JP2017141703A - Exhaust emission control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress a difference between an estimated adsorption amount of ammonia adsorbed to an SCR and an actual adsorption amount.SOLUTION: A control device 100 includes: an estimated adsorption amount acquisition section 122 for acquiring an estimated adsorption amount of ammonia adsorbed to an SCR 40 that eliminates NOx in exhaust gas by using the ammonia generated from urea water injected from an urea water injection device 50 as a reducing agent; an injection control section 123 for causing the urea water injection device 50 to inject urea water on the basis of the estimated adsorption amount; an elimination rate acquisition section 121 for acquiring an NOx elimination rate of the SCR 40; and a determination section 124 for determining whether or not the NOx elimination rate is lowered to a level lower than a first threshold value C1 when the urea water injection device 50 does not inject the urea water. When the determination section 124 determines that the NOx elimination rate has been lowered to the level lower than the first threshold value C1, the injection control section 123 causes the amount of the urea water corresponding to an upstream side NOx value detected by an upstream side NOx sensor 60 to be injected.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an exhaust purification control apparatus that purifies exhaust using a selective reduction catalyst (hereinafter also referred to as SCR) that reduces and purifies NOx in exhaust.

  2. Description of the Related Art Conventionally, there has been known an exhaust gas purification system including an SCR that selectively reduces and purifies NOx in exhaust gas using ammonia generated by hydrolysis from urea water as a reducing agent. As such an exhaust purification system, for example, the following Patent Document 1 discloses a urea water injection amount according to a difference between an estimated adsorption amount of SCR ammonia calculated based on sensor values of various sensors and a target adsorption amount. Techniques for controlling are disclosed.

JP 2003-293737 A

  By the way, the estimated adsorption amount of ammonia may deviate from the actual adsorption amount of ammonia actually adsorbed on the SCR. For example, when the exhaust gas temperature is low, ammonia is hardly generated from urea water, and thus the estimated adsorption amount may be significantly larger than the actual adsorption amount. Since the urea water injection is stopped when the estimated adsorption amount is large, the NOx purification is not performed due to the stop of the urea water injection even if the NOx purification is actually required. An abnormal rate is detected.

  Therefore, the present invention has been made in view of these points, and an object thereof is to suppress the difference between the estimated adsorption amount of ammonia and the actual adsorption amount of SCR.

In one aspect of the present invention, the estimated adsorption amount of ammonia adsorbed on the selective reduction catalyst that purifies NOx in the exhaust gas using ammonia generated from urea water injected from the urea water injection section as a reducing agent. An estimated adsorption amount acquisition unit to be acquired; an injection control unit that causes the urea water injection unit to inject urea water based on the estimated adsorption amount; and a purification rate acquisition unit that acquires the NOx purification rate of the selective reduction catalyst; A determination unit that determines whether or not the NOx purification rate has decreased below a first threshold when the urea water injection unit is not injecting the urea water, and the injection control unit includes the determination If the NOx purification rate is determined to be lower than the first threshold value by the control unit, the upstream NOx detected by the NOx detection unit that detects the NOx value upstream of the selective reduction catalyst in the exhaust passage. In value Performing a first injection control for injecting the Flip injection amount of urea water, to provide an exhaust purification control device.
According to such an exhaust purification control device, when the estimated adsorption amount of ammonia of the selective reduction catalyst is larger than the target adsorption amount and urea water is not injected, the NOx purification rate is lowered below the first threshold by the determination unit. If it is determined that the NOx detection unit has detected, the injection amount of urea water corresponding to the upstream NOx value detected by the NOx detection unit is injected. In such a case, even if the estimated adsorption amount of ammonia is excessively deviated from the actual adsorption amount due to the low exhaust gas temperature, the injection amount of urea water corresponding to the upstream NOx value is injected. Thus, the difference between the estimated adsorption amount of ammonia and the actual adsorption amount can be suppressed.

  In addition, when the determination unit determines that the NOx purification rate has exceeded a second threshold value during execution of the first injection control, the injection control unit determines a preset target adsorption amount and the estimated adsorption. The second injection control for injecting the urea water based on the amount may be performed.

