JP2581301B2 - Exhaust gas purification device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention is provided in an exhaust passage of an internal combustion engine,
NO _X catalyst and an exhaust gas purifying apparatus having a three-way catalyst downstream thereof.

(Prior Art) A vehicle exhaust gas purification device detoxifies exhaust gas generated by a vehicle and discharges it into the atmosphere, and plays an important role in protecting the natural environment.

This exhaust gas purification device, for example, a three-way catalyst includes both oxidation-reduction catalysts, and by maintaining the air-fuel ratio in a narrow window region including stoichiometry, the oxidation catalyst removes CO and HC in the exhaust gas.
Reduction catalyst acts to convert the NO _X in the exhaust gas into harmless components, respectively. Moreover, the efficiency of reducing excess oxygen under the three-way catalyst nitrogen oxides in (lean air-fuel ratio) (NO _X) is significantly reduced.

However, the internal combustion engine must supply fuel in accordance with the operating conditions of the engine, and in particular, in order to properly operate the three-way catalyst for purifying exhaust gas, it is necessary to regulate the air-fuel ratio within a narrow window area including stoichiometry. The air-fuel ratio control is always performed to keep the air-fuel ratio at the target value.

This air-fuel ratio control detects the O ₂ concentration in the exhaust gas,
O ₂ feedback control is performed so that the value is maintained within the window area.

Here, the concept of the air-fuel ratio feedback is shown in FIG. In this case, the air-fuel ratio control means swings the feedback coefficient corresponding to the target air-fuel ratio toward the lean side and the rich side around the stoichiometric air-fuel ratio (stoichio) as indicated by the O1 line. As a result, the actual air-fuel ratio swings toward the lean side and the rich side with a delay in phase around the stoichiometric air-fuel ratio (stoichio) as indicated by the O2 line. As a result, the dynamic air-fuel ratio is maintained within a narrow window including stoichiometry (λ = 1).

In the meantime, the required air-fuel ratio of the internal combustion engine differs depending on the load and the engine speed. For example, as shown in FIG. It is desirable to have a cut area, a lean area, a stoichiometric area, and a power area. For this reason, the air-fuel ratio control means sets a target air-fuel ratio according to the driving condition information of the vehicle,
The fuel supply amount is calculated so as to have the same value, and the fuel is supplied by injection. Therefore, every time the target air-fuel ratio changes, the air-fuel ratio of the engine becomes lean and rich.

For example, when the engine continues low-load steady operation, lean operation is desirable for improving fuel efficiency. However, when the lean operation is performed, the exhaust gas also becomes lean, and the exhaust gas goes out of the window region of the three-way catalyst, so that the exhaust gas purifying operation does not work properly. For this reason, in this type of lean burn engine, a lean NO _X catalyst capable of purifying NO _X under a lean atmosphere is disposed upstream of the three-way catalyst, whereby the three-way catalyst is used in the stoichiometric state, and the lean NO _X catalyst is used in the lean state. Exhaust gas purification can be performed accurately with a lean NOx catalyst.

Here, an example of a lean NO _X catalyst capable of reducing NO _X by oxygen excess is disclosed in JP-A-60-125250.

This lean NO _X catalyst is Cu / ZSM5 and HC as reducing agent
And the NO _X purification rate [η _NOX ] is set to HC as shown in FIG.
Varies depending on the / NO ratio. Here, if the HC / CO ratio in the exhaust gas is not more than a predetermined value, the NO _X purification rate [η _NOX ] cannot be sufficiently increased and normal operation cannot be performed. Therefore, the lean NO _X catalyst is provided upstream of the three-way catalyst.

In (INVENTION It is an object) processing, when sequentially arranging the lean NO _X catalyst and the three-way catalyst in the exhaust passage, resulting in the following problems. That is, as shown in FIG. 3, the air-fuel ratio in the initial stage of the air-fuel ratio switching (part A) shifts to the lean side due to the influence of O ₂ stored in the lean NO _X catalyst. This effect continues in minutes of an order, become insensitive to a later point in time O ₂ storage in B, exhibits a stoichiometric.

Thus, in the initial stage of the stoichiometric operation after the lean operation, O ₂ temporarily stored upstream of the catalyst in the exhaust system
As a result, the air-fuel ratio shifts lean (shown by a broken line in FIG. 3), reaches the three-way catalyst, and the purifying action is reduced.

