JPH03225013A - Exhaust purifying device for internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent the intrusion of the exhaust rich in air-fuel ratio into a lean NOx catalyst, by installing an estimating means which stimates an air- fuel ratio rich state from the output of an operation state detecting means and opens a bypass passage. CONSTITUTION:An air-fuel ratio adjusting means 12 adjusts the air-fuel ratio by the output of an operation state detecting means 10. A lean NOx catalyst 4 is installed in the exhaust system of an internal combustion engine 2, and consists of the zeolite loading the transition metals or precious metals, and reduces the NOx in the exhaust gas under the presence of HC in the oxidation environment. In this case, an estimating means 14 for estimating the air-fuel ratio rich state from the output of the operation state detecting means 10 is installed, a bypass valve 8 is controlled so that a bypass passage 6 for bypassing the catalyst 4 is opened, when the air-fuel ratio rich state is estimated. Accordingly, even if a certain time is necessary for setting the bypass valve 8 from a closed state to an opened state, the bypass valve 8 is put into opened state when the air-fuel ratio becomes rich, and the intrusion of the exhaust rich in air-fuel ratio into the catalyst 4 is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention is directed to the production of NOx in the exhaust system of a lean-burn internal combustion engine in the presence of HC (unburnt hydrocarbons) in an oxidizing atmosphere (oxygen-excess atmosphere). The present invention relates to an exhaust gas purification device equipped with a zeolite-based catalyst that can be reduced, and particularly relates to an exhaust gas purification device that prevents durability deterioration of the catalyst.

[Conventional technology]

Recently, in order to improve fuel efficiency, the development of lean-burn internal combustion engines that burn at a lean air-fuel ratio has been progressing, and some of them have been put into practical use. In the lean air-fuel ratio region, conventional catalysts cannot purify NOx, so reducing NOx is a challenge for lean-burn engines.
Catalysts that can purify are attracting attention.

Japanese Unexamined Patent Publication No. 1-130735, Japanese Patent Application No. 1983-9502
No. 6 is made of zeolite supported with transition metals,
It teaches a catalyst that reduces NOx in the presence of HC in an oxidizing atmosphere (hereinafter referred to as a lean NOx catalyst).

In addition, since the lean NOx catalyst deteriorates when placed in a reducing atmosphere, that is, in an atmosphere with a rich air-fuel ratio, when the air-fuel ratio sensor determines that the air-fuel ratio is rich,
It has been proposed to introduce secondary air to create an oxidizing atmosphere (Japanese Unexamined Patent Publication No. 1999-203609).

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

[Problem to be solved by the invention]

However, if the air-fuel ratio sensor detects the actual air-fuel ratio and based on it determines that the air-fuel ratio is rich, then if the bypass valve is switched to the bypass passage open side, the air-fuel ratio will be lower due to the control delay/bypass valve operation delay.

A part of the hot exhaust gas is introduced into the lean NOx catalyst, and this is not a sufficient measure against catalyst durability deterioration and NOx increase.

This will be explained in more detail with reference to FIG. 10, taking as an example a case where the state changes 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, 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). The bypass valve is controlled to be open when
Part II '<8 Due to the delay (ECU - bypass valve) and the operation time of the bypass valve "close" and "open", it takes time for the bypass to "open", and during this time, the exhaust gas with a rich air-fuel ratio becomes a lean NOx catalyst. This will lead to accelerated deterioration of the durability of the catalyst.

The present invention "opens" the bypass earlier than conventional control methods when the air-fuel ratio is expected to change from lean to rich.
The purpose is to prevent NOx from being introduced into the catalyst from exhaust air with a rich air-fuel ratio, and to suppress deterioration in the durability of the catalyst.

[Means to solve the problem]

In order to achieve the above object, the exhaust gas purification device for an internal combustion engine of the present invention, as shown in FIG. an air-fuel ratio adjustment means 12 that adjusts the air-fuel ratio; and an air-fuel ratio adjustment means 12 that is provided in the exhaust system of the internal combustion engine 2 and is made of zeolite that supports a transition metal or a noble metal, and is
A catalyst that reduces NOx in exhaust gas in the presence of HC, a so-called lean NOx catalyst 4, a bypass passage 6 that bypasses the lean NOx catalyst 4, and a prediction means 14 that predicts an air-fuel ratio richness based on the output of the operating state detection means 10. and a bypass valve 8 that opens the bypass passage 6 when the air-fuel ratio is predicted to be rich by the prediction means 14.

[Effect]

The prediction means 14 predicts that the air-fuel ratio will become lean in the following cases, for example.

(a) When lean correction coefficient KLEAN≧1.0.

However, KLEAN corresponds to the control target air-fuel ratio and is calculated based on the operating state of the engine.

