JP2022007519A - Exhaust emission control system for internal combustion engine - Google Patents

Abstract

To maintain high exhaust emission control rate of a catalyst irrespective of atmospheric pressure.SOLUTION: An exhaust emission control system for an internal combustion engine includes: a catalytic converter 22 disposed in an exhaust passage; an exhaust control valve 26 disposed downstream in the exhaust passage relative to the catalytic converter 22; and an atmospheric pressure sensor 44a for detecting atmospheric pressure. The exhaust emission control system controls the opening of the exhaust control valve to be decreased when the atmospheric pressure is low as compared to that when the atmospheric pressure is high.SELECTED DRAWING: Figure 1

Description

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

An internal combustion engine in which a catalyst is arranged in an exhaust passage and the exhaust gas is purified by this catalyst is known (see, for example, Patent Document 1). For example, in the catalyst, HC and CO in the exhaust gas are oxidized and NOx is reduced. In Patent Document 1, the catalyst is supported on a particulate filter for collecting particulate matter in the exhaust gas.

Japanese Unexamined Patent Publication No. 4-246224

By the way, the exhaust passage is open to the atmosphere. Therefore, when the atmospheric pressure decreases, the differential pressure between the front and rear of the catalyst increases, the flow velocity of the exhaust gas passing through the catalyst increases, and the contact time between the exhaust gas and the catalyst becomes short. As a result, the exhaust gas purification capacity of the catalyst may decrease as the atmospheric pressure decreases.

According to the present disclosure, the following are provided.
It is an exhaust purification device for internal combustion engines.
With the catalyst placed in the exhaust passage,
An exhaust control valve arranged in the exhaust passage downstream of the catalyst,
Atmospheric pressure sensor for detecting atmospheric pressure and
Equipped with
When the atmospheric pressure is low, the opening degree of the exhaust control valve is made smaller than when the atmospheric pressure is high.
Exhaust purification device for internal combustion engine.

The exhaust gas purification rate of the catalyst can be maintained high regardless of the atmospheric pressure.

It is a schematic whole view of the internal combustion engine of the Example by this disclosure. It is a diagram which shows an example of the relationship between the atmospheric pressure and the exhaust gas flow velocity. It is a diagram which shows an example of the time-dependent change of the NOx passage amount integrated value. It is a figure which shows the map of the target opening degree of the exhaust control valve in the Example by this disclosure. It is a flowchart for executing the control routine of the exhaust control valve in the Example by this disclosure. It is a schematic whole view of the internal combustion engine of another Example by this disclosure. It is a schematic whole view of the internal combustion engine of still another Example by this disclosure. It is a time chart for explaining PM reproduction processing. It is a figure which shows the map of the upper limit value QPMU and the lower limit value QPML. It is a flowchart for executing the control routine of PM reproduction processing.

Referring to FIG. 1, the internal combustion engine 1 of the embodiment according to the present disclosure includes an engine body 1a. The internal combustion engine 1 is composed of a spark ignition engine or a compression ignition engine. An intake branch pipe 11 is connected to an intake port (not shown) of the engine body 1a, and the intake branch pipe 11 is connected to an intake duct 13 via a surge tank 12. The intake duct 13 is open to the atmosphere. An electromagnetic throttle valve 14, an air cleaner (not shown), and the like are arranged in the intake duct 13.

On the other hand, an exhaust manifold 21 is connected to the exhaust port (not shown) of the engine body 1a, the exhaust manifold 21 is connected to the inlet of the catalytic converter 22, and the outlet of the catalytic converter 22 is a particulate filter via the exhaust pipe 23. It is connected to the entrance of 24. An exhaust pipe 25 is connected to the outlet of the particulate filter 24. The exhaust pipe 25 is open to the atmosphere. In one example, the catalytic converter 22 includes, for example, a three-way catalyst and an oxidation catalyst.

The catalytic converter 22 of the embodiment according to the present disclosure is a so-called straight flow type. That is, the catalytic converter 22 includes a plurality of exhaust flow passages extending in parallel with each other. Exhaust flow passages include exhaust gas passages with open upstream and downstream ends. The exhaust gas passage is arranged via a porous partition wall. The catalyst component is supported on the partition wall. The exhaust gas that has reached the catalyst converter 22 flows through the exhaust gas passage and comes into contact with the catalyst component. As a result, the exhaust gas is purified by the catalytic converter 22.

The particulate filter 24 of the embodiment according to the present disclosure is a so-called wall flow type. That is, the particulate filter 24 includes a plurality of exhaust flow passages extending in parallel with each other. The exhaust gas flow passage includes an exhaust gas inflow passage in which the upstream end is open and the downstream end is closed, and an exhaust gas outflow passage in which the upstream end is closed and the downstream end is open. The exhaust gas inflow passage and the exhaust gas outflow passage are alternately arranged via the porous partition wall. The exhaust gas that has reached the particulate filter 24 first flows into the exhaust gas inflow passage, and then flows out into the adjacent exhaust gas outflow passage through the surrounding partition wall. As a result, particulate matter (PM) contained in the exhaust gas, which is mainly formed of solid carbon, is collected on the particulate filter 24. Further, for example, a catalyst having an oxidizing function is supported on the partition wall. As a result, oxidation of not only particulate matter but also HC, CO and the like in the exhaust gas is promoted.

