JP3203445B2 - 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 turbocharged engine.

[0002]

2. Description of the Related Art Generally, in an engine for an automobile or the like, exhaust gas recirculation (EGR) to an intake system for the purpose of reducing NOx in a normal operation region from a low load region to a medium load region of the engine.
), An exhaust gas recirculation passage that connects the exhaust gas passage with the intake air passage, and an exhaust gas recirculation valve (E) that opens and closes the exhaust gas recirculation passage.
An exhaust gas recirculation device including a GR valve is provided.

[0003] In the case of a turbocharged engine, the high-speed full-opening performance of the engine is limited in part by the maximum supercharging pressure set for suppressing abnormal combustion, and the other is the reliability of the exhaust system. Limited by exhaust gas temperature limits to ensure. Therefore, in order to improve the output of the engine, it is necessary to increase the supercharging pressure by relaxing the abnormal combustion limit or to lower the exhaust gas temperature. Therefore, in addition to EGR for reducing NOx from a low load range to a medium load range, attempts have been made to perform EGR for reducing exhaust gas temperature in a high-speed high-load range of an engine.

[0004] Separately, Japanese Unexamined Patent Application Publication No.
No. 62, an exhaust gas recirculation passage is provided to connect the turbine upstream of the exhaust passage with the blower downstream of the intake passage, and the EGR is performed even in a supercharging region where the intake pipe boost pressure is positive.
And Japanese Patent Application Laid-Open No. 54-148927.
As described in the publication, when the supercharging pressure is higher than the exhaust pressure in the supercharged diesel engine, the exhaust gas upstream of the turbine is introduced into the blower upstream, and when the supercharging pressure is lower than the exhaust pressure upstream of the turbine, the turbine is exhausted. There is a known exhaust gas that introduces upstream exhaust gas downstream of a blower in an intake passage.

[0005]

When EGR is to be performed in a turbocharged engine with an engine at a high rotation speed and a high load in order to reduce the exhaust gas temperature, the conventional apparatus is capable of reducing NOx in a low and medium load range. Therefore, exhaust gas is introduced upstream of the blower in a high-rotation, high-load region by a method of expanding an operation region of the exhaust gas recirculation device. However, in order to reduce the exhaust gas temperature, it is necessary to perform the EGR particularly near the turbine rotation limit. Since the vicinity of the turbine rotation limit is a region in which the supercharger cannot be further increased, the upstream of the blower in this region. Introducing a large amount of exhaust gas to
As a result, the amount of fresh air introduced is reduced, and the engine output is reduced.

Japanese Unexamined Patent Application Publication No. Sho 61-43262 and Japanese Unexamined Patent Application Publication No.
Japanese Patent Application Laid-Open No. 4-148927 discloses a method in which exhaust gas is introduced downstream of a blower as described above. However, these are related to EGR for reducing NOx, and a high rotation and high load near a turbine rotation limit. It does not disclose the above-mentioned problems when EGR is performed in order to reduce the exhaust gas temperature in the region, and the countermeasures therefor.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has been made without reducing the amount of fresh air introduced into an engine in a high-speed and high-load region near a turbine rotation limit of a turbocharger. The purpose is to reduce the exhaust gas temperature by performing reflux.

[0008]

SUMMARY OF THE INVENTION The present invention is directed to a conventional turbocharger engine, which is used for reducing the exhaust gas temperature in a high-speed, high-load range, in order to reduce the exhaust gas temperature.
Exhaust gas was introduced upstream of the blower in the same way as exhaust gas recirculation to reduce the amount of fresh air introduced and the engine output was reduced as described above, and exhaust gas temperature was reduced by exhaust gas recirculation. It is particularly necessary to perform a high rotation and high load region close to the turbine rotation limit, and this region is a region where the relationship between the supercharging pressure and the exhaust pressure upstream of the turbine is reversed by opening the waste gate valve, In the region where the exhaust pressure upstream of the turbine is sufficiently higher than the supercharging pressure, a large amount of exhaust gas upstream of the turbine can be introduced downstream of the blower by utilizing the pressure difference between the exhaust pressure and the supercharging pressure, This led to the finding that the above problems could be solved and the exhaust gas temperature could be reduced without reducing the amount of fresh air introduced in the high-speed, high-load range near the turbine speed limit. Is shall. Further, the configuration includes a turbocharger including a turbine disposed in the exhaust passage and driven by exhaust energy and a blower disposed in the intake passage and driven by the turbine, and bypasses the turbine in the exhaust passage. The exhaust gas of a turbocharged engine provided with a bypass passage which is provided with a wastegate valve which opens the passage when the boost pressure downstream of the blower of the intake passage reaches a predetermined maximum supercharging pressure is provided in the bypass passage. A recirculation device, an exhaust recirculation passage communicating the turbine upstream of the exhaust passage and the blower downstream of the intake passage, an exhaust recirculation valve for opening and closing the exhaust recirculation passage, and an engine rotation range in which the wastegate valve is opened. In addition, an engine in which the turbine speed is equal to or higher than a predetermined turbine speed on a higher rotation side than the rotation speed at which the wastegate valve starts to open. In that a recirculation control means for controlling the exhaust gas recirculation valve to open the exhaust gas recirculation passage in rotation and high load region, characterized.

