JP7347345B2 - Purification control device - Google Patents

Description

The present disclosure relates to a purification control device.

Conventionally, in vehicles such _as commercial vehicles, _NOx storage reduction catalysts (LNT catalysts, LNT: Lean _NO A purification device such as a catalyst or SCR (Selective Catalytic Reduction) is disposed in an exhaust pipe, and a purification control device for controlling this purification device has been put into practical use. For example, the purification control device controls the storage and reduction of _NOx in the LNT catalyst by adjusting the air-fuel ratio of the exhaust gas.

Here, ammonia (NH ₃ ) may slip from the purification device, and the ammonia may cause various effects on the vehicle, such as corroding the exhaust pipe. For example, the LNT catalyst generates ammonia in the _NOx reduction reaction, and the ammonia may slip from the LNT catalyst and corrode the exhaust pipe.

Therefore, as a technique for suppressing ammonia slip from a purification device, for example, Patent Document 1 discloses an exhaust gas purification device that suppresses ammonia slip while improving the _NOx purification rate. This exhaust purification device suppresses ammonia slip by increasing the storage amount of ammonia in the SCR catalyst when the amount of ammonia produced in the LNT catalyst increases.

Japanese Patent Application Publication No. 2015-151929

However, since the device of Patent Document 1 does not suppress the slip of ammonia from the LNT catalyst itself, the ammonia that slips from the LNT catalyst may cause a decrease in the purification rate of the SCR catalyst and corrosion of the exhaust pipe. .

An object of the present disclosure is to provide a purification control device that suppresses slip of ammonia from a _NOx storage reduction catalyst.

The purification _control device according to the present disclosure adjusts the air-fuel ratio of exhaust gas flowing into _{the NO} The purification control device is configured to control a purification control device, comprising: an acquisition unit that acquires a reduction timing at which the reduction amount of the _NO an air-fuel ratio control section that controls the air -fuel ratio of the exhaust gas flowing into the _NO Based on the lowering timing, the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst is controlled to increase to a lean air-fuel ratio _.
The purification _control device according to the present disclosure adjusts the air-fuel ratio of exhaust gas flowing into _{a NO} a purification control device that controls a reduction amount of the _NO an air-fuel ratio control unit that controls the air-fuel ratio of the exhaust gas flowing into _the NO an inlet lambda sensor that is disposed upstream of the NO X _storage reduction catalyst and detects _the air-fuel ratio of the exhaust gas flowing into the NO _X storage reduction catalyst; A temperature sensor that detects temperature, and a reduction device that indicates the reduction amount of the NO _X storage reduction catalyst relative to the air-fuel ratio of the exhaust gas flowing into the NO _X storage reduction catalyst and the temperature of the exhaust gas flowing through the NO _X storage reduction catalyst. A reduction amount map is stored in advance, and based on the reduction amount map, the reduction amount of the _NO and a calculation unit that acquires a reduction timing, and the air-fuel ratio control unit controls the air-fuel ratio of exhaust gas flowing into the _NOx storage reduction catalyst based on the reduction timing acquired by the calculation unit. It is something.

According to the present disclosure, it is possible to suppress slip of ammonia from the NO _X storage reduction catalyst.

1 is a diagram showing the configuration of a vehicle equipped with a purification control device according to Embodiment 1 of the present disclosure. 7 is a flowchart showing the operation of the first embodiment. It is a graph showing changes in air-fuel ratio and ammonia slip amount. FIG. 3 is a diagram showing a configuration of main parts of a purification control device according to a second embodiment. 7 is a flowchart showing the operation of the second embodiment.

Embodiments according to the present disclosure will be described below based on the accompanying drawings.

(Embodiment 1)
FIG. 1 shows the configuration of a vehicle equipped with a purification control device according to Embodiment 1 of the present disclosure. The vehicle has an internal combustion engine 1 , an intake pipe 2 , an exhaust pipe 3 , an internal combustion engine control section 4 , and a purification device 5 . Note that the vehicle includes, for example, a commercial vehicle such as a truck.

The internal combustion engine 1 is for driving a vehicle, and is comprised of, for example, a so-called four-stroke engine that repeats four strokes: an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke. Examples of the internal combustion engine 1 include a diesel engine.

The intake pipe 2 has a distal end connected to an intake port of the internal combustion engine 1, and is a flow path that supplies air taken in from the outside to the internal combustion engine 1.
The exhaust pipe 3 is arranged to extend outward from the exhaust port of the internal combustion engine 1, and is a flow path for discharging exhaust gas exhausted from the internal combustion engine 1 to the outside.

