JP2000045881A - Exhaust gas purification device for internal combustion engine - Google Patents

Abstract

(57) [Problem] To prevent various problems (clogging of an exhaust gas recirculation passage, etc.) occurring when exhaust gas is recirculated when fuel is sub-injected. In 16), the fuel is sub-injected from the corresponding fuel injection valve (31 to 36). The EGR pipe 47 that returns a part of the exhaust gas from the exhaust manifold 40 to the intake manifold 3 is provided with an oxidation catalyst 50, an EGR cooler 48, and an EGR valve 49 in order from the upstream side. H in the exhaust gas due to the sub-injection of fuel
C, CO, and SOF have high concentrations, but this exhaust gas is E
When flowing into the EGR pipe 47 as GR gas, HC, CO, and SOF in the exhaust gas are oxidized by the oxidation catalyst 50 and purified.

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 capable of purifying NOx in exhaust gas discharged from the internal combustion engine.

[0002]

2. Description of the Related Art As measures for reducing nitrogen oxides (NOx) in exhaust gas discharged from an internal combustion engine, there are a method of suppressing the generation of NOx itself and a method of purifying the generated NOx.

[0003] As one of the former methods for suppressing the generation of NOx, there is a so-called exhaust gas recirculation (hereinafter abbreviated as EGR) in which a part of exhaust gas is returned to an intake system. EGR is to reduce the combustion temperature by introducing an inert gas (exhaust gas) into the combustion chamber to reduce the amount of NOx generated.

On the other hand, as one of the latter methods for purifying NOx in exhaust gas, there is a method using a catalyst. NOx
There are various types of catalysts that can purify NOx, but a NOx catalyst that reduces or decomposes NOx in the presence of hydrocarbons (HC) in an oxygen-excess atmosphere, a so-called selective reduction NOx catalyst, is an internal combustion that burns in a lean air-fuel ratio state. It is frequently used for NOx purification of exhaust gas discharged from an engine, for example, a diesel engine or a lean burn gasoline engine. In order to purify NOx with this selective reduction type NOx catalyst, an appropriate amount of HC component is required around the catalyst. However, the amount of the HC component in the exhaust gas during the normal operation of the internal combustion engine is extremely small. Therefore, in order to purify NOx during the normal operation, it is necessary to supply the HC component to the NOx selective reduction catalyst.

[0005] As one of the methods for supplying the HC component, there is a sub-injection of fuel (Japanese Patent Laid-Open No. Hei 8-261502). This is because the air-fuel ratio of the exhaust gas is made rich by injecting fuel from a fuel injection valve into the cylinder during an intake stroke, an expansion stroke, or an exhaust stroke of a predetermined cylinder of the internal combustion engine (sub-injection), thereby selectively reducing the fuel. This is a method for supplying an HC component to the type NOx catalyst.

[0006]

Here, suppression of NOx generation by EGR and NOx generation by a selective reduction type NOx catalyst are described.
Combined with purification, it should be possible to significantly reduce NOx emissions, but in this case, selective reduction type NO
If the supply of HC to the x catalyst is performed by sub-injection, the following problem occurs.

[0007] HC, CO in exhaust gas by sub-injection
And PM (Pa) such as SOF (Soluble Organic Fraction)
However, when a part of the exhaust gas is introduced into the cylinder through the exhaust gas recirculation passage as a recirculated gas (hereinafter, referred to as an EGR gas), the combustion gas is adversely affected. There is a fear.

Further, when high concentration of HC or PM is introduced into the cylinder as described above, there is a possibility that an oil film may be cut off at a sliding portion of the engine to accelerate the wear of the bore or to accelerate the deterioration of oil properties. There is.

In the exhaust gas recirculation passage, an exhaust gas recirculation control valve (hereinafter abbreviated as EGR valve) for controlling the amount of EGR gas recirculated, and a recirculated gas cooler for cooling the EGR gas (hereinafter abbreviated as EGR cooler). However, when high concentration HC and PM flow into the exhaust gas recirculation passage as described above, PM and the like adhere to and accumulate on the devices, impairing the functions of these devices and causing malfunction. May be caused. For example, the EGR valve is closed to make exhaust gas recirculation impossible, the EGR valve is fixed to make the recirculation amount uncontrollable, a part of the EGR cooler is closed,
The heat exchange performance of the GR cooler may be reduced.

[0010] Further, if PM or a nucleus of PM is contained in the intake air of the internal combustion engine, smoke is likely to be generated. Therefore, it is necessary to reduce the EGR rate in order to suppress the generation of smoke. Also occurs.

SUMMARY OF THE INVENTION The present invention has been made in view of such problems of the prior art, and an object of the present invention is to purify a reducing agent in EGR gas and then feed the EGR gas to an intake system. The purpose of the present invention is to eliminate adverse effects on combustion, to allow each device to operate normally, and to suppress bore wear and deterioration of oil properties.

