CN111819349A

CN111819349A - Exhaust gas purification device, vehicle, and exhaust gas purification control device

Info

Publication number: CN111819349A
Application number: CN201980017347.8A
Authority: CN
Inventors: 阿野田洋
Original assignee: Isuzu Motors Ltd
Current assignee: Isuzu Motors Ltd
Priority date: 2018-03-08
Filing date: 2019-03-07
Publication date: 2020-10-23
Also published as: JP2019157667A; WO2019172357A1

Abstract

The present invention provides an exhaust gas purification device, comprising: an exhaust pipe through which exhaust gas generated by the internal combustion engine flows; a NOx selective reduction catalyst disposed in the exhaust pipe and purifying nitrogen oxides in the exhaust gas by adsorbing a reducing agent; a NOx storage reduction catalyst that is provided in the exhaust pipe at a position upstream of the NOx selective reduction catalyst in an exhaust direction in which the exhaust gas flows, and that stores nitrogen oxides in the exhaust gas; an adjustment unit that adjusts the flow rate of exhaust gas returned from an exhaust pipe to an intake pipe of an internal combustion engine; and a control unit that controls the adjustment unit so as to promote a reducing action of the reducing agent with respect to nitrogen oxides contained in the exhaust gas, in accordance with an amount of the reducing agent adsorbed by the NOx selective reduction catalyst.

Description

Exhaust gas purification device, vehicle, and exhaust gas purification control device

Technical Field

The invention relates to an exhaust gas purification device, a vehicle, and an exhaust gas purification control device.

Background

Conventionally, there has been known an exhaust gas purification apparatus including a NOx storage reduction catalyst for purifying nitrogen oxides (hereinafter referred to as "NOx") contained in exhaust gas generated by an internal combustion engine and a NOx selective reduction catalyst for reducing the NOx (see, for example, patent document 1). The NOx selective reduction catalyst adsorbs a reducing agent (e.g., ammonia) generated from a precursor (e.g., urea water) supplied into the exhaust pipe, and reduces NOx contained in the exhaust gas with the adsorbed ammonia.

The NOx storage reduction catalyst has a property of storing NOx in a low temperature state where the NOx selective reduction catalyst is in an inactive region. Therefore, even in this low temperature state, NOx can be stored by the NOx storage reduction catalyst and then reduced. In this way, in the case where the exhaust gas purification apparatus uses both the NOx selective reduction catalyst and the NOx storage reduction catalyst, the exhaust gas purification apparatus can efficiently perform the exhaust gas purification process.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2016-125390

Disclosure of Invention

Problems to be solved by the invention

However, the exhaust gas purifying apparatus may be provided with a trap portion for trapping particulate matter. When the exhaust gas flowing into the trap portion is heated to burn the trapped particulate matter and perform the regeneration process, the temperature in the exhaust gas purification apparatus is increased. Since a problem of ammonia desorption from the NOx selective reduction catalyst occurs due to a temperature rise in the exhaust gas purification apparatus (exhaust pipe), it is preferable to reduce the ammonia in the NOx selective reduction catalyst as much as possible when the temperature in the exhaust gas purification apparatus is raised.

However, when the NOx storage amount of the NOx storage reduction catalyst is small, the NOx contained in the exhaust gas is stored in the NOx storage reduction catalyst, and therefore ammonia in the NOx selective reduction catalyst cannot be reduced by the NOx contained in the exhaust gas. As a result, ammonia is still released from the NOx selective reduction catalyst.

An object of the present invention is to provide an exhaust gas purification device, a vehicle, and an exhaust gas purification control device that can suppress the release of a reducing agent from a NOx selective reduction catalyst due to a temperature rise in an exhaust pipe.

Means for solving the problems

The exhaust gas purification device of the present invention includes:

an exhaust pipe through which exhaust gas generated by the internal combustion engine flows;

a NOx selective reduction catalyst disposed in the exhaust pipe and configured to adsorb a reducing agent to purify nitrogen oxides in the exhaust gas;

a NOx storage reduction catalyst that is provided in the exhaust pipe upstream of the NOx selective reduction catalyst in an exhaust direction in which the exhaust gas flows, and that stores nitrogen oxides in the exhaust gas;

a recirculation path portion that connects an intake pipe of the internal combustion engine and the exhaust pipe from the exhaust pipe and recirculates the exhaust gas in the exhaust pipe to the intake pipe;

an adjusting portion that adjusts a flow rate of the exhaust gas recirculated by the recirculation path portion; and

and a control unit that controls the adjustment unit so as to promote a reducing action of the reducing agent and nitrogen oxides contained in the exhaust gas, based on an amount of the reducing agent adsorbed by the NOx selective reduction catalyst.