The internal combustion engine control section 4 controls the internal combustion engine 1, and is connected to the internal combustion engine 1 and the purification control section 12 of the purification device 5, respectively. The internal combustion engine control unit 4 controls, for example, the flow rate of intake air, the flow rate of exhaust gas, the supply of fuel, and the engine speed. Incidentally, examples of the fuel include light oil.

The purification device 5 includes an NO _X storage reduction catalyst (LNT catalyst) 6, a selective reduction catalyst (SCR catalyst) 7, and a purification control device 8.

The LNT catalyst 6 is disposed within the exhaust pipe 3, and purifies the exhaust gas by storing and reducing _NOx contained in the exhaust gas. For example, the LNT catalyst 6 can be constituted by a molded body in which a noble metal catalyst such as platinum and an _NOx storage material formed of an alkaline earth metal such as barium are supported on a carrier. As a result, the LNT catalyst 6 converts NO _X contained in the exhaust gas into an _NO To absorb. In the LNT catalyst 6, when the exhaust gas is brought to a rich air-fuel ratio, that is, the air-fuel ratio is higher than the stoichiometric air-fuel ratio, the oxygen concentration decreases and the amount of reducing agents such as carbon monoxide and hydrocarbons increases. Therefore, due to the three-way function of the noble metal catalyst, _{the NO X stored} in the NO
Note that in the present disclosure, the air-fuel ratio is expressed as an excess air ratio.

The SCR catalyst 7 is disposed downstream of the LNT catalyst 6 in the exhaust pipe 3, and reduces and purifies _NOx contained in the exhaust gas by supplying a reducing agent. For example, the SCR catalyst 7 can be composed of a zeolite catalyst such as iron ion-exchanged aluminosilicate and copper ion-exchanged aluminosilicate. As a result, for example, when urea water is supplied into the exhaust pipe 3 as a reducing agent, the urea water is thermally decomposed and hydrolyzed by the high temperature heat of the exhaust gas to generate ammonia, and the generated ammonia is used as an SCR. It is stored in the catalyst 7. Then, the SCR catalyst 7 uses the stored ammonia to purify the _NOx contained in the exhaust gas by reducing it to nitrogen or the like.

The purification control device 8 includes an inlet lambda sensor 9a, an outlet lambda sensor 9b, temperature sensors 10a and 10b, a supply section 11, and a purification control section 12. Further, the purification control section 12 includes an air-fuel ratio control section 13 and a supply control section 14. The air-fuel ratio control section 13 is connected to the inlet lambda sensor 9a, the outlet lambda sensor 9b, and the temperature sensor 10a, respectively. Further, the supply control section 14 is connected to the temperature sensor 10b and the supply section 11, respectively. Further, the air-fuel ratio control section 13 and the supply control section 14 are each connected to the internal combustion engine control section 4.

The inlet lambda sensor 9a is arranged upstream of the LNT catalyst 6 in the exhaust pipe 3, and detects the air-fuel ratio of the exhaust gas flowing into the LNT catalyst 6. That is, the inlet lambda sensor 9a detects the air-fuel ratio before the LNT catalyst 6 reacts with _NOx .

The outlet lambda sensor 9b is arranged downstream of the LNT catalyst 6 in the exhaust pipe 3, and detects the air-fuel ratio of the exhaust gas flowing out from the LNT catalyst 6. That is, the outlet lambda sensor 9b detects the air-fuel ratio after the LNT catalyst 6 reacts with _NOx .

Here, during the rich period in which the exhaust gas flowing into the LNT catalyst 6 is controlled to a rich air-fuel ratio, when the amount of reduction by the LNT catalyst 6 decreases in accordance with the decrease in _NOx stored in the LNT catalyst 6, the amount of reduction decreases. As the amount of oxygen decreases, the amount of oxygen produced also decreases. As a result, the air-fuel ratio of the exhaust gas decreases, and this decrease in the air-fuel ratio is detected by the outlet lambda sensor 9b. That is, in the rich period, the timing at which the reduction amount of the LNT catalyst 6 decreases in accordance with the decrease in _NOx can be obtained by detecting the air-fuel ratio of the exhaust gas with the exit lambda sensor 9b.
Note that the exit lambda sensor 9b constitutes an acquisition unit in the present disclosure.

The temperature sensor 10a is disposed upstream of the LNT catalyst 6 in the exhaust pipe 3 and detects the temperature of exhaust gas flowing through the LNT catalyst 6.
The temperature sensor 10b is disposed upstream of the SCR catalyst 7 in the exhaust pipe 3, and detects the temperature of exhaust gas flowing through the SCR catalyst 7.

