JP3485076B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purification device for an internal combustion engine, which purifies harmful components in exhaust gas discharged from the internal combustion engine capable of lean burn.

[0002]

2. Description of the Related Art Emission from an internal combustion engine capable of lean combustion
As an exhaust gas purification device that purifies NOx from exhaust gas,
There are NOx catalysts such as a NOx reduction catalyst. NOx catalyst
Cleans the generated NOx before releasing it to the atmosphere
And the air-fuel ratio of the inflowing exhaust gas is lean (immediately
When it is in an oxygen excess atmosphere), it absorbs NOx and flows in.
NOx absorbed when the oxygen concentration of the exhaust gas decreases
To release. Also, the fuel contains sulfur (S)
And when the sulfur in the fuel burns, SO₂ And SO ₃ Na
Which sulfur oxide (SOx) is generated and NOx catalyst is exhausted
It also absorbs these SOx in the gas. Touch NOx like this
The SOx absorption mechanism of the medium is almost the same as the NOx absorption mechanism.
It is considered to be almost the same.

For example, the NOx storage reduction catalyst absorbs NOx (SOx) when the air-fuel ratio of the inflowing exhaust gas is lean and absorbs Nx when the oxygen concentration of the inflowing exhaust gas decreases.
It is a catalyst that releases Ox (SOx) and reduces it to N ₂ (S0 ₂ ).

When this NOx storage reduction catalyst is used for exhaust gas purification of an internal combustion engine, the NOx in the exhaust gas is absorbed by the NOx catalyst because the air-fuel ratio of the exhaust gas during normal operation is lean in the internal combustion engine. become. However, if the exhaust gas with a lean air-fuel ratio is continuously supplied to the NOx catalyst,
When the NOx absorption capacity of the NOx catalyst reaches saturation, and beyond that,
NOx cannot be absorbed and NOx is leaked. Therefore, in the NOx storage reduction catalyst, a fuel (HC component), for example, is added to the exhaust passage as a reducing agent at a predetermined timing before the NOx absorption capacity is saturated to make the inflow exhaust gas air-fuel ratio rich. It is necessary to extremely reduce the concentration and release the NOx absorbed by the NOx catalyst to reduce it to N ₂ to restore the NOx absorbing ability of the NOx catalyst.

Therefore, conventionally, the time when the NOx (SOx) absorption capacity becomes saturated (timing at which fuel can be added), the amount of added fuel, and the operating time, rotational speed, etc. are set so that the optimum pattern is obtained in advance. The fuel is set in advance in association with the operating state, and the addition amount of the fuel added in the exhaust gas according to the operating state based on the pattern is added at a predetermined time.

[0006]

By the way, even if the fuel addition is carried out based on the set value in the optimum pattern adapted in advance, the amount of the fuel added and the timing of the addition may be changed due to various system variations and equipment deterioration. An error may occur and the addition of fuel may not always be the optimum pattern. Also,
The NOx (SOx) absorption capacity of the NOx catalyst changes depending on the activation temperature of the catalyst and the aged deterioration of the catalyst. Therefore, when the catalyst is cooled by the outside air or the catalyst is deteriorated, the absorption capacity of the catalyst is lowered, and the absorption capacity of the catalyst is slightly varied.

As described above, even if the addition amount and the addition timing based on the set value are performed, the actual addition may be different from the optimum addition amount and timing, and in this case, NOx is added.
Absorption and release of (SOx) is not performed accurately.

From the above, the present invention has been made in view of the above-mentioned problems, and in the system for reducing the stored NOx and recovering the poisoned SOx by adding the reducing agent to the NOx catalyst from the exhaust passage. It is a technical object to provide an exhaust gas purification device for an internal combustion engine that performs optimal addition of a reducing agent without being affected by the occurrence of various variations and the like.

[0009]

In order to achieve the above object, the exhaust gas purifying apparatus for an internal combustion engine of the present invention employs the following means. That is, the exhaust gas purification apparatus for an internal combustion engine of the present invention comprises a NOx catalyst provided in the exhaust passage of a multi-cylinder internal combustion engine capable of lean combustion, and a reducing agent addition means provided in the exhaust passage upstream of the NOx catalyst. An addition that the reducing agent adding means adds from the actual air-fuel ratio in the operating state of the vehicle, the intake air amount to the internal combustion engine, and the catalyst-containing gas temperature that is the temperature of the exhaust gas flowing into the NOx catalyst. When adding the reducing agent of the added reducing agent amount from the reducing agent adding means to the reducing amount calculating means for calculating the reducing agent amount to the NOx catalyst, the air-fuel ratio changes from the lean state immediately before the reducing agent addition to the reducing agent addition. Depth calculation means for calculating the rich depth which is the displacement amount until the maximum rich state, and the displacement amount by changing the air-fuel ratio to the lean state from the value which became the maximum rich state after adding the reducing agent. In From the time calculating means for calculating the time required to reach a lean state of a value multiplied by the ratio, the rich depth calculated by the depth calculating means and the time calculated by the time calculating means, and the added reducing agent. The addition amount correction means for correcting the amount to calculate the next addition reducing agent amount, and the reducing agent addition interval from the addition of the reducing agent to the next addition of the reducing agent, the rich depth obtained by the depth calculation means. Based on the interval calculation means for calculating the amount of added reducing agent, the amount of added reducing agent for the next time corrected by the addition amount correction means, and the interval for addition of the reducing agent for the next time calculated by the interval calculation means. And a control means for controlling.