The vehicle of the present invention is provided with the exhaust gas purification device.

The exhaust gas purification control apparatus of the present invention is an exhaust gas purification control apparatus of an exhaust gas purification apparatus,

the exhaust gas purification device is provided with: an exhaust pipe through which exhaust gas generated by the internal combustion engine flows; a NOx selective reduction catalyst disposed in the exhaust pipe and configured to adsorb a reducing agent to purify nitrogen oxides in the exhaust gas; a NOx storage reduction catalyst that is provided in the exhaust pipe upstream of the NOx selective reduction catalyst in an exhaust direction in which the exhaust gas flows, and that stores nitrogen oxides in the exhaust gas; and a recirculation path portion that connects an intake pipe of the internal combustion engine and the exhaust pipe from the exhaust pipe and recirculates the exhaust gas in the exhaust pipe to the intake pipe,

it is provided with: an adjusting portion that adjusts a flow rate of the exhaust gas recirculated by the recirculation path portion; and

Effects of the invention

According to the present invention, it is possible to suppress the release of the reducing agent from the NOx selective reduction catalyst due to the temperature rise in the exhaust pipe.

Drawings

Fig. 1 is a schematic configuration diagram showing an exhaust system of an internal combustion engine to which an exhaust gas purification device according to an embodiment of the present invention is applied.

Fig. 2 is a schematic diagram showing the change in NOx storage efficiency of the NOx storage reduction catalyst with temperature.

Fig. 3 is a schematic diagram showing the change in NOx purification rate of the NOx selective reduction catalyst with temperature.

Fig. 4 is a flowchart showing an example of the operation of the purification control in the exhaust gas purification device.

Fig. 5 is a flowchart showing an example of the operation of controlling the flow rate of the exhaust gas in the recirculation path unit.

Detailed Description

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Fig. 1 is a schematic configuration diagram showing an exhaust system of an internal combustion engine 1 to which an exhaust gas purification apparatus 100 according to an embodiment of the present invention is applied.

As shown in fig. 1, an internal combustion engine 1 is mounted on a vehicle V, for example, a diesel engine, and is provided with an exhaust gas purification apparatus 100 for guiding exhaust gas generated in the internal combustion engine 1 to the atmosphere. Exhaust gas purification device 100 includes intake pipe 110, exhaust pipe 120, first temperature detection unit 130, second temperature detection unit 140, urea solution injection unit 150, recirculation path unit 160, and control unit 300.

An intake valve, not shown, is provided in the intake pipe 110, and the intake pipe 110 draws outside air into the internal combustion engine 1 as the intake valve is opened under the control of the controller 300.

The exhaust pipe 120 is for flowing exhaust gas generated by the internal combustion engine 1. In the exhaust pipe 120, an NOx storage reduction catalyst 210, a DPF (Diesel Particulate Filter) 220 as an example of a trap portion, an NOx selective reduction catalyst 230, and the like are provided in this order from the upstream side in the direction in which exhaust gas flows (from the left to the right in the drawing, hereinafter referred to as "exhaust direction").

The NOx storage reduction catalyst 210 is provided in the exhaust pipe 120 at a position upstream of the DPF220 and the NOx selective reduction catalyst 230 in the exhaust direction, and stores nitrogen oxides (hereinafter referred to as NOx) in the exhaust gas.

Specifically, the NOx storage reduction catalyst 210 stores NOx in the exhaust gas when the exhaust gas temperature is the storage temperature and the exhaust gas air-fuel ratio is lean (lean). The range of the storage temperature includes a temperature at which the NOx selective reduction catalyst 230 is in an inactive region.

The exhaust gas air-fuel ratio is set to a rich (rich) state under the control of the control unit 300, whereby NOx stored in the NOx storage reduction catalyst 210 reacts with hydrocarbons and carbon monoxide in the exhaust gas and is reduced.

