JP2001041107A - Egr device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the exhaust gas performance by changing the position of an EGR gas return port in an air intake passage so that variations in the EGR rate become smaller in response to the rotating speed of an engine, and by reducing dispersion in the EGR rate between respective cylinders not only in the specified operating range of the engine, but in the full operating range of the engine. SOLUTION: In an EGR device 1 in which the EGR gas Ge branched out from an exhaust passage 11 of an engine is returned to an intake passage 15 through an EGR passage 12 for recirculation, the distances between the conflueense parts 13a, 13b, 13c for supplying the EGR gas Ge to an intake air A of the intake passage 15, and cylinders 18a, 18b, 18c, 18d of the engine E are formed so that the distances can be changed in accordance with the detected values Ne indicating the operating conditions of the engine E.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine, such as a diesel engine, which recirculates part of exhaust gas to intake air in order to reduce the amount of NOx emitted from the exhaust gas.
It relates to a GR device.

[0002]

2. Description of the Related Art In exhaust gas countermeasures for diesel engines and the like, in order to reduce the amount of NOx emission in exhaust gas, a part of the exhaust gas is recirculated to intake air to suppress the combustion temperature and reduce NOx emission. EGR to suppress generation
(Exhaust gas recirculation) is known to be effective, and is widely used.

In this EGR device, an EGR passage for dividing exhaust gas from an exhaust passage of an engine is connected to an intake passage side, and EGR is performed while adjusting a flow rate of the EGR gas by an EGR valve provided in the EGR passage. I have.

In a conventional EGR system, as shown in FIG. 6, an intake pipe 11 and an exhaust pipe 15 are connected to an EGR valve 19.
Are connected by one EGR pipe 12 having
A part of the exhaust gas G is recirculated to the intake pipe 15 due to the pressure difference between the exhaust gas 15 and the exhaust pipe 15 and mixes with the intake air A.
Ge flows through the intake manifold 17 to each of the cylinders 18a, 18a.
b, 18c and 18d.

However, since the pressure inside the intake pipe 11 and the inside of the exhaust pipe 15 fluctuate due to the piston stroke of the engine E, both flows are pulsating.
The EGR gas Ge sent to a, 18b, 18c, and 18d does not uniformly mix with the intake air A, and the EGR rate varies among the cylinders.

When the EGR rate varies, the EGR
Even in a cylinder having a high rate or a cylinder having a low EGR rate, combustion is not performed at an optimum EGR rate, so that the output is reduced, the exhaust gas component is deteriorated, and the exhaust gas performance as a whole is also deteriorated. Become. Therefore, it is very important to improve the variation in the EGR rate between the cylinders in the entire operation range of the engine, and various measures have been taken.

As one of the countermeasures, Japanese Patent Application Laid-Open No. 9-151
In Japanese Patent Publication No. 80, an EGR gas variable throttle valve is provided between an EGR valve in an EGR passage and an EGR gas return port (a junction between the EGR passage and the intake passage) to vary a passage cross-sectional area.
EG that mixes GR gas early with intake air for uniform distribution
An R device has been proposed, and FIGS.
An EGR having a configuration in which a plurality of EGR gas return ports each having an EGR gas variable throttle valve are arranged along the flow of intake air.
Devices have also been proposed.

The E having a plurality of EGR gas return ports
In the GR device, the throttle amount of the EGR gas variable throttle valve is individually controlled so that E is returned from each EGR gas return port.
The outflow speed of the GR gas is controlled to make a difference in the inflow speed, and the depth of penetration into the intake air flow is changed so that each stream line of the EGR gas flow is mixed with the intake air without substantially overlapping. Is configured.

With this configuration, the EGR in the intake pipe
The gas is mixed early with the intake air, and the distribution of the EGR gas with respect to the intake air in the cross section of the intake pipe is made uniform, so that the EGR gas is uniformly distributed to each cylinder.

[0010]

However, the EGR in the intake manifold of the engine performed by the present inventors was carried out.
According to the simulation calculation result regarding the gas distribution, the correlation between the non-uniformity of the EGR gas in the cross section of the intake pipe and the variation of the EGR rate between the cylinders is small, and the correlation between the EGR gas return port and the intake port is small. Was found to be important.

