JP2000314310A - Exhaust gas purification device for internal combustion engine - Google Patents

Abstract

(57) [Problem] To provide a case in which the control is shifted to a control for preventing the heating and heating of the exhaust gas purifying material on the internal combustion engine side while the temperature rising control of the exhaust gas purifying material of the internal combustion engine is being performed. Also, it is possible to reduce the influence of the exhaust gas purifying material on the heating and heating state, and to provide an exhaust gas purifying apparatus for an internal combustion engine having good emission and good fuel efficiency. An exhaust gas purifying material disposed in exhaust passages of an internal combustion engine, and an exhaust gas purifying material disposed in the exhaust passage.
A bypass passage provided in each of the exhaust gas purifying material and the exhaust gas purifying material to increase the temperature of the exhaust gas purifying material by heating the exhaust gas purifying material; In the exhaust gas purifying apparatus for an internal combustion engine, the exhaust gas flowing into the exhaust gas purifying material 20 during the temperature raising control of the internal combustion engine 1 in which the temperature raising means raises the temperature of the exhaust gas purifying material 20. When shifting to the internal combustion engine control for lowering the gas temperature, the exhaust gas is caused to flow down via the bypass passage 26.

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 and raising the temperature of the exhaust gas purifying material when controlling the temperature of the exhaust gas purifying material. The present invention relates to an exhaust gas purification device for an internal combustion engine that can reduce the influence on the temperature rise of an exhaust gas purification material even when the control is shifted to control.

[0002]

2. Description of the Related Art Generally, in an internal combustion engine capable of lean combustion, an air-fuel ratio of inflowing exhaust gas is conventionally used as an exhaust purification device for purifying nitrogen oxides (NOx) contained in exhaust gas discharged from the internal combustion engine. In the lean state, while absorbing NOx, the oxygen concentration of the exhaust gas is reduced, and when the stoichiometric or rich state is reached, the absorbed NOx is released and reduced.
Catalysts are known.

[0003] Further, since sulfur is contained in the fuel and the lubricating oil of the engine, SOx is contained in the exhaust gas. However, the NOx catalyst is the same as that used to absorb the NOx. SOx is absorbed by the mechanism. in this case,
Since the SOx absorbed by the NOx catalyst forms a stable sulfate over time, the NOx from the NOx catalyst
SOx is not emitted under the conditions when releasing NOx, and NOx
There is a problem that the amount of SOx increases in the absorber, and as a result, the amount of NOx absorbed decreases, and the NOx purification efficiency decreases.

[0004] Therefore, in order to avoid such a problem, conventionally, the NOx catalyst is heated to a predetermined temperature (for example, about 700 ° C) at a fixed cycle to increase the temperature of the NOx catalyst, thereby reducing the exhaust purification capability of the NOx catalyst. A technique for burning and removing such substances has been proposed. That is, for example, an adhering amount estimating means for estimating the adhering amount of a substance (for example, sulfur or the like) other than NOx that reduces the exhaust purifying ability attached to the exhaust purifying catalyst of the internal combustion engine; There has also been proposed an exhaust gas purification device for an internal combustion engine provided with catalyst heating means for supplying fuel and air to an exhaust gas purification catalyst when the amount of adhesion reaches a predetermined amount and burning the fuel to raise the temperature of the exhaust gas purification catalyst. (See JP-A-8-61052).

Conventionally, such a temperature rise control of the exhaust gas purifying catalyst is performed by controlling the air-fuel ratio for each cylinder in a multi-cylinder engine. Such control is called cylinder-by-cylinder air-fuel ratio control. For example, in a V-type engine, rich combustion is performed in a cylinder on one bank side, and lean combustion is performed in a cylinder on the other bank side. The fuel containing NOx released from the air 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 it with the residual oxygen. By increasing the temperature of the catalyst, a substance that decreases the exhaust gas purification ability attached to the catalyst is burned and removed. As a result, the rich combustion operation in which the output of the internal combustion engine is increased and the lean combustion operation in which the output of the internal combustion engine is reduced are alternately performed in a well-balanced manner, and the output fluctuation of the internal combustion engine is suppressed to a small level.

Conventionally, in order to efficiently purify both particulates and NOx composed of solid particulates of unburned HC, a fuel injection control means provided in a cylinder of an internal combustion engine and an exhaust passage are provided. Exhaust processing means, exhaust temperature estimating means for estimating exhaust temperature, and temperature comparing means for comparing the output of the temperature estimating means with a predetermined value, wherein the fuel injection control means is provided when the exhaust temperature is lower than a predetermined value. Is configured to instruct a post-injection of fuel after the main fuel injection for generating the engine output, and to control the exhaust gas temperature of the engine to a temperature range suitable for the operation of the exhaust processing means by the post-injection. (See JP-A-8-303290). Therefore, conventionally, so-called SOx poisoning due to sulfur is eliminated or particulates are purified.