The supply unit 11 is disposed upstream of the SCR catalyst 7 in the exhaust pipe 3 and supplies the SCR catalyst 7 with a reducing agent. The reducing agent includes not only those that directly reduce _NOx , such as ammonia, but also its precursors, such as urea water, which is a precursor of ammonia.

The air-fuel ratio control section 13 controls the air-fuel ratio of the exhaust gas flowing into the LNT catalyst 6 via the internal combustion engine control section 4 based on the detection values detected by the inlet lambda sensor 9a, the outlet lambda sensor 9b, and the temperature sensor 10a. and controls the storage and reduction of _NOx in the LNT catalyst 6.

For example, the air-fuel ratio control unit 13 controls the inlet lambda sensor 9a to maintain the rich air-fuel ratio during the rich period. At this time, when the lowering timing is detected by the outlet lambda sensor 9b, the air-fuel ratio control unit 13 controls the air-fuel ratio of the exhaust gas flowing into the LNT catalyst 6 to be higher than before the lowering timing based on the lowering timing. Control. For example, the air-fuel ratio control unit 13 increases the air-fuel ratio of the exhaust gas flowing into the LNT catalyst 6 so that the air-fuel ratio detected by the outlet lambda sensor 9b maintains the value before the lowering timing.

The supply control unit 14 controls the supply unit 11 to inject an amount of reducing agent according to the storage capacity of ammonia in the SCR catalyst 7 based on the temperature detected by the temperature sensor 10b.

Note that the functions of the internal combustion engine control section 4, the purification control section 12, the air-fuel ratio control section 13, and the supply control section 14 can also be realized by a computer program. For example, a reading device of a computer reads a program for realizing the functions of the internal combustion engine control section 4, the purification control section 12, the air-fuel ratio control section 13, and the supply control section 14 from a recording medium that records the program, and reads the program from the storage medium. to be memorized. Then, the CPU copies the program stored in the storage device to the RAM, and sequentially reads out and executes the instructions included in the program from the RAM, thereby controlling the internal combustion engine control section 4, the purification control section 12, and the air-fuel ratio control section. 13 and the functions of the supply control unit 14 can be realized.

Next, the operation of this embodiment will be explained with reference to the flowchart of FIG.

First, as shown in FIG. 1, when the internal combustion engine control unit 4 controls the internal combustion engine 1 and the vehicle is driven, exhaust gas generated by the internal combustion engine 1 flows through the exhaust pipe 3 and is discharged to the outside. . For example, in the internal combustion engine 1, exhaust gas with a lean air-fuel ratio is generated, and when this exhaust gas flows through the LNT catalyst 6 disposed in the exhaust pipe 3, _NOx contained in the exhaust gas is sequentially removed by the LNT catalyst 6. occluded.

The amount of _NOx stored in the LNT catalyst 6 is calculated by the air-fuel ratio control section 13. The air-fuel ratio control unit 13 calculates the content of _NOx in the exhaust gas based on, for example, the flow rate of the intake air of the internal combustion engine 1 that is sequentially input from the internal combustion engine control unit 4, and calculates the content of _NOx in the exhaust gas. Based on this, the amount of _NOx stored in the LNT catalyst 6 can be calculated. In addition, the air-fuel _ratio control unit 13 detects the amount of NO _X in the exhaust gas flowing into the LNT catalyst 6 using a NO _X sensor (not shown), and calculates the amount of _NO You can also do that.

When the calculated NO _X storage amount exceeds a predetermined value, the air-fuel ratio control unit 13 lowers the air-fuel ratio of the exhaust gas flowing into the LNT catalyst 6 to a rich air-fuel ratio in step S1. For example, as shown in FIG. 3, the air-fuel ratio control unit 13 controls the exhaust gas flowing into the LNT catalyst 6 so that the excess air ratio of the air-fuel ratio R1 detected by the inlet lambda sensor 9a becomes approximately 0.95 at time T1. Decrease the air-fuel ratio of the gas.
Note that the predetermined value for the amount of NO _X stored can be set based on the capacity of NO _X that can be stored in the LNT catalyst 6, for example. Further, the period from time T1 to time T3 during which the exhaust gas flowing into the LNT catalyst 6 is controlled to have a rich air-fuel ratio is defined as a rich period.