The DPF220 traps particulate matter contained in exhaust gas passing therethrough. In the DPF220, the particulate matter trapped therein is removed by performing a regeneration process of burning the particulate matter under the control of the control unit 300. Specifically, by performing post injection (post injection) into the cylinder of the internal combustion engine 1 or supplying fuel into the exhaust pipe 120 under the control of the control unit 300, for example, hydrocarbons are supplied to an unillustrated oxidation catalyst, and the oxidation reaction of the oxidation catalyst occurs, so that the exhaust gas temperature of the exhaust pipe 120 rises. Thus, the exhaust gas having an increased temperature flows into the DPF220 to burn the particulate matter.

The NOx selective reduction catalyst 230 is provided on the downstream side of the DPF220 in the exhaust pipe 120, and adsorbs ammonia as an example of the reducing agent generated from the urea water injected from the urea water injection unit 150. The NOx selective reduction catalyst 230 reduces NOx contained in the exhaust gas passing through it by reacting the adsorbed ammonia with the NOx.

The first temperature detection portion 130 is provided upstream of the NOx storage reduction catalyst 210 in the exhaust direction, and detects the temperature of the exhaust pipe 120 in the vicinity of the NOx storage reduction catalyst 210.

The second temperature detection portion 140 is provided upstream of the NOx selective reduction catalyst 230 in the exhaust direction, and detects the temperature of the portion of the exhaust pipe 120 immediately before the NOx selective reduction catalyst 230.

The urea solution injector 150 is provided in the exhaust pipe 120 upstream of the NOx selective reduction catalyst 230. When the urea solution is supplied into exhaust pipe 120 from urea solution injection unit 150, the urea solution is hydrolyzed by the temperature in exhaust pipe 120, and ammonia is generated. The ammonia is then adsorbed on the NOx selective reduction catalyst 230.

The recirculation path portion 160 is a path branched from the exhaust pipe 120 and recirculating the exhaust gas in the exhaust pipe 120 to the intake pipe 110, and the recirculation path portion 160 is connected to the intake pipe 110 and the exhaust pipe 120.

The recirculation path portion 160 is provided with an adjusting portion 161, and the adjusting portion 161 adjusts the flow rate of the exhaust gas returned from the exhaust pipe 120 to the intake pipe 110 through the recirculation path portion 160. The adjusting unit 161 adjusts the flow rate of the exhaust gas returned from the exhaust pipe 120 to the intake pipe 110 by switching the passage of the exhaust gas from an open state to a closed state under the control of the control unit 300.

The Control Unit 300 is, for example, an Electronic Control Unit (ECU) and includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and an input/output circuit (not shown). The control unit 300 executes, according to a preset program, a regeneration process for burning particulate matter trapped in the DPF220, a rich process for making the air-fuel ratio of the exhaust gas in the exhaust pipe 120 rich, a process for adjusting the flow rate of the exhaust gas in the recirculation path 160, and the like. The control portion 300 corresponds to "exhaust gas purification control means" of the present invention.

When the regeneration process of DPF220 is executed, control unit 300 estimates the amount of ammonia adsorbed by NOx selective reduction catalyst 230. Then, the control portion 300 controls the regulation portion 161 so as to promote a reducing action between the ammonia adsorbed by the NOx selective reduction catalyst 230 and the NOx contained in the exhaust gas, based on the estimated adsorption amount of the ammonia. The control section 300 corresponds to an "estimating section" of the present invention.

More specifically, the control unit 300 estimates the amount of NOx stored in the NOx storage reduction catalyst 210, and determines whether to control the adjustment unit 161 based on the estimated amount of stored ammonia when the amount of stored ammonia is larger than a predetermined target amount. When the estimated stored amount is smaller than the prescribed stored amount of the NOx storage reduction catalyst 210, the control portion 300 controls the adjustment portion 161 to reduce the flow rate of the exhaust gas in the recirculation path portion 160. The predetermined target amount is, for example, an amount of ammonia that allows the slip concentration of ammonia in the NOx selective reduction catalyst 230 to be equal to or lower than a target value during the regeneration process.

The estimated adsorption amount of ammonia is estimated from the following formula (1).

