JP3508691B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art NO of exhaust gas discharged from an internal combustion engine
An exhaust gas recirculation device (hereinafter abbreviated as EGR) is one of the x reduction means. The EGR returns a part of the exhaust gas to the intake system again, introduces an inert gas to increase the heat capacity of the gas in the combustion chamber, and lowers the maximum combustion temperature to reduce the generation of NOx.

Further, as another means for reducing NOx in exhaust gas discharged from an internal combustion engine capable of lean combustion, lean NOx such as a selective reduction type NOx catalyst or a storage reduction type NOx catalyst is used.
There is a catalyst. This is not a technology to suppress the generation of NOx itself like EGR, but NOx that has been generated.
Is purified before being released to the atmosphere.

The selective reduction type NOx catalyst is a catalyst for reducing or decomposing NOx in the presence of hydrocarbons (HC) in an atmosphere of excess oxygen, and this selective reduction type NOx catalyst has an appropriate amount for purifying NOx. HC component (reducing agent) is required. When this selective reduction type NOx catalyst is used for exhaust gas purification of the internal combustion engine, the amount of HC components in the exhaust gas during normal operation of the internal combustion engine is extremely small, so NOx during normal operation is reduced.
In order to purify the exhaust gas, it is necessary to supply the HC component to the NOx selective reduction catalyst.

On the other hand, the NOx storage reduction catalyst absorbs NOx when the air-fuel ratio of the inflowing exhaust gas is lean, and releases the absorbed NOx when the oxygen concentration of the inflowing exhaust gas decreases and reduces it to N _2. It is a catalyst.

When this NOx storage reduction catalyst is used to purify the exhaust gas of the internal combustion engine, since the air-fuel ratio of the exhaust gas during normal operation of the internal combustion engine is lean, the N in the exhaust gas is reduced.
Ox will be absorbed by the NOx catalyst. However, if exhaust gas with a lean air-fuel ratio is continuously supplied to the NOx catalyst, the NOx absorption capacity of the NOx catalyst reaches saturation, and NOx cannot be absorbed any more, resulting in NOx leakage. Therefore, in the NOx storage reduction catalyst, the oxygen concentration is extremely reduced and the reducing agent is supplied by making the air-fuel ratio of the inflowing exhaust gas rich at a predetermined timing before the NOx absorption capacity is saturated, and the reducing agent is supplied to the NOx catalyst. It is necessary to release the absorbed NOx and reduce it to N ₂ to restore the NOx absorption capacity of the NOx catalyst. Thus, in order to purify NOx with the lean NOx catalyst, it is necessary to add the reducing agent to the exhaust gas continuously or intermittently.

Then, in order to make the NOx reduction of the exhaust gas discharged from the internal combustion engine more effective, for example, as disclosed in JP-A-6-74022,
In some cases, EGR and lean NOx catalyst are combined.

The above publication exemplifies a case of a four-cylinder engine, and an exhaust gas recirculation pipe (EGR) is connected to a branch pipe connected to exhaust ports of three cylinders in an exhaust manifold.
(Pipes) are connected, part of the exhaust gas is sucked from these three branch pipes, and is returned to the intake pipe via the EGR pipe. In addition, a reducing agent addition nozzle is attached so as to face the exhaust port of the remaining one cylinder, and the reducing agent is added to the exhaust gas from this reducing agent addition nozzle to add the reducing agent to the downstream lean NOx catalyst. We are supplying. In this way, the cylinder connected to the reducing agent addition nozzle is divided from the cylinder group connected to the EGR pipe in order to prevent the reducing agent added from the reducing agent addition nozzle from being taken into the intake system via the EGR pipe. Is.

[0009]

However, in the internal combustion engine described in the above publication, the EGR pipe is connected to three (plural) branch pipes, and welding is usually used as this connecting means. As the number of points increases, the cost increases, and the probability of damage increases, which is disadvantageous in terms of durability.

Further, if many branch pipes are connected to the EGR pipe, the influence of exhaust pulsation on the EGR gas flow becomes large, and there is a problem that precise control of the EGR gas flow rate becomes difficult.

The present invention has been made in view of the above problems of the prior art, and the problem to be solved by the present invention is to provide a lean NOx catalyst in an internal combustion engine equipped with EGR and a lean NOx catalyst. Therefore, it is to prevent the reducing agent added to the EGR system from sneaking in, improve durability and reduce cost.

[0012]

The present invention adopts the following means in order to solve the above problems. The present invention relates to an exhaust manifold connected to an exhaust port of each cylinder of a lean-burn multi-cylinder internal combustion engine, an exhaust collecting pipe connecting the exhaust manifold and the exhaust pipe, an exhaust manifold, and an intake system of the internal combustion engine. An exhaust gas recirculation device for recirculating a part of the exhaust gas to the intake system, a lean NOx catalyst provided in the exhaust pipe, and a reducing agent added to the exhaust system upstream of the lean NOx catalyst. A reducing agent addition device, in an exhaust gas purification device of an internal combustion engine, the upstream end of the exhaust collecting pipe is connected to one end side of the exhaust manifold, the addition port of the reducing agent addition device to the one end side of the exhaust manifold The exhaust port of the exhaust gas recirculation device is attached so as to face the exhaust port of a cylinder located close to the exhaust port, and the exhaust gas inlet of the exhaust gas recirculation device is provided on the other end side of the exhaust manifold. .

