JPH0586847A - Exhaust emission control device for engine having mechanical supercharger - Google Patents

Abstract

PURPOSE:To improve exhaust gas purification performance, improve an output performance and knocking-resistance and suppress temperature rise of exhaust under a high load by serving an exhaust gas circulation passage as a secondary air passage, while giving full play to functions of both. CONSTITUTION:An EGR passage 35 is connected to a portion between an exhaust passage 12 on an upstream side of a catalyst 38 and an intake passage 11 on a downstream side of a mechanical supercharger 24. There are provided a means which opens an EGR valve 36 in an operation range from a total load to a set load lower than it by a specified rate, and a means which controls an air-fuel ratio in a combustion chamber so as to be substantially a theoretical air-fuel ratio in an operation range where an intake pressure is lower than an exhaust pressure, and to be rich in an range where the intake pressure is higher than the exhaust pressure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine with a mechanical supercharger in which an intake passage is provided with a mechanical supercharger and exhaust gas is recirculated to an intake passage downstream of the supercharger. The present invention relates to an exhaust gas purification device in.

[0002]

2. Description of the Related Art Conventionally, an exhaust gas recirculation passage (EGR passage) is connected between an exhaust passage and an intake passage of an engine,
A control valve (EGR
Exhaust gas recirculation devices provided with valves are generally known.

In an engine having a mechanical supercharger in the intake passage, for example, as disclosed in Japanese Utility Model Laid-Open No. 61-47479, between the exhaust passage and the intake passage downstream of the mechanical supercharger. By connecting the exhaust gas recirculation passage and forcibly opening the control valve of the exhaust gas recirculation passage during high supercharging operation, this passage is used as a bypass passage for the supercharger and the supercharged air is recirculated to the exhaust gas. There is one that bypasses the exhaust passage through the passage.

[0004]

By the way, a technique is known in which secondary air is supplied upstream of the catalyst in the exhaust passage to enhance the exhaust gas purification action (for example, JP-A 1-2).
See Japanese Patent No. 37320).

Therefore, in the apparatus disclosed in Japanese Utility Model Laid-Open No. 61-47479, it is conceivable to use the air bypassed to the exhaust passage through the exhaust gas recirculation passage as the secondary air at the time of high supercharging.

However, there is room for improvement in order to improve the exhaust gas recirculation performance in this case, the purification performance when used as secondary air, the output performance in the high load region, and the knock resistance. ..

In view of the above circumstances, the present invention uses the exhaust gas recirculation passage also as a secondary air passage to enhance the exhaust gas purifying performance by exerting its respective functions satisfactorily, and at the same time, to improve the output performance under high load and durability. An object of the present invention is to provide an exhaust gas purifying apparatus for an engine with a mechanical supercharger that can improve knocking and suppress an increase in exhaust temperature.

[0008]

To achieve the above object, the present invention provides a mechanical supercharger in an intake passage of an engine, and connects an exhaust gas recirculation passage between the exhaust passage and the intake passage. , In an engine with a mechanical supercharger having a control valve in this passage, connect an exhaust gas recirculation passage between the exhaust passage upstream of the catalyst for exhaust purification and the intake passage downstream of the mechanical supercharger Then, in the supercharging region where the intake pressure acting on the exhaust gas recirculation passage is higher than the exhaust pressure, the secondary air is guided from the intake passage to the exhaust passage through the exhaust gas recirculation passage, while the low load is applied. Control valve control means for opening the control valve of the exhaust gas recirculation passage, and combustion in the operating region in which the intake pressure is lower than the exhaust pressure, in the operating region over a set load lower than the full load in the supercharging region by a predetermined amount. The air-fuel ratio of the mixture of the inner and the stoichiometric air-fuel ratio, in a region where the intake pressure is higher than the exhaust pressure is obtained and a air-fuel ratio control means for the air-fuel ratio rich.

In this structure, the catalyst may be a three-way catalyst, and the NOx auxiliary catalyst may be arranged upstream of the exhaust gas recirculation passage connecting portion of the exhaust passage.

