JP3496572B2 - 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 purifying apparatus for an internal combustion engine, and more particularly to preventing the internal combustion engine from heating up the exhaust gas purifying material while controlling the temperature rise of the exhaust gas purifying material. The present invention relates to an exhaust gas purification device for an internal combustion engine, which can reduce the influence on the temperature rise of the exhaust gas purification material even when shifting to control.

[0002]

2. Description of the Related Art Generally, in an internal combustion engine capable of lean burn, as an exhaust gas purification device for purifying nitrogen oxides (NOx) contained in an exhaust gas discharged from the internal combustion engine, conventionally, an air-fuel ratio of an inflowing exhaust gas is conventionally used. Is a lean state, it absorbs NOx, and when the oxygen concentration of the exhaust gas decreases, and when it reaches a stoichiometric or rich state, the absorbed NOx is released and reduced, a so-called storage reduction type NOx.
Catalysts are known.

Further, since sulfur is contained in the fuel and the lubricating oil of the engine, SOx is contained in the exhaust gas, but the NOx catalyst is the same as in the case of absorbing the NOx. SOx is absorbed by a mechanism. in this case,
SOx absorbed by the NOx catalyst forms a stable sulfate with the passage of time.
SOx is not emitted under the conditions for releasing NOx
There is a problem that the amount of SOx in the absorbent increases, and as a result, the amount of NOx absorbed decreases and the NOx purification efficiency decreases.

Therefore, in order to avoid such a problem, conventionally, SOx which heats and raises the NOx catalyst to a predetermined temperature (for example, about 700 ° C.) at a constant cycle to reduce the exhaust purification capacity of the NOx catalyst. Techniques have been proposed for burning and removing such substances. That is, for example, an adhesion amount estimating means for estimating an adhesion amount of a substance other than NOx (for example, sulfur) which adheres to the exhaust purification catalyst of the internal combustion engine to reduce the exhaust purification performance, and a substance which reduces the exhaust purification performance An exhaust gas purification apparatus for an internal combustion engine is also proposed, which is provided with a catalyst heating unit that supplies fuel and air to the exhaust purification catalyst when the adhered amount reaches a predetermined amount and burns the fuel to raise the temperature of the exhaust purification catalyst. (See JP-A-8-61052).

It has been conventionally practiced to perform such air-fuel ratio control for each cylinder in a multi-cylinder engine for controlling the temperature rise of the exhaust purification catalyst. Such control is referred to as cylinder-by-cylinder air-fuel ratio control. For example, in a V-type engine, one cylinder on the bank side performs rich combustion, and the other cylinder on the lean side performs lean combustion, thereby performing rich combustion. The fuel containing NOx released from the exhaust gas and the air containing residual oxygen discharged from the lean side are simultaneously supplied to the exhaust purification catalyst to purify NOx by the residual heat of the catalyst and burn with the residual oxygen. By increasing the temperature of the catalyst, the substance adhering to the catalyst that reduces the exhaust gas purification performance is burned and removed. As a result, the rich combustion operation in which the output of the internal combustion engine becomes large and the lean combustion operation in which the output of the internal combustion engine becomes small are alternately performed with a good balance, and the output fluctuation of the internal combustion engine can be suppressed to a small level.

Conventionally, in particular, in order to efficiently purify both NOx and particulates composed of solid particles of unburned HC, the fuel injection control means provided in the cylinder of the internal combustion engine and the exhaust passage are provided. The exhaust gas treatment means, the exhaust temperature estimation means for estimating the exhaust temperature, and the temperature comparison means for comparing the output of the temperature estimation means with a predetermined value. Is configured to instruct post-injection of fuel after main fuel injection for generating engine output, and control the exhaust temperature of the engine to a temperature range suitable for operation of the exhaust treatment means by this post-injection. (See Japanese Patent Application Laid-Open No. 8-303290). Therefore, conventionally, so-called SOx poisoning due to sulfur has been conventionally eliminated, or particulates are purified.

However, in this way, control is performed so that the exhaust purification catalyst is supplied with fuel and air to burn the fuel to heat the exhaust purification catalyst or to perform post injection to raise the exhaust temperature. In this case, for example, when a situation occurs in which the running vehicle is decelerated, the internal combustion engine is in the so-called fuel cut control, the fuel gas is not supplied to the internal combustion engine, the exhaust gas temperature becomes low, and the exhaust purification catalyst does not Exhaust gas having a low temperature will be supplied.
On the other hand, when acceleration is required in the traveling vehicle, the air-fuel ratio control of the internal combustion engine shifts to the stoichiometric control. Gas will be supplied to the exhaust purification catalyst.

As a result, the temperature of the exhaust purification catalyst may not be sufficiently increased, or the temperature of the exhaust purification catalyst once increased may be decreased. Therefore, in this way, during the temperature rise control of the exhaust catalyst, when the internal combustion engine side controls the temperature rise of the exhaust catalyst, the temperature of the exhaust purification catalyst is raised to a certain temperature. However, the temperature of the exhaust purification catalyst will decrease.