At this time, the air-fuel ratio control section 13 lowers the air-fuel ratio of the exhaust gas flowing into the LNT catalyst 6 by controlling at least one of the intake system and the fuel system of the internal combustion engine 1 via the internal combustion engine control section 4. can be done. For example, the air-fuel ratio control unit 13 controls the intake system and fuel system of the internal combustion engine 1 to reduce the flow rate of intake air to the internal combustion engine 1 and increase the amount of fuel injected, thereby controlling the exhaust gas flowing into the LNT catalyst 6. Decrease the air-fuel ratio of the gas.

Here, the intake system of the internal combustion engine 1 adjusts the flow rate of intake air, and includes, for example, an intake throttle, an exhaust throttle, an EGR (Exhaust Gas Recirculation) valve, and a turbocharger. The fuel system of the internal combustion engine 1 injects fuel, such as after-injection in the cylinder and fuel injection into the exhaust pipe 3.

Subsequently, the air-fuel ratio control unit 13 controls the air-fuel ratio of the exhaust gas flowing into the LNT catalyst 6 so that the excess air ratio of the air-fuel ratio R1 detected by the inlet lambda sensor 9a is maintained at approximately 0.95. . For this reason, the exhaust gas flowing into the LNT catalyst 6 has a reduced oxygen concentration and an increased amount of reducing agents such as carbon monoxide and hydrocarbons, compared to a lean air-fuel ratio.
Thereby, the _NOx stored in the LNT catalyst 6 can be released and reduced to purify it into substances such as nitrogen, water, and carbon dioxide.

At this time, oxygen is generated according to the release and reduction of _NOx by the LNT catalyst 6. Therefore, the air-fuel ratio R2 detected by the outlet lambda sensor 9b disposed downstream of the LNT catalyst 6 has a higher value than the air-fuel ratio R1 detected by the inlet lambda sensor 9a, for example, the excess air ratio is about 1.0. The air-fuel ratio will be maintained at a stoichiometric air-fuel ratio. Then, as the purification of NO _X progresses and the _latter half of the rich period begins, NO

Conventionally, the air-fuel ratio R1a of the exhaust gas flowing into the LNT catalyst 6 has been controlled to maintain the value before the drop timing, that is, the excess air ratio of about 0.95, even after the drop timing T2. After the decrease timing T2, the oxygen generated by the reduction reaction decreases in accordance with the decrease in the reduction amount of the LNT catalyst 6, so the air-fuel ratio R2a detected by the outlet lambda sensor 9b gradually decreases. . In this way, when oxygen decreases around the LNT catalyst 6, _NOx , for example _NO2 , released from the LNT catalyst 6 reacts with _H2 etc. to generate ammonia, and a large amount of ammonia N1 is released from the LNT catalyst 6. may slip.

The SCR catalyst 7 arranged downstream of the LNT catalyst 6 stores ammonia, and uses the stored ammonia to reduce and purify _NOx contained in the exhaust gas. Therefore, if ammonia N1 slips from the LNT catalyst 6, it will affect the calculation of the amount of ammonia to be stored in the SCR catalyst 7, which may lead to an increase in the amount of ammonia slip in the SCR catalyst 7 and a decrease in the _NOx purification rate. There is.
Furthermore, since ammonia N1 has corrosive properties, there is a possibility that the exhaust pipe 3 will be corroded. In particular, when an LP-EGR (Low Pressure-EGR) is provided downstream of the LNT catalyst 6, ammonia N1 that has slipped from the LNT catalyst 6 is returned to the intake pipe 2 via the LP-EGR, and is sent to various pipes. This may have a significant impact on the production of NOx and _NOx .

Therefore, in the present disclosure, when the air-fuel ratio control unit 13 detects the air-fuel ratio R2 with the outlet lambda sensor 9b and the reduction timing T2 is obtained, the air-fuel ratio control unit 13 changes the air-fuel ratio R1 of the exhaust gas flowing into the LNT catalyst 6 to the reduction timing. Increase it from before T2.

Specifically, in step S2, the air-fuel ratio control unit 13 determines whether the amount of decrease in the air-fuel ratio R2 detected by the outlet lambda sensor 9b is larger than a predetermined threshold value. When the air-fuel ratio control unit 13 determines that the amount of decrease in the air-fuel ratio R2 detected by the outlet lambda sensor 9b is larger than a predetermined threshold value, the air-fuel ratio control unit 13 determines that time as the decrease timing T2, that is, when the LNT is stored in the LNT catalyst 6. It is determined that the amount of reduction has decreased in accordance with the decrease in _NOx . Here, the predetermined threshold value can be set based on the amount of variation in the air-fuel ratio R2 when the air-fuel ratio R1 is kept constant, and can be set to about 0.01 as the excess air ratio, for example.