According to this structure, since the addition amount is calculated in consideration of the actual air-fuel ratio, the intake air amount, and the temperature of the gas containing the catalyst, the optimum addition of the reducing agent is not affected by the occurrence of various system variations. Can be carried out. The reducing agent may be an HC (hydrocarbon) component, and for example, a fuel can be used. In addition, the amount of added reducing agent to be added next is corrected from the value of the air-fuel ratio (rich depth) after addition of the reducing agent and the time (time constant) for which the value of this air-fuel ratio changes to the value of the predetermined air-fuel ratio. By calculating the next addition interval, it is possible to compensate for the dispersion and deterioration of the reducing agent addition system, catalyst, etc. even after the second addition.
It becomes possible to perform air-fuel ratio control in which absorption and release of (SOx) are accurately performed.

When the time is calculated by the time calculating means, the predetermined ratio by which the displacement amount is multiplied is preferably 63% as a result of an experiment in consideration of the correction of the amount of the added reducing agent to be added next time. There is.

In the exhaust gas purifying apparatus for an internal combustion engine according to the present invention, the reducing agent addition interval is configured to be proportional to the magnitude of the rich depth obtained by the depth calculating means. Is properly performed, and more efficient air-fuel ratio control becomes possible.

Further, the exhaust gas purifying apparatus for an internal combustion engine according to the present invention may be configured to have a propriety judging means for judging whether or not the reducing agent should be added according to the operating state of the vehicle.
It is preferable that the propriety determination means is configured to determine whether the addition of the reducing agent is a single injection in which the entire amount of the reducing agent is injected at one time. Since this single injection (addition pattern) differs depending on the amount of addition, it is necessary for the control means to periodically relearn to an appropriate addition pattern according to the addition amount. In particular, during normal operation, the amount of fuel added is inevitably large because the HC component in the exhaust gas is extremely low. Therefore, during normal operation, it is desirable that the control means relearn to the addition pattern when the addition amount is large.

Further, when the addition amount is calculated, the gas amount containing the catalyst may be used instead of the intake air amount, and the exhaust manifold temperature may be used instead of the gas temperature containing the catalyst.

In the present invention, examples of the lean burn internal combustion engine include a direct injection type lean burn gasoline engine and a diesel engine.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, an exhaust emission control system for an internal combustion engine according to an embodiment of the present invention will be described in detail with reference to FIGS. The embodiment described below is a mode in which the present invention is applied to a vehicle-driving diesel engine as an internal combustion engine.

First, an exhaust gas purification apparatus for an internal combustion engine according to an embodiment will be described with reference to FIG. Engine 1
As shown in the overall configuration of FIG. 1, it is an in-line 4-cylinder diesel engine, and an intake manifold 2 is provided in the combustion chamber of each cylinder.
And intake air is introduced via the intake pipe 3. An air cleaner 4 is provided at the start end of the intake pipe 3, and an air flow meter 5, a compressor 6a of a turbocharger 6, an inter clerk 7, and a throttle valve 8 are provided in the middle of the intake pipe 3.

The air flow meter 5 outputs an output signal corresponding to the amount of fresh air flowing into the intake pipe 3 via the air cleaner 4 to an electronic control unit for engine control (hereinafter, referred to as E).
(Abbreviated as CU) 9 and ECU 9 outputs the air flow meter 5
The intake air amount Ga is calculated based on the output signal of.

Fuel (light oil) is injected from the fuel injection valve 10 into the combustion chamber of each cylinder of the engine 1.
This fuel is pumped up from a fuel tank (not shown) by the fuel pump 12 and supplied to the fuel injection valve 10 via the common rail 11. The fuel pump 12 is driven by a crankshaft (not shown) of the engine 1. The valve opening timing and the valve opening period of each fuel injection valve 10 are controlled by the ECU 9 according to the operating state of the engine 1.

Exhaust gas produced in the combustion chamber of each cylinder of the engine 1 is exhausted to the exhaust manifold 14 from the exhaust port 13 of each cylinder. Here, for convenience of explanation, the cylinder number of the engine 1 is set to the cylinder arranged at the right end in the figure as the first cylinder, and the cylinders arranged at the left end in the figure as the second cylinder and the third cylinder in order to the left. Is the fourth cylinder. An exhaust collecting pipe 15 that guides the exhaust gas to the turbine 6b of the turbocharger 6 is connected to a portion of the exhaust manifold 14 that faces the fourth cylinder. The turbine 6b is driven by the exhaust gas, and drives the compressor 6a connected to the turbine 6b to boost the pressure of intake air.

