JPH1077912A - Exhaust gas recirculation system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure an appropriate EGR ratio by providing an operating state detecting means for detecting the operating state of an engine, a variable means that can change intake flow cross-sectional area of a narrow part, and a control means for controlling the operation of the variable means on the basis of detected information from the operating state detecting means. SOLUTION: An ECU 40 controls a core 23 constituting a variable means 22 by a stepping motor on the basis of detected information from an engine speed sensor 42a, an accelerator opening sensor 42b and a cooling water temperature sensor 42c constituting an operating state detecting means 42. The variable means 22 is provided upstream of a venturi 21 of a by-pass passage 20 so as to change the opening of the by-pass passage 20 (intake flow cross-sectional area of the venturi). Intake pressure at an exhaust gas joining part can thereby be regulated, and even in the case of intake pressure becoming high, intake pressure can be controlled to become lower than exhaust gas pressure so as to ensure an appropriate EGR ratio.

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 device suitable for use in a turbocharged engine, particularly a turbocharged diesel engine.

[0002]

2. Description of the Related Art Conventionally, in order to reduce NO _x (nitrogen oxide) contained in exhaust gas of an internal combustion engine (engine),
2. Description of the Related Art An exhaust gas recirculation device (hereinafter, referred to as an EGR device) for recirculating a part of exhaust gas of an engine to an intake system according to an operation state of the engine has been developed and put into practical use.

FIG. 7 is a diagram schematically showing a turbocharged engine equipped with a conventional EGR device.
Note that, in FIG. 7, arrows indicate intake air (hereinafter, also referred to as intake air).
And the flow of exhaust gas. Reference numeral 1 denotes a combustion chamber. The combustion chamber 1 is connected so that an intake passage 2 and an exhaust passage 3 can communicate with each other. The communication between the intake passage 2 and the combustion chamber 1 is controlled by an intake valve 4. Together with the exhaust passage 3
The communication between the combustion chamber 1 and the combustion chamber 1 is controlled by an exhaust valve 5.

A turbocharger 6 is provided in the exhaust passage 3.
A turbine 6a constituting the turbocharger 6 is interposed in the intake passage 2
The turbine 6a and the compressor 6b are connected via a turbine shaft 6c. Then, the turbine 6a is rotated by the exhaust gas in the exhaust passage 3, the rotational force of the turbine 6a is transmitted to the compressor 6b, and the compressor 6b is rotated to pressurize the intake air in the intake passage 2. I have.

Further, an intercooler (I / C) 7 is provided in the intake passage 2 on the downstream side of the compressor 6b to cool intake air which has been heated by the compressor 6b and has become hot. Next, the EGR device 10 will be described. The EGR device 10 includes an exhaust gas recirculation passage (EGR passage) 10b that connects the exhaust passage 3 and the intake passage 2 of the engine.
And an EGR valve 10a disposed in the EGR passage 10b and controlling the recirculation ratio of the exhaust gas.

The EGR valve 10a includes a valve body 10c and a diaphragm 10d attached to the valve body 10c. The EGR valve 10a moves the position of the diaphragm 10d by the pressure supplied from the pressure source 11 to move the valve body 10c.
Can be controlled. The valve element 10c attached to the diaphragm 10d is a spring 10c.
e to close the EGR passage 10b (in FIG. 7,
Upward).

Here, the control of the opening degree of the valve body 10c, that is, the adjustment of the pressure supplied from the pressure source 11 is performed based on the output signal from the control unit (C / U) 12, and the two electromagnetic valves 13 , 14 by performing on / off control (duty control). The control unit (C / U) 12 is provided with an engine speed N
e, engine load (accelerator opening) Rw, cooling water temperature T
A signal is output based on detection information such as w.

By using such an EGR device 10 to mix the exhaust gas (EGR gas) taken in from the exhaust passage 3 into the intake air, the combustion in the combustion chamber 1 is slowed down and the combustion temperature is reduced. To suppress the generation of NO _X.