Estimated ammonia adsorption amount (ammonia last adsorption amount + ammonia supply amount-ammonia consumption amount-ammonia desorption amount … … (1)

The supplied ammonia amount is the amount of ammonia supplied to the NOx selective reduction catalyst 230, and is calculated based on the amount of urea water injected by the urea water injection unit 150.

The consumed ammonia amount is an amount of ammonia consumed by the NOx purification reaction, and is calculated based on the amount of NOx passing through the NOx selective reduction catalyst 230, the result of temperature detection by the second temperature detection portion 140, the flow rate of the exhaust gas, the ratio of NO2 in NOx, and the amount of ammonia adsorbed.

The amount of NOx passing through the NOx selective reduction catalyst 230 is detected by a sensor or the like, not shown. The ratio of NO2 in NOx is estimated by correcting the NOx storage amount and the temperature of the NOx storage reduction catalyst 210 based on the map based on the engine speed and the fuel injection amount. The last adsorption amount of ammonia is the current adsorption amount of ammonia obtained when the previous calculation is made by the formula (1).

The desorbed ammonia amount is the amount of ammonia desorbed from the NOx selective reduction catalyst 230 and is calculated based on the ammonia adsorption amount, the temperature detection result of the second temperature detection unit 140, and the flow rate of the exhaust gas.

The estimated storage amount of NOx is estimated according to the following equation (2).

NOx storage (A + B × C-D-E. cndot. (2)

A: stored amount of NOx

B-NOx concentration on the upstream side of the NOx storage reduction catalyst 210

NOx storage efficiency of the NOx storage reduction catalyst 210

D amount of NOx discharged from the NOx storage reduction catalyst 210

E amount of NOx reduced from the NOx storage reduction catalyst 210

The stored amount of NOx is the amount of NOx that has been stored in the NOx storage reduction catalyst 210, and for example, an estimated value of the NOx storage amount that was estimated last time may be used.

The NOx concentration upstream of the NOx storage reduction catalyst 210 is the NOx concentration in the exhaust gas upstream of the NOx storage reduction catalyst 210 in the exhaust pipe 120, and as this concentration, for example, the NOx concentration detected by a sensor, not shown, can be used.

The NOx storage efficiency of the NOx storage reduction catalyst 210 is calculated based on the result of the temperature detection by the first temperature detection portion 130, the flow rate of the exhaust gas, the NOx concentration on the upstream side of the NOx storage reduction catalyst 210, the stored amount of NOx, and the like. The flow rate of the exhaust gas is the amount of the exhaust gas flowing into the exhaust pipe 120, and is detected by a sensor or the like, not shown.

The amount of NOx discharged from the NOx storage reduction catalyst 210 is calculated based on the temperature detection result of the first temperature detection portion 130, the stored amount of NOx, and the like.

The amount of NOx reduced by the NOx storage reduction catalyst 210 is calculated based on the temperature detection result of the first temperature detection portion 130, the exhaust gas flow rate, the stored amount of the NOx storage reduction catalyst 210, the exhaust gas air-fuel ratio, and the like. The exhaust gas air-fuel ratio is calculated based on the fuel injection amount in the exhaust pipe 120 and the like.

At this time, if the temperature in the exhaust pipe 120 rises due to a regeneration process or the like, a problem arises in that ammonia is desorbed from the NOx selective reduction catalyst 230, and therefore it is preferable to reduce the ammonia in the NOx selective reduction catalyst 230 as much as possible when the temperature in the exhaust pipe 120 rises.

However, when the NOx storage amount of the NOx storage reduction catalyst 210 is small, since NOx contained in the exhaust gas is stored by the NOx storage reduction catalyst 210, ammonia in the NOx selective reduction catalyst 230 cannot be reduced by NOx contained in the exhaust gas. As a result, ammonia is still released from the NOx selective reduction catalyst 230.

In this case, the flow rate of the exhaust gas in the recirculation path portion 160 is reduced by controlling the adjustment portion 161, so that the exhaust gas returned to the intake pipe 110 through the recirculation path portion 160 is reduced. Since the exhaust gas contains NOx, the NOx concentration of the exhaust gas flowing through the exhaust pipe 120 is increased by controlling the regulator 161.

This increases the amount of NOx stored in the NOx storage reduction catalyst 210, and at the same time, causes a purification reaction with NOx contained in the exhaust gas, thereby reducing the amount of ammonia adsorbed by the NOx selective reduction catalyst 230.