Exhaust gas is discharged from the turbine 6b to the exhaust pipe 16 and discharged to the atmosphere through a muffler (not shown). A casing 18 that accommodates a NOx storage-reduction type NOx catalyst (hereinafter abbreviated as NOx catalyst) 17 is provided in the middle of the exhaust pipe 16. The NOx catalyst 17 will be described later.

Further, the cylinder head 30 of the engine 1 is provided with a fuel addition nozzle 19 which faces the exhaust port 13 of the fourth cylinder and injects a reducing agent (fuel is used in this embodiment). . The fuel pumped up by the fuel pump 12 can be supplied to the fuel addition nozzle 19 through the fuel pipe 20 and the fuel passage 21 provided in the cylinder head 30.
The addition amount is controlled by the control valve 22 provided on the way. The control valve 22 is controlled by the ECU 9 to open and close and control the opening.

The fuel addition nozzle 19 is attached so that fuel is injected toward the exhaust collecting pipe 15. Further, in this embodiment, the fuel pump 12,
Fuel addition nozzle 19, fuel pipe 20, fuel passage 21,
The control valve 22 constitutes a reducing agent adding means.

An end of an exhaust gas recirculation pipe (hereinafter abbreviated as an EGR pipe) 23 for returning a part of exhaust gas to the intake system is connected to a portion of the exhaust manifold 14 facing the first cylinder. The other end of the EGR pipe 23 is connected to the intake manifold 2. In the middle of the EGR pipe 23, EGR
A cooler 24 and an EGR valve 25 are provided. The opening of the EGR valve 25 is controlled by the ECU 9 according to the operating state of the engine 1 to control the exhaust gas flow rate. EGR pipe 23
The EGR cooler 24 and the EGR valve 25 constitute an exhaust gas recirculation device (EGR).

In this EGR, a part of the exhaust gas is returned to the intake system again, the heat capacity of the gas in the combustion chamber is increased by the introduction of the inert gas, and the maximum combustion temperature is lowered to reduce NO.
It reduces the occurrence of x.

In the exhaust pipe 16, the casing 1
Immediately upstream of 8, a catalyst-containing gas temperature sensor 31 that outputs an output signal (catalyst-containing gas temperature Tcin) corresponding to the temperature of the exhaust gas flowing into the casing 18 to the ECU 9 is provided. Further, upstream of the casing 18 adjacent to the catalyst-containing gas temperature sensor 31, an air-fuel ratio sensor 32 that detects the air-fuel ratio (measurement A / F) of the exhaust gas flowing into the casing 18 and outputs a corresponding output signal to the ECU 9. Is provided.

As the air-fuel ratio sensor 32, a sensor whose output voltage changes according to the oxygen concentration in the exhaust gas is used. The output voltage of the air-fuel ratio sensor 32 becomes a reference voltage when the air-fuel ratio is the stoichiometric air-fuel ratio, takes a value larger than the reference voltage when the air-fuel ratio becomes rich, and a value smaller than the reference voltage when the air-fuel ratio becomes lean. I take the.

The ECU 9 (control means) comprises a digital computer, and ROM (read only memory), RAM (random access memory), CPU (central processing unit), input port, which are mutually connected by a bidirectional bus.
It has an output port. The input port of the ECU 9 includes an air flow meter 5, an accelerator opening sensor 26, a crank angle 2
7, the catalyst-containing gas temperature sensor 31, and the air-fuel ratio sensor 32 are connected, and the respective output signals are input. Also, the ECU
The output port of the fuel injection valve 10, the control valve 22, the EG
It is connected to the R valve 25 and a control command is output to each.

The accelerator opening sensor 26 outputs an output voltage proportional to the opening of the throttle valve 8 to the ECU 9,
The ECU 9 calculates the engine load based on the input signal of the accelerator opening sensor 26. In addition, the crank angle sensor 2
7 outputs an output pulse to the ECU 9 each time the crankshaft rotates by a certain angle, and the ECU 9 calculates the engine speed based on the output pulse. Then, the engine state is determined by the engine load and the engine speed, and the ECU 9 determines the fuel injection valve 10 according to the engine state.
The valve opening timing and the valve opening period of are controlled.

For example, in the fuel injection valve control, the ECU 9
Determines the amount of fuel injected from the fuel injection valve 10, and then determines the timing of fuel injection from the fuel injection valve 10. When determining the fuel injection amount, the ECU 9 reads the engine speed and the output signal (accelerator opening) of the accelerator opening sensor 26 stored in the RAM. The ECU 9
For example, a map for controlling the fuel injection amount is accessed, and the basic fuel injection amount (basic fuel injection time) corresponding to the engine speed and the accelerator opening is calculated. The ECU 9 corrects the basic fuel injection time based on the output signal value of the air flow meter 5, the output signal value of the water temperature sensor or the output signal value of the intake air temperature sensor, and determines the final fuel injection time.

When determining the fuel injection timing, the ECU 9
Accesses a map for controlling the fuel injection start timing, and calculates a basic fuel injection timing corresponding to the engine speed and the accelerator opening. The ECU 9 corrects the basic fuel injection timing using the output signal value of the air flow meter 5, the output signal value of the water temperature sensor or the output signal value of the intake air temperature sensor as a parameter, and determines the final fuel injection timing.