[0009]

However, in such a conventional EGR device, it may not be possible to recirculate the exhaust gas under high load in an engine equipped with a turbocharger. That is, FIG. 8 shows the exhaust pressure (hereinafter referred to as turbine inlet pressure) P at the inlet of the turbine 6a.
FIG. 7 is a diagram showing a relationship between ti and an intake pressure (hereinafter, referred to as a boost pressure) Pb supercharged by a compressor 6b;
The vertical axis indicates the pressure, and the horizontal axis indicates the engine output torque Trq corresponding to the engine load. In FIG. 8, a curve a indicates the boost pressure Pb, and a curve b indicates the turbine inlet pressure Pti.

According to this, as shown by curves a and b,
When the load is low (that is, when the torque Trq is small), the boost pressure Pb is lower than the turbine inlet pressure Pti, but the boost pressure Pti has a larger rate of increase, and when the load is high (that is, when the torque Trq is large). ) Indicates that the boost pressure Pb is higher than the turbine inlet pressure Pti. As described above, when the load is high, the boost pressure Pb is increased by the turbine inlet pressure Pt.
If the pressure is higher than i, the gas does not flow from a lower pressure to a higher pressure, so that the exhaust gas cannot be recirculated.

That is, in an area where the boost pressure Pb is lower than the turbine inlet pressure Pti (low load area where the load is smaller than the dotted line Y in FIG. 8), an appropriate EGR rate can be ensured. In a region higher than the inlet pressure Pti (a high load region where the load is larger than the dotted line Y), the EGR rate may be insufficient or the exhaust gas may not be recirculated, so that an appropriate EGR rate cannot be secured. There is a problem that.

To solve such a problem, for example, there is a technique disclosed in Japanese Patent Application Laid-Open No. 4-47157. In this technique, as shown in FIG. 9, a bypass pipe 124 is provided in an intake pipe 122, and a contraction section 125 having a small cross-sectional area is provided in an intermediate portion of the bypass pipe 124. An EGR pipe 126 is connected so as to communicate with the pipe 115, and a switching valve 127 is attached to a branch portion between the intake pipe 122 and the bypass pipe 124.

As described above, when the intake air supplied from the compressor 119 is passed through the bypass line 124, the pressure of the contraction section 125 is reduced, so that the EGR is performed.
The exhaust gas can be sucked from the exhaust pipe 115 through the pipe 126 so that the exhaust gas can be recirculated even in the case of high supercharging (high load). But,
In such a technique, since the contraction part 125 is formed in a fixed shape and the pressure of the contraction part 125 cannot be adjusted, the EGR rate is positively adjusted according to the load state of the engine.
In addition, there is a problem that fine adjustment cannot be performed.

The present invention has been made in view of such a problem, and it is possible to positively and finely adjust the EGR rate even when the pressure on the intake side becomes higher than the pressure on the exhaust side. It is an object of the present invention to provide an exhaust gas recirculation device capable of ensuring an appropriate EGR rate.

[0015]

Therefore, in the exhaust gas recirculation system according to the first aspect of the present invention, a bypass passage for bypassing intake air is connected to an intake passage downstream of the compressor of the turbocharger, and the bypass passage is connected to the bypass passage. In an exhaust gas recirculation device in which a narrow portion is formed and an exhaust gas recirculation passage for recirculating exhaust gas is connected to the narrow portion,
Operating state detecting means for detecting the operating state of the engine, variable means capable of changing the intake flow cross-sectional area of the narrow portion, and control means for controlling the operation of the variable means based on detection information from the operating state detecting means It is characterized by having.

According to a second aspect of the present invention, there is provided the exhaust gas recirculation apparatus according to the first aspect, wherein the control means operates based on detection information from the operation state detection means when the engine is operated under a high load. The operation of the variable means is controlled so that the intake flow cross-sectional area of the narrow portion is reduced, and the operation of the variable means is controlled such that the intake flow cross-sectional area of the narrow portion is increased during low-load operation of the engine. It is characterized by doing.

