JP2727718B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing NOx in an exhaust system of an internal combustion engine capable of lean combustion in an oxidizing atmosphere (oxygen excess atmosphere) in the presence of HC (unburned hydrocarbon). The present invention relates to an exhaust gas purification device provided with a zeolite-based catalyst that can be reduced, and more particularly to an exhaust gas purification device that prevents deterioration of durability of the catalyst.

[Conventional technology]

Recently, in order to improve fuel efficiency, a lean-burn internal combustion engine that burns at an air-fuel ratio in a lean region has been developed, and a part thereof has been put to practical use. In the lean air-fuel ratio region, since NOx cannot be purified by a conventional catalyst, a low NOx region has become an issue of a lean burn engine, and a catalyst capable of purifying NOx even at a lean air-fuel ratio has attracted attention.

Japanese Patent Application Laid-Open No. 1-130735 and Japanese Patent Application No. 63-95026 teach a catalyst comprising a transition metal-supported zeolite and reducing NOx in the presence of HC in an oxidizing atmosphere (hereinafter referred to as a lean NOx catalyst). doing.

In addition, the lean NOx catalyst deteriorates when placed in a reducing atmosphere, that is, an atmosphere with an air-fuel ratio rich, so when the air-fuel ratio sensor determines that the air-fuel ratio is rich, secondary air is introduced to change the oxidizing atmosphere. (Japanese Patent Laid-Open Publication No. 1-203609).

By the way, in order to prevent catalyst deterioration, a bypass valve that switches the flow of exhaust gas between the lean NOx catalyst and the bypass passage is provided by bypassing the lean NOx catalyst when the air-fuel ratio is rich by providing a bypass valve that bypasses the lean NOx catalyst. It is conceivable to control the flow of exhaust gas (hereinafter referred to as a conventional control method).

[Problems to be solved by the invention]

However, if the air-fuel ratio sensor detects the actual air-fuel ratio and determines that the air-fuel ratio is rich based on the actual air-fuel ratio, and then switches the bypass valve to the bypass passage opening side, control delay / operation delay of the bypass valve causes an exhaust gas rich in air-fuel ratio. Part of lean NO
It is introduced into the x-catalyst and is not sufficient as a countermeasure against catalyst durability deterioration and NOx increase.

This will be described in more detail with reference to FIG. 10 by taking, for example, the case of changing from steady state to acceleration. When the throttle opening changes from “closed” to “open”, the air-fuel ratio changes from lean to rich with a time delay. In the conventional control method, when the air-fuel ratio A / F detected by the air-fuel ratio sensor becomes richer than a predetermined air-fuel ratio level (for example, stoichiometric air-fuel ratio: A / F stoichiometric ≒ 14.5 for a gasoline engine), Since the bypass valve is controlled to open, the control delay (ECU to bypass valve) and the bypass valve closed to open
It takes time from the operation time of
During this time, the exhaust gas rich in the air-fuel ratio enters the lean NOx catalyst, and the durability of the catalyst deteriorates.

The present invention prevents the introduction of rich air-fuel ratio exhaust gas into the lean NOx catalyst by opening the bypass earlier than the conventional control method when the air-fuel ratio is expected to change from lean to rich. It is another object of the present invention to suppress the deterioration of the durability of the catalyst.

[Means for solving the problem]

In order to achieve the above object, an exhaust gas purifying apparatus for an internal combustion engine according to the present invention comprises an operating state detecting means 10 for detecting an operating state of the internal combustion engine 2 as shown in FIG.
Air-fuel ratio adjusting means 12 for adjusting the air-fuel ratio based on the output of the operating state detecting means 10, and zeolite carrying a transition metal or a noble metal provided in the exhaust system of the internal combustion engine 2; A lean NOx catalyst 4 for reducing NOx in exhaust gas in the presence of gas, a bypass passage 6 for bypassing the lean NOx catalyst 4, a predicting means 14 for predicting an air-fuel ratio rich from the output of the operating state detecting means 10, Thus, when opened, exhaust gas is flown into the bypass passage 6 and exhaust gas is prevented from flowing into the lean NOx catalyst 4, and when closed, exhaust gas is flown into the lean NOx catalyst 4 and at the same time, exhaust gas is prevented from flowing into the bypass passage 6. A bypass valve 8 that is opened when the air-fuel ratio is predicted to be rich by the means 14.

