JP2021143616A - Exhaust emission control system of internal combustion engine - Google Patents

Abstract

To restrain an increase in back pressure of an internal combustion engine.SOLUTION: An exhaust emission control system 200 includes a catalyst 7 provided in an exhaust passage of an internal combustion engine, a bypass passage 5 bypassing the catalyst, a bypass valve 6 for opening and closing the bypass passage, a control unit 100 controlling the bypass valve, and an exhaust pressure sensor 61 for detecting exhaust pressure on the upstream side of the catalyst. The control unit controls the bypass valve so that an opening of the bypass passage is larger when the exhaust pressure detected by the exhaust pressure sensor is high than when the detected exhaust pressure is low.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to an exhaust gas purification system for an internal combustion engine.

Generally, a catalyst is provided in the exhaust passage of an internal combustion engine to purify harmful components in the exhaust.

Japanese Unexamined Patent Publication No. 2005-320937

However, the catalyst may become an exhaust resistance and the exhaust pressure on the upstream side of the catalyst, that is, the back pressure may rise excessively. When this increase in back pressure occurs, the combustion efficiency of the internal combustion engine decreases. Therefore, it is desired to suppress such an increase in back pressure.

Therefore, the present disclosure was devised in view of such circumstances, and an object thereof is to provide an exhaust gas purification system for an internal combustion engine capable of suppressing an increase in back pressure of the internal combustion engine.

According to one aspect of the present disclosure
The catalyst provided in the exhaust passage of the internal combustion engine and
A bypass passage that bypasses the catalyst and
A bypass valve that opens and closes the bypass passage and
A control unit configured to control the bypass valve and
An exhaust pressure sensor that detects the exhaust pressure on the upstream side of the catalyst, and
With
The internal combustion engine is characterized in that when the exhaust pressure detected by the exhaust pressure sensor is high, the control unit controls the bypass valve so as to increase the opening degree of the bypass passage as compared with the case where the exhaust pressure is low. Exhaust purification system is provided.

Preferably, the exhaust purification system further comprises a concentration sensor that detects the concentration of the purification component of the catalyst in the exhaust on the downstream side of the catalyst.
When the concentration detected by the concentration sensor is high, the control unit controls the bypass valve so as to reduce the opening degree of the bypass passage as compared with the case where the concentration is low.

Preferably, the catalyst is a NOx catalyst.

Preferably, the exhaust purification system further comprises a downstream catalyst provided in the exhaust passage located downstream of the confluence of the bypass passages.

Preferably, the exhaust purification system further comprises an exhaust temperature sensor that detects the upstream exhaust temperature of the downstream catalyst.
With
When the exhaust temperature detected by the exhaust temperature sensor is high, the control unit controls the bypass valve so as to increase the opening degree of the bypass passage as compared with the case where the exhaust temperature is low.

Preferably, the downstream catalyst is a NOx catalyst.

According to the present disclosure, an increase in back pressure of an internal combustion engine can be suppressed.

It is the schematic which shows the exhaust gas purification system. It is a cross-sectional plan view which shows the exhaust gas purification apparatus. It is the same longitudinal front view. It is a vertical sectional front view which shows the exhaust gas purification device of a modification. It is a figure for demonstrating 1st Embodiment of control. It is a flowchart about 1st Embodiment of control. It is a figure for demonstrating the 2nd Embodiment of control. It is a flowchart about the 2nd Embodiment of control.

Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. It should be noted that the present disclosure is not limited to the following embodiments.

FIG. 1 shows an exhaust gas purification system of this embodiment. The internal combustion engine (not shown, also referred to as an engine) to which this system is applied is a vehicle diesel engine. The vehicle (not shown) is a large vehicle such as a truck. However, the type and application of the internal combustion engine are not limited.

The exhaust purification system 200 generally controls the catalyst 7 provided in the exhaust passage of the engine, the bypass hole 5 forming the bypass passage for bypassing the catalyst 7, the bypass valve 6 for opening and closing the bypass hole 5, and the bypass valve 6. An electronic control unit (referred to as an ECU (Electronic Control Unit)) 100 as a control unit configured to perform the above operation, and an exhaust pressure sensor 61 for detecting the exhaust pressure on the upstream side of the catalyst 7 are provided.

The exhaust passage means an arbitrary passage through which the exhaust of the engine flows. The catalyst 7 is arranged in this exhaust passage and purifies the harmful component to be purified, that is, the purified component. The catalyst 7 of the present embodiment is a selective reduction NOx catalyst (SCR (Selective Catalytic Reduction) catalyst) that reduces NOx (nitrogen oxides) in the exhaust. Therefore, the purifying component is NOx. Catalyst 7, by reaction with ammonia NH ₃ and NOx obtained by hydrolyzing the urea water, to reduce NOx in the exhaust into nitrogen N _2.