[0012]

The present invention has the following features to attain the object mentioned above. The present invention relates to a NOx catalyst provided in an exhaust passage of an internal combustion engine, and the NOx catalyst
An exhaust gas recirculation passage returning from an exhaust passage upstream of the catalyst to an intake passage of the internal combustion engine; and sub-injecting fuel into the cylinder during an intake stroke, an expansion stroke, or an exhaust stroke of a predetermined cylinder of the internal combustion engine to the NOx catalyst. An exhaust gas purifying apparatus for an internal combustion engine, comprising: a sub-injection unit for supplying a reducing agent; a recirculation gas purifying catalyst for purifying a reducing agent in the recirculated gas is provided in the exhaust gas recirculation passage.

When the fuel is sub-injected into the cylinder, exhaust gas containing high concentration PM such as HC, CO and SOF flows into the exhaust gas recirculation passage as recirculated gas. However, HC, CO, SOF and the like in the recirculated gas are purified when passing through the recirculated gas purifying catalyst, and the purified recirculated gas is returned to the intake passage. Therefore, various adverse effects on the EGR caused by the sub-injection can be prevented.

Examples of the internal combustion engine in the present invention include a diesel engine and a lean burn gasoline engine.

Examples of the NOx catalyst provided in the exhaust passage include a selective reduction type NOx catalyst and a storage reduction type NOx catalyst. The selective reduction type NOx catalyst includes a catalyst in which a transition metal such as Cu is ion-exchanged and supported on zeolite, and a catalyst in which a noble metal is supported on zeolite or alumina. The storage reduction type NOx catalyst includes, for example, alumina as a carrier and, for example, potassium K,
At least one selected from alkali metals such as sodium Na, lithium Li and cesium Cs; alkaline earths such as barium Ba and calcium Ca; rare earths such as lanthanum La and yttrium Y; and a noble metal such as platinum Pt. This 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 in the inflowing exhaust gas decreases. I do.

Examples of the reflux gas purifying catalyst include an oxidation catalyst, a selective reduction type NOx catalyst, a storage reduction type NOx catalyst, and the like.

In the exhaust gas purifying apparatus for an internal combustion engine according to the present invention, a recirculating gas cooler for cooling recirculating gas may be provided in the exhaust gas recirculating passage, and the recirculating gas purifying catalyst may be provided upstream of the recirculating gas cooler. It is. By doing so, it is possible to prevent SOF and the like in the recirculated gas from adhering to the recirculated gas cooler, and to prevent clogging of the recirculated gas cooler and a decrease in heat exchange performance.

In the exhaust gas purifying apparatus for an internal combustion engine according to the present invention, the bypass passage for bypassing the reflux gas purification catalyst and allowing the reflux gas to flow therethrough, and the flow of the reflux gas passing through the reflux gas purification catalyst and the bypass passage are controlled. Circulating gas flow control means.

In this case, the recirculation gas flow control means controls the recirculation gas to flow the recirculation gas to either the recirculation gas purification catalyst or the bypass passage according to the magnitude of the exhaust gas temperature. The flow can be switched. By doing so, the durability of the reflux gas purification catalyst is improved.

Further, a second reflux gas purifying catalyst having an activation temperature different from that of the reflux gas purifying catalyst may be provided in the bypass passage. In this way, the reflux gas can be purified over a wide temperature range.

Further, the recirculation gas flow control means causes the recirculation gas to flow through the recirculation gas purification catalyst and not to flow into the bypass passage when fuel is sub-injected into the cylinder, so that the fuel flows into the cylinder. When the sub-injection is not performed, the flow of the recirculation gas can be switched so that the recirculation gas flows through the bypass passage and does not flow through the recirculation gas purification catalyst. By doing so, the durability of the reflux gas purification catalyst is improved.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an exhaust gas purifying apparatus for an internal combustion engine according to the present invention will be described below with reference to FIGS. The embodiment described below is an aspect in which the exhaust emission control device according to the present invention is applied to a vehicle diesel engine as an internal combustion engine.

[First Embodiment] FIG. 1 is a diagram showing an overall configuration of an exhaust gas purifying apparatus for an internal combustion engine according to a first embodiment. The engine 1 is a six-cylinder diesel engine, and each cylinder 1 of the first cylinder (# 1) to the sixth cylinder (# 6)
The combustion chambers 1, 12, 13, 14, 15, 16 have an intake pipe (intake passage) 2, an intake manifold (intake passage) 3,
And an intake branch pipe 21 branched from the intake manifold 3,
Fresh air is introduced via 22,23,24,25,26. In the middle of the intake pipe 2, a compressor 5, an intercooler 6, and an intake throttle valve 7 of the turbocharger 4 are provided. The intake throttle valve 7 is provided with an electronic control unit (E) for engine control according to the operating state of the engine 1.
CU) 100.

