JP3456133B2 - Exhaust gas recirculation system for turbocharged engine - Google Patents

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 system for a supercharged engine that recirculates a part of exhaust gas to an engine equipped with a supercharger.

[0002]

2. Description of the Related Art A diesel engine mounted on a vehicle is combined with a turbocharger (supercharger) to supercharge intake air supplied to a combustion chamber to improve engine output. .

Also in this supercharged diesel engine, the exhaust gas discharged from the engine in accordance with the operating condition of the engine in order to improve the exhaust gas performance, specifically, to reduce the emission of NOx (nitrogen oxide). A so-called EGR device (exhaust gas recirculation device) is used to return a part of the exhaust gas to the intake air of the engine for recirculation.

The EGR device for such a supercharged engine is required to have the ability to recirculate exhaust gas to the intake side over the entire operating region of the engine. However, in an engine with a supercharger, as the engine speed increases, the rotation of the compressor of the turbocharger increases and the supercharging pressure increases, so when the supercharging pressure becomes equal to or higher than the exhaust pressure. , Exhaust gas cannot be pushed into the combustion chamber, EG
R (exhaust gas recirculation) cannot be performed.

Therefore, the EGR is the operating range [high engine torque (high load) /
High engine speed (high speed side)], and the range of EGR is limited to low / medium load / low / medium speed.

Therefore, in order to prevent the exhaust gas from being pushed in, the negative pressure on the intake side of the engine is used to make the EG even at high engine torque / high engine speed.
An EGR device has been proposed in which the R effect is exhibited.

This EGR device uses a structure in which supercharged intake air is guided to the combustion chamber of the engine through two intake passages, and an opening / closing valve is provided in one of the intake passages, and an upstream side of this opening / closing valve is used. The structure in which the outlet of the EGR passage is connected to is used. When the supercharging pressure is lower than the exhaust pressure in the operating region of the engine, the on-off valve is opened and the exhaust gas from the EGR passage is introduced into the combustion chamber through one of the intake passages so that the supercharging pressure is equal to the exhaust pressure. When it becomes higher or higher, the on-off valve is closed and a negative pressure is applied to the upstream passage portion from the on-off valve to the combustion chamber so that the exhaust gas is introduced into the combustion chamber from the EGR passage, thereby increasing the load. / It was designed to achieve EGR near the high rotation speed.

[0008]

However, this EGR
Even in the apparatus, there is a limit to the region where EGR can be performed due to the restriction of the excess air ratio λ (= air amount / theoretical mixture) in the combustion chamber. That is, when combustion is performed at an air-fuel ratio having a concentration higher than the stoichiometric mixture ratio, oxygen required for combustion is insufficient, so black smoke is generated and exhaust gas performance deteriorates.
Therefore, the EGR can be performed only while the air-fuel ratio of the combustion chamber is kept thin by the intake air supercharged from one side of the intake passage.

However, the maximum intake amount of fresh air taken in at high engine load / high engine speed is determined by the size of one intake passage, so EGR is a high engine torque / fuel ratio in which the combustion chamber has a theoretical air-fuel ratio. It can only be continued halfway through the high engine speed range.

Moreover, if EGR is continued forcibly, the exhaust gas performance of the engine deteriorates. On the other hand, if the opening / closing valve of the closed intake passage is opened from the point where the stoichiometric air-fuel ratio is reached, EGR cannot be performed because the intake pressure becomes higher than the exhaust gas pressure due to supercharging.

For this reason, it is difficult for the supercharged engine to sufficiently exert the EGR effect in the high engine torque / high engine rotation range, and an EGR device that improves this is desired.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an exhaust gas recirculation system for an engine with a supercharger capable of expanding the high load / high speed operation range of the engine capable of performing EGR. To provide.

[0013]

In the exhaust gas recirculation device according to claim 1 in order to achieve the above object, according to an aspect of the over-guides to the combustion chamber of the engine through the first intake passage turbocharged from the supercharger Second intake air taken without passing through the feeder
It led to the combustion chamber of the engine through the intake passage, and exhaust gas of an engine with a supercharger having a first mode for introducing a part of the exhaust gas from the engine into the combustion chamber through the second intake passage
In the recirculation device, a first intake passage and a second intake passage
The flow is cut so that supercharged intake air is guided to the combustion chamber through both
And the engine exhaust through the second intake passage
Form a second mode that introduces some of the gas into the combustion chamber
A means is provided, and the supercharging pressure is high according to the supercharging pressure of the supercharger.
When the boost pressure is low, switch to the first mode.
A means for switching to two modes is provided .

