JPH05187329A - Exhaust gas circulation device for engine with supercharger - Google Patents

Abstract

PURPOSE:To suppress generation of an agglutinated material due to fusion of condensed water by EGR gas cooling and solid component of such as carbon when cold exhaust gas (EGR gas) is refluxed upstream from a supercharger. CONSTITUTION:A check valve 15, a filter 16 composed of catalyzer, a cooler 17, and a control valve 18 are interposed in an EGR passage 14 connected upstream from supercharger 6 in flow direction of gas in order. The EGR gas first passes through the filter 16 to become free of solid component, and is refluxed to an intake passage 2 (located upstream from the supercharger 6) after being cooled by the cooler 17 thereafter. The filter 16 is composed of the catalyzer, therefore carbon and the like stuck to the filter 16 is promoted in combustion by catalytic action, and the filter 16 acquires self-purification function.

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 with a supercharger, which is provided with a supercharger in an intake passage and recirculates a part of exhaust gas (EGR gas) to the intake passage.

[0002]

2. Description of the Related Art Japanese Unexamined Patent Publication No. 1-285651 discloses a technique in which exhaust gas (EGR gas) taken from the downstream side of a catalyst converter is recirculated to the upstream side of a supercharger. According to this, there is an advantage that a large amount of EGR can be performed in the supercharging region where the supercharger exhibits its supercharging ability.

Further, the publication discloses that a cooler is arranged in the EGR passage through which the EGR gas passes and the EGR gas is cooled by the cooler. According to this, by cold EGR gas (cold EGR),
In particular, the exhaust gas temperature can be lowered in the high load operation region, and the exhaust system when the compression ratio of the engine is increased and / or the supercharging pressure generated by the supercharger is increased. There is an advantage that thermal damage to the parts (particularly the catalyst converter) can be prevented.

[0004]

However, the EGR
When a cooler is installed in the passage, this cooler allows EGR
Condensed water generated when the gas is cooled, and EG
There is a problem in that a coagulate is generated by fusion with carbon and the like mixed in the R gas, and the EGR gas containing the coagulate is recirculated to the intake passage. Of course,
When the above-mentioned coagulated material is introduced into the intake passage, this coagulated material enters the supercharger, which may impair the reliability of the supercharger.

Therefore, an object of the present invention is to provide an exhaust gas recirculation system for an engine with a supercharger, which suppresses the generation of the above-mentioned deposits, which is a problem when a cooler is arranged in the EGR passage. is there.

[0006]

In order to achieve the above technical object, the present invention adopts the following constitution.
That is, a supercharger disposed in the intake passage of the engine for supercharging, a catalyst converter disposed in the exhaust passage of the engine for purifying exhaust gas, and a part of the exhaust gas flowing in the exhaust passage. And an EGR passage that recirculates the EGR passage into the intake passage, and the inlet end of the EGR passage is the catalyst converter.
Is connected to an exhaust passage on the downstream side of the turbocharger, the outlet end is connected to an intake passage on the upstream side of the supercharger, and the EGR passage includes the EGR passage in order from the upstream side to the downstream side. A filter for removing solid components in the EGR gas flowing through the passage and a cooler for cooling the EGR gas are arranged.

[0007]

According to the above construction, since the filter is arranged on the upstream side of the cooler arranged in the EGR passage, E
Before the GR gas flows into the cooler, the carbon and the like mixed with the EGR gas are removed, so that the EGR gas containing no solid components such as the carbon flows into the cooler. .. For this reason, even if condensed water is generated by cooling the EGR gas in the cooler, it is possible to suppress the generation of the coagulated matter generated by the fusion of the condensed water and the carbon or the like.

[0008]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

In FIG. 1, reference numeral 1 is an engine body,
In the intake passage 2, an air cleaner 3, an air flow meter 4, a throttle valve 5, a supercharger 6 and a fuel injection valve 7 are arranged in this order from the upstream side to the downstream side. The supercharger 6 is a mechanical supercharger and is mechanically driven by the output of the engine 1.

A bypass passage 8 for bypassing the supercharger 6 is attached to the intake passage 2, and a bypass valve 9 is provided in the bypass passage 8 so that the supercharging pressure has a predetermined value. When the above is reached, the bypass valve 9 is opened.

A catalyst converter 11 containing a three-way catalyst is provided in the exhaust passage 10 of the engine body 1, and a silencer (not shown) is provided at the downstream end of the exhaust passage 10. ..

A first secondary air passage 13 and an EGR passage 14 are provided between the intake passage 2 and the exhaust passage 10.

The first secondary air passage 13 has an inlet end whose intake end is located upstream of the air flow meter 4, more specifically, an air intake passage sandwiched between the air flow meter 4 and the air cleaner 3. 2 while the outlet end is a catalyst converter
A control valve 15 is provided in the first secondary air passage 13 connected to the exhaust passage 10 upstream of the control valve 11.

The EGR passage 14 has its inlet end connected to the exhaust passage 10 on the downstream side of the catalyst converter 11, and its outlet end on the upstream side of the supercharger 6, more specifically, the intake passage 2. Is connected to the intake passage 2 sandwiched between the supercharger 6 and the throttle valve 5. A check valve 15, a filter 16, a cooler 17, and a control valve 18 are provided in this EGR passage 14 in this order from the upstream side to the downstream side.

The check valve 15 allows the exhaust gas passing through the exhaust passage 10 to flow into the EGR passage 14, while preventing the gas in the EGR passage 14 from flowing back into the exhaust passage 10. is there.

The filter 16 is composed of a three-way catalyst or an oxidation catalyst, and traps carbon etc. contained in the exhaust gas (EGR gas) passing through the EGR passage 14,
It has a self-cleaning function that burns and purifies the attached carbon.

A second secondary air passage 20 is attached to the engine body 1. This second secondary air passage 2
0 is the intake passage 2 whose inlet end is downstream of the air flow meter 4, more specifically, the throttle valve 5 and the air flow path.
Connected to the intake passage 2 sandwiched between the filter 4 and the outlet end of the EGR passage 14 upstream of the filter 16,
A control valve 21 is provided in the middle of the second secondary air passage 20.

In FIG. 1, reference numeral U is a control unit, and the control unit U is composed of, for example, a microcomputer.
It is equipped with RAM and the like. To the control unit U, various signals representing the engine speed, engine load, etc. are input from the sensor group 25 in addition to the signal indicating the intake air amount from the air flow meter 4. On the other hand, various control signals are output from the control unit U to the actuator 23 for the EGR control valve 18 and the like.

The contents of the control performed by the control unit U will be described below. Air-fuel ratio control: Explaining only in the high load region, in the high load region, in the low rotation region, for example, A / F = about 13,
An air-fuel ratio richer than the stoichiometric air-fuel ratio is set. On the other hand,
In the high engine speed range, an air-fuel ratio leaner than the stoichiometric air-fuel ratio or a stoichiometric air-fuel ratio (λ = 1) is set. Since the specific air-fuel ratio control method is the same as the conventional one, its detailed description is omitted.

The control of the secondary air supplied to the upstream side of the first secondary air control catalyst converter 11 will be described by limiting it to the high load region. In the low rotation region where the rich air-fuel ratio is set, the control is performed. -The valve 15 is fully closed and the supply of secondary air is stopped. On the other hand, in the high load and high rotation speed region (lean air-fuel ratio or stoichiometric air-fuel ratio region), the control valve 15 is opened and the secondary air is supplied to the upstream side of the catalyst converter 11.

In the low rotation speed region where the air-fuel ratio is made rich by the secondary air control, unburned components are contained in the exhaust gas, and when the secondary air is supplied in this low rotation speed region, the exhaust system is operated. The unburned components burn and become a factor of raising the temperature of the exhaust gas. On the other hand, if the air-fuel ratio is the theoretical air-fuel ratio or the
In the high rotation region where the air-fuel ratio is high, the unburned components in the exhaust gas are small, so that the secondary air mainly acts to cool the exhaust gas, and the reliability of the catalyst converter 11 is improved. It will contribute to increase.

The EGR control valve 18 is opened in the EGR control high load region. When the EGR valve 18 is opened, a part of the exhaust gas passing through the exhaust passage 10 is taken into the EGR passage 14, and the EGR gas first passes through the filter 16 so that the carbon contained in the EGR gas is removed. The solid components such as are removed. Further, the EGR gas is cooled by the cooler 17 and then returned to the intake passage 2 (cold EGR).

As described above, since the cold EGR is performed in the high load operation, for example, when the engine body 1 is a high compression ratio engine and / or the supercharger 6 generates a high supercharging pressure. Even if it does, it is possible to suppress the exhaust gas temperature to a low level, and it is possible to prevent thermal damage to the exhaust system components, especially the catalyst converter 11.

Further, as described above, the filter 16 is arranged upstream of the cooler 17, that is, the EG
Since the carbon gas in the EGR gas is trapped before the R gas passes through the cooler 17, condensed water and carbon generated when the EGR gas is cooled by the cooler 17 are trapped.
It is possible to prevent the formation of a cohesive substance which is a fusion product with a bon or the like.

Furthermore, since the filter 16 is composed of a catalyst, the combustion of carbon attached to the filter 16 is promoted by the catalytic action, and the filter 16
Will have a self-cleaning function.

In the second secondary air control high load region (the above-mentioned high load EGR region), the control valve 21 is opened in the low rotation region where the rich air-fuel ratio is set, and the secondary air flows into the EGR passage 14. Is supplied. On the other hand, the control valve 21 is closed and the supply of secondary air to the EGR passage 14 is stopped in the high load / high speed region where the lean air-fuel ratio or the stoichiometric air-fuel ratio is set.

That is, in the region where the rich air-fuel ratio is set, the amount of exhaust gas per unit time is small (the EGR passage 14 is The amount of EGR gas that passes through is small).
Even if the combustion of bon and the like is promoted, the rise in the EGR gas temperature accompanying this can be compensated by the cooler 17. Therefore, by supplying the secondary air in the low rotation region, EGR
It is possible to achieve compatibility with cold EGR while thoroughly removing carbon and the like mixed in the gas.

On the other hand, in the region where the stoichiometric air-fuel ratio or the lean air-fuel ratio is set, the amount of unburned components in the exhaust gas is relatively small. Therefore, it is not necessary to dare to supply the secondary air to promote the combustion of carbon or the like in the filter 16. In other words, when the secondary air is supplied, the EGR gas temperature rises due to the activation of the catalytic action of the filter 16. In addition, since the engine speed is high in this region, the EGR gas amount per unit time passing through the EGR passage 14 is large, and the cooler 17 absorbs the rise in the EGR gas temperature due to the secondary air supply. Things get harder.
That is, the cold EGR can be secured by stopping the supply of the secondary air in the high load and high rotation speed range.

Further, in the high load and high rotation speed region, as described above, the secondary air is supplied to the upstream side of the catalyst converter 11, and the catalyst converter 11 unburns the unburned gas in the exhaust gas. Since the components have been removed, the need for activation of the catalytic action in the filter 16 (supply of secondary air using the intake passage 20) is further reduced.

When the air-fuel ratio in this region (high-load high-rotation region) is set to a large lean air-fuel ratio such as A / F = 22, the secondary air conditioner control valve 21 is set. It may be used to supply the secondary air to the upstream side of the filter 16.

That is, when the lean degree of the air-fuel ratio is increased, almost no unburned components are mixed in the exhaust gas, so the secondary air supplied to the EGR passage 20 is mainly EG.
This contributes to lowering the R gas temperature, and the effect of cold EGR can be improved. Of course, since the secondary air supplied to the EGR passage 20 is taken in at the downstream side of the air flow meter 4, the secondary air supplied to the EGR passage 14 is exhausted by the check valve 15 to the exhaust passage. Since it does not leak to the fuel cell 10, the air-fuel ratio control is not affected by the supply of the secondary air.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments and includes the following modifications. (1) The supercharger 6 is not limited to the mechanical supercharger, and may be a turbocharger driven by exhaust energy. (2) The cooler 17 may be a water cooling type or an air cooling type.

[0033]

As is apparent from the above description, according to the present invention, it is possible to suppress the generation of coagulation, which is a problem when cold EGR cooled by a cooler is performed, and therefore the cold is applied. The reliability of the supercharger is not impaired by performing EGR.

[Brief description of drawings]

FIG. 1 is an overall system diagram of an engine with a supercharger according to an embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Engine main body 2 Intake passage 4 Air flow meter 5 Throttle valve 6 Supercharger 10 Exhaust passage 11 Catalyst converter 14 EGR passage 15 Check valve 16 Filter 17 Cooler 18 EGR valve 20 EGR passage secondary air passage 21 2 Next Air conditioner control valve 25 Sensor group U control unit

Claims (3)

[Claims] 1. A supercharger arranged in an intake passage of an engine for supercharging, a catalyst converter arranged in an exhaust passage of an engine for purifying exhaust gas, and an exhaust gas flowing in the exhaust passage. And an EGR passage for returning a part of the EGR passage to the intake passage. The EGR passage has an inlet end connected to an exhaust passage downstream of the catalyst converter and an outlet end connected to the supercharger. Is also connected to the intake passage on the upstream side, and the EGR passage has a filter for removing solid components in the EGR gas flowing through the EGR passage in order from the upstream side to the downstream side.
An exhaust gas recirculation device for a supercharged engine, comprising a cooler for cooling GR gas. 2. The intake air amount detector according to claim 1, wherein the filter is composed of a catalyst for purifying EGR gas, and further, an intake air amount detector disposed at an upstream end of the intake passage, and an intake air amount detector more than the intake air amount detector. An exhaust gas recirculation system for a supercharged engine, comprising: a downstream intake passage; and a secondary air passage connected to an EGR passage upstream of the filter. 3. The EGR control valve provided in the EGR passage, the secondary air control valve provided in the secondary air passage, and load detecting means for detecting an engine load. A rotation speed detection device for detecting the engine rotation speed, and a signal from the load detection means and the rotation speed detection means, and the air-fuel ratio of the air-fuel mixture sucked by the engine is higher than the theoretical air-fuel ratio in the high load low rotation speed region The air-fuel ratio control means for controlling the air-fuel ratio to be a lean air-fuel ratio rather than the stoichiometric air-fuel ratio or the theoretical air-fuel ratio in the high load and high rotation region, Signal from the EGR control means for opening the EGR control valve to recirculate a part of the exhaust gas to the intake passage when the engine load is in the high load region, and the load detection means and the rotation speed detection means. In response to the signal, the secondary air control valve is opened in the high load low rotation region where the rich air-fuel ratio is set, and the secondary air control valve is opened in the high load high rotation region where the stoichiometric air-fuel ratio or the lean air-fuel ratio is set. An exhaust gas recirculation device for an engine with a supercharger, comprising: a secondary air control means for closing a secondary air control valve.