The engine 1 has cylinders 11 to 16.
Fuel injection valves 31, 32, 33, 34 for injecting fuel into
35 and 36 are provided. Fuel injection valves 31 to 36
The ECU 100 performs main injection of fuel to the corresponding cylinder near the compression top dead center, and sub-injects fuel from the fuel injection valve of the corresponding cylinder in the intake stroke, expansion stroke or compression stroke of the predetermined cylinder. Is controlled. The HC component of the sub-injected fuel is supplied to a selective reduction type NOx catalyst 10a described later. In this embodiment, the fuel injection valves 31 to 36 and the ECU 100 constitute sub injection means.

The valve opening timing and valve opening time of the fuel injection valves 31 to 36 in the main injection or the sub-injection are controlled by the ECU 100 according to the operating state of the engine 1, and are selected from the first cylinder 11 to the sixth cylinder 16. Which cylinder is to be subjected to sub-injection is determined by the EC according to the operating state of the engine 1.
U100 is determined.

Exhaust gas generated in the combustion chambers of the cylinders 11 to 16 is exhausted through exhaust branch pipes 41, 42, 43, 44, 45, 46 provided for the cylinders 11 to 16, respectively. (Exhaust passage) 40.

Exhaust gas flowing into the exhaust manifold 40 is discharged to the atmosphere through a collective exhaust pipe (exhaust passage) 8. A turbine 9 of the turbocharger 4 and a catalytic converter 10 are provided in the middle of the collective exhaust pipe 8. The exhaust gas drives the turbine 9 and drives the compressor 5 connected to the turbine 9 to supercharge the intake air.

The catalytic converter 10 has a selective reduction type NOx
The catalyst 10a is housed. Selective reduction type NOx catalyst 1
0a is NOx in the presence of hydrocarbons in an oxygen-rich atmosphere
The selective reduction type NOx catalyst includes a catalyst in which a transition metal such as Cu is ion-exchanged on zeolite and a noble metal is supported on zeolite or alumina.

In the collective exhaust pipe 8, the catalytic converter 10
An output signal corresponding to the temperature of the exhaust gas flowing into the catalytic converter 10 or the temperature of the exhaust gas flowing out of the catalytic converter 10 is provided near the inlet and the outlet of the ECU 10.
Inlet gas temperature sensor 51 and output gas temperature sensor 52 that output 0
Is attached. Based on the output signals of the incoming gas temperature sensor 51 and the outgoing gas temperature sensor 52, the ECU 100
Calculates the catalyst bed temperature (catalyst temperature) of the catalytic converter 10.

A part of the exhaust gas flowing into the exhaust manifold 40 is used as an EGR gas (recirculation gas).
The air can be recirculated to the intake manifold 3 via a pipe (exhaust gas recirculation passage) 47. In the middle of the EGR pipe 47, an oxidation catalyst (reflux gas purification catalyst) 5
0, EGR cooler (reflux gas cooler) 48, EGR valve 4
9 are installed. Incidentally, the oxidation catalyst 50 is connected to the EGR pipe 4.
7 (ie, immediately downstream of the connection port with the exhaust manifold 40).

The EGR cooler 48 is a heat exchanger having a shell-and-tube structure as shown in FIG. 2, and a large number of heat exchange tubes 48b are provided in a cooling chamber 48a through which cooling water can flow.
The EGR gas is cooled by exchanging heat with cooling water when passing through the heat exchange tube 48b. The opening of the EGR valve 49 is controlled by the ECU 100 in accordance with the operating state of the engine 1, and controls the amount of EGR gas recirculation.

The ECU 100 is composed of a digital computer and includes a ROM (Read Only Memory), a RAM (Random Access Memory), a CPU (Central Processor Unit), an input port, and an output port interconnected by a bidirectional bus. In addition to performing basic control such as the first fuel injection amount control, in this embodiment, auxiliary injection control for supplying HC to the catalytic converter 10 is performed.

For these controls, an input signal from the accelerator opening sensor 71 and an input signal from the crank angle sensor 72 are input to input ports of the ECU 100. The accelerator opening sensor 71 outputs an output voltage proportional to the accelerator opening to the ECU 100, and the ECU 100 calculates an engine load based on an output signal of the accelerator opening sensor 71. The crank angle sensor 72 outputs an output pulse to the ECU 100 every time the crankshaft rotates by a certain angle, and the ECU 100 calculates an engine rotation speed based on the output pulse. The engine operation state is determined based on the engine load and the engine rotation speed.

Next, the operation of the exhaust gas purifying apparatus according to this embodiment will be described.