In the exhaust gas purifying apparatus for an internal combustion engine of the present invention, in the exhaust manifold, the connecting portion of the exhaust gas collecting pipe and the exhaust suction port connecting portion of the exhaust gas recirculation device are spaced far apart from each other, and the reducing agent addition device The addition port is located facing the exhaust port near the exhaust manifold connection in the exhaust manifold, preventing the reducing agent added from the reducing agent addition device from flowing into the intake system via the exhaust gas recirculation device. can do.

Further, since the exhaust gas recirculation device is connected to the exhaust manifold at one place, the durability is improved and the cost can be reduced.

In the exhaust gas purification apparatus for an internal combustion engine according to the present invention, it is preferable that the exhaust port of the cylinder to which the addition port of the reducing agent addition device is attached has a reduced cross-section at the portion where the addition port is attached. By doing this, the flow velocity of the exhaust gas flowing through the exhaust port can be increased,
As a result, atomization of the reducing agent added from the reducing agent addition device can be promoted.

Further, in the exhaust gas purifying apparatus for an internal combustion engine according to the present invention, during the opening period of the exhaust valve of the cylinder located close to the one end side of the exhaust manifold, the reducing agent is added from the adding port of the reducing agent adding apparatus. It is preferred that a reducing agent be added. By doing this, it is possible to suppress the reducing agent added from the reducing agent addition device from adhering to the exhaust manifold, and suppress the fuel adhering to the exhaust manifold from flowing into the intake system via the exhaust gas recirculation device. can do.

In the exhaust gas purifying apparatus for an internal combustion engine of the present invention, main injection for injecting fuel for obtaining engine output from the fuel injection valve is executed only in the cylinder to which the addition port of the reducing agent addition apparatus is attached. After that, it is also possible to execute the sub-injection in which the fuel is injected from the fuel injection valve in the expansion stroke or the exhaust stroke. Exhaust gas temperature can be raised by secondary injection of fuel, and atomization and vaporization of fuel added from the reducing agent addition device are promoted.

In the exhaust gas purifying apparatus for an internal combustion engine of the present invention, a turbocharger for pressurizing intake air downstream of the exhaust collecting pipe, and a turbocharger at the time of light load for reducing agent addition by the reducing agent addition device A bypass passage that bypasses the charger and guides the exhaust gas to the lean NOx catalyst. The exhaust gas temperature is low during light load operation, and when passing through the turbocharger, the exhaust gas temperature decreases at that time, which hinders atomization and vaporization of the reducing agent added from the reducing agent addition device. When exhaust gas is caused to flow through the bypass passage to bypass the turbocharger and lead to the lean NOx catalyst at such a time, since there is no temperature drop due to the turbocharger, atomization and vaporization of the reducing agent are not hindered, and the NOx purification rate is reduced. improves.

Further, in this case, the bypass passage may be provided with a catalyst having an oxidizing ability. By doing this, when the exhaust gas passes through the catalyst having oxidizing ability,
The reducing agent added from the reducing agent addition device is oxidized, and the exhaust gas temperature rises due to the reaction heat at that time.
The NOx purification rate of the x catalyst is improved. Examples of the catalyst having oxidizing ability include an oxidation catalyst, a three-way catalyst, and a lean NOx catalyst (a storage reduction type NOx catalyst, a selective reduction type NOx catalyst).

In the exhaust gas purification apparatus for an internal combustion engine according to the present invention, the second reducing agent addition device for supplying a reducing agent to the lean NOx catalyst when recovering the lean NOx catalyst from sulfur poisoning is upstream of the lean NOx catalyst. It is also possible to provide. Since the reducing agent added from the second reducing agent addition device does not flow into the intake system via the exhaust gas recirculation device, smoke is generated due to the addition of the reducing agent for the sulfur poisoning recovery process. Can be prevented.

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

In the present invention, examples of the lean NOx catalyst include a storage reduction type NOx catalyst or a selective reduction type NOx catalyst. The NOx storage reduction catalyst is a catalyst that absorbs NOx when the air-fuel ratio of the inflowing exhaust gas is lean, releases the absorbed NOx when the oxygen concentration in the inflowing exhaust gas decreases, and reduces it to N _2. . This occlusion reduction type NOx catalyst uses, for example, alumina as a carrier, and potassium K, sodium Na, lithium Li, an alkali metal such as cesium Cs, or barium B is used on the carrier.
a, alkaline earth such as calcium Ca, lanthanum L
a, at least one selected from rare earths such as yttrium Y, and a noble metal such as platinum Pt.

The selective reduction type NOx catalyst is a catalyst that reduces or decomposes NOx in the presence of hydrocarbons in an atmosphere of excess oxygen, and is a catalyst in which a transition metal such as Cu is ion-exchanged and carried, zeolite or alumina. Include a catalyst supporting a noble metal.

In the present invention, as the reducing agent, those containing HC components such as light oil and gasoline are preferable.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of an exhaust gas purifying apparatus for an internal combustion engine according to the present invention will be described below with reference to the drawings of FIGS. 1 to 7. The embodiment described below is an embodiment in which the exhaust emission control device for an internal combustion engine according to the present invention is applied to a vehicle-driving diesel engine as an internal combustion engine.

[First Embodiment] First, an exhaust gas purification apparatus for an internal combustion engine according to a first embodiment will be described with reference to the drawing of FIG. FIG. 1 is a diagram showing an overall configuration of an exhaust emission control system for an internal combustion engine in this embodiment. In this figure, the engine 1 is an in-line 4-cylinder diesel engine, and intake air is introduced into the combustion chamber of each cylinder via an intake manifold 2 and an intake pipe 3. An air cleaner 4 is provided at the starting end of the intake pipe 3, and in the middle of the intake pipe 3,
An air flow meter 5, a compressor 6a of a turbocharger 6, an intercooler 7, and a throttle valve 8 are provided.