[0009] More specifically, the control means for controlling the exhaust gas recirculation valve is, more specifically, a turbine rotating speed higher than the rotating speed at which the wastegate valve starts to open, a fixed width exceeding the turbine rotating limit for preventing damage. The exhaust gas recirculation valve can be controlled so as to open the exhaust gas recirculation passage only in the high engine speed and high load region where the turbine speed is equal to or higher than the predetermined turbine speed on the low rotation side.

[0010] The present invention can also perform normal exhaust gas recirculation for NOx reduction. In this case, a second exhaust gas recirculation that communicates between the turbine downstream of the exhaust passage and the blower upstream of the intake passage. A passage, a second exhaust gas recirculation valve that opens and closes the second exhaust gas recirculation passage, and a second exhaust gas recirculation control valve that opens the second exhaust gas recirculation passage in a predetermined exhaust gas recirculation region outside the high-speed high-load region. A second control means is provided.

[0011]

In the engine speed range in which the wastegate bubble is opened and the supercharging pressure is controlled to a predetermined maximum supercharging pressure,
In addition, an engine high-speed high-load region where the turbine speed is equal to or higher than a predetermined turbine speed higher than the speed at which the wastegate bubble starts to open, preferably equal to or higher than a predetermined turbine speed lower than the turbine speed limit by a certain width from the turbine speed limit. Then
The exhaust gas recirculation valve is opened, and the exhaust gas recirculation passage connecting the turbine upstream of the exhaust passage and the blower downstream of the intake passage is opened.
At this time, the exhaust pressure upstream of the turbine is higher than the boost pressure (supercharging pressure) downstream of the blower. Therefore, by controlling the exhaust gas recirculation valve, a required amount of exhaust gas is introduced to the downstream of the blower through the exhaust gas recirculation passage to reduce the exhaust gas temperature. Can be reduced. Further, since the exhaust gas is introduced without passing through the blower, the required work of the supercharger does not increase. Therefore, the amount of fresh air does not decrease and the engine output does not decrease.

Further, in a predetermined exhaust gas recirculation region outside the high-rotation high-load region, exhaust gas from the turbine downstream of the exhaust passage is introduced into the intake passage upstream of the blower, thereby reducing NOx.

[0013]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is an overall view of an embodiment of the present invention.
In the figure, 1 is an engine body of an in-line four-cylinder engine, 2 is an intake system of the engine, and 3 is an exhaust system.

The intake system 2 of the engine includes an independent intake passage 4 for each cylinder, a surge tank 5 located at a gathering portion of the independent intake passages 4, and an upstream side connecting the surge tank 5 to an air cleaner (not shown). A blower 7a of a turbocharger 7 is disposed in the intake passage 6 upstream of the surge tank 5 and an intake passage downstream of the blower 7a and immediately upstream of the surge tank 5. A throttle valve 8 for adjusting the intake air amount by narrowing the throttle 6 is disposed, and a fuel injection valve 9 is disposed in each independent intake passage 4.

The exhaust system 3 of the engine comprises an independent exhaust passage 10 for each cylinder and an exhaust passage 11 on the downstream side where the independent exhaust passages are gathered. In the passage 11, a turbine 7b of the turbocharger 7 for driving the blower 7a is arranged, and a bypass passage 12 is formed to bypass the turbine 7b. A waste gate valve 13 for controlling pressure is arranged. Further, a catalyst device 14 for purifying exhaust gas is arranged downstream of the turbine 7b.