(b) When throttle opening TA is above a predetermined value, or OTP increase (overtemperature protection increase)
When there is.

(c) During acceleration.

(d) When cold or during warm-up (increase in water temperature, etc.).

When the prediction means 14 predicts that the air-fuel ratio will change from lean to rich, 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," by the time the actual air-fuel ratio falls below a predetermined value (rich), the bypass valve 8 will be "open". The exhaust gas with rich air-fuel ratio is the lean NOx catalyst 4.
It never enters.

As described above, in the exhaust purification device of the present invention, the bypass valve 8
By executing the "close"-"open" control early, exhaust gas with a rich air-fuel ratio is prevented from entering the lean NOx catalyst 4, durability deterioration of the lean NOx catalyst 4 is suppressed, and NO
x is effectively reduced over a long period of 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 installed in the exhaust system of an internal combustion engine 2 consisting of a gasoline engine or a diesel engine.
and a bypass passage 6 that bypasses the lean NOx catalyst 4.
And the exhaust is lean N.

A bypass valve 8 that switches between the X catalyst 4 and the bypass passage 6, an air-fuel ratio sensor 18 provided upstream of the lean NOx catalyst 4, and a three-way catalyst or An oxidation catalyst 22 is provided.

A throttle/nottle valve 28 is provided in the intake system of the internal combustion engine 2, and the opening degree of the throttle valve 28 is detected by a throttle/nottle opening sensor 30.

An intake pipe pressure sensor 32 is provided downstream of the throttle valve 28, and an intake temperature sensor 36 is provided in the intake system as necessary.
is provided.

Each intake boat (in the case of a diesel engine, each cylinder) connected to each cylinder of the internal combustion engine 2 is provided with a fuel injection valve 16 . For spark ignition engines, each cylinder has 38 spark plugs.
40 is an igniter, and 24 is a distributor that distributes 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 2G for detecting the engine rotation speed and crank angle is provided inside the distributor 24. Note that a water temperature sensor 34 for detecting the temperature of the cooling water of the internal combustion engine 2 is also provided.

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

As shown in FIG. 3, the engine control computer 20 includes a central processor (CPU) 20a that executes calculations, a read-only memory (ROM) 20b, and a random access memory (RAM) for storing time. ) 20c, an input interface 20d1 for analog signals, an A/D converter 20e for converting analog signals into digital signals, an input interface 20r1 for digital signals, and an output interface 20g, and is supplied with power from a constant voltage power supply 20h.

The outputs of the intake pipe pressure sensor 32, water temperature sensor 34, intake temperature sensor 36, and air-fuel ratio sensor 18 are input to the input interface 20d, and the outputs of the crank angle sensor 26 and throttle opening sensor (in the case of digital signals) 30 are input to the input interface. 20f. CPU20a
Then, the calculations described later are performed, and the output is sent to each fuel injection valve (injector) 1 via the output interface 20g.
6. Bypass control, transmitted to control valve 8, etc., and controls 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, every 180' CA (crank angle) based on the rack crank angle from the crank angle sensor 26.

In step 101, the herring 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, in step 102, a basic fuel injection amount Tp is calculated from the intake pipe pressure and engine rotation speed so that the air-fuel ratio becomes the stoichiometric air-fuel ratio.

Next, an operation is performed to correct the basic fuel injection amount according to operating conditions such as water temperature and intake air temperature. First, in step 103, the output THW from the water temperature sensor 34 or the output THA from the intake air temperature sensor 36 is read.

Next, in step 104, increase the water temperature (or intake air temperature) F.
Calculate WL. The water temperature increase is an increase in fuel injection to improve drivability during warm-up, and is determined by, for example, the THW-FWL map shown in FIG.

The basic fuel injection amount Tp is also corrected based on the engine rotational speed NE and the intake pipe pressure PM. In step 105, LEANPM is set as the lean correction coefficient for the intake pipe pressure.
For example, PM-KLEANPl! shown in FIG. Find it from the map. Next, in step 106, a lean correction coefficient KLEANNE for the engine speed NE (corresponding to the calculated target air-fuel ratio) is calculated from the NE-KL4ANNE map shown in FIG. 7, for example.

In addition, the fuel injection amount may be increased for acceleration, increased at high throttle opening, and increased to prevent catalyst overheating, which may be necessary when installing a catalyst. In step 108, eight P
It enters when M>α (α is a constant value), and the acceleration increase FACC is calculated from 8PM in order to improve the torque during acceleration.

Step 109 enters when the throttle opening degree TA>C (C is a constant value), and in order to improve the output at a high throttle opening degree, the increased amount FPOWER at a high throttle opening degree is calculated from the throttle opening degree TA. In step 110, a catalyst overheat prevention increase OTP (overtemperature protection) is determined from the intake air amount Q/N per engine rotation and the engine rotation speed NE.