As a result , regardless of the increase in boost pressure, E
GR continues.

[0015] Thus, the engine operating region capable of EGR may expand <br/> is that the high engine torque / high engine speed side. Moreover, E in the operating range of the engine with low boost pressure
Since the GR effect is promoted, the engine operating range is wide
A large amount of EGR can be performed over a long period.

In the exhaust gas recirculation system according to the second aspect, the supercharged intake air is guided to the combustion chamber through the first intake passage and only the exhaust gas of the engine is supplied through the second intake passage so as to ensure a high EGR rate. Is introduced into the combustion chamber, and the third mode is switched when a high EGR rate is required.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below based on an embodiment shown in FIGS. FIG. 1 shows a structure around a direct injection type (direct injection type) diesel engine with a supercharger mounted on a vehicle, to which an exhaust gas recirculation system of the present invention is applied, and in the figure, 1 is an engine room of the vehicle (shown in the figure. It is the main body of the engine that is housed in.

As is well known, the engine body 1 includes a cylinder 4 surrounded by a cylinder block 2 and a cylinder head 3.
For example, two intake valves 6a and 6b and two exhaust valves 7a and 7b each having a piston 5 reciprocally inserted therein and assembled for each cylinder of the cylinder head 3, and further a fuel injection nozzle assembled for each cylinder. By (not shown), the intake process, the compression process, the fuel injection process, the expansion process, and the exhaust process are repeated in the combustion chamber 8 to generate a shaft output from a crankshaft (not shown). It should be noted that the intake / exhaust valves 6a, 6b, 7a, 7b are independently formed in the cylinder head 3 such that two valves are provided for each of the intake ports 9a, 9b and exhaust ports 10a, 10b.
It is attached to.

Reference numeral 11 is a supercharger, for example, a turbocharger, which is housed in the engine room together with the engine body 1. As is well known, the turbocharger 11 is constructed by assembling an exhaust gas turbine section 13 and an air compressor section 14 at both ends of a single shaft 12. And
The exhaust gas turbine section 13 is interposed in an exhaust passage 15 extending from each exhaust port end, and is driven by the thermal energy of the exhaust gas discharged from the exhaust ports 10a and 10b. The air compressor unit 13 is interposed in one of the intake ports 9a and 9b, for example, in the middle of an intake passage 17 (which constitutes the first intake passage together with the intake port 9a) connected between the intake port 9a and the air cleaner 16. Is
The pressure of the intake air taken in from the air cleaner 16 is increased by the pressure feeding performed by the air compressor unit 14 so that the intake air can be supercharged from the intake port 9a to the combustion chamber 8.
An intercooler 18 is provided in the middle of the intake passage 17.

The other remaining intake port 9b is connected to the intake passage 1
In another independent intake passage 19 and 7 (constituting the second intake passage with the intake port 9 b), be connected to the air cleaner 16, so that it can supply the intake air to the combustion chamber 8 without passing through the turbocharger 11 I am doing it.

At the downstream side of the intake passage 19, an outlet of an EGR passage 20 branched from the middle of the exhaust passage 15 is connected. An EGR valve 21 that opens and closes the EGR passage 20 is interposed in the EGR passage 20 so that a part of the exhaust gas discharged from the engine can be introduced into the combustion chamber 8 from the intake port 9b.

The intake passage 19 on the upstream side from the outlet of the EGR passage 20 has an intercooler of the intake passage 17 via a bypass passage 23 in which a bypass valve 22 constituted by an opening / closing valve whose opening degree is variable is provided. 18 is connected to the upstream side portion. An on-off valve 24 that opens and closes the intake passage 19 upstream from the connection portion of the bypass passage 23 is provided, and supercharging is performed by the flow passage control performed by the bypass valve 22 and the on-off valve 24. Intake the intake port 9a
And a flow mode in which exhaust gas from the EGR passage 20 is introduced into the combustion chamber 8 from the intake port 9b as it is (flow passage control means). ).

On the other hand, 25 is an ECU composed of, for example, a microcomputer. The ECU 25 determines the injection timing and the fuel injection amount according to the operating state of the engine (engine speed, accelerator opening) from a map of preset injection timing and fuel injection amount, and determines the fuel injection valve. A function of driving (not shown) to inject fuel according to the operation of the engine from the injection nozzle is set.