When the fuel injection time and the fuel injection timing are determined, the ECU 9 compares the fuel injection timing with the output signal of the crank position sensor, and the output signal of the crank position sensor is compared with the fuel injection timing. When they coincide, application of driving power to the fuel injection valve 10 is started. The ECU 9 starts applying drive power to the fuel injection valve 10. The ECU 9 stops the application of the drive power to the fuel injection valve 10 when the elapsed time from the start of the application of the drive power to the fuel injection valve 10 reaches the fuel injection time.

In the fuel injection control, when the operating state of the engine 1 is the idle operating state, the ECU 9 determines the output signal value of the water temperature sensor and the rotational force of the crankshaft like the compressor of the vehicle interior air conditioner. The target idle speed of the engine 1 is calculated by using the operating state of the auxiliary machines that are operated by using the parameters as parameters. And EC
U9 feedback-controls the fuel injection amount so that the actual idle speed matches the target idle speed.

Next, in the control of the fuel pump, the ECU 9
Reads out the engine speed and the accelerator opening, which are stored in the RAM, for example. The ECU 9 accesses a map for controlling the common rail pressure and calculates a target pressure corresponding to the engine speed and the accelerator opening. Then E
The CU 9 accesses the map for controlling the fuel discharge pressure, calculates the discharge pressure of the fuel pump 12 (drive current of the fuel pump 12) corresponding to the target pressure, and applies the calculated drive current to the fuel pump 12. .

FIG. 2 schematically shows the concentrations of typical components in the exhaust gas discharged from the exhaust manifold 14. As can be seen from this figure, the concentrations of unburned HC and CO in the exhaust gas discharged from the exhaust manifold 14 increase as the air-fuel ratio of the air-fuel mixture supplied into the cylinder head 30 becomes richer. The concentration of oxygen O _{2 in} the discharged exhaust gas increases as the air-fuel ratio of the air-fuel mixture supplied into the cylinder head 30 becomes leaner.

NOx catalyst 1 housed in casing 18
7 is, for example, alumina (Al ₂ O ₃ ) as a carrier, on which potassium K, sodium Na, lithium L
i, alkali metal such as cesium Cs, barium B
a, alkaline earth such as calcium Ca, lanthanum L
a, at least one selected from rare earths such as yttrium Y, and a noble metal such as platinum Pt.

The NOx catalyst 17 absorbs NOx when the air-fuel ratio of the inflowing exhaust gas (hereinafter referred to as the exhaust air-fuel ratio) is leaner than the theoretical air-fuel ratio, and the exhaust air-fuel ratio is equal to or higher than the theoretical air-fuel ratio. When it becomes rich and the oxygen concentration in the inflowing exhaust gas decreases, the absorbed NOx is converted into NO ₂ or NO _2.
It acts to absorb and release NOx that is released as. And N
NOx released from Ox catalyst 17 (NO ₂ or NO)
Is immediately reduced to N ₂ by reacting with unburned HC and CO in the exhaust gas.

It is considered that this absorbing and releasing action is performed by the mechanism shown in FIG. Next, this mechanism will be described by taking as an example the case where platinum Pt and barium Ba are supported on a carrier, but other noble metals,
The same mechanism can be obtained by using alkali metals, alkaline earths, and rare earths.

That is, when the inflowing exhaust gas becomes considerably lean, the oxygen concentration in the inflowing exhaust gas greatly increases, and as shown in FIG. 3 (A), oxygen O ₂ is in the form of O ₂ ⁻ or O ^{2 −.} Adheres to the surface of platinum Pt. On the other hand, NO contained in the inflowing exhaust gas reacts with O ₂ ⁻ or O ^{2 −} on the surface of platinum Pt to become NO ₂ (2NO + O ₂ → 2NO ₂ ).

Next, a part of the generated NO ₂ is absorbed on the NOx catalyst 17 while being oxidized on the platinum Pt and is bonded to the barium oxide BaO, as shown in FIG. ₃ ^- diffuses into the NOx catalyst 17 in the form of. In this way, NOx is absorbed in the NOx catalyst 17.

As long as the oxygen concentration in the inflowing exhaust gas is high, NO ₂ is produced on the surface of platinum Pt, and NO in the NOx catalyst 17 is generated.
As long as the x absorption capacity is not saturated, NO ₂ is NOx catalyst 17
It is absorbed into the inside to generate nitrate ion NO ₃ ⁻ .

On the other hand, the oxygen concentration in the inflowing exhaust gas
Is lowered and NO₂ When the production amount of
(NO₃ ^-→ 2 NO₂) To NOx catalyst 17 nitrate ion
NO ₃ ^-Is NO₂Or released from NOx catalyst 17 in the form of NO
To be done. That is, the oxygen concentration in the inflowing exhaust gas decreases.
Then, NOx is released from the NOx catalyst 17.
It As shown in Fig. 3, the degree of leanness of the inflowing exhaust gas
Lowering the oxygen concentration in the inflowing exhaust gas
Therefore, if the lean degree of the incoming exhaust gas is lowered,
NOx is released from the NOx catalyst 17.

