JP3341087B2 - Exhaust recirculation system for turbocharged engines - 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.

[0002]

2. Description of the Related Art Engines for automobiles and the like are generally provided with an exhaust gas recirculation device. In an ordinary operating region from a low load region to a medium load region of the engine, the engine recirculates exhaust gas (referred to as EGR) to an intake system to reduce NOx. Do. The exhaust gas recirculation device includes an exhaust gas recirculation passage that communicates the exhaust gas passage with the intake air passage, and a negative pressure operated recirculation control valve (EGR valve) that operates by introducing an intake pipe pressure (boost pressure) into the actuator chamber. it is common to configuration by) that. Also, in the case of a supercharged engine, if a normal negative pressure operated EGR valve is used, EGR cannot be performed up to a supercharging region where the boost pressure becomes a positive pressure. For example, as described in Japanese Patent Application Laid-Open No. Sho 61-43262, attempts have been made to change the control system of an engine-equipped engine so that EGR can be performed up to a supercharging region.

[0003] In addition to the EGR performed for reducing NOx from the low load range to the medium load range as described above, EGR is performed for reducing the exhaust gas temperature in a high engine speed and high load range.
Performing GR has conventionally been attempted.

[0004] Separately, in the case of a supercharged engine, a bypass passage bypassing the intercooler is provided so that the intake system is switched to a bypass passage having a small intake resistance to improve acceleration response during acceleration. Attempts have been made to do so.

[0005]

In the operating range of the engine from a low load range to a medium load range, normal EGR for reducing NOx is performed, and by expanding the EGR range to a high load range, for example, exhaust gas is reduced. Even when the temperature is to be reduced, the low-rotation side of the high-load region is an operation region where the acceleration frequency is high. In this region, it is not advisable to perform EGR that reduces the fresh air introduction amount and deteriorates the acceleration. .
In particular, in the case of a turbocharged engine, since the boost pressure in a low rotation range is poor, the EGR in a low rotation and high load region significantly deteriorates the acceleration response. Therefore, even when the EGR region is expanded to the high load side, the low rotation high load region is usually set to the non-EGR region. By the way, in order to perform EGR up to the supercharging region in the supercharged engine, it is necessary to perform EGR from the upstream side of the supercharger. In this case, if the low-speed high-load region is defined as the non-EGR region, Even if the EGR valve is closed when there is exhaust gas remaining in the intercooler volume downstream of the supercharger when the EGR valve jumps into the non-EGR region with low rotation and high load, for example, from the low load region, the exhaust gas transiently enters the engine. Since it is introduced, the amount of fresh air introduced during the acceleration transition is reduced by that amount, and a sufficient acceleration response cannot be obtained.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and is directed to a low-load EGR in a supercharged engine.
It is an object of the present invention to improve acceleration when shifting from a region to a non-EGR region with low rotation and high load.

[0007]

SUMMARY OF THE INVENTION The present invention relates to a turbocharged engine, in which an exhaust gas remaining in an intercooler when accelerating from a low-load EGR region and shifting to a low-rotation, high-load non-EGR region. It has been found that the gas causes a problem of deteriorating the acceleration response.
Based on the fact that attempts have been made to provide a bypass passage that bypasses the intercooler in order to improve the acceleration response, technology for introducing intake air bypassing the intercooler has been used in exhaust recirculation devices, and By using the passage, the intake effect in the low-rotation, high-load region is improved by the resonance effect to increase the torque. That is, the present invention provides a supercharger in which an exhaust gas recirculation passage for introducing exhaust gas upstream of a supercharger of an intake system is provided with a recirculation control valve, and the recirculation control valve controls exhaust gas recirculation in a low engine speed and low load region. An exhaust gas recirculation device for an engine
A recirculation suppressing means for suppressing recirculation of exhaust gas in a predetermined low-speed high-load region is provided, and a downstream of the supercharger is provided in the intake system.
And intercooler bypass passage that branches bypassing the supercharger downstream of the intercooler from the engine operating condition is the
Switching means for switching the intake system from the main passage side through the intercooler to the intercooler bypass passage side when shifting from the low rotation low load region to the predetermined low rotation high load region is provided, and the intercooler bypass passage is provided. D
It has a characteristic characteristic of an air column having a natural frequency tuned to the rotation speed of the engine in a low rotation range .

Further , in order to tune the natural frequency of the air column in the intercooler bypass passage to the engine speed in a low rotation range and increase the torque in the low rotation range, the diameter of the intercooler bypass passage must be reduced or the passage must be reduced. However, if the passage diameter is too small, the intake resistance will increase.Therefore, it is necessary to increase the passage length by making it approximately the same diameter as the intake passage part that connects the intercooler of the main passage and the surge tank. On the other hand, it is preferable that the intake passage portion connecting the intercooler and the surge tank is as short as possible for improving the supercharging response, and is at least shorter than the passage length of the intercooler bypass passage.