An object of the present invention is to provide an exhaust gas purifying apparatus capable of preventing a reduction in purification efficiency when the exhaust gas air-fuel ratio fluctuates.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a lean NO _X catalyst which is disposed on an exhaust passage and has an O ₂ storage function of purifying NO _X during lean control. A three-way catalyst disposed downstream of the lean NO _X catalyst is provided,
In particular, a bypass is provided that bypasses the lean NO _X catalyst and directly guides the exhaust gas from the upstream of the exhaust passage to the three-way catalyst and that is opened and closed by an on-off valve.The bypass passage is opened only when the exhaust gas air-fuel ratio is lean. Control means for driving the on-off valve so as to close the valve.

(Operation) Since the control means closes the bypass by closing the on-off valve only when the exhaust gas air-fuel ratio is lean, the entire exhaust gas can be supplied to the lean NO _X catalyst when the exhaust gas air-fuel ratio is lean. Exhaust gas from the upstream of the road can be led directly to the three-way catalyst.

(Embodiment) The exhaust gas purifying apparatus shown in FIG. 1 is mounted on an exhaust passage 2 of a gasoline engine 1.

The engine 1 is controlled in fuel supply amount by an engine control unit (hereinafter simply referred to as a controller) 3 so as to adjust and control the current air-fuel ratio to a target air-fuel ratio according to load information and engine speed information at each time. It is configured.

That is, an injector 5 is attached to an intake passage 4 connected to the engine body, and a catalytic converter 8 is attached to an exhaust passage 2 in the middle of an exhaust pipe 7 and a linear air-fuel ratio sensor 9 is provided in front of the catalytic converter.

Inside the catalytic converter 8, a lean NO _X catalyst 10 having an O ₂ storage function is disposed upstream of the exhaust passage 2, and a three-way catalyst 11 is disposed downstream thereof. In particular, the lean NO _X catalyst 10 directly bypasses the lean NO _X catalyst 10. A bypass passage 12 that allows exhaust gas to reach the three-way catalyst 11 is formed. The bypass passage 12 is formed by a pipe 14 which is provided outside the casing 13 of the catalytic converter 8 and is integrally attached thereto. An on-off valve 15 which can open and close the bypass passage 12 is attached in the middle of the pipe 14.

The on-off valve 15 is provided with an actuator 16 which is an air cylinder capable of switching and holding the valve between an open position P1 and a closed position P2. An air source 18 such as high-pressure air is connected to the actuator 16 via a solenoid valve 17.
Are connected to the controller 3.

In the lean NO _X catalyst 10, a catalytically active component is attached to the entire inner wall surface of the monolith-type carrier. Here, the catalytically active component is capable of reducing NO _X by oxygen excess. As shown in FIG. 9, when the HC / NO ratio is equal to or higher than a predetermined value, the NO _X purification rate [η _NOX ] Indicates that the characteristic becomes a high level. That is, the air-fuel ratio of the exhaust gas at that time is under a lean atmosphere,
Moreover, at the activation temperature, NOx is reduced by HC as a reducing agent, and HC and CO are reduced by oxidized HC, and HC and CO are reduced.
It is configured to make CO harmless by oxidation treatment.

In the three-way catalyst 11, a catalytically active component capable of being subjected to an oxidation-reduction treatment in a stoichiometric atmosphere is attached to the entire inner wall surface of the supporting region of the monolithic carrier. When the three-way catalyst 11 has an exhaust gas air-fuel ratio in the vicinity of stoichiometry and is at an activation temperature, HC, CO, NO
_A well-known configuration that can perform a redox treatment of _X and discharge detoxified exhaust gas is adopted.

As the linear A / F sensor 10, for example, a linear A / F sensor as disclosed in JP-A-63-36140 is used.

In the intake passage 4 of the internal combustion engine, a throttle valve 20 is disposed upstream of the injector 5. An accelerator opening sensor 21 serving as load information is attached to the throttle valve 20, and further upstream thereof, an intake air temperature sensor 22, an atmospheric pressure sensor 23, and an intake air flow rate A
An airflow sensor 24 that emits information is provided.

Reference numeral 25 denotes a crank angle sensor that outputs crank information and engine speed information.

The controller 3 is constituted by a microcomputer, the main part of which is a microcomputer. In particular, a drive circuit 301 for receiving the output signals of the above-described sensors and fetching the information in a timely manner or outputting a drive signal to the injector 5 in a timely manner. And an input / output circuit 303 for outputting a control signal to a drive circuit 302 for driving the solenoid valve 17, an exhaust gas control program shown in FIGS. 4 to 6, a main control program, various maps,
It comprises a storage circuit 304 in which characteristic values and the like are written, a control circuit 305 that calculates control values according to each control program, and the like.