Therefore, it is necessary to raise the temperature of the exhaust purification catalyst again until it reaches a predetermined temperature. As a result, in order to regenerate the so-called SOx poisoning of the exhaust purification catalyst, the temperature control of the exhaust purification catalyst is hindered. As compared with the case where the control is not performed on the side of the internal combustion engine, it takes a longer time to raise the temperature of the exhaust purification catalyst, and the emission of the exhaust purification catalyst also decreases. Further, the fuel consumption efficiency is low during the temperature rise control as in the stoichiometric control, and therefore the temperature rise control time has been desired to be shortened from the viewpoint of improving the fuel efficiency.

Further, not only for the internal combustion engine capable of lean burn, but generally for warm-up operation at the time of starting the internal combustion engine, it is necessary to heat and raise the temperature until the exhaust purification catalyst is activated. In this case, when a situation that hinders the temperature rise of the exhaust purification catalyst during the stoichiometric warm-up operation, such as deceleration, is required, the exhaust purification catalyst reaches a predetermined temperature in the same manner as above. It took a long time to raise the temperature, and there was the same problem as above.

[0011]

Therefore, an object of the present invention is to provide an internal combustion engine that raises the temperature of the NOx catalyst.
When the temperature increase control of Seki is being performed, for example, during acceleration
If the air-fuel ratio control reaches a stoichiometric state,
Even so, it is an object of the present invention to provide an exhaust gas purification device for an internal combustion engine, which can reduce the influence on the heating temperature rising state of the NOx catalyst , have good emissions, and can improve fuel efficiency.

[0012]

[0013]

[0014]

An object of the invention according to claim 2 is to provide an exhaust gas purification device for an internal combustion engine configured to switch exhaust gas by the exhaust gas switching means.

[0016]

In order to solve such a technical problem, according to the invention of claim 1, an exhaust gas is arranged in an exhaust passage of an internal combustion engine and flows from the internal combustion engine.
Absorbs NOx when the air-fuel ratio of the engine is lean
If the oxygen concentration of the inflowing exhaust gas is low
The NOx catalyst that releases the absorbed NOx and the NOx catalyst
In the exhaust purification apparatus for an internal combustion engine having a bypass passage that bypasses the medium, the exhaust gas of the rich exhaust air-fuel ratio and the Li
Exhaust gas with a rich exhaust air-fuel ratio flows into the NOx catalyst
Then, during the temperature increase control of the internal combustion engine for increasing the temperature of the NOx catalyst , when the stoichiometric control is performed at the time of high load of the internal combustion engine , the exhaust gas is caused to flow down through the bypass passage. It is characterized in that it is configured.

Here, “ the exhaust gas with a rich exhaust air-fuel ratio is
And a lean exhaust air-fuel ratio exhaust gas
The "temperature increase control of the internal combustion engine that causes the temperature of the NOx catalyst to rise by flowing into the cylinder" corresponds to, for example, cylinder-by-cylinder air-fuel ratio control in the internal combustion engine that allows lean combustion. Further, the control corresponds to the post-injection of the fuel after the main fuel injection for generating the engine output, and the post-injection to bring the exhaust temperature of the engine into a temperature range suitable for the operation of the exhaust processing means.

[0018]

[0019]

[0020]

[0021]

[0022]

[0023]

[0024]

[0025]

[0026] In the invention of 請 Motomeko 1 wherein, when the Atsushi Nobori control of the internal combustion engine being carried out, when the vehicle is accelerated if necessary, an air-fuel ratio control of the internal combustion engine is stoichiometric control Becomes

In this way, the exhaust gas temperature in the stoichiometric control is not as high as the exhaust gas temperature in the temperature increase control, and as a result, the exhaust gas whose combustion temperature is lower than that in the temperature increase control is generated. Occur. In such a case, the exhaust gas having a low combustion temperature flows down through the bypass passage and is not supplied to the NOx catalyst .

As a result, in the invention according to claim 1 , even when the control shifts to the stoichiometric control for preventing the heating and heating of the NOx catalyst on the internal combustion engine side, the influence on the heating and heating state of the NOx catalyst is exerted. Can be reduced, emission of exhaust gas can be improved, and fuel efficiency can be improved.

[0029] In the second aspect of the present invention, in the prior SL exhaust passage, the exhaust gas the NOx catalyst or the exhaust switching means which can be supplied provided to one of said bypass <br/> scan path cage, during temperature increase control of the internal combustion engine, the stoichiometric system
Upon transition to your is characterized by being composed of pre-Symbol exhaust switching means exhaust gas by operating the so as to flow down through the bypass passage.

Therefore, in the invention according to claim 2 , when the stoichiometric control at the time of high load of the internal combustion engine is performed during the temperature increase control of the internal combustion engine for increasing the temperature of the NOx catalyst , the internal combustion engine is operated. The temperature of the exhaust gas flowing out of the engine drops. At this time, since the exhaust gas switching means is arranged at the switching position where the bypass passage is opened and the NOx catalyst is closed, the exhaust gas whose temperature has dropped is introduced into the bypass passage by the exhaust gas switching means, and the bypass passage is opened. It does not flow into the NOx catalyst because it flows down through the NOx catalyst .

