JPH04175453A - Exhaust gas recirculation device for engine - Google Patents

Abstract

PURPOSE:To prevent the knocking by providing a cooling means to cool the EGR gas at least in a high load operation of an engine to an exhaust recirculation passage, to reduce the temperature of the EGR gas so as to reduce the combustion temperature while preventing the reduction of the volume efficiency. CONSTITUTION:An EGR passage 15 to communicate the downstream side of a catalyst converter 14 in a common exhaust gas passage 13 to independent inlet gas passages 9 respectively is branched to the first and the second branch passages 15A and 15B on the way of the passage 15, and EGR valves 16A and 16B are provided to the branch passages 15A and 15B respectively. And a water cooling type cooler 17 is provided to only the second branch passage 15B. The cooler 17 is provided on the way of a cooling water passage 18 through which the cooling water of the engine main body 1 flows, for example. And in a low load area, the EGR valve 16A of the first branch passage 15A which does not have the cooler 17 is opened to recirculate the EGR gas to an inlet system 2, but as the load increases, the EGR valve 16B is opened while the EGR valve 16A is closed, and the EGR gas whose temperature is lowered by the cooler 17 is to be recirculated.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an exhaust gas recirculation device that recirculates a portion of engine exhaust gas to an intake system.

(Conventional technology) In order to purify exhaust gas, automobile engines reduce NOx (nitrogen oxides) in exhaust gas by circulating a portion of the exhaust gas back into the intake system to lower the temperature of combustion gas (EGR). (Special Public Interest Publication 1986-16)
(See Publication No. 0052).

By the way, in the high load range of the engine, the lower the temperature of EGR gas, the better the volumetric efficiency, and the larger the amount of EGR gas,
Since the combustion temperature is lowered, this is advantageous in terms of reducing NOx and preventing knocking. However, in light load ranges, if the temperature of EGR gas is low, the combustion speed will slow and combustion will become unstable, and even at the same EGR rate, pumping loss will increase compared to high temperature EGR, so EGR gas is It turned out to be good.

In addition, in a turbocharged engine, the position of the EGR gas intake in the exhaust system and the position of the EGR gas intake in the intake system
There is a problem in that turbine efficiency decreases unless the position of the R gas supply port is set appropriately.

(Objective of the Invention) Therefore, an object of the present invention is to provide an exhaust gas recirculation device that can always perform optimal EGR in both a naturally aspirated engine and a supercharged engine and in a wide operating range.

(Structure of the Invention) The invention of claim 1 is characterized in that the exhaust gas recirculation passage is provided with a cooling means for cooling EGR gas at least during high load of the engine. A first exhaust gas recirculation passage provided with a cooling means, and a second exhaust gas recirculation passage not provided with a cooling means,
The invention according to claim 3 is characterized in that a control means is provided for increasing the amount of the cooled reflux gas passing through the second exhaust gas recirculation passage in accordance with an increase in load. In a supercharged engine equipped with a cooling intercooler,
In the invention according to claim 4, characterized in that an inlet for EGR gas into the intake system is provided on the upstream side of the intercooler in the intake passage, in the turbocharged engine equipped with the cooling means according to claim 1, The engine is characterized in that EGR gas is recirculated from downstream of the turbine to the intake system during low speed and high load conditions.

(Effects of the Invention) According to the invention of claim 1, it is possible to lower the combustion temperature and prevent knocking while lowering the temperature of EGR gas and preventing a decrease in volumetric efficiency.

According to the invention of claim 2, by increasing the EGR gas temperature during low loads and lowering it during high loads, the combustion rate can be maintained at an appropriate level regardless of the load, and pumping loss can be reduced in the light load range. can be achieved.

According to the third aspect of the invention, the effect of lowering the combustion temperature due to EGR can be further improved.

According to the invention of claim 4, it is possible to prevent a decrease in turbine efficiency due to EGR.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic configuration diagram showing a first embodiment of the present invention.
2 indicates the engine body of the 4-cylinder engine, 2 indicates the engine intake system, and 8 indicates the engine exhaust system.