[Action]

The predicting unit 14 predicts that the air-fuel ratio lean becomes rich in the following cases, for example.

(A) When the leaning correction coefficient KLEAN ≧ 1.0. However, KLEA
N corresponds to the control target air-fuel ratio, and is calculated from the operating state of the engine and the like.

(B) When the throttle opening TA is equal to or greater than a predetermined value, or when OT
When there is P increase (overtemperature protection increase).

(C) During acceleration.

(D) During cold or warm-up (water temperature increase, etc.).

When the predicting means 14 predicts that the air-fuel ratio becomes rich from lean, it sends a control signal to open the bypass valve 8 before the actual air-fuel ratio becomes rich. Therefore, even if it takes some time for the bypass valve 8 to change from “closed” to “open”, the actual air-fuel ratio is equal to or less than a predetermined value (rich).
By the time, the bypass valve 8 is “open”, and the exhaust gas rich in the air-fuel ratio does not enter the lean NOx catalyst 4.

As described above, in the exhaust gas purifying apparatus of the present invention, the control of the bypass valve 8 from “closed” to “opened” is executed early, so that the exhaust gas rich in the air-fuel ratio is prevented from entering the lean NOx catalyst 4, and the lean NOx catalyst is prevented. The durability of the catalyst 4 is deteriorated, and NOx is effectively reduced for a long time.

〔Example〕

 Next, specific examples of the present invention will be described.

FIG. 2 shows a system configuration of an embodiment of the present invention. In FIG. 2, a lean NOx catalyst 4 is provided in an exhaust system of an internal combustion engine 2 composed of a gasoline engine or a diesel engine.
And a bypass passage 6 that bypasses the lean NOx catalyst 4.
A bypass valve 8 for switching the exhaust gas between the lean NOx catalyst 4 and the bypass passage 6, an air-fuel ratio sensor 18 provided upstream of the lean NOx catalyst 4, and provided downstream of the lean NOx catalyst 4 as necessary. A three-way catalyst or oxidation catalyst 22 is provided.

A throttle valve 28 is provided in the intake system of the internal combustion engine 2, and the opening of the throttle valve 28 is detected by a throttle opening sensor 30. An intake pipe pressure sensor 32 is provided downstream of the throttle valve 28, and an intake air temperature sensor 36 is provided in the intake system as needed.

A fuel injection valve 16 is provided at each intake port (each cylinder in the case of a diesel engine) connected to each cylinder of the internal combustion engine 2. In the case of a spark ignition type engine, a spark plug 38 is provided for each cylinder, 40 is an igniter, and 24 is a distributor for distributing current for spark ignition. The rotating shaft of the distributor 24 is interlocked with the crankshaft of the internal combustion engine 2, and a crank angle sensor 26 for detecting the engine speed and the crank angle is provided inside the distributor 24. In addition, a water temperature sensor 34 for detecting a cooling water temperature of the internal combustion engine 2 is also provided.

The internal combustion engine 2 is controlled by an engine control computer 20. FIG. 3 shows the internal configuration of the engine control computer 20 and the relationship with various sensors and various actuators.

As shown in FIG. 3, the engine control computer 20 includes a central processor unit (CPU) 20a for executing an operation, a read-only memory (RO)
M) 20b, random access memory (RAM) 2 for temporary storage
0c, input interface 20d for analog signals, A / D converter 20 for converting analog signals to digital signals
e, an input interface 20f for digital signals, and an output interface 20g. Power is supplied from a constant voltage power supply 20h.

Intake pipe pressure sensor 32, water temperature sensor 34, intake temperature sensor 3
6. The output of the air-fuel ratio sensor 18 is input to the input interface 20d, and the output of the crank angle sensor 26 and the throttle opening sensor (in the case of a digital signal) 30 is input to the input interface 20f. The CPU 20a performs an operation described below, and the output is transmitted to each fuel injection valve (injector) 16, the bypass control valve 8 and the like via the output interface 20g to control each actuator.

FIG. 4 shows an arithmetic routine according to the first embodiment of the present invention, which is stored in the ROM 20b and read out by the CPU 20a to perform bypass control.

The routine of FIG. 4 is interrupted, for example, at every 180 ° C. (crank angle) based on the crank angle from the crank angle sensor 26.

In step 101, the engine rotational speed NE is read from the output of the crank angle sensor 26, and the intake pipe pressure PM is read from the output of the intake pipe pressure sensor 32.