Further, the ECU 25 is provided with an air pressure sensor 2 for detecting the operating state of the engine and further the pressure of the supercharged intake air.
6. The function of controlling the exhaust gas recirculation device is set according to the output from the turbine inlet pressure sensor 27 that detects the pressure (exhaust pressure) at the turbine inlet of the exhaust gas turbine unit 13.

Specifically, the following functions are set in the ECU 25, for example. That is, a function of determining the engine operation at full load without EGR and the engine operation other than EGR.

At full load operation without EGR, each E
With the GR valve 21 kept closed, a function of bringing only the supercharged intake air into the combustion chamber 8 from both the intake ports 9a and 9b (open / close valve 24: closed, bypass valve 22: open).

During an EGR operation, the supercharging pressure Pb
Is lower than the turbine inlet pressure Pti, the supercharged intake air is introduced into the combustion chamber 8 from both the intake ports 9a and 9b, and the exhaust gas is returned from the EGR passage 20 to the combustion chamber 8 through one intake port 9b. function.

During the operation for performing EGR, the supercharging pressure Pb
Is higher than the turbine inlet pressure Pti, the supercharged intake air is guided from the intake port 9a to the combustion chamber 8 through the intake passage 17, and independently of this, the non-supercharged intake air is introduced into the intake passage 19
Through the intake port 9b to the combustion chamber 8, and the EGR passage 20 is introduced through the intake port 9b through which the unsupercharged intake air flows.
From the exhaust gas to the combustion chamber 8. At this time, if the partial load range where the air amount is insufficient,
By adjusting the opening of the bypass valve 22 to the open side, the intake port 9
A function to slightly supercharge the b side to increase the amount of air.

In addition, when a high EGR rate is required, supercharged intake air is introduced into the combustion chamber 8 through the intake passage 17 and the intake port 9a, and the EG connected directly to the intake port 9b.
A function of setting a mode in which exhaust gas is recirculated from the R passage 20 to the combustion chamber 8.

With such control, the area where the EGR of the diesel engine with a supercharger can be performed is expanded, and a large amount of E
I am trying to do GR. That is, to explain the operation of the exhaust gas recirculation device, it is assumed that the diesel engine is now operating at full load. At this time, the ECU 25
Determines that EGR is not required and closes the on-off valve 24, opens the bypass valve 22 and closes the EGR valve 21 according to the "full load" mode, as shown in FIG.

Then, as shown by the thick line in FIG. 2, the intake air supercharged by the turbocharger 11 is supplied from the intake port 9a to the combustion chamber 8 and at the same time the bypass valve 2
2 is supplied to the combustion chamber 8 from the intake port 9b.

As a result, intake air from both the intake ports 9a and 9b is supercharged into the combustion chamber 8 to operate the diesel engine with increased engine output (no EGR).
Then, the operation of the diesel engine from full load operation,
It is assumed that the supercharging pressure Pb is lower than the turbine inlet pressure Pti.

At this time, according to a command from the ECU 25,
According to the "supercharging pressure low" mode, the EGR valve 21 changes to open. Then, as shown by the thick line in FIG.
The exhaust gas from the passage 20 is pushed into the fresh air having a low boost pressure, and returns from the intake passage 19 and the intake port 9b to the intake side of the engine.

As a result, the engine is operated with the EGR effect. Subsequently, it is assumed that the diesel engine is operated in a high load / high speed range and the supercharging pressure Pb is higher than the turbine inlet pressure Pti.

Then, according to the command from the ECU 25, the bypass valve 22 is closed and the on-off valve 24 is opened according to the "high boost pressure" mode. As a result, the intake air supercharged by the turbocharger 11 becomes an independent passage as shown by the thick line in FIG.
Is supplied to the combustion chamber 8. In addition, unsupercharged intake
It is supplied to the combustion chamber 8 through an intake passage 19 and an intake port 9b which are independent passages.

Then, the exhaust gas from the EGR passage 20 is pushed into the fresh air at atmospheric pressure and returns to the intake side of the engine via the intake passage 19 and the intake port 9b.
Exhibits the EGR effect.

As a result, the exhaust gas from the EGR passage 20 is always recirculated to the intake side of the engine together with the fresh air in the non-supercharged state, so that the EGR is continued regardless of the increase of the supercharging pressure.