However, as described above, control is performed to increase the exhaust gas temperature by heating the exhaust gas purification catalyst by supplying fuel and air to the exhaust gas purification catalyst and burning the fuel, or by performing post-injection. In such a case, for example, when a situation occurs in which the running vehicle is decelerated, the internal combustion engine is in a so-called fuel cut control, and since no fuel is supplied to the internal combustion engine, the exhaust gas temperature decreases, and the Exhaust gas with a low temperature will be supplied.
On the other hand, in the case where it is necessary to accelerate the traveling vehicle, the air-fuel ratio control of the internal combustion engine shifts to the stoichiometric control. The gas is supplied to the exhaust purification catalyst.

As a result, there are cases where the temperature of the exhaust gas purification catalyst does not rise sufficiently, and cases where the temperature of the exhaust gas purification catalyst once rises drops. Therefore, when the internal combustion engine performs control to prevent the temperature of the exhaust catalyst from increasing during the temperature increase control of the exhaust catalyst, the temperature of the exhaust purification catalyst is increased to a certain temperature. Despite this, the temperature of the exhaust purification catalyst decreases.

Therefore, it is necessary to heat the exhaust purification catalyst to a predetermined temperature again, and as a result, in order to regenerate SOx poisoning of the exhaust purification catalyst, the temperature rise control of the exhaust purification catalyst is hindered. As compared with the case where the control is not performed on the internal combustion engine side, there is a problem that a longer time is required for raising the temperature of the exhaust purification catalyst, and the emission of the exhaust purification catalyst is reduced. Further, the fuel consumption is low during the temperature rise control as in the case of the stoichiometric control, so that the fuel efficiency is low. From the viewpoint of improving the fuel efficiency, a reduction in the temperature rise control time has been desired.

[0010] Further, in addition to the internal combustion engine capable of lean burn, generally, when the internal combustion engine is warmed up at the time of start-up, it is necessary to raise the temperature to a temperature at which the exhaust purification catalyst is activated. In this case, if a situation that hinders the temperature rise of the exhaust gas purifying catalyst during the stoichiometric warm-up operation, for example, if the need for deceleration occurs, the exhaust gas purifying catalyst reaches the predetermined temperature as described above. It took a long time to raise the temperature, and the same problem as described above existed.

[0011]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to heat an exhaust gas purifying material on the side of the internal combustion engine when temperature control of the exhaust gas purifying material of the internal combustion engine is performed. Even when the control is shifted to a control that hinders the temperature increase, it is possible to reduce the influence of the exhaust gas purifying material on the heating and temperature rising state, thereby achieving good emission and improving fuel efficiency. An object of the present invention is to provide an exhaust emission control device.

A second object of the present invention is to provide an internal combustion engine capable of lean combustion.
When the temperature rise control of the exhaust gas purifying material is being performed, even when the internal combustion engine shifts to a control that hinders the heating temperature rise of the exhaust gas purifying material, the temperature of the exhaust gas purifying material is raised. It is an object of the present invention to provide an exhaust gas purifying apparatus for an internal combustion engine that can reduce the influence thereof, achieve good emission, and improve fuel efficiency.

A third object of the present invention is to provide a control apparatus for controlling the temperature of the exhaust gas purifying material even when the temperature of the exhaust gas purifying material is reduced. It is an object of the present invention to provide an exhaust gas purifying apparatus for an internal combustion engine, which can reduce the influence on a temperature state, achieve good emission, and improve fuel efficiency.

An object of the invention described in claim 4 is that, when the temperature rise control of the exhaust gas purifying material is performed, for example, even if the air-fuel ratio control reaches a stoichiometric state at the time of acceleration, the exhaust gas purifying material may be exhausted. It is an object of the present invention to provide an exhaust gas purifying apparatus for an internal combustion engine, which can reduce the influence of a gas purifying material on a heating and heating state, improve emission, and improve fuel efficiency.

It is an object of the present invention to provide an exhaust gas purifying apparatus for an internal combustion engine, wherein the exhaust gas is switched by an exhaust gas switching means.

[0016]

In order to solve such technical problems, according to the present invention, an exhaust gas purifying material disposed in an exhaust passage of an internal combustion engine and the exhaust gas purifying material are provided. And a temperature increasing means capable of heating the exhaust gas purifying material to increase the temperature of the catalyst by heating the exhaust gas purifying material. During the temperature rise control of the internal combustion engine to raise the temperature, when the process shifts to the internal combustion engine control to lower the temperature of the exhaust gas flowing into the exhaust gas purifying material, the exhaust gas is caused to flow down through the bypass passage. It is characterized by having.