Further, in the embodiment according to the present disclosure, an electromagnetic exhaust control valve 26 is further arranged in the exhaust pipe 23.

Further referring to FIG. 1, the internal combustion engine 1 of the embodiment according to the present disclosure includes an electronic control unit 40. The electronic control unit 40 includes, for example, an input / output port 41, one or more processors 42, and one or more memories 43, which are communicably connected to each other by a bidirectional bus. The processor 42 includes a microprocessor (CPU) and the like. The memory 43 includes, for example, a ROM (read-only memory), a RAM (random access memory), and the like. Various programs are stored in the memory 43, and various routines are executed when these programs are executed by the processor 42.

One or more sensors 44 are communicably connected to the input / output port 41. The sensor 44 detects, for example, a depression amount sensor (not shown) for detecting the depression amount of the accelerator pedal (not shown), a crank angle sensor (not shown) for detecting the crank angle, and the temperature of the particulate filter 24. A temperature sensor for detecting an atmospheric pressure, an atmospheric pressure sensor 44a for detecting an atmospheric pressure, and the like are included. In the processor 42, which is a temperature sensor for detecting the temperature of the catalytic converter 22, the engine speed is calculated based on the output from the crank angle sensor. On the other hand, the input / output port 41 is communicably connected to a throttle valve 14, an exhaust control valve 26, a fuel injection valve (not shown), a spark plug (not shown), and the like. These exhaust control valves 26 and the like are controlled based on the signal from the electronic control unit 40.

FIG. 2 shows an example of the relationship between the atmospheric pressure Pa and the flow velocity Vg of the exhaust gas passing through the catalytic converter 22. As can be seen from FIG. 2, as the atmospheric pressure Pa decreases, the exhaust gas flow velocity Vg increases. Generally speaking, the atmospheric pressure Pa is lower in a place where the altitude is high than in a place where the altitude is low.

As the exhaust gas flow velocity Vg increases, the contact time between the exhaust gas and the catalyst becomes shorter. As a result, as the atmospheric pressure Pa decreases, the exhaust gas purification capacity of the catalytic converter 22 may decrease. FIG. 3 shows an example of a change over time in the integrated value SQNOx of the amount of NOx that has passed through the catalytic converter 22 without being purified. As can be seen from FIG. 3, as the atmospheric pressure Pa decreases, the passing NOx amount integrated value SQNOx increases. This also applies to other components such as HC and CO that should be purified by the catalytic converter 22.

Therefore, in the embodiment according to the present disclosure, as shown in FIG. 4, the target opening degree Dtgt of the exhaust control valve 26 is set so as to decrease as the atmospheric pressure Pa decreases. Next, the exhaust control valve 26 is controlled so that the actual opening degree becomes the target opening degree Dtgt. As a result, as the atmospheric pressure Pa becomes lower, the pressure loss in the downstream portion of the catalytic converter 22 is increased by the exhaust control valve 26. Therefore, even if the atmospheric pressure Pa becomes low, the exhaust gas flow velocity Vg is limited to be high. Therefore, the exhaust gas purification rate of the catalytic converter 22 is maintained high regardless of the atmospheric pressure Pa. The opening degree Dtgt of the exhaust control valve 26 is stored in the memory 43 in the form of a map shown in FIG. 4, for example.

FIG. 5 shows a routine for controlling the exhaust control valve 26 of the embodiment according to the present disclosure. Referring to FIG. 5, the atmospheric pressure Pa is read in step 100. In the following step 101, the target opening degree Dtgt of the exhaust control valve 26 is calculated from the map of FIG. In the following step 102, the exhaust control valve 26 is controlled so that the actual opening degree becomes the target opening degree Dtgt.

FIG. 6 shows another embodiment according to the present disclosure. The embodiment shown in FIG. 6 differs from the embodiment shown in FIG. 1 in that the exhaust control valve 26 is arranged in the exhaust pipe 25. As a result, not only the flow velocity of the exhaust gas passing through the catalytic converter 22 but also the flow velocity of the exhaust gas passing through the particulate filter 24 is appropriately maintained. Therefore, not only the exhaust gas purification rate in the catalytic converter 22 but also the PM collection rate and the exhaust gas purification rate in the particulate filter 24 are maintained high.

FIG. 7 shows yet another embodiment of the embodiment according to the present disclosure. The embodiment shown in FIG. 7 differs from the embodiment shown in FIG. 1 in that the exhaust control valve 26 is not arranged in the exhaust pipes 23 and 25.