After the lean correction coefficient KLEAN and various increases are calculated, the process proceeds to step 111 to correct the fuel injection amount.

The fuel injection amount TAU is calculated from the following equation.

TAU=Tp-KLEAN-FWL (1+FACC+FPOWER+0TP) Next, proceed to step 112, set TAtJ,
Executes fuel injection only at TAU.

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

If it is not being bypassed in step 113, that is,
If F=1 not, steps 114.115.116
, 117.11B to predict whether the air-fuel ratio will be rich or not. That is, in step 114, if there is an increase in water temperature, such as during cold time or warm-up, FWL
>1.0, it is predicted that the air-fuel ratio will be rich. In step 115, it is predicted whether the air-fuel ratio will become richer based on the lean correction coefficient KLEAN. However, K.L.E.
There is a relationship between AN = stoichiometric air-fuel ratio/target air-fuel ratio, and KLEA
If N > 1.0, the air-fuel ratio is expected to be rich, and KLE
If AN≦1.0, the air-fuel ratio is expected to be lean. In step 116, if the acceleration increase is positive, that is, F
If ACC>0, it is expected that the air-fuel ratio will become rich. In step 117, if the output correction at high throttle opening is positive, that is, if FPOWER>0, it is predicted that the air-fuel ratio will become rich. In step 118, if the catalyst overheat prevention increase is positive, that is, if OTP>0, then the air/fuel ratio is predicted to be 7. In the above, at least one of steps 114, 115, 116, 117, and 118 constitutes the prediction means 14 that predicts that the air-fuel ratio will change from lean to rich.

If the air-fuel ratio is expected to become rich in any of steps 114, 115, 116, 117. Performs execution processing. In other words, even if it takes some time for the bypass valve 8 to open, it takes more time for the air-fuel ratio to actually become rich after the air-fuel ratio is expected to become rich. After the bypass valve 8 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 "opens" execution process in step 123 is completed, step Proceeding to step 124, the bypass determination flag XF is set to 1 to indicate that bypass is in progress.

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 is set to a predetermined value. Determine whether it is large or not. If A/F>b is not determined in step 122, the air-fuel ratio is rich, so the process proceeds to step 123, and the bypass valve 8 is
Then, proceed to step 124 and leave the bypass determination flag XF at 1.

If A/F > b in step 122, that is, if the actual air-fuel ratio changes from rich to lean, step 1
Proceeding to step 19, the bypass valve 8 is "closed". Therefore, when the air-fuel ratio changes from rich to lean, the process to close the bypass valve 8 is not performed based on the expectation that the air-fuel ratio will change from rich to lean, but based on the actual air-fuel ratio change. - This is done by determining that the air-fuel ratio has changed from deep to lean. Therefore, the bypass valve 8 is closed after the actual air-fuel ratio changes to lean, so exhaust gas with a rich air-fuel ratio is introduced into the lean NOx catalyst 4. There is no problem, so proceed to step 120 and set the Nominox judgment flag XF to 0 (.

FIG. 8 shows an arithmetic routine according to the second embodiment of the present invention, in which steps different from the first embodiment are numbered in the 200s, and steps corresponding to the first embodiment are the same as the first embodiment. It is indicated by a number. In the first embodiment, switching the bino gas valve 8 to "close" when the air-fuel ratio changes from rich to lean was performed after the actual air-fuel ratio became lean, whereas in the second embodiment, , K=KLEAN-FWL (1+FACC+FPOWER+FOTP)>1.0, that is, after a predetermined period of time has elapsed since the air-fuel ratio was expected to be on the whole.

More specifically, in the second embodiment, when it is determined that the steering knob 113 is in bypass (XF=1), step 20
1, and determines whether K>1.0. If K>1.0 is not the case, that is, if the air-fuel ratio is expected to be lean overall, the process proceeds to step 202 via step 2.
Proceed to step 03 and count up the time elapsed CLEAN one by one. CLEAN increases by interrupting the routine every 180° crank angle and repeatedly executing the calculation, and in the interrupt calculation where CLEAN becomes larger than the predetermined value e, that is, in the calculation after a predetermined time elapses,
When CLEAN>e in step 202, it is assumed that the air-fuel ratio has changed from lean to rich, and step 20
5, proceed to step 119, and bypass valve 8 "close".
Perform execution processing. Steps 203 and 202 are prediction means 1
4. In other cases, the process proceeds to the steering knob 123 and the bypass valve 8 remains open.

Steps 204 and 205 are steps for keeping CLEAN at 0 or clearing it to O. The rest is the same as in the first embodiment.

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

For example, when driving in the following manner: steady running → acceleration - deceleration Constant running (A/F lean) (rich) (lean) (lean), the throttle opening TA changes as shown in the top row of Figure 6. become.