Here, the "temperature raising control of the internal combustion engine for raising the temperature of the exhaust gas purifying material by the temperature raising means" corresponds to, for example, cylinder-by-cylinder air-fuel ratio control in a lean-burn internal combustion engine. In addition, the fuel injection is performed after the main fuel injection for generating the engine output, and the post-injection controls the exhaust gas temperature of the engine to a temperature range suitable for the operation of the exhaust processing means.

Therefore, according to the first aspect of the present invention,
During the temperature raising control of the internal combustion engine in which the temperature of the exhaust gas purifying material is raised by the temperature raising means, when the control is shifted to the internal combustion engine control in which the temperature of the exhaust gas flowing into the exhaust gas purifying material is lowered, The temperature of the exhaust gas flowing out of the exhaust gas falls, but the exhaust gas whose temperature has dropped flows through the bypass passage, and does not flow into the exhaust gas purifying material.

As a result, according to the first aspect of the invention, when the temperature rise control of the exhaust gas purifying material of the internal combustion engine is performed, the control for preventing the temperature rise of the exhaust gas on the internal combustion engine side is performed. Even in the case of shifting, it is possible to reduce the influence of the exhaust gas purifying material on the heating and heating state, thereby improving emission purification and improving fuel efficiency.

According to the second aspect of the present invention, the exhaust gas purifying material absorbs NOx and inflows when the air-fuel ratio of the exhaust gas flowing from the internal combustion engine capable of lean combustion is lean. It is a NOx catalyst that releases absorbed NOx when the oxygen concentration of the exhaust gas to be exhausted is low.

Therefore, according to the second aspect of the present invention,
In the internal combustion engine capable of lean combustion, during the temperature raising control of the internal combustion engine in which the temperature of the exhaust gas purifying material is raised by the temperature raising means, the control is shifted to the internal combustion engine control in which the temperature of the exhaust gas flowing into the exhaust gas purifying material is lowered. When this occurs, the temperature of the exhaust gas flowing out of the internal combustion engine falls, but the exhaust gas whose temperature has fallen flows down through the bypass passage.
It does not flow into the exhaust gas purifying material.

As a result, according to the second aspect of the present invention, when the temperature rise control of the exhaust gas purification material of the internal combustion engine is performed in the internal combustion engine capable of lean combustion, the exhaust gas Even if the control is shifted to a control that prevents heating and heating, the effect of the exhaust gas purifying material on the heating and heating state can be reduced, the emission of exhaust gas can be improved, and fuel efficiency can be improved. Can be done.

According to a third aspect of the present invention, the control of the internal combustion engine for lowering the temperature of the exhaust gas flowing into the exhaust gas purifying apparatus is a fuel cut control. Therefore, according to the third aspect of the present invention, when the temperature of the exhaust gas purification device of the internal combustion engine is being controlled and the vehicle is decelerated as necessary, the fuel cut control is performed and the internal combustion engine is controlled. The fuel supply to the cylinder is stopped. As a result, exhaust gas having a combustion temperature lower than that at the time of the temperature increase control is generated. In such a case, the exhaust gas having a low combustion temperature flows down through the bypass passage and is not supplied to the exhaust gas purifying material.

As a result, according to the third aspect of the present invention, even if the fuel injection control is shifted to the fuel cut control in which the heating of the exhaust gas purification device is prevented from heating up on the internal combustion engine side,
It is possible to reduce the influence of the exhaust purification catalyst on the heating and temperature rising state, thereby improving emission purification emission and improving fuel efficiency.

According to a fourth aspect of the present invention, the control of the internal combustion engine for lowering the temperature of the exhaust gas flowing into the exhaust purification device is a stoichiometric control at a high load of the internal combustion engine.

Therefore, in the invention according to claim 4,
When the vehicle is accelerated as required during the temperature rise control of the exhaust gas purification device of the internal combustion engine, the air-fuel ratio control of the internal combustion engine is stoichiometric control.

The exhaust gas temperature when the stoichiometric control is performed is not as high as the exhaust gas temperature during the temperature raising control. As a result, the exhaust gas having a combustion temperature lower than that during the temperature raising control is generated. appear. In such a case, the exhaust gas having a low combustion temperature flows down through the bypass passage and is not supplied to the exhaust gas purifying material.

As a result, according to the present invention, even when the internal combustion engine shifts to the stoichiometric control in which the heating of the exhaust gas purifying device is prevented from being heated, the exhaust gas purifying catalyst is heated to the heated state. Influence can be reduced,
It is possible to improve emission purification and improve fuel efficiency.