The ECU 100 opens each of the fuel injection valves 31 to 36 at a predetermined valve opening timing for a predetermined time in accordance with the operation state of the engine 1 to main-inject a predetermined amount of fuel into each of the cylinders 11 to 16. . The fuel mainly injected into each of the cylinders 11 to 16 is:
After explosion and combustion, each exhaust branch pipe 41-
The exhaust gas is exhausted to the atmosphere through an exhaust manifold, an exhaust manifold, and a catalytic converter.

The ECU 100 determines the amount of reducing agent required to purify the NOx in the exhaust gas generated by the explosion and combustion of the main injected fuel by the catalytic converter 10 according to the operating state of the engine 1. The sub-injection amount of the corresponding fuel is calculated, and the fuel injection valve of a predetermined cylinder is opened for a predetermined time at a predetermined valve opening timing in the expansion stroke or the exhaust stroke of the cylinder in order to sub-inject the fuel of the sub-injection amount. Give a valve. The HC component of the sub-injected fuel is reformed into light HC by the heat of the explosion process, and supplied to the catalytic converter 10 through the exhaust path together with the exhaust gas. As a result, NOx in the exhaust gas is reduced in the selective reduction type NOx catalyst 10a of the catalytic converter 10, and is released to the atmosphere as N ₂ , H ₂ O, and CO ₂ .

A part of the exhaust gas discharged from each of the cylinders 11 to 16 of the engine 1 passes through the EGR pipe 47 from the exhaust manifold 40 as the EGR gas, passes through the EGR cooler 48 and the EGR valve 49, and flows into the intake manifold 3. And is mixed with fresh air sucked from the intake pipe 2 and is taken into the cylinders 11 to 16 via the intake branch pipes 21 to 26.

Incidentally, the sub-injected fuel may flow into the EGR pipe 47 together with the exhaust gas. Therefore, PM such as high concentration HC, CO, SOF, etc.
7 may flow. However, in this exhaust gas purification apparatus, since the oxidation catalyst 50 is installed at the most upstream portion of the EGR pipe 47 (that is, immediately downstream of the connection port with the exhaust manifold 40), the exhaust gas flowing into the EGR pipe 47 PM such as HC, CO and SOF in the oxidation catalyst 5
Oxidized by 0 to become H ₂ O, CO _2, etc. Therefore, in this exhaust gas purification apparatus, high concentration HC, CO, SO
The exhaust gas, such as F, whose PM has been purified, flows through the EGR pipe 47, the EGR cooler 48, and the EGR valve 49 as EGR gas, and returns to the intake manifold 3.

As a result, the EGR gas does not adversely affect the combustion of the main injected fuel. Further, the EGR gas introduced into the cylinders 11 to 16 at this time does not promote the breakage of the oil film of the lubricating oil, and thus does not promote the wear of the engine sliding portion. Further, the EGR gas does not adversely affect oil properties. Further, the EGR effect when the fuel sub injection is performed and the EGR is performed, and the EGR effect when the fuel sub injection is not performed and the EGR is performed.
When compared with the GR effect, substantially the same EGR effect can be obtained, and the same suppression of smoke generation can be achieved at the same EGR rate (equal EGR rate).

Further, no SOF or soot adheres to the inner wall surface of the EGR pipe 47, and no SOF or soot adheres to the inner wall surface of the heat exchange tube 48b of the EGR cooler 48. Since SOF and soot do not adhere to the operating portion, the flow path of the EGR gas is not blocked and the EGR gas does not stop flowing. In addition, the heat exchange performance of the EGR cooler 48 is not reduced, and the EGR valve 49 is not fixed to cause an operation failure, and the control of the EGR gas recirculation amount is not inferior or disabled.

As shown in FIG. 3, the EGR cooler 48
Oxidation catalyst 5 on the inner wall surface 48c of the heat exchange tube 48b.
If HC, CO, and SOF that cannot be completely purified by the oxidation catalyst 50 are present in the EGR gas, they are removed from the heat exchange tube 48b.
When passing through, it can be oxidized and purified by the oxidation catalyst 53, which is more effective. Since the oxidation catalyst 53 provided on the inner surface of the heat exchange tube 48b is cooled by the cooling water flowing through the cooling chamber 48a of the EGR cooler 48, the catalyst surface temperature becomes a predetermined temperature (for example, 300
゜ C) is not exceeded. Therefore, the oxidation catalyst 5
Since No. 3 is not likely to be thermally degraded, it is possible to employ an oxidation catalyst having a very low temperature activity.

[Second Embodiment] FIG. 4 is a diagram showing an overall configuration of an exhaust gas purifying apparatus for an internal combustion engine according to a second embodiment of the present invention. The exhaust gas purifying apparatus according to the second embodiment is obtained by adding the following configuration to the exhaust gas purifying apparatus according to the first embodiment.