On the other hand, if the air-fuel mixture supplied into the cylinder head 30 is made stoichiometric or rich at this time and the exhaust air-fuel ratio becomes stoichiometric or rich, a large amount of unburned HC, CO is emitted from the engine as shown in FIG. Are discharged, and these unburned HC and CO react with oxygen O ₂ ⁻ or O ^{2 −} on platinum Pt to oxidize.

When the exhaust air-fuel ratio becomes stoichiometric or rich, the NOx catalyst 17 releases NO ₂ or NO because the oxygen concentration in the inflowing exhaust gas extremely decreases.
This NO ₂ or NO reacts with unburned HC and CO and is reduced to N ₂ as shown in FIG. 3 (B).

That is, HC and CO in the inflowing exhaust gas
It is first platinum Pt on the oxygen O ₂ ^- or O ^2- reacts with been oxidized, and then the oxygen on the platinum Pt O ₂ ^- or O ^2-
If HC and CO still remain after the consumption of
NO released from NOx catalyst 17 by C and CO
x and NOx emitted from the engine are reduced to N ₂ .

When NO ₂ or NO is no longer present on the platinum Pt in this way, NO ₂ or NO is released from the NOx catalyst 17 one after another and further reduced to N ₂ . Therefore, if the exhaust air-fuel ratio is made stoichiometric or rich, the NOx catalyst 17 will emit NO in a short time.
x will be emitted.

As described above, when the exhaust air-fuel ratio becomes lean, NOx is absorbed by the NOx catalyst 17, and when the exhaust air-fuel ratio is made stoichiometric or rich, NOx becomes NOx catalyst 17.
Is released within a short time and is reduced to N ₂ . Therefore, if the exhaust air-fuel ratio is controlled appropriately, the H in the exhaust gas
C, CO, NOx can be purified and N into the atmosphere
Ox emissions can be prevented.

Here, the exhaust air-fuel ratio is the ratio of the total amount of air and the total amount of fuel (hydrocarbon) supplied to the exhaust passage upstream of the NOx catalyst 17, the engine combustion chamber, the intake passage, etc. Shall mean. Therefore, NO
x When the fuel, reducing agent or air is not supplied into the exhaust passage upstream of the catalyst 17, the exhaust air-fuel ratio matches the air-fuel ratio of the air-fuel mixture supplied into the engine combustion chamber.

By the way, in the case of a diesel engine,
Since the combustion is performed in a much leaner range than stoichiometric (theoretical air-fuel ratio, A / F = 14 to 15), the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 17 is very lean in the normal operating condition. NOx in the exhaust gas is absorbed by the NOx catalyst 17 and released from the NOx catalyst 17.
The quantity is extremely small.

Further, in the case of a gasoline engine, the air-fuel ratio of the exhaust gas is made stoichiometric or rich by making the air-fuel mixture supplied to the combustion chamber a stoichiometric or rich air-fuel ratio, and the oxygen in the exhaust gas is Lower the concentration,
The NOx absorbed in the NOx catalyst 17 can be released, but in the case of a diesel engine, if the air-fuel mixture supplied to the combustion chamber is stoichiometric or rich air-fuel ratio, soot is generated during combustion. There is, and it cannot be adopted.

Therefore, in a diesel engine, NOx
At a predetermined timing before the NOx absorption capacity of the catalyst 17 is saturated, fuel (light oil that is the fuel of the diesel engine) is supplied to the exhaust gas to reduce the oxygen concentration in the exhaust gas, and the NOx catalyst 17 absorbs it. It is necessary to release and reduce NOx.

Therefore, in this embodiment, the ECU 9
By the history of the operating state of the engine 1, the NOx catalyst 17
The amount of NOx absorbed in the fuel cell is estimated, and when the estimated NOx amount reaches a preset predetermined value, the opening / closing of the control valve 22 is controlled based on the reducing agent addition control process described later to supply a predetermined amount of fuel. It is injected into the exhaust gas from the addition nozzle 19 and N
The oxygen concentration in the exhaust gas flowing into the Ox catalyst 17 is reduced to release the NOx absorbed by the NOx catalyst 17,
I try to reduce it to ₂ .