According to the fifth aspect of the present invention, the exhaust passage is provided with exhaust switching means for supplying exhaust gas to either the exhaust gas purifying material or the bypass passage. During the temperature rise control of the internal combustion engine for raising the temperature of the exhaust gas purifying material, when the process shifts to the internal combustion engine control for lowering the temperature of the exhaust gas purifying material, the exhaust gas switching means is operated to bypass the exhaust gas. It is configured to flow down through a passage.

Therefore, in the invention according to claim 5,
During the temperature raising control of the internal combustion engine for raising the temperature of the exhaust gas purifying material by the temperature raising means, during the transition to the internal combustion engine control for lowering the temperature of the exhaust gas flowing into the exhaust gas purification device, The temperature of the exhaust gas flowing out drops. At this time, the exhaust gas switching means is disposed at a switching position for opening the bypass passage and closing the exhaust gas purifying material, so that the exhaust gas whose temperature has decreased flows into the bypass passage by the exhaust gas switching means, Since it flows down through the bypass passage, it does not flow into the exhaust gas purifying material.

As a result, in the invention according to claim 5, when the temperature rise control of the exhaust gas purification device of the internal combustion engine is performed, the control for preventing the heating temperature rise of the exhaust gas purification device on the internal combustion engine side is performed. Even in the case of shifting, it is possible to reduce the influence of the exhaust purification catalyst on the heating and temperature rising state, improve the emission of exhaust purification, and improve fuel efficiency.

[0032]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of an exhaust gas purifying apparatus for an internal combustion engine according to an embodiment of the present invention;

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

The intake port 6 is connected to a 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.
And an exhaust pipe 19 which is joined to a casing 21 containing a storage-reduction type NOx catalyst 20 as an exhaust gas purifying material. The storage reduction type NOx 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 can supply exhaust gas by bypassing the NOx storage reduction catalyst 20 is provided between the exhaust pipe 19 and the exhaust pipe 22. I have. An actuator 27 is provided at an inlet 21 a of the casing 21 which is a branch of the bypass pipe 26.
An exhaust switching valve 28 is provided as switching means, which is configured to operate the valve body.

The exhaust switching valve 28 is connected to an actuator 27
As a result, as shown by the solid line in FIG.
A bypass closing position for closing the inlet portion of the NOx catalyst 20 and fully opening the inlet portion to the downstream NOx catalyst 20, and closing the inlet portion 21a to the downstream NOx catalyst 20 as shown by the broken line in FIG. It is configured to operate by selecting one of the bypass open positions for fully opening the inlet portion of 26.

An electronic control unit (ECU) 30 for engine control is composed of a digital computer, and is connected to a ROM (Read Only Memory) 32, a RAM (Random Access Memory) 33, and a CPU (Central Processor) interconnected by a bidirectional bus 31. Unit) 3
4, an input port 35 and an output port 36 are provided. The air flow meter 13 generates an output voltage proportional to the amount of intake air, and this output voltage is input to an input port 35 via an 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. The voltage is input to the input port 35 via the AD converter 38. The input port 35 is connected to a rotation speed sensor 41 that generates an output pulse indicating the engine rotation speed. Output port 36
Are connected to the ignition plug 4, the fuel injection valve 11, and the actuator 27 via corresponding drive circuits 39, respectively.

In this gasoline engine, the fuel injection time TAU is calculated based on, for example, the following equation. TAU = TP · K Here, TP indicates a basic fuel injection time, and K indicates a correction coefficient. The basic fuel injection time TP indicates a fuel injection time required for setting the air-fuel ratio of the air-fuel mixture supplied into the engine cylinder to the stoichiometric air-fuel ratio. This basic fuel injection time TP is obtained in advance by an experiment, 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.
2 is stored. The correction coefficient K is a coefficient for controlling the air-fuel ratio of the air-fuel mixture supplied to the engine cylinder. If K = 1.0, the air-fuel mixture supplied to the engine cylinder becomes the stoichiometric air-fuel ratio. On the other hand, if 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, lean, and K> 1.
When it becomes 0, the air-fuel ratio of the mixture supplied to the engine cylinder becomes smaller than the stoichiometric air-fuel ratio, that is, becomes rich.

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

In the internal combustion engine, the operation is usually performed most frequently at low to medium load. Therefore, during most of the operation period, the value of the correction coefficient K is made smaller than 1.0, and the lean mixture is burned. become.

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

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

When an NOx storage reduction catalyst such as the NOx catalyst 20 is disposed in the exhaust passage of the engine, the NOx storage reduction catalyst becomes NOx when the air-fuel ratio of the inflowing exhaust gas (hereinafter referred to as exhaust air-fuel ratio) is lean. And absorbs and releases NOx when the oxygen concentration in the inflowing exhaust gas decreases. Here, the exhaust air-fuel ratio refers to the air and fuel (hydrocarbon) supplied into the exhaust passage upstream of the engine intake passage and 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 mixture supplied to the combustion chamber is lean, and absorbs NOx when the oxygen concentration in the mixture supplied to the combustion chamber decreases. Will be released.