Next, at step 102, the basic fuel injection amount Tp is calculated from the intake pipe pressure and the engine rotation speed so that the air-fuel ratio becomes the stoichiometric air-fuel ratio.

Next, an operation of correcting the basic fuel injection amount according to operating conditions such as water temperature and intake air temperature is performed. First, in step 103,
The output THW from the water temperature sensor 34 and the output THA from the intake temperature sensor 36 are read. Next, at step 104, a water temperature (or intake air temperature) increase FWL is calculated. The water temperature increase is an increase in fuel injection for improving drivability during warm-up, and is obtained, for example, from a THW-FWL map shown in FIG.

The basic fuel injection amount TP is also corrected by the engine speed NE and the intake pipe pressure PM. In step 105, a leaning correction coefficient KLEANPM for the intake pipe pressure is obtained from, for example, a PM-KLEANPM map shown in FIG. Next, at step 106, a leaning correction coefficient KLEANNE for the engine speed NE is calculated, for example, by NE-KLEANNE shown in FIG.
Calculate from the map. Then, in step 107, KLEAN
The leaning correction coefficient KLEAN (corresponding to the target air-fuel ratio of the control) is calculated from PM · KLEANNE.

In addition, the fuel injection amount may be increased by increasing the amount of acceleration, increasing the amount of throttle at a high opening, or increasing the amount of catalyst overheating which may be required when the catalyst is installed. In step 108, ΔPM
> Α (α is a certain constant value), and the acceleration increase FACC is calculated from ΔPM in order to improve the torque during acceleration. Steps
At 109, the throttle opening TA> c (c is a certain constant value) is entered, and the throttle opening TA increase FPOWER is calculated from the throttle opening TA in order to improve the output at the throttle high opening. In step 110, the intake air amount Q per one revolution of the engine
From N / N and the engine speed NE, the catalyst overheat prevention increase OTP (overtemperature protection) is obtained.

After the leaning correction coefficient KLEAN and various increases are calculated, the routine proceeds to step 111, where the fuel injection amount is corrected. The fuel injection amount TAU is calculated by the following equation.

TAU = Tp · KLEAN · FWL · (1 + FACC + FPOWER + OTP) Then, the routine proceeds to step 112, where TAU is set, and fuel injection is performed only for TAU.

Next, the process proceeds to the bypass control step after step 113. In step 113, it is determined whether or not the bypass is being performed, that is, whether or not the bypass determination flag XF = 1 (during the bypass).

If not in step 113, ie, XF
If = 1, the process proceeds to steps 114, 115, 116, 117, and 118 to predict whether the air-fuel ratio becomes rich. That is, in step 114, it is predicted that the air-fuel ratio will be rich if there is an increase in the water temperature as in the case of cold or warm-up, that is, if FWL> 1.0. In step 115, it is predicted whether the air-fuel ratio becomes rich based on the leaning correction coefficient KLEAN. However, there is a relationship of KLEAN = stoichiometric air-fuel ratio / target air-fuel ratio, and if KLEAN> 1.0, we expect that the air-fuel ratio will be rich,
If KLEAN ≤ 1.0, it is expected that the air-fuel ratio will be lean. In step 116, if the acceleration increase is positive, that is, FACC>
If 0, the air-fuel ratio is expected to be rich. Step 117
Then, if the output correction at the time of the throttle high opening is positive, that is, if FPOWER> 0, it is expected that the air-fuel ratio will be rich. In step 118, if the catalyst overheat prevention increase is positive, that is, if OTP> 0, it is expected that the air-fuel ratio will be rich. In the above, steps 114, 115, 116, 117,
Any one of 118 constitutes the prediction means 14 for predicting that the air-fuel ratio changes from lean to rich.

If it is predicted that the air-fuel ratio becomes rich in any of steps 114, 115, 116, 117, and 118, the process proceeds to step 123, where the bypass valve 8 is opened before the actual air-fuel ratio changes from lean to rich. Perform the execution process of That is, even if it takes some time for the bypass valve 8 to open, it takes more time for the air-fuel ratio to become rich after it is predicted that the air-fuel ratio becomes rich. Becomes "open", the actual air-fuel ratio becomes rich, and exhaust gas with a rich air-fuel ratio does not flow into the lean NOx catalyst 4. When the bypass valve 8 "open" execution process in step 123 is completed, the process proceeds to step 124, in which the bypass determination flag XF is set to 1 indicating that bypass is being performed.