In the EGR pipe 47, the exhaust manifold 3 is connected to the exhaust manifold 3 downstream of the EGR cooler 48 and upstream of the EGR valve 49 by a bypass pipe (bypass passage) 54. In the EGR pipe 47, a first control valve 55 is provided between the oxidation catalyst 50 and the EGR cooler 48, and a second control valve 56 is provided in the bypass pipe 54. The first control valve 55 and the second control valve 56 are controlled by the ECU 100 in accordance with the operating state of the engine 1. The first control valve 55 and the second control valve 56
A reflux gas flow control means for controlling the flow of the GR gas is constituted.

An EGR cooler outlet gas temperature sensor 57 for outputting an output signal corresponding to the temperature of the EGR gas flowing out of the EGR cooler 48 to the ECU 100 is provided near the outlet of the EGR cooler 48 in the EGR pipe 47. In addition, the intake manifold 3 is provided with an intake air temperature sensor 58 for outputting an output signal corresponding to the intake air temperature in the intake manifold 3 to the ECU 100, and the exhaust manifold 40 is adapted to correspond to the exhaust gas temperature in the exhaust manifold 40. An exhaust manifold temperature sensor 59 that outputs an output signal to the ECU 100 is attached.

In the exhaust gas purifying apparatus of the second embodiment configured as described above, the first control valve 55 and the second control valve 56 can be controlled as follows.

<First Control Example> Since the temperature of the exhaust gas discharged from the engine 1 changes depending on the operating state of the engine 1, the EGR gas may also become high in temperature. Therefore, it is necessary to use a catalyst that can withstand high temperatures as the oxidation catalyst 50, and must sacrifice low-temperature activity. Therefore, when the low-temperature EGR gas passes through the oxidation catalyst 50, there is almost no catalytic effect, and there is almost no meaning in passing the oxidation catalyst 50, and the deterioration of the oxidation catalyst 50 is rather accelerated.

Therefore, in the first control example, the ECU 1
00, when it is determined based on the output signal of the exhaust manifold temperature sensor 59 that the exhaust gas temperature in the exhaust manifold 40 is equal to or lower than the predetermined set temperature T1, the first control valve 55 is fully closed and the second control valve 56 is fully opened. When it is determined that the exhaust gas temperature in the exhaust manifold 40 exceeds the set temperature T1, the first control valve 55 is fully opened and the second control valve 56 is fully closed. Control.

With this control, when the exhaust gas temperature in the exhaust manifold 40 is equal to or lower than the set temperature T1,
The EGR gas returns to the intake manifold 3 through the bypass pipe 54 and the EGR valve 49 without passing through the oxidation catalyst 50 and the EGR cooler 48. As a result, the low-temperature exhaust gas does not pass through the oxidation catalyst 50, so that the oxidation catalyst 5
0 can be suppressed. Further, in this case, since the EGR gas flows bypassing the EGR cooler 48, PM or the like existing in the EGR gas is removed from the EGR cooler 48.
Can be prevented.

When the temperature of the exhaust gas in the exhaust manifold 40 exceeds the set temperature T1, the EGR gas returns to the intake manifold 3 through the oxidation catalyst 50, the EGR cooler 48, and the EGR valve 49. EGR gas does not flow through the bypass pipe 54. EGR in this case
The flow of gas is the same as that of the exhaust gas purification apparatus of the first embodiment, and the operation and effect are the same as those of the first embodiment, so that the description is omitted.

<Second Control Example> The sub-injection of fuel to the engine 1 is not always executed, but an operation region in which the sub-injection is to be executed according to the operating state of the engine 1 and the sub-injection is to be executed. There is an operating area that is not. Exhaust gas discharged from the engine 1 in the operation region where the sub-injection is to be performed contains high concentrations of HC, CO, and PM. Therefore, if this exhaust gas is returned to the intake gas as EGR gas, a problem occurs. Since the exhaust gas discharged from the engine 1 in the operating region in which is not to be performed has low concentrations of HC, CO, and PM, there is no particular problem even if this exhaust gas is returned to the intake air as the EGR gas.

Therefore, in the second control example, the ECU 1
00 is to determine whether the operating state of the engine 1 is in the operating region in which the sub-injection is to be executed, and when it is in the operating region in which the sub-injection is to be executed, the first control valve 55 is fully opened and the second The control valve 56 is controlled so as to be fully closed, and the first control valve 5
5 is fully closed and the second control valve 56 is fully opened.

With this control, when the engine 1 is in the operating region where the sub-injection is to be executed, the exhaust gas can be purified by passing it through the oxidation catalyst 50 and then converted into the EGR gas. When the engine is in an operation region that should not be performed, the exhaust gas can be converted into the EGR gas without passing through the oxidation catalyst 50 by passing the exhaust gas through the bypass pipe 54. Thereby, the deterioration of the oxidation catalyst 50 can be suppressed, the durability can be increased, and the life can be prolonged.