Between the intake system 2 and the exhaust system 3 of the engine, a first exhaust gas recirculation passage (hereinafter, EGR) for introducing exhaust gas upstream of the turbine 7b of the exhaust passage 11 downstream of the blower 7a of the intake passage 6 is provided. The first EGR passage 15 is provided with a first exhaust gas recirculation valve 16 that opens the passage 15 and recirculates exhaust gas in a predetermined high-speed high-load region of the engine. A second exhaust gas recirculation passage (EGR passage) 17 is provided for introducing exhaust gas downstream of the catalyst device 14 in the exhaust passage 11 upstream of the blower 7a of the intake passage 6 and upstream of the blower 7a of the intake passage 6. EGR
In the passage 17, a second exhaust gas recirculation valve (EGR valve) 18 that opens the passage 17 and recirculates exhaust gas in a predetermined region from a low load region to a medium load region of the engine is disposed.

The waste gate valve 16 is opened and closed by an actuator (not shown) driven by the boost pressure downstream of the blower 7a, and controls the discharge pressure (supercharging pressure) of the blower 7a to a predetermined maximum supercharging pressure to abnormal combustion. To prevent engine damage. The first and second two EGR valves 16 and 18 are controlled by a control unit 19. Therefore, an engine rotation signal is input to the control unit 19 as control information from a crank angle sensor 20 provided in the engine body 1, and an intake air amount signal is input from an air flow sensor 21 provided upstream of the blower 7a in the intake passage 6. Is done.

FIG. 2 shows a first EG for reducing the exhaust gas temperature.
The control area and control characteristics of the blower downstream EGR for controlling the opening of the R valve 16 to introduce exhaust gas downstream of the blower 7a are shown. The engine high-speed high-load region shaded in the figure is the execution region of the blower downstream EGR under the control of the first EGR valve 16. In FIG. 2, the horizontal axis is the engine speed, the vertical axis is the engine load, the lower row is the load, the upper row shows changes in the supercharging pressure and the exhaust pressure upstream of the turbine 7b, and the lower row shows the downstream of the blower. The execution area of the side EGR is shown. Here, WOT is a throttle fully open line. In addition, N ₀ indicates that the waste gate valve 13
Is the engine speed at which opening begins, that is, the intercept point, and the broken line starting from the intercept point is the wastegate valve opening line (the turbine speed, etc.). The dashed line in the figure indicates the turbine rotation limit (the number of revolutions of the turbine, etc.).

As shown in FIG. 2, until the waste gate valve 13 opens, the exhaust pressure increases and the supercharging pressure increases as the engine speed increases. At this time, the supercharging pressure is higher than the exhaust pressure. Then, when the supercharging pressure reaches a predetermined maximum supercharging pressure, the wastegate valve 13 opens, and the supercharging pressure is kept constant on the higher rotation side, and the exhaust pressure continues to rise as it is. As a result, the pressure relationship is reversed on the higher rotation side than the intercept rotation speed, and the exhaust pressure becomes higher than the supercharging pressure, and the pressure difference increases as the engine rotation speed increases. Here, the execution region of the blower downstream EGR is on the high rotation side from the waste gate valve opening line (broken line) in the drawing and is based on the turbine equal rotation speed line (L line) on the low rotation side by a certain width from the turbine rotation limit. The engine is set in a high rotation and high load region of the engine which is closer to the turbine rotation limit than the L line. In this high rotation and high load region, the first
The EGR valve 16 is opened, and exhaust gas is introduced downstream of the blower 7a, thereby reducing the exhaust gas temperature. Incidentally, N ₁ of the figure are the engine speed of the blower downstream EGR begins with Sutorroru fully open.