At this time, the control target air-fuel ratio (lean correction coefficient KLEAN
As shown in the 2nd and 3rd rows from the top of Figure 6, these are determined from the engine operating conditions and the signals from various sensors, so some control is required, such as detection delays and calculation time. There is a delay.

To achieve the above target air-fuel ratio, the ECU 20 sends a signal to the fuel injection valve 16 to inject fuel, and the fuel passes through the intake boat and enters the cylinder. Since the exhaust gas passes through the exhaust system and reaches the air-fuel ratio sensor 18, it takes a considerable amount of time until the air-fuel ratio sensor 18 detects the actual air-fuel ratio.Therefore, the actual air-fuel ratio (detection by the air-fuel ratio sensor 18) is delayed, as shown in the fourth row from the top of 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", so the control delay (ECLI~ As mentioned above, it takes time for the bypass valve to close and open until the bypass opens, and during this time, exhaust gas with a rich air-fuel ratio enters the lean NOx catalyst. It is.

However, in the present invention, as shown in the bottom row of FIG.
Send the l11m signal to open. therefore,
Even if it takes some time to close and open the bypass valve 8, by the time the actual air-fuel ratio falls below a predetermined value (rich), the bypass valve 8 will be open and the air Exhaust gas with a rich fuel ratio never enters the lean NOx catalyst 4.

On the other hand, when the air-fuel ratio changes from rich to lean,
Similar to the conventional control method, the bypass valve 8 is switched between "open" and "close" after the actual air-fuel ratio becomes lean using the air-fuel ratio sensor.
Since the control is performed, exhaust gas with a rich air-fuel ratio is not led to the lean NOx catalyst 4 in this case as well.

In the present invention, as described above, the bypass valve 8 "closed" = "open"
By executing the control early (and executing the control between "open" and "close" late), it is possible to prevent exhaust gas with a rich air-fuel ratio from entering the lean NOx catalyst 4.

〔Effect of the invention〕

According to the present invention, a prediction means for predicting air-fuel ratio richness;
A bypass valve is provided that opens the bypass passage when the air-fuel ratio is predicted to be rich by the prediction means, so the bypass valve can be closed before the actual air-fuel ratio changes from lean to rich.
It can be switched from ``open'' to ``lean N'' for exhaust with a rich air-fuel ratio.

It can be prevented from being introduced into the X catalyst. Therefore, durability deterioration of the lean NOx catalyst can be suppressed, and NOx can be effectively reduced over a long period of time.

[Brief explanation of 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 an equipment system diagram of an exhaust gas purification device for an internal combustion engine according to an embodiment of the present invention, and FIG. Among them, 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, and FIG. 5 shows the water temperature T used in the calculation of step 104 in FIG. 4.
HW - water temperature increase FWL map diagram, Figure 6 is the intake pipe pressure PM - lean chemical engineering positive coefficient 'LE, ANPM map diagram used in the calculation of step 105 in Figure 4, Figure 7 is the map diagram of step 106 in Figure 4. Engine rotational speed NE - lean correction coefficient KLEANNE map diagram used in calculations, Fig. 8 is a control flowchart according to the second embodiment of the present invention, and Fig. 9 shows air-fuel ratio from lean to rich using lean correction coefficient KLEAN. Throttle opening when predicting changes in
Target air-fuel ratio, KLEAN, actual air-fuel ratio, timing chart between opening and closing of the bypass valve, Figure 10 is a timing chart between throttle opening, air-fuel ratio, bypass opening and closing, in the control method considered from the conventional method. be. 2...Internal combustion engine 4...Lean NOx catalyst 6...Bypass passage 8...Bypass valve lO...Operating state detection means 12. ... Air-fuel ratio adjustment means 14 ... Prediction means 16 ... Fuel injection valve 18 ... Air-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 permission Applicant Toyota Motor Corporation Fig. 1 Fig. 5 Fig. 4 rsw No. Figure 6 Figure 7 + NE

Claims (1)

[Scope of Claims] 1. An operating state detecting means for detecting the operating state of the internal combustion engine; an air-fuel ratio adjusting means for adjusting the air-fuel ratio based on the output of the operating state detecting means; provided in the exhaust system of the internal combustion engine; It is made of zeolite supported with transition metals or noble metals, and in an oxidizing atmosphere, H
A catalyst that reduces NOx in exhaust gas in the presence of C, a so-called lean NOx catalyst, a bypass passage that bypasses the lean NOx catalyst, a prediction means for predicting an air-fuel ratio richness based on the output of the operating state detection means, and a prediction means. An exhaust purification device for an internal combustion engine, comprising: a bypass valve that opens a bypass passage when an air-fuel ratio is predicted to be rich.