Moreover, this EGR is performed while increasing the excess air ratio of the combustion chamber 8 by the inflow of fresh air in the non-supercharged state. Therefore, with the exhaust gas recirculation device of the present invention, the operating range of the engine capable of performing EGR is that the amount of fresh air supplied from the intake passage 19 and the intake port 9b to the combustion chamber 8 increases, that is, the amount of intake air increases. As the excess rate increases, it can be expanded to the high engine torque / high engine speed side as shown in the diagram of FIG. Moreover, if an air shortage occurs at this time (partial load range, etc.), the bypass valve 22 that has been closed is slightly opened, and the intake port 9b side is slightly supercharged.
Higher engine torque /
EGR can be continued near the high engine speed.

In addition to this, when the supercharging pressure is low, the exhaust gas recirculating device recirculates the exhaust gas together with the supercharging intake air supplied to the combustion chamber 8 from both the intake ports 9a and 9b. Large amount of EG even in low engine operating range
R can be performed, and EGR is high throughout the engine operating range.
The effect can be secured.

In addition, the exhaust gas recirculation system shuts off the path for supplying unsupercharged fresh air as shown in FIG. 5 in the operating region where a high EGR rate is required, so that the exhaust gas in the EGR passage 20 is exhausted. Since the gas is returned to the intake side of the engine as it is, a high EGR rate can be secured.

In addition, the recirculation structure that brings about such effects is a structure in which exhaust gas is introduced into fresh air without supercharging.
A simple structure is achieved by only combining a bypass valve 22 that opens and closes the intake passages 17 and 19 on the upstream side of the EGR passage 20 and an open / close valve 24 that opens and closes the intake passage 19 on the downstream side of the bypass valve 22.

In the embodiment, the exhaust gas recirculation system for the engine supercharged by the turbocharger is taken as an example, but the exhaust gas recirculation system for the engine supercharged by the supercharger other than the turbocharger is of course applicable to the present invention. May be applied.

[0043]

As described above, according to the invention of claim 1, the EGR is continued regardless of the increase of the supercharging pressure, so that the operating range of the engine capable of performing the EGR is high engine torque / high engine torque. It can be expanded to the engine speed side. Moreover, the EGR effect can be promoted in the engine operating region where the boost pressure is low, and a large amount of EGR can be performed over a wide range of the engine operating region.

[0044]

According to the invention of claim 2, high EG
It is possible to secure the R rate .

[Brief description of drawings]

FIG. 1 is a diagram for explaining the configuration of an exhaust gas recirculation device according to an embodiment of the present invention.

FIG. 2 is a diagram for explaining a flow of intake air during engine operation without EGR.

FIG. 3 EGR when the boost pressure is lower than the turbine inlet pressure
FIG.

FIG. 4 is a diagram for explaining EGR when the boost pressure is higher than the turbine inlet.

FIG. 5 is a diagram for explaining a case where EGR is performed at a high EGR rate.

FIG. 6 is a diagram for explaining that high engine torque / high engine rotation side EGR in an engine operating region is realized.

[Explanation of symbols]

8 ... Combustion chamber 9a, 17 ... Intake port, intake passage (first intake passage) 9b, 19 ... Intake port, intake passage (second intake passage) 20 ... EGR passage 21 ... EGR valve 22 ... Bypass valve 24 ... Open / close valve.

Front page continued (58) Fields surveyed (Int.Cl. ⁷ , DB name) F02M 25/07 550 F02M 25/07 570 F02B 37/00 302 F02B 37/16

Claims (2)

(57) [Claims] 1. A supercharged intake air taken in through a supercharger is introduced into a combustion chamber of an engine through a first intake passage, and an intake air taken in without passing through the supercharger is burned in the engine through a second intake passage. An exhaust gas recirculation system for a supercharged engine having a first mode in which a portion of exhaust gas of the engine is introduced into the combustion chamber through the second intake passage, Means for forming a second mode in which a flow is switched so that supercharged intake air is guided to the combustion chamber through both of the second intake passages, and a part of the exhaust gas of the engine is introduced into the combustion chamber through the second intake passage. According to the supercharging pressure of the supercharger, when the supercharging pressure is high,
An exhaust gas recirculation device for an engine with a supercharger, comprising means for switching to the first mode and for switching to the second mode when the supercharging pressure is low. 2. A third mode in which supercharged intake air is introduced into the combustion chamber through the first intake passage and only exhaust gas of the engine is introduced into the combustion chamber through the second intake passage, The exhaust gas recirculation device for a supercharged engine according to claim 1, wherein the third mode is switched when a high EGR rate is required.