The detailed mechanism of the NOx absorption / release operation by the NOx storage reduction catalyst is not clear in some parts. However, it is considered that this absorption / release action is performed by a mechanism as shown in FIG. next,
This mechanism will be described by taking platinum Pt and barium Ba supported on a carrier as an example, 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 the 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, absorbed in the NOx storage reduction catalyst, and combined with barium oxide BaO, as shown in FIG. nitrate ions NO ₃ ^- storage reduction NO in the form of
x Diffusion into 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 generated on the surface of platinum Pt, and as long as the NOx absorption capacity of the NOx storage reduction catalyst is not saturated, NO ₂ is absorbed in the NOx storage reduction catalyst. As a result, nitrate ions NO ₃ ^- are generated.

On the other hand, when the oxygen concentration in the inflowing exhaust gas decreases and the NO ₂ generation amount decreases, the reaction proceeds in the reverse direction (NO ₃ ⁻ → NO ₂ ), and the nitric acid in the NOx storage reduction catalyst is reduced. The ions NO ₃ ^- are stored and reduced N in the form of NO ₂ or NO.
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 degree of leanness of the inflowing exhaust gas decreases, the oxygen concentration in the inflowing exhaust gas decreases. Therefore, when the degree of leanness of the inflowing exhaust gas decreases, NOx is reduced from the NOx storage reduction catalyst. Will be released.

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

[0053] Further, the NOx storage reduction catalyst is NO ₂ or NO is released to the air-fuel ratio of exhaust gas oxygen concentration of the inflowing exhaust gas becomes stoichiometric or rich to extremely lowered, the NO ₂ or NO, FIG. As shown in FIG. 4 (B), it reacts with unburned HC and CO to be 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 consumption, this H
C, NOx discharged from the released NOx, the engine from the NOx storage reduction catalyst by CO is made to reduction to N _2.

In this way, NO _{2 is} deposited 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, if the exhaust air-fuel ratio is made stoichiometric or rich, the storage reduction type N
NOx will be released from the Ox catalyst.

As described above, when the exhaust air-fuel ratio becomes lean, NOx is absorbed by the NOx storage reduction catalyst, and when the exhaust air-fuel ratio is made stoichiometric or rich, NOx is stored in the NOx storage reduction catalyst.
Released in a short time from the Ox catalyst is reduced to N _2. Therefore, emission of NOx into the atmosphere can be prevented.

During the full load operation, the air-fuel mixture supplied into the combustion chamber is made rich. At the time of high load operation, warm-up operation at the time of engine start, acceleration, and 120 km / h.
During the above constant speed operation, the air-fuel ratio is calculated based on the theoretical air-fuel ratio (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 the NOx storage reduction catalyst is used during full load operation and high load operation. NOx is released from the catalyst and reduced. However, if the frequency of full-load operation or high-load operation is low and the frequency of low-medium load operation is high and the operation time is long, the release and reduction of NOx cannot be made in time, and the NOx absorption capacity (NOx absorption 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 stoichiometric operation is performed in a relatively short cycle. In some cases, a method of controlling the air-fuel ratio of the air-fuel mixture so that the rich air-fuel mixture is burned and releasing and reducing NOx in a short cycle may be employed.

As described above, due to the absorption and release of NOx, the exhaust air-fuel ratio (air-fuel ratio of the air-fuel mixture in this embodiment) is set to a relatively short cycle of "lean" and "spike-like stoichiometric or rich (hereinafter, referred to as" rich "). This is referred to as a rich-spike control) is referred to as a lean-rich spike control, and the present embodiment also employs a lean-rich spike control. 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).
When the sulfur in the fuel burns, SO_TwoAnd SO_ThreeSuch as sulfur
Oxides (SOx) are generated, and the NOx storage reduction catalyst is exhausted.
These SOx in the gas are also absorbed. NOx storage reduction catalyst
SOx absorption mechanism is the same as NOx absorption mechanism
It is believed that there is. That is, the NOx absorption mechanism is explained.
Pt and barium B on the carrier as described above
If the case where a is carried out is explained as an example,
Thus, when the exhaust air-fuel ratio is lean, the oxygen O_TwoIs O_Two
^-Or O^2-Pt surface of NOx storage reduction catalyst in the form of
And SOx in the inflowing exhaust gas (for example, S
O_Two) Is oxidized on the surface of platinum Pt to form SO _ThreeBecomes