That is, not all of the EGR gas supplied to the intake manifold during one pulsation is taken into the cylinder, but there is residual EGR gas remaining in the cylinder. The remaining EG is sucked into the cylinder with the EGR gas supplied in the next pulsation.
Depending on the positional relationship between the position of the R gas and the cylinder to be sucked next, there are cases where the remaining EGR gas is easily sucked and cases where it is hard to be sucked.

For example, in the case of a three-cylinder engine, NO. No. 3 cylinder is NO. Although the remaining EGR gas in the cylinder No. 2 is easily sucked, the NO. No. 1 cylinder is NO. Since the distance from the cylinder No. 3 is large, NO. It is difficult to inhale the residual gas left by the third cylinder.

That is, the amount of the residual gas and the difficulty of sucking the residual gas, that is, the change in the EGR gas concentration with time and the timing at which the EGR gas reaches each cylinder are better determined by the cross-sectional flow path in the intake pipe. The influence on the variation in the EGR rate between cylinders is greater than the uneven distribution of the EGR gas in the cylinder.

Since the distance between the EGR gas return port and the intake port greatly influences the inflow timing of the EGR gas, the position of the EGR gas return port where the EGR passage merges with the intake passage is determined by the EGR gas between the cylinders. There is an optimum position for minimizing the variation in the rate, and in the related art, optimization is performed in accordance with a predetermined rotational speed according to an engine tuning target.

However, there is a problem that the optimum position of the EGR gas return port for minimizing the variation of the EGR rate between the cylinders varies depending on the rotation speed (rotation speed) of the engine. In a region other than the rotation speed of the engine, the variation of the EGR rate between the cylinders cannot be reduced, and the EGR ratio between the cylinders over the entire operation range of the engine is not obtained.
There is a problem that the variation in GR rate cannot be improved.

FIG. 5 shows a simulation result of the change of the optimum position. FIG. 5 shows the relationship between the position of the EGR gas return port and the EGR rate variation in a certain engine. 36
At the rotation speed of 00 rpm, the position of the EGR gas return port is 25 c
m, the variation in the EGR rate is smallest when
At a rotation speed of 200 rpm and 3000 rpm, it is understood that the position 15 cm upstream is optimal as indicated by the marks ○ and ●.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and an object of the present invention is to change the position of an EGR gas return port in an intake passage in accordance with the rotational speed of an engine so that the EGR rate among cylinders varies. The present invention provides an EGR device which can be changed to reduce the EGR rate, thereby reducing the variation of the EGR rate between the cylinders in the entire operating region of the engine as well as the specific engine operating region and improving the exhaust gas performance. is there.

[0018]

Means for Solving the Problems 1) An EGR device for achieving the above object is an EGR device which recirculates EGR gas branched from an exhaust passage of an engine to an intake passage via an EGR passage. This is a device that is configured to be able to change the distance between a junction of the engine and a cylinder that supplies EGR gas to the intake air in the intake passage according to a detection value indicating an operating state of the engine. 2) This device uses an EG branched from an exhaust passage of an engine.
The downstream side of the R main passage is branched into a plurality of EGR branch passages,
The EGR branch passage is connected to the intake passage in order from the upstream side to the downstream side, and only one of the EGR branch passages is selected according to the operation state of the engine, and the selected EGR branch passage is connected to the intake passage via the selected EGR branch passage. It is provided with a control means for returning EGR gas to the intake passage. 3) Further, one EGR valve is provided in the EGR passage, and an opening / closing valve is provided in each of the EGR branch passages, and the control means is configured to select one of the opening / closing valves in accordance with a rotation speed of an engine. It is configured to open only one valve. 4) In addition, the control means is configured to set the EGR to a communication state.
In the branch passage selection control, when the rotation speed of the engine is high, the EGR branch passage upstream of the intake passage is selected, and as the rotation speed of the engine decreases,
It is configured to shift to the EGR branch passage connected to the downstream side of the intake passage.

That is, the EGR device according to the present invention is an EGR device which is a converging portion which serves as an inflow port where EGR gas flows into the intake passage.
By selecting and switching the R gas return port according to a detected value indicating the operating state of the engine, for example, the rotation speed,
The position of the junction where the GR gas is supplied to the intake of the intake passage is changed, that is, the distance between the junction with the intake of the EGR gas and the intake manifold and each cylinder is changed with respect to the operating state of the engine. This is a device that improves the EGR rate variation among the cylinders in each operation region by changing the position to an optimal position.