4 is a common intake passage, and in this intake passage 4, an air cleaner 5, an air flow meter 6 for detecting the amount of intake air, and a throttle valve 7 are arranged in order from the upstream side to the downstream side. A surge tank 8 is connected to the downstream end of the common intake passage 4, and four independent intake passages 9 branched from the surge tank 8 are connected to the intake boat IO of each cylinder, respectively. Since the engine of this embodiment has two intake valves and two exhaust valves for each cylinder, two intake boats 10 and two exhaust ports 11 are provided for each cylinder. Independent exhaust passages 12 are connected to each exhaust port 11, and these independent exhaust passages 1
The downstream ends of the exhaust gases 2 are gathered together in a common exhaust passage 13, and a catalytic converter 14 is provided in this common exhaust passage 13.

Reference numeral 15 denotes an exhaust gas recirculation passage (
(hereinafter referred to as "rEGR passage"), this EGR passage 15 has a first branch passage 15A and a second branch passage 15B on the way.
EGR valves 16A and 16B are provided in each of the branch passages 15A and 15B, respectively, and are driven by diaphragm actuators 19A and 19B to control the flow rate of EGR gas passing through the passages 15A and 15B. A water-cooled cooler 17 for cooling the EGR gas passing through the second branch passage 15B is provided only in the second branch passage 15B. In this embodiment, this cooler 17
is provided in the middle of the cooling water passage 18 through which the cooling water of the engine body 1 flows. first and second branch passages 15A;
15B are merged on the downstream side and connected to each independent intake passage 9.

Actuators 19A and 1 for each EGR valve 16A and 16B
The negative pressure chamber 9B communicates with the surge tank 8 through negative pressure conduits 2OA and 20B, respectively.
20B is provided with electromagnetic solenoid valves 21A and 21B, respectively.

Note that the electromagnetic solenoid valve 21B is normally open. 22 is a control unit, and this control unit 22 controls the electromagnetic solenoid valves 21A and 2 based on the outputs of the air flow meter 6 and the throttle opening sensor 23, and the output of an engine speed sensor (not shown).
1B is duty-controlled, thereby controlling the EGR valve 16A.
, 16B (lift amount) are controlled in the manner shown in the graph of FIG.

FIG. 2 is a graph showing the relationship between the engine load and the opening degrees of the EGR valves 16A and 16B. As is clear from FIG. 2, in the low load range, the control unit 22 opens the EGR valve 16A of the first branch passage 15A, which is not equipped with the cooler 17 of the EGR passage 15, and supplies EGR gas to the first branch passage 15A. However, as the load increases, the EGR valve 16A is closed and the EGR
The R valve 16B is opened and the electromagnetic solenoid valves 21A and 21B are duty-controlled so that the ratio of EGR gas whose temperature has been lowered by the cooler 17 is increased. In addition, the second
In the figure, the total amount of EGR is almost constant in the high load range, but in an engine with a high compression ratio, it is necessary to increase the total amount of EGR as the load increases to prevent knocking. good. In addition, in order to ensure combustion stability in the extremely light load range, both EGR valves 16A
, 16B are closed to stop external EGR. Furthermore, in this embodiment, the EGR passage 15 in the exhaust system 3
An EGR gas inlet is provided on the downstream side of the catalytic converter 15 so that lower temperature EGR gas is recirculated to the intake system 2.

The above is a description of the configuration and operation of the first embodiment of the present invention, but an air-cooled cooler may be provided in place of the water-cooled cooler 17 provided in the second branch passage 15B of the EGR passage 15. . Alternatively, the EGR gas may be cooled by lengthening the second branch passage 15B itself or by providing a large number of parallel passages without providing the above-mentioned cooler in the second branch passage 15B.

As mentioned above, in the light load range, high temperature EGR gas is recirculated,
The reason why low-temperature EGR gas is recirculated in the high load range is shown below.

FIG. 3 is a graph showing the relationship between EGR gas temperature and pumping loss reduction degree using EGR rate as a parameter. In a light load range, the degree of restriction of the intake air by the throttle valve 7 is large, resulting in a large pumping loss, but as is clear from Figure 3, in a light load range, the higher the temperature of the EGR gas, the smaller the pumping loss. Since a large pumping loss reduction efficiency can be obtained with the amount of EGR, it is desirable that the temperature of the EGR gas is high in the light load range.