Thereafter, the generated SO ₃ is further oxidized on the surface of the platinum Pt, absorbed in the NOx storage reduction catalyst, combined with the barium oxide BaO, and the sulfate ion SO 3
_{4 The} sulfate BaS diffuses into the NOx storage reduction catalyst in the form of ^2-
Generate O ₄ . This sulfate BaSO ₄ is stable and hard to decompose, and is not decomposed 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, and is not decomposed into the NOx storage reduction catalyst. Will remain. Therefore, the storage reduction type N
When the amount of BaSO ₄ generated in the Ox catalyst increases, the amount of BaO that can participate in the absorption of the NOx storage reduction catalyst decreases, and N
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. In general, N
Although the temperature required for activating the Ox catalyst is about 250 ° C. to 300 ° C., 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 purifying apparatus according to the present embodiment, the NOx catalyst 20 is heated and heated by performing the cylinder-by-cylinder air-fuel ratio control, and the SOx in the NOx catalyst 20 is forcibly released, thereby purifying the NOx of the NOx catalyst. It is configured to restore abilities.

That is, in the present embodiment, for example,
In the case of a 4-cylinder engine, air-fuel of the 1st and 4th cylinders
Control the air-fuel ratio of the second and third cylinders.
Control, the exhaust discharged from these four cylinders
When gas is mixed in the NOx catalyst 20,
The air-fuel ratio of the entire exhaust gas is stoichiometric. Also,
Large amount in exhaust gas discharged from cylinder 2 and cylinder 3
HC, CO, and exhausted from the first and fourth cylinders
A large amount of oxygen in the exhaust gas reacts on the NOx catalyst.
The NOx catalyst 20 is heated by combustion. So
As a result, the temperature of the NOx catalyst 20 rises, and this temperature rise
As a result, SOx in the NOx catalyst 20 becomes SOx _TwoReleased as
Thus, the situation of S poisoning of the NOx catalyst 20 is eliminated.

During the process of heating and raising the temperature of the NOx catalyst 20, for example, a situation in which the traveling vehicle needs to be decelerated may occur. When the vehicle decelerates like this,
Fuel supply control to stop the fuel supply to the engine body 1 is performed. When the fuel cut control is performed as described above, the fuel supply into the cylinder is stopped, and the combustion temperature of the exhaust gas in the cylinder becomes low. Therefore, the exhaust gas at the time of the fuel cut is supplied to the NOx catalyst 20 as it is. In this case, the exhaust gas having a low temperature flows into the NOx catalyst 20, and the temperature of the NOx catalyst 20 is lowered even though the heat treatment of the NOx catalyst 20 is originally performed.

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

That is, during the temperature increase 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 When the inflow of exhaust gas having a temperature lower than the predetermined temperature is detected, the exhaust switching valve 28 is operated by the actuator 27 to reach the bypass open position in FIG. The pipe 26 is opened, and exhaust gas lower than a predetermined temperature is supplied to the exhaust pipe 22 via the bypass pipe 26. As a result, the low-temperature exhaust gas does not flow into the NOx catalyst 20, so that the temperature of the NOx catalyst 20, which has reached a predetermined high temperature due to the temperature increase control, is prevented from being lowered by the flowing exhaust gas. can do.

Such a situation can also occur, for example, when the vehicle accelerates. That is, NO as described above
When the vehicle accelerates during the temperature increase control of the x catalyst 20,
The engine enters a high load state, and the air-fuel ratio control reaches a stoichiometric state. In this case, although the stoichiometric control is performed, if the exhaust gas temperature is lower than the exhaust gas temperature in the cylinder-by-cylinder air-fuel ratio control and flows into the NOx catalyst 20 as described above,
This results in a decrease in the temperature of the NOx catalyst whose temperature is being controlled. Therefore, even in such a case, the exhaust gas switching valve 28 is operated in the same manner as described above, and the inlet 21a of the NOx catalyst 20 is opened.
And the bypass pipe 26 is opened to supply the low-temperature exhaust gas to the exhaust pipe 22 via the bypass pipe 26.

Hereinafter, the operation of the exhaust gas purifying apparatus for an internal combustion engine according to the present embodiment will be described based on a bypass processing execution routine shown in FIG. A flowchart including the steps constituting this routine is stored in the ROM 32 of the ECU 30, and all the processes in the steps of the flowchart are executed by the CPU 34 in the ECU 30.

<Step 101> It is premised that the exhaust gas switching valve 28 is disposed 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 up by the cylinder-by-cylinder air-fuel ratio control. Temperature control is performed to forcibly release SOx in the NOx catalyst 20 to reduce
The control is performed so as to restore the NOx purification ability of the Ox catalyst.