More specifically, a plurality of EGR gas return ports are provided along the flow direction of the intake passage, and an on-off valve or a flow control valve is provided for each of the EGR gas return ports so that the engine speed and load of the engine can be controlled. One of the EGR gas return ports for supplying the EGR gas is selected according to the detected value indicating the operating state of the EGR gas, and the EGR gas is returned to the intake passage from the EGR gas return port.

Although the number of the EGR gas return ports is not particularly limited, an appropriate number is provided in consideration of the relationship between the engine operating area and the optimum position and the balance of the entire EGR apparatus such as the number of valves.

In order to select one of the EGR branch passages, it is simple and preferable to provide an on-off valve in each EGR branch passage and open only one of the EGR branch passages. In addition, each EG
The valve provided in the R branch passage is constituted by a flow control valve, and EG
The flow rate adjusting function of the R valve can be used together. However,
In this case, the number of flow control valves is equal to the number of EGR branch passages.

In the engine speed control section, the EGR branch passage on the most upstream side with respect to the intake passage is in the communicating state in the section of the highest rotational speed, and the EGR branch passage in the section of the lowest rotational speed is the highest in the section of the intake passage. The downstream EGR branch passage is in a communicating state, and the intermediate portion thereof is configured to shift to the upstream side when the rotation speed increases and to the downstream side when the rotation speed decreases.

Incidentally, as a configuration that allows the position at which the EGR gas joins with the intake air in the intake passage to be changed, a configuration in which an EGR branch passage is formed and one of the EGR branch passages is selected is exemplified. The configuration is not limited, and another configuration may be used. For example, the connection between the EGR passage and the intake pipe may be provided so as to be movable in the flow direction of the intake pipe.

With the above configuration, the distance between the EGR gas return port and each cylinder is optimized, the variation in the EGR rate between the cylinders over the entire operating region of the engine is reduced, and the exhaust gas characteristics are improved.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an EGR device according to the present invention will be described with reference to FIGS. [First Embodiment] As shown in FIG. 1, an EGR device 1 according to a first embodiment includes an EGR main pipe (EGR main passage) 12 branched from an exhaust pipe (exhaust passage) 11 of an engine E. It branches into a plurality (three in the drawing) of EGR branch pipes (EGR branch passages) 12a, 12b, and 12c, and an intake pipe (intake passage) 15
At the EGR gas return ports 13a, 13b, 13c.

The EGR gas return ports 13a, 13b, 13c
Indicates that the rotation speed Ne of the engine E is in a high rotation range,
When the engine is in the middle rotation range and the low rotation range, each cylinder 18a, 18b,
In order to minimize the variation in the EGR rate between 18c and 18d, they are arranged at positions determined in advance by experiments, simulation calculations as shown in FIG. 5, and the like.

FIG. 5 shows, as a standard deviation, a variation in the EGR rate with respect to a change in the shift amount for shifting the position of the ERG return port to the upstream side of the intake pipe 15. In the engine shown in FIG. 15 at 3200 rpm
cm, 3600 rpm and 4000 rpm, the variation becomes the smallest with a shift amount of 25 cm.

That is, in the case of the engine shown in FIG. 5, the higher the rotation speed Ne, the better the EGR gas is merged with the intake air A on the upstream side.

The EGR main pipe 12 is provided with an EGR valve 19, and the EGR branch pipes 12a, 12b, 12c are provided with on-off valves 14a, 14b, 14c, respectively.

Further, a rotational speed Ne and a load Acc representing the operating state of the engine E are detected, and the EGR valve 19 is operated in accordance with a control program set in advance based on the detected values.
The control means 16a for controlling the flow rate of the engine and controlling the opening and closing of the on-off valves 14a, 14b, 14c is provided in a part of the controller 16 for controlling the operation of the entire engine.

The control means 16a controls the engine E
Is located in the intake passage 15 such that the EGR rate among the cylinders 18a, 18b, 18c, and 18d is reduced to an optimum position in the high rotation range when the rotation speed Ne is in the high rotation range. The on-off valve (for example, 14a) provided in the branched path (for example, 12a) is opened, and the other on-off valves 14b, 14c are closed.

