JP3359681B2 - Engine exhaust gas recirculation system - 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 recirculation system for an engine.

[0002]

2. Description of the Related Art Conventionally, an exhaust gas recirculation device (EGR device) of a supercharged engine is provided with a means for performing an EGR by holding an EGR valve open even in a supercharging region, so that nitrogen in this region is provided. There is known a technique that enables reduction of oxides (Japanese Patent Laid-Open No. 60-237153). That is, as shown in FIG. 8, the EGR passage 4 is provided in the intake manifold 38 of the engine body 39 having the supercharger 31.
2 and a negative pressure type EGR
A valve 43 is provided, and an EGR sensing port 44 of the throttle body 37 and a diaphragm chamber 43 a of the EGR valve 43 communicate with each other through a passage 45. A negative pressure switch 47 is provided in a passage 46 for detecting a port negative pressure. An operation signal of the switch 47 is input to a control unit 48, and a solenoid valve 49 provided in the middle of the passage 45 is connected to a control unit 48. Open / close with output signal. That is, immediately before entering the supercharging region, the solenoid valve 49 is closed and a predetermined negative pressure is applied to the EGR valve 43.
Of the EG during the supercharging region.
The EGR control is performed while the R valve 43 is kept open.

[0003] Incidentally, 31a is a compressor of the supercharger, 31a
b is a turbine, 32 is a duct, 33 is an air cleaner, 3
4 is an air flow meter, 35 is an intake pipe, 36 is a throttle valve, 40 is an exhaust pipe, and 41 is an exhaust port.

[0004]

By the way, in the case where the EGR gas is introduced into the downstream of the supercharger 31 by the differential pressure between intake and exhaust as described above, a sufficient amount of the intake gas is required to increase in the supercharge region. Is difficult to supply, and especially in a high supercharging region, almost no EGR can be performed. Therefore, it is considered that the EGR effect can be exerted in the supercharging region only in a low supercharging region where the supercharging pressure is not so high, for example, in a so-called medium load region just before the fully open region of the throttle. It can be said that this technology has enabled the reduction of nitrogen oxides even in the region.

[0005] However, it is desirable to reduce the nitrogen oxides over the entire supercharging region. Therefore, there has been a demand for the development of an EGR device capable of supplying a sufficient amount of EGR gas even in a high supercharging region. I have. Here, one method for supplying a sufficient amount of EGR gas even in a high supercharging region is EG
Although it is conceivable to connect the R gas passage to the upstream side of the supercharger, adoption of the R gas passage has the following problems that must be solved.

That is, since the unburned hard carbon component is contained in the exhaust gas of the engine, when this is directly introduced into the intake system upstream of the supercharger and subjected to EGR,
The supercharger is damaged by the unburned carbon component, and durability cannot be obtained. In particular, "cold EGR" which is being developed by the present inventors, that is, E
In the case of adopting the technology of cooling the GR gas to around 100 ° C or lower and putting it in the engine cylinder, in order to suppress knocking, the water in the exhaust gas is condensed and liquefied by cooling, The carbon is mixed and becomes a highly viscous liquid and is recirculated to the intake system, which directly leads to a serious trouble that the carbon is clogged between the rotor and the casing of the supercharger.

[0007] The effect of the unburned carbon is not limited to the turbocharger. For example, the unburned carbon deposits and accumulates in the cylinder,
In addition, there are problems such as accumulation and sticking in various passages and valves connected to the intake system. These problems must be avoided as much as possible from the viewpoint of reliability. It is also a problem for the entire intake system of an engine equipped with an exhaust gas recirculation device.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an engine which can prevent the unburned carbon component from being introduced into the intake system as much as possible and can improve reliability. An object of the present invention is to provide an exhaust gas recirculation device.

[0009]

According to a first aspect of the present invention , there is provided an exhaust gas recirculation system for an engine, wherein a stoichiometric air-fuel ratio is set to λ = 1 and an air-fuel ratio of an air-fuel mixture supplied to the engine. Is an exhaust gas recirculation device for an engine that extracts a part of the exhaust gas from the exhaust system under the rich condition of λ <1 and recirculates the exhaust gas to the intake system. Secondary air supply means for supplying secondary air so that the oxygen concentration in the catalyst device becomes lean from approximately λ = 1 to λ> 1 when converted to an air-fuel ratio; An exhaust gas recirculation means for extracting exhaust gas from a downstream exhaust system and recirculating the exhaust gas to an intake system ; the exhaust purification catalyst device includes a main catalyst;
A secondary catalyst located at least upstream of the primary catalyst,
At least, it is partially exhausted to the sub-catalyst under rich conditions of λ <1.
Means for circulating air, and the secondary air supply
The means is capable of supplying secondary air to the sub-catalyst under the rich condition of λ <1.
And the exhaust gas recirculation means operates at the time of the secondary air supply.
Means for extracting and refluxing exhaust gas from downstream of the auxiliary catalyst
It has the structure which has.

[0010] The engine according to claim 2 of the present invention.
The exhaust gas recirculation device sets the stoichiometric air-fuel ratio to λ = 1,
Rich conditions where the air-fuel ratio of the mixture supplied to the gin is λ <1
Engine exhaust that recirculates some of the exhaust gas to the intake system
A gas recirculation device that is located upstream of the exhaust purification catalyst device.
The oxygen concentration in the catalytic device under the rich conditions
It is approximately λ = 1 to λ> 1 when converted to air-fuel ratio.
Secondary air supply means for supplying secondary air,
Exhaust gas from the exhaust system downstream from the catalyst device during air supply
And cool it to the intake system upstream of the turbocharger.
Exhaust gas recirculation means for recirculating the exhaust gas,
The main unit is located at least upstream of the main catalyst
Under the rich condition of at least λ <1
Means for partially circulating exhaust gas to the auxiliary catalyst.
The secondary air supply means may be configured to perform the rich condition of λ <1.
The secondary air is supplied to the sub-catalyst below, and the exhaust gas recirculation means is
When supplying secondary air, exhaust gas is taken from downstream of the sub-catalyst.
It is configured to have a means for taking out and refluxing.

[0011]

[0012]

In the exhaust gas recirculation device of the first aspect, when the stoichiometric air-fuel ratio is λ = 1, the secondary air is supplied upstream of the catalyst device under the rich condition of the air-fuel ratio λ <1. That is, under the catalytic device, the amount of air is increased so that the oxygen concentration in the exhaust gas becomes lean from λ = 1 to λ> 1 in terms of the air-fuel ratio, thereby promoting the reaction between carbon and oxygen. As a result, the exhaust gas is reduced in carbon. Then, the purified exhaust gas with less carbon is guided to the intake system as EGR gas. Accordingly, knocking suppression and NOx reduction in a rich region where the air-fuel ratio is λ <1 (mainly in a high load region where output can be increased) are achieved while improving reliability by preventing carbon introduction into the intake system. Becomes possible.

[0013] In the exhaust gas recirculation device of the second aspect, in the engine provided with the supercharger, the cold EGR gas cooled upstream of the supercharger is recirculated when the secondary air is supplied. Here, the “cold EGR gas” is a gas that is cooled to about 100 ° C. or less by passing an exhaust gas (for example, 200 ° C.) of an engine in a high load region through an external conduit or by using a cooler. By introducing the EGR gas purified by the oxidation reaction of the catalyst into the engine cylinder from the upstream of the supercharger as cold EGR gas, a sufficient amount over the entire supercharge region can be obtained while avoiding carbon sticking to the supercharger. The EGR gas can be supplied, and the knocking can be suppressed together with the reduction of NOx. Here, it is considered that the reason why the knocking resistance is improved when the cold EGR is performed is that the temperature is cooled. That is, when adiabatic compression is performed, the temperature at the time of compression decreases because excess gas is contained, the temperature during combustion decreases, and the temperature of exhaust gas also decreases. Therefore, when cold EGR is performed, knocking resistance and reliability can be improved, the output can be set in a direction that can increase the output, and fuel efficiency can be improved.

Further, the exhaust gas recirculation device according to claims 1 and 2
In both cases, under the rich condition of λ <1, exhaust gas partially flows through the sub-catalyst, and the EGR gas is recirculated from downstream of the sub-catalyst. For this reason, the amount of secondary air required for the oxidation reaction in the sub-catalyst can be small. This means that the load on the pump can be reduced by that much, and the fuel efficiency improves accordingly. Further, since the pipe of the EGR gas drawn from the downstream side of the sub-catalyst to the intake system becomes a thin pipe, it is advantageous also in the cold EGR.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the illustrated embodiments.

In FIG. 1, a common intake pipe 1 is used as an intake system for left and right banks 8 and 9 of a V-type engine body.
, An air cleaner 2, an air flow meter 3, a throttle valve 4, a screw-type supercharger 5, and an intercooler 6 are arranged in this order from the upstream side to the downstream side.
The common intake pipe 1 is provided with the screw-type supercharger 5.
A bypass passage 7 for bypassing the air conditioner and the intercooler 6 is provided. The bypass passage 7 is provided with a bypass valve V1. The bypass valve V1 is fully opened to allow natural aspiration in a region where sufficient supercharging is not required, such as at the time of starting, and is closed in a region where sufficient supercharging is required.

As the exhaust system of the engine body, exhaust manifolds 10 and 11 from the left and right banks 8 and 9 are joined by a common exhaust pipe 12, and an exhaust purification catalyst device comprising a three-way catalyst in the common exhaust pipe 12. (Catalyst) 13 is interposed. The secondary air passage 19 bypasses the left and right banks 8 and 9 and the pipes 10 and 11 so that the catalyst 1 in the common exhaust pipe 1 to the common exhaust pipe 12
3, and a secondary air valve V4 is provided in the middle of the secondary air passage 19.

The engine body has first and second two external EGR passages (both of which are formed of external piping).
1 and 22 are attached, the first external EGR passage 21 is used in a low load region, while the second external EGR passage 22 is used in a high load region. The first external EGR passage 21
The passage is drawn out from the outlet side of the catalyst 13 by the common external pipe 20 and reaches the outlet side of the intercooler 6 in the common intake pipe 1.
An R valve V5 is provided. The second external EGR passage 22 is a passage that is also drawn out from the outlet side of the catalyst 13 through the common pipe 20 and reaches the common intake pipe 1 downstream of the throttle valve 4. A cold EGR valve V6 is interposed.

FIG. 6 shows three operating regions, namely, a low load region (a), a medium load region (b), and a high load region (c) including full opening, in relation to the engine speed and the load. This shows how to take the air-fuel ratio in the region.

In the high load region (c) of the three regions, when the stoichiometric air-fuel ratio (A / F = 14.7) is replaced with λ = 1, the air-fuel ratio is rich when λ <1. Drive as Under such rich air-fuel ratio conditions, the first
The EGR valve V5 is closed, and the second EGR valve V6 is opened at a required opening to perform cold EGR.
The high load region is a region where the EGR is normally stopped in the past. However, in the present invention, the effect of mainly suppressing knocking is obtained by performing the cold EGR of returning the cooled EGR gas to the intake system. There are features.

More specifically, the supercharging region under a high load (λ <1)
When performing cold EGR control in
The R valve V5 is closed and the cold EGR amount is controlled by the cold EGR valve V6. Further, in the present invention, the secondary air amount is also controlled by the secondary air valve V4. That is, while the entire amount of the exhaust gas is circulated through the catalyst of the catalyst 13, the oxygen concentration in the exhaust gas under the catalyst is converted to an air-fuel ratio from approximately λ = 1 to λ> 1 due to the oxidation reaction by the catalyst. The amount of secondary air is controlled so as to be lean and supplied appropriately. Then, a part of the clean exhaust gas extracted from the catalyst downstream of the catalyst 13 is introduced as EGR gas to the upstream of the supercharger 5 through the pipe 20 and the second external EGR passage 22.

When the supply of secondary air to the catalyst is not considered, rich conditions (λ / F = 13, A / F = 12, etc.) smaller than the stoichiometric air-fuel ratio A / F = 14.7 (λ In <1), naturally, a large amount of unburned carbon is also generated, which is disadvantageous because it enters the engine cylinder. However, in this embodiment, when the air-fuel ratio is rich such that λ <1, the catalyst of the catalyst 13 that is at a high temperature is
Since the secondary air amount is controlled and supplied so that this functions most efficiently, carbon and oxygen rapidly undergo an oxidation reaction, and the exhaust gas is reduced in carbon and is sufficiently purified. For this reason, the purified exhaust gas after the purification is taken out from the downstream of the catalyst, and is taken as the EGR gas in the intake system 1.
Refluxed to

As described above, by taking out the EGR gas after the catalyst, the carbon purifying function of the catalyst is utilized,
EGR gas with very little carbon can be guided upstream of the supercharger. Therefore, even under high load, cold E
The effect of suppressing the introduction of carbon into the intake system can be obtained while improving the effect of suppressing knocking due to GR.

Next, the embodiment shown in FIG. 2 will be described.

In FIG. 2, the exhaust manifold 1 from the left and right banks 8 and 9 serves as an exhaust system of the engine body.
0 and 11 are joined by a common exhaust pipe 12, a bypass control valve V 2 is provided at the junction, and a main catalyst device (main catalyst) 13 composed of a three-way catalyst is provided in the common exhaust pipe 12. Also, the exhaust manifolds 1 of the left and right banks 8 and 9 are provided.
Branch pipes 15 and 16 from the middle of 0 and 11 are shared with common pipe 1
7, a common passage 17 is formed between the bypass control valve V2 and the main catalyst 13 to form a bypass passage 14. The common passage 17 of the bypass passage 14 has a three-way passage. An auxiliary catalyst device (precatalyst) 18 made of a catalyst and a precatalyst passage control valve V3 are interposed in this order. Then, the secondary air passage 19 is connected from the common intake pipe 1 to the branch pipes 15 and 16 so as to bypass the left and right bank sections 8 and 9,
A secondary air valve V4 is provided on the way.

As in the case of FIG. 1, the engine body has first and second two external EGs formed by external pipes.
R passages 21 and 22 are provided, and light load EGRs are respectively provided.
A valve V5 and a cold EGR valve V6 are provided. However, the first external EGR passage 21 here is drawn out from the outlet side of the pre-catalyst 18 interposed in the common piping 17 of the bypass passage 14 through a common piping 20, and an interface in the common intake pipe 1 is formed. The passage leading to the outlet side of the cooler 6. Further, the second external EGR passage 22
Is a passage which is also drawn out from the outlet side of the pre-catalyst 18 through the common pipe 20 and reaches the common intake pipe 1 downstream of the throttle valve 4. In other words, exhaust manifold 1
The exhaust manifolds 10, 11, branch pipes 15, 16, pre-catalyst 18, common pipe 2 are provided from main exhaust systems 0, 11, a common exhaust pipe 12, and a main catalyst 13.
A circulating system of 0, first and second external EGR passages 21 and 22 is branched. The circulation system is connected to a main exhaust system by a pipe 17, and the precatalyst 18 is connected to the upstream side by the pipe 17 and the main catalyst 13 is connected to the downstream side by the pipe 17. In terms of capacity, the pre-catalyst 18 is smaller than the main catalyst 13.

Reference numeral 23 denotes an EGR control unit, which controls the following.

First, during warm-up, the bypass control valve V2 is closed and only the pre-catalyst passage control valve V3 is opened as shown in FIG. Exhaust gas flows through list 13. That is, since the amount of exhaust gas is small during warm-up, the entire amount of exhaust gas is passed through the small-capacity precatalyst 18,
The temperature of the catalyst is quickly raised, and the catalyst temperature of the main catalyst 13 is waited for to rise.

After the warm-up, that is, after the catalyst temperature of the main catalyst 13 has risen, the bypass control valve V2 is opened to open the main catalyst 13 as shown in FIG.
The exhaust gas can also flow directly.

The EGR control after the warm-up is performed in the following three regions (a), (b), and (c) shown in FIG.

In the low load region (a), the air-fuel ratio is λ
= 1, that is, the stoichiometric air-fuel ratio A / F = 14.7, and the exhaust gas is sufficiently purified by the three-way catalyst to become a clean gas. In this case, general hot EGR control is performed. That is, as shown in FIG. 3, the cold EGR valve V6 is closed, the secondary air valve V4 is also closed, and the light load EGR valve V5 and the pre-catalyst passage control valve V3 are controlled by the EG.
Control the amount of R. The hot exhaust gas that has passed through the precatalyst 18 is returned to the downstream of the intercooler 6 from the second external EGR passage 22. The amount returned to the intake system is adjusted by the bypass control valve V2 and the pre-catalyst passage control valve V3.

In the middle load range (b), the air-fuel ratio is λ ≧ 1, that is, lean, from the viewpoint of emphasizing fuel efficiency. Therefore, as in the case of λ = 1, the purifying action of the three-way catalyst is sufficient. Demonstrated and becomes a clean gas. The supercharging region is a region above the middle of the medium load region.

The last high-load region (c) is, for example, a region in which the transmission is shifted to the fourth speed and the accelerator pedal is depressed to 5000 rpm, and the air-fuel ratio is naturally λ <
1 in a rich state, and usually generates a lot of carbon. Therefore, in this high load region (C), the cold EGR control and the control of the secondary air supply to the catalyst are performed as follows.

That is, as shown in FIG. 2, the light load EGR valve V5 is closed, the cold EGR amount is controlled by the cold EGR valve V6 and the pre-catalyst passage control valve V3, and the secondary air valve V4 is used to control the cold EGR amount. The next air volume is also controlled. As a result, part of the exhaust gas in the exhaust manifolds 10 and 11 from the left and right bank portions 8 and 9 flows to the pre-catalyst 18 from the pipes 15 and 16. The amount of part of the exhaust gas flowing to the precatalyst 18 and the amount of the exhaust gas returned to the intake system as cold EGR gas can be adjusted by the bypass control valve V2 and the precatalyst passage control valve V3 as necessary. Also, the amount of secondary air supplied to the precatalyst 18 is adjusted accordingly.

Also in this embodiment, the secondary air is supplied to the sub-catalyst of the pre-catalyst 18, and the amount of the secondary air is determined by converting the oxygen concentration in the exhaust gas under the sub-catalyst from approximately λ = 1 to λ >
It is controlled to be 1 lean. That is, the carbon in the exhaust gas is removed by the oxidation reaction of the precatalyst 18 by the catalyst, and is introduced upstream of the supercharger 5 as clean EGR gas. However, unlike the case of FIG. 1,
The amount of exhaust gas flowing to the precatalyst 18 is a part of the total exhaust amount. However, the amount of gas actually required as EGR is small when viewed from the total amount of exhaust gas, so that no inconvenience occurs. Rather, the required amount of secondary air is reduced, the pump load is reduced, and there is an advantage that the control can be performed with high accuracy.

As described above, according to the embodiment of FIG. 2, the flow rate of exhaust gas in the bypass section to the precatalyst 18 side can be set to a flow rate required for EGR. The amount of carbon in the exhaust gas extracted as EGR gas can be reduced with a very small amount of secondary air. In addition, the structure is simplified by sharing the bypass system and the EGR system. Further, since a small amount of secondary air is required, the load on the pump can be reduced correspondingly, and in other words, the fuel efficiency can be improved accordingly. Further, since it becomes a thin tube, it is also advantageous on cold EGR.

FIG. 7 shows the relationship between the air-fuel ratio and the amount of carbon emitted from the exhaust gas. The carbon emission (g / h) was trapped by filter paper, and the carbon emission (g / h) was
h) decreases before and after the catalyst, indicating that the catalyst was purified by the oxidation reaction of the catalyst. It should be noted that as the air-fuel ratio A / F becomes leaner, that is, as the air-fuel ratio A / F becomes closer to the right side of the figure, the amount of carbon decreases, and the stoichiometric air-fuel ratio A / F
It is a point that the carbon emission becomes zero when going to = 14.7. Therefore, the oxygen concentration in the exhaust gas under the catalytic converter is converted into an air-fuel ratio, and the stoichiometric air-fuel ratio A / F = 1
By controlling the supply amount of the secondary air so as to be always lean from 4.7, it can be determined that carbon can be almost completely eliminated from the exhaust gas discharged from the catalyst device. Therefore, by taking out the exhaust gas from the downstream of the catalyst device and performing the cold EGR from the upstream of the supercharger, a sufficient amount of the EGR gas can be obtained over the entire supercharging region while avoiding carbon sticking to the supercharger. Can be supplied, and the knocking can be suppressed as much as possible together with the reduction of NOx.

In the above embodiment, as suggested by a two-dot chain line in FIG. 2, a filter 24 may be provided to more strictly remove carbon.

In the above embodiment, the stoichiometric air-fuel ratio A / F = 1
Although the description has been made in the rich region where the air-fuel ratio is smaller than λ = 1 around 4.7, taking into account the problem of A / F control accuracy,
In the case of λ = 1, a median width of A / F = about 14 to 15 is allowed.

[0040]

As described above, according to the present invention, the following excellent effects can be obtained. (1) In the first aspect, secondary air is provided to accelerate the oxidation reaction of the catalyst, and the EGR gas from which the carbon has been removed can be taken out after the catalyst.
Gas can be led to the intake system. Therefore, even when the load is high, the effect of suppressing the knocking can be exhibited, and the effect of improving the reliability by preventing the introduction of carbon into the intake system can be obtained. Furthermore, it is necessary to distribute exhaust gas to the sub-catalyst.
Since the required secondary air volume is small, the pump load is reduced accordingly.
The fuel consumption can be reduced. In addition,
It is also advantageous on cold EGR because it becomes a pipe. (2) According to the second aspect, while knocking is suppressed by the cold EGR, reliability can be improved by preventing carbon from being introduced into the supercharger. For this reason, the output can be set in a direction in which the output can be increased, and the fuel efficiency is improved. In addition,
A small amount of secondary air is required to circulate exhaust gas through the medium.
Therefore, the pump load can be reduced by that much,
Fuel efficiency is improved. In addition, cold E
It is also advantageous on GR.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing one embodiment of the present invention.

FIG. 2 is a configuration diagram showing another embodiment of the present invention, and is a diagram showing a cold EGR state.

FIG. 3 is a diagram showing a hot EGR state in the embodiment of FIG. 2;

FIG. 4 is a diagram showing a state during warm-up in the embodiment of FIG. 2;

FIG. 5 is a diagram showing a state after warming up in the embodiment of FIG. 2;

FIG. 6 is a diagram showing a relationship between a region in which cold EGR is performed and an operation region.

FIG. 7 is a diagram illustrating changes in the amount of carbon emission and the temperature of exhaust gas with respect to the air-fuel ratio.

FIG. 8 is a diagram showing a conventional engine exhaust gas recirculation device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Common intake pipe 2 Air cleaner 3 Air flow meter 4 Throttle valve 5 Screw type supercharger 6 Intercooler 8, 9 Right and left bank part of V type engine main body 10, 11 Exhaust manifold 12 Common exhaust pipe 13 Main catalyst (main catalyst) 19 Secondary air passage 21 First external EGR passage 22 Second external EGR passage 14 Bypass passage 18 Pre-catalyst (width catalyst)

────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI F01N 3/22 F01N 3/22 311L ZAB ZAB 3/24 ZAB 3/24 ZABC (56) References JP-A-4-175452 (JP) JP-A-4-370314 (JP, A) JP-A-4-17710 (JP, A) JP-A-54-81717 (JP, U) JP-A-57-92051 (JP, U) JP-A 59-54708 (JP, U) Japanese Utility Model Showa 62-24009 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) F02M 25/07 550 F02M 25/07 570 F02M 25/07 580 F01N 3/22 311 F01N 3/22 ZAB F01N 3/24 ZAB F02D 43/00

Claims (2)

(57) [Claims] 1. An engine in which a part of exhaust gas is extracted from an exhaust system and recirculated to an intake system under a rich condition in which an air-fuel ratio of an air-fuel mixture supplied to the engine is λ <1, assuming that a stoichiometric air-fuel ratio is λ = 1. An exhaust gas recirculation device, wherein the oxygen concentration in the exhaust system upstream of the exhaust purification catalyst device is approximately λ in terms of the air-fuel ratio under the rich condition,
= 1> secondary air supply means for supplying secondary air so that λ> 1, and exhaust gas which is taken out of an exhaust system downstream of the catalyst device and supplied to the intake system when supplying the secondary air. A recirculation means , wherein the exhaust gas purifying catalyst device comprises a main catalyst and less than the main catalyst.
At least λ <
Partially circulate exhaust gas to the sub-catalyst under rich conditions
Means, and the secondary air supply means is provided under the rich condition of λ <1.
The secondary air is supplied to the sub-catalyst, and the exhaust gas recirculation means operates under the sub-catalyst when the secondary air is supplied.
It has means for extracting exhaust gas from the stream and recirculating it.
That the exhaust gas recirculation system for an engine, characterized in that. 2. An exhaust gas recirculation device for an engine that recirculates a part of exhaust gas to an intake system under a rich condition where an air-fuel ratio of an air-fuel mixture supplied to an engine is λ <1, where stoichiometric air-fuel ratio is λ = 1. In the exhaust system upstream of the exhaust purification catalyst device, the oxygen concentration in the catalyst device under the above-mentioned rich condition is approximately λ
= 1 to λ> 1 secondary air supply means for supplying secondary air, exhaust gas is taken out from an exhaust system downstream from the catalyst device when the secondary air is supplied, and cooled to cool An exhaust gas recirculation means for recirculating air to an intake system upstream of the feeder , wherein the exhaust gas purification catalyst device has a main catalyst and less than the main catalyst.
At least λ <
Partially circulate exhaust gas to the sub-catalyst under rich conditions
Means, and the secondary air supply means is provided under the rich condition of λ <1.
Secondary air subjected feeding the auxiliary catalytic, said exhaust gas recirculation means and the auxiliary catalyst so when the secondary air supply
It has means for extracting exhaust gas from the stream and recirculating it.
That the exhaust gas recirculation system for an engine, characterized in that.