The exhaust purification system 200 of the present embodiment further includes a downstream catalyst 50 provided in the exhaust passage located on the downstream side of the confluence of the bypass passages (described later). The downstream catalyst 50 is also a selective reduction NOx catalyst. Hereinafter, for convenience, the catalyst 7 is referred to as a front-stage catalyst 7, and the downstream-side catalyst 50 is referred to as a rear-stage catalyst 50.

The relationship between the first-stage catalyst 7 and the second-stage catalyst 50 in the present embodiment will be described. The second-stage catalyst 50 is the main catalyst, and the first-stage catalyst 7 is an auxiliary catalyst. Therefore, the capacity of the post-stage catalyst 50 is larger than that of the pre-stage catalyst 7. Exhaust gas is constantly flowed through the post-stage catalyst 50. When NOx cannot be sufficiently removed by the latter-stage catalyst 50 alone, the first-stage catalyst 7 is used as an auxiliary. By adding the pre-stage catalyst 7 in this way, the amount of NOx that can be reduced can be increased, and it becomes possible to respond to the tightening of exhaust gas regulations.

At least one of the catalysts 7 and 50 may be a storage-reducing NOx catalyst (LNT (Lean NOx Trap) catalyst) or a catalyst other than the NOx catalyst (for example, an oxidation catalyst, a three-way catalyst, etc.). .. Other catalysts may be added in addition to these catalysts 7 and 50. Here, the catalyst includes a continuously regenerating particulate filter on which the catalyst is supported.

The pre-stage catalyst 7, the bypass hole 5, and the bypass valve 6 are provided in the case 2 of the exhaust gas purification device 1, which will be described in detail later. The post-stage catalyst 50 is housed in a catalyst casing 51 arranged on the downstream side of the exhaust gas purification device 1. The latter stage catalyst 50 and the catalyst casing 51 are both cylindrical. The inlet pipe 52 of the catalyst casing 51 is connected to the outlet pipe 11 of the exhaust purification device 1 via an exhaust pipe (not shown). The outlet pipe 53 of the catalyst casing 51 is connected to another catalyst (for example, an ammonia oxidation catalyst) or is opened to the atmosphere via an exhaust pipe (not shown).

The exhaust G from the engine is introduced into the exhaust purification device 1 through the inlet pipe 9. The flow of exhaust G is indicated by a broken line arrow. In the case of the present embodiment, the exhaust gas discharged from the turbine of the turbocharger is introduced into the inlet pipe 9.

The exhaust gas purification device 1 will be described with reference to FIGS. 2 and 3. 2 is a cross-sectional plan view (II-II cross-sectional view of FIG. 3), and FIG. 3 is a longitudinal front view (III-III cross-sectional view of FIG. 2). For convenience, each direction of the three orthogonal axes, that is, each direction of front, back, left, right, up and down is defined as shown in the figure. However, it should be noted that each of these directions is merely defined for convenience of explanation regarding the arrangement shown in the figure. Here, for convenience, sensors such as the exhaust pressure sensor 61 are omitted.

As shown in the figure, the exhaust gas purification device 1 includes a sealed case 2, a partition plate 3 for partitioning the inside of the case 2, and a U-shaped passage 4 defined by the case 2 and the partition plate 3. As indicated by the reference numeral G1, the U-shaped passage 4 has a first passage 41 in which exhaust gas flows from the rear to the front (first direction) and a second direction (front) opposite to the first direction. It has a second passage 42 for flowing exhaust gas from the first passage 41 to the second passage 42, and a third passage 43 for flowing exhaust gas from the first passage 41 to the second passage 42.

Further, the exhaust purification device 1 is provided on the partition plate 3, and has a bypass hole 5 that communicates the first passage 41 and the second passage 42, a bypass valve 6 that opens and closes the bypass hole 5, and an upstream side from the outlet side of the bypass hole 5. It is provided with a front-stage catalyst 7 provided in the second passage 42 on the side.

The case 2 is a closed container in which a plurality of members as shown in the figure are compactly packed and housed in a canning state. Case 2 of this embodiment has a rectangular parallelepiped shape. The partition plate 3 extends in the front-rear direction in a vertical state (extended in the vertical direction), its rear end is connected to the rear end wall 31 of the case 2, and its front end is separated from the front end wall 32 of the case 2 by a predetermined distance X1. NS. As a result, the partition plate 3 partitions the inside of the case 2 in the left-right direction, and at the same time forms a U-shaped passage 4.