When the rotational speed Ne of the engine E is in the middle rotation region, the control means 16a controls the branch passage (the branch passage) disposed in the intake passage 15 so as to be at an optimum position in the middle rotation region. For example, the on-off valve (for example, 14b) provided in 12b) is opened, the other on-off valves 14a, 14c are closed, and when the engine is in a low rotational speed range, the optimal position is obtained in this low rotational speed range. Thus, a branch passage (for example, 12c) arranged in the intake passage 15
The on-off valve (for example, 14c) provided in the valve is opened, and the other on-off valve 14 is opened.
a, 14b are closed.

That is, the EGR branched from the exhaust pipe 11, which is a part of the exhaust gas G discharged from the exhaust manifold 22
The gas Ge is supplied to the EGR main pipe 12 and the EGR branch pipes 12a, 12b,
It is formed so as to merge with the intake air A of the intake pipe 15 via any one of 12c and to be supplied to the intake manifold 17 as an air-fuel mixture A + Ge.

With this configuration and control, the distance relationship between the position where the EGR gas Ge flows into the intake passage 15 and the position with respect to the intake manifold 17 in each rotational speed range, or in other words, each cylinder 18a, 18b, 18c, 18d. Is switched to an optimal distance relationship that minimizes the variation in the EGR rate between the cylinders, and the variation in the EGR rate is reduced over the entire operating range of the engine E, so that the cylinders 18a, 18b, 18c , 18d
, The combustion in the fuel cell is improved, and the exhaust gas characteristics can be improved. [Second Embodiment] As shown in FIG. 2, an EGR device 1A according to a second embodiment has a valve 14 provided in each of the EGR branch pipes 12a, 12b, 12c instead of providing the EGR valve 19.
Aa, 14Ab, and 14Ac are provided by changing from an on-off valve to a flow control valve, and the adjustment of the EGR amount is performed by the valves 14Aa, 14Ab, and 14Ab.
14Ac. Others are the same as the EGR device 1 of the first embodiment.

According to the EGR device 1A having this configuration, the EG
Since the function of the R valve is performed by the valves 14Aa, 14Ab, 14Ac provided in each of the EGR branch pipes 12a, 12b, 12c, the number of valves can be reduced by one, which is advantageous in space. [Third Embodiment] As shown in FIG. 3, an EGR device 1B according to a third embodiment includes EGR branch pipes 12a, 12b,
Instead of the on-off valves 14a, 14b, 14c provided in 12c, each E
A switching valve 20 is provided at a branch portion of the GR branch pipes 12a, 12b, and 12c, and the selection of the EGR branch pipes 12a, 12b, and 12c is performed by the switching valve.
This is configured to be performed by switching 20. Others are the same as the EGR device 1 of the first embodiment.

According to the EGR device 1B having this configuration, the EG
Since the selection of the R branch pipes 12a, 12b, and 12c is performed by the switching valve 20, the number of valves can be reduced as compared with the selection by the on-off valve. [Fourth Embodiment] As shown in FIG. 4, an EGR device 1C according to a fourth embodiment includes EGR branch pipes 12a, 12b,
EG instead of 12c and on-off valves 14a, 14b, 14c
The EGR gas return port 13 of the R pipe 12 is provided so as to be movable in the flow direction of the intake pipe 15, and the actuator 30 that changes the operation amount of the rod 31 according to the rotation speed Ne of the engine E,
E at the tip end of the flexible joint 32 provided on the EGR pipe 12
It is configured to move the GR gas return port 13. Others are the same as the EGR device 1 of the first embodiment.

According to the EGR device 1B having this configuration, the EG
Since the selection of the R branch pipes 12a, 12b, and 12c is performed by the switching valve 20, the number of valves can be reduced as compared with the selection by the on-off valve. [Effects] According to the EGR devices 1, 1A, 1B having the above-described configuration, a plurality of EGR gas return ports 13a, 13b, 13c are provided along the flow direction of the intake passage 15, and the on-off valves 14a, 14b, 14c or flow control valve 14Aa, 14Ab, 14
Ac is provided, and the EGR gas Ge is determined according to the engine speed Ne, which is one index indicating the operating state of the engine.
From one of the EGR gas return ports 13a, 13b, and 13c for supplying EG, and the EG is supplied from the selected EGR gas return port.
Since the R gas Ge is recirculated to the intake passage 15, the EGR gas return ports 13a, 13b, 13c, the intake manifold 17, and each cylinder
The distance between 18a, 18b, 18c and 18d can be changed to an optimum position for the operating state of the engine,
Variations in the EGR rate among the cylinders 18a, 18b, 18c, 18d in each operation region can be improved.