[0031] As a result, in the second aspect of the invention, when the Atsushi Nobori control of the internal combustion engine have been made, there when a transition to the control that prevents the heating Atsushi Nobori of the NOx catalyst in an internal combustion engine side However, it is possible to reduce the effect on the heating temperature rising state of the NOx catalyst, improve the emission of exhaust gas purification, and improve the fuel efficiency.

[0032]

BEST MODE FOR CARRYING OUT THE INVENTION An exhaust gas purification apparatus for an internal combustion engine according to the present invention will be described below in detail with reference to an embodiment shown in the accompanying drawings, as an example, in which it is applied to a lean burn internal combustion engine.

FIG. 1 is a diagram showing a schematic configuration when the present invention is applied to a gasoline engine for a vehicle capable of lean burn. In this figure, reference numeral 1 is an engine body, reference numeral 2 is a piston, reference numeral 3 is a combustion chamber, reference numeral 4 is an ignition plug, reference numeral 5 is an intake valve, reference numeral 6 is an intake port, reference numeral 7 is an exhaust valve, and reference numeral 8 is an exhaust port. Are shown respectively.

The intake port 6 is connected to the surge tank 10 via a corresponding branch pipe 9, and each branch pipe 9 is provided with a fuel injection valve 11 for injecting fuel into the intake port 6. The surge tank 10 is connected to an air cleaner 14 via an intake duct 12 and an air flow meter 13, and a throttle valve 15 is arranged in the intake duct 12.

On the other hand, the exhaust port 8 is connected to the exhaust manifold 16
Further, it is joined via an exhaust pipe 19 to a casing 21 containing a NOx storage reduction catalyst 20 as an exhaust gas purification material. The NOx storage reduction catalyst 20 absorbs NOx when the air-fuel ratio of the inflowing exhaust gas (hereinafter referred to as exhaust air-fuel ratio) is lean, and releases the absorbed NOx when the oxygen concentration of the inflowing exhaust gas is low. And is reduced to N ₂ . An exhaust pipe 22 is connected to the NOx storage reduction catalyst 20, and the exhaust pipe 22 is joined to a muffler (not shown).

In the present embodiment, a bypass pipe 26 that bypasses the NOx storage reduction catalyst 20 and can supply exhaust gas is provided between the exhaust pipe 19 and the exhaust pipe 22. There is. An actuator 27 is provided at an inlet portion 21 a of the casing 21, which is a branch portion of the bypass pipe 26.
An exhaust gas switching valve 28 serving as a switching unit is provided so that the valve element is actuated by.

The exhaust switching valve 28 is an actuator 27.
The bypass pipe 26 as shown by the solid line in FIG.
1 is closed and the inlet portion to the downstream NOx catalyst 20 is fully opened, and the inlet portion 21a to the downstream NOx catalyst 20 is closed and the bypass pipe is closed as shown by the broken line in FIG. It is configured to operate by selecting either one of the bypass open positions where the inlet of 26 is fully opened.

An electronic control unit (ECU) 30 for engine control is composed of a digital computer, and a ROM (Read Only Memory) 32, a RAM (Random Access Memory) 33, a CPU (Central Processor) which are mutually connected by a bidirectional bus 31. Unit) 3
4, an input port 35, and an output port 36. The air flow meter 13 generates an output voltage proportional to the intake air amount, and this output voltage is input to the input port 35 via the AD converter 37.

On the other hand, a temperature sensor 23 for generating an output voltage proportional to the temperature of the exhaust gas flowing out of the engine body 1 via the exhaust manifold 16 is attached to the exhaust pipe 19, and the output of the temperature sensor 23. The voltage is input to the input port 35 via the AD converter 38. Further, the input port 35 is connected to a rotation speed sensor 41 that generates an output pulse representing the engine rotation speed. Output port 36
Are respectively connected to the spark plug 4, the fuel injection valve 11 and the actuator 27 via the corresponding drive circuit 39.

In this gasoline engine, the fuel injection time TAU is calculated based on the following equation, for example. TAU = TP · K Here, TP indicates the basic fuel injection time, and K indicates the correction coefficient. The basic fuel injection time TP indicates the fuel injection time required to make the air-fuel ratio of the air-fuel mixture supplied into the engine cylinder the stoichiometric air-fuel ratio. This basic fuel injection time TP is obtained by an experiment in advance, and the engine load Q / N
As a function of (intake air amount Q / engine speed N) and engine speed N, the ROM 3 is previously stored in the form of a map as shown in FIG.
It is stored in 2. The correction coefficient K is a coefficient for controlling the air-fuel ratio of the air-fuel mixture supplied to the engine cylinder, and if K = 1.0, the air-fuel mixture supplied to the engine cylinder has a stoichiometric air-fuel ratio. On the other hand, when K <1.0, the air-fuel ratio of the air-fuel mixture supplied into the engine cylinder becomes larger than the stoichiometric air-fuel ratio, that is, becomes lean, and K> 1.
When it becomes 0, the air-fuel ratio of the air-fuel mixture supplied into the engine cylinder becomes smaller than the stoichiometric air-fuel ratio, that is, it becomes rich.