The air flow meter 5 outputs an output signal according to the amount of fresh air flowing into the intake pipe 3 via the air cleaner 4 to an electronic control unit (ECU) 9 for engine control.
The ECU 9 calculates the intake air amount based on the output signal of the air flow meter 5.

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

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

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

A fuel addition nozzle (addition port of a reducing agent addition device) 19 is attached to the cylinder head 30 of the engine 1 so as to face the exhaust port 13 of the fourth cylinder. The fuel pumped up by the fuel pump 12 can be supplied to the fuel addition nozzle 19 through the fuel pipe 20 and the fuel passage 21 provided in the cylinder head 30, and is provided in the middle of the fuel pipe 20. The control valve 22 controls the addition amount. The control valve 2
The ECU 2 is opened / closed and its opening is controlled by the ECU 9.
The fuel addition nozzle 19 is attached so that fuel is injected toward the exhaust collecting pipe 15. In the present embodiment, the fuel pump 12, the fuel addition nozzle 19, the fuel pipe 20, the fuel passage 21, and the control valve 22 are
Configure a reducing agent addition device.

One end of an exhaust gas recirculation pipe (hereinafter abbreviated as an EGR pipe) 23 for returning a part of exhaust gas to the intake system is connected to a portion of the exhaust manifold 14 facing the first cylinder. The other end of the pipe 23 is connected to the intake manifold 2. An EGR cooler 24 and an EGR valve 25 are provided in the middle of the EGR pipe 23. EGR valve 2
The opening degree 5 is controlled by the ECU 9 according to the operating state of the engine 1 to control the exhaust gas recirculation amount. The EGR pipe 23, the EGR cooler 24, and the EGR valve 25 are connected to the exhaust gas recirculation device (E
GR).

Further, in the exhaust pipe 16, the casing 18
An exhaust temperature sensor 26 that outputs an output signal corresponding to the temperature of the exhaust gas flowing out of the casing 18 to the ECU 9 is provided immediately downstream of the exhaust temperature sensor 26.

The ECU 9 is composed of a digital computer, has a ROM (read only memory), a RAM (random access memory), a CPU (central processor unit), an input port and an output port, which are connected to each other by a bidirectional bus. Basic control such as fuel injection amount control of No. 1 is performed.

For these controls, an input signal from the accelerator opening sensor 26 and an input signal from the crank angle sensor 27 are input to the input port of the ECU 9. The accelerator opening sensor 26 outputs an output voltage proportional to the opening of the throttle valve 8 to the ECU 9, and the ECU 9 calculates the engine load based on the output signal of the accelerator opening sensor 26. The crank angle sensor 27 outputs an output pulse to the ECU 9 every time the crankshaft rotates by a certain angle,
9 calculates the engine speed based on this output pulse. The engine operating state is determined by the engine load and the engine speed, and the ECU 9 controls the valve opening timing and the valve opening period of the fuel injection valve 10 according to the engine operating state.

Storage reduction type N housed in the casing 18
The Ox catalyst (hereinafter sometimes abbreviated as NOx catalyst) 17 is
For example, alumina (Al ₂ O ₃ ) is used as a carrier, and potassium K, sodium Na, lithium Li, an alkali metal such as cesium Cs, alkaline earth such as barium Ba, calcium Ca, lanthanum La, yttrium is used on the carrier. At least one selected from rare earths such as Y and a noble metal such as platinum Pt are supported.

The NOx catalyst 17 absorbs NOx when the air-fuel ratio of the inflowing exhaust gas (hereinafter referred to as the exhaust air-fuel ratio) is leaner than the theoretical air-fuel ratio, and the exhaust air-fuel ratio is equal to or higher than the theoretical air-fuel ratio. When it becomes rich and the oxygen concentration in the inflowing exhaust gas decreases, the absorbed NOx is released to release the absorbed NOx as NO ₂ or NO. And NOx
NOx (NO ₂ or NO) released from the catalyst 17 immediately reacts with unburned HC and CO in the exhaust gas and is reduced to N ₂ . Therefore, by appropriately controlling the exhaust air-fuel ratio, it is possible to purify HC, CO, and NOx in the exhaust gas.

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

By the way, in the case of a diesel engine,
Since combustion is performed in a much leaner range than stoichiometric (theoretical air-fuel ratio, A / F = 14 to 15), the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 17 is very lean under normal engine operating conditions. , NOx in exhaust gas is NOx catalyst 1
The amount of NOx absorbed by the NOx catalyst 7 and released from the NOx catalyst 17 is extremely small.

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

Therefore, in a diesel engine, N
At a predetermined timing before the NOx absorption capacity of the Ox catalyst 17 is saturated, a reducing agent is supplied to the exhaust gas to reduce the oxygen concentration in the exhaust gas, and the Nx absorbed by the NOx catalyst 17 is reduced.
Ox must be released and reduced. As the reducing agent, light oil, which is a fuel for diesel engines, is generally used in many cases.

Therefore, in this embodiment, the ECU 9
From the history of the operating state of the engine 1, the NOx catalyst 17
The NOx amount absorbed in the control valve 2 is estimated, and when the estimated NOx amount reaches a preset predetermined value, the control valve 2
The valve 2 is opened to inject a predetermined amount of fuel from the fuel addition nozzle 19 into the exhaust gas to reduce the oxygen concentration in the exhaust gas flowing into the NOx catalyst 17, and the NOx absorbed by the NOx catalyst.
Is released and reduced to N ₂ .

