the exhaust passage and detecting an exhaust air-fuel ratio;
When the internal combustion engine is in a steady operation state, fuel is injected from the fuel injection valve in the exhaust passage within a range in which the exhaust air / fuel ratio becomes lean, and the measured value of the exhaust air / fuel ratio detected by the air / fuel ratio detection means Learning means for calculating an actual fuel injection amount from the fuel injection valve in the exhaust passage on the basis of, and learning a relationship between the actual fuel injection amount and a target fuel injection amount in the fuel injection valve in the exhaust passage;
A filter provided in the exhaust passage for collecting particulate matter in the exhaust;
Filter regeneration means for controlling the fuel injection valve in the exhaust passage to inject fuel into the exhaust passage, burning and removing the particulate matter collected by the filter, and regenerating the filter;
The exhaust purification device for an internal combustion engine, wherein the learning means learns a relationship between an actual fuel injection amount from the fuel injection valve in the exhaust passage and a target fuel injection amount at the time of filter regeneration by the filter regeneration means . A nitrogen oxide storage catalyst that is provided in an exhaust passage of the internal combustion engine, stores nitrogen oxides in exhaust under a lean air-fuel ratio atmosphere, and reduces and removes the stored nitrogen oxides under a stoichiometric or rich air-fuel ratio atmosphere ;
An exhaust passage fuel injection valve that is provided in an exhaust passage upstream of the nitrogen oxide storage catalyst and injects fuel into the exhaust passage;
An air-fuel ratio detecting means provided in an exhaust passage downstream of the fuel injection valve in the exhaust passage and detecting an exhaust air-fuel ratio;
When the internal combustion engine is in a steady operation state, fuel is injected from the fuel injection valve in the exhaust passage within a range in which the exhaust air / fuel ratio becomes lean, and the measured value of the exhaust air / fuel ratio detected by the air / fuel ratio detection means Learning means for calculating an actual fuel injection amount from the fuel injection valve in the exhaust passage on the basis of, and learning a relationship between the actual fuel injection amount and a target fuel injection amount in the fuel injection valve in the exhaust passage;
The fuel injection valve in the exhaust passage is controlled so that nitrogen oxide or sulfur oxide stored in the nitrogen oxide storage catalyst is reduced and removed, and fuel as a reducing agent is supplied to the nitrogen oxide storage catalyst. comprising a purging means for supplying the, the,
The learning means temporarily increases or decreases the target fuel injection amount within a range in which the exhaust air-fuel ratio becomes lean during the purge processing by the purge processing means, so that the actual fuel injection amount from the fuel injection valve in the exhaust passage and the target exhaust gas purification apparatus for an internal combustion engine you characterized by learning the relationship between the fuel injection amount. The purge processing means intermittently injects a target fuel injection amount at which the exhaust air-fuel ratio becomes rich to the fuel injection valve in the exhaust passage a plurality of times,
The learning means sets at least one target fuel injection amount of the fuel to be injected a plurality of times within a range in which the exhaust air-fuel ratio becomes lean, and the actual fuel injection amount and the target fuel injection amount from the fuel injection valve in the exhaust passage The exhaust gas purification apparatus for an internal combustion engine according to claim 2 , wherein the relationship is learned.

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