On the other hand, the fuel contains sulfur (S).
And when the sulfur in the fuel burns, SO₂And SO₃ Sulfur
Yellow oxide (SOx) is generated, and NOx catalyst 17 becomes exhaust gas.
These SOx in the gas are also absorbed. SO of NOx catalyst 17
x absorption mechanism is the same as NOx absorption mechanism
it is conceivable that. That is, the NOx absorption mechanism was explained
Oxygen O₂ Is O₂ ^-Or O^2-In the form of
SO that is attached to the surface of platinum Pt and is contained in the inflowing exhaust gas
x (eg SO₂ ) Is O on the surface of platinum Pt. ₂ ^-Also
Is O^2-Reacts with SO₃ Becomes

After that, a part of the generated SO ₃ is absorbed in the NOx catalyst 17 while being oxidized on the platinum Pt and is bonded with barium oxide BaO, and in the NOx catalyst 17 in the form of sulfate ion SO ₄ ²⁻ . diffuse into, to produce a sulfate salt BaS0 _4. The sulphate BaS0 ₄ is Zuraku decomposes have stabilized, may remain in the NOx catalyst 17 to the air-fuel ratio of the inflowing exhaust gas is not decomposed even in the rich. Therefore, as the amount of sulfate BaS0 ₄ produced in the NOx catalyst 17 increases with the passage of time, the amount of BaO that can participate in NOx absorption decreases and the NOx absorption capacity decreases. This is the so-called SOx poisoning.

However, when the temperature of the NOx catalyst 17 is higher than a predetermined temperature (hereinafter, this temperature is referred to as SOx release temperature), the sulfate BaS0 ₄ produced in the NOx catalyst 17 has a theoretical inflow exhaust air-fuel ratio. When the air-fuel ratio or richer than it is decomposed, sulfate ions SO ₄ ²⁻ are released from the NOx catalyst 17 in the form of SO ₃ . Therefore, in this embodiment, when the SOx absorption amount of the NOx catalyst 17 becomes larger than a predetermined set amount, the inflow exhaust air-fuel ratio is temporarily increased to the theoretical air-fuel ratio or slightly rich (while heating the NOx catalyst 17). (For example, about 13.5 to 14.0)
Therefore, SOx is released from the NOx catalyst 17. The SO ₃ released at this time is reduced to SO ₂ by HC and CO in the inflowing exhaust gas.

Next, the reducing agent addition control process performed by the ECU 9 will be described with reference to the flowchart of FIG. The reducing agent addition control process is a process routine that is stored in advance in the ROM of the ECU 9 and is repeatedly executed by the CPU.

When the process starts, the ECU 9 calculates the added fuel amount Qex to be added to the exhaust port 13 from the fuel addition nozzle 19 (step 101: addition amount calculation means). The addition fuel amount Qex is calculated based on the target air-fuel ratio map 41, the basic addition fuel amount map 42, and the addition fuel correction coefficient map 43, as shown in FIG.

The target air-fuel ratio map 41 uses the engine speed NE and the injection amount (or the fuel injection time TAU) as parameters, estimates the NOx amount absorbed by the NOx catalyst 17 from these parameters, and estimates the NOx amount. A map in which the relationship between the parameters and the target air-fuel ratio A / Ftrg is set in advance based on experimental values so that the exhaust pipe 16 attains the target exhaust air-fuel ratio A / Ftrg when the predetermined value set in advance is reached. Is stored in advance in the ROM of the ECU 9. The ECU 9 determines the engine speed NE as described above.
The target air-fuel ratio A / Ftrg can be obtained by calculating the injection amount data and referring to the target air-fuel ratio map 41.

The basic added fuel amount map 42 shows the intake air amount Ga measured by the air flow meter 5, the exhaust air-fuel ratio (measured air-fuel ratio) A / Fmes and the target air-fuel ratio A / Ftrg actually measured by the air-fuel ratio sensor 32. This is a map in which the relationship between this parameter and the basic added fuel amount Qexb is set as a parameter, and is stored in advance in the ROM of the ECU 9. The basic added fuel amount Qexb is a value calculated by the following formula Qexb = Ga / (A / Ftrg) -Ga / (A / Fmes). This equation means that the numerical value of the predetermined target air-fuel ratio A / Ftrg is corrected in real time based on the actual intake air amount Ga and the measured air-fuel ratio A / Fmes. Then, the ECU 9 causes the intake air amount Ga,
If the measured air-fuel ratio A / Fmes and the target air-fuel ratio A / Ftrg are obtained, the basic added fuel amount Qexb can be obtained by referring to the basic added fuel amount map 42.

The added fuel correction coefficient map 43 uses the intake air amount Ga measured by the air flow meter 5 and the catalyst-containing gas temperature Tcin measured by the catalyst-containing gas temperature sensor 31 as parameters, and the added fuel correction coefficient Cqex.
It is a map that sets the relationship with
It is stored in advance in the ROM of U9. The added fuel correction coefficient Cqex is a coefficient for correcting the change in the processing capacity of the NOx catalyst 17 due to the temperature. Then, if the intake air amount Ga and the catalyst-containing gas temperature Tcin are obtained based on the input signals of the air flow meter 5 and the catalyst-containing gas temperature sensor 31, the ECU 9 refers to the added fuel correction coefficient map 43 and checks the added fuel correction coefficient Cqex. Can be asked.

Next, the ECU 9 determines the basic added fuel amount Qexb.
Is multiplied by the added fuel correction coefficient Cqex to obtain the added fuel amount Qex.