In the gasoline engine according to the present embodiment, the correction coefficient K is set to a value smaller than 1.0 in the engine low / medium load operating range, lean air-fuel ratio control is performed, and the engine high load operating range is achieved. The correction coefficient K is set to 1.0 and stoichiometric control is performed during warm-up operation when starting the engine, during acceleration, and at constant speed operation of 120 km / h or more, and the correction coefficient K is used in the engine full load operation region. Is set to a value larger than 1.0 and rich air-fuel ratio control is performed.

In an internal combustion engine, the frequency of low-medium load operation is usually highest, and therefore the correction coefficient K is made smaller than 1.0 in most of the operating period to burn the lean air-fuel mixture. become.

FIG. 3 schematically shows the concentrations of typical components in the exhaust gas discharged from the combustion chamber 3. As can be seen from this figure, the concentrations of unburned HC and CO in the exhaust gas discharged from the combustion chamber 3 increase as the air-fuel ratio of the air-fuel mixture supplied into the combustion chamber 3 becomes richer, The concentration of oxygen O ₂ in the exhaust gas discharged increases as the air-fuel ratio of the air-fuel mixture supplied into the combustion chamber 3 becomes leaner.

NOx contained in the casing 21
The catalyst 20 uses, for example, alumina as a carrier, and potassium K, sodium Na, lithium Li, an alkali metal such as cesium Cs, an alkaline earth such as barium Ba, calcium Ca, lanthanum La, and yttrium Y are supported on the carrier. At least one selected from such rare earths and a noble metal such as platinum Pt are supported.

When a storage reduction type NOx catalyst such as the NOx catalyst 20 is arranged in the exhaust passage of the engine, the storage reduction type NOx catalyst is NOx when the air-fuel ratio of the inflowing exhaust gas (hereinafter referred to as exhaust air-fuel ratio) is lean. Is absorbed, and when the oxygen concentration in the inflowing exhaust gas decreases, the absorbed and released NOx is released. Here, the exhaust air-fuel ratio is the air and fuel (hydrocarbons) supplied to the engine intake passage and the exhaust passage upstream of the NOx storage reduction catalyst.
The ratio of

When fuel (hydrocarbon) or air is not supplied into the exhaust passage upstream of the NOx storage reduction catalyst, the exhaust air-fuel ratio matches the air-fuel ratio of the air-fuel mixture supplied into the combustion chamber, Therefore, in this case, the NOx storage reduction catalyst absorbs NOx when the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber is lean, and the NOx absorbed when the oxygen concentration in the air-fuel mixture supplied to the combustion chamber decreases. Will be released.

There is a part where the detailed mechanism of the NOx absorption / release action by the NOx storage reduction catalyst is not clear. However, 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 the carrier, but the same mechanism can be obtained by using other noble metals, alkali metals, alkaline earths and rare earths.

That is, when the air-fuel ratio of the inflowing exhaust gas becomes considerably lean, the oxygen concentration in the inflowing exhaust gas greatly increases,
As shown in FIG. 4A, oxygen O ₂ adheres to the surface of platinum Pt in the form of O ₂ ⁻ or O ²⁻ . 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 oxidized on the platinum Pt and absorbed in the occlusion-reduction type NOx catalyst to bond with barium oxide BaO, as shown in FIG. 4 (A). nitrate ions NO ₃ ^- storage reduction NO in the form of
x Diffuses in the catalyst. In this way, NOx is absorbed in the NOx storage reduction catalyst 20.

As long as the oxygen concentration in the inflowing exhaust gas is high, NO ₂ is produced on the surface of platinum Pt, and unless the NOx absorption capacity of the NOx storage reduction catalyst is saturated, NO ₂ is absorbed in the NOx storage reduction catalyst. As a result, nitrate ions NO ₃ ⁻ are generated.

[0051] In contrast, the reaction with the amount of NO ₂ concentration of oxygen in the inflowing exhaust gas is lowered to decrease the reverse ^- proceed to (NO ₃ → NO _2), nitric acid storage reduction in NOx catalyst Ion NO ₃ ^- is a storage reduction type N in the form of NO ₂ or NO
It is released from the Ox catalyst. That is, when the oxygen concentration in the inflowing exhaust gas decreases, NOx is released from the NOx storage reduction catalyst. As shown in FIG. 3, when the lean degree of the inflowing exhaust gas is low, the oxygen concentration in the inflowing exhaust gas is low. Therefore, when the leanness of the inflowing exhaust gas is low, NOx is emitted from the NOx storage reduction catalyst. Will be released.

On the other hand, when the air-fuel mixture supplied to the combustion chamber becomes stoichiometric or rich at this time, a large amount of unburned HC, CO is discharged from the engine as shown in FIG. Is oxygen O ₂ ⁻ or O ²⁻ on platinum Pt.
It reacts with and is oxidized.

Further, when the exhaust air-fuel ratio becomes stoichiometric or rich, the oxygen concentration in the inflowing exhaust gas extremely decreases, so NO ₂ or NO is released from the NOx storage reduction catalyst, and this NO ₂ or NO is As shown in FIG. 4 (B), it reacts with unburned HC and CO and is reduced to N ₂ .