When the air-fuel ratio control unit 13 determines that it is the lowering timing T2, the process proceeds to step S3, and controls at least one of the intake system and the fuel system of the internal combustion engine 1 via the internal combustion engine control unit 4, and controls the exit lambda. The air-fuel ratio R1 of the exhaust gas flowing into the LNT catalyst 6 is increased so that the air-fuel ratio R2 detected by the sensor 9b maintains the value before the reduction timing T2. That is, the air-fuel ratio control unit 13 increases the excess air ratio of the air-fuel ratio R1 of the exhaust gas flowing into the LNT catalyst 6 to about 0.98 so that the excess air ratio of the air-fuel ratio R2 is maintained at about 1.0. .

In this way, even if oxygen decreases around the LNT catalyst 6, the amount of oxygen at the air-fuel ratio R1 is increased to compensate for the decrease, so the amount of oxygen existing around the LNT catalyst 6 can be maintained. . Thereby, the generation of ammonia N2 can be suppressed, and the slip amount of ammonia N2 from the LNT catalyst 6 can be greatly reduced. At this time, the air-fuel ratio control unit 13 can suppress the slip of ammonia N2 from the LNT catalyst 6 by simply adding control without adding a new device.

Furthermore, the air-fuel ratio control unit 13 increases the air-fuel ratio R1 of the exhaust gas flowing into the LNT catalyst 6 so that the air-fuel ratio R2 detected by the outlet lambda sensor 9b maintains the value before the reduction timing T2. As a result, since the air-fuel ratio R1 is maintained at a value where the excess air ratio is smaller than about 1.0, the reduction of _NOx by the LNT catalyst 6 can be maintained even after the reduction timing T2.

Here, when the air-fuel ratio R1 of the exhaust gas flowing into the LNT catalyst 6 was actually increased from an excess air ratio of approximately 0.95, the air-fuel ratio was adjusted so that the excess air ratio was 0.96 or more and 0.98 or less. By increasing R1, the excess air ratio of the air-fuel ratio R2 can be maintained at approximately 1.0 with high precision even after the lowering timing T2, and the slip amount of ammonia N2 from the LNT catalyst 6 can be reliably reduced. Understood.
From this, the air-fuel ratio control unit 13 determines that if the excess air ratio of the air-fuel ratio R2 detected by the outlet lambda sensor 9b is maintained at approximately 1.0 before the drop timing T2, the air-fuel ratio controller 13 determines that when the excess air ratio of the air-fuel ratio R2 detected by the outlet lambda sensor 9b is maintained at approximately 1.0 before the reduction timing T2, It is preferable to increase the air-fuel ratio R1 of the exhaust gas to an excess air ratio of 0.96 or more and 0.98 or less.

In addition, the air-fuel ratio control unit 13 controls the fuel system of the intake system and fuel system of the internal combustion engine 1, and specifically increases the air-fuel ratio R1 of the exhaust gas flowing into the LNT catalyst 6 by performing after-injection. It is preferable to let After-injection has a quick response to the air-fuel ratio R1 and can quickly increase the air-fuel ratio R1, so that slip of ammonia N2 from the LNT catalyst 6 can be suppressed more reliably.

Furthermore, the air-fuel ratio control unit 13 gradually increases the air-fuel ratio R1 by changing the air-fuel ratio R1 of the exhaust gas flowing into the LNT catalyst 6 with respect to the target excess air ratio of 0.98. I can do it. For example, when raising the air-fuel ratio R1 from about 0.95 to about 0.98, the air-fuel ratio control unit 13 can raise the air-fuel ratio R1 in three steps in increments of 0.01. Thereby, when adjusting the air-fuel ratio R1 to the target value, the air-fuel ratio control unit 13 can suppress fluctuations up and down with respect to the target value, and adjust the air-fuel ratio R1 to the target value with high precision. can do.

In this way, the air-fuel ratio R2 detected by the exit lambda sensor 9b is maintained at an excess air ratio of approximately 1.0 even after the reduction timing T2, and the _NO Reduction is maintained. Then, when the _NO It gradually decreases toward 0.98, which is the same as R1.

At this time, when the exit lambda sensor 9b detects the drop timing T3, the air-fuel ratio control unit 13 maintains the excess air ratio of the air-fuel ratio R2 at about 1.0, which was before the drop timing T3, in the same way as described above. Thus, the air-fuel ratio R1 of the exhaust gas flowing into the LNT catalyst 6 may be further increased. That is, the air-fuel ratio control unit 13 can repeatedly increase the air-fuel ratio R1 every time the decrease timings T2 and T3 are detected so that the air-fuel ratio R2 maintains the value before the decrease timings T2 and T3.