Further, the ECU 9 determines in step 102 (possibility determination means) whether or not the exhaust fuel addition pattern is a learning condition, and if it is a learning condition (step 102: YES), the process proceeds to step 103. If it is not the learning condition (step 102: NO), the fuel addition control process is ended. It should be noted that the learning condition referred to here is, as shown in FIG. 7, after the control valve 22 is closed (OFF) to open (ON) by the addition command of the ECU 9 and the addition time corresponding to the added fuel amount Qex ends. It will be closed (OFF) again,
Refers to the addition pattern. That is, this is a single injection pattern in which the added fuel amount Qex instructed by the ECU 9 is not divided and added, but the entire amount is added at once. Since this single injection pattern (addition pattern) differs depending on the amount of addition, it is necessary for the ECU 9 to periodically relearn to an appropriate addition pattern according to the addition amount. In particular, during normal operation, the amount of fuel added is inevitably large because the HC component in the exhaust gas is extremely low. Therefore, during normal operation, it is desirable for the ECU 9 to relearn to the addition pattern when the addition amount is large.

Next, at step 103, the ECU 9
Controls the control valve 22 to add the total amount of the added fuel Qex to the exhaust port 13 from the fuel addition nozzle 19 based on the learning condition. Then, the measured value of the air-fuel ratio sensor 32 changes as time passes, as shown in FIG. 8, for example. That is, the exhaust air-fuel ratio changes from the lean state (A) immediately before the addition to the rich state by the above addition to the peak (B) of the rich state, and then changes to the lean state.

Therefore, the ECU 9 monitors the change (waveform) of the measured value of the air-fuel ratio sensor 32 after the fuel addition and reads the rich depth h1 and the time constant t1 (step 104: depth calculation means, time calculation). means). The rich depth h1 is the displacement amount (A → B) from the lean state (A) immediately before the addition to the rich peak (B). The time constant t1 is the displacement amount h1 from the time when the rich depth h1 is recorded.
The time t1 until the state changes to the lean state up to 63%, which is the predetermined ratio. The predetermined ratio of 63% multiplied by the displacement amount h1 is an experimental value obtained in consideration of the correction of the added fuel amount to be added next time. Note that the target air-fuel ratio A / Ftrg and the rich depth h1 (air-fuel ratio at point B) should theoretically match (on the map), but the error in the air-fuel ratio due to catalyst function variations and deterioration Therefore, when the rich depth h1 (air-fuel ratio at the point B) and the target air-fuel ratio A / Ftrg are different, the ECU 9 executes air-fuel ratio feedback processing to correct the difference.

The ECU 9 controls the rich depth h1 and the time constant t1.
Based on the above, the addition interval (interval) Tex and the added fuel amount Qex for the second and subsequent times are calculated (step 105: addition amount correction means, interval calculation means). The addition interval Tex and the addition fuel amount Qex are obtained based on the addition interval map 46 and the correction coefficient map 47, as shown in FIG.

The addition interval map 46 is a map in which the relationship between the rich depth h1 and the time constant t1 and the addition interval Tex is set based on experimental values, and is stored in the ROM of the ECU 9 in advance. The addition interval map 46
In addition, the addition interval Tex shows a larger value as the amount of displacement from the peak B in the rich state to the time constant t1 increases. ECU
In step 9, after determining the rich depth h1 and the time constant t1, the addition interval map 46 is referred to determine the addition interval Tex until the time of the next addition.

The correction coefficient map 47 has a time constant t1.
3 is a map in which the relationship between the addition interval Tex and the correction coefficient Cqm is set based on experimental values, and is stored in the ROM of the ECU 9 in advance. The ECU 9 determines the time constant t1 and the addition interval Tex.
Is calculated, the correction coefficient Cqm is calculated with reference to the correction coefficient map 47.

After obtaining the correction coefficient Cqm, the ECU 9 multiplies the added fuel amount Qex added first (or last time) by the correction coefficient Cqm to calculate the added fuel amount Qex to be added next time. When the next addition pattern (addition interval Tex and added fuel amount Qex) is determined, the ECU 9 ends the fuel addition control process.

The ECU 9 executes the second and subsequent fuel additions based on the addition interval Tex and the added fuel amount Qex obtained in step 105.

[0070]

According to the present invention, the addition amount is calculated in consideration of the actual air-fuel ratio, the intake air amount, and the temperature of the gas containing the catalyst, so that the optimum reduction can be achieved without being affected by various system variations. Agent addition can be carried out. The reducing agent may be an HC (hydrocarbon) component, and for example, a fuel can be used.

Further, according to the present invention, the reducing agent is added next time from the value of the air-fuel ratio (rich depth) after addition of the reducing agent and the time (time constant) for changing the value of this air-fuel ratio to the value of the predetermined air-fuel ratio. By correcting the amount of reducing agent added and calculating the next addition interval, it is possible to compensate for variations and deterioration of the reducing agent addition system and catalyst even after the second addition.
It becomes possible to perform air-fuel ratio control in which absorption and release of (SOx) are accurately performed.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of an exhaust gas purification apparatus for an internal combustion engine according to the present invention.

[Fig. 2] Unburned HC and C in exhaust gas discharged from the engine
It is a diagram which shows the concentration of O and oxygen roughly.