If XF = 1 in step 113, that is, if bypass is in progress, the process proceeds to step 121, where the current actual air-fuel ratio is read from the output of the air-fuel ratio sensor 18, and the process proceeds to step 122, where the actual air-fuel ratio A / F exceeds the predetermined value b. It is determined whether it is large. If A / F> b is not satisfied in step 122, the air-fuel ratio is rich, so the routine proceeds to step 123, where the bypass valve 8 is kept "open". Then, the routine proceeds to step 124, where the bypass determination flag XF is kept at 1.

If A / F> b in step 122, that is, if the actual air-fuel ratio has changed from rich to lean, the process proceeds to step 119, and the "close" execution process of the bypass valve 8 is performed. Therefore, the “closed” execution process of the bypass valve 8 when the air-fuel ratio changes from rich to lean is not performed in anticipation of the air-fuel ratio changing from rich to lean, but is performed when the actual air-fuel ratio changes from rich to lean. Judge that it has changed to lean.
Therefore, after the actual air-fuel ratio changes to lean, the bypass valve 8 is closed, so that the exhaust gas rich in air-fuel ratio is not introduced into the lean NOx catalyst 4. Next, the routine proceeds to step 120, where the bypass determination flag XF is set to 0.

FIG. 8 shows an arithmetic routine according to the second embodiment of the present invention, wherein steps different from those of the first embodiment are numbered in the 200s, and steps corresponding to the first embodiment are the same numbers as those of the first embodiment. Is shown. The switching of the bypass valve 8 to "closed" when the air-fuel ratio changes from rich to lean is executed after the actual air-fuel ratio becomes lean in the first embodiment, whereas in the second embodiment, K is changed to K. = KLEAN · FWL · (1 + FACC + FPOWER + FOTP)> 1.0, that is, after a predetermined time has elapsed from the time when the air-fuel ratio is expected to be lean as a whole.

More specifically, in the second embodiment, when it is determined in step 113 that the bypass is being performed (XF = 1), the process proceeds to step 201, where it is determined whether or not K> 1.0. Is expected to be overall lean, go to step 203 via step 202 and
CLEAN is counted up one by one. By interrupting the routine at every 180 ° crank angle and repeatedly executing the calculation, CLEAN increases, and in an interrupt calculation in which CLEAN becomes larger than a predetermined value e, that is, in a calculation after a predetermined time elapses, CLEAN is performed in step 202. > E, it is considered that the air-fuel ratio has changed from lean to rich, and
The routine proceeds to step 119 via 205, where the bypass valve 8 is closed. Steps 203 and 202 constitute the prediction means 14. Otherwise, proceed to step 123 and proceed to bypass valve 8
Remains open. Steps 204 and 205 are steps for keeping CLEAN at 0 or clearing it to 0. Others are the same as in the first embodiment.

Next, the operation of the present invention will be described with reference to the time chart of FIG. However, the fuel correction is based on the lean correction coefficient KLEAN alone as an example.

For example, , The throttle opening degree TA changes as shown at the top of FIG.

At this time, the control target air-fuel ratio (replaced by the leaning correction coefficient KLEAN) is obtained from the operating state of the engine and signals from various sensors as shown in the second and third stages from the top of FIG. There are some control delays such as detection delay and calculation time.

To execute the above-described target air-fuel ratio, a signal is sent from the ECU 20 to the fuel injection valve 16 to inject fuel, the fuel enters the cylinder through the intake port (transportation period), burns, and Since the exhaust gas reaches the air-fuel ratio sensor 18 through the exhaust system, it takes a considerable time before the air-fuel ratio sensor 18 detects the actual air-fuel ratio. Therefore, the actual air-fuel ratio (detected by the air-fuel ratio sensor 18) is delayed as shown in the fourth row from the top in FIG.

In the conventional control method, when the actual air-fuel ratio value detected by the air-fuel ratio sensor 18 becomes richer than a predetermined air-fuel ratio level, the bypass valve is controlled to “open”. It takes a long time from the time of the bypass valve) and the time of the bypass valve “closed” to “open” to the time the bypass is “opened”, and during this time, the exhaust gas rich in the air-fuel ratio enters the lean NOx catalyst as described above. It is.