As described above, in the case of the cylinder-by-cylinder air-fuel ratio control, the ECU 30 sets the internal combustion engine to a high load state at the time of fuel cut at the time of deceleration or at the time of acceleration.
It is determined whether or not a situation has occurred in which the cylinder-by-cylinder air-fuel ratio control is interrupted to shift to stoichiometric control.

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

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

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

The determination as to whether or not the engine speed of the engine body 1 is equal to or higher than a predetermined threshold value is made via a speed sensor 41. 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 rotation speed of the engine body 1 is not higher than the threshold value, the next step 103 , The cylinder-by-cylinder air-fuel ratio control is continuously executed. 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 when it is determined that the rotation speed of the engine body 1 is equal to or higher than the threshold value during acceleration. If so, the process proceeds 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 when the rotation 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, where the exhaust gas flows 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 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 main body 1 via the exhaust manifold 16 and the exhaust pipe 19 becomes NO
It does not flow into the x catalyst 20 but flows down through the bypass pipe 26 and reaches the exhaust pipe 22.

In the present embodiment, when the temperature rise control of the NOx catalyst 20 is performed by the cylinder-by-cylinder air-fuel ratio control, for example, a deceleration or acceleration situation occurs, and the temperature of the exhaust gas becomes lower than a certain temperature. In this case, since the exhaust gas flows down through the bypass pipe 26, the NOx catalyst 2
The temperature does not flow to zero, and the temperature of the NOx catalyst 20 does not drop significantly.

Therefore, when the situation of deceleration or acceleration is completed and the control is shifted again to the temperature increase control by the cylinder-by-cylinder air-fuel ratio control, the temperature required for purifying the NOx catalyst 20 (for example, 70
0 ° C.).

As a result, the time required for controlling the temperature rise of the NOx catalyst 20 can be reduced as compared with the case where the exhaust gas whose temperature has dropped flows into the NOx catalyst 20 without employing the above-described structure. Good fuel efficiency can be maintained. Further, since the NOx catalyst 20 can recover the exhaust gas purifying ability in a form in which the influence of the fuel cut during deceleration or the stoichiometric control during acceleration is reduced, the emission of the exhaust purifying catalyst can be improved.

In the above-described embodiment, in the exhaust gas purifying apparatus for an internal combustion engine according to the present invention, the NOx catalyst 2
0 is the SOx poisoning situation, this S
In order to solve the situation of the Ox poisoning, for example, the case of the temperature raising control in which the NOx catalyst 20 is heated and heated to release the SOx by the cylinder-by-cylinder air-fuel ratio control has been described as an example, but is limited to the above embodiment. However, the present invention can be applied to, for example, a warm-up operation when the engine is started.

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

Therefore, even in such a case, the ECU 3 determines in step 101 according to the flowchart of FIG.
If 0 is determined to be a fuel cut situation during deceleration, the process proceeds to step 102, where it is determined whether the temperature of the exhaust gas detected by the temperature sensor 23 is equal to or lower than a predetermined threshold. . In this case, if it is determined that the pressure is equal to or less than the threshold value, the CPU 34 activates the actuator 27 by the drive circuit 39 via the output port 36 to switch the exhaust switching valve 28 to the inlet 21 of the NOx catalyst 20.
a is closed and the bypass pipe 26 is arranged at a position to be opened. As a result, the exhaust gas flowing from the engine body 1 via the exhaust manifold 16 and the exhaust pipe 19 does not flow into the NOx catalyst 20 and the bypass pipe 26
And flows down to the exhaust pipe 22.

As a result, since the flow of the exhaust gas having a low temperature into the NOx catalyst 20 is prevented, the influence of the fuel cut control by the deceleration on the NOx catalyst 20 due to the deceleration during the temperature increase control of the NOx catalyst 20 is minimized. It will be. Therefore, similarly to the previous period, the exhaust gas whose temperature has dropped is the NOx catalyst 2
The time required for the temperature increase control for activating the NOx catalyst 20 can be reduced,
Good fuel efficiency can be maintained.

Further, the NOx catalyst 20 reduces the influence of the fuel cut at the time of deceleration and reduces the influence of the NOx catalyst 2.
0 can be activated, and the emission of the exhaust purification catalyst can be improved.

Although the present embodiment has been described with reference to an example in which 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 combustion, the present invention is not limited to the above embodiment. Instead, the present invention can be applied to general internal combustion engines.

[0087]

According to the first aspect of the present invention, when the temperature rise control of the exhaust gas purifying material of the internal combustion engine is performed,
Even when the internal combustion engine shifts to a control that prevents heating and heating of the exhaust gas purifying material, the influence on the heating and heating state of the exhaust gas purifying material can be reduced, resulting in good emission and fuel efficiency. An exhaust gas purification device for an internal combustion engine that can improve efficiency can be provided.