On the other hand, in a high load range, the lower the temperature of EGR gas and the greater the amount of EGR gas, the lower the combustion temperature. FIG. 4 is a graph showing the relationship between pressure and combustion temperature in an equal volume cycle, and TA in FIG.

Ttoc+ ΔT and Tb are expressed by the following 0-0 formula.

TT, )C= TA・ε−1, , , , ■Tb
= Ttnc+ΔT, old,,
■Here, TA: Temperature at the start of compression TTl) c: Compression top dead center temperature Tb: Temperature after combustion ε: Effective compression pressure Cp: Isobaric specific heat Cv: Isovolume specific heat A/F: Air-fuel ratio suffix a: Fresh air Suffix e: Exhaust (EGR) Q: Total calorific value QocGa (when A/F is constant) G: Gas weight As is clear from the 0 to 0 formula, the lower the EGR gas temperature in the high load range, the lower the EGR gas amount. The larger the amount, the lower the combustion temperature. When the combustion temperature decreases, the combustion chamber wall temperature also decreases,
This means that the heat load on the engine is reduced. Further, even during combustion, since the temperature of the burnt gas is low, the radiant heat to the unburned gas is reduced, and the temperature of the unburned gas is also suppressed, resulting in improved knocking resistance. Furthermore, lowering the combustion temperature brings about a lowering of the exhaust gas temperature, which has the advantage of making the exhaust system parts more heat resistant. For the above reasons, E
It cools the GR gas.

Next, FIG. 5 is a schematic configuration diagram showing a second embodiment of the present invention, and this embodiment is an example in which the present invention is applied to a supercharged engine. That is, a supercharger 25 driven by an engine, and a supercharger 25
The common intake passage 4 is equipped with an intercooler 26 that cools the intake air compressed by the engine, and a relief valve driven by a diaphragm actuator 29 is provided in the bypass passage 27 that bypasses the supercharger 25 and the intercooler 26. 28 are provided. The pressure chamber of the actuator 29 communicates with the surge tank 8, and when the boost pressure exceeds a predetermined value, the relief valve 28 opens the bypass passage 27 for relief.

In this embodiment, the EGR gas inlet to the intake system of the first branch passage 15A, which is not provided with the cooler 17 of the EGR passage 15, opens into each independent intake passage 9, as in the first embodiment shown in FIG. The second branch passage 15 is equipped with a cooler 17.
The EGR gas introduction port to the intake system B opens on the upstream side of the supercharger 25 in the common intake passage 4. Note that this cooled EGR gas inlet is connected to the supercharger 25 and intercooler 26.
It may be provided between the intercooler 26 and the intercooler 26 . As is clear from FIG. 5, except for the above points, the second embodiment of the present invention has the same configuration as the first embodiment shown in FIG. Duplicate explanations will be omitted.

Also in this embodiment, in the light load range, high-temperature EGR passes through the first branch passage 15A that is not equipped with the cooler 17.
The gas is returned to the intake system, and in high load areas, the cooler 1
The mount roll unit 22 duty-controls the electromagnetic solenoid valves 21A and 21B so that the cooled EGR gas that has passed through the second branch passage 15B equipped with the cooler 17 is recirculated to the intake system. EGR cooled by
By circulating the gas to the upstream side of the intercooler 26 of the intake system 2, EGR gas whose temperature has further decreased is supplied to the engine. In such a supercharged engine, by increasing the total amount of EGR as the supercharging pressure increases in the high load range,
The occurrence of knocking can be prevented. Note that a sensor is provided to detect the opening degree of the relief valve 28.
The opening degrees of the EGR valves 16A and 16B may be set in relation to the opening degrees of the EGR valves 16A and 16B.