Here, since the fuel addition nozzle 19 injects the fuel toward the exhaust collecting pipe 15, the added fuel smoothly flows into the exhaust collecting pipe 15. The fuel addition nozzle 19 is attached to the exhaust port 13 of the No. 4 cylinder, while the connection part of the EGR pipe 23 in the exhaust manifold 14 is close to the No. 1 cylinder.
The fuel added from the fuel addition nozzle 19 is the EGR pipe 23.
There is no turning around.

Further, the exhaust manifold 14 and the EGR pipe 2
Since there is only one connection point with 3, the durability is improved,
It is also possible to reduce costs. Furthermore, the EGR pipe 2
3 is provided at a portion of the exhaust manifold 14 where the exhaust gas flowing from each cylinder gathers, the exhaust gas flowing through the EGR pipe 23 is less likely to be affected by the exhaust pulsation, and the EGR amount can be accurately controlled. Control becomes possible.

[Second Embodiment] Next, an exhaust purification system for an internal combustion engine according to a second embodiment will be described with reference to FIGS. 2 and 3.
Will be described with reference to. The second embodiment is a further development of the exhaust emission control device of the first embodiment described above in order to more reliably prevent the fuel added from the fuel addition nozzle 19 from flowing into the EGR system. Is.

FIG. 2 is a sectional view around the exhaust port 13 of the fourth cylinder to which the fuel addition nozzle 19 is attached in the second embodiment. In the exhaust port 13 of the fourth cylinder, a bulging portion 31 is formed so as to project at a portion where the fuel addition nozzle 19 is attached, and the bulging portion 31 reduces the cross section of the exhaust port 13. This allows
When the exhaust valve 32 is opened and the exhaust gas is discharged from the combustion chamber 33, the flow velocity of the exhaust gas passing through the bulging portion 31 is increased.

Further, in the second embodiment, the fuel addition timing from the fuel addition nozzle 19 is synchronized with the opening timing of the exhaust valve 32 of the fourth cylinder. As a result, the fuel is added from the fuel addition nozzle 19 to the exhaust gas flowing at high speed through the bulging portion 31 of the exhaust port 13, and atomization of the fuel is promoted. Further, the fuel added from the fuel addition nozzle 19 rides on the flow of the exhaust gas and flows smoothly through the exhaust manifold 14 toward the exhaust collecting pipe 15. These synergistic effects make it difficult for the fuel added from the fuel addition nozzle 19 to adhere to the exhaust manifold 14.

When the operating condition of the engine 1 is low rotation and light load, the exhaust gas flow rate is small and the exhaust gas temperature is low. Therefore, when the bulging portion 31 is not provided in the exhaust port 13, the fuel addition nozzle 19 is used. The added fuel easily adheres to the exhaust manifold 14, and the supply of the reducing agent to the NOx catalyst 17 is delayed. Further, the fuel adhering to the exhaust manifold 14 easily flows around into the intake system via the EGR system, which may lead to deterioration of smoke.

However, in the second embodiment, the bulging portion 31 is provided in the exhaust port 13 as described above,
Since the fuel addition from the fuel addition nozzle 19 and the valve opening timing of the exhaust valve 32 are synchronized, it is difficult for the fuel to adhere to the exhaust manifold 14 even when the engine operating condition is low rotation and light load, and the addition fuel It is possible to prevent the air from flowing into the intake system, and suppress the generation of smoke.
In addition, the amount of added fuel can be reduced, and fuel consumption can be improved.

In FIG. 2, reference numeral 34 is a cylinder block, and reference numeral 35 is a piston. The other configuration is the same as that of the first embodiment, and therefore its explanation is omitted.

Regarding the timing of fuel addition from the addition nozzle 19, that is, the opening timing of the control valve 22, the ECU 9 sets
The opening timing of the exhaust valve 32 can be estimated and controlled by the crank angle with reference to the operation timing of the fuel injection valve 10 of the No. cylinder.

FIG. 3 shows a fuel addition control routine in the second embodiment. This fuel addition control routine is a routine that is stored in advance in the ROM of the ECU 9 and that is repeatedly executed by the CPU.

<Step 101> First, in step 101, the ECU 9 determines whether or not the reducing agent addition condition is satisfied. Here, the condition for satisfying the reducing agent addition condition is that the catalyst temperature of the NOx catalyst 17 is at the activation temperature and the NOx absorbed by the NOx catalyst 17 should be released / reduced. When a negative determination is made in step 101, the ECU 9 once ends the execution of this routine.

<Step 102> When the affirmative judgment is made in Step 101, the ECU 9 advances to Step 102 and judges whether or not the exhaust valve 32 of the fourth cylinder is at the valve opening timing.
Whether or not it is the opening timing of the exhaust valve 32 is determined from the crank angle from the operation of the fuel injection valve 10 of the fourth cylinder to the present time. When a negative determination is made in step 102, the ECU 9
Ends the execution of this routine once.

<Step 103> When the affirmative judgment is made in Step 102, the ECU 9 advances to Step 103, and opens the control valve 22 at a predetermined opening degree for a predetermined time. As a result, a predetermined amount of fuel is added to the exhaust gas from the fuel addition nozzle 19.

[Third Embodiment] Next, an exhaust purification system for an internal combustion engine according to a third embodiment will be described with reference to FIGS. 4 and 5.
Will be described with reference to. In the exhaust emission control device of the first embodiment described above, when the engine operating condition is light load, the amount of exhaust gas flow is small and the exhaust gas temperature is low, so atomization of the fuel added from the fuel addition nozzle 19 is sufficient. Even if the fuel added from the fuel addition nozzle 19 can be atomized, the fuel is atomized and vaporized in the turbine 6b because it is cooled by the turbine 6b after that. There is a fear that the NOx absorbed in the NOx catalyst 17 cannot be sufficiently released / reduced because the NOx cannot be accelerated.