For convenience, the rear side is the first passage 41 and the second passage 42, and the front side is the third passage 43, with the position X2 of the front end of the front end wall 31 in the front-rear direction as a boundary. The left-right width Y1 of the first passage 41 is smaller than the left-right width Y2 of the second passage 42, and the front-rear width of the third passage 43 (equal to the distance X1 between the partition plate 3 and the case 2) is the left-right width Y1 of the first passage 41. It is said to be about the same as. The third passage 43 allows exhaust to flow in a third direction (direction from the left side to the right side) perpendicular to the first direction. The cross-sectional shape of the first passage 41, the second passage 42, and the third passage 43 perpendicular to the exhaust flow G1 direction is a quadrangle.

An exhaust inlet 8 for introducing exhaust gas is connected to the upstream end or the rear end of the first passage 41. The exhaust inlet 8 is formed by an inlet pipe 9, and the inlet pipe 9 is fixed to the rear end wall 31 of the case 2.

An exhaust outlet 10 for exhausting exhaust gas is connected to the downstream end or the rear end of the second passage 42. The exhaust outlet 10 is formed by an outlet pipe 11, and the outlet pipe 11 is fixed to the right side wall 33 of the case 2.

The inlet pipe 9 is connected to the downstream end of an exhaust pipe (not shown) located on the upstream side of the inlet pipe 9. The outlet pipe 11 is connected to the upstream end of an exhaust pipe (not shown) located on the downstream side of the outlet pipe 11 and connected to the inlet pipe 52 on the rear stage catalyst 50 side. As a result, the U-shaped passage 4 communicates with the exhaust passages in both exhaust pipes.

The bypass hole 5 is provided at the rear end of the partition plate 3. The bypass hole 5 of the present embodiment is formed by cutting out the entire height of the partition plate 3, and when the bypass hole 5 is fully closed, the bypass valve 6 fits into the bypass hole 5 to completely close the bypass hole 5. ing. Therefore, the bypass hole 5 and the bypass valve 6 have a vertically long rectangular shape. 2 and 3 show when the bypass hole 5 is fully opened. FIG. 3 shows the shape of the bypass valve 6.

However, the shape is not limited to this, and the shapes of the bypass hole 5 and the bypass valve 6 are arbitrary. Only the intermediate portion in the height direction of the partition plate 3 may be cut out to form the bypass hole 5, and the bypass hole 5 may be fully closed by fitting or overlapping the bypass valve 6 with the bypass hole 5.

The bypass valve 6 is composed of a butterfly valve and can rotate around the rotation shaft 12. The rotating shaft 12 is fixed to the front end edge of the bypass valve 6 when the bypass hole is fully closed, is located at the front end of the bypass hole 5, and extends in the vertical direction. The rotation shaft 12 is rotationally driven by, for example, an actuator 13 formed by a servomotor. The actuator 13 is controlled by the ECU 100 shown in FIG.

As shown in FIG. 2, the angle θ of the bypass valve 6 when the bypass hole 5 is fully closed is defined as the fully closed angle θa, and the angle θ of the bypass valve 6 when the bypass hole 5 is fully opened is defined as the fully open angle θb. θa = 0 ° and θb = 90 °. As the angle θ of the bypass valve 6 increases, the opening degrees of the bypass valve 6 and the bypass hole 5 increase. The opening degree when θ = θa is 0%, and the opening degree when θ = θb is 100%.

The bypass valve 6 is configured to fully close the first passage 41 when the bypass hole 5 is fully opened, and to fully open the first passage 41 when the bypass hole 5 is fully closed. In particular, when the bypass hole 5 is fully opened, the bypass valve 6 is fitted into the first passage 41 so as to completely close the first passage 41.

The exhaust gas purification device 1 further includes an injection valve 14 for injecting urea water U into the U-shaped passage 4 on the upstream side of the pre-stage catalyst 7. In the case of the present embodiment, the injection valve 14 is arranged at the upstream end of the third passage 43 and is fixed to the left side wall 34 of the case 2. Then, the urea water U is injected from the left side to the right side toward the downstream side of the third passage 43. The third passage 43 serves as a mixing passage for mixing the urea water U injected from the injection valve 14 with the exhaust gas.

The pre-stage catalyst 7 has a cylindrical shape having a central axis C extending in the front-rear direction, and is housed in a circular protective tube 15. The assembly of the pre-stage catalyst 7 and the protective tube 15 is coaxially arranged in the second passage 42. In order to prevent exhaust gas from flowing to the outer periphery of the protective tube 15, the gap between the front end of the protective tube 15 and the case 2 and the partition plate 3 is closed by the front end plate 16. The gap between the rear end of the protective tube 15 and the case 2 and the partition plate 3 is closed by the rear end plate 17.