According to a third aspect of the present invention, in the exhaust gas recirculation device according to the first aspect, the flow rate of the intake air flowing through the intake passage is provided downstream of the bypass passage branch portion of the intake passage. An on-off valve for controlling is provided, and the control means is configured to control the operation of the on-off valve together with the variable means in accordance with detection information from the operating state detecting means.

According to a fourth aspect of the present invention, there is provided the exhaust gas recirculation apparatus according to the third aspect, wherein the control means is configured to perform a high load operation of the engine based on detection information from the operation state detection means. While controlling the operation of the variable means so that the intake flow cross-sectional area of the narrow portion is reduced, and controlling the operation of the on-off valve so that the opening degree of the on-off valve is reduced, during low load operation of the engine The operation of the variable means is controlled so as to increase the intake flow cross-sectional area of the narrow portion, and the operation of the on-off valve is controlled so as to increase the opening degree of the on-off valve.

According to a fifth aspect of the present invention, there is provided an exhaust gas recirculation apparatus according to any one of the first to fourth aspects, wherein the narrow portion gradually reduces the cross-sectional area of the bypass passage. The variable means has a core formed as a Venturi and movable in the axial direction of the Venturi, and changes the intake flow cross-sectional area in the bypass passage by moving the core in the axial direction by an actuator. It is characterized by having such a configuration.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIGS. 1 to 6 show an exhaust gas recirculation apparatus according to the present embodiment. The present exhaust gas recirculation device (hereinafter, referred to as an EGR device) is attached to a turbocharged engine 50 as shown in FIG. In FIG. 1, arrows indicate flows of intake air (hereinafter, also referred to as intake air) and exhaust gas.

Reference numeral 1 denotes a combustion chamber, to which an intake passage 2 and an exhaust passage 3 are connected so that they can communicate with each other. The intake passage 2 and the combustion chamber 1 are communicated by an intake valve 4. At the same time, the communication between the exhaust passage 3 and the combustion chamber 1 is controlled by the exhaust valve 5. Also,
A turbine 6a constituting the turbocharger 6 is interposed in the exhaust passage 3, and a compressor 6b constituting the turbocharger 6 is interposed in the intake passage 2. The turbine 6a and the compressor 6b are connected to a turbine shaft. 6c. Then, the turbine 6a is rotated by the exhaust gas in the exhaust passage 3, the rotational force of the turbine 6a is transmitted to the compressor 6b, and the compressor 6b is rotated to pressurize the intake air in the intake passage 2. I have.

Further, an intercooler (I / C) 7 is disposed in the intake passage 2 on the downstream side of the compressor 6b to cool intake air which has been heated by the compressor 6b and has become high temperature. Further, a bypass passage 20 for bypassing the intake air is connected to the intake passage 2 a on the downstream side of the intercooler 7. In the bypass passage 20, the engine 5
An exhaust gas recirculation passage (EGR passage) 10b for recirculating exhaust gas discharged from the exhaust gas to the intake side is connected. The flow rate of the exhaust gas recirculated into the bypass passage 20 via the EGR passage 10b is controlled by adjusting the opening of an EGR valve 10a described later.

The bypass passage 20 is provided with a venturi (narrow portion) 21. The venturi 21 is formed so as to gradually reduce the cross-sectional area of the bypass passage 20, as shown in FIGS. That is,
The venturi 21 has a cross section in which the upstream portion 21 a is gradually reduced toward the downstream side of the bypass passage 20, and the downstream portion 21 b is formed in the bypass passage 2.
It is formed as a cross section that gradually expands toward the downstream side of 0. In FIG. 2, arrows indicate the flow of intake air.

The reason why the venturi 21 is provided in the bypass passage 20 is that the cross-sectional area of the bypass passage 20 is reduced, the flow velocity of the intake air is increased, and the portion of the bypass passage 20 where the venturi 21 is provided is provided. By reducing the pressure, the exhaust gas can be recirculated even during high-load operation of the engine, thereby preventing the EGR rate from decreasing,
This is to ensure that an appropriate EGR rate can be ensured even during high load operation of the engine. The reason why the sectional area of the bypass passage 20 is restored is to restore the intake pressure to a high pressure state.

As shown in FIG. 2, an annular groove 21c is formed in a portion of the Venturi 21 having the smallest sectional area, and the annular groove 21c is formed through a communication passage 21d.
The GR passage 10b is connected. Here, FIG. 3 is a schematic cross-sectional view of a portion having the smallest cross-sectional area of the venturi 21, and is a cross-sectional view taken along the line BB of FIG. Note that FIG.
What is shown in the middle and center is a core (movable core) 23 that constitutes a variable means 22 described later.

The venturi 21 of the bypass passage 20
As shown in FIGS. 1 and 2, a variable means 22 that can change the opening degree of the bypass passage 20 (cross-sectional area of the intake passage of the venturi 21) is mounted on the further upstream side. The variable means 22 has a core 23 movable in the axial direction of the venturi 21, and the opening degree of the bypass passage 20 can be changed by moving the core 23 in the axial direction by the actuator 30. Is configured.

More specifically, as shown in FIG. 2, the core 23 of the variable means 22 includes, for example, a thin cylindrical core support portion 24 and core mounting portions 25 and 26 formed of thin flat members. Through the actuator 30
Attached to. That is, the core 23 is screwed to one end of the core support portion 24, and the core mounting portions 25 and 26 are screwed to the other end.
3 is attached to the core attachment portions 25 and 26.

Then, the core mounting portions 25 and 26 to which the core 23 is mounted are moved by the actuator 30 in the axial direction of the bypass passage 20 while sliding on the inner peripheral surface of the bypass passage 20, so that the venturi 21 and the core are moved. 23, that is, the opening degree of the bypass passage 20 can be adjusted. Here, FIG. 4 is a view taken in the direction of the arrow A in FIG. 2 and is a schematic view for explaining an attached state of the core 23. As shown in FIG. 4, the core mounting portions 25 and 26 are mounted in the bypass passage 20 so as to be orthogonal to each other, and the core support portion 24 is screwed to a portion where the core mounting portions 25 and 26 intersect. Note that the core mounting portions 25, 2
The end of 6 can slide on the inner peripheral surface of the bypass passage 20.

As shown in FIG. 2, an actuator 30 for moving the core 23 forward and backward is provided with a stepping motor 31.
The stepping motor 31 is attached to a case 37, and a rotating shaft 31 a of the stepping motor 31 is connected to a long bolt 32 in the case 37. A moving portion (ball screw type LM guide) 34 formed in a U-shape is screwed into the bolt 32. For this reason, a female screw is formed on the side surface of the moving part 34 so as to correspond to the bolt 32. The bolt 32 is supported by fixing portions 33a and 33b.

Then, both ends 3 of the U-shaped moving portion 34
The end portion 25a of the core attachment portion 25 is attached to 4a, 34b. For this reason, a hole (not shown) is formed in the bypass passage 20 so that the connecting part between the moving part 34 and the core mounting part 25 can move. Also, in FIG.
Reference numerals 35 and 36 denote guide portions that regulate the rotation of the moving portion 34 and guide the moving portion 34 in the axial direction of the rotating shaft 31a.

Further, the stepping motor 31 is driven on the basis of an output signal from an ECU (control means) 40, which will be described later. ,
A signal for controlling the stepping motor 31 is output based on detection information from the accelerator opening sensor 42b and the cooling water temperature sensor 42c.

On the other hand, as described above, the EGR passage 1
0b is EGR for controlling the recirculation ratio of exhaust gas
A valve 10a is attached. And this EG
The flow rate of the exhaust gas from the exhaust passage 3 to the intake passage 2 can be controlled by the R valve 10a. The operation of the EGR valve 10a is controlled by the ECU 40. The ECU 40 controls the operation of the EGR valve 10a in accordance with the operating state of the engine detected by each of the sensors 42a to 42c. The control signal is set.