As a result, when the temperature in the exhaust pipe 120 rises due to the regeneration treatment or the like, ammonia in the NOx selective reduction catalyst 230 can be reduced by NOx contained in the exhaust gas, and desorption of ammonia due to the temperature rise can be suppressed.

Further, the control section 300 may determine whether to control the adjustment section 161 based on the detection result of the first temperature detection section 130. Fig. 2 is a schematic diagram showing the NOx storage efficiency of the NOx storage reduction catalyst 210 as a function of temperature.

As shown in fig. 2, the NOx storage efficiency of the NOx storage reduction catalyst 210 is comparatively high, for example, in the range of the temperature T1 to the temperature T2. Therefore, when the storage efficiency is in the temperature range higher than the predetermined efficiency, the control unit 300 determines that the adjustment unit 161 is to be controlled. The predetermined efficiency may be appropriately determined in accordance with the storage amount of the NOx storage reduction catalyst 210 and the like. Thereby, the storage efficiency of the NOx storage reduction catalyst 210 can be improved, and ammonia in the NOx selective reduction catalyst 230 can be reduced by NOx contained in the exhaust gas.

The control unit 300 may determine whether or not to control the adjustment unit 161 based on the detection result of the second temperature detection unit 140. Fig. 3 is a schematic diagram showing the change in NOx purification rate of the NOx selective reduction catalyst 230 with temperature.

It was confirmed that, as shown in fig. 3, if the NOx selective reduction catalyst 230 reached the activation temperature T3 or higher in the active region, the NOx purification rate was a relatively high purification rate. Therefore, the control unit 300 determines that the adjustment unit 161 is to be controlled when the activation temperature T3 or higher. This improves the efficiency of reduction of ammonia by the NOx selective reduction catalyst 230, and facilitates reduction of ammonia in the NOx selective reduction catalyst 230.

The control portion 300 may control the adjustment portion 161 based on the temperature of the NOx storage reduction catalyst 210 and the temperature of the NOx selective reduction catalyst 230. Table 1 is a schematic diagram showing the relationship between the estimated stored amount of NOx, the temperature of the NOx storage reduction catalyst 210, the temperature of the NOx selective reduction catalyst 230, and the flow rate of the exhaust gas in the recirculation passage 160.

[ Table 1]

The "estimated storage amount" in table 1 indicates the estimated storage amount of the NOx storage reduction catalyst 210. The "first temperature" in table 1 indicates the temperature of the NOx storage reduction catalyst 210 (the result of detection of the temperature of the first temperature detection portion 130). The "second temperature" in table 1 indicates the temperature of the NOx selective reduction catalyst 230 (the result of detection of the temperature by the second temperature detecting portion 140). The "flow rate" in table 1 indicates the flow rate of the exhaust gas of the recirculation path portion 160.

In table 1, "more" in the "estimated stored amount" indicates a case where the estimated stored amount of the NOx storage reduction catalyst 210 is larger than the predetermined stored amount, and "less" indicates a case where the estimated stored amount of the NOx storage reduction catalyst 210 is smaller than the predetermined stored amount.

For example, the control unit 300 reads the relationship shown in table 1 from a storage unit not shown in the figure according to the conditions, and controls the adjustment unit 161. In this way, the control of the adjustment section 161 can be simplified.

Specifically, when the storage amount is estimated to be large and the temperature of the NOx selective reduction catalyst 230 is below the activation temperature (row 1 in table 1), the flow rate of the exhaust gas is set to the "normal" amount in the fully open state of the passage in the recirculation path portion 160.

When the temperature of the NOx selective reduction catalyst 230 is equal to or lower than the activation temperature, NOx and ammonia are difficult to reduce, and NOx is easily discharged to the outside. Therefore, since the necessity of reducing the amount of NOx contained in the exhaust gas by the recirculation path portion 160 increases, the control shown in row 1 in table 1 is effective.

When the storage amount is estimated to be large and the temperature of the NOx selective reduction catalyst 230 is equal to or higher than the activation temperature (row 2 in table 1), the flow rate of the exhaust gas is set to a flow rate after "reduction" from the "normal" flow rate. The degree of the decrement is determined based on the estimated storage amount, the estimated adsorption amount of ammonia, and the like.