  In the second injection control, the exhaust purification control device, when the determination unit determines that the NOx purification rate is lower than a third threshold when the urea water is not injected, An estimated adsorption amount correction unit that corrects the estimated adsorption amount acquired by the estimated adsorption amount acquisition unit may be further provided.

  Further, when the NOx purification rate is determined to be lower than a third threshold by the determination unit when the urea water is not injected in the second injection control, the injection control unit Third injection control for injecting urea water in an injection amount corresponding to the side NOx value and an injection amount corresponding to the target adsorption amount may be performed.

  According to the present invention, it is possible to suppress the difference between the estimated adsorption amount and the actual adsorption amount of ammonia in the SCR.

It is a mimetic diagram showing the composition of exhaust gas purification system S concerning one embodiment of the present invention. It is a block diagram which shows the detailed structure of the control apparatus 100 which concerns on one Embodiment. It is a schematic diagram for demonstrating the relationship between transition of a purification rate, and the injection quantity of urea water. It is a graph which shows the relationship between an upstream NOx value and the injection amount of urea water.

<Configuration of exhaust purification system>
A configuration of an exhaust purification system S according to an embodiment of the present invention will be described with reference to FIG.

  FIG. 1 is a schematic diagram showing a configuration of an exhaust purification system S according to one embodiment. As shown in FIG. 1, the exhaust purification system S includes an engine 10, an exhaust passage 20, a diesel particulate (hereinafter referred to as DPF) 30, a selective reduction catalyst (hereinafter referred to as SCR) 40, urea. The water injection device 50, the upstream NOx sensor 60, the downstream NOx sensor 65, and the control device 100 are included. The exhaust purification system S is mounted on a vehicle such as a truck and purifies NOx in the exhaust of the engine 10.

  Here, the engine 10 is a four-cylinder diesel engine, but is not limited thereto, and may be an engine other than the four-cylinder engine. The engine 10 generates power by burning and expanding a mixture of fuel and intake air (air). The engine 10 has an exhaust manifold 12 that is a manifold to which an exhaust passage 20 is connected.

  The exhaust passage 20 is a passage for discharging exhaust collected in the exhaust manifold 12 to the outside of the vehicle. In the exhaust passage 20, a DPF 30, an SCR 40, a urea water injection device 50, and the like are provided.

  The DPF 30 is a filter that collects particulate matter (PM) contained in the exhaust gas. The DPF 30 is made of, for example, a honeycomb body made of metal or ceramics. The DPF 30 combusts the collected PM when the amount of accumulated PM reaches a predetermined amount.

  The SCR 40 is formed, for example, by supporting zeolite or the like on the surface of a ceramic support such as a honeycomb structure. The SCR 40 includes a large number of cells partitioned by a porous partition wall. The SCR 40 adsorbs ammonia supplied from the urea water injection device 50 as a reducing agent, and selectively reduces and purifies NOx from the exhaust gas passing through the SCR 40 by the adsorbed ammonia.

  The urea water injection device 50 is provided between the DPF 30 and the SCR 40 and injects urea water into the exhaust passage 20. From the urea water injected by the urea water injection device 50, ammonia that is adsorbed by the SCR 40 is generated. The urea water injection device 50 includes a urea water addition valve 51, a urea water tank 52, and a urea water pump 53. The urea water pumped from the urea water tank 52 by the urea water pump 53 is injected from the urea water addition valve 51.

  The upstream NOx sensor 60 is provided on the upstream side of the SCR 40 in the exhaust passage 20, and the downstream NOx sensor 65 is provided on the downstream side of the SCR 40. The upstream NOx sensor 60 detects the NOx concentration (upstream NOx value) at the inlet of the SCR 40, and the downstream NOx sensor 65 detects the NOx concentration (downstream NOx value) at the outlet of the SCR 40. The upstream NOx sensor 60 and the downstream NOx sensor 65 detect NOx in the exhaust. Therefore, the amount of ammonia added to the SCR 40 can be estimated from the difference between the upstream NOx value that is the detection value of the upstream NOx sensor 60 and the downstream NOx value that is the detection value of the downstream NOx sensor 65. .