Subsequently, in step S4, the air-fuel ratio control unit 13 determines whether the value of the air-fuel ratio R2 matches the air-fuel ratio R1. When the air-fuel ratio control unit 13 determines that the value of the air-fuel ratio R2 matches the air-fuel ratio R1 at time T4, that is, when it determines that the _NOx stored in the LNT catalyst 6 has been completely reduced, the process proceeds to step S5. The air-fuel ratio R1 of the exhaust gas flowing into the LNT catalyst 6 is controlled to increase to a lean air-fuel ratio. As a result, the rich period ends, and the reduction of _NOx stored in the LNT catalyst 6 is stopped. Then, _NOx contained in the exhaust gas is stored in the LNT catalyst 6 again.

On the other hand, the supply control unit 14 supplies urea water to the SCR catalyst 7, for example, when the temperature detected by the temperature sensor 10b falls within a range suitable for the reduction reaction of the SCR catalyst 7. At this time, the supply control unit 14 calculates the amount of urea water supplied to the SCR catalyst 7 based on the storage capacity of ammonia in the SCR catalyst 7.
The urea water injected from the supply section 11 is thermally decomposed and hydrolyzed by the heat of the exhaust gas to generate ammonia, and the ammonia is stored in the SCR catalyst 7. Then, _NOx contained in the exhaust gas is purified by being reduced to nitrogen or the like using ammonia stored in the SCR catalyst 7.

At this time, the supply control section 14 accurately calculates the supply amount of urea water from the supply section 11 according to the storage capacity of the SCR catalyst 7, since the slip amount of ammonia N2 from the LNT catalyst 6 is reduced. be able to. Thereby, an appropriate amount of ammonia can be supplied to the SCR catalyst 7, and an increase in the slip amount of ammonia and a decrease in the _NOx purification rate in the SCR catalyst 7 can be suppressed.

According to the present embodiment, when the air-fuel ratio control unit 13 detects the air-fuel ratio R2 of exhaust gas with the outlet lambda sensor 9b and obtains the lowering timing T2, the air-fuel ratio detected by the outlet lambda sensor 9b is The air-fuel ratio R1 of the exhaust gas flowing into the LNT catalyst 6 is increased so as to maintain the value before the decrease timing T2. Therefore, the slip of ammonia from the LNT catalyst 6 can be suppressed while maintaining the reduction of _NOx by the LNT catalyst 6.

(Embodiment 2)
Embodiment 2 of the present disclosure will be described below. Here, differences from the first embodiment described above will be mainly explained, and common points with the first embodiment described above will be denoted by common reference numerals, and detailed explanation thereof will be omitted.

In the first embodiment described above, the air-fuel ratio control unit 13 controls the air-fuel ratio R1 based on the decrease timing T2 obtained by detecting the air-fuel ratio R2 of the exhaust gas with the outlet lambda sensor 9b, but the decrease timing T2 It is sufficient if the air-fuel ratio R1 can be controlled based on the above, and the present invention is not limited to this.

For example, as shown in FIG. 4, a calculation section 21 can be newly arranged between the inlet lambda sensor 9a and temperature sensor 10a of the first embodiment and the air-fuel ratio control section 13.

The calculation unit 21 stores in advance a reduction amount map showing the reduction amount of the LNT catalyst 6 with respect to the air-fuel ratio R1 of the exhaust gas flowing into the LNT catalyst 6 and the temperature of the exhaust gas flowing through the LNT catalyst 6. Subsequently, the calculation unit 21 calculates the reduction amount of the LNT catalyst 6 based on the reduction amount map from the air-fuel ratio R1 detected by the inlet lambda sensor 9a and the temperature detected by the temperature sensor 10a, and determines the reduction timing T2. get. Note that the reduction amount map can be created by, for example, experiments and simulations.

Here, the inlet lambda sensor 9a, the temperature sensor 10a, and the calculation unit 21 constitute an acquisition unit in the present disclosure.

The air-fuel ratio control unit 13 controls the air-fuel ratio R1 of the exhaust gas flowing into the LNT catalyst 6 to be higher than before the decrease timing T2 based on the decrease timing T2 acquired by the calculation unit 21.

Next, the operation of this embodiment will be explained with reference to the flowchart of FIG.

First, when the storage amount of _NO from a lean air-fuel ratio to a rich air-fuel ratio. Then, the air-fuel ratio control unit 13 reduces and purifies the _NO .