When the flow rate of the exhaust gas in the recirculation path portion 160 is reduced, NOx contained in the exhaust gas flowing through the exhaust pipe 120 increases. However, when the temperature of the NOx selective reduction catalyst 230 is equal to or higher than the activation temperature, NOx is likely to undergo a reduction reaction with ammonia, and therefore ammonia can be efficiently reduced. As a result, the control shown in row 2 in table 1 is effective.

Further, when it is estimated that the storage amount is small, the temperature of the NOx storage reduction catalyst 210 is outside the storage temperature range, and the temperature of the NOx selective reduction catalyst 230 is equal to or higher than the activation temperature (row 3 in table 1), the flow rate of the exhaust gas is set to "decrease". The storage temperature range is, for example, the range from the temperature T1 to the temperature T2 in fig. 2.

When the temperature of the NOx storage reduction catalyst 210 is outside the storage temperature range and the estimated storage amount is small, NOx cannot be stored in the NOx storage reduction catalyst 210 and NOx discharged from the NOx storage reduction catalyst 210 cannot be used. Therefore, in this case, the exhaust gas in the recirculation path portion 160 is reduced to increase the concentration of NOx in the exhaust gas in the exhaust pipe 120, and the ammonia can be reduced by this NOx. As a result, the control shown in row 3 in table 1 is effective.

Further, when it is estimated that the storage amount is small, the temperature of the NOx storage reduction catalyst 210 is outside the storage temperature range, and the temperature of the NOx selective reduction catalyst 230 is below the activation temperature (row 4 in table 1), the flow rate of the exhaust gas is set to "normal".

In this case, it is difficult to reduce ammonia in the NOx selective reduction catalyst 230 and to store NOx in the NOx storage reduction catalyst 210, so it is desirable to reduce NOx in the exhaust pipe 120 as much as possible. Therefore, by performing the control shown in row 4 of table 1, NOx contained in the exhaust gas flowing through the exhaust pipe 120 can be reduced by the recirculation path unit 160. As a result, the control shown in the 4 th row in table 1 is effective.

Further, when the estimated storage amount is small and the temperature of the NOx storage reduction catalyst 210 is within the storage temperature range (row 5 in table 1), the flow rate of the exhaust gas is set to "decrease". In this case, the NOx storage reduction catalyst 210 can be made to actively store NOx while promoting the reduction action of NOx and ammonia contained in the exhaust gas. As a result, the control shown in the 5 th row in table 1 is effective.

When the regeneration process is executed, the control unit 300 prohibits the rich process.

By prohibiting the rich spike, the storage amount of NOx in the NOx storage reduction catalyst 210 can be easily increased. That is, since ammonia in the NOx selective reduction catalyst 230 can be easily reduced by NOx in the exhaust gas, the regeneration process can be performed quickly.

An example of the operation of the purification control in the exhaust gas purification device 100 configured as described above will be described. Fig. 4 is a flowchart showing an example of the operation of the purification control in the exhaust gas purification apparatus 100. The processing in fig. 4 may be appropriately executed when the vehicle V is running, for example.

As shown in fig. 4, the control unit 300 determines whether or not the reproduction process needs to be executed (step S101). The determination as to whether or not the regeneration process needs to be executed in step S101 is made based on the amount of trapped particulate matter in the DPF220, for example. Specifically, when the amount of trapped particulate matter in the DPF220 reaches an amount to be burned, the control unit 300 determines that the regeneration process needs to be executed.

When the execution of the regeneration process is not necessary as a result of the determination (no in step S101), the present control is terminated. On the other hand, when the regeneration process needs to be executed (yes in step S101), the control unit 300 prohibits the rich process (step S102).

Next, the control unit 300 estimates the amount of ammonia adsorbed by the NOx selective reduction catalyst 230 (step S103). Next, the control unit 300 determines whether or not the adsorption amount of ammonia is larger than a predetermined target amount (step S104).

As a result of the determination, when the adsorption amount of ammonia is larger than the predetermined target amount (yes in step S104), the control unit 300 executes the flow rate control of the exhaust gas in the recirculation path unit 160 (step S105), which will be described later. After step S105, the process returns to step S103.

On the other hand, when the adsorption amount of ammonia is equal to or less than the predetermined target amount (no in step S104), the control unit 300 determines whether or not the regeneration process condition is satisfied (step S106). The regeneration process conditions include, for example, the temperature conditions of the NOx storage reduction catalyst 210.