On the other hand, a butterfly valve (open / close valve) is provided in the intake passage 2a downstream of the branch from the bypass passage 20.
41, and the butterfly valve 41 is also E-shaped.
The opening and closing operation is controlled based on a control signal output from the CU 40. Thus, the flow rate of the intake air flowing through the intake passage 2a can be controlled.

The ECU 40 includes an engine speed sensor 42a and an accelerator opening sensor 42
b, based on the detection information from the cooling water temperature sensor 42c,
During high load operation of the engine, the operation of the variable means 22 is controlled so that the opening of the bypass passage 20 is reduced, and the butterfly valve 4 is controlled so that the opening of the butterfly valve 41 is reduced.
1 to control the operation of the variable means 22 so that the opening of the bypass passage 20 increases during low-load operation of the engine, and the operation of the butterfly valve 41 so that the opening of the butterfly valve 41 increases. Has the function of controlling

Since the present exhaust gas recirculation device is constructed as described above, the pressure in the bypass passage 20 in which the venturi 21 is mounted changes as shown in FIG. FIG.
The middle and vertical axes indicate the pressure, and the horizontal axis indicates the position in the bypass passage 20. In FIG. 5, a curve a indicates the intake pressure in the bypass passage 20, and a straight line b indicates the EGR gas pressure (turbine inlet pressure) Pti. The horizontal axes C, B, and D in FIG. 5 correspond to the positions C, B, and D in FIG. 2, respectively. The intake pressure in the bypass passage 20 in FIG. 5 indicates the intake pressure when the core 23 is moved to the rightmost position as shown in FIG.

As shown in FIG. 5, at the position C, the intake pressure becomes E
Even when the pressure is higher than the GR gas pressure Pti, the position B,
That is, the intake pressure can be considerably lower than the EGR gas pressure Pti in the vicinity of the Venturi 21, and the boost pressure Pb can be increased again in the downstream portion of the Venturi 21. The operation of the core 23, the butterfly valve 41, and the EGR valve 10a in the exhaust gas recirculation device of the present embodiment will be described below.

That is, when the exhaust gas is not recirculated,
The EGR valve 10a is closed to prevent the exhaust gas from recirculating. At this time, the opening of the bypass passage 20 is
(Moved to the left in FIG. 2) to open the butterfly valve 41 fully, and control the intake air to flow into the intake passage 2a.
Thereby, pressure loss can be prevented.

Although the position of the core 23 may be arbitrary,
Here, the bypass passage 20 in which high-pressure exhaust gas is recirculated
In consideration of the cooling inside, it is controlled to be located on the leftmost side. The cases where the exhaust gas is not recirculated include, for example, idling, high load (low speed side), warm-up (low water temperature), and acceleration. On the other hand, when the exhaust gas is recirculated, the EGR valve 10a is opened to recirculate the exhaust gas. At this time, the butterfly valve 41 is closed to control the intake air to flow only into the bypass passage 20 side, and the core 23 Is moved to a position where the target EGR rate is obtained, thereby controlling the bypass passage 20 to have an appropriate opening degree.

That is, as the core 23 closes the bypass passage 20, the pressure at the position B of the bypass passage 20 shown in FIGS. 2 and 5 can be reduced, so that the flow rate of the EGR gas taken in from the EGR passage 10b is increased. EG
The R rate can be increased. Therefore, when the target EGR rate is large, the core 23 is connected to the bypass passage 2
0 is moved in the closing direction (to the right in FIG. 2) to reduce the opening degree of the bypass passage 20. Conversely, when the target EGR rate is small, the core 23 is moved through the bypass passage 20. The bypass passage 20 is controlled to be moved in the opening direction (left direction in FIG. 2) to increase the opening degree of the bypass passage 20.

In particular, when the load is high, the position of the core 23 is moved to reduce the opening degree of the bypass passage 20, so that the flow speed of the intake air can be increased and the intake pressure can be reduced. Is the turbine inlet pressure Pti
Even if it is higher, a sufficient EGR rate can be secured. The amount of movement of the core 23 is set based on a map prepared in advance based on the engine speed, load, and cooling water temperature. The recirculation of the exhaust gas is, for example, a case other than the above-described idling, high load (low speed side), warm-up (low water temperature), and acceleration.

Here, the opening degree of the bypass passage 20 and the EGR
The relationship between the load, the ratio, the boost pressure Pb, and the turbine inlet pressure Pti will be described with reference to FIG. First,
FIG. 6C shows the relationship between the boost pressure Pb, the turbine inlet pressure Pti, and the load. FIG. 6 (c)
The curve d indicates the boost pressure Pb and the curve e indicates the turbine inlet pressure Pti. According to this, at a low load, the boost pressure Pb is lower than the turbine inlet pressure Pti, but the boost pressure Pb increases as the load increases. That is, when the load is smaller than the straight line X, the boost pressure Pb is lower than the turbine inlet pressure Pti, and when the load is larger than the straight line X, the boost pressure Pb is higher than the turbine inlet pressure Pti.

Therefore, the opening degree of the bypass passage 20 is
In consideration of the above-described relationship between the boost pressure Pb and the turbine inlet pressure Pti, the characteristic is controlled to the characteristic shown by the line a in FIG. That is, since the boost pressure Pb is lower than the turbine inlet pressure Pti at a low load, the EGR rate does not decrease. Therefore, the position of the core 23 is controlled so that the opening degree of the bypass passage 20 increases.

As the load increases, the boost pressure Pb becomes higher than the turbine inlet pressure Pti, and the EGR rate decreases.
The position of the core 23 is controlled so that the opening degree of the core 23 decreases. In FIG. 6A, the engine load (X in the figure) is such that the boost pressure Pb becomes larger than the turbine inlet pressure Pti.
Before starting the control, the control of the core 23 is started so that the opening degree of the bypass passage 20 decreases. However, this reduces the EGR rate and makes it impossible to recirculate the exhaust gas. This is to prevent

By controlling the opening of the bypass passage 20 in this way, the EGR rate can be adjusted as shown in FIG. Here, in FIG. 6, a solid line b indicates E when the opening degree of the bypass passage 20 is controlled as described above.
The GR rate and the broken line c indicate the EGR rates when the opening degree of the bypass passage 20 is not controlled as in the related art.

According to this, when the opening of the bypass passage 20 is not controlled, the EGR rate decreases as the load increases, and eventually the EGR rate becomes zero. When the opening degree of the bypass passage 20 is controlled, a decrease in the EGR rate can be effectively prevented, and the exhaust gas recirculation can be performed even in a high-load operation region of the engine where exhaust gas recirculation was conventionally impossible. It turns out that it becomes possible. The EGR rate of 0 indicates that the exhaust gas cannot be recirculated.

According to the exhaust gas recirculation device of this embodiment,
By changing the opening degree of the bypass passage 20, the pressure of the intake air at the portion where the recirculated exhaust gas joins can be adjusted. Therefore, even when the pressure of the intake air becomes high, the pressure of the intake air is exhausted. There is an advantage that the pressure can be controlled to be lower than the gas pressure, and a sufficient EGR rate can be secured.

In particular, even during high load operation of the engine in which the intake pressure increases, the intake pressure at the portion where the recirculated exhaust gas joins can be reduced, and a sufficient EGR rate can be secured. Therefore, there is an advantage that NO _X can be significantly reduced even during high load operation of the engine. That is, the boost pressure Pb is higher than the turbine inlet pressure Pti by moving the core 23 with respect to the venturi 21 provided in the intake passage 2 to adjust the opening degree of the bypass passage 20 and increasing the flow velocity of the intake air. Even at the time of high load operation, the pressure at the portion where the exhaust gas recirculated by the EGR device 10 and the intake air merge is controlled to be lower than the exhaust gas pressure (turbine inlet pressure) Pti. since it is, it is possible to ensure a sufficient EGR rate, it is possible to significantly reduce the NO _X even during high-load operation of the engine.