At this time, the calculation unit 21 sequentially calculates the amount of NO _X reduced by the LNT catalyst 6 from the air-fuel ratio R1 detected by the inlet lambda sensor 9a and the temperature detected by the temperature sensor 10a based on the reduction amount map. .

Subsequently, in step S21, the air-fuel ratio control unit 13 determines whether the amount of _NOx reduced by the LNT catalyst 6 calculated by the calculation unit 21 is smaller than a predetermined threshold value. When the air-fuel ratio control unit 13 determines that the amount of _NOx reduced by the LNT catalyst 6 calculated by the calculation unit 21 is smaller than a predetermined threshold value, the air-fuel ratio control unit 13 determines that time as the reduction timing T2. Here, the predetermined threshold value can be set in advance based on, for example, a change in the slip amount of ammonia from the LNT catalyst 6 with respect to a decrease in the reduction amount of the LNT catalyst 6.

At this time, when the air-fuel ratio control unit 13 determines the reduction timing T2 based on the air-fuel ratio R2 detected by the outlet lambda sensor 9b as in the first embodiment, the reduction in the amount of reduction of the LNT catalyst 6 is caused by the air-fuel ratio There is a possibility that a detection delay may occur until the signal is reflected in R2. Therefore, as in the present embodiment, by determining the reduction timing T2 based on the reduction amount of the LNT catalyst 6 calculated by the calculation unit 21, the reduction timing T2 can be promptly adjusted to match the actual reduction reaction. can be determined.

Subsequently, as in the first embodiment, in step S3, the air-fuel ratio control unit 13 controls the air-fuel ratio flowing into the LNT catalyst 6 so that the air-fuel ratio R2 detected by the outlet lambda sensor 9b maintains the value before the decrease timing T2. The air-fuel ratio R1 of the exhaust gas is increased.

According to the present embodiment, the calculation unit 21 calculates the reduction amount of the LNT catalyst 6 from the air-fuel ratio R1 detected by the inlet lambda sensor 9a and the temperature detected by the temperature sensor 10a based on the reduction amount map. calculate. Thereby, the air-fuel ratio control unit 13 can quickly determine the lowering timing T2, and can reliably raise the air-fuel ratio R1 of the exhaust gas flowing into the LNT catalyst 6 at the lowering timing T2.

Note that the air-fuel ratio control unit 13 uses a method of determining the drop timing T2 based on the air-fuel ratio R1 detected by the outlet lambda sensor 9b as in the first embodiment, and a method of determining the decrease timing T2 based on the air-fuel ratio R1 detected by the outlet lambda sensor 9b as in the second embodiment. A method of determining the reduction timing T2 based on the calculated amount of _NOx reduced by the LNT catalyst 6 can be selectively used.
As in the first embodiment, the method of determining the drop timing T2 based on the air-fuel ratio R2 detected by the outlet lambda sensor 9b is different from the method of the second embodiment in that the method uses a value that reflects the actual reduction reaction. , it is possible to reliably determine the drop timing T2. Therefore, by selectively using the methods of Embodiments 1 and 2, it is possible to take advantage of the advantages of both methods and determine the drop timing T2 with high precision.

(Embodiment 3)
Embodiment 3 of the present disclosure will be described below. Here, we will mainly explain the differences from the above embodiments 1 and 2, and common points with the above embodiments 1 and 2 will be described in detail using common reference numerals. Omitted.

In the first and second embodiments described above, the air-fuel ratio control unit 13 controls the air-fuel ratio of the exhaust gas flowing into the LNT catalyst 6 so that the air-fuel ratio R2 detected by the outlet lambda sensor 9b maintains the value before the reduction timing T2. Although the fuel ratio R1 is increased, the air-fuel ratio R1 of the exhaust gas flowing into the LNT catalyst 6 may be increased from before the lowering timing T2, and the present invention is not limited to this.

For example, the air-fuel ratio control unit 13 can control the air-fuel ratio R1 of the exhaust gas flowing into the LNT catalyst 6 to increase to a lean air-fuel ratio based on the decrease timing T2. That is, the air-fuel ratio control unit 13 increases the air-fuel ratio R1 to a lean air-fuel ratio at the drop timing T2 to start the rich period without maintaining the excess air ratio of the air-fuel ratio R2 at approximately 1.0 after the drop timing T2. Terminate it.

In this manner, the air-fuel ratio control unit 13 increases the air-fuel ratio R1 to a lean air-fuel ratio at the reduction timing T2, and therefore can reliably suppress the slip amount of ammonia N2 from the LNT catalyst 6.