Further, while an O ₂ sensor is provided in the exhaust passage downstream of the exhaust gas recirculation passage, the air-fuel ratio control means has the O ₂ sensor in an operating region where the control valve of the exhaust gas recirculation passage is opened. It is preferable to perform feedback control so that the apparent air-fuel ratio detected by the above is approximately the theoretical air-fuel ratio.

[0011]

According to the above construction, exhaust gas is recirculated from the exhaust passage to the intake passage through the exhaust gas recirculation passage in the operating region on the low load side where the intake pressure downstream of the supercharger is lower than the exhaust pressure. On the other hand, in the area up to the above set load,
In the region where the intake pressure is higher than the exhaust pressure, secondary air is supplied from the intake passage to the exhaust passage through the exhaust gas recirculation passage, and the air-fuel mixture in the combustion chamber is made rich to reduce NOx. .. Further, in the high load region, the exhaust gas recirculation and the secondary air supply are stopped, and the scavenging property by supercharging is enhanced.

[0012]

Embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows an entire engine equipped with an exhaust gas recirculation system according to an embodiment of the present invention. The illustrated engine is a V-type engine, and an engine body 1 includes a cylinder block 2, a pair of cylinder heads 3 above the cylinder block 3, a head cover 4 on each cylinder head 3, and the like.
It has a and 1b. A plurality of cylinders are arranged in each bank 1a, 1b, and a combustion chamber 6 is provided above the piston 5 in each cylinder.
Are formed. A crankshaft 7 is arranged below the cylinder block 2.

An intake port 9 and an exhaust port 10 are opened in the combustion chamber 6, and an intake passage 11 is provided in the intake port 9.
Each independent intake passage 11a on the downstream side is connected to the exhaust port 10, and an independent intake passage provided on the exhaust manifold 13 for each bank on the upstream side of the exhaust passage 12 is connected to the exhaust port 10. An injector 14 is provided to inject and supply fuel to the intake port 9. Further, the intake port 9 and the exhaust port 10 are provided with an intake valve 15 and an exhaust valve 16, respectively.

The intake passage 11 has a common intake passage 11b in the upstream portion, and an air cleaner 21, an air flow meter 22, a throttle valve 23, a supercharger 24 and an intercooler 25 are provided in the common intake passage 11b from the upstream side. A portion downstream of the intercooler 25 is divided into two passages 11c and connected to the surge tanks 26 for each bank. Each surge tank 26 is provided for each bank.
Is connected to the upstream end of each of the independent intake passages 11a. The supercharger 24 is a mechanical supercharger that is operated by the rotational power of the crankshaft 7 being transmitted through a belt 27, and in particular, a Risholum internal compression type supercharger is used. ..

The two passages 11c between the intercooler 25 and each surge tank 26 are communicated with each other by a communication portion 28. Between the intake passage upstream of the supercharger 24 and downstream of the throttle valve 23 and the communication portion 28,
A supercharger bypass passage 29 that bypasses the supercharger 24 and the intercooler 25 is provided. In the supercharger bypass passage 29, an actuator valve 31 operated by the intake pressure introduced through a solenoid valve 30.
Is provided, and the actuator valve 31 is opened and closed by controlling the solenoid valve 30 according to the operating state. For example, when the load is low, the drive of the supercharger 24 is stopped and the actuator valve 31 is opened, so that the intake air bypasses the supercharger 24 and is supplied to the engine body 1. Also, the supercharger 2
4, an intercooler bypass passage 32 that bypasses the intercooler 25 is provided between the intake passage upstream of the intercooler 25 and upstream of the intercooler 25.
In the intercooler bypass passage 32, an opening / closing valve 33 that is opened / closed by an actuator (not shown) according to the operating state is provided. Then, for example, in an operating region up to a medium load where the rise in intake air temperature due to supercharging is relatively small, the opening / closing valve 33 is opened and supercharging air is supplied to the engine body 1 through the intercooler bypass passage 32. It has become so.

An EGR passage (exhaust gas recirculation passage) 35 is provided between the exhaust passage 12 and the intake passage 11 downstream of the supercharger 24. The EGR passage 35 is, for example, divided into two on the exhaust passage side so that both banks 1a, 1
While being connected to the collecting portion of the exhaust manifold 13 for each b, the intake passage side has passages 11c on both sides of the communication passage 28.
It is connected in the vicinity. The EGR passage 35 is provided with an EGR valve (control valve) 36 that operates in response to a control signal.

Further, the exhaust passage 12 is provided with an O ₂ sensor 37 for detecting an air-fuel ratio, a catalyst 38 for purifying exhaust gas, and a silencer 39. In the example shown in FIG. 1, the O ₂ sensor 37 and the catalyst 38 are provided in the exhaust passage for each bank. An O ₂ sensor 37 is provided downstream of the EGR passage connecting portion, and a catalyst 38 is provided further downstream thereof.

As shown in FIG. 2, the passage 35a on the exhaust passage side of the EGR passage 35, which is branched for each bank, is further branched for each cylinder, and the branch portion opens to the vicinity of each exhaust port. The EGR valve 36 is controlled by an ECU (control unit) 40. In this ECU 40,
The signals from the air flow meter 22 and the O ₂ sensor 37, the signal from the engine speed sensor 41 for detecting the engine speed, etc. are input. Further, the ECU 40 outputs a control signal to the EGR valve 36 and also outputs a control signal (injection pulse) to the injector 14.

The ECU 40 controls the EGR valve 36 and the injector 14 based on the control map shown in FIG.
Is controlled. That is, in this figure, La is a set load line for switching the opening and closing of the EGR valve 36, and this set load La is in the supercharging region where the intake pressure downstream of the supercharger is higher than the atmospheric pressure (see FIG. 4). Above the line of 0 mmHg indicated by the alternate long and short dash line), the load is lower than the full load by a predetermined amount. For example, while the intake pressure is 700 mmHg at full load, the set load La is 400 to 500 mmHg. It is supposed to be equivalent to the intake pressure of. And at least the low rotation range (2500-300)
The operating regions A1 and A2 on the low load side of the set load La at about 0 rpm or less) are the EGR valve open region.

In this EGR valve open region, the supercharger 24
A region A1 in which the intake pressure is lower than the atmospheric pressure (an operating region in which the intake pressure is lower than the exhaust pressure) is an EGR region. In this region A1, the EGR amount is adjusted appropriately so as to adjust the EGR amount. The opening degree of the valve 36 is adjusted,
The supercharging region where the intake pressure is higher than the atmospheric pressure (the region where the intake pressure is higher than the exhaust pressure) A2 is a secondary air supply region. In this region, the intake air is increased in accordance with the increase of the intake pressure. The opening degree of the EGR valve 36 is controlled so that the amount of secondary air flowing from the passage side to the exhaust passage side is appropriately adjusted. For example, as shown in FIG. 4, in the EGR region where the pressure difference between the supercharging pressure and the exhaust pressure (supercharging pressure-exhaust pressure) is negative, the opening degree of the EGR valve 36 is increased as the pressure difference approaches 0. In the secondary air region where the pressure difference exceeds 0 and becomes positive, the opening degree of the EGR valve 36 is reduced as the pressure difference increases.

On the other hand, the air-fuel ratio is controlled by the above EGR.
In the EGR region A1 of the valve opening region, the air-fuel ratio of the air-fuel mixture in the combustion chamber is set to a substantially stoichiometric air-fuel ratio (λ = 1), and in the secondary air supply region A2, the air-fuel ratio is set rich. In this embodiment, when the secondary air is supplied upstream of the 0 ₂ sensor, the air-fuel ratio in the combustion chamber becomes richer than the apparent air-fuel ratio by the 0 ₂ sensor, and the EGR region A1 and the secondary air are In any of the supply regions A2, feedback control is performed so that the apparent air-fuel ratio by the 0 ₂ sensor is set to a substantially stoichiometric air-fuel ratio. Further, in the region on the higher load side than the set load La, the feedback control is stopped, and the open control is performed so that the set air-fuel ratio is richer than the theoretical air-fuel ratio.

The control area map of FIG. 3 and E of FIG.
The map of the GR valve opening degree is stored in the ECU 40 in advance. Then, the ECU 40 detects the operating state based on the signals from the air flow meter 22, the rotation speed sensor 41, and the like, and based on the comparison between the operating state and the map,
In the EGR valve open regions A1 and A2, the EGR valve 36 is opened, and the opening thereof is controlled by the characteristic shown in FIG. 4, and the fuel from the injector 14 is controlled by the feedback control based on the signal from the O ₂ sensor 37. Control the injection amount. On the other hand, in regions other than the EGR valve open regions A1 and A2, the EGR valve 36 is closed and the fuel injection amount from the injector 14 is controlled by open control. In this way, the ECU 40 constitutes the control valve control means 43 and the air-fuel ratio control means 44 (see FIG. 5).

According to the apparatus of this embodiment as described above, the EGR valve opening region A including the low load region and a part of the supercharging region.
In 1 and A2, the EGR valve 36 is opened. Since the exhaust pressure is higher than the intake pressure in the EGR region A1, EGR is performed, NOx is thereby reduced, and feedback control is performed so that the air-fuel ratio becomes substantially the stoichiometric air-fuel ratio. , HC, CO, etc. are catalysts 3
8 and the exhaust gas purification performance is kept good.

In the secondary air supply region A2, the intake pressure becomes higher than the exhaust pressure, so that the EGR is stopped but the secondary air is supplied to the upstream of the catalyst 38 in the exhaust passage 12 through the EGR passage 35. To be done. With this,
In this secondary air supply state, feedback control is performed so that the apparent air-fuel ratio becomes the stoichiometric air-fuel ratio, so that the actual air-fuel ratio in the combustion chamber is made rich. When the air-fuel ratio in the combustion chamber is made rich, the NOx generation amount decreases, and
Since the performance of the catalyst 38 is kept good by the supply of the secondary air, the exhaust purification performance becomes good also in this region.

On the higher load side than the set load La, the EGR valve 36 is closed to stop both the EGR and the secondary air supply, and the entire amount of the supercharged air is supplied to the combustion chamber, so that scavenging, The filling efficiency is improved. Also,
A situation in which the catalyst temperature and the exhaust temperature are excessively increased by the secondary air on the high load side is prevented. Further, in this region, even if the air-fuel ratio is made rich, the rise in exhaust temperature is suppressed.

FIG. 6 shows another embodiment of the present invention. In this embodiment, the main catalyst 3 composed of a three-way catalyst is provided in the exhaust passage 12.
In addition to 8, the auxiliary catalyst 45 for NOx is provided, the EGR passage 35 is connected upstream of the main catalyst 38, and the auxiliary catalyst 45 is disposed further upstream thereof. Also in this embodiment, the structure of the entire exhaust purification system may be the same as that shown in FIG. 1, and the control of the EGR valve and the control of the air-fuel ratio may be the same as those in the above embodiments.

According to this embodiment, the auxiliary catalyst 45 reduces NOx even in the high load region where the EGR passage 35 is closed and the EGR and secondary air supply is stopped. Further, in the secondary air supply region, the secondary air is supplied downstream of the auxiliary catalyst 45 and upstream of the main catalyst 38, so that the respective catalytic functions are well exhibited.

As the control of the air-fuel ratio, in the above-mentioned embodiment, O ₂ is applied to both the regions A1 and A2 in FIG.
The air-fuel ratio in the combustion chamber is made rich in the secondary air region A2 by performing feedback control according to the sensor output, but in the secondary air region, the set air-fuel ratio richer than the theoretical air-fuel ratio is made by open control. The fuel may be increased and corrected so that

[0029]

According to the present invention, the exhaust gas recirculation passage is connected between the exhaust passage upstream of the catalyst for purification of exhaust gas and the intake passage downstream of the mechanical supercharger, while the exhaust gas recirculation passage is connected to the exhaust gas recirculation passage. The control valve of the exhaust gas recirculation passage is opened in an operating region up to a set load that is lower by a predetermined amount, and the air-fuel ratio of the air-fuel mixture in the combustion chamber is set in an operating region where the intake pressure downstream of the supercharger is lower than the exhaust pressure. The air-fuel ratio is set to a substantially stoichiometric ratio, and the air-fuel ratio is controlled to be rich in a region where the intake pressure is higher than the exhaust pressure. Therefore, in the supercharging region in which the intake pressure is higher than the exhaust pressure in the region up to the set load, NOx is reduced by making the air-fuel ratio in the combustion chamber rich, and the EGR passage is utilized. The secondary air can be supplied to the catalyst in the exhaust passage to improve the exhaust purification performance.
Also, in the high load range above the set load, exhaust gas recirculation and secondary air supply are stopped to promote scavenging due to supercharging, improve output performance and knock resistance, and suppress rise in exhaust temperature. You can

Further, the above catalyst is a three-way catalyst, and N is provided upstream of the exhaust gas recirculation passage connecting portion of the exhaust passage.
By disposing the Ox auxiliary catalyst, the exhaust gas purification performance in the high load region and the like becomes good.

Further, while an O ₂ sensor is provided in the exhaust passage downstream of the exhaust gas recirculation passage, the air-fuel ratio control means has the O ₂ sensor in an operating region where the control valve of the exhaust gas recirculation passage is opened. If feedback control is carried out so that the apparent air-fuel ratio detected by is approximately the stoichiometric air-fuel ratio, the air-fuel ratio is set to the substantially stoichiometric air-fuel ratio in the region where exhaust gas recirculation is performed and the air-fuel ratio is set in the region where secondary air supply is performed. The control for enriching the fuel ratio can be performed easily and reliably.

[Brief description of drawings]

FIG. 1 is a schematic view of an entire engine with a mechanical supercharger equipped with an exhaust gas purification device according to an embodiment of the present invention.

FIG. 2 is a structural explanatory view of a main part.

FIG. 3 is a diagram showing a map of control regions for an EGR valve and an injector.

FIG. 4 is a diagram showing a control characteristic of an EGR valve opening degree in an EGR valve open region.

FIG. 5 is a functional block diagram of a control system.

FIG. 6 is a structural explanatory view of a main part showing another embodiment.

[Explanation of symbols]

 1 Engine Body 11 Intake Passage 12 Exhaust Passage 24 Mechanical Supercharger 35 EGR Passage 36 EGR Valve 38 EGR Valve 38 Catalyst 40 ECU 43 Control Valve Control Means 44 Air-Fuel Ratio Control Means

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location F02D 41/02 330 D 9039-3G 41/14 310 A 9039-3G F02M 25/07 550 G 8923- 3G 570 P 8923-3G 580 Z 8923-3G

Claims (3)

[Claims] 1. A mechanical supercharger in which a mechanical supercharger is provided in an intake passage of an engine, an exhaust gas recirculation passage is connected between an exhaust passage and an intake passage, and a control valve is provided in the passage. In an engine, an exhaust gas recirculation passage is connected between an exhaust passage upstream of an exhaust purification catalyst and an intake passage downstream of a mechanical supercharger, and the intake pressure acting on this exhaust gas recirculation passage is the exhaust pressure. In the supercharging region, which is higher than the above, secondary air is guided from the intake passage to the exhaust passage through the exhaust gas recirculation passage, while operating region from low load to a set load that is a predetermined amount lower than the full load in the supercharging region. The control valve control means for opening the control valve of the exhaust gas recirculation passage and the air-fuel ratio of the air-fuel mixture in the combustion chamber in the operating region where the intake pressure is lower than the exhaust pressure are substantially stoichiometric air-fuel ratios. An exhaust gas purifying apparatus for an engine with a mechanical supercharger, comprising: an air-fuel ratio control means for making the air-fuel ratio rich in a region where is higher than the exhaust pressure. 2. The exhaust gas of an engine with a mechanical supercharger according to claim 1, wherein the catalyst is a three-way catalyst, and an auxiliary catalyst for NOx is arranged upstream of the exhaust gas recirculation passage connecting portion of the exhaust passage. Purification device. 3. An O ₂ sensor is provided in the exhaust passage downstream of the exhaust gas recirculation passage, while the air-fuel ratio control means has the O ₂ sensor in an operating region where a control valve of the exhaust gas recirculation passage is opened. The exhaust gas purifying apparatus for an engine with a mechanical supercharger according to claim 1 or 2, wherein feedback control is performed so that the apparent air-fuel ratio detected by the above is substantially stoichiometric air-fuel ratio.