In the third embodiment, in order to prevent such a situation, the exhaust purification system of the first embodiment is further provided with the following configuration. A portion of the exhaust manifold 14 adjacent to the connecting portion of the exhaust collecting pipe 15 and the exhaust pipe 16
A casing 42 in which the turbine 6b and the casing 18 are connected by a bypass pipe (bypass passage) 40, and the oxidation catalyst 41 is housed in the middle of the bypass pipe 40.
To provide.

Further, the exhaust manifold 14 is provided with a flow passage switching valve 43 for opening and closing the exhaust collecting pipe 15 and for opening and closing the bypass pipe 40.
Controlled by. The flow passage switching valve 43 is normally controlled so as to close the bypass pipe 40, open the exhaust collecting pipe 15 and guide the exhaust gas to the turbine 6b through the exhaust collecting pipe 15, and as will be described later, a predetermined flow control valve 43 is provided. The exhaust collecting pipe 15 is closed to bypass the bypass pipe 40 only when the engine is operating.
Is opened and exhaust gas is controlled to flow into the bypass pipe 40.

Further, in the exhaust emission control system of the third embodiment, only for the cylinder provided with the fuel addition nozzle 19, that is, the fourth cylinder, the fuel injection valve is operated only when the engine is under a light load operation. The fuel injection from 10 is controlled so that the auxiliary injection of fuel is executed in the expansion stroke or the exhaust stroke of the fourth cylinder, separately from the fuel injection for obtaining the engine output. The fuel sub-injected from the fuel injection valve 10 is post-burned in the expansion stroke or the exhaust stroke to raise the exhaust gas temperature.

Further, in the exhaust gas purification apparatus of the third embodiment, the exhaust gas collecting pipe 15 is provided only when the sub-injection is executed for the fourth cylinder, that is, only when the engine is in the light load operation. The flow path switching valve 43 is controlled so as to close the valve and open the bypass pipe 40. This allows
The flow path of the exhaust gas is switched, the exhaust gas is guided to the bypass pipe 40, bypasses the turbine 6b, bypasses the turbine 6b, and is discharged through the oxidation catalyst 41 and the NOx catalyst 17.

In the exhaust emission control system of the third embodiment, when the engine is operating under a light load, the sub-injection of the fuel is executed for the fourth cylinder, so that the fuel comes out of the combustion chamber of the fourth cylinder. The temperature of the exhaust gas is raised to promote atomization and vaporization of the fuel added from the fuel addition nozzle 19. In order to achieve this object, also in the third embodiment, when the engine is operating under a light load, the fuel addition timing from the fuel addition nozzle 19 is synchronized with the opening period of the exhaust valve of the fourth cylinder. .

Then, the flow passage switching valve 43 is controlled in accordance with the sub-injection of the fuel to switch the flow passage, and the exhaust gas is caused to flow through the bypass pipe 40 to bypass the turbine 6b. This allows
It is possible to prevent the exhaust gas from being cooled in the turbine 6b, and it is possible to eliminate a factor that deteriorates atomization and vaporization of the added fuel.

Moreover, in this embodiment, the bypass pipe 4
Since the oxidation catalyst 41 is provided in the middle of 0, when the exhaust gas passes through the oxidation catalyst 41, the fuel addition nozzle 19
Part of the fuel added from is oxidized, the temperature of the exhaust gas is raised by this reaction heat, the temperature of the downstream NOx catalyst 17 is raised, and the NOx purification rate is improved.

Further, in the exhaust purification system of this embodiment, since the atomization and vaporization of the fuel added from the fuel addition nozzle 19 are promoted as described above, the NOx catalyst 1
7 HC poisoning (also referred to as SOF poisoning) is suppressed.

EG in the exhaust manifold 14
Since only the No. 4 cylinder farthest from the connection with the R pipe 23 is sub-injected, it is possible to prevent the sub-injected fuel from flowing into the intake system via the EGR system. It is possible to prevent the generation of smoke due to this wraparound.

FIG. 5 shows an exhaust gas bypass control routine according to the third embodiment. This exhaust gas bypass control routine is stored in advance in the ROM of the ECU 9,
This is a routine that is repeatedly executed by the CPU.

<Step 201> First, in step 201, the ECU 9 reads the current engine operating state such as the engine speed and the engine load.

<Step 202> Next, the ECU 9 proceeds to step 202 and determines whether or not the current operating state of the engine 1 is a predetermined light load operating state. The predetermined light load operating state mentioned here is an operating state in which the secondary injection of fuel in the fourth cylinder is required, and the determination standard is the ECU 9 in advance.
It is stored in the ROM. When a negative determination is made in step 202, the ECU 9 once ends the execution of this routine.

<Step 203> When the affirmative determination is made in Step 202, the ECU 9 proceeds to Step 203 and executes the fuel sub injection control for the fourth cylinder.

<Step 204> Next, the ECU 9 proceeds to step 204 to operate the passage switching valve 41 to close the exhaust collecting pipe 15 and open the bypass pipe 40 to switch the exhaust passage. As a result, the exhaust gas is emitted from the turbine 6b.
Is guided to the NOx catalyst 17 through the bypass pipe 40.

[Fourth Embodiment] Next, an exhaust purification system for an internal combustion engine according to a fourth embodiment will be described with reference to FIGS. 6 and 7.
Will be described with reference to.