According to the present embodiment, the air-fuel ratio control unit 13 controls the air-fuel ratio R1 of the exhaust gas flowing into the LNT catalyst 6 to increase to a lean air-fuel ratio based on the reduction timing T2. It is possible to reliably suppress the amount of slip of ammonia N2 from the inside.

In the first to third embodiments described above, the air-fuel ratio control unit 13 immediately increases the air-fuel ratio R1 of the exhaust gas flowing into the LNT catalyst 6 from before the drop timing T2 upon detecting the drop timing T2. However, the control may be performed based on the lowering timing T2, and is not limited to this. For example, the air-fuel ratio control unit 13 can control the air-fuel ratio R1 of the exhaust gas flowing into the LNT catalyst 6 to be higher than before the reduction timing T2 after a predetermined time has elapsed from the reduction timing T2.

In addition, the above-mentioned embodiments are merely examples of implementation of the present invention, and the technical scope of the present invention should not be construed as limited by these. be. That is, the present invention can be implemented in various forms without departing from its gist or main features. For example, the disclosure regarding the shape, number, etc. of each part described in the above embodiment is merely an example, and can be implemented with appropriate changes.

The purification control device according to the present disclosure can be used as a device that controls the storage and reduction of _NOx in the LNT catalyst by adjusting the air-fuel ratio of exhaust gas flowing into the LNT catalyst.

1 Internal combustion engine 2 Intake pipe 3 Exhaust pipe 4 Internal combustion engine control unit 5 Purification device 6 _NO Purification control section 13 Air-fuel ratio control section 14 Supply control section 21 Calculation section N1, N2 Ammonia R1, R1a, R2, R2a Air-fuel ratio T1, T4 Time T2, T3 Decrease timing

Claims (5)

A purification control device that controls the storage and reduction of NO _{X in the NO X storage} reduction catalyst by adjusting the air-fuel ratio of exhaust gas flowing into the NO _X storage reduction catalyst disposed in the exhaust pipe of a vehicle, ,
an acquisition unit that acquires a reduction timing at which the reduction amount of the _NO
an air-fuel ratio control unit that controls the air-fuel ratio of exhaust gas flowing into the NO _X storage reduction catalyst to be higher than before the decrease timing based on the decrease timing acquired by the acquisition unit ;
The air-fuel ratio control unit is a purification control device that controls the air-fuel ratio of the exhaust gas flowing into the _NO . The acquisition unit includes an exit lambda sensor that is disposed in the exhaust pipe on the downstream side of the _NO
The air-fuel ratio control unit increases the air-fuel ratio of the exhaust gas flowing into the _NOx storage reduction catalyst from before the lowering timing based on the lowering timing acquired by the outlet lambda sensor. purification control device. A purification control device that controls the storage and reduction of NO _{X in the NO X storage} reduction catalyst by adjusting the air-fuel ratio of exhaust gas flowing into the NO _X storage reduction catalyst disposed in the exhaust pipe of a vehicle, ,
an acquisition unit that acquires a reduction timing at which the reduction amount of the _NO
an air-fuel ratio control unit that controls the air-fuel ratio of exhaust gas flowing into the NO X storage reduction catalyst to be higher than before the decrease timing based on the decrease timing acquired by the acquisition _unit ;
The acquisition unit includes:
an inlet lambda sensor that is disposed upstream of the NO _X storage reduction catalyst in the exhaust pipe and detects an air-fuel ratio of exhaust gas flowing into the NO _X storage reduction catalyst;
a temperature sensor that detects the temperature of exhaust gas flowing through the NO _X storage reduction catalyst;
storing in advance a reduction amount map showing the reduction amount of the NO _X storage reduction catalyst with respect to the air-fuel ratio of the exhaust gas flowing into the NO _X storage reduction catalyst and the temperature of the exhaust gas flowing through the NO _X storage reduction catalyst; a calculation unit that calculates the reduction amount of the _NO and has
The air-fuel ratio control unit is a purification control device that controls the air-fuel ratio of exhaust gas flowing into the _NOx storage reduction catalyst based on the decrease timing obtained by the calculation unit. The acquisition unit is configured to acquire the NO in the exhaust pipe. _X an outlet lambda sensor disposed downstream of the storage reduction catalyst to detect the air-fuel ratio of the exhaust gas and obtain the lowering timing;
The air-fuel ratio control section is configured to adjust the NO. _X The purification control device according to claim 3, wherein the air-fuel ratio of the exhaust gas flowing into the storage reduction catalyst is increased from before the lowering timing. The air-fuel ratio control unit controls the NO _X The purification control device according to claim 4, which increases the air-fuel ratio of exhaust gas flowing into the storage reduction catalyst.