Therefore, the EGR gas return ports 13a, 13b, 13
The distance between the cylinder c and each of the cylinders 18a, 18b, 18c, 18d is optimized, and each cylinder 18
Variations in the EGR rate among a, 18b, 18c, and 18d can be reduced, and the exhaust gas characteristics can be improved.

That is, according to the rotational speed Ne of the engine E, the valves 14a, 14b, 14c or 14Aa, 14Ab, 14Ac
Alternatively, by controlling 20 and changing the inflow position of the EGR gas, it is possible to improve the variation of the EGR rate in the entire rotation speed range of the engine E.

[0041]

As described above, according to the EGR device of the present invention, one EGR gas return port for supplying EGR gas is selected according to the operating state of the engine such as the engine speed and load. Thus, while changing the distance between the EGR gas return port and the manifold and each cylinder to an optimum position for the operating state of the engine, it is possible to recirculate the EGR gas from the EGR gas return port to the intake passage. Therefore, it is possible to improve the variation in the EGR rate between the cylinders in each operation region.

Accordingly, in each engine operating region, the EGR operation can be performed at the distance between the EGR gas return port and each cylinder in which the variation in the EGR rate between the cylinders is reduced. Of the EGR rate can be reduced, and the exhaust gas characteristics can be greatly improved.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an EGR device according to a first embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of an EGR device according to a second embodiment of the present invention.

FIG. 3 is a schematic configuration diagram of an EGR device according to a third embodiment of the present invention.

FIG. 4A shows a case where EGR gas is supplied from an upstream side, and FIG. 4B shows a case where EGR gas is supplied from a downstream side.

FIG. 5 is a diagram showing a relationship between a position of an EGR return port and a variation in an EGR rate.

FIG. 6 is a schematic configuration diagram of a conventional EGR device.

[Explanation of symbols]

 1, 1A, 1B EGR device 11 Exhaust pipe (exhaust passage) 12 EGR main pipe (EGR main passage) 12a, 12b, 12c EGR branch pipe (EGR branch passage) 13a, 13b, 13c EGR gas return ports 14a, 14b, 14c On-off valve 14Aa, 14Ab, 14Ac Valve (flow regulating valve) 15 Intake pipe (intake passage) 16 Controller 16a Control means 17 Intake manifold 18a, 18b, 18c, 18d Cylinder 19 EGR valve 20 Switching valve Ne Rotation speed

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02D 21/08 301 F02D 21/08 301A F02M 35/10 311 F02M 35/10 311E

Claims (4)

[Claims] An EGR branched from an exhaust passage of an engine
EGR for returning gas to the intake passage via the EGR passage
An EGR device, characterized in that a distance between a converging portion for supplying EGR gas to the intake air in the intake passage and a cylinder of the engine can be changed according to a detected value indicating an operating state of the engine. 2. An EGR branched from an exhaust passage of an engine.
The downstream side of the main passage is branched into a plurality of EGR branch passages, the EGR branch passages are sequentially connected to the intake passage from the upstream side to the downstream side, and the EGR branch passage is determined in accordance with a detection value indicating an operating state of the engine. An EGR device comprising: a control unit that selects only one of the passages and recirculates EGR gas to the intake passage via the selected EGR branch passage. 3. An EGR valve is provided in the EGR main passage, and an opening / closing valve is provided in each of the EGR branch passages. The control means is configured to control one of the opening / closing valves in accordance with a rotation speed of an engine. 3. The EGR device according to claim 2, wherein only one valve is opened. 4. The control unit according to claim 1, wherein
In the selection control of the GR branch passage, when the rotation speed of the engine is high, the EGR branch passage on the upstream side of the intake passage is selected, and the EGR branch passage is connected to the downstream side of the intake passage as the rotation speed of the engine decreases. The EGR device according to claim 3, wherein the EGR device is configured to shift to the EGR branch passage.