[0054] That is, HC in the inflowing exhaust gas, CO, first oxygen O ₂ on the platinum Pt ^- or O ^2- immediately be reacted with oxidized, then the platinum Pt on the oxygen O ₂ ^- or O ^2- If HC and CO still remain after the consumption of
NOx released from the NOx storage reduction catalyst and NOx emitted from the engine are reduced to N ₂ by C and CO.

In this way, NO ₂ is formed on the surface of platinum Pt.
Alternatively, when NO is no longer present, NO ₂ or NO is released one after another from the NOx storage reduction catalyst and is further reduced to N ₂ . Therefore, when the exhaust air-fuel ratio is made stoichiometric or rich, the storage reduction type N is reduced within a short time.
NOx will be released from the Ox catalyst.

As described above, when the exhaust air-fuel ratio becomes lean, NOx is absorbed by the storage reduction type NOx catalyst, and when the exhaust air-fuel ratio is stoichiometric or rich, NOx is stored reduction type Nx.
It is released from the Ox catalyst in a short time and reduced to N ₂ . Therefore, it is possible to prevent the emission of NOx into the atmosphere.

By the way, during full load operation, the air-fuel mixture supplied into the combustion chamber is made rich, and during high load operation, during warm-up operation at engine start, during acceleration, and 120 km / h.
At constant speed operation above, the air-fuel mixture is stoichiometric.
When the air-fuel mixture is lean during low-medium-load operation, NOx in the exhaust gas is absorbed by the NOx storage reduction catalyst during low-medium-load operation, and NOx storage-reduction type during full-load operation and high-load operation. NOx is released from the catalyst and is reduced. However, if the frequency of full load operation or high load operation is low and the frequency of low and medium load operation is high and the operation time is long, NOx release / reduction will not be in time, and the NOx absorption capacity (NOx absorption capacity) of the NOx storage reduction catalyst. (Capacity) is saturated and NOx cannot be absorbed.

Therefore, in such a case, when the lean air-fuel mixture is being burned, that is, when the medium-low load operation is being performed, the stoichiometric or short-time stoichiometry is performed in a relatively short cycle. A method may be adopted in which the air-fuel ratio of the air-fuel mixture is controlled so that the rich air-fuel mixture is burned, and NOx is released / reduced in a short cycle.

As described above, due to the intake and release of NOx, the exhaust air-fuel ratio (air-fuel ratio of the air-fuel mixture in this embodiment) is "lean" and "spiky stoichiometric or rich (hereinafter, This is called lean rich spike control, which is referred to as lean rich spike control, and lean rich spike control is also adopted in this embodiment. In this application, the lean / rich spike control is included in the lean air-fuel ratio control.

On the other hand, the fuel contains sulfur (S).
And when the sulfur in the fuel burns, SO₂And SO₃Such as sulfur
Oxide (SOx) is generated, and the NOx storage reduction catalyst is exhausted.
It also absorbs these SOx in the gas. Storage reduction type NOx catalyst
SOx absorption mechanism is the same as NOx absorption mechanism
It is believed that there is. That is, the mechanism of NOx absorption is explained.
Platinum Pt and barium B were deposited on the carrier in the same manner as when revealed.
Explaining the case of carrying a as an example, it was mentioned above.
Thus, when the exhaust air-fuel ratio is lean, oxygen O₂Is O₂
^-Or O^2-Surface of platinum Pt of NOx storage reduction catalyst in the form of
SOx (for example, S
O₂) Is oxidized on the surface of platinum Pt to form SO ₃Becomes

Thereafter, the produced SO ₃ is further oxidized on the surface of platinum Pt, absorbed in the occlusion-reduction type NOx catalyst and combined with barium oxide BaO to form sulfate ion SO.
₄ ² -diffuse in the NOx storage-reduction type catalyst to form sulfate BaS
Generates O ₄ . This sulfate BaSO ₄ is stable and difficult to decompose, and even if the air-fuel ratio of the inflowing exhaust gas is stoichiometric or rich for a short time by the lean rich spike control described above, it is not decomposed and is stored in the NOx storage reduction catalyst. I will remain. Therefore, as time passes, the storage reduction type N
When the amount of BaSO ₄ produced in the Ox catalyst increases, the amount of BaO that can participate in the absorption of the NOx storage reduction catalyst decreases, and
Ox absorption capacity is reduced. This situation is S
Ox poisoning.

In this case, as described above, the NOx catalyst 20
In order to release the SOx absorbed by the NOx catalyst, it is necessary to raise the temperature of the NOx catalyst to a predetermined temperature or higher. Generally, N
The temperature required to activate the Ox catalyst is about 250 ° C. to 300 ° C., but in order to release SOx and eliminate so-called S poisoning, the air-fuel ratio of the exhaust gas is controlled to be in a stoichiometric state. At the same time, it is necessary to raise the temperature of the NOx catalyst 20 to about 700 ° C. In the exhaust gas purification apparatus according to the present embodiment, the NOx catalyst 20 is heated and raised by performing the cylinder-by-cylinder air-fuel ratio control, and SOx in the NOx catalyst 20 is forcibly released to purify the NOx catalyst. It is designed to restore abilities.