Further, as a modified example of the above-mentioned second control example, the following control can be performed. Engine 1
The sub-injection of fuel to the cylinders is not necessarily performed for all cylinders, but is performed only for some of the cylinders (for example, the fourth cylinder 14, the fifth cylinder 15, and the sixth cylinder 16 out of the six cylinders). Sub injection is often performed.

In this case, the concentrations of HC, CO, and PM in the exhaust gas discharged from the cylinder that does not perform the sub-injection are such that no problem occurs even if the exhaust gas is returned to the intake air as the EGR gas without performing purification by the oxidation catalyst. It is. If the EGR gas that does not cause a problem without purification is passed through the oxidation catalyst 50, the deterioration of the oxidation catalyst 50 is promoted and the life is shortened.

Therefore, in a modified example of the second control example,
The ECU 100 controls the first control valve 55 to be fully opened and the second control valve 56 to be fully closed at the timing when the exhaust gas is discharged from the sub-injected cylinder. Is discharged at the timing
The control is performed such that the first control valve 55 is fully closed and the second control valve 56 is fully opened.

With this control, the exhaust gas containing high concentrations of HC, CO, and PM may be converted to the EGR gas only by the sub-injection, so that the oxidation catalyst 50
And then purified to produce EGR gas.
When the exhaust gas having a low concentration of C, CO, and PM becomes the EGR gas, the exhaust gas can be converted into the EGR gas without passing through the oxidation catalyst 50 by passing through the bypass pipe 54. Thereby, the deterioration of the oxidation catalyst 50 is suppressed to increase the durability,
Life can be extended.

<Third Control Example> In the first embodiment,
An EGR cooler 48 is provided in the middle of the EGR pipe 47, and the EGR gas is always cooled by the EGR cooler 48. However, if the EGR gas is excessively cooled during the light load operation of the engine 1, the combustion in each of the cylinders 11 to 16 may deteriorate, and white smoke may be generated. There is a demand to weaken the cooling of the car.

Therefore, in the third control example, the ECU 1
00 is based on the output signals of the EGR cooler outlet gas temperature sensor 57, the intake air temperature sensor 58, and the exhaust manifold temperature sensor 59,
The opening control of the first control valve 55 and the second control valve 56 is performed, and E
By controlling the flow ratio between the EGR gas cooled through the GR cooler 48 and the EGR gas not cooled because it passes through the bypass pipe 54, the temperature of the EGR gas is controlled to be an optimum temperature according to the operating state of the engine 1. I do. The EGR gas passing through the EGR cooler 48 purifies HC, CO, SOF, and the like when passing through the oxidation catalyst 50 upstream thereof.

FIG. 5 is a diagram showing a main configuration of a modification of the exhaust emission control device of the second embodiment. In this modified example, the bypass pipe 54 is arranged so as to connect the exhaust manifold 40 with the EGR pipe 47 on the downstream side of the oxidation catalyst 50 and on the upstream side of the EGR cooler 48. There is no change in other configurations. In this modification, the first control example and the second control example can be adopted, and the deterioration of the oxidation catalyst 50 can be suppressed. However, in this modification, the entire amount of the EGR gas passes through the EGR cooler 48, so that the third control example cannot be employed.

[Third Embodiment] FIG. 6 is a diagram showing an overall configuration of an exhaust gas purifying apparatus for an internal combustion engine according to a third embodiment of the present invention. In the exhaust gas purifying apparatus of the third embodiment, another oxidation catalyst (second recirculated gas purifying catalyst) 60 is provided in the bypass pipe 54 of the exhaust gas purifying apparatus of the second embodiment. . A high-temperature active oxidation catalyst is used as the oxidation catalyst 50, and a low-temperature active oxidation catalyst is used as the oxidation catalyst 60.

In the exhaust gas purifying apparatus of the third embodiment configured as described above, the first control valve 55 and the second control valve 56 can be controlled as follows. When the ECU 100 determines that the exhaust gas temperature in the exhaust manifold 40 is equal to or higher than the predetermined set temperature T2 based on the output signal of the exhaust manifold temperature sensor 59, the ECU 100 fully opens the first control valve 55 and fully opens the second control valve 56. When the exhaust gas temperature in the exhaust manifold 40 is determined to be lower than the set temperature T2, the first control valve 55 is fully closed and the second control valve 56 is fully opened. To control.

With this control, the oxidation catalysts 50 and 60 having different activation temperatures can be selectively used in accordance with the EGR gas temperature, so that the catalyst performance can be maintained high over a wide temperature range, and the EGR gas can be maintained at a high level. It is more effective to purify.