FIG. 3 shows the output performance when the exhaust gas temperature is reduced in the high rotation and high load region by the blower downstream EGR as described above, compared with the case where the blower upstream EGR is performed. It is a characteristic diagram. The line indicated by a solid line in the figure is a line for the number of revolutions of a turbine or the like. Now, when shifting from the point A in the area where EGR is not performed to the EGR execution area, in the case of the blower upstream EGR, it is necessary to increase the blower flow rate by the exhaust gas introduction amount in order to obtain the same fresh air introduction amount. In this case, the turbine rotation limit is the area A 'in the figure. On the other hand, when the blower downstream EGR is performed, the blower flow rate is unchanged, and the turbine rotation limit is the area A "in the figure. As described above, the blower upstream EGR
In the case of (1), the margin of boost pressure increase is small in the region where the turbine rotation limit is A ′, whereas in the case of the blower downstream EGR, the margin of boost pressure increase is large in the region of the turbine rotation limit of A ″. A large amount of EGR can be performed, or the output during EGR can be improved.

[0022]

Since the present invention is constructed as described above, the exhaust gas is introduced into the intake passage without passing through the blower in the high rotation and high load region near the turbine rotation limit of the turbocharger. A large amount of exhaust gas can be recirculated without reducing the amount of fresh air introduced into the engine, and it is possible to secure both engine output and improve reliability by reducing exhaust gas temperature.

[Brief description of the drawings]

FIG. 1 is an overall view of an embodiment of the present invention.

FIG. 2 is a diagram illustrating a control region and characteristics of a blower downstream EGR according to an embodiment of the present invention.

FIG. 3 is a graph showing a supercharging pressure-blower flow rate characteristic for explaining the effect of one embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Engine main body 6 Intake passage 7 Turbocharger 7a Blower 7b Turbine 11 Exhaust passage 12 Bypass passage 13 Wastegate valve 15 First exhaust return passage 16 First exhaust return valve 17 Second exhaust return passage 18 Second Exhaust gas recirculation valve 19 Control unit

Continuation of the front page (56) References JP-A-4-17755 (JP, A) JP-A-4-175453 (JP, A) JP-A-4-148012 (JP, A) JP-A-6-193517 (JP) , A) Japanese Utility Model 2-40960 (JP, U) Japanese Utility Model 63-115567 (JP, U) Japanese Utility Model 61-29053 (JP, U) Japanese Utility Model 56-101424 (JP, U) Japanese Utility Model 61-19666 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) F02M 25/07 570 F02M 25/07 550 F02M 25/07 580 F02B 37/00 302 F02B 37/18

Claims (3)

(57) [Claims] 1. A turbocharger comprising a turbine disposed in an exhaust passage and driven by exhaust energy and a blower disposed in an intake passage and driven by the turbine, wherein the turbine is disposed in the exhaust passage. An engine with a turbocharger provided with a bypass passage for bypassing, and a wastegate valve for opening the passage when the boost pressure downstream of the blower of the intake passage reaches a predetermined maximum supercharging pressure in the bypass passage An exhaust gas recirculation device that communicates between a turbine upstream of the exhaust gas passage and a blower downstream of the intake gas passage, an exhaust gas recirculation valve that opens and closes the exhaust gas recirculation passage, and the waste gate valve is opened. A predetermined turbine rotation speed in the engine rotation range and at a rotation speed higher than the rotation speed at which the waste gate valve starts opening the waste gate valve. An exhaust gas recirculation device for an engine with a turbocharger, comprising: a recirculation control means for controlling the exhaust gas recirculation valve so as to open the exhaust gas recirculation passage in an engine high-speed high-load region where the number is equal to or more than a number. The control means for controlling the exhaust gas recirculation valve includes a predetermined turbine rotation speed on a higher rotation speed side than the rotation speed at which the waste gate valve starts to open and a lower rotation speed side by a certain width from a turbine rotation limit for preventing damage. 2. The exhaust gas recirculation device for an engine with a turbocharger according to claim 1, wherein the exhaust gas recirculation valve is controlled to open the exhaust gas recirculation passage in an engine high-speed high-load region where the number is more than a few. 3. A second exhaust gas recirculation passage communicating between a turbine downstream of the exhaust passage and a blower upstream of the intake passage.
A second exhaust gas recirculation valve that opens and closes the exhaust gas recirculation passage, and a second exhaust gas recirculation control valve that controls the second exhaust gas recirculation control valve to open the second exhaust gas recirculation passage in a predetermined exhaust gas recirculation region outside the high-speed high-load region. 2. The exhaust gas recirculation system for a turbocharged engine according to claim 1, further comprising a control unit.