That is, in the present embodiment, for example,
In the case of a 4-cylinder engine, air-fuel in the 1st and 4th cylinders
The lean ratio is used to control the air-fuel ratio of the 2nd and 3rd cylinders.
When exhaust control is performed, the exhaust gas emitted from these four cylinders
When the gases are mixed in the NOx catalyst 20,
The air-fuel ratio of the exhaust gas as a whole becomes stoichiometric. Also,
Large amount of exhaust gas discharged from No. 2 cylinder and No. 3 cylinder
HC, CO, and exhausted from cylinders 1 and 4
A large amount of oxygen in the exhaust gas reacts on the NOx catalyst.
The NOx catalyst 20 is heated by burning by burning. So
As a result, the temperature of the NOx catalyst 20 rises, and this temperature rise
SOx in the NOx catalyst 20 becomes SO ₂Released as
Thus, the situation of S poisoning of the NOx catalyst 20 is resolved.

During the heating / heating process of the NOx catalyst 20, there may occur a situation in which it is necessary to decelerate the traveling vehicle, for example. When the vehicle slows down like this,
Fuel supply control to stop the fuel supply to the engine body 1 is performed. When the fuel cut control is performed in this manner, the fuel supply to the cylinder is stopped and the combustion temperature of the exhaust gas in the cylinder becomes low. Therefore, the exhaust gas at the fuel cut is directly supplied to the NOx catalyst 20. In such a case, the exhaust gas having a low temperature flows into the NOx catalyst 20, and the temperature of the NOx catalyst 20 will drop even though the NOx catalyst 20 is being heated.

Therefore, in the present embodiment, the NOx catalyst 20 is controlled during the temperature increase control of the NOx catalyst 20, as in the case where the vehicle is decelerated during the temperature increase control of the NOx catalyst.
When the engine is controlled so as to lower the temperature of the exhaust gas flowing into the exhaust gas, the exhaust gas having a low temperature is made to flow down through the bypass passage 26 so as not to flow into the NOx catalyst 20.

That is, during the temperature rise control of the NOx catalyst 20, when the exhaust gas having a temperature lower than the set predetermined temperature flows into the NOx catalyst 20 from the engine body 1, the temperature sensor 23 is used. When the inflow of exhaust gas at a temperature lower than the predetermined temperature is detected, the exhaust switching valve 28 is actuated by the actuator 27 to reach the bypass open position in FIG. 1 to close the inlet 21a of the NOx catalyst 20 and bypass the bypass. The pipe 26 is opened, and exhaust gas having a temperature lower than a predetermined temperature is supplied to the exhaust pipe 22 via the bypass pipe 26. As a result, this low-temperature exhaust gas does not flow into the NOx catalyst 20, so that the temperature of the NOx catalyst 20 that has reached a predetermined high temperature due to the temperature rise control is prevented from decreasing due to the inflowing exhaust gas. can do.

Further, such a situation may occur, for example, when the vehicle accelerates. That is, the above NO
x When the vehicle accelerates during the temperature rise control of the catalyst 20,
The engine is in a high load state and the air-fuel ratio control reaches a stoichiometric state. In this case, although the stoichiometric control is performed, the temperature is still lower than the exhaust gas temperature during the cylinder-by-cylinder air-fuel ratio control, and when the NOx catalyst 20 is flowed in the same manner as above,
As a result, the temperature of the NOx catalyst whose temperature is controlled is lowered. Therefore, even in such a case, the exhaust switching valve 28 is operated in the same manner as described above to operate the inlet portion 21a of the NOx catalyst 20.
Is closed, the bypass pipe 26 is opened, and the exhaust gas having a low temperature is supplied to the exhaust pipe 22 via the bypass pipe 26.

The operation of the exhaust gas purification apparatus for an internal combustion engine according to this embodiment will be described below with reference to the bypass processing execution routine shown in FIG. A flow chart including each step constituting this routine is stored in the ROM 32 of the ECU 30, and the processes in each step of the flow chart are all executed by the CPU 34 in the ECU 30.

<Step 101> As a premise, the exhaust switching valve 28 is arranged at a position where the bypass pipe 26 is closed and the inlet 21a of the NOx catalyst 20 is opened, and the NOx catalyst 20 is heated and raised by the cylinder-by-cylinder air-fuel ratio control. The temperature is controlled and the SOx in the NOx catalyst 20 is forcibly released to generate N
It is controlled so as to restore the NOx purification capacity of the Ox catalyst.

In the case of the cylinder-by-cylinder air-fuel ratio control as described above, the ECU 30 causes the fuel cut during deceleration or the internal combustion engine to be under high load during acceleration.
It is determined whether or not a situation occurs in which the cylinder-by-cylinder air-fuel ratio control is interrupted and the stoichiometric control is performed.