The NOx storage reduction catalyst 17 is a sulfur oxide (SOx) produced by combustion of sulfur contained in fuel.
As a result, poisoning (hereinafter referred to as sulfur poisoning or SOx poisoning) reduces the NOx purification rate, so it is necessary to perform poisoning recovery processing for recovering from SOx poisoning at an appropriate time. To recover from this poisoning, the temperature of the NOx catalyst 17 is set to NOx.
Predetermined high temperature (eg,
It is known that it is effective to maintain the temperature at 600 to 650 ° C.) and make the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 17 the stoichiometric air-fuel ratio or the rich air-fuel ratio.

Therefore, when carrying out this SOx poisoning recovery process, first, a temperature raising process for raising the temperature of the NOx catalyst 17 to the above-mentioned predetermined temperature is carried out. As a method of raising the temperature, for example, as described in the third embodiment, the fuel is injected from the fuel injection valve 10 into the cylinder during the expansion stroke or the exhaust stroke to raise the exhaust gas temperature. A method of raising the temperature of the NOx catalyst 17 or adding fuel into the exhaust gas from the fuel addition nozzle 19
Combustion is carried out in the Ox catalyst 17, whereby the NOx catalyst 1
A method of raising the temperature of 7 can be considered.

However, as described above, since the temperature of the NOx catalyst 17 needs to be raised significantly at the time of recovery from SOx poisoning, the auxiliary injection amount or the fuel addition amount from the fuel addition nozzle 19 becomes large. A large amount of fuel may flow into the intake system via the EGR system and cause smoke.

Therefore, in the exhaust purification system of the fourth embodiment, the fuel addition nozzle dedicated to SOx poisoning recovery is set to NOx.
By providing the catalyst upstream of the catalyst 17, these problems are prevented. Hereinafter, the exhaust emission control system for an internal combustion engine of the fourth embodiment will be described, mainly focusing on the differences from the first embodiment.

In the exhaust purification system of the fourth embodiment, a fuel addition nozzle 45 dedicated to SOx poisoning recovery is provided immediately upstream of the casing 18 accommodating the NOx catalyst 17. The fuel pumped up by the fuel pump 12 can be supplied to the fuel addition nozzle 45 through a fuel pipe 46, and a fuel control valve 47 is provided in the middle of the fuel pipe 46. Fuel addition nozzle 45
Is attached so that fuel is injected toward the NOx catalyst 17, and opening / closing of the fuel control valve 47 is controlled by the ECU 9. In addition, in this embodiment, the fuel pump 12, the fuel addition nozzle 45, the fuel pipe 46, and the fuel control valve 47 form a second reducing agent addition device.

In the exhaust pipe 16, the casing 18
The casing 4 accommodating the oxidation catalyst 48 is located downstream of the casing 4.
9 is provided. Furthermore, the exhaust pipe 16 located downstream of the casing 18 and upstream of the casing 49 and the intake pipe 3 located downstream of the compressor 6 a and upstream of the intercooler 7 are connected by the air introduction pipe 50. An air control valve 51 is provided in the middle of the air introduction pipe 50. The opening and closing of the air control valve 51 is controlled by the ECU 9.

In the exhaust emission control system of the fourth embodiment, when the SOx poisoning recovery process is executed on the NOx catalyst 17, the fuel control valve 47 is opened and the fuel addition nozzle 4 is opened.
By injecting fuel from No. 5 and making the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 17 the stoichiometric air-fuel ratio or slightly richer than it, and burning the fuel added from the fuel addition nozzle 45 with the NOx catalyst 17, the NOx The temperature of the catalyst 17 is raised to a temperature at which SOx can be released, and the NOx catalyst 17
Is maintained at that temperature, the NOx catalyst 17 converts the S
It releases Ox and reduces it to SO ₂ for purification. At the same time, the air control valve 51 is opened to introduce the air pressurized by the compressor 6a into the exhaust gas downstream of the NOx catalyst 17 to return the air-fuel ratio of the exhaust gas to almost the stoichiometric air-fuel ratio. As a result, during the SOx poisoning recovery process, HC and CO that could not be purified by the NOx catalyst 17 are removed by the downstream oxidation catalyst 4
It can be oxidized and purified at 8.

When the fuel addition nozzle 45 dedicated to SOx poisoning recovery is provided in this way, the fuel added to the exhaust gas from the fuel addition nozzle 45 does not flow into the intake system via the EGR system. Smoke does not occur due to poisoning recovery processing.

When the fuel addition nozzle 19 is not provided with the fuel addition nozzle 45 dedicated to SOx poisoning recovery and fuel is added at the time of SOx poisoning recovery, the injection amount increases when SOx poisoning is recovered. Therefore, the injection hole diameter of the fuel injection nozzle 19 must be increased, and when this is done, the fuel addition amount when the fuel is added from the fuel addition nozzle 19 for NOx purification at the time of non-SOx poisoning recovery and light load operation Since the amount is small, atomization and vaporization of fuel are not sufficiently performed, and there is a possibility that the NOx purification rate may decrease.

However, in the case of the fourth embodiment, since the fuel addition nozzle 45 dedicated to SOx poisoning recovery is provided, the fuel addition nozzle 19 uses the fuel required for NOx release / reduction of the NOx catalyst 17. It is only necessary to inject the added amount, and therefore the injection hole diameter of the fuel addition nozzle 19 can be reduced. As a result, the fuel added from the fuel addition nozzle 19 is sufficiently atomized even during light load operation, and the NOx purification rate is also improved.

FIG. 6 shows S in the fourth embodiment.
The Ox poisoning recovery control routine is shown. This SOx poisoning recovery control routine is a routine that is stored in advance in the ROM of the ECU 9 and that is repeatedly executed by the CPU.

