JPH055414A - Exhaust emission control system for engine with mechanical supercharger - Google Patents

Abstract

(57) [Abstract] [Purpose] In order to avoid the occurrence of knocking phenomenon, the engine with a mechanical supercharger operates in a high load operation state and the mechanical supercharger operates in each cylinder. The valve opening overlap period is set to be relatively long,
Even when the amount of the air-fuel mixture blown out increases, the increase in the content of HC components, CO components, etc. in the exhaust gas discharged to the outside through the exhaust passage portion in which the exhaust purification catalyst portion is arranged is suppressed. [Structure] Three-way catalytic converter (18) in a common exhaust passage section (16) in which a three-way catalytic converter (18) is arranged
The engine main body (1) and the air supply passage (68) that selectively takes an air replenishment state in which air from the surge tank (33) flows into a portion on the more upstream side are in a high load operation state satisfying a predetermined condition. At this time, a control block (50) for causing the air supply passage (68) to be in an air supply state is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mechanical supercharger for purifying exhaust gas discharged to the outside through an exhaust passage provided in an engine having a mechanical supercharger arranged in an intake passage. Exhaust gas purification device for engine

[0002]

2. Description of the Related Art In the field of an engine mounted on a vehicle, an exhaust gas purification catalyst portion such as a three-way catalytic converter having an exhaust gas purification function is provided in an exhaust passage portion connected to the engine body. Exhaust gas exhausted through the exhaust passage is purified, and, for example, as disclosed in JP-A-58-220933, a plurality of cylinders arranged in the engine body are provided corresponding to each cylinder. Fuel is supplied by a plurality of fuel injection valves that have been set to improve the control accuracy of the air-fuel ratio, improve the fuel supply responsiveness, and improve the mixing of the air-fuel mixture. A mechanical supercharger that is driven by transmission of rotation of the crankshaft and placed in an operating state is attached to an intake passage connected to the engine body. High output are also known those achieved by intake air charging efficiency in people each of a plurality of cylinders provided in the engine body is increased by supercharging operation.

In an engine equipped with a mechanical supercharger which is driven by transmitting the rotation of the crankshaft, the mechanical supercharger is operated when operating under a relatively low load. The mechanical turbocharger is activated when it is inactive and operating under a relatively high load, so that it is operating under a relatively high load. At this time, it is often the case that supercharging is performed for each cylinder to increase intake charge efficiency and increase engine output.

In such an engine with a mechanical supercharger, which has been designed to achieve a high output by installing a mechanical supercharger,
There is a problem that the temperature rise in each cylinder becomes significant under the operation of the mechanical supercharger, which causes a knocking phenomenon to occur easily. Therefore, for example, as disclosed in Japanese Patent Laid-Open No. 2-119621, in an engine with a mechanical supercharger, the intake air supercharged to each cylinder by the mechanical supercharger is used to In order to suppress the temperature rise in each cylinder by performing scavenging of the residual gas after combustion in the cylinder, the intake air provided for each cylinder during the high load operation state where the knocking phenomenon is likely to occur It has been proposed that the overlap period in which both the valve and the exhaust valve are opened is set to be relatively long so that the scavenging of each cylinder is performed well.

[0005]

However, in an engine provided with a mechanical supercharger, when the mechanical supercharger is operated under a relatively high load operating condition. In the overlap period in which both the intake valve and the exhaust valve provided corresponding to each of the cylinders are in the open state, the supercharging pressure becomes higher than the exhaust pressure so that the pressure is supplied to each cylinder. Blowing of the air-fuel mixture to the exhaust passage side occurs. Then, as the air-fuel mixture blows through to the exhaust passage portion side, the fuel attached to the intake port wall, which is a part of the fuel injected during the intake stroke, blows out toward the exhaust passage portion side, The air-fuel ratio of the air-fuel mixture blown into the exhaust passage is made richer than the theoretical air-fuel ratio.For example, even when a three-way catalytic converter is installed in the exhaust passage, When purifying the gas, the lack of oxygen is mimicked, and the content of hydrocarbon (HC) components and carbon monoxide (CO) components in the exhaust gas discharged to the outside through the exhaust passage is increased. There is a problem of becoming. Moreover, when the engine is in the high load and high rotation operating state, the amount of fuel injected and supplied from the fuel injection valve is increased as compared to when the engine is in the high load and low rotating operating state, and therefore, the fuel is distributed to the exhaust passage portion. The lack of oxygen amount when purifying exhaust gas by the installed three-way catalytic converter becomes more problematic. Therefore, as described above, the engine equipped with the mechanical supercharger is operating under a relatively high load in order to avoid the occurrence of the knocking phenomenon. When the overlap period for each cylinder during operation is set to be relatively long, if the engine speed during supercharging operation of the mechanical supercharger becomes relatively high, As the amount of air-fuel mixture supplied to each cylinder to the exhaust passage portion increases, the amount of fuel to the exhaust passage portion also increases, and is discharged to the outside through the exhaust passage portion. There is a possibility that the content of HC component, CO component and the like in the exhaust gas tends to be further increased.

In view of this point, the present invention is provided in an engine body having a mechanical supercharger attached to an intake passage, and the engine body is in a high load operating state in order to avoid occurrence of a knocking phenomenon. The intake valve and exhaust valve provided for each cylinder are set so that the overlap period is relatively long while the mechanical turbocharger is operating. Therefore, even when the amount of the air-fuel mixture supplied to each cylinder is increased to the exhaust passage portion side, the exhaust gas is exhausted to the outside through the exhaust passage portion where the exhaust purification catalyst portion is arranged. It is an object of the present invention to provide an exhaust gas purifying apparatus for an engine with a mechanical supercharger, which is capable of suppressing an increase in the content of HC components, CO components, and the like in the generated exhaust gas.

[0007]

In order to achieve the above object, an exhaust gas purifying apparatus for an engine with a mechanical supercharger according to the present invention is provided with a mechanical supercharger driven by an engine output. An exhaust passage portion extending from the engine body and an exhaust passage portion extending from the engine body, each of the plurality of cylinders being provided with a plurality of fuel supply means for injecting fuel in synchronism with each intake stroke. In addition to the exhaust gas purification catalyst portion disposed in the exhaust passage portion for purifying the exhaust gas guided to the exhaust gas portion, the air from the air supply source is supplied to the portion of the exhaust passage portion upstream of the exhaust gas purification catalyst portion. An air supply unit that selectively takes in the air supply state to flow in, and
When the engine body is in a high-load operation state satisfying a predetermined condition, the air supply section is provided with operation control means for keeping the air supply state.

[0008]

In the exhaust gas purifying apparatus for an engine with a mechanical supercharger according to the present invention configured as described above, the mechanical supercharger can be used when the engine is in a high load operating condition satisfying a predetermined condition. Under the operating condition, the air supply portion causes the air from the air supply source to flow into the exhaust passage portion on the upstream side of the exhaust purification catalyst portion. As a result, when the engine is placed in a high-load operating condition that satisfies a predetermined condition, the overlap period in which both the intake valve and the exhaust valve are open in each cylinder is relatively long, and as a result, Even when the amount of the air-fuel mixture supplied to each cylinder is blown out toward the exhaust passage portion, the air supplied by the air supply portion to the portion upstream of the exhaust purification catalyst portion in the exhaust passage portion When exhaust gas is purified in the exhaust purification catalyst portion arranged in the passage portion, a situation in which a shortage of oxygen amount is mimicked is avoided, and therefore,
Exhaust gas is properly purified in the exhaust purification catalyst portion, and an increase in the content of HC components, CO components, and the like in the exhaust gas discharged to the outside through the exhaust passage portion is suppressed.

[0009]

1 and 2 show an example of an exhaust gas purifying apparatus for an engine with a mechanical supercharger according to the present invention, together with an in-line 4-cylinder engine to which it is applied.

In FIGS. 1 and 2, the engine body 1
A cylinder block 2, an oil pan 3 arranged below the cylinder block 2, a cylinder head 4 arranged above the cylinder block 2, and a head cover 5 arranged above the cylinder head 4. It is said that. Inside the cylinder block 2, four cylinders 6 each having a piston 17 inserted therein are arranged in series, and the cylinder head 4 has a downstream end portion of an intake manifold 11 and an upstream end portion of an exhaust manifold 13. The side ends are connected.

Above each of the four cylinders 6, a pair of downstream end portions of a branch portion of a branch intake port 7 formed in the cylinder head 4, and a branch formed in the cylinder head 4 as well. A pair of upstream end portions of the branch portion of the exhaust port 9 are opened. The upstream end of the branch intake port 7 is connected to the individual passage 35 in the intake manifold 11, and the branch intake port 7 and the individual passage 35 form an individual intake passage portion 39. The upstream end of the intake manifold 11 is connected to the surge tank 33 forming the downstream portion of the common intake passage portion 10, and therefore each of the four cylinders 6 is
It connects with the surge tank 33 which forms the downstream side part of the common intake passage part 10 through the individual intake passage part 39 which consists of the branch intake port 7 and the individual passage 35.

A pair of intake valves 20 are respectively arranged at a pair of downstream end portions of the branch portion of the branch intake port 7.
Each of the intake valves 20 is selectively opened and closed to open and close an opening of each of the pair of downstream ends of the branch intake port 7 with respect to each cylinder 6. .. An individual fuel injection valve 38 is arranged in the individual passage 35 of the intake manifold 11 forming the individual intake passage portion 39. Each of the four individual fuel injection valves 38 is, for example, the corresponding cylinder 6
The fuel injection operation is performed in synchronism with the intake stroke.

On the other hand, the downstream end portion of the collection portion of the branch exhaust ports 9 has an individual passage 14 in the exhaust manifold 13.
The collecting passage 15 in the exhaust manifold 13 is connected to the common exhaust passage portion 16. In the common exhaust passage portion 16, a three-way catalytic converter 18 forming an exhaust purification catalyst portion is arranged. A pair of exhaust valves 23 are arranged at a pair of upstream end portions of the branch portion of the branch exhaust port 9, and each of the exhaust valves 23 has a pair of upstream end portions of the branch portion of the branch exhaust port 9. The valve opening state and the valve closing state for opening and closing the openings of the respective cylinders 6 are selectively set.

In the common intake passage portion 10, an air cleaner 25 having an intake inlet portion, an air flow sensor 26, a throttle valve 27 with a throttle opening sensor 27A, and an engine body 1 are sequentially arranged from the upstream side thereof. The rotation of the crankshaft 28 (FIG. 2) is caused by the belt 29 and the electromagnetic clutch 3.
A Rishorum type mechanical supercharger 31, which is selectively transmitted via 0 to be operated, an intercooler 32 for cooling intake air in the common intake passage portion 10, and a surge tank 33 are arranged.

In the electromagnetic clutch 30 provided in the mechanical supercharger 31, the operating state of the engine body 1 is such that the vertical axis represents an engine load Th that is changed according to the opening degree of the throttle valve 27, and the horizontal axis represents the engine load Th. When the engine is in the region A or the region B corresponding to the operating state under a relatively low speed and a low load shown in the characteristic diagram of FIG. Further, when the operating state of the engine body 1 is in the region C or the region D corresponding to the operating state under relatively high speed or high load shown in the characteristic diagram of FIG. 3, it is put in the connected state. As a result, the mechanical supercharger 31 does not transmit the rotation of the crankshaft 28 and is in a non-operating state when the engine body 1 is operating under low speed and low load. He And, when in the operating condition under relatively high speed or high load engine body 1, the rotation of the crank shaft 28 is transmitted, it is placed in the boost operating state to increase the intake air charging rate in the cylinder 6.

The portion of the common intake passage 10 between the throttle valve 27 and the mechanical supercharger 31 and the surge tank 3
3 is connected by an intake bypass 41, and the intake bypass 41 is provided with a diaphragm-type intake bypass control valve 43 driven by a solenoid valve 42. The solenoid valve 42 has a control signal S supplied to it.
According to S, when the engine body 1 is operating under low speed and low load, the intake pressure obtained in the surge tank 33 is guided to the pressure chamber of the intake bypass control valve 43 through the intake bypass 41. The operating state of
In addition, when the engine body 1 is in an operating state under high speed or high load, an operating state in which the intake pressure obtained in the surge tank 33 is not guided to the pressure chamber of the intake bypass control valve 43 is taken. It is said that. Thereby,
The intake bypass control valve 43 sets the intake bypass 41 to the open state when the engine body 1 is in the operating state under low speed and low load and the mechanical supercharger 31 is in the non-operating state. The intake air passing through the throttle valve 27 in the common intake passage portion 10 directly flows into the surge tank 33 through the intake bypass 41, and the passage resistance to the intake air is reduced.

Further, the intake bypass control valve 43 operates when the engine main body 1 is operating under high speed or under high load and the mechanical supercharger 31 is in the supercharging operation state.
The intake bypass 41 is controlled so that the intake pressure in the portion of the common intake passage 10 downstream of the mechanical supercharger 31 becomes a predetermined value that is equal to or lower than a preset sufficiently high value.
Is controlled so that the intake air through the throttle valve 27 in the common intake passage portion 10 is used for supercharging by the mechanical supercharger 31 and a relatively high intake pressure is obtained in the surge tank 33. Become. Then, under such circumstances, when the intake pressure in the portion of the common intake passage portion 10 downstream of the mechanical supercharger 31 exceeds a preset sufficiently high value, the solenoid valve 42 becomes
The intake pressure obtained in the surge tank 33 is the intake bypass 41.
Through the pressure chamber of the intake bypass control valve 43,
The intake bypass control valve 43 is placed in a state that opens the intake bypass 41, whereby the intake pressure obtained in the surge tank 33 is reduced through the intake bypass 41, and the common intake passage 10 Is adjusted so that the intake pressure in the portion on the downstream side of the mechanical supercharger 31 is equal to or lower than a preset sufficiently high value,
It is possible to avoid a situation in which the intake pressure in the common intake passage portion 10 becomes excessively large and adversely affects each portion.

The control signal SS is supplied to the solenoid valve 42 for controlling the intake bypass control valve 43 provided in the above-mentioned intake bypass 41 by the control block 50 provided in the engine body. The control block 50 includes a detection output signal Sn representing the engine speed obtained from the engine speed sensor 65, a detection output signal Sc representing the crank rotation angle obtained from the crank rotation angle sensor 66, and an intake flow rate obtained from the air flow sensor 26. Is supplied, and various detection output signals representing the operating state of the engine body 1 such as a detection output signal St representing the throttle opening obtained from the throttle opening sensor 27A are supplied. Then, the control block 50 responds to the operating state of the engine body 1 under the relatively low speed and low load shown in the characteristic diagram of FIG. 3, based on the various detection output signals supplied. When it is in the region A or the region B to be operated, the solenoid valve 42
First, the control signal SS is sent to bring the intake pressure obtained in the surge tank 33 into an operating state in which the intake pressure is guided through the intake bypass 41 to the pressure chamber of the intake bypass control valve 43.

A pair of intake valves 20 for respectively opening and closing a pair of openings for the cylinder 6 in the branch portion of the branch intake port 7 provided for each cylinder 6, and a branch provided for each cylinder 6 as well. The pair of exhaust valves 23, which respectively open and close the pair of openings for the cylinder 6 in the branch portion of the exhaust port 9, constitute a variable valve timing mechanism 4 which constitutes a valve mechanism arranged in the cylinder head 4.
Each operation is controlled by 5. The variable valve timing mechanism 45 is additionally provided with a hydraulic circuit section 49 provided in the engine body 1 and controlled by a control block 50 to supply an operating hydraulic pressure to the variable valve timing mechanism 45.

The variable valve timing mechanism 45 is constructed, for example, as shown in FIG. 4, and the rotation of the crankshaft 28 is transmitted to the gears 47 and 48 via the cogged belt 46 so that the gears 47 and 48 are respectively assembled. The intake side cam shaft 51 and the exhaust side cam shaft 52 are driven. An annular spacer 5 that is bolted to one end surface of the intake side cam shaft 51 and projects in the extension direction of the intake side cam shaft 51.
3 and a cover member 54 for covering the spacer 53
And are assembled. The cover member 54 is a first tubular member 5 fitted to one end of the intake-side camshaft 51.
4A, a second tubular member 54B which is bolted to the first tubular member 54A and the gear 47, and forms a space 55 between the outer peripheral surface portion of the spacer 53, and the spacer 53. A gap 57 communicating with an oil passage 56 penetrating the intake-side camshaft 51 and the spacer 53 is formed between them and is formed by a disc-shaped member 54C that covers the protruding end surface portion of the spacer 53. In the space 55 formed between the second tubular member 54B and the spacer 53, an annular piston member 59 biased by the coil spring 58 toward the disc-shaped member 54C is arranged. ..

The piston member 59 is the first tubular member 54.
The first annular body 59A located on the A side and the disk-shaped member 54
The first annular body 5 is located on the C side by the plurality of pins 59B.
And a second annular body 59C connected to 9A, the outer peripheral surface portion is helically spline-engaged with the inner peripheral surface portion of the second tubular member 54B, and the inner peripheral surface portion is the outer periphery of the spacer 53. A helical spline is engaged with the surface portion. Piston member 59 and second tubular member 5
4B with helical spline engagement and piston member 59
And the helical spline engagement between the spacer 53 and the spacer 53 have opposite twist directions. Such a piston member 59
Is maintained at the position on the side of the disk-shaped member 54C by the urging force of the coil spring 58 when the working hydraulic pressure from the hydraulic circuit unit 49 is not applied, and the working hydraulic pressure from the hydraulic circuit unit 49 is When the second annular member 59C is acted on by 56 through the gap 57 formed between the disk-shaped member 54C and the spacer 53, the coil spring 5
8 is moved in the direction along the intake-side cam shaft 51 against the biasing force of 8.

Four pairs of intake side cam portions 60 are formed on the intake side cam shaft 51, and the pair of intake side cam portions 6 is formed.
0 drives a pair of intake valves 20 that respectively open and close a pair of openings for the cylinder 6 in the branch portion of the branch intake port 7 provided for each cylinder 6. On the other hand, the exhaust-side cam shaft 52 is also formed with four pairs of exhaust-side cam portions 63, and the pair of exhaust-side cam portions 63 are respectively provided in the branch exhaust ports 9 provided for the respective cylinders 6. The pair of exhaust valves 23, which respectively open and close the pair of openings for the cylinder 6 in the branch portion, are driven. Then, the pair of intake side cam portions 6
0 causes the pair of intake valves 20 to simultaneously perform the opening / closing operation, and the pair of exhaust side cam portions 63 causes the pair of exhaust valves 23 to simultaneously perform the opening / closing operation.

The hydraulic circuit section 49 is controlled by the control block 50, and the control block 50 supplies a control signal Co formed on the basis of various detection output signals supplied thereto to the hydraulic circuit section 49, and the engine body 1 According to the operating state of the variable valve timing mechanism 45 of the hydraulic circuit unit 49.
Control the supply state of the operating hydraulic pressure to the piston member 59.

Under the control of the control signal Co from the control block 50, the hydraulic circuit section 49 changes the operating state of the engine body 1 to the low speed and low load operating states shown in the characteristic diagram of FIG. When in the corresponding area A, the piston member 59 in the variable valve timing mechanism 45
Take the condition that the hydraulic pressure is not applied to. Under such circumstances, each of the pair of intake valves 20 has the intake side camshaft 51.
According to the rotation of the pair of intake side cam portions 60 accompanying the rotation of
In both cases, the valve opening displacement amount Ds is taken on the vertical axis and the time t is taken on the horizontal axis, and the valve opening displacement amount as shown by the curve α in the characteristic diagram of FIG. Time tb earlier than TDCe at the top dead center in the process
At the time point te which is later than the bottom dead center BDCi in the next intake stroke, a transition from the valve closed state to the valve opened state is started, and then the valve opening state in which the maximum valve opening displacement amount is taken is reached. Will be completed. On the other hand, each of the pair of exhaust valves 23 follows the rotation of the pair of exhaust side cam portions 63 as the exhaust side cam shaft 52 rotates.
It is assumed that the valve will operate with the valve opening displacement as shown by the curve β in the characteristic diagram of Fig. 1, and the transition from the valve closed state to the valve opened state is started at a time earlier than the bottom dead center BDCc in the explosion stroke, and then the maximum opening is performed. The valve is opened at the time point ta while the valve opening state is taken, and the transition from the valve open state to the valve close state is completed at the time tc later than the top dead center TDCe in the next exhaust stroke. To be taken. As a result, the overlap period TA in which both the pair of intake valves 20 and the pair of exhaust valves 23 are opened is set as a relatively short period from time tb to time tc. Then, under such circumstances, the fuel injection valves 38 provided in the plurality of individual intake passage portions 39 are
Control signals SI1, SI2, SI from control block 50
3 and SI4, the operation is controlled to start the fuel injection within the overlap period TA in which the corresponding pair of intake valves 20 and the corresponding pair of exhaust valves 23 are both opened.

On the other hand, in the hydraulic circuit portion 49, the operating state of the engine body 1 is a region C corresponding to the operating state under a relatively high speed or high load shown in the characteristic diagram of FIG.
And D are included in a region other than the region A, the hydraulic pressure is applied to the piston member 59 of the variable valve timing mechanism 45. Under such circumstances, the piston member 59 is moved along the intake side cam shaft 51 against the biasing force of the coil spring 58 by the action of the operating hydraulic pressure from the hydraulic circuit portion 49, and the intake side cam shaft 51 is moved. Of the rotation of the exhaust side camshaft 52 with respect to the rotation of the exhaust side camshaft 52, causing a mutual rotation phase change. As a result, the respective operations of the pair of exhaust valves 23 are not changed, and the valve opening displacement amount as shown by the curve β in the characteristic diagram of FIG. 20 is operated with a valve opening displacement amount as indicated by a curve γ in the characteristic diagram of FIG. 5, in accordance with the rotation of the pair of intake side cam portions 60 accompanying the rotation of the intake side cam shaft 51. Time point ta even earlier than time point tb earlier than the top dead center TDCe in the exhaust stroke
At the time point td which is later than the bottom dead center BDCi in the next intake stroke and is earlier than the time point te, the valve is opened from the valve closed state to the valve opened state in the above state, and then the valve is opened at the maximum valve opening displacement amount. It is assumed that the transition from the state to the valve closed state is completed. That is, at this time, a time point ta at which the pair of intake valves 20 starts transitioning from the closed state to the valve open state, and a time point after which the pair of intake valves 20 completes transition from the valve open state to the valve close state. td is the engine body 1
Area A corresponding to low speed and low load operating conditions
At the time point tb at which the pair of intake valves 20 starts transitioning from the closed state to the open state, and after that, the pair of intake valves 20 completes transition from the open state to the closed state. Therefore, the overlap period T during which the pair of intake valves 20 and the pair of exhaust valves 23 are both opened is set.
B will be set as a relatively long period. Then, even under such circumstances, the plurality of individual intake passage portions 3
The fuel injection valves 38 installed in the No. 9 control signals SI1, SI2, SI3 and SI4 from the control block 50, respectively.
Corresponding to the pair of intake valves 20 and the pair of exhaust valves 2
The operation is controlled to start the fuel injection within the overlap period TB in which both 3 and 3 are opened.

In this way, the operating state of the engine body 1 corresponds to a region other than the region A shown in the characteristic diagram of FIG. 3, and the pair of intake valves 20 and the pair of exhaust valves 23 are both opened. When the overlap period of the valve state is set to be a relatively long period, the residual gas after combustion is scavenged well in each cylinder 6, whereby the temperature rise in each cylinder 6 is suppressed. The occurrence of the knocking phenomenon is effectively suppressed.

In addition to the above-described structure, in the example shown in FIGS. 1 and 2, the portion of the common exhaust passage 16 on the upstream side of the three-way catalytic converter 18 is the solenoid valve 67.
The surge tank 33 is configured to be connected to the surge tank 33 through the air supply passage 68 in which the solenoid valve 67 is interposed, and the surge tank 33 serves as an air supply source. When the air is opened, the air from the surge tank 33 flows into the air supply passage 6
8 is replenished to the upstream side portion of the three-way catalytic converter 18 in the common exhaust passage portion 16. The solenoid valve 67 is closed according to the control signal SV supplied thereto when the engine body 1 is in an operating state under a relatively low load, and closes the air supply passage 68. When the main body 1 is in a high load operation state in which the engine load value is equal to or higher than a predetermined value, the main body 1 is set to an open state in which the air supply passage 68 is opened.

The supply of the control signal SV to the solenoid valve 67 provided in the air supply passage 68 is also performed by the engine body 1.
The control block 50 provided in FIG. Based on various detection output signals supplied to the control block 50, the operating state of the engine body 1 is changed according to the opening degree of the throttle valve 27 shown in the characteristic diagram of FIG. When the value of is less than the predetermined value Thv and is in the area A, the area B, or the area C corresponding to the operating state under a relatively low load, the solenoid valve 67 closes the air supply passage 68. While the control signal SV for causing the operating state is sent, the operating state of the engine body 1 is changed to the high load operating state in which the value of the engine load Th is equal to or larger than the predetermined value Thv shown in the characteristic diagram of FIG. When it is in the corresponding region D, the control signal SV for sending the solenoid valve 67 to the operating state of opening the air supply passage 68 is sent.

As described above, when the engine body 1 is in the high load operation state corresponding to the region D in the characteristic diagram of FIG. 3, the air from the surge tank 33 passes through the air supply passage 68 and the common exhaust passage. By replenishing the upstream side portion of the three-way catalytic converter 18 in the section 16,
At this time, the exhaust gas, which is led out from each cylinder 6 in the engine body 1 through the exhaust valve 23 to the exhaust manifold 13 and flows through the common exhaust passage portion 16, together with the air from the surge tank 33, the three-way catalytic converter 1
It will be passed through 8. Therefore, at this time, from the viewpoint of suppressing the occurrence of the knocking phenomenon in each cylinder 6, in each cylinder 6, the pair of intake valves 20 corresponding thereto shift from the closed state to the open state in the initial stage of the intake stroke. In the above, the overlap period in which both the pair of intake valves 20 and the pair of exhaust valves 23 are opened is set to be a relatively long period, whereby the pair of exhaust valves from the side of the pair of intake valves 20 of the air-fuel mixture is exhausted. The amount of air blown to the valve 23 side is increased, and the air-fuel mixture blown from the pair of intake valves 20 to the pair of exhaust valves 23 passes through the three-way catalytic converter 18 in the common exhaust passage portion 16 together with the exhaust gas. However, even if the three-way catalytic converter 18 is supplied to the upstream side of the three-way catalytic converter 18 in the common exhaust passage 16 through the air supply passage 68, the three-way Situation in which a lack of oxygen during the purification of exhaust gas in the medium converter 18 is invite is avoided, as a result,
Exhaust gas is appropriately purified in the three-way catalytic converter 18, and an increase in the content of HC components, CO components and the like in the exhaust gas discharged to the outside through the exhaust passage portion 16 is suppressed.

Further, the fuel injection by the fuel injection valves 38 respectively provided in the individual intake passage portions 39 is controlled by the control signals SI1, SI2 and SI3 from the control block 50.
And SI4, each fuel injection valve 38 is controlled to start within the overlap period in which the pair of intake valves 20 and the pair of exhaust valves 23 are both in the open state. The timing at which the fuel injected and supplied is actually supplied to each cylinder 6 is a period from immediately before the end of the overlap period to after the end of the overlap period, whereby a pair of intakes of fuel during the overlap period is performed. The blowout amount is reduced from the valve 20 side to the pair of exhaust valves 23 side.

In the above example, the air supply passage 6 for supplying air from the surge tank 33 to the portion of the common exhaust passage 16 on the upstream side of the three-way catalytic converter 18.
The replenishment through the engine 8 is stopped when the engine body 1 is not in the high load operation state corresponding to the region D in the characteristic diagram of FIG. When it is detected that the supplied air-fuel mixture is leaner than the stoichiometric air-fuel ratio, the three-way catalytic converter 1 in the common exhaust passage portion 16 is detected.
The replenishment of the air from the surge tank 33 to the upstream portion of 8 through the air supply passage 68 may be stopped. In such a case, for example, an oxygen concentration sensor (O ₂ sensor) is provided in the exhaust manifold 13 or the common exhaust passage portion 16, and a detection output signal obtained from the oxygen concentration sensor is supplied to the control block 50, and the control block 5
At 0, it is detected that the air-fuel mixture supplied to each cylinder 6 is leaner than the stoichiometric air-fuel ratio.

[0032]

As is clear from the above description, according to the exhaust gas purifying apparatus for an engine with a mechanical supercharger according to the present invention, the engine is in a high load operating condition satisfying a predetermined condition and the mechanical engine is overloaded. Under the condition that the feeder is operated,
By the air supply unit, for example, air from an air supply source, which is a surge tank on the intake passage unit side, flows into a portion of the exhaust passage unit on the upstream side of the exhaust purification catalyst unit.
When the engine is in a high load operating condition that satisfies a predetermined condition, from the viewpoint of suppressing the occurrence of knocking phenomenon, the overlap period in which both the intake valve and the exhaust valve are open for each cylinder is relatively long. As a result, even when the amount of air-fuel mixture supplied to each cylinder is increased to the exhaust passage portion side, the air supply portion causes the exhaust passage portion to reach a portion upstream of the exhaust purification catalyst portion. Due to the supplied air, it is possible to avoid a situation in which an oxygen amount is insufficient when purifying the exhaust gas in the exhaust purification catalyst portion arranged in the exhaust passage portion, and as a result, the exhaust gas is properly purified in the exhaust purification catalyst portion. Therefore, it is possible to effectively suppress an increase in the content of HC components and CO components in the exhaust gas discharged to the outside through the exhaust passage portion. It becomes Rukoto.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an example of an exhaust gas purifying apparatus for an engine with a mechanical supercharger according to the present invention, together with an engine to which the exhaust gas purifying apparatus is applied.

FIG. 2 is a cross-sectional view showing a main part in the example shown in FIG.

FIG. 3 is a characteristic diagram provided for explaining the operation of the example shown in FIG.

4 is a plan view including a partial cross-sectional view showing a variable valve timing mechanism in the example shown in FIG. 1. FIG.

FIG. 5 is a characteristic diagram provided for explaining the operation of the example shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 engine body 6 cylinder 10 common intake passage part 11 intake manifold 13 exhaust manifold 16 common exhaust passage part 18 three-way catalytic converter 20 intake valve 23 exhaust valve 38 individual fuel injection valve 39 individual intake passage part 45 variable valve timing mechanism 50 control block 67 Solenoid valve 68 Air supply passage

Claims (1)

Claim: What is claimed is: 1. An intake passage section in which a mechanical supercharger driven by an engine output is arranged. Fuel is injected into each of a plurality of cylinders in synchronization with each intake stroke. An exhaust passage portion extending from the engine body, which is provided with a plurality of fuel supply means for supplying, and an exhaust gas disposed in the exhaust passage portion for purifying exhaust gas guided from the engine body to the exhaust passage portion. The purification catalyst section, an air supply section that selectively takes an air supply state in which air from an air supply source flows into a portion of the exhaust passage section upstream of the exhaust purification catalyst section, and the engine body An exhaust emission control device for a mechanical turbocharger engine, comprising: an operation control unit that causes the air supply unit to be in the air supply state when in a high-load operating condition that satisfies the conditions. 2. A fuel supply means corresponding to each of a plurality of cylinders provided in an engine body, and an intake valve and an exhaust valve provided for the corresponding cylinder are both in an open state during an overlap period. The exhaust gas purification device for an engine with a mechanical supercharger according to claim 1, characterized in that the fuel supply operation is started.