  The control device 100 controls the operation of the exhaust purification system S. In the present embodiment, the control device 100 functions as an exhaust purification control device that controls operations of the urea water injection device 50, the upstream NOx sensor 60, and the downstream NOx sensor 65 to control purification of NOx in the exhaust. .

<Detailed configuration of control device>
An example of a detailed configuration of the control device 100 will be described with reference to FIG.
FIG. 2 is a block diagram illustrating a detailed configuration of the control device 100 according to the embodiment. The control device 100 includes a storage unit 110 and a control unit 120.

  The storage unit 110 includes, for example, a ROM (Read Only Memory) and a RAM (Random Access Memory). The storage unit 110 stores programs and various data to be executed by the control unit 120. For example, the storage unit 110 stores a target adsorption amount of ammonia adsorbed on the SCR 40, which is used when controlling urea water injection.

  The control unit 120 is, for example, a CPU (Central Processing Unit). The control unit 120 controls the operation of the exhaust purification system S by executing a program stored in the storage unit 110. In the present embodiment, the control unit 120 functions as a purification rate acquisition unit 121, an estimated adsorption amount acquisition unit 122, an injection control unit 123, a determination unit 124, and an estimated adsorption amount correction unit 125.

  The purification rate acquisition unit 121 acquires the NOx purification rate of the SCR 40. For example, the purification rate acquisition unit 121 is based on the upstream NOx value detected by the upstream NOx sensor 60 upstream of the SCR 40 and the downstream NOx value detected by the downstream NOx sensor 65 downstream of the SCR 40. Thus, the NOx purification rate of the SCR 40 is calculated.

  The estimated adsorption amount acquisition unit 122 acquires an estimated adsorption amount of ammonia adsorbed on the SCR 40. For example, the estimated adsorption amount acquisition unit 122 calculates the total consumption amount of ammonia consumed by the SCR 40 from the NOx purification rate acquired by the purification rate acquisition unit 121. Then, the estimated adsorption amount acquisition unit 122 calculates the current estimated adsorption amount by subtracting the total consumption amount from the total supply amount of ammonia supplied to the SCR 40. Note that the method for calculating the estimated adsorption amount of ammonia is not limited to the above, and other known calculation methods may be used.

  The injection control unit 123 controls the urea water injection by the urea water injection device 50 based on the estimated adsorption amount acquired by the estimated adsorption amount acquisition unit 122. For example, the injection control unit 123 causes the urea water to be injected based on a difference between a preset target adsorption amount of ammonia (for example, a target adsorption amount stored in the storage unit 110) and the estimated adsorption amount.

  The determination unit 124 compares the NOx purification rate acquired by the purification rate acquisition unit 121 with a predetermined threshold value. For example, during the urea water injection control by the injection control unit 123, the determination unit 124 decreases or increases the NOx purification rate from the first threshold value C1, the second threshold value C2, and the third threshold value C3 shown in FIG. Determine whether. The first threshold value C1 to the third threshold value C3 are stored in the storage unit 110, for example.

  The estimated adsorption amount correction unit 125 corrects the estimated adsorption amount acquired by the estimated adsorption amount acquisition unit 122. For example, the estimated adsorption amount correction unit 125 corrects the estimated adsorption amount when the NOx purification rate falls below the third threshold C3 shown in FIG.

  In the present embodiment, the injection control unit 123 controls the injection of urea water according to the determination result by the determination unit 124 when the NOx purification rate varies with the injection of urea water. In addition, the estimated adsorption amount correction unit 125 corrects the estimated adsorption amount based on the determination result by the determination unit 124. Here, it demonstrates concretely, referring FIG.

  FIG. 3 is a schematic diagram for explaining the relationship between the transition of the purification rate and the injection amount of urea water. In FIG. 3, the transition of the purification rate is indicated by a bold line. Further, since the estimated adsorption amount is larger than the target adsorption amount before time t1, it is assumed that the urea water injection device 50 does not inject urea water. For this reason, the NOx purification rate gradually decreases, and at the time t1, the NOx purification rate is lower than the first threshold value C1.