The front-stage catalyst 7, the protective pipe 15, and the rear end plate 17 are located in the second passage 42 on the outlet side of the bypass hole 5 and in front of the exhaust outlet 10, that is, on the upstream side in the exhaust G1 flow direction. Therefore, the space 20 in the second passage 42 on the rear side thereof functions as a passage for the exhaust gas from at least one of the catalyst 7 and the bypass hole 5 to go to the exhaust outlet 10.

This space 20 forms the confluence of the bypass passages described above. That is, assuming that the U-shaped passage 4 through which the exhaust G1 flows is the main exhaust passage, the bypass hole 5 through which the exhaust G2 flows forms a bypass passage that bypasses the pre-stage catalyst 7. This bypass passage merges with the U-shaped passage 4 at the space 20. Therefore, the space 20 forms a confluence of bypass passages.

The exhaust gas purification device 1 has a structure in which a metal (for example, stainless steel) case 2, a partition plate 3, and the like are assembled by welding or the like.

Regarding the operation, when the bypass valve 6 is at the position of the fully open angle θb as shown in the figure and the bypass hole 5 is fully opened, the first passage 41 is fully closed by the bypass valve 6. Therefore, the exhaust gas introduced into the first passage 41 from the exhaust inlet 8 is exhausted from the exhaust outlet 10 through the second passage 42 through the total amount bypass hole 5, as shown by the arrow G2. As a result, the exhaust gas bypasses the pre-stage catalyst 7, and the increase in exhaust resistance due to the exhaust gas flowing through the pre-stage catalyst 7 and the increase in back pressure can be suppressed.

On the other hand, when the bypass valve 6 is at the position of the fully closed angle θa and the bypass hole 5 is fully closed, the total amount of exhaust gas introduced into the first passage 41 from the exhaust inlet 8 is as shown by the arrow G1. It is flowed to the catalyst 7 by following the paths of the first passage 41, the third passage 43, and the second passage 42. Then, after passing through the pre-stage catalyst 7, the exhaust gas is once discharged from the exhaust outlet 10 via the second passage 42. As a result, the exhaust gas flows through the pre-stage catalyst 7 and NOx in the exhaust gas can be purified.

If the bypass valve 6 is set to an intermediate angle between the fully closed angle θa and the fully open angle θb, exhaust gas can flow through both the bypass hole 5 and the pre-stage catalyst 7. Then, by adjusting the opening degree of the bypass valve 6, the back pressure and NOx purification can be optimally balanced.

According to this exhaust purification device 1, since the bypass hole 5 is provided in the partition plate 3 that partitions the inside of the case 2, for example, the inlet pipe 52 and the outlet pipe 53 of the rear-stage catalyst casing 51 shown in FIG. 1 are exhausted for another bypass. The configuration of the exhaust gas purification device can be made simpler and more compact than the conventional configuration in which the exhaust gas is connected by a pipe.

Further, since the bypass valve 6 is composed of a butterfly valve, the bypass hole 5 and the first passage 41 can be alternately fully opened and closed with a single bypass valve 6, which also makes the configuration of the exhaust gas purification device simple and compact. can do.

The case does not have to have a rectangular parallelepiped shape, and may have any shape. For example, as shown in FIG. 4, the case 2 may have a substantially cylindrical shape or a Dharma shape when viewed from the front. In the case of the illustrated example, the case 2 is configured by combining a large-diameter cylindrical tube 18 defining the second passage 42 and a small-diameter semi-cylindrical tube 19 defining the first passage 41. A partition plate 3 is provided at a connection position between the large-diameter cylindrical tube 18 and the small-diameter semi-cylindrical tube 19. The bypass valve 6 has a semicircular shape that can be fitted into the first passage 41 having a semicircular cross section. Other configurations are roughly the same.

The pre-stage catalyst 7 may be provided at a position other than the second passage 42. For example, it may be provided in the first passage 41 on the downstream side of the inlet side of the bypass hole 5 in the exhaust G1 flow direction. Alternatively, it may be provided in the third passage 43. It may be provided in each of two or more passages among the first to third passages 41 to 43.

The outlet pipe 11 may be fixed to the rear end wall 31 of the case 2.

Returning to FIG. 1, the inlet pipe 52 of the rear-stage catalyst casing 51 is provided with an injection valve 54 for injecting urea water U for the rear-stage catalyst 50. The injection valve 54 may be provided on the upstream side, or may be provided on the exhaust pipe connecting the outlet pipe 11 and the inlet pipe 52.