More specifically, in a high temperature region where the exhaust gas temperature in the exhaust manifold 40 is equal to or higher than the set temperature T 2, the EGR gas flows only to the high-temperature active type oxidation catalyst 50 and does not flow to the low-temperature active type oxidation catalyst 60. . As a result, after the HC, CO, and SOF in the exhaust gas are purified by the high-temperature activation type oxidation catalyst 50, the EGR cooler 4 converts the HC, CO, and SOF into EGR gas.
8. Return to the intake manifold 3 through the EGR valve 49. Since high-temperature exhaust gas does not flow through the oxidation catalyst 60, deterioration of the oxidation catalyst 60 is suppressed, durability is improved, and the life can be extended.

In a low temperature region in which the exhaust gas temperature in the exhaust manifold 40 is lower than the set temperature T2, the EGR gas flows only to the low-temperature active oxidation catalyst 60 and does not flow to the high-temperature active oxidation catalyst 50. As a result, H in the exhaust gas
After C, CO, and SOF are purified by the low-temperature activation type oxidation catalyst 60, they return to the intake manifold 3 through the EGR valve 49 as EGR gas. Since low-temperature exhaust gas does not flow through the oxidation catalyst 50, deterioration of the oxidation catalyst 50 is suppressed, durability is improved, and the life can be extended.

In the exhaust gas purifying apparatus according to the third embodiment, the opening control of the first control valve 55 and the second control valve 56 is performed as in the third control example of the second embodiment. To perform temperature control of the EGR gas.

FIG. 7 is a diagram showing a main configuration of a modification of the exhaust emission control device according to the third embodiment. In this modified example, the bypass pipe 54 is arranged so as to connect the exhaust manifold 40 with the EGR pipe 47 on the downstream side of the oxidation catalyst 50 and on the upstream side of the EGR cooler 48. There is no change in other configurations.

[0067]

According to the present invention, the NOx catalyst provided in the exhaust passage of the internal combustion engine, and a part of the exhaust gas discharged from the internal combustion engine is used as the recirculation gas from the exhaust passage upstream of the NOx catalyst. An exhaust recirculation passage returning to the intake passage of the engine; and sub-injecting fuel into the cylinder during an intake stroke, an expansion stroke, or an exhaust stroke of a predetermined cylinder of the internal combustion engine, and
a sub-injection means for supplying a reducing agent to the x catalyst, in an exhaust gas purification device for an internal combustion engine, wherein the exhaust gas recirculation passage is provided with a recirculating gas purifying catalyst for purifying the reducing agent in the recirculating gas. High concentration of HC and C in exhaust gas
After purifying PM such as O and SOF, it can be returned to the intake passage as recirculated gas. As a result, various problems that occur when exhaust gas is recirculated when fuel is sub-injected (for example, combustion in a cylinder) Deterioration, blocked exhaust gas recirculation passage, reduced heat exchange performance of recirculated gas cooler, poor control of exhaust gas recirculation control valve,
It is possible to prevent the wear of the sliding portion of the engine and the deterioration of the oil performance.

Also, there is provided a bypass passage for bypassing the reflux gas purifying catalyst and allowing the reflux gas to flow, and a reflux gas flow control means for controlling the flow of the reflux gas passing through the reflux gas purifying catalyst and the bypass passage. The reflux gas flow control means switches the flow of the reflux gas in accordance with the magnitude of the exhaust gas temperature so as to flow the reflux gas to either the reflux gas purification catalyst or the bypass passage. Thus, the durability of the reflux gas purification catalyst can be improved.

Further, when a second recirculation gas purifying catalyst having a different activation temperature from the recirculation gas purifying catalyst is provided in the bypass passage, the recirculating gas can be purified over a wide temperature range. Can be.

Further, there are provided a bypass passage for bypassing the reflux gas purifying catalyst and allowing the reflux gas to flow, and a reflux gas flow control means for controlling the flow of the reflux gas passing through the reflux gas purifying catalyst and the bypass passage. When the fuel is sub-injected into the cylinder, the recirculated gas flow control means causes the recirculated gas to flow through the recirculated gas purification catalyst and not through the bypass passage, and when the fuel is not sub-injected into the cylinder. When the flow of the recirculated gas is switched so that the recirculated gas is allowed to flow through the bypass passage and not to the recirculated gas purification catalyst, the durability of the recirculated gas purification catalyst can be improved.

[Brief description of the drawings]

FIG. 1 shows a first embodiment of an exhaust gas purification apparatus for an internal combustion engine according to the present invention.
FIG. 2 is a system diagram showing a schematic configuration according to the embodiment.

FIG. 2 is a schematic cross-sectional view of a recirculation gas cooler used in the exhaust gas purification apparatus of the first embodiment.

FIG. 3 is an enlarged sectional view of a heat exchange tube of the reflux gas cooler.