  When the determination unit 124 determines that the NOx purification rate is lower than the first threshold C1, the injection control unit 123 has an injection amount of urea water corresponding to the upstream NOx value detected by the upstream NOx sensor 60. The first injection control for injecting is performed. That is, the injection control unit 123 injects urea water according to the upstream NOx value without being influenced by the estimated adsorption amount. At this time, the update of the estimated adsorption amount is stopped. When the injection amount of urea water increases according to upstream NOx, if the estimated adsorption amount is continuously updated, the estimated adsorption amount may increase and the deviation from the actual adsorption amount may increase. The above problem can be suppressed by stopping.

  In FIG. 3, the injection control unit 123 performs the first injection control between times t1 and t2. Thereby, even if there is a divergence between the estimated adsorption amount and the actual adsorption amount, the divergence can be suppressed by performing the first injection control. The urea water injection amount in the first injection control is an amount corresponding to a preset coefficient. Here, the coefficient is set to suppress ammonia slip, and is corrected based on the estimated purification rate at the target adsorption amount, the actual purification rate, the exhaust temperature, the exhaust flow rate, and the like. When the difference between the estimated purification rate and the actual purification rate is small, the urea water injection amount is small, and when the difference between the estimated purification rate and the actual purification rate is large, the urea water injection amount is large. Further, the exhaust temperature and the exhaust flow rate are related to the upper limit of the injection amount.

  FIG. 4 is a graph showing the relationship between the upstream NOx value and the urea water injection amount. The horizontal axis of the graph indicates the upstream NOx value detected by the upstream NOx sensor 60, and the vertical axis indicates the urea water injection amount by the urea water injection device 50. The injection control unit 123 causes the urea water to be injected so that the injection amount increases as the upstream NOx value increases.

Returning to FIG. 3, it is assumed that the NOx purification rate is improved by the first injection control described above, and that the NOx purification rate is higher than the second threshold C2 at time t2. Here, the second threshold C2 is slightly larger than the first threshold C1, but is not limited thereto, and may be, for example, the same size as the second threshold C1.
When the determination unit 124 determines that the NOx purification rate has exceeded the second threshold C2 during execution of the first injection control, the injection control unit 123 determines urea based on the target adsorption amount and the estimated adsorption amount. Second injection control for injecting water is performed. That is, the injection control unit 123 determines that it has returned to a normal state, and performs normal urea water injection control. In FIG. 3, the injection control unit 123 performs the second injection control between times t2 and t3. The injection amount of urea water at this time is larger than the injection amount between times t1 and t2.

  If the determination unit 124 determines that the NOx purification rate does not exceed the second threshold C2 even after a predetermined time has elapsed, the control unit 120 determines that some failure has occurred in the exhaust purification system S.

  In FIG. 3, after time t3, the estimated adsorption amount becomes larger than the target adsorption amount, and urea water is not injected. Here, it is assumed that the NOx purification rate gradually decreases due to the abnormality of the device, and the NOx purification rate is lower than the third threshold C3 at time t4. The third threshold C3 is a value smaller than the second threshold C2.

  When it is determined by the determination unit 124 that the NOx purification rate has decreased below the third threshold C3, the injection control unit 123 sets the injection amount corresponding to the upstream NOx value and the injection amount corresponding to the target adsorption amount. Third injection control for injecting urea water is performed. The injection control unit 123 performs the third injection control between times t4 and t5, and temporarily injects a lot of urea water.

The injection control unit 123 performs normal urea water injection control after the time t5, similarly to the times t2 to t3. The injection control unit 123 continues normal urea water injection control when the NOx purification rate exceeds the second threshold C2.
On the other hand, when the NOx purification rate is not improved even when the third injection control is performed (specifically, when the determination unit 124 determines that the NOx purification rate does not exceed the second threshold C2). The control unit 120 determines that a failure has occurred in the exhaust purification system S.