However, in the present invention, as shown at the bottom of FIG.
When the target air-fuel ratio (KLEAN value) becomes equal to or less than a predetermined value (for example, richer than the stoichiometric air-fuel ratio), a control signal is sent to open the bypass valve 8. Therefore, even if a certain amount of time is spent from “close” to “open” of the bypass valve 8,
By the time the actual air-fuel ratio becomes equal to or less than a predetermined value (rich), the bypass valve 8 is “open”, and exhaust gas rich in air-fuel ratio does not enter the lean NOx catalyst 4.

On the other hand, when the air-fuel ratio changes from rich to lean, the bypass valve 8 is changed from “open” to “closed” after the actual air-fuel ratio becomes lean with the air-fuel ratio sensor, as in the conventional control method.
, The exhaust gas rich in the air-fuel ratio is not guided to the lean NOx catalyst 4 in this case as well.

In the present invention, as described above, the bypass valve 8 is “closed” →
The control of “open” is executed early, and the control of “open” → “close” is executed late, thereby preventing the exhaust gas rich in the air-fuel ratio from entering the lean NOx catalyst 4.

〔The invention's effect〕

According to the present invention, a predicting means for predicting an air-fuel ratio rich, and openable and closable, exhaust gas flows to the bypass passage at the time of opening and prevents exhaust gas from flowing to the lean NOx catalyst, and exhaust gas to the lean NOx catalyst when closed. The bypass valve that opens when the air-fuel ratio is predicted to be rich by the prediction means is provided.
Before the actual air-fuel ratio changes from lean to rich, the bypass valve can be switched from “closed” to “open”, and exhaust gas rich in air-fuel ratio can be prevented from being introduced into the lean NOx catalyst. Therefore, the deterioration of the lean NOx catalyst in durability can be suppressed, and NOx can be effectively reduced over a long period of time.

[Brief description of the drawings]

FIG. 1 is a control system diagram of an exhaust gas purification device for an internal combustion engine according to the present invention, FIG. 2 is a device system diagram of an exhaust gas purification device for an internal combustion engine according to an embodiment of the present invention, and FIG. 4 is a block diagram showing the relationship between the ECU, various sensors, and various actuators. FIG. 4 is a control flowchart according to the first embodiment of the present invention. FIG. 5 is a water temperature THW- used in the calculation of step 104 in FIG.
FIG. 6 is an intake pipe pressure PM-leaning correction coefficient KLEANPM map used in the calculation in step 105 of FIG. 4, and FIG. 7 is an engine rotation speed used in the calculation of step 106 in FIG. FIG. 8 is a control flowchart according to a second embodiment of the present invention, and FIG. 9 is a diagram in the case where a change from an air-fuel ratio lean to rich is predicted by the lean correction coefficient KLEAN. Timing chart between throttle opening, target air-fuel ratio, KLEAN, actual air-fuel ratio, opening and closing of bypass valve. Fig. 10 shows timing between throttle opening, air-fuel ratio, bypass opening and closing in a control method that can be considered from the conventional method. Chart. 2 ... internal combustion engine 4 ... lean NOx catalyst 6 ... bypass path 8 ... bypass valve 10 ... operating state detecting means 12 ... air-fuel ratio adjusting means 14 ... predicting means 16 ... fuel injection valve 18 ... empty Fuel ratio sensor 20… ECU 26 …… Crank angle sensor 30 …… Throttle opening sensor 32 …… Intake pipe pressure sensor 34 …… Water temperature sensor 36 …… Intake temperature sensor 38 …… Spark plug

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Toshiaki Tanaka 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (72) Inventor Shinichi Takeshima 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation ( 56) References JP-A-3-74515 (JP, A) JP-A-1-203609 (JP, A)

Claims (1)

(57) [Claims] 1. An operating state detecting means for detecting an operating state of an internal combustion engine, an air-fuel ratio adjusting means for adjusting an air-fuel ratio from an output of the operating state detecting means, and a transition metal or an exhaust gas provided in an exhaust system of the internal combustion engine. Made of zeolite supporting noble metal, in an oxidizing atmosphere, HC
A lean NOx catalyst that reduces NOx in exhaust gas in the presence of gas, a bypass passage that bypasses the lean NOx catalyst, a predictor that predicts an air-fuel ratio rich from the output of the operating state detector, Exhaust gas was flown into the bypass passage and exhaust gas was prevented from flowing into the lean NOx catalyst.When closed, exhaust gas was flown into the lean NOx catalyst and exhaust gas was prevented from flowing into the bypass passage. An exhaust gas purifying apparatus for an internal combustion engine, comprising: