JPH09151805A - E.g.r. device for diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve exhaust characteristics of a diesel engine with a tubocharger by realizing the E.G.R. in a high load region, a fact which has been considered impossible so far. SOLUTION: An intercooler 6 is interposed in a feeding passage 5, which extends from a compressor 2a of a turbocharger 2 down to a collecting part of an intake manifold 4. An E.G.R. valve 8, which variably controls the opening of an upper-stream-end of an E.G.R. passage 7, which is branched from an exhaust manifold 3b of a system in order to be merged into the feeding passage 5 standing on the downstream side than the intercoller 6, is installed in the exhaust manifold 3b. In addition, an exhaust pressure control valve 10, which variably controls the opening of an exhaust passage 9 standing on the downstream side than a turbine 2b of the turbo charger 2, is provided, while a controller 12, which controls to the optimum both E.G.R. valve 8 and exhaust control valve 10 in correspondence to the operating siutation of a diesel engine 1, is provided. With this contrivance, the E.G.R. region can be enlarged to a high load region where the boost pressure rises.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an EGR device for a diesel engine equipped with a turbocharger, and more particularly,
The present invention relates to an EGR device capable of expanding the application range of EGR and improving exhaust characteristics.

[0002]

2. Description of the Related Art As one of means for improving exhaust characteristics of a diesel engine, EGR is known in which a part of exhaust gas is returned to a combustion chamber. When performing EGR in this manner, a part of the exhaust gas is usually recirculated into the intake air (combustion chamber) by utilizing the pressure difference between the intake air and the exhaust gas.

However, in a turbo intercooler diesel engine in which a turbocharger and an intercooler are provided to increase the excess air ratio in order to improve the fuel efficiency of the diesel engine, when the efficiency of the turbocharger increases, the boost pressure is higher than the exhaust pressure. E to get higher
The application range of the GR is limited to the low load range, or when a large amount of EGR is performed, there is a problem that the excess air ratio decreases and the emission of black smoke increases. E for cooler diesel engine
Applying GR has been virtually impossible.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and enables EGR to be performed even in a high load range, which was conventionally impossible in a turbocharged diesel engine. The challenge is to improve the characteristics.

[0005]

In order to solve the above problems, the present invention is directed to a multi-cylinder diesel engine in which an exhaust manifold is divided into a plurality of systems, in which air is supplied from a compressor of a turbocharger to a collecting portion of an intake manifold. While installing an intercooler in the passage, an EGR valve that variably controls the opening degree of the upstream end of the EGR passage that branches from the exhaust manifold of one system and joins the air supply passage downstream from the intercooler is attached to the exhaust manifold. There is. An exhaust pressure control valve that variably controls the opening degree of the exhaust passage downstream of the turbine of the turbocharger is provided, and a signal that responds to the operating condition of the diesel engine is input as control information to the EGR valve and the exhaust pressure control valve. It is characterized in that a controller for optimally controlling the control signal supplied to is provided. The EGR valve may be an open / close valve and the exhaust pressure control valve may be a throttle valve.

Further, the present invention is a multi-cylinder diesel engine in which an exhaust manifold is divided into a plurality of systems, in which a turbine nozzle of a turbocharger is constituted by a variable nozzle, and a diffuser of a compressor is branched from an exhaust manifold of one system. An EGR valve that variably controls the opening degree of the upstream end of the EGR passage leading to the EGR port provided in the section is attached to the exhaust manifold. A controller is provided for optimally controlling the control signal supplied to the turbine nozzle and the EGR valve by inputting a signal corresponding to the operating condition of the diesel engine as control information.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a configuration diagram showing an embodiment of an EGR device for a diesel engine according to the present invention, in which the ignition sequence is as follows: first cylinder → fourth cylinder → second cylinder → sixth cylinder → third cylinder → fifth cylinder. Alternatively, the turbocharger 2 is mounted on the in-line 6-cylinder diesel engine 1 which is set to the first cylinder → the fifth cylinder → the third cylinder → the sixth cylinder → the second cylinder → the fourth cylinder.

The turbocharger 2 is composed of a turbine 2a connected to the collecting portion of the exhaust manifold 3 of the diesel engine 1, a compressor 2b driven by the turbine 2a, and the like. Further, an intercooler 6 is provided in the middle of an intake passage 5 extending from the outlet of the compressor 2b to the collecting portion of the intake manifold 4 of the diesel engine 1. Therefore, the air discharged from the compressor 2b is cooled by the intercooler 6 and then supplied to the combustion chamber of the diesel engine 1 through the intake manifold 4.

The exhaust manifold 3 has a first
By comprising the first manifold 3a connected to the cylinder, the second cylinder and the third cylinder, and the second manifold 3b connected to the fourth cylinder, the fifth cylinder and the sixth cylinder,
We try to prevent mutual interference of exhaust gas. Then, an EGR passage 7 that branches from the second manifold 3b and joins the air supply passage 5 downstream of the intercooler 6 is provided, and an EGR valve 8 constituted by an opening / closing valve is attached to the exhaust manifold 2b, so that the EG
The opening of the EGR passage 7 is variably controlled (open / close control) by the R valve 8.

Further, the turbine 2a of the turbocharger 2
To a muffler (not shown), an exhaust pressure control valve 10 composed of a throttle valve is provided, and a diesel engine speed output from a sensor (not shown), load, boost pressure and exhaust passage 9 are provided. A controller 12 is provided for inputting signals output from the oxygen concentration sensor 11 as control information.

The control signal output from the controller 12 is supplied to the electromagnetic opening / closing valve 13 and the pressure control valve 14 to control the opening / closing of the EGR valve 8 based on the control information supplied to the controller 12.
The opening degree of the exhaust pressure control valve 10 is variably controlled. Reference numeral 15 is an actuator that opens and closes the EGR valve 8 in accordance with opening and closing of the electromagnetic opening / closing valve 13, and 16 is continuously variable control of the opening degree of the exhaust pressure control valve 10 in response to the air pressure output from the pressure control valve 14. Actuator.

In the EGR device configured as described above, when the diesel engine 1 is operated, the controller 12 receives control signals corresponding to the rotational speed, the load, the boost pressure, and the residual oxygen concentration in the exhaust gas. Supplied as. The controller 12 determines the operating condition of the engine on the basis of these pieces of control information to determine the EGR.
EG when determining whether or not to perform EGR
Calculate the R rate.

When it is determined that EGR is necessary, the controller 12 outputs a valve opening signal to the solenoid valve 13 to open the EGR valve 8, so that the second manifold 3 is opened.
Part of the exhaust gas of b passes through the EGR passage 7 and the intake passage 5
Is supplied to the cylinder.

In a diesel engine equipped with a turbocharger, the efficiency of the turbocharger 2 increases as the load increases. Then, the internal pressure of the intake passage 5 (hereinafter referred to as boost pressure) becomes higher than the internal pressure of the exhaust manifold 3 to which the upstream end of the EGR passage 7 is connected (hereinafter referred to as exhaust pressure), and the pressures of the exhaust pressure and the boost pressure are increased. The difference becomes small, or the boost pressure becomes higher than the exhaust pressure, so that it becomes difficult to perform EGR.

However, when the load becomes high in this way, the output pressure of the pressure control valve 14 becomes high based on the control signal supplied from the controller 12, so that the opening degree of the exhaust pressure control valve 10 becomes small. . Further, when the opening degree of the exhaust pressure control valve 10 becomes smaller, the exhaust pressure is corrected to increase,
Moreover, as the exhaust pressure rises, the flow rate of the exhaust gas recirculated to the intake passage 5 through the EGR passage 7 increases. Therefore, by changing the pressure of the air supplied from the pressure control valve 14 to the exhaust pressure control valve 10 according to the operating state of the diesel engine 1, the exhaust gas at a flow rate suitable for the operating state at that time is supplied to the air supply passage. Reflux to 5.

FIG. 2 shows the relationship between boost pressure and exhaust pressure. As is clear from this figure, if the exhaust pressure had the characteristics as shown by the broken line in the same figure when the exhaust pressure control valve 10 was fully opened, then based on the signal from the controller 12, When the opening degree of the exhaust pressure control valve 10 is decreased by the above, the increase correction is performed as shown by the alternate long and short dash line in FIG. The degree of correction of the exhaust pressure varies depending on the opening degree of the exhaust pressure control valve 10. Further, the EG depends on the pressure difference between the boost pressure and the exhaust pressure shown by the solid line in FIG.
The R rate changes.

That is, when the exhaust pressure control valve 10 is not provided, or when the exhaust pressure control valve 10 is held fully open, the exhaust pressure is reduced even though the boost pressure has the characteristic shown by the solid line. Since the characteristics shown by the broken line in FIG. 2 change, EGR is possible only in the low load region where the boost pressure is lower than the exhaust pressure. However, when the exhaust pressure control valve 10 is provided so that the exhaust pressure can be increased and corrected as in the present invention, the opening of the exhaust pressure control valve 10 is adjusted so that the exhaust pressure is indicated by a chain line in FIG. Since the characteristic can be increased and corrected as shown, the EGR region can be expanded to the high load region.

Further, by opening and closing the EGR valve 8, the EG
The EGR rate can be changed by selecting whether to perform R or not and changing the opening degree of the exhaust pressure control valve 10. Therefore, while controlling the operating state of the diesel engine 1 based on the control information supplied from various sensors, the opening degree of the EGR valve 8 and the exhaust pressure control valve 10 is controlled according to a map stored in advance in the controller 12. By doing so, the flow rate of the exhaust gas recirculated to the air supply passage 5 can be optimally controlled.

Further, since a part of the exhaust gas is recirculated to the intake passage 5 downstream of the intercooler 6, there is no possibility that the inner surface of the intercooler 6 will be corroded by the exhaust gas. Furthermore, since the EGR valve 8 for variably controlling the opening degree of the EGR passage 7 is provided in the one exhaust manifold 3b, it is possible to perform EGR without exhaust interference, and the EGR valve 8 is provided separately. In contrast to this case, the dead volume is reduced, so that the deterioration of the supercharging efficiency is prevented.

In the above embodiment, the EGR valve 8 is an open / close valve and the exhaust pressure control valve 10 is a throttle valve, so that the EGR rate can be controlled easily and accurately. The valve 8 may be a throttle valve, or the EGR valve 8 and the exhaust pressure control valve 1
The EGR rate can be controlled more finely by configuring 0 as a duty-controlled on-off valve. Further, in the above embodiment, the oxygen concentration sensor 11 is provided so that the EGR is performed when the residual oxygen concentration in the exhaust gas becomes lower than a predetermined value.
Is temporarily suspended or the EGR rate is temporarily reduced to avoid the deterioration of the exhaust gas concentration due to the reduction of the excess air ratio, but it is not always necessary to provide the oxygen concentration sensor 11.

FIG. 3 is a block diagram showing another embodiment of the EGR device for a diesel engine according to the present invention. In this embodiment, instead of the exhaust pressure control valve, the turbine nozzle 2c of the turbocharger 2 is composed of a variable nozzle. Further, the EGR passage 7 branched from the second exhaust manifold 3b is opened to the EGR port 2e provided in the diffuser portion of the compressor 2b.

The control signal output from the controller 12, to which various signals related to the operating state of the diesel engine 1 are supplied as control information, is transmitted to the turbine nozzle 2.
The configuration is different from that of the above-described embodiment in that the actuator 2d of c and the actuator 15 of the EGR valve 8 are supplied, and other parts have substantially the same configuration.

E of a diesel engine having such a configuration
In the GR device, as shown in FIG. 4, the pressure in the diffuser portion shown by the alternate long and short dash line becomes lower than the boost pressure shown by the solid line and the exhaust pressure shown by the broken line in FIG. Therefore, also in the case of this embodiment, the EGR region can be expanded to the high load region similarly to the case of the above-described embodiment, and a large amount of EGR can be performed by utilizing the differential pressure between the pressure of the diffuser portion and the exhaust pressure.

By the way, when a large amount of EGR is performed as described above, there is a concern that the boost pressure is lowered and the excess air ratio is lowered, so that the smoke concentration is deteriorated. However,
When performing such a large amount of EGR, the controller 12
The opening of the turbine nozzle 2c is narrowed based on the signal from. Then, the output of the turbine 2a increases, the efficiency of the compressor 2a increases, and the boost pressure is corrected to be increased and a large amount of air is sent out. Therefore, the excess air ratio of the engine 1 is corrected to be increased and the exhaust gas due to the large amount of EGR is exhausted. Deterioration of concentration is prevented.

Therefore, as in this embodiment, the EGR passage 7 is merged with the diffuser portion of the compressor 2b so that the EG
When the R region is expanded to the high load region and the turbine nozzle 2c is configured by a variable nozzle to correct the turbine output so as to prevent a decrease in the excess air ratio during a large amount of EGR, there is a concern during a large amount of EGR. It is possible to effectively suppress the generation of NOx while avoiding the deterioration of the generated exhaust gas concentration.

In the above embodiment, the EGR valve 8 is an on-off valve, and the turbine nozzle 2c
The opening degree of the EGR valve 8 is changed by continuously changing the opening degree of the EGR valve 8 to obtain a predetermined EGR rate.
Alternatively, the turbine nozzle 2c may be configured by a nozzle whose opening is controlled stepwise.

[0027]

As is apparent from the above description, according to the present invention, it is possible to perform EGR at an optimum rate even in a high load range, which was considered impossible in the conventional diesel engine with a turbocharger. . Therefore, it is possible to prevent the generation of NOx by the accurate combustion suppressing action by EGR while preventing the deterioration of the smoke concentration by securing the excess air ratio by providing the turbocharger.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an embodiment of an EGR device for a diesel engine according to the present invention.

FIG. 2 is a characteristic diagram showing a relationship between boost pressure and exhaust pressure.

FIG. 3 is a configuration diagram showing another embodiment of an EGR device for a diesel engine according to the present invention.

FIG. 4 is a characteristic diagram showing a relationship among boost pressure, exhaust pressure, and diffuser pressure.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Diesel engine 2 Turbocharger 2a Turbine 2b Compressor 2c Turbine nozzle 2d EGR port 3 Exhaust manifold 3a 1st manifold 3b 2nd manifold 4 Intake manifold 5 Air supply passage 6 Intercooler 7 EGR passage 8 EGR valve 9 Exhaust passage 10 Exhaust pressure control valve 11 oxygen concentration sensor 12 controller 13 electromagnetic on-off valve 14 pressure control valve 15, 16 actuator

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location F02D 45/00 301 F02B 37/12 301N

Claims (3)

[Claims] 1. In a multi-cylinder diesel engine in which an exhaust manifold is divided into a plurality of systems, an intercooler is provided in a supply passage from a compressor of a turbocharger to a collecting portion of an intake manifold, and an exhaust manifold of one system is provided. An EGR valve that variably controls the opening degree of the upstream end of the EGR passage that branches and joins the air supply passage downstream of the intercooler is attached to the exhaust manifold to variably control the opening degree of the exhaust passage downstream of the turbocharger turbine. The exhaust pressure control valve is provided, and a signal responding to the operating condition of the diesel engine is input as control information to obtain the EGR.
An EGR device for a diesel engine, comprising a controller that optimally controls a control signal supplied to a valve and an exhaust pressure control valve. 2. The EGR valve is an open / close valve, and the exhaust pressure control valve is a throttle valve.
An EGR device for a diesel engine as described in the above. 3. In a multi-cylinder diesel engine in which an exhaust manifold is divided into a plurality of systems, a turbine nozzle of a turbocharger is composed of a variable nozzle,
An EGR valve that variably controls the opening of the upstream end of the EGR passage that branches from one system exhaust manifold to the EGR port provided in the diffuser section of the compressor is attached to the exhaust manifold and responds to the operating status of the diesel engine. The turbine nozzle and the EGR
EG of diesel engine characterized by having a controller for optimally controlling the control signal supplied to the valve
R device.