On the other hand, at the time of low load operation of the engine having a low intake pressure, an appropriate EGR rate can be secured by controlling the intake pressure so as not to be low. There is also an advantage that deterioration of fuel efficiency can be prevented. Further, by controlling the butterfly valve 41 and the variable means 22, there is an advantage that the EGR rate can be finely controlled.

When it is not necessary to recirculate the exhaust gas, the opening of the butterfly valve 41 is increased so that the intake passage 2
By flowing the intake air to the a side, there is an advantage that a pressure loss can be prevented, an appropriate amount of air can be secured, and further, the inside of the bypass passage 20 and the EGR device 10 can be cooled. Although the cross section of the venturi 21 is shown in a substantially circular shape in the drawing, the cross sectional shape is not limited to this.

[0050]

As described above in detail, according to the exhaust gas recirculation apparatus of the first aspect of the present invention, the exhaust gas recirculated by the exhaust gas recirculation apparatus is changed by changing the intake flow cross-sectional area of the narrow portion. Since the intake pressure at the portion where the gas merges can be adjusted, even when the intake pressure is high, the intake pressure can be controlled so as to be lower than the exhaust gas pressure. There is an advantage that a high EGR rate can be secured.

According to the exhaust gas recirculation device of the present invention, during high load operation of the engine in which the pressure of the intake air increases, the pressure of the intake air at the portion where the exhaust gas recirculated by the exhaust gas recirculation device joins is reduced. Consequently, it is possible to lower, it is possible to ensure a sufficient EGR rate, while the nO _X can be reduced significantly, during low load operation of the low pressure in the intake engine, as the pressure in the intake does not decrease By controlling, an appropriate EGR rate can be ensured, so that there is also an advantage that deterioration of fuel efficiency can be prevented.

According to the third aspect of the present invention, the exhaust gas recirculation device is controlled by controlling the on-off valve and the variable means.
There is an advantage that fine control of the EGR rate becomes possible.
According to the exhaust gas recirculation device of the present invention, at the time of high load operation, the opening degree of the on-off valve is reduced to allow the intake air to flow to the bypass passage side, and the variable means is used to reduce the intake air flow sectional area of the narrow portion. On the other hand, during low-load operation, the opening degree of the on-off valve is increased to allow the intake air to flow to the intake passage side, and the variable means is controlled so that the intake flow cross-sectional area of the narrow portion increases. Thus, there is an advantage that the EGR rate can be appropriately controlled.

According to the fifth aspect of the present invention, there is an advantage that an appropriate EGR rate can be secured with a simple configuration.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an overall configuration of an exhaust gas recirculation device as one embodiment of the present invention.

FIG. 2 is a schematic diagram showing a part of a bypass passage in the exhaust gas recirculation device as one embodiment of the present invention.

FIG. 3 is a cross-sectional view of a bypass passage in the exhaust gas recirculation device as one embodiment of the present invention, and is a cross-sectional view taken along line BB of FIG.

FIG. 4 is a side view of a bypass passage in the exhaust gas recirculation device as one embodiment of the present invention, and is a view as viewed from an arrow A in FIG.

FIG. 5 is a diagram showing a change in pressure in a bypass passage of the exhaust gas recirculation device as one embodiment of the present invention.

FIGS. 6A and 6B are diagrams for explaining the effect of the exhaust gas recirculation device as one embodiment of the present invention, wherein FIG. 6A shows the relationship between the opening degree of the bypass passage 20 and the load, and FIG. (C) shows the relationship between the boost pressure Pb and the turbine inlet pressure Pti and the load, respectively.

FIG. 7 is a schematic diagram showing an overall configuration of a conventional exhaust gas recirculation device.

FIG. 8 is a diagram for explaining a problem in a conventional exhaust gas recirculation device.