In particular, the controller 3 has a function as a control unit that drives the on-off valve 15 so that the bypass passage 12 is closed only when the exhaust gas air-fuel ratio is lean.

Here, the exhaust gas control processing performed together with the fuel injection supply control by the controller 3 will be described with reference to the control programs shown in FIGS.

First, in the main routine, after initial settings (not shown),
The output from each sensor is taken in as driving information, and a predetermined address is updated. In step a2, it is determined whether or not the fuel cut mode is set, by determining the engine speed N and the load θ.
(Based on the output of the accelerator opening sensor), and is calculated based on a driving range calculation map as shown in FIG.

In the fuel cut, proceed to step a3, where the fuel cut flag
The FCF is set, the LF flag indicating the lean area is set to 1, and the process returns to step a1.

If step a5 is reached assuming that the fuel is not cut from step a2, the fuel cut flag FCF is cleared and step a6
move on. Here, the engine speed N and the load θ are taken in, and it is determined whether or not the air-fuel ratio feedback condition is satisfied. When the air-fuel ratio feedback condition is not satisfied, for example, in a transient operation range such as a power operation range, the current operation information is obtained. The process proceeds to step a7 in order to perform air-fuel ratio control in an open loop based on.

Here, the stoichiometric feedback flag SFB and the lean flag LF are cleared, and the process reaches step e9.

Here, an address for calculating the enrichment coefficient KMPA, which is an air-fuel ratio correction coefficient, according to the load information A / N of the vehicle and the engine speed N based on a map (not shown) and storing the air-fuel ratio.
Input processing to KAF.

Then, in step a10, other fuel injection pulse width correction coefficients KDT and correction values TD are set according to the operation state, and the process returns to step a1.

Assuming that the air-fuel ratio feedback control condition is satisfied from step a6, when step a11 is reached, the engine speed N and the load θ are fetched, and based on the operating range calculation map as shown in FIG. If it is determined that the vehicle is under the lean operation condition, the process proceeds to step a12.

Here, the stoichiometric feedback flag SFB is cleared, the lean flag LF is set to 1, and the process proceeds to step a14.

Here, a target air-fuel ratio (A / F) is set according to the load information A / N and the engine speed N, and a base lean coefficient KLEAN is set according to the values. Further, a deviation ΔAF between the air-fuel ratio signal Vout of the air-fuel ratio sensor and the target air-fuel ratio data is calculated. Further, in steps a16 and a17, a known PID process is performed on the deviation ΔAF, a lean feedback coefficient KLFB is set, and a value obtained by multiplying the base lean coefficient KLEAN by the lean feedback coefficient is stored in an address KAF storing the air-fuel ratio. Then, proceed to step a10.

In step a10, the other fuel injection pulse width correction coefficient K
Set DT and correction value TD according to the operating state, and
Return to

If it is not lean in step a11, step a18 on the stoichiometric feedback control side is reached.

Here, the stoichiometric flag SFB is set to 1, the lean flag LF is cleared, and the process reaches step a20.

Here, the target air-fuel ratio is stoichiometric, and the set value KSFB
Is stored in the address KAF, the process proceeds to step a10, and returns to step a1.

During such a main routine, an injector driving routine shown in FIG. 5 and an exhaust gas control routine shown in FIG. 6 are performed.

In the injector drive routine, when step b1 is reached by a crank pulse interruption, the intake air amount A / N and the engine speed N are fetched, the fuel cut flag FCF returns when it is 1, and returns to 0, and proceeds to step b3. Here, setting the basic fuel pulse width T _B according to the intake air quantity A / N, to calculate the main pulse width data _{Tinj = T B × KAF × KDT} + TD, the process proceeds to step b5.

In step b5, Tinj is set to the driver for driving the injector, the driver is triggered, fuel injection is performed, and the routine returns.

In the non-gas control routine, when step c1 is reached by a predetermined crank pulse interruption, it is determined whether or not the LE flag has changed from 1 to 0 based on the previous value and the current value of the LE flag. Goes to step c3, and if it has changed, goes to step c2. If there is no change and the process reaches step c3, it is determined here whether or not the LE flag has changed from 0 to 1 based on the previous value and the current value of the LE flag. Step c4 when there is a change
Proceed to.