If the determination result is that the reproduction processing condition is not satisfied (no in step S106), the process returns to step S103. Here, the reason why the processing returns to step S103 after step S106 is no and step S105 is that the stored amount of NOx and the adsorbed amount of ammonia change when the exhaust gas flows through the exhaust pipe 120 when the processing from step S103 to step S106 is performed.

On the other hand, when the regeneration process condition is satisfied (yes in step S106), the control unit 300 executes the regeneration process (step S107). After the regeneration process is completed, the present control is ended. Then, the above control is repeatedly executed during the traveling of the vehicle V.

Next, an example of the operation of controlling the flow rate of the exhaust gas in step S105 in fig. 4 will be described. Fig. 5 is a flowchart showing an operation example of the exhaust gas flow rate control in the recirculation path unit 160. The process of fig. 5 is executed when step S104 of fig. 4 is yes.

As shown in fig. 5, the control portion 300 estimates the NOx storage amount of the NOx storage reduction catalyst 210 (step S201). Next, control unit 300 determines whether the estimated stored amount of NOx is smaller than a predetermined stored amount (step S202).

If the estimated storage amount is equal to or larger than the predetermined storage amount as a result of the determination (no in step S202), the process proceeds to step S204. On the other hand, when the estimated storage amount is smaller than the predetermined storage amount (yes in step S202), the control unit 300 determines whether or not the first temperature of the NOx storage reduction catalyst 210 is within the predetermined range (step S203). The first temperature is, for example, a detection result of the first temperature detection unit 130. The predetermined range is, for example, the range of T1 and T2 in fig. 2.

If the first temperature is within the predetermined range as a result of the determination (yes at step S203), the process proceeds to step S205. On the other hand, if the first temperature is not within the predetermined range (no in step S203), the control unit 300 determines whether or not the second temperature of the NOx selective reduction catalyst 230 is equal to or higher than the activation temperature (step S204). The second temperature is, for example, a detection result of the second temperature detection unit 140.

If the second temperature is lower than the activation temperature as a result of the determination (no in step S204), the control is terminated. On the other hand, when the second temperature is equal to or higher than the activation temperature (yes in step S204), the control unit 300 controls the adjustment unit 161 to reduce the flow rate of the exhaust gas in the recirculation passage 160 (step S205). Then, this control is ended. After the current control is finished, the process returns to step S103 in fig. 4.

According to the present embodiment configured as described above, the control portion 300 controls the adjustment portion 161 so as to promote the reducing action between the ammonia and the NOx contained in the exhaust gas, based on the estimated amount of ammonia adsorbed by the NOx selective reduction catalyst 230.

That is, the ammonia in the NOx selective reduction catalyst 230 is reduced by the NOx contained in the exhaust gas. As a result, ammonia can be prevented from being desorbed from the NOx selective reduction catalyst 230 due to the temperature rise in the exhaust pipe 120 as in the case of the regeneration process.

Further, when the adsorption amount of ammonia is larger than the prescribed target amount and the estimated stored amount is smaller than the prescribed stored amount of the NOx storage reduction catalyst 210, the control portion 300 controls the adjustment portion 161 to reduce the flow rate of the exhaust gas. This makes it possible to increase the concentration of NOx in the exhaust gas, store NOx in the NOx storage reduction catalyst 210, and reduce ammonia in the NOx selective reduction catalyst 230 by the NOx contained in the exhaust gas.

In the above embodiment, the stored amount of NOx is estimated using the above equation (2), but the present invention is not limited to this, and the stored amount of NOx may be estimated by other methods. For example, sensors for detecting NOx may be provided on the upstream side and the downstream side of the NOx storage reduction catalyst 210, respectively, and the amount of stored NOx may be estimated using the difference in the detected amount of each sensor.

In the above embodiment, the control of the adjustment unit 161 is performed when the regeneration process is executed, but the present invention is not limited to this, and the control of the adjustment unit 161 may be performed when the temperature in the exhaust pipe 120 is increased by a factor other than the regeneration process.

In the above embodiment, the control unit 300 is described as an example of the estimation unit, but the present invention is not limited to this, and the estimation unit may be provided separately from the control unit 300.