FIG. 9 is a diagram for explaining a problem in a conventional exhaust gas recirculation device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Combustion chamber 2 Intake passage 2a Intake passage 3 Exhaust passage 4 Intake valve 5 Exhaust valve 6 Turbocharger 6a Turbine 6b Compressor 6c Turbine shaft 7 Intercooler (I / C) 10a EGR valve 10b Exhaust gas recirculation passage (EGR passage) 10c EGR valve 10d Diaphragm 10e Spring 11 Pressure source 12 Control unit (C / U) 13,14 Solenoid valve 20 Bypass passage 21 Venturi (narrow part) 21a Upstream part of venturi 21b Downstream part of venturi 21c Venturi annular groove 21d Communication path 22 Variable means 23 Core (movable core) 24 Core support part 25, 26 Core mounting part 25a End of core mounting part 30 Actuator 31 Stepping motor 31a Rotation axis of stepping motor 32 Bolt 33a 33b Fixed part 34 Moving part (ball screw type LM guide) 34a, 34b Both ends of moving part 35, 36 Guide part 37 Case 40 Electronic control unit (ECU) 41 Butterfly valve (open / close valve) 42 Operating state detecting means 42a Engine rotation Number sensor 42b Accelerator opening sensor 42c Cooling water temperature sensor 50 Engine with turbocharger 110 Cylinder head 111 Intake manifold 112 Exhaust manifold 113 Turbocharger 114 Exhaust turbine 115 Exhaust pipe 116 Muffler 119 Compressor 120 Intake pipe 121 Air cleaner 122 Intake pipe 123 Intercooler 124 Pipeline 125 Contraction part 126 EGR pipe 127 Switching valve

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical indication F02M 25/07 550 F02M 25/07 550J 550Q 580 580B F02B 37/00 302 F02B 37/00 302F F02D 9 / 02 F02D 9/02 CS 321 321A 361 361J 9/12 9/12 21/08 311 21/08 311B 23/00 23/00 J

Claims (5)

[Claims] 1. A bypass passage for bypassing intake air is connected to an intake passage downstream of a compressor of a turbocharger, and a narrow portion is formed in the bypass passage.
In an exhaust gas recirculation device in which an exhaust gas recirculation passage for recirculating exhaust gas is connected to the narrow portion, an operating state detecting means for detecting an operating state of an engine, and a variable means for changing an intake air cross-sectional area of the narrow portion And a control means for controlling the operation of the variable means based on the detection information from the operation state detecting means. 2. The control means controls the operation of the variable means based on the detection information from the operation state detection means so that the intake air flow cross-sectional area of the narrow portion is reduced during high load operation of the engine. 2. The exhaust gas recirculation apparatus according to claim 1, wherein the operation of the variable means is controlled so that the intake flow cross-sectional area of the narrow portion increases during low load operation of the engine. 3. An on-off valve for controlling the flow rate of intake air flowing through the intake passage is provided downstream of the bypass passage branching portion of the intake passage. 2. The exhaust gas recirculation device according to claim 1, wherein an operation of the on-off valve is controlled together with the variable means according to the detection information. 4. The control means controls the operation of the variable means based on the detection information from the operating state detection means so that the intake flow cross-sectional area of the narrow portion is reduced during high load operation of the engine. And controlling the operation of the on-off valve so that the opening degree of the on-off valve decreases, and controlling the operation of the variable means so that the intake air flow cross-sectional area of the narrow portion increases during low-load operation of the engine. The exhaust gas recirculation device according to claim 3, wherein the operation of the on-off valve is controlled so that the opening degree of the on-off valve increases. 5. The narrow portion is formed as a venturi such that the cross-sectional area of the bypass passage is gradually reduced, and the variable means has a core movable in the axial direction of the venturi, and By moving the actuator forward and backward in the axial direction, it is configured to change the intake air cross-sectional area in the bypass passage,
The exhaust gas recirculation device according to claim 1.