Regarding the electrical configuration, the exhaust purification system 200 includes an exhaust pressure sensor 61, an exhaust temperature sensor 62, and a concentration sensor 63 that detect the exhaust pressure PA, the exhaust temperature TA, and the NOx concentration NA on the upstream side of the pre-stage catalyst 7, respectively. These sensors are provided in the exhaust gas purification device 1 and detect each value on the inlet side of the bypass hole 5.

Further, the exhaust purification system 200 includes an exhaust temperature sensor 64 and a concentration sensor 65 that detect the exhaust temperature TB and the NOx concentration NB on the downstream side of the front-stage catalyst 7 and the upstream side of the rear-stage catalyst 50 in the exhaust G1 flow direction, respectively. These sensors are also provided in the exhaust gas purification device 1 and detect each value in the outlet side of the bypass hole 5, that is, the rear space 20 of the second passage 42.

Further, the exhaust gas purification system 200 includes a concentration sensor 66 that detects the NOx concentration NC on the downstream side of the post-stage catalyst 50. Although the concentration sensor 66 is provided in the outlet pipe 53, it may be provided in the exhaust pipe connected to the outlet pipe 53.

The above sensors 61 to 66 are electrically connected to the ECU 100. The ECU 100 is configured to control the bypass valve 6 and the injection valves 14 and 54 based on the detected values of the sensors 61 to 66 and the like.

Next, control will be described.

When the exhaust pressure PA detected by the exhaust pressure sensor 61 is high, the ECU 100 controls the bypass valve 6 so as to increase the opening degree of the bypass hole 5 as compared with the case where the exhaust pressure PA is low.

When the opening degree of the bypass hole 5 is increased, the flow rate of the exhaust gas G2 passing through the bypass hole 5 can be increased, and the flow rate of the exhaust gas G1 passing through the pre-stage catalyst 7 can be decreased. Therefore, when the exhaust pressure PA is high, by increasing the opening degree of the bypass hole 5, it is possible to suppress the exhaust resistance due to the passage of the front-stage catalyst 7, and thus the increase in the back pressure, and reduce the exhaust pressure PA. Then, it is possible to suppress a decrease in the combustion efficiency of the engine and suppress a deterioration in fuel efficiency.

Further, when the NOx concentration NB detected by the concentration sensor 65 is high, the ECU 100 controls the bypass valve 6 so as to reduce the opening degree of the bypass hole 5 as compared with the case where the NOx concentration NB is low.

When the opening degree of the bypass hole 5 is reduced, the flow rate of the exhaust gas G2 passing through the bypass hole 5 can be reduced, and the flow rate of the exhaust gas G1 passing through the pre-stage catalyst 7 can be increased. Therefore, when the NOx concentration NB is high, by reducing the opening degree of the bypass hole 5, NOx purification by the pre-stage catalyst 7 can be promoted and the NOx concentration NB can be lowered. And the exhaust emission can be improved.

Further, when the exhaust temperature TA detected by the exhaust temperature sensor 62 is high, the ECU 100 controls the bypass valve 6 so as to increase the opening degree of the bypass hole 5 as compared with the case where the exhaust temperature TA is low.

When the exhaust temperature TA is high, the purification rate of the post-stage catalyst 50 tends to increase as compared with the case where the exhaust temperature TA is low. Therefore, in this case, even if the flow rate of the exhaust gas G1 passing through the front-stage catalyst 7 is reduced, there is often no problem because NOx can be purified by the rear-stage catalyst 50. Therefore, when the exhaust temperature TA is high, the opening degree of the bypass hole 5 is increased to increase the bypass flow rate of the exhaust G2. This makes it possible to reduce the back pressure. For example, a case where the exhaust temperature TA is high means a state after the engine warm-up is completed, and a case where the exhaust temperature TA is low means a state before the engine warm-up is completed.

In the above control, NOx concentration NA or NC may be used instead of NOx concentration NB. Further, the exhaust temperature TB may be used instead of the exhaust temperature TA.

Hereinafter, more specific examples of control will be described.

(First Example)
As shown in FIG. 5A, when the exhaust pressure PA detected by the exhaust pressure sensor 61 is equal to or higher than a predetermined threshold PAs, the ECU 100 opens the bypass valve 6 (opens the bypass hole 5) and discharges the bypass valve 6. The bypass valve 6 is controlled so that the bypass valve 6 is closed (the bypass hole 5 is closed) when the atmospheric pressure PA is less than the threshold PAs. As a result, when the exhaust pressure PA is equal to or higher than the threshold PAs, the opening degree of the bypass hole 5 is increased as compared with the case where the exhaust pressure PA is less than the threshold PAs. The threshold PAs are the maximum values of the exhaust pressure that can be tolerated in consideration of the combustion efficiency and fuel consumption of the engine, and are set to a value equal to or close to the experimentally obtained value, and are set in advance in the ECU 100. It will be remembered. The opening degree when the valve is closed is preferably fully closed (0%), and the opening degree when the valve is opened is preferably fully open (100%). However, if the same effect can be achieved, it does not have to be fully closed and fully opened, and the opening may be close to them. The same applies to the following.