FIG. 3 is a diagram for explaining a NOx absorption / release action of an NOx storage reduction catalyst.

FIG. 4 is a flowchart of a fuel addition control process.

FIG. 5 is an explanatory diagram of how to determine the amount of added fuel.

FIG. 6 is an explanatory diagram of how to determine an addition interval and a correction coefficient.

FIG. 7 is an explanatory diagram of a single injection pattern.

FIG. 8 is a diagram showing a change in air-fuel ratio after the addition is performed.

[Explanation of symbols]

1 ... engine 2 ... Intake manifold 3 ... Intake pipe 4 ... Air cleaner 5 ... Air flow meter 6 ... Turbocharger 7 ... Inter Clark 8 ... Throttle valve 9 ... ECU 10 ... Fuel injection valve 11 ... Common rail 12 ... Fuel pump 13 ... Exhaust port 14 ... Exhaust manifold 15 ... Exhaust collecting pipe 16 ... Exhaust pipe 17 ... NOx catalyst 18 ... Casing 19 ... Fuel addition nozzle 20 ... Fuel pipe 21 ... Fuel passage 22 ... Control valve 23 ... EGR tube 24 ... EGR Clark 25 ... EGR valve 26 ... Accelerator opening sensor 27 ... Crank angle sensor 31 ... Gas temperature sensor with catalyst 32 ... Air-fuel ratio sensor 41 ... Target air-fuel ratio map 42 ... Basic added fuel amount map 43 ... Additive fuel correction coefficient map 46 ... Addition interval map 47 ... Correction coefficient map

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI F01N 3/36 ZAB B01D 53/36 101A 101B (72) Inventor Hiroki Matsuoka 1 Toyota-cho, Aichi Prefecture Toyota Automobile Co., Ltd. (72) Inventor Kotaro Hayashi 1 Toyota Town, Toyota City, Aichi Prefecture, Toyota Motor Corporation (72) Inventor Shinobu Ishiyama 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation (72) Inventor, Yasuhiko Otsubo Aichi Toyota City, Toyota, Japan 1 Toyota Motor Co., Ltd. (72) Inventor Naofumi Kaguda Toyota, Aichi, Toyota City 1 Toyota Motor Co., Ltd. (72) Inventor, Masaaki Kobayashi Toyota City, Aichi 1 Toyota Motor Corporation (72) Inventor Daisuke Shibata 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation Stock In-house (72) Inventor Akihiko Negami 1 Toyota-cho, Toyota-shi, Aichi Toyota Motor Co., Ltd. (72) Inventor Yasushi Harada 1 Toyota-cho, Toyota-shi, Aichi Toyota-car Co., Ltd. (72) Inventor Tomoyuki Ono 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Co., Ltd. (56) Reference JP-A-6-129237 (JP, A) JP-A-10-47048 (JP, A) JP-A-2001-132500 (JP, A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) F01N 3/08-3/36 B01D 53/94 F02D 41/04

Claims (4)

(57) [Claims] 1. A NOx catalyst provided in an exhaust passage of a multi-cylinder internal combustion engine capable of lean combustion, a reducing agent addition means provided in the exhaust passage upstream of the NOx catalyst, and an actual NOx catalyst in an operating state of a vehicle. Amount added to calculate the amount of added reducing agent added by the reducing agent adding means from the air-fuel ratio, the amount of intake air to the internal combustion engine, and the catalyst-containing gas temperature that is the temperature of the exhaust gas flowing into the NOx catalyst. When adding the reducing agent of the added reducing agent amount to the NOx catalyst from the calculating means and the reducing agent adding means, the air-fuel ratio changes from a lean state immediately before the reducing agent addition to a maximum rich state after the reducing agent addition. Depth calculation means for calculating a rich depth which is a displacement amount, and a value obtained by multiplying the displacement amount by a predetermined ratio by changing the air-fuel ratio to a lean state from a value that becomes the maximum rich state after adding the reducing agent. Lean and Next, the addition reduction is performed by correcting the amount of the added reducing agent based on the time calculation means for calculating the time required for the calculation, the rich depth calculated by the depth calculation means and the time calculated by the time calculation means. An addition amount correction means for calculating the amount of the agent, and an interval calculation means for calculating the reducing agent addition interval from the addition of the reducing agent to the next addition of the reducing agent based on the rich depth obtained by the depth calculation means. And a control means for controlling the next reducing agent addition based on the next reducing agent amount corrected by the addition amount correcting means and the next reducing agent addition interval calculated by the interval calculating means, An exhaust emission control device for an internal combustion engine, which is characterized. 2. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the reducing agent addition interval is proportional to the magnitude of the rich depth obtained by the depth calculating means. 3. The exhaust emission control device for an internal combustion engine according to claim 1, further comprising an adequacy determining means for determining whether to add the reducing agent according to an operating state of the vehicle. 4. The internal combustion engine according to claim 1, wherein the propriety determining unit determines whether the addition of the reducing agent is a single injection in which the entire amount of the reducing agent is injected at one time. Exhaust purification device.