If it is determined in this step that the situation is not fuel cut or transition to stoichiometric control, it is not necessary to proceed to the next step 102.
The cylinder-by-cylinder air-fuel ratio control is continuously executed. On the other hand, when the ECU 30 determines in step 101 that the fuel cut situation has occurred or the stoichiometric control has been performed, the process proceeds to step 102.

<Step 102> In Step 102,
The ECU 30 determines whether or not the temperature of the exhaust gas flowing from the engine body 1 into the NOx catalyst 20 via the exhaust manifold 16 and the exhaust pipe 19 is equal to or lower than a predetermined threshold value, or the engine speed of the engine body 1 is equal to a predetermined threshold value. It is determined whether or not the above.

In this case, whether or not the temperature of the exhaust gas flowing into the NOx catalyst 20 is less than or equal to a predetermined threshold value is determined through the temperature sensor 23. An output voltage proportional to the temperature of the gas is generated, and this output voltage is input to the input port 35 via the AD converter 38.

Further, the determination as to whether the engine speed of the engine body 1 is equal to or higher than a predetermined threshold value is made through the speed sensor 41, and the speed sensor 41 outputs an output pulse representing the engine speed. The generated output pulse is input to the input port 35.

If it is determined in step 102 that the temperature of the inflowing exhaust gas is not lower than the threshold value, or if it is determined that the engine speed of the engine body 1 is not higher than the threshold value, the next step 103 The above-mentioned cylinder-by-cylinder air-fuel ratio control is continuously executed without proceeding to. On the other hand, in step 102, when it is determined that the temperature of the exhaust gas flowing in due to the fuel cut during deceleration is equal to or lower than the threshold value, or it is determined that the engine speed of the engine body 1 is equal to or higher than the threshold value during acceleration. If so, go to the next step 103.

<Step 103> As described above, when it is determined in step 102 that the temperature of the exhaust gas flowing into the NOx catalyst 20 is equal to or lower than the threshold value, or it is determined that the engine speed of the engine body 1 is equal to or higher than the threshold value. If so, the process proceeds to the next step 103, and the exhaust gas is processed to flow down through the bypass pipe 26.

That is, in this case, the CPU 34 sends a signal to the drive circuit 39 via the output port 36, and the drive circuit 39 supplies power to operate the actuator 27. The exhaust switching valve 28 is driven by the actuator 27 and is arranged at a position where the inlet portion 21a of the NOx catalyst 20 is closed and the bypass pipe 26 is opened. As a result, the exhaust gas flowing from the engine body 1 through the exhaust manifold 16 and the exhaust pipe 19 is NO
The x-catalyst 20 does not flow into the catalyst 20 but flows down through the bypass pipe 26 to reach the exhaust pipe 22.

In the present embodiment, when the temperature increase control of the NOx catalyst 20 is performed by the cylinder-by-cylinder air-fuel ratio control, for example, a situation of deceleration or acceleration occurs, and the temperature of the exhaust gas is below a certain temperature. In this case, the exhaust gas flows down through the bypass pipe 26, so that the NOx catalyst 2
The NOx catalyst 20 does not flow into 0, and the temperature of the NOx catalyst 20 does not drop significantly.

Therefore, when the situation of deceleration or acceleration is completed and the temperature rise control by the cylinder-by-cylinder air-fuel ratio control is performed again, the temperature required for purifying the NOx catalyst 20 (for example, 70
There is no significant loss of time until reaching 0 ° C.

As a result, the time required for the temperature rise control of the NOx catalyst 20 can be shortened as compared with the case where the exhaust gas having a lowered temperature flows into the NOx catalyst 20 without the above-mentioned configuration. It is possible to maintain good fuel efficiency. Further, since the NOx catalyst 20 can restore the exhaust gas purification capacity in a form in which the influence of fuel cut during deceleration or stoichiometric control during acceleration is reduced, the emission of the exhaust purification catalyst can be improved.

In the above embodiment, the NOx catalyst 2 is used in the exhaust purification system for an internal combustion engine according to the present invention.
If 0 becomes a so-called SOx poisoning situation, this S
In order to eliminate the situation of Ox poisoning, for example, the case of the temperature raising control in which the NOx catalyst 20 is heated and raised by the cylinder-by-cylinder air-fuel ratio control to release SOx has been described as an example, but the present invention is not limited to the above embodiment. However, the present invention can also be applied to the case of warm-up operation when starting the engine, for example.

That is, during the warm-up operation when starting the engine, the air-fuel ratio control of the engine is in a stoichiometric state, and the exhaust gas of relatively high temperature flows into the NOx catalyst 20. In this case, when the vehicle is running and decelerates, fuel cut control is performed in the same manner as described above, and fuel supply to the cylinders is stopped. As a result, the exhaust gas having a temperature lower than that at the time of stoichiometric control flows into the NOx catalyst 20, and the heating of the NOx catalyst 20 is prevented from being heated.