In addition to the control based on the exhaust pressure, the ECU 100 performs the control based on the NOx concentration as shown in FIG. 5 (B) and the control based on the exhaust temperature as shown in FIG. 5 (C).

That is, as shown in FIG. 5 (B), the ECU 100 closes the bypass valve 6 when the NOx concentration NB detected by the concentration sensor 65 is larger than the predetermined threshold value NBs, and the NOx concentration NB is the threshold value NBs. The bypass valve 6 is controlled so as to open the bypass valve 6 in the following cases. As a result, when the NOx concentration NB is larger than the threshold value NBs, the opening degree of the bypass hole 5 is reduced as compared with the case where the NOx concentration NB is equal to or less than the threshold value NB. The threshold value NBs is the maximum value of the NOx concentration NB at which the NOx concentration NC on the downstream side of the post-stage catalyst 50 is an acceptable value in consideration of the legal regulation value and the like, and is equal to the experimentally obtained value. It is set to a value at or near it, and is stored in the ECU 100 in advance.

Further, as shown in FIG. 5C, the ECU 100 opens the bypass valve 6 when the exhaust temperature TA detected by the temperature sensor 62 is equal to or higher than the predetermined threshold TAs, and the exhaust temperature TA is the threshold TAs. When the temperature is less than the above, the bypass valve 6 is controlled so as to close the bypass valve 6. As a result, when the exhaust temperature TA is equal to or higher than the threshold TAs, the opening degree of the bypass hole 5 is increased as compared with the case where the exhaust temperature TA is less than the threshold TAs. The threshold TAs is the minimum value of the exhaust temperature such that the purification rate of the post-stage catalyst 50 is sufficiently high and the NOx concentration NC is equal to or less than the predetermined threshold NCs even if the exhaust is bypassed, and is experimentally obtained. It is set to a value equal to or close to the value set and stored in the ECU 100 in advance. The threshold NCs are set to a value equal to or close to, for example, a legally regulated upper limit.

The control routine of the first embodiment will be described with reference to FIG. The illustrated routine is repeatedly executed by the ECU 100 every predetermined calculation cycle τ (for example, 10 msec).

First, in step S101, the ECU 100 acquires the exhaust pressure PA, NOx concentration NB, and exhaust temperature TA detected by the exhaust pressure sensor 61, the concentration sensor 65, and the temperature sensor 62, respectively.

Next, in step S102, the ECU 100 determines whether or not the exhaust pressure PA is equal to or greater than the threshold PAs.

When the threshold value is PAs or more, the ECU 100 determines in step S103 whether or not the NOx concentration NB is equal to or less than the threshold value NBs.

When the threshold value is NBs or less, the ECU 100 determines in step S104 whether or not the exhaust air temperature TA is equal to or higher than the threshold value TAs.

When the threshold value TAs or more, the ECU 100 opens the bypass valve 6 in step S105 and ends the routine.

On the other hand, in the ECU 100, the exhaust pressure PA is less than the threshold PAs in step S102, the NOx concentration NB is larger than the threshold NBs in step S103, and the exhaust temperature TA is less than the threshold TAs in step S104. In either case, in step S106, the bypass valve 6 is closed and the routine is completed.

In this way, even when the exhaust pressure PA is equal to or higher than the threshold PAs, when the NOx concentration NB is larger than the threshold NBs, the bypass valve 6 is closed, so that the NOx suppression is prioritized over the back pressure suppression. This can be done, and the amount of NOx discharged from the subsequent catalyst 50 can be suppressed to a predetermined value or less, for example, a regulated value or less.

Further, even when the exhaust pressure PA is equal to or higher than the threshold PAs, if the exhaust temperature TA is less than the threshold TAs, the bypass valve 6 is closed because NOx purification by the post-stage catalyst 50 alone cannot be sufficiently guaranteed. Therefore, NOx purification can be performed prioritizing the suppression of back pressure, and the amount of NOx discharged from the post-stage catalyst 50 can be finally suppressed. In such a case, it may occur before the warm-up of the engine is completed.

Incidentally, at least one of steps S103 and S104 may be omitted. NOx concentration NC may be used instead of NOx concentration NB.

(Second Example)
Next, a second embodiment of control will be described.

As shown in FIG. 7A, in this embodiment, a map (a function may be used; the same applies hereinafter) that defines the relationship between the exhaust pressure P and the exhaust temperature T and the angle θ (that is, the opening degree) of the bypass valve 6. Is stored in the ECU 100 in advance, and the ECU 100 basically controls the opening degree of the bypass valve 6 according to this map. Hereinafter, for convenience, the angle θ will be referred to as the opening degree θ.

In the map, the opening degree θ of the bypass valve 6 that optimally balances the back pressure and NOx, and the experimentally obtained value is input.

FIG. 7B shows the relationship between the exhaust pressure P in the map and the bypass valve opening degree θ by the solid line a. As the exhaust pressure P increases, the bypass valve opening degree θ increases. As a result, as the back pressure increases, the bypass flow rate passing through the bypass hole 5 can be increased, and the increase in back pressure can be suppressed.

FIG. 7C shows the relationship between the exhaust temperature T in the map and the bypass valve opening degree θ by the solid line b. As the exhaust temperature T rises, the bypass valve opening degree θ increases. As a result, as the exhaust temperature T rises, the bypass flow rate is increased to allow the post-stage catalyst 50 to take charge of NOx purification more, and the increase in back pressure can be suppressed by that amount.

By the way, when the NOx concentration NC of the exhaust gas finally discharged from the post-stage catalyst 50 is equal to or less than the threshold value NCs, there is no problem only with the control based on the map as described above. However, the NOx concentration NC may temporarily exceed the threshold value NCs only on the map due to changes in the engine operating state or the like. Therefore, in that case, the map value is corrected based on the NOx concentration NC.

Specifically, when the NOx concentration NC exceeds the threshold value NCs, the ECU 100 corrects the basic value of the bypass valve opening degree θ in the map to the opening degree decreasing side so that it becomes equal to the corrected value. The actual bypass valve opening degree θ is controlled. 7 (B) and 7 (C) show the corrected bypass valve opening degree θ with broken lines c and d.

As shown in FIG. 7B, when the NOx concentration NC exceeds the threshold value NCs, the corrected bypass valve opening degree θ (line c) for the same exhaust pressure P is from the basic value (line a). It will be reduced. The reduction correction amount at this time is increased as the NOx concentration NC becomes larger than the threshold value NCs. Preferably, the reduction correction amount is calculated according to the PID control method based on the difference ΔN = NC-NCs between the actual NOx concentration NC and the threshold value NCs. The ECU 100 subtracts the reduction correction amount from the basic value to calculate the corrected bypass valve opening degree θ (map value).

The same applies to the exhaust temperature. As shown in FIG. 7 (C), when the NOx concentration NC exceeds the threshold value NCs, the corrected bypass valve opening degree θ (line d) for the same exhaust temperature T is from the basic value (line b). It will be reduced. The reduction correction amount at this time is increased as the NOx concentration NC becomes larger than the threshold value NCs. Preferably, the reduction correction amount is calculated based on the difference ΔN = NC-NCs between the actual NOx concentration NC and the threshold value NCs, for example, according to the method of PID control. The ECU 100 subtracts the reduction correction amount from the basic value to calculate the corrected bypass valve opening degree θ (map value).

The correction of the map value based on the NOx concentration NC may be performed only for the relationship between the exhaust pressure P and the bypass valve opening degree θ as shown in FIG. 7 (B), or as shown in FIG. 7 (C). It may be performed only for the relationship between the exhaust temperature T and the bypass valve opening degree θ. Instead of the NOx concentration NC, the NOx concentration NB or NA on the upstream side may be used. In this case, the respective threshold values NBs and NAs are set to be larger than the threshold NCs so that NC = NCs when NB = NBs or NC = NCs.

Also in this embodiment, when the NOx concentration NC exceeds the threshold value NCs, the bypass valve opening degree θ is reduced as compared with the case where the NOx concentration NC exceeds the threshold value NCs.

The control routine of the second embodiment will be described with reference to FIG. The illustrated routine is repeatedly executed by the ECU 100 every predetermined calculation cycle τ (for example, 10 msec).

First, in step S201, the ECU 100 acquires the exhaust pressure PA, the exhaust temperature TA, and the NOx concentration NC detected by the exhaust pressure sensor 61, the temperature sensor 62, and the concentration sensor 66, respectively.

Next, in step S202, the ECU 100 calculates the basic value θ of the bypass valve opening degree from the map of FIG. 7A based on the exhaust pressure PA and the exhaust temperature TA.