FIG. 6 is a schematic configuration diagram showing a third embodiment of the present invention, and this embodiment is an example in which the present invention is applied to a turbocharged engine. That is, this engine has a turbocharger 30 consisting of an exhaust turbine 31 provided in the common exhaust passage 13 and a supercharger 32 provided in the common intake passage 4 and driven by the exhaust turbine 31.
Furthermore, an intercooler 26 is provided in the common intake passage 4 between the supercharger 32 and the throttle valve 7. Further, a gate valve 35 driven by a diaphragm actuator 34 is provided in a bypass passage 33 that bypasses the exhaust turbine 31 . The pressure chamber of the actuator 34 communicates with the downstream side of the supercharger 32 in the common intake passage 4, and when the supercharging pressure exceeds a predetermined value, the gate valve 35 opens the bypass passage 27 to relieve exhaust gas. It has become.

The feature of this embodiment is that the first and second E
It is provided with GR passages 36A and 36B. That is, the first EGR passage 36A communicates between one of the independent exhaust passages 12 of the engine and each independent intake passage 9, and the first EGR passage 36A has an E
A GR valve 16A is provided. Also, the second EGR valve 16
B communicates between the downstream side of the exhaust turbine 31 in the common exhaust passage 13 and the upstream side of the supercharger 32 in the common intake passage 4, and the second EGR passage 36B is provided with cooling as in the previous embodiment. 17 and an EGR valve 16B.

The rest of the configuration is the same as that of the previous embodiment, so redundant explanation will be omitted, but in this embodiment, the first EGR passage 36A that recirculates EGR gas in the light load range is connected to the independent exhaust passage 12 of the engine and the independent intake By providing it between the passage 9 and the passage 9, high temperature EGR gas is supplied to the engine in a light load range. This prevents an increase in the work of the supercharger 32 due to EGR in the light load range, thereby increasing the rotational speed of the supercharger 32 and increasing turbine efficiency. On the other hand, a second EGR passage 36 equipped with a cooler 17
The EGR gas intake port B is provided downstream of the exhaust turbine 31 in the common exhaust passage 13, and in high load areas, especially low speed and high load areas, relatively low temperature exhaust gas is transferred to the second EGR passage 36.
After being further cooled by the cooler 17, it is returned to the common intake passage 4 on the upstream side of the supercharger 32. Therefore, low-temperature EGR gas is supplied to the engine in the low-speed, high-load range where knocking is particularly likely to occur, thereby preventing knocking and reducing turbine efficiency.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing a first embodiment of the present invention, and FIG.
4 to 4 are graphs for explaining the operation, and FIGS. 5 and 6 are schematic configuration diagrams showing second and third embodiments of the present invention. 1... Engine body 4... Common intake passage 7.
...Anti-throttle valve 9...Independent intake passage 12...
・Independent exhaust passage 18...Common exhaust passage 14...
Catalytic converter 15... EGR passage 15A... First branch passage 15B... Second branch passage 16A, 16B
...EGR valve 17...Cooler 19AS19B, 29.34...Diaphragm actuator 21A, 21B...Electromagnetic solenoid valve 22...Control unit 23...Throttle opening sensor 25... ...Supercharger 26...Intercooler 30...Turbocharger 31...Exhaust turbine 32...Supercharger 36A...
...First EGR passage 36B...Second EGR passage

Claims (1)

[Claims] 1. In an exhaust gas recirculation device for an engine that recirculates part of the exhaust gas to the intake system through an exhaust gas recirculation passage, the exhaust gas recirculation passage is provided with a cooling means for cooling the recirculation gas at least when the engine is under high load. An engine exhaust gas recirculation device characterized by: 2. A first exhaust gas recirculation passage provided with the cooling means and a second exhaust gas recirculation passage not provided with the cooling means are provided, and the amount of the cooled recirculation gas passing through the second exhaust gas recirculation passage is controlled by the load. 2. The exhaust gas recirculation device according to claim 1, further comprising a control means for increasing the amount in accordance with the increase. 3. The exhaust gas according to claim 1, wherein in a supercharged engine having an intercooler for cooling intake air in an intake passage, an inlet for introducing the recirculated gas into the intake system is opened on the upstream side of the intercooler in the intake passage. Reflux device. 4. The exhaust gas recirculation system according to claim 1, wherein in a turbocharged engine, the recirculated gas is recirculated from downstream of the exhaust turbine to the intake system at low speed and high load.