[0009]

The recirculation control valve is controlled to open in a low-speed low-load region of the engine. Then, the exhaust gas recirculation passage communicates with the opening control of the recirculation control valve, and exhaust gas is introduced upstream of the supercharger in the intake system. However, the recirculation of the exhaust gas is suppressed in a predetermined low rotation high load region. And the engine is low negative
When the vehicle accelerates from the load area and shifts to a predetermined low rotation high load area that suppresses exhaust gas recirculation, the intake system is switched to the bypass passage that bypasses the intercooler, and fresh air is supplied without passing through the intercooler. Accordingly, deterioration of the acceleration response due to the exhaust gas remaining in the intercooler at the time of acceleration being introduced into the engine is prevented. In addition, since the intake system is switched to a path that bypasses the intercooler during acceleration in this way, the intake resistance during acceleration is reduced, and the intercooler bypass passage is synchronized with the engine speed in the low rotation range. By having the air column frequency, a resonance effect is obtained in a low rotation and high load region, the intake air charge is increased, and the acceleration response is further improved.

In addition, the intercooler bypass passage has substantially the same diameter as the intake passage portion communicating the intercooler of the main passage and the surge tank, thereby suppressing an increase in intake resistance of the passage passing through the intercooler bypass passage. Since the passage length of the intake passage portion that connects the intercooler and the surge tank is shorter than the passage length of the intercooler bypass passage, an increase in intake resistance in the main passage is suppressed, and a good supercharging response is obtained.

[0011]

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

FIG . 1 is an overall view of one 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.

[0013] intake system 2 of the engine, the independent intake passage 4 for each cylinder, a surge tank 5 is located in the collection portion of their independent intake passage 4, on the upstream side to be connected to an air cleaner (not shown) the surge tank 5 An intake passage 6 upstream of the surge tank 5;
Is provided with a blower 7a of the turbocharger 7.
An intercooler 8 for cooling the supercharged air is disposed downstream of a, and a throttle valve 9 for adjusting the intake air amount by restricting the intake passage 6 immediately downstream of the surge tank 5 further downstream thereof. Have been. Further, the intake system 2 is provided with an intercooler bypass passage 10 that directly communicates the intake tank portion between the blower 7 a and the intercooler 8 with the surge tank 5 so as to bypass the intercooler 8. In the intake passage portion upstream of the intercooler 8, the intake passage portion is opened and closed immediately downstream of the position where the intercooler bypass passage 10 branches, thereby controlling the flow of intake air to the intercooler 8 side or the intercooler bypass passage 10 side. A first solenoid-operated switching valve 11 for switching the intercooler bypass passage 10 is disposed at a connection portion of the intercooler bypass passage 10 with the surge tank 5 in synchronization with the opening and closing of the first solenoid-operated switching valve. A second electromagnetic switching valve 12 that opens and closes with respect to the surge tank 5 is disposed.

[0014] The exhaust system 3 of the engine, the independent exhaust passage 13 for each cylinder, there is their independent exhaust passage 13 is constituted by the exhaust passage 14 on the downstream side of the assembled exhaust downstream thereof A turbine 7b of the turbocharger 7 that drives the blower 7a is disposed in the passage 14, and a turbine bypass passage 15 that bypasses the turbine 7b is formed. The turbine bypass passage 15 is opened and closed by opening and closing the passage 15. A wastegate valve 16 for controlling the supercharging pressure is arranged. Further, a catalyst device 17 for purifying exhaust gas is disposed downstream of the turbine 7b.

Between the intake system 2 and the exhaust system 3 of the engine, an exhaust gas recirculation passage (hereinafter, referred to as a part) for introducing a part of the exhaust gas from the downstream of the catalyst device 17 of the exhaust passage 14 upstream of the blower 7a of the intake passage 6. An EGR passage 18 is provided, and the E
The GR passage 18 is provided in a preset operation region.
Reflux control valve (hereinafter referred to as EG)
19 (referred to as an R valve).

Wastegate valve 16, EGR valve 1
9, and control of the first and second electromagnetic switching valves 11, 12 is controlled by a control unit 20, respectively. Therefore, the control unit 20 receives the engine speed, the boost pressure, and the like from each sensor (not shown) as control information.

FIG . 2 shows an EGR control region in this embodiment. The horizontal axis in the figure is the engine speed, the vertical axis is the load (boost pressure), and the shaded side is the region (EG
The R-region and the low-rotation, high-load, non-hatched region are regions where EGR is not performed (non-EGR region). Load line and full load line of the non-EGR region than atmospheric pressure line low load side (W
OT) and up to an engine speed slightly above the intercept point at which the wastegate valve opens. In the hatched area in the figure, the EGR valve 19
Is opened, the EGR passage 19 is opened, and exhaust gas is introduced into the intake system. In the non-hatched area, the EGR
The valve 18 is controlled to be closed, and the recirculation of the exhaust gas is stopped or restricted.