Next, in step S203, the ECU 100 determines whether or not the NOx concentration NC exceeds the threshold value NCs.

When the threshold value is NCs or less, the ECU 100 sets the final target value θt of the bypass valve opening degree equal to the basic value θ in step S204. Then, in step S205, the actual opening degree of the bypass valve 6 is controlled to be equal to the target value θt, and the routine is completed.

On the other hand, when the NOx concentration NC exceeds the threshold value NCs in step S203, the ECU 100 calculates the reduction correction amount Δθ based on the difference ΔN = NC-NCs between the acquired NOx concentration NC and the threshold value NCs in step S206. do. The larger the difference ΔN, the larger the reduction correction amount Δθ. A map or function can be used for this calculation.

Next, in step S207, the ECU 100 calculates a value obtained by subtracting the reduction correction amount Δθ from the basic value θ as the target value θt. Then, in step S205, the actual opening degree of the bypass valve 6 is controlled to be equal to the target value θt, and the routine is completed.

When the NOx concentration NC exceeds the threshold value NCs in this way, the bypass valve opening degree can be reduced, so that the passing flow rate of the pre-stage catalyst 7 is increased and the NOx purification rate of the entire system is increased. Can be done. Finally, the amount of NOx discharged from the post-stage catalyst 50 can be suppressed to a predetermined value or less, for example, a regulated value or less.

Further, when the NOx concentration NC is equal to or less than the threshold value NCs, the actual bypass valve opening is controlled to the optimum opening obtained from the map based on the exhaust pressure PA and the exhaust temperature TA. NOx can be optimally balanced.

Although the embodiments of the present disclosure have been described in detail above, various other embodiments and modifications of the present disclosure can be considered.

(1) For example, the bypass structure for bypassing the catalyst is not limited to that of the above embodiment, and any structure can be adopted. For example, a conventional structure in which the inlet pipe 52 and the outlet pipe 53 of the rear-stage catalyst casing 51 shown in FIG. 1 are connected by another bypass exhaust pipe can also be adopted.

(2) If necessary, the post-stage catalyst 50 may be omitted. For example, the post-stage catalyst 50 can be omitted when performing bypass valve control based only on exhaust pressure and when performing bypass valve control based only on exhaust pressure and NOx concentration.

The embodiments of the present disclosure are not limited to the above-described embodiments, and all modifications, applications, and equivalents included in the ideas of the present disclosure defined by the claims are included in the present disclosure. Therefore, this disclosure should not be construed in a limited way and may be applied to any other technique that falls within the scope of the ideas of this disclosure.

5 Bypass hole 6 Bypass valve 7 Catalyst (pre-stage catalyst)
50 Downstream catalyst (post-stage catalyst)
61 Exhaust pressure sensor 62,64 Exhaust temperature sensor 63, 65, 66 Concentration sensor 100 Electronic control unit (ECU)
200 Exhaust purification system

Claims (6)

The catalyst provided in the exhaust passage of the internal combustion engine and
A bypass passage that bypasses the catalyst and
A bypass valve that opens and closes the bypass passage and
A control unit configured to control the bypass valve and
An exhaust pressure sensor that detects the exhaust pressure on the upstream side of the catalyst, and
With
The internal combustion engine is characterized in that when the exhaust pressure detected by the exhaust pressure sensor is high, the control unit controls the bypass valve so as to increase the opening degree of the bypass passage as compared with the case where the exhaust pressure is low. Exhaust purification system. A concentration sensor for detecting the concentration of the purification component of the catalyst in the exhaust gas on the downstream side of the catalyst is further provided.
The internal combustion engine according to claim 1, wherein the control unit controls the bypass valve so as to reduce the opening degree of the bypass passage when the concentration detected by the concentration sensor is high as compared with the case where the concentration is low. Exhaust purification system. The exhaust gas purification system for an internal combustion engine according to claim 1 or 2, wherein the catalyst is a NOx catalyst. The exhaust gas purification system for an internal combustion engine according to any one of claims 1 to 3, further comprising a downstream catalyst provided in the exhaust passage located on the downstream side of the confluence of the bypass passages. An exhaust temperature sensor for detecting the exhaust temperature on the upstream side of the downstream catalyst is further provided.
With
The internal combustion engine according to claim 4, wherein the control unit controls the bypass valve so as to increase the opening degree of the bypass passage when the exhaust temperature detected by the exhaust temperature sensor is high, as compared with the case where the exhaust temperature is low. Engine exhaust purification system. The exhaust gas purification system for an internal combustion engine according to claim 4 or 5, wherein the downstream catalyst is a NOx catalyst.

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