Further, although the exhaust gas purification apparatus 100 of the above embodiment is mounted on a vehicle V mounted with a diesel engine, the present invention is not limited to this, and may be mounted on a vehicle mounted with a gasoline engine, for example.

In the above embodiment, the DPF220 is exemplified as an example of the trapping portion, but the present invention is not limited to this, and any filter may be used as long as it can trap particulate matter. When the exhaust gas purification apparatus 100 is mounted on a vehicle equipped with a gasoline engine, the trap unit may be a GPF (gasoline particulate Filter).

The above embodiments are merely specific examples for carrying out the present invention, and are not to be construed as limiting the technical scope of the present invention. That is, the present invention can be implemented in various forms without departing from the spirit or essential characteristics thereof.

The present application is based on the japanese patent application filed 3, 8, 2018 (japanese patent application 2018-041868), the entire contents of which are hereby incorporated by reference.

Industrial applicability

The exhaust gas purification device of the present invention is useful as an exhaust gas purification device, a vehicle, and an exhaust gas purification control device that can suppress the separation of the reducing agent from the NOx selective reduction catalyst due to a temperature rise in the exhaust pipe.

Description of the reference numerals

1 internal combustion engine

100 exhaust gas purifying apparatus

110 air suction pipe

120 exhaust pipe

130 first temperature detecting part

140 second temperature detecting part

150 urea solution injection part

160 recirculation path part

161 adjustment unit

210 NOx storage reduction catalyst

220 DPF (Diesel Particulate Filter)

230 NOx selective reduction catalyst

300 control part

V vehicle

Claims

1. An exhaust gas purification device, comprising:

and a control unit configured to control the adjustment unit so as to promote a reducing action of the reducing agent and nitrogen oxides contained in the exhaust gas, based on an amount of the reducing agent adsorbed by the NOx selective reduction catalyst.

2. The exhaust gas purifying apparatus according to claim 1,

the NOx selective reduction catalyst system further includes an estimation unit that estimates an amount of adsorption of the reducing agent by the NOx selective reduction catalyst.

3. An exhaust gas purifying apparatus as claimed in claim 2,

the estimating portion estimates a storage amount of nitrogen oxides of the NOx storage reduction catalyst;

when the adsorption amount of the reducing agent is larger than a predetermined target amount, the control unit determines whether or not to adjust the adjustment unit based on the estimated storage amount of the nitrogen oxide estimated by the estimation unit.

4. An exhaust gas purifying apparatus as claimed in claim 3,

the control portion reduces the flow rate of the exhaust gas returned to the intake pipe side when the estimated storage amount is smaller than a prescribed storage amount of the NOx storage reduction catalyst.

5. The exhaust gas purifying apparatus according to claim 1,

further comprises a trap part for trapping particulate matter contained in the exhaust gas,

the control section controls the adjustment section when a regeneration process of burning the particulate matter is performed.

6. An exhaust gas purifying apparatus as claimed in claim 5,

the control portion prohibits the rich process that makes the exhaust gas air-fuel ratio in the exhaust pipe rich when the regeneration process is executed.

7. The exhaust gas purifying apparatus according to claim 1,

the control unit determines whether or not to control the adjustment unit based on the temperature of the NOx storage reduction catalyst.

8. The exhaust gas purifying apparatus according to claim 1,

the control unit determines whether to control the adjustment unit based on the temperature of the NOx selective reduction catalyst.

9. A vehicle, characterized in that,

an exhaust gas purification device according to claim 1.

10. An exhaust gas purification control device, which is an exhaust gas purification control device of an exhaust gas purification device, characterized in that,

the exhaust gas purification device is provided with:

an exhaust pipe through which exhaust gas generated by the internal combustion engine flows; a NOx selective reduction catalyst disposed in the exhaust pipe and configured to adsorb a reducing agent to purify nitrogen oxides in the exhaust gas; a NOx storage reduction catalyst that is provided in the exhaust pipe upstream of the NOx selective reduction catalyst in an exhaust direction in which the exhaust gas flows, and that stores nitrogen oxides in the exhaust gas; and a recirculation path portion that connects an intake pipe of the internal combustion engine and the exhaust pipe from the exhaust pipe and recirculates the exhaust gas in the exhaust pipe to the intake pipe,

the exhaust gas purification control device is provided with: