KR20220026386A - Control method for exhaust device of engine - Google Patents

Abstract

The present invention comprises: a step of enabling a controller to receive exhaust gas temperature of a front end of an LNT and signals of lambda sensors of the front end and a rear end of the LNT during DeNOx; and a step of enabling the controller to determine at least one among whether a breakthrough phenomenon, where a lambda value of the lambda sensor of the rear end is smaller than the lambda value of the lambda sensor of the front end, during the DeNOx and whether an average value of a difference between the lambda value of the lambda sensor of the rear end and the lambda value of the lambda sensor of the front end during the DeNOx is at least a predetermined reference value. The controller determines whether there is deterioration of purification performance of the LNT according to at least one result among whether the breakthrough phenomenon occurs and whether the average value is at least the reference value.

Description

CONTROL METHOD FOR EXHAUST DEVICE OF ENGINE

The present invention relates to a method for controlling an exhaust system of an engine, and more particularly, to a technology for Lean NOx Trap (LNT).

LNT is a device for purifying nitrogen oxides accompanying lean combustion of an engine, and performs the function of occluding NOx in exhaust gas under lean condition and reducing it to N2 under rich condition. The reduction of nitrogen oxides stored in the catalyst to nitrogen is called DeNOx.

The purification performance of LNT gradually decreases while the vehicle is driving, and the degradation of the purification performance is divided into reversible degradation and irreversible degradation.

Reversible deterioration is deterioration caused by sulfur poisoning, and recovery of purification performance is possible through the desulfurization process, but irreversible deterioration is thermal deterioration, and recovery of purification performance is impossible.

In operating the LNT mounted on the vehicle, the most accurate and direct way to check the state of the purification performance of the LNT is to determine the state of the LNT through the NOx sensor at the front and rear of the LNT, but the NOx sensor is The downside is that it is high.

The matters described as the background technology of the present invention are only for enhancing the understanding of the background of the present invention, and should not be taken as acknowledging that they correspond to the prior art already known to those of ordinary skill in the art. will be

KR 101684540 B1

The present invention judges the purification performance of LNT without using an expensive NOx sensor, and when the purification performance deteriorates, distinguishes whether the degradation is reversible or irreversible, and improves the purification performance of LNT within a possible range. It is an object of the present invention to provide a method for controlling an exhaust system of an engine, which can improve the marketability of a vehicle by ultimately reducing the emission of nitrogen oxides and satisfying various emission regulations.

The method for controlling the exhaust system of the engine of the present invention for achieving the object as described above,

In case of DeNOx, the controller receives the exhaust gas temperature of the front end of the LNT and signals from the lambda sensor at the front of the LNT and the lambda sensor at the rear of the LNT;

In the controller, whether a breakthrough phenomenon in which the lambda value of the rear end lambda sensor becomes smaller than the lambda value of the front end lambda sensor occurs during the DeNOx, and between the lambda value of the rear end lambda sensor and the lambda value of the front end lambda sensor determining at least one of whether the average value during the DeNOx with respect to the difference of ΔNOx is greater than or equal to a predetermined reference value;

consists of,

The controller may determine whether the purification performance of the LNT is degraded according to at least one result of whether the break-through phenomenon occurs and whether the average value is equal to or greater than the reference value.

When the break-through phenomenon occurs or the average value is equal to or greater than the reference value, the controller may determine that the purification performance of the LNT is normal.

When the break-through phenomenon does not occur and the average value is less than the reference value, the controller may determine that the purification performance of the LNT is abnormally deteriorated.

When the controller determines that the purification performance of the LNT is abnormally reduced,

The controller may perform a DeSOx (desulfurization process) step to restore the purification performance of the LNT.

After performing the DeSOx step, the controller performs the RE-DeNOx step of performing DeNOx again to determine whether the degradation of the purification performance of the LNT catalyst is reversible or irreversible;

During the RE-DeNOx step, when the break-through phenomenon does not occur and the average value is less than the reference value, the controller determines that the degradation of the purification performance of the LNT is irreversible degradation, and displays it;

can be further performed.

In the display step, at least one of lighting a warning lamp, generating a warning sound, storing a fault code, and transmitting the corresponding information to a specific wireless terminal may be performed.

When it is determined that the degradation of the LNT purification performance is irreversible, the controller may reduce the high temperature exposure of the LNT catalyst by lowering the DeSOx target temperature and controlling the subsequent DeSOx performance.

The reference value may be determined according to the exhaust gas temperature of the front end of the LNT from a predetermined map.

The reference value map may have a tendency for the reference value to increase as the temperature increases.

The present invention judges the purification performance of LNT without using an expensive NOx sensor, and when the purification performance deteriorates, distinguishes whether the degradation is reversible or irreversible, and improves the purification performance of LNT within a possible range. By maintaining the state, ultimately, it is possible to reduce the emission of nitrogen oxides and to satisfy various emission regulations, thereby improving the marketability of the vehicle.

1 is a view illustrating a part of an engine exhaust system to which the present invention can be applied;
2 is a flowchart showing an embodiment of a method for controlling an exhaust system of an engine according to the present invention;
3 is a graph illustrating the behavior of the reaction and lambda upon DeNOx of LNT;
4 is a graph showing cases in which break-through occurs when the purification performance of the LNT catalyst is normal;
5 is a graph showing cases in which the average value during DeNOx for the difference between the front-end lambda sensor measurement value and the rear-end lambda sensor measurement value of LNT in a normal state of the purification performance of the LNT catalyst is greater than or equal to a predetermined reference value;
6 is a graph explaining that the purification performance of the LNT catalyst in a reversible deterioration state is restored after performing DeSOx by performing the RE-DeNOx step;
7 is a graph showing the increase in OSC of the LNT catalyst according to the temperature of the LNT catalyst.

1 is a conceptual view of a part of an engine exhaust system to which the present invention can be applied, and is configured to be purified and discharged after exhaust gas is introduced into the LNT, and a front end lambda sensor 1 and a temperature sensor (3) is provided, and a rear end lambda sensor 5 is provided at the rear end, and the controller 7 receives signals from these sensors.

The controller 7 receives the signals of the sensors as described above, and performs control according to the present invention.

For reference, the lambda sensor refers to a sensor that measures the air excess ratio lambda (λ), and various oxygen sensors may be used.

Here, the excess air ratio (λ) means the actual air-fuel ratio/theoretical air-fuel ratio.

Referring to FIG. 2, in the embodiment of the exhaust system control method of the engine of the present invention, during DeNOx, the controller 7 controls the exhaust gas temperature and the LNT front end lambda sensor 1 and the LNT rear end lambda sensor 5 receiving a signal (S10); The controller 7 determines whether a breakthrough phenomenon in which the lambda value of the rear end lambda sensor 5 becomes smaller than the lambda value of the front end lambda sensor 1 occurs during the DeNOx, and the rear end lambda sensor 5 ) and whether the average value (a) during the DeNOx for the difference between the lambda value of the front end lambda sensor 1 is greater than or equal to a predetermined reference value (a1), determining at least one (S20) consists of including

The controller 7 determines whether the purification performance of the LNT is degraded according to at least one result of whether the break-through phenomenon occurs and whether the average value a is equal to or greater than the reference value a1.

That is, when the break-through phenomenon occurs or the average value a is equal to or greater than the reference value a1, the controller 7 determines that the purification performance of the LNT is normal, and the break-through phenomenon does not occur, When the average value (a) is less than the reference value (a1), it is determined that the purification performance of the LNT is abnormally deteriorated.

3 shows the change in the lambda value of the lambda sensor 1 at the front end of the LNT and the lambda value of the lambda sensor 5 at the rear end of the LNT while DeNOx is performed to reduce nitrogen oxides stored in the LNT to nitrogen by making the exhaust gas rich. As a conceptual example, the lambda value of the front end lambda sensor 1 indicates a rich state of lambda 1 or less immediately after DeNOx starts, but the lambda value of the rear end lambda sensor 5 is the lambda after the delay time It is lowered to 1 or less, which means that while reducing agents such as CO, H2, and HC are oxidized due to oxygen stored in the oxygen storage material in the LNT catalyst, the downstream lambda sensor 5 cannot output a rich measurement value, This is because the rich measurement value is output only after the oxygen stored as described above is consumed.

As described above, when the WGS (Water Gas Shift) and SR (Steam Reforming) reactions occur actively after the oxygen stored in the LNT is consumed, H2 is generated, and the measurement value of the lambda sensor 5 at the rear end is Breakthrough occurs, which becomes smaller than the measured value of the lambda sensor 1, because as the amount of H2 in the exhaust gas increases, the lambda value of the lambda sensor tends to be biased toward richness.

The present invention focuses on the behavior of the LNT front end lambda sensor 1 and the rear end lambda sensor 5 measured values during DeNOx as described above, and the LNT rear end lambda sensor 5 measured value and the front end lambda sensor ( 1) The average value (a) during DeNOx for the difference between the measured values changes according to the oxygen storage and release capacity (OSC) that the oxygen storage material of the LNT catalyst can provide, and the If the OSC is greater than a certain level, since the purification performance of the corresponding LNT catalyst can be determined to be normal, when the average value (a) is equal to or greater than the reference value (a1), the purification performance of the LNT is determined to be normal.

For reference, FIG. 5 shows that the break-through did not occur, but during DeNOx in each corresponding situation, the average value (a) was greater than or equal to the predetermined reference value (a1), confirming that the LNT catalyst has normal purification performance. examples are shown.

Therefore, the reference value (a1) should be set in consideration of the OSC that can indicate that the LNT catalyst has a normal purification performance as described above, and the OSC is, as illustrated in FIG. 7, as the LNT catalyst temperature rises. In consideration of this, the controller 7 sets the reference value a1 differently according to the temperature of the exhaust gas obtained from the temperature sensor 3 at the front end of the LNT and compares it with the average value a do.

For example, the controller 7 selects a corresponding reference value a1 according to the temperature of the exhaust gas in that situation using the following reference value a1 map, and the average value ( a) is compared to determine the purification performance of the LNT catalyst.

temperature 200℃ 300℃ 400℃ 500℃ 600℃ Reference value (a1) 0.012 0.050 0.076 0.092 0.101

On the other hand, when the above-described break-through occurs during DeNOx, the purification performance of the LNT catalyst can be considered normal. In FIG. 4, break-through occurs during each DeNOx, and the purification performance of the corresponding LNT catalyst returns to a normal state. It shows examples that can be judged.

As described above, in the controller 7, when the break-through phenomenon does not occur and the average value a is less than the reference value a1, that is, when both conditions are satisfied, the purification performance of the LNT is improved. judged to be abnormally degraded.

When it is determined that the purification performance of the LNT is abnormally degraded, the controller 7 performs a DeSOx (desulfurization process) step S30 to restore the purification performance of the LNT.

In addition to the meaning of recovering the purification performance of the LNT as described above, the performance of the DeSOx step can be combined with the RE-DeNOx step to be described later, whether the degradation of the purification performance of the LNT catalyst is due to reversible degradation or irreversible degradation. It also has the meaning of being able to determine whether it was caused by it.

That is, after performing the DeSOx step (S30), the controller 7 performs a RE-DeNOx step (S40) of performing DeNOx again to determine whether the degradation of the purification performance of the LNT catalyst was reversible or irreversible. do,

During the RE-DeNOx step (S40), when the break-through phenomenon does not occur and the average value (a) is less than the reference value (a1), the controller 7 converts the degradation of the purification performance of the LNT into irreversible degradation. A display step (S50) of determining and displaying this is further performed.

Of course, during the RE-DeNOx step, when the break-through phenomenon occurs or the average value (a) is greater than or equal to the reference value (a1), it can be seen that the degradation of the purification performance of the LNT catalyst is a temporary and reversible deterioration.

As illustrated in FIG. 6 , break-through does not occur, and the difference between the measured value of the rear end lambda sensor 5 and the front end lambda sensor 1 is not large, so the lambda value of the rear end lambda sensor 5 and the front end From the state of degradation of the purification performance of the LNT catalyst, which can easily be expected that the average value (a) during DeNOx for the difference between the lambda values of the lambda sensor (1) is less than the corresponding reference value (a1), RE-DeNOx after DeSOx At this time, as shown, the difference between the measured value of the lambda sensor 5 and the measured value of the front end lambda sensor 1 was significantly increased, and the purification performance of the LNT catalyst was restored to normal. It is shown that it can be confirmed that it was caused by .

In the display step, at least one of turning on a warning lamp, generating a warning sound, storing a fault code, and transmitting the corresponding information to a specific wireless terminal may be performed.

That is, the engine warning lamp is turned on or a warning sound is generated to induce repair, the fault code is stored and the related information can be provided during vehicle maintenance, Various display methods such as transmitting a message or the like may be used.

On the other hand, when it is determined that the degradation of the LNT purification performance is irreversible deterioration, the controller 7 lowers the DeSOx target temperature and controls it downward to reduce the high temperature exposure of the LNT catalyst when performing DeSOx. It may be possible to delay the progress of deterioration.

As described above, the present invention monitors the purification performance of the LNT catalyst based on measurement values of a relatively inexpensive lambda sensor, and when the purification performance is abnormally reduced, attempts to restore the purification performance, furthermore, the degradation of the purification performance of the LNT catalyst It determines whether the deterioration is reversible or irreversible, and if it is irreversible deterioration, informs it in an appropriate display method so that appropriate measures can be taken later, so that it can respond more effectively to various exhaust gas regulations of vehicles.

Although the present invention has been shown and described with reference to specific embodiments, it is within the art that the present invention can be variously improved and changed without departing from the spirit of the present invention provided by the following claims. It will be obvious to those of ordinary skill in the art.

One; lambda sensor
3; temperature Senser
7; controller
a; medium
a1; reference value

Claims (9)

In case of DeNOx, the controller receives the exhaust gas temperature of the front end of the LNT and signals from the lambda sensor at the front of the LNT and the lambda sensor at the rear of the LNT;
The controller determines whether a break-through phenomenon in which the lambda value of the rear-end lambda sensor becomes smaller than the lambda value of the front-end lambda sensor occurs during the DeNOx, and the difference between the lambda value of the rear-end lambda sensor and the lambda value of the front-end lambda sensor determining at least one of whether the average value for the DeNOx is equal to or greater than a predetermined reference value;
consists of,
The controller determines whether the purification performance of the LNT is degraded according to at least one result of whether the break-through phenomenon occurs and whether the average value is equal to or greater than the reference value
An engine exhaust system control method, characterized in that. The method according to claim 1,
The controller determines that the purification performance of the LNT is normal when the break-through phenomenon occurs or the average value is greater than or equal to the reference value
An engine exhaust system control method, characterized in that. 3. The method according to claim 2,
The controller determines that the purification performance of the LNT is abnormally degraded when the break-through phenomenon does not occur and the average value is less than the reference value
An engine exhaust system control method, characterized in that. 4. The method according to claim 3,
When the controller determines that the purification performance of the LNT is abnormally reduced,
The controller performs the DeSOx step to restore the purification performance of LNT
An engine exhaust system control method, characterized in that. 5. The method of claim 4,
After performing the DeSOx step, the controller performs the RE-DeNOx step of performing DeNOx again to determine whether the degradation in the purification performance of the LNT catalyst is reversible or irreversible;
During the RE-DeNOx step, when the break-through phenomenon does not occur and the average value is less than the reference value, the controller determines that the degradation in the purification performance of the LNT is irreversible degradation, and displays the determination;
An exhaust system control method of an engine, characterized in that it further performs. 6. The method of claim 5,
In the display step, at least one of lighting a warning light, generating a warning sound, storing a fault code, and transmitting the corresponding information to a specific wireless terminal
An engine exhaust system control method, characterized in that. 6. The method of claim 5,
When it is determined that the degradation of the LNT purification performance is irreversible, the controller lowers and controls the DeSOx target temperature when performing the subsequent DeSOx, thereby reducing the high temperature exposure of the LNT catalyst
An engine exhaust system control method, characterized in that. The method according to claim 1,
The reference value is determined according to the exhaust gas temperature of the front end of the LNT from a predetermined map
An engine exhaust system control method, characterized in that. 9. The method of claim 8,
In the reference value map, the reference value tends to increase as the temperature increases.
An engine exhaust system control method, characterized in that.

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