[0018] The first and second electromagnetic switching valve 11 is normally connected to the surge tank 5 of the intercooler bypass passage 10 is opened first electromagnetic switching valve 11 disposed upstream of the intercooler 8 When the engine is accelerated and jumps from the low load region to the non-EGR region, the non-EG
Control is performed such that the first electromagnetic switching valve 11 is closed and the second electromagnetic switching valve 12 is opened until the vehicle leaves the R region. When the first electromagnetic switching valve 11 closes and the second electromagnetic switching valve 12 opens,
An intake passage bypassing the intercooler 8 is formed by the intercooler bypass passage 10. Here, the intercooler bypass passage 10 has substantially the same diameter as that of an intake passage portion connecting the intercooler 8 and the surge tank 5, and the natural frequency of the air column of the intercooler bypass passage 10 is lower than the intercept point. The passage length is increased to synchronize with the engine speed. On the other hand, the intake passage portion between the intercooler 8 and the surge tank 5, which is the main passage, is made as short as possible in order to improve the supercharging response particularly in a high-speed high-load region.

In FIG . 2, when the vehicle is fully accelerated from a low rotation speed and low load, for example, the state of A, the state temporarily becomes the atmospheric pressure state of B,
Thereafter, as shown by the arrow, the pressure gradually increases to the set boost pressure of WOT. Then, the pressure reaches the intercept point (C) and is controlled to a constant supercharging pressure. Then, during this time, the stop or restriction of the EGR is started just before the atmospheric pressure line, and at the same time, the intake system 2 is switched to the intercooler bypass passage 10 side, and the stop or the restriction of the EGR is continued until the time passes the intercept point. , Intercooler bypass passage 1
The intake on the 0 side is continued. At this time, the acceleration performance is not hindered by the exhaust gas remaining in the intercooler 8, and the resonance effect by the intercooler bypass passage is obtained, so that the intake air filling amount is improved and the acceleration response is improved.

Although the above embodiment has been described with reference to an engine having a turbocharger, the present invention can also be applied to an engine having a mechanical supercharger.

[0021]

As described above, the present invention is configured as described above. When the engine is shifted from the EGR region to the non-EGR region by acceleration in the supercharged engine, the intake system is switched to a route bypassing the intercooler. It is possible to prevent a decrease in the intake charge amount due to the exhaust gas remaining in the intercooler and the like, and to improve the acceleration performance particularly in an engine with a turbocharger, and to increase the charge amount in a low engine speed region by a resonance effect. It is possible to compensate for the lack of supercharging in the low rotation range.

Further , by switching the intake system to a path bypassing the intercooler, the acceleration performance in the low rotation range is ensured, and the intake passage on the intercooler side is shortened to improve the supercharging response at all times. You can make it.

[Brief description of the drawings]

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

FIG. 2 is a control region diagram of EGR in one embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Engine main body 2 Intake system 3 Exhaust system 5 Surge tank 6 Intake passage 7 Turbocharger 8 Intercooler 10 Intercooler bypass passage 11 First switching valve 12 Second switching valve 16 Wastegate valve 19 EGR valve 20 Control unit

Continuation of the front page (56) References JP-A-4-136467 (JP, A) JP-A-5-99078 (JP, A) JP-A-4-34451 (JP, U) JP-A-60-57740 (JP) , U) Japanese Utility Model Showa 60-49230 (JP, U) Japanese Utility Model Showa 62-20128 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) F02M 25/07 570 F02M 25/07 550 F02B 27/00 F02B 29/04 F02B 37/18 F02D 41/00 F02D 43/00

Claims (2)

(57) [Claims] 1. A supercharger in which a recirculation control valve is provided in an exhaust recirculation passage for introducing exhaust gas upstream of a supercharger in an intake system, and the recirculation control valve controls exhaust recirculation in a low engine speed and low load region. An exhaust gas recirculation device for an engine, comprising: a recirculation suppression means for suppressing recirculation of exhaust gas in a predetermined low-speed high-load region; and an intercooler branched from a supercharger downstream to an intake system and downstream of the supercharger. An intercooler bypass passage that bypasses the engine, and the engine operating state is changed from the low-speed low-load region to the predetermined speed.
Provided switching means for switching to the intercooler bypass passage side intake system when a transition to the low speed and high load region from the main passage side through the intercooler, and the intercooler bypass passage of an engine low
An exhaust gas recirculation device for a supercharged engine, wherein the exhaust gas recirculation device has an air column natural frequency synchronized with a rotation speed in a rotation range . 2. The intercooler bypass passage has substantially the same diameter as an intake passage portion communicating the intercooler of the main passage with the surge tank, and the passage length of the intake passage portion is at least the passage length of the intercooler bypass passage. 2. The exhaust gas recirculation device for a supercharged engine according to claim 1 , wherein the exhaust gas recirculation device is shorter.