<Step 301> First, in step 301, the ECU 9 determines whether or not it is time to execute the SOx poisoning recovery process for the NOx catalyst 17. Where S
The time for executing the Ox poisoning recovery process may be, for example, when the fuel consumption amount reaches a predetermined value or when the traveling distance reaches a predetermined distance. When a negative determination is made in step 301, the ECU 9 once ends the execution of this routine.

<Step 302> When the affirmative judgment is made in Step 301, the ECU 9 proceeds to Step 302 and executes the temperature raising process and the SOx poisoning recovery process. That is, the fuel control valve 47 and the air control valve 51 are opened, fuel is added from the fuel addition nozzle 45, and air is introduced into the exhaust pipe 16 upstream of the oxidation catalyst 50. In addition,
The operation patterns such as the opening degree of the fuel control valve 47 and the air control valve 51 and the valve opening time are stored in advance in the ROM of the ECU 9 as a two-dimensional map of the engine speed and the engine load.

<Step 303> Next, the ECU 9 proceeds to step 303 and determines whether or not the NOx catalyst 17 has recovered from SOx poisoning. Here, the NOx catalyst 17 is SOx
The determination as to whether or not the poisoning has been recovered can be made, for example, by determining that the SOx poisoning recovery process has been recovered when the SOx poisoning recovery process is continued for a predetermined time.

If a negative decision is made in step 303,
The ECU 9 returns to step 302 and continues the SOx poisoning recovery process. When a positive determination is made in step 303, the ECU 9 once ends this routine.

[0087]

According to the exhaust gas purification apparatus for an internal combustion engine of the present invention, an exhaust manifold connected to the exhaust port of each cylinder of a multi-cylinder internal combustion engine capable of lean combustion, and the exhaust manifold and the exhaust pipe are connected. An exhaust gas recirculation device for connecting an exhaust manifold and an intake system of an internal combustion engine to recirculate a part of exhaust gas to the intake system; a lean NOx catalyst provided in the exhaust pipe; Lean N
In an exhaust gas purification device for an internal combustion engine, comprising: a reducing agent addition device for adding a reducing agent to an exhaust system upstream of an Ox catalyst, an upstream end of the exhaust collecting pipe is connected to one end side of the exhaust manifold, The addition port of the agent addition device is attached to face the exhaust port of the cylinder located close to the one end side of the exhaust manifold, and the exhaust suction port of the exhaust gas recirculation device is provided on the other end side of the exhaust manifold. As a result, it is possible to prevent the reducing agent added from the reducing agent addition device from flowing into the intake system through the exhaust gas recirculation device, and it is possible to prevent smoke from being produced. . Further, since the exhaust gas recirculation device is connected to the exhaust manifold at one place, the excellent effect is obtained that the durability is improved and the cost can be reduced.

In the exhaust gas purifying apparatus for an internal combustion engine of the present invention, when the cross section of the exhaust port of the cylinder to which the addition port of the reducing agent addition device is attached is reduced at the portion where the addition port is attached, the reducing agent is added. It is possible to promote atomization of the reducing agent added from the addition device, and lean NOx
This has the effect of improving the NOx purification rate of the catalyst.

In the exhaust gas purifying apparatus for an internal combustion engine according to the present invention, the reducing agent is supplied from the addition port of the reducing agent addition device during the opening period of the exhaust valve of the cylinder located near the one end side of the exhaust manifold. If it is added,
The reducing agent added from the reducing agent addition device can be suppressed from adhering to the exhaust manifold, and the fuel adhering to the exhaust manifold can be suppressed from flowing into the intake system via the exhaust gas recirculation device, As a result, it is possible to prevent smoke from being generated.

In the exhaust gas purifying apparatus for an internal combustion engine according to the present invention, the main injection for injecting the fuel for obtaining the engine output from the fuel injection valve is executed only in the cylinder to which the addition port of the reducing agent addition apparatus is attached. After that, when the sub-injection for injecting the fuel from the fuel injection valve is executed in the expansion stroke or the exhaust stroke, the exhaust gas temperature can be raised by the sub-injection of the fuel, and the fuel added from the reducing agent adding device can be increased. Promotes atomization and vaporization of NOx and NOx of lean NOx catalyst
There is an effect that the purification rate can be improved.

In the exhaust gas purifying apparatus for an internal combustion engine according to the present invention, a turbocharger for pressurizing intake air downstream of the exhaust collecting pipe, and the turbocharger at the time of light load when the reducing agent is added by the reducing agent addition device And a bypass passage for bypassing the exhaust gas to the lean NOx catalyst, the temperature drop of the exhaust gas due to the turbocharger can be eliminated at the time of light load operation. There is an effect that atomization and vaporization of the reduced reducing agent are not hindered, and the NOx purification rate of the lean NOx catalyst is improved. Further, when the bypass passage is provided with a catalyst having an oxidizing ability, the exhaust gas temperature can be raised, so that the NOx purification rate of the lean NOx catalyst is improved.

In the exhaust gas purification apparatus for an internal combustion engine of the present invention, the second reducing agent addition device for supplying the reducing agent to the lean NOx catalyst when recovering the lean NOx catalyst from sulfur poisoning is upstream of the lean NOx catalyst. When installed in
Since the reducing agent added from the second reducing agent addition device does not flow into the intake system via the exhaust gas recirculation device, smoke is generated due to the addition of the reducing agent for the sulfur poisoning recovery process. The effect is that it can be prevented.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of an exhaust emission control system for an internal combustion engine according to a first embodiment of the present invention.

FIG. 2 is a sectional view around an exhaust port in a second embodiment of an exhaust purification system for an internal combustion engine according to the present invention.