  When the determination unit 124 determines that the NOx purification rate has decreased below the third threshold C3, the estimated adsorption amount correction unit 125 determines that the estimated adsorption amount is different from the actual adsorption amount, and the estimated adsorption amount The estimated adsorption amount acquired by the amount acquisition unit 122 is corrected. That is, the estimated adsorption amount correction unit 125 corrects the estimated adsorption amount to a value close to the actual adsorption amount. Thereby, the NOx purification rate returns to normal, and proper urea water injection can be performed.

  Even if the first injection control described above is performed, the injection control unit 123 executes the third injection control when the NOx purification rate becomes a value close to 0 or when the degree of decrease in the NOx purification rate is large. May be.

<Effect in this embodiment>
The control device 100 described above determines that the NOx purification rate is lower than the first threshold C1 by the determination unit 124 when the estimated ammonia adsorption amount of the SCR 40 is larger than the target adsorption amount and urea water is not injected. If it is, the urea water of the injection amount corresponding to the upstream NOx value detected by the upstream NOx sensor 60 is injected.

In such a case, even if the estimated adsorption amount of ammonia is excessively deviated from the actual adsorption amount due to the low exhaust temperature, the injection amount of urea water corresponding to the upstream NOx value is injected. Thus, it is possible to suppress the deviation between the estimated adsorption amount and the actual adsorption amount.
On the other hand, when the injection amount is controlled in consideration of the downstream NOx value, the injection amount is excessive because the injection is performed in a state where the actual ammonia adsorption amount is unknown, and ammonia slip may occur. In contrast, the occurrence of ammonia slip can be suppressed by injecting less urea water according to the upstream NOx value as in this embodiment.

  In the above description, the exhaust purification system S is mounted on a vehicle such as a truck. However, the present invention is not limited to this. For example, the exhaust purification system S may be mounted on a generator, construction machine, ship, or the like.

  As mentioned above, although this invention was demonstrated using embodiment, the technical scope of this invention is not limited to the range as described in the said embodiment. It will be apparent to those skilled in the art that various modifications or improvements can be added to the above embodiment. It is apparent from the scope of the claims that the embodiments added with such changes or improvements can be included in the technical scope of the present invention.

40 SCR
DESCRIPTION OF SYMBOLS 50 Urea water injection apparatus 60 Upstream side NOx sensor 100 Control apparatus 121 Purification rate acquisition part 122 Estimated adsorption amount acquisition part 123 Injection control part 124 Judgment part 125 Estimated adsorption amount correction | amendment part

Claims (4)

An estimated adsorption amount acquisition unit that acquires an estimated adsorption amount of ammonia adsorbed on a selective reduction catalyst that purifies NOx in exhaust gas using ammonia generated from urea water injected from the urea water injection unit as a reducing agent;
An injection control unit for injecting urea water to the urea water injection unit based on the estimated adsorption amount;
A purification rate acquisition unit for acquiring a NOx purification rate of the selective reduction catalyst;
A determination unit that determines whether or not the NOx purification rate has decreased below a first threshold when the urea water injection unit is not injecting the urea water;
With
The injection control unit detects a NOx value upstream of the selective reduction catalyst in the exhaust passage when the determination unit determines that the NOx purification rate is lower than the first threshold value. An exhaust purification control apparatus that performs a first injection control for injecting an injection amount of urea water corresponding to an upstream NOx value detected by a detection unit. When the determination unit determines that the NOx purification rate has exceeded a second threshold during execution of the first injection control, the injection control unit includes a preset target adsorption amount and the estimated adsorption amount. Performing second injection control for injecting the urea water based on
The exhaust purification control device according to claim 1. When the determination unit determines that the NOx purification rate has decreased below a third threshold when the urea water is not injected in the second injection control, the estimated adsorption amount acquisition unit acquires An estimated adsorption amount correction unit for correcting the adsorption amount;
The exhaust purification control apparatus according to claim 2. In the second injection control, when the determination unit determines that the NOx purification rate is lower than a third threshold value when the urea water is not injected in the second injection control, the injection control unit Performing a third injection control for injecting urea water of an injection amount corresponding to the value and an injection amount corresponding to the target adsorption amount;
The exhaust purification control device according to claim 2 or 3.

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