FIG. 4 shows a second embodiment of the exhaust gas purifying apparatus for an internal combustion engine according to the present invention.
FIG. 2 is a system diagram showing a schematic configuration according to the embodiment.

FIG. 5 is a diagram showing a main configuration of a modification of the exhaust emission control device of the second embodiment.

FIG. 6 shows a third embodiment of the exhaust gas purifying apparatus for an internal combustion engine according to the present invention.
FIG. 2 is a system diagram showing a schematic configuration according to the embodiment.

FIG. 7 is a diagram showing a main configuration of a modification of the exhaust emission control device according to the third embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Diesel engine (internal combustion engine) 2 Intake pipe (intake passage) 3 Intake manifold (intake passage) 8 Collective exhaust pipe (exhaust passage) 10 Catalytic converter 10a Selective reduction type NOx catalyst 31-36 Fuel injection valve (sub injection means) 40 Exhaust manifold (exhaust passage) 47 EGR pipe (exhaust recirculation passage) 48 EGR cooler (recirculation gas cooler) 50 Oxidation catalyst (recirculation gas purification catalyst) 54 Bypass pipe (bypass passage) 55 First control valve (recirculation gas flow control means) 56 Second control valve (recirculation gas flow control means) 60 Oxidation catalyst (second recirculation gas purification catalyst) 100 ECU (sub injection means, recirculation gas flow control means)

[Procedure amendment]

[Submission date] October 26, 1998 (1998.10.
26)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0024

[Correction method] Change

[Correction contents]

The engine 1 has cylinders 11 to 16.
Fuel injection valves 31, 32, 33, 34 for injecting fuel into
35 and 36 are provided. Fuel injection valves 31 to 36
The main injection of fuel to the corresponding cylinder near the compression top dead center, the intake stroke or expansion stroke of the predetermined cylinder or
The ECU 100 controls the sub-injection of fuel from the fuel injection valve of the corresponding cylinder in the exhaust stroke . The HC component of the sub-injected fuel is supplied to a selective reduction type NOx catalyst 10a described later. In this embodiment, the fuel injection valves 31 to 36 and the ECU 100 constitute sub injection means.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F01N 3/24 F01N 3/24 SC 3/36 3/36 A F Term (Reference) 3G062 AA01 AA06 BA04 ED08 ED09 ED11 GA04 GA06 GA09 GA10 GA12 3G091 AA11 AA12 AA18 AA28 AB02 AB05 BA07 BA14 CA00 CA07 CA12 CB01 CB02 CB03 CB07 EA01 EA07 EA14 EA17 FB01 FB10 GB05W GB09X HA08 HB05

Claims (6)

[Claims] 1. NOx provided in an exhaust passage of an internal combustion engine
A catalyst, an exhaust gas recirculation passage that returns a part of exhaust gas discharged from the internal combustion engine as a recirculated gas from an exhaust passage upstream of the NOx catalyst to an intake passage of the internal combustion engine, and an intake stroke of a predetermined cylinder of the internal combustion engine or A sub-injection unit for sub-injecting fuel into the cylinder during an expansion stroke or an exhaust stroke to supply a reducing agent to the NOx catalyst.The exhaust gas purification device for an internal combustion engine further comprises: An exhaust gas purification device for an internal combustion engine, comprising a reflux gas purification catalyst for purifying a reducing agent. 2. A recirculation gas cooler for cooling recirculation gas is provided in the exhaust gas recirculation passage, and the recirculation gas purification catalyst is provided upstream of the recirculation gas cooler. An exhaust gas purifying apparatus for an internal combustion engine according to claim 1. 3. A bypass passage for bypassing the reflux gas purification catalyst and allowing the reflux gas to flow therethrough, and a reflux gas flow control means for controlling a flow of the reflux gas through the reflux gas purification catalyst and the bypass passage. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein: 4. The recirculation gas flow control means switches a flow of the recirculation gas so that the recirculation gas flows through one of the recirculation gas purification catalyst and the bypass passage according to the magnitude of the exhaust gas temperature. The exhaust gas purifying apparatus for an internal combustion engine according to claim 3, wherein: 5. The exhaust gas of an internal combustion engine according to claim 4, wherein a second recirculation gas purifying catalyst having an activation temperature different from that of the recirculation gas purifying catalyst is provided in the bypass passage. Purification device. 6. The recirculation gas flow control means, when fuel is sub-injected into the cylinder, causes the recirculation gas to flow through the recirculation gas purification catalyst and not to flow into the bypass passage. 4. The exhaust gas purifying apparatus for an internal combustion engine according to claim 3, wherein when the sub-injection is not performed, the flow of the recirculated gas is switched so that the recirculated gas flows through the bypass passage and not through the recirculated gas purification catalyst.