When step c4 is reached assuming that the LE flag has changed to 1, the output to the on-off valve 15 is turned on, the bypass path 12 is closed,
After all exhaust gas has been led to the lean NO _X catalyst 10, the three-way catalyst 11
Performs a process of supplying to the NO _X in the exhaust gas are lean and reduced under a lean atmosphere, carried out further not be clean HC, and oxidizing the CO by the three way catalyst.

On the other hand, when it is determined in step c1 that the air-fuel ratio has changed from lean to stoichiometric and the flow reaches step c2, the output to the on-off valve 15 is turned off and the bypass passage 12 is opened.
As a result, the exhaust gas branches and passes through the bypass passage 12,
Immediately after that, the amount reaching the three-way catalyst 11 increases.

This makes it possible to eliminate the lean exhaust gas (see the broken line in FIG. 3) due to the O ₂ storage action of the lean NO _X catalyst 10 immediately after switching from lean to stoichiometric. reaching the catalyst 11, where NO _X reduction and HC, oxidation of CO becomes possible to be performed properly, it can prevent a reduction in the purification rate of the exhaust gas.

In the above-described process, the switching of the on-off valve 15 takes in the engine speed N and the load θ, and sets the lean range, the stoichiometric range, and the acceleration range based on the operating range calculation map. The exhaust gas control routine may be simply performed so that the bypass is closed only when the exhaust gas air-fuel ratio is in the lean region.

Furthermore, inside the lean NO _X catalyst 10 and accommodating a three-way catalyst 11, the mounting pipe 14 is integrally constituting the bypass passage 12 to the casing 13 of the catalytic converter 8 the exhaust gas purifying apparatus of Figure 1 is the catalytic converter 8 Instead of this,
The arrangement shown in FIG. 7 may be adopted. In this case, the lean NO _X catalyst 10 and the three-way catalyst 11 are arranged in this order at predetermined intervals in the exhaust pipe 7. Then, a bypass pipe 27 is arranged so as to bypass the casing 26 of the lean NO _X catalyst 10, and an inlet and an outlet of the bypass pipe 27 are communicated with the exhaust pipe 7. Also in this case, the on-off valve 15 controlled by the controller 3 is provided in the middle of the bypass pipe 27 so as to open and close the bypass passage 12 in a timely manner. Also in this case, the first
The same operation and effect as those of the exhaust gas purifying apparatus shown in the figure can be obtained.

As described above, according to the present invention, only when the exhaust gas air-fuel ratio is lean, the entire exhaust gas leaned by closing the bypass with a simple structure is reduced to the lean NO _X catalyst 10 and the three-way downstream thereof. It led to the catalyst 11, detoxification can, at the time of variation of the stoichiometric by lean, direct exhaust gas through the bypass passage, and supplies the three-way catalyst, the effect of lean of the exhaust gas by the O ₂ storage effect of the lean NO _X catalyst receiving the exhaust gas stoichiometric atmosphere is supplied to the three-way catalyst 11 not, where NO _X reduction and HC, will be properly perform the oxidation treatment of CO, it can prevent a reduction in the purification rate of the exhaust gas.

[Brief description of the drawings]

FIG. 1 is a schematic overall configuration diagram of an exhaust gas purifying apparatus as an embodiment of the present invention, FIG. 2 is a characteristic diagram of an operating range calculation map incorporated in the above-mentioned device controller, and FIG. FIG. 4 to FIG.
FIG. 7 is a flowchart of control programs for main, exhaust gas purification, and injector driving performed by the controller of the above device. FIG. 7 is a schematic layout diagram of main parts of an exhaust gas control device as another embodiment of the present invention. FIG. 9 is an air-fuel ratio change characteristic diagram of the device, and FIG. 9 is a purification rate characteristic diagram of the lean NO _X catalyst. 1 ... engine, 2 ... exhaust path, 3 ... controller,
8: Catalytic converter, 9: Linear air-fuel ratio sensor, 10
...... lean NO _X catalyst, 11 ...... three-way catalyst, 12 ...... bypass passage, 15 ...... off valve.

Claims (1)

(57) [Claims] 1. A lean NOx disposed on an exhaust passage and having an O ₂ storage function for purifying NOx during lean control.
In an exhaust gas purifying apparatus provided with a catalyst and a three-way catalyst disposed downstream of the lean NOx catalyst,
Bypassing the exhaust gas from the upstream of the exhaust passage to the three-way catalyst by bypassing the NOx catalyst and providing a bypass passage opened and closed by an on-off valve, and opening and closing the bypass passage so as to close the bypass passage only when the exhaust gas air-fuel ratio is lean. An exhaust gas purifying apparatus comprising: a control unit that drives a valve.