As the engine operation time becomes longer, the amount of particulate matter collected by the particulate filter 24, that is, the PM collection amount QPM increases. The PM collection amount QPM represents the pressure loss of the particulate filter 24, and as the PM collection amount QPM increases, the pressure loss of the particulate filter 24 increases. As the pressure loss of the particulate filter 24 increases, the engine back pressure increases. It is not desirable for the engine back pressure to be excessively high. Therefore, in the embodiment shown in FIG. 7, when the PM collection amount QPM reaches the upper limit QPMU (QPM ≧ QPMU), the PM regeneration treatment that promotes the oxidation of the particulate matter collected by the particulate filter 24 is performed. Will be executed. In one example, under an oxidizing atmosphere, the temperature of the exhaust gas flowing into the particulate filter 24 is increased, thereby promoting the oxidation of particulate matter. In order to raise the temperature of the exhaust gas, for example, fuel is secondarily injected into the combustion chamber during the combustion stroke or the exhaust stroke, or the ignition timing is retarded.

When the PM regeneration process is performed, the PM collection amount QPM gradually decreases. In the embodiment shown in FIG. 7, when the PM collection amount QPM reaches the lower limit value QPML during the PM regeneration process (QPM ≦ QPML), the PM regeneration process is stopped. FIG. 8 shows an example of the change over time in the PM collection amount QPM.

The PM collection amount QPM is calculated, for example, by calculating the increase and decrease of the PM collection amount QPM per unit time, respectively, and repeatedly accumulating these increase and decrease amounts. The increase is calculated based on, for example, the engine load and the engine speed. The decrease is calculated based on, for example, the temperature of the particulate filter 24 and the flow velocity of the exhaust gas flowing through the particulate filter 24. In another embodiment (not shown), the PM collection amount QPM is calculated based on the front-rear differential pressure of the particulate filter 24.

Now, when such a PM regeneration process is performed, the PM collection amount QPM changes between the upper limit value QPMU and the lower limit value QPML as shown in FIG. Or, roughly speaking, the PM collection amount QPM does not exceed the upper limit QPMU and does not fall below the lower limit QPML. Therefore, when the lower limit value QPML is set to a large value, the PM collection amount QPM is maintained in a large state. On the other hand, as described above, the PM collection amount QPM represents the pressure loss of the particulate filter 24. Therefore, as the lower limit QPML increases, the pressure loss of the particulate filter 24 increases.

Therefore, in the embodiment shown in FIG. 7, as shown in FIG. 9, the lower limit value QPML is set so as to increase as the atmospheric pressure Pa decreases. As a result, the pressure loss of the particulate filter 24 increases as the atmospheric pressure Pa decreases. Therefore, the flow velocity of the exhaust gas passing through the catalytic converter 22 and the flow velocity of the exhaust gas passing through the particulate filter 24 are appropriately maintained, and the exhaust gas purification rate in the catalytic converter 22 and the PM collection rate and exhaust purification in the particulate filter 24 are maintained. The rate is kept high.

On the other hand, as shown in FIG. 9, the upper limit value QPMU is set to be constant regardless of the atmospheric pressure Pa. The upper limit value QPMU is for limiting the excessively high back pressure of the engine, and is not affected by the atmospheric pressure Pa.

FIG. 10 shows a routine for executing the control of the PM reproduction process described above. This routine is executed repeatedly. Referring to FIG. 10, in step 200, the atmospheric pressure Pa is read from the atmospheric pressure sensor 44a. In the following step 201, the upper limit value QPMU and the lower limit value QPML are calculated using the map of FIG. In the following step 202, the PM collection amount QPM is calculated. In the following step 203, it is determined whether or not the PM collection amount QPM is equal to or higher than the upper limit value QPMU. When QPM ≧ QPMU, the process proceeds to step 204, and the PM reproduction process is executed. On the other hand, when QPM <QPMU, the process proceeds to step 205, and it is determined whether or not the PM collection amount QPM is equal to or less than the lower limit value QPML. When QPM> QPML, the processing cycle is terminated. That is, the PM reproduction process is continuously executed or stopped. On the other hand, when QPM ≦ QPML, the process proceeds to step 206, and the PM reproduction process is stopped.

In another embodiment, the PM regeneration process described above is performed in the internal combustion engine shown in FIG. 1 or the internal combustion engine shown in FIG.

1a Engine body 23,25 Exhaust pipe 22 Catalytic converter 24 Particulate filter 26 Exhaust control valve 40 Electronic control unit

Claims (1)

It is an exhaust purification device for internal combustion engines.
With the catalyst placed in the exhaust passage,
An exhaust control valve arranged in the exhaust passage downstream of the catalyst,
Atmospheric pressure sensor for detecting atmospheric pressure and
Equipped with
When the atmospheric pressure is low, the opening degree of the exhaust control valve is made smaller than when the atmospheric pressure is high.
Exhaust purification device for internal combustion engine.

Images