FIG. 3 is a flowchart showing a fuel addition control routine in the second embodiment.

FIG. 4 is a diagram showing a schematic configuration of an exhaust purification system for an internal combustion engine according to a third embodiment of the present invention.

FIG. 5 is a flowchart showing an exhaust gas bypass control routine according to a third embodiment.

FIG. 6 is a diagram showing a schematic configuration of an exhaust purification system for an internal combustion engine according to a fourth embodiment of the present invention.

FIG. 7 is a flowchart showing a SOx poisoning recovery control routine in a fourth embodiment.

[Explanation of symbols]

1 Engine (Internal Combustion Engine) 2 Intake Manifold (Intake System) 3 Intake Pipe 6 Turbocharger 6a Compressor 6b Turbine 9 ECU (Electronic Control Unit for Engine Control) 10 Fuel Injection Valve 12 Fuel Pump (Reducing Agent Addition Device, Second Reduction) Agent addition device) 13 Exhaust port 14 Exhaust manifold 15 Exhaust collecting pipe 16 Exhaust pipe 17 Storage reduction type NOx catalyst (lean NOx catalyst) 19 Fuel addition nozzle (addition port of reducing agent addition device) 20 Fuel pipe (reducing agent addition device) 21 Fuel Passage (Reducing Agent Addition Device) 22 Control Valve (Reducing Agent Addition Device) 23 EGR Pipe (Exhaust Gas Recirculation Device) 24 EGR Cooler (Exhaust Gas Recirculation Device) 25 EGR Valve (Exhaust Gas Recirculation Device) 40 Bypass Pipe (Bypass) Passage) 41 oxidation catalyst 45 fuel addition nozzle (second reducing agent addition device) 46 combustion Pipe (second reducing agent adding device) 47 fuel control valve (second reducing agent adding device)

Front page continuation (51) Int.Cl. ⁷ Identification code FI F02D 43/00 F02D 43/00 301J 301N 301T F02F 1/42 F02F 1/42 B F02M 25/07 550 F02M 25/07 550C 550R 580 580A 45 / 02 45/02 (72) Inventor Shinobu Ishiyama 1 Toyota Town, Toyota City, Aichi Prefecture, Toyota Motor Co., Ltd. (72) Inventor Takahiro Ooba 1 Toyota Town, Toyota City, Aichi Prefecture, Toyota Motor Co., Ltd. (72) Invention Atsushi Tahara 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Co., Ltd. (72) Inventor Daisuke Shibata, Toyota City, Aichi Prefecture Toyota City 1 Toyota Motor Corporation, (72) Inventor Akihiko Negami Toyota City, Aichi Prefecture Toyota Town No. 1 Toyota Motor Corporation (56) References JP-A-11-294145 (JP, A) JP-A-6-74022 (JP, A) JP-A-2000-38962 (JP, A) (58) Survey Areas (Int.Cl. ⁷ , DB name) F01N 3/08-3/36 F02D 41/40 F0 2D 43/00 F02F 1/42 F02M 25/07 F02M 45/02

Claims (7)

(57) [Claims] 1. An exhaust manifold connected to an exhaust port of each cylinder of a lean-burn multi-cylinder internal combustion engine, an exhaust collecting pipe connecting the exhaust manifold and the exhaust pipe, an exhaust manifold and an intake system of the internal combustion engine. An exhaust gas recirculation device that connects to and recirculates part of the exhaust gas to the intake system,
An exhaust gas purification device for an internal combustion engine, comprising: a lean NOx catalyst provided in the exhaust pipe; and a reducing agent addition device for adding a reducing agent to an exhaust system upstream of the lean NOx catalyst, wherein the exhaust gas collecting pipe is upstream of the exhaust gas collecting pipe. The end is connected to one end side of the exhaust manifold, the addition port of the reducing agent addition device is attached to face the exhaust port of the cylinder located near the one end side of the exhaust manifold, and the exhaust gas of the exhaust gas recirculation device is attached. An exhaust emission control device for an internal combustion engine, wherein an intake port is provided on the other end side of the exhaust manifold. 2. The exhaust port of the cylinder to which the addition port of the reducing agent addition device is attached has a reduced cross-section at a portion where the addition port is attached.
An exhaust emission control device for an internal combustion engine as set forth in. 3. The reducing agent is added from an addition port of the reducing agent addition device during an opening period of an exhaust valve of a cylinder located close to the one end side of the exhaust manifold. Item 2. An exhaust gas purification device for an internal combustion engine according to item 1. 4. Only in the cylinder to which the addition port of the reducing agent addition device is attached, in the expansion stroke or the exhaust stroke after the main injection for injecting fuel for obtaining the engine output from the fuel injection valve is executed. The exhaust gas purification device for an internal combustion engine according to claim 1 or 3, wherein a sub-injection for injecting fuel from the fuel injection valve is executed. 5. A turbocharger for pressurizing intake air downstream of the exhaust collecting pipe, and a lean exhaust gas bypassing the turbocharger when the load is light and the reducing agent is added by the reducing agent addition device. The exhaust gas purification device for an internal combustion engine according to claim 1, further comprising: a bypass passage that leads to the NOx catalyst. 6. The exhaust gas purification device for an internal combustion engine according to claim 5, wherein the bypass passage is provided with a catalyst having an oxidizing ability. 7. A second reducing agent addition device for supplying a reducing agent to the lean NOx catalyst when recovering the lean NOx catalyst from sulfur poisoning is provided upstream of the lean NOx catalyst. The exhaust emission control device for an internal combustion engine according to claim 1.