According to the second aspect of the present invention, in the internal combustion engine capable of lean combustion, when the temperature rise control of the exhaust gas purifying material is performed, the temperature rise of the exhaust gas purifying material is performed on the internal combustion engine side. Even if you shift to control that prevents
It is possible to provide an exhaust gas purifying apparatus for an internal combustion engine, which can reduce the influence of the exhaust gas purifying material on the heating and heating state, improve emission, and improve fuel efficiency.

According to the third aspect of the present invention, when the temperature rise control of the exhaust gas purifying material is performed, for example, even if the fuel cut control is performed due to deceleration, the exhaust gas purifying material is controlled. It is possible to provide an exhaust gas purifying apparatus for an internal combustion engine, which can reduce the influence of the gas purifying material on the heating and heating state, improve emission, and improve fuel efficiency.

According to the fourth aspect of the present invention, when the temperature rise control of the exhaust gas purifying material is performed, for example, even when the air-fuel ratio control reaches the stoichiometric control state during acceleration. In addition, it is possible to provide an exhaust gas purifying apparatus for an internal combustion engine that can reduce the influence of the exhaust gas purifying material on the heating and temperature rising state, achieve good emission, and improve fuel efficiency.

According to the fifth aspect of the present invention, it is possible to provide an exhaust gas purifying apparatus for an internal combustion engine, wherein the exhaust gas is switched by the exhaust gas switching means.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an exhaust gas purifying apparatus for an internal combustion engine according to an embodiment of the present invention, in which an exhaust pipe has NOx;
It is a figure showing the state where the bypass pipe which bypasses the catalyst is provided.

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

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

FIG. 4 is a diagram for explaining the NOx absorbing / releasing action of a storage reduction type NOx catalyst.

FIG. 5 illustrates a case where exhaust gas is caused to flow down through a bypass passage when engine control is performed so as to prevent a temperature rise control of an exhaust gas purification catalyst in an exhaust gas purification apparatus for an internal combustion engine according to an embodiment of the present invention. 5 is a flowchart illustrating a control routine.

[Explanation of symbols]

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

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) 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 F term (reference) 3G084 AA03 BA03 BA04 BA13 BA24 CA04 CA06 DA02 DA10 EA04 EB01 EB08 EB12 EC03 FA07 FA13 FA18 FA26 FA27 FA33 3G091 AA13 AA17 AA23 AA28 AB06 BA13 BA17 BA12 CA16 CA26 CB02 DA04 DB10 DC01 EA01 EA05 EA17 FA05 FA14 FA17 FA19 FB02 FB03 FB06 FB07 FB10 FB11 FB12 FC07 GB02W GB03W GB04W GB05W GB06W GB17X HA36 HB03 3G301 HA01 HA06 HA18 JA02 JA25 JA26 KA09 KA12 NE12 LC08 PD11Z PE01Z

Claims (5)

[Claims] 1. An exhaust gas purifying material disposed in an exhaust passage of an internal combustion engine, a bypass passage bypassing the exhaust gas purifying material, and heating the exhaust gas purifying material to increase the temperature of the exhaust gas purifying material. An exhaust gas purification device for an internal combustion engine, comprising: a temperature increasing means for heating the exhaust gas purifying material to increase the temperature of the exhaust gas purifying material. An exhaust gas purifying apparatus for an internal combustion engine, wherein exhaust gas is caused to flow down via a bypass passage when the control is shifted to internal combustion engine control for lowering the temperature of exhaust gas flowing into the gas purifying material. 2. The exhaust gas purifying material absorbs NOx when the air-fuel ratio of the exhaust gas flowing from the internal combustion engine capable of lean combustion is lean and reduces the oxygen concentration of the flowing exhaust gas. 2. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the exhaust gas purifying device is a NOx catalyst that releases absorbed NOx. 3. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the internal combustion engine control for decreasing the temperature of the exhaust gas flowing into the exhaust gas purifying material is a fuel cut control. 4. The internal combustion engine control for decreasing the temperature of exhaust gas flowing into the exhaust gas purifying material is stoichiometric control when the internal combustion engine is under a high load.
3. An exhaust gas purifying apparatus for an internal combustion engine according to claim 2. 5. An exhaust switching means for supplying exhaust gas to either an exhaust gas purifying material or an exhaust bypass passage is provided in the exhaust passage, and the exhaust gas purifying material is raised by the temperature raising means. During the internal combustion engine temperature raising control, when the internal combustion engine control is shifted to lower the temperature of the exhaust gas purifying material, the exhaust gas switching means is operated to cause the exhaust gas to flow down through the bypass passage. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the exhaust gas purifying apparatus is configured.