Therefore, even in such a case, the ECU 3 is determined in step 101 in accordance with the flowchart of FIG.
When 0 is determined to be a fuel cut situation during deceleration, the routine proceeds to step 102, where it is determined whether the temperature of the exhaust gas detected by the temperature sensor 23 is below a predetermined threshold value. . In this case, when it is determined that the value is equal to or less than the threshold value, the CPU 34 operates the actuator 27 by the drive circuit 39 via the output port 36 to cause the exhaust gas switching valve 28 to move to the inlet portion 21 of the NOx catalyst 20.
A is closed and the bypass pipe 26 is placed at an open position. As a result, the exhaust gas flowing from the engine body 1 through the exhaust manifold 16 and the exhaust pipe 19 does not flow into the NOx catalyst 20 and does not flow into the bypass pipe 26.
And flows down to the exhaust pipe 22.

As a result, the inflow of exhaust gas having a low temperature into the NOx catalyst 20 is blocked, so that the influence of the fuel cut control on the NOx catalyst 20 due to deceleration during the temperature increase control of the NOx catalyst 20 is minimized. Will be things. Therefore, as in the previous term, the exhaust gas whose temperature has dropped is the NOx catalyst 2
As compared with the case where the NOx catalyst 20 has flowed into 0, the time required for the temperature rise control for activating the NOx catalyst 20 can be shortened,
It is possible to maintain good fuel efficiency.

Further, the NOx catalyst 20 reduces the influence of fuel cut during deceleration.
The activation of 0 can be performed, and the emission of the exhaust purification catalyst can be improved.

In addition, although the case where the exhaust gas purifying apparatus for an internal combustion engine according to the present invention is applied to an internal combustion engine capable of lean burn according to the present embodiment has been described as an example, the present invention is not limited to the above embodiment. Instead, it can be applied to a general internal combustion engine.

[0087]

According to the first aspect of the invention, when the temperature rise control of the internal combustion engine is being performed, for example, during acceleration.
Even when the air-fuel ratio control reaches the stoichiometric control state, it is possible to reduce the influence on the heating temperature rising state of the NOx catalyst , improve the emission, and improve the fuel efficiency. An exhaust gas purification device for an internal combustion engine can be provided.

[0088]

[0089]

[0090]

According to the second aspect of the present invention, it is possible to provide an exhaust gas purification device for an internal combustion engine configured to switch exhaust gas by the exhaust gas switching means.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an exhaust emission control device engine for an internal combustion engine according to an embodiment of the present invention, with NOx in an exhaust pipe.
It is a figure which shows the state in which the bypass pipe which bypasses a catalyst is provided.

FIG. 2 is a diagram showing an example of a map of basic fuel injection time.

FIG. 3 Unburned HC and C of exhaust gas discharged from the engine
It is a graph which shows the concentration of O and oxygen roughly.

FIG. 4 is a diagram for explaining the NOx absorption / release action of the NOx storage reduction catalyst.

FIG. 5 shows a case where exhaust gas is caused to flow down through a bypass passage when engine control is performed so as to obstruct temperature rising control of an exhaust purification catalyst in an exhaust purification system for an internal combustion engine according to an embodiment of the present invention. It is a flow chart which shows a control routine.

[Explanation of symbols]

1 engine body 3 Combustion chamber 4 Spark plug 11 Fuel injection valve 16, 19, 22 Exhaust pipe (exhaust passage) 20 Exhaust gas purification material (NOx catalyst) 23 Temperature sensor 26 Bypass pipe (bypass passage) 28 Switching means (exhaust gas switching valve) 20 ECU

Continuation of the front page (51) Int.Cl. ⁷ Identification code FI F01N 3/28 301 F01N 3/28 301C F02D 41/04 305 F02D 41/04 305D 41/12 330 41/12 330J 43/00 301 43/00 301H 301T (56) Reference JP-A-6-346724 (JP, A) JP-A-4-194312 (JP, A) JP-A-6-346768 (JP, A) Actual development Sho-55-140705 (JP, U) (58) Fields investigated (Int.Cl. ⁷ , DB name) F01N 3/08-3/28 F02D 41/04 F02D 41/12 F02D 43/00

Claims (2)

(57) [Claims] 1. A disposed in an exhaust passage of an internal combustion engine, the internal combustion
When the air-fuel ratio of the exhaust gas flowing from the engine is lean
In the case of
NO that releases absorbed NOx when the oxygen concentration is low
In an exhaust gas purification apparatus for an internal combustion engine , which comprises an x-catalyst and a bypass passage bypassing the NOx catalyst , an exhaust gas having a rich exhaust air-fuel ratio and a lean exhaust air-fuel ratio
Exhaust gas is allowed to flow into the NOx catalyst to contact the NOx.
During the temperature increase control of the internal combustion engine to increase the temperature of the medium, the internal combustion engine
When shifting to stoichiometric control under heavy load on Seki ,
An exhaust emission control device for an internal combustion engine, wherein the exhaust gas is configured to flow down through a bypass passage. Wherein the front Symbol exhaust passage, wherein the exhaust gas NOx
Exhaust switching means capable of supplying to the one of the catalyst or the bypass passage is provided with, in the temperature increase control of the internal combustion engine, when a transition to the stoichiometric control actuates the pre Symbol exhaust switching means The exhaust gas is configured to flow down through the bypass passage.
An exhaust gas purification device for an internal combustion engine as described.