JP2009103084A - Control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control device of an internal combustion engine attaining both improvement of fuel economy and torque increase by properly combining a filling efficiency improving technique using a scavenging effect and a filling efficiency improving technique by a supercharger according to a situation. <P>SOLUTION: The control device of the internal combustion engine according to the invention mainly operates a small turbocharger 16 in a small turbocharger using region and mainly operates a large turbocharger 18 in a large turbocharger using region on a higher rotation and larger load side than the small turbocharger using region. When an exhaust pressure level is low during use of the small turbocharger 16, the filling efficiency can be improved with use of the scavenging effect by agreeing timing in which the pulsation of exhaust pressure becomes a trough with a valve overlapping period. Accordingly, when the exhaust pressure level is low, the small turbocharger using region is expanded in which the torque increase and the fuel economy improvement are both attained by the improvement of the filling efficiency using the scavenging effect and the large turbocharger using region in which a pump loss is relatively large is reduced. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a control device for an internal combustion engine.

  In Japanese Patent Application Laid-Open No. 2005-83285, the injection direction of the fuel injection valve is directed to the first intake port, the opening timing of the second intake valve that opens and closes the second intake port, and the first intake port is opened and closed. There is disclosed a valve operating device for an engine with a supercharger that is advanced by a predetermined angle with respect to the opening timing of the first intake valve. According to this device, by opening the opening timing of the second intake valve, first, in the valve overlap period in which both the exhaust valve and the intake valve are opened, the second intake valve is opened and the fuel is discharged. The inside of the cylinder is scavenged only with the supercharged fresh air that is not accompanied, and then the first intake valve is opened, so that a mixture of fresh air and atomized fuel is supplied into the cylinder. For this reason, it is described in the publication that scavenging of the cylinder with fresh air can be efficiently performed, the charging efficiency can be improved, and fuel blow-off can be prevented.

  Japanese Patent Laid-Open No. 10-176558 discloses that the center timing of the overlap period in which both the intake valve and the exhaust valve are open substantially coincides with the top dead center in the low-speed rotation and low-load operation region of the engine. In most of the operating range, the intake and exhaust valve opening and closing timings are variably controlled so that they are after top dead center, and the negative pressure wave of the exhaust pulsation is tuned at the time of overlap, thereby enhancing the scavenging effect. An engine operation control device that increases the amount of intake air and torque is disclosed.

JP 2005-83285 A JP 2007-154684 A Japanese Patent Laid-Open No. 10-176558 Japanese Patent Laid-Open No. 11-324746

  By using the scavenging effect during the valve overlap period as in the conventional technique, it is possible to improve the charging efficiency and increase the in-cylinder air amount.

  By the way, as a method of increasing the charging efficiency (in-cylinder air amount), there is a method of supercharging. However, when the supercharger is operated, the pump loss (in the case of a turbocharger) or the mechanical loss (in the case of a mechanical supercharger) increases, so that the fuel consumption tends to deteriorate. On the other hand, a method for improving the charging efficiency using the scavenging effect is preferable because it does not deteriorate the fuel consumption.

  On the other hand, the method for improving the filling efficiency using the scavenging effect has the following problems. For the scavenging effect to occur, the exhaust pressure must be lower than the intake pressure at least during the valve overlap period. Therefore, when this condition is not satisfied, the filling efficiency cannot be improved by using the scavenging effect. For example, in the case of a system equipped with an exhaust filter that collects particulate matter such as PM (Particulate Matter), if the exhaust filter clogs, the exhaust pressure level rises. In some cases, the differential pressure between the pressure and the exhaust pressure becomes small, or the exhaust pressure becomes higher than the intake pressure. In such a case, there is a problem that the scavenging effect is not exhibited and the torque cannot be increased.

  The present invention has been made in view of the above points. By appropriately combining a charging efficiency improvement method using a scavenging effect and a charging efficiency improvement method using a supercharger according to the situation, fuel consumption improvement and torque can be improved. It is an object of the present invention to provide a control device for an internal combustion engine that can achieve both increase.

In order to achieve the above object, a first invention is a control device for an internal combustion engine,
A turbocharger,
Supercharger switching means that does not substantially operate the supercharger in the first operation region, and operates the supercharger in the second operation region on the high rotation high load side from the first operation region; ,
Exhaust pressure level determining means for determining whether the exhaust pressure level is lower than a predetermined level;
When the exhaust pressure level is lower than the predetermined level, compared with a case where the exhaust pressure level is higher than the predetermined level, region changing means for expanding the first operating region and reducing the second operating region;
A charging efficiency improving means for providing a valve overlap period in which the intake valve opening period and the exhaust valve opening period overlap, and matching the timing at which the pulsation of the exhaust pressure becomes a valley with the valve overlap period;
It is characterized by providing.

The second invention is a control device for an internal combustion engine,
A small turbocharger,
A large supercharger having a larger capacity than the small supercharger;
The supercharger that mainly operates the small supercharger in the small supercharger use region, and that mainly operates the large supercharger in the large supercharger use region on the high rotation and high load side from the small supercharger use region. Switching means;
Exhaust pressure level determining means for determining whether the exhaust pressure level is lower than a predetermined level;
Region change means for expanding the small supercharger use region and reducing the large supercharger use region when the exhaust pressure level is lower than the predetermined level, compared to when the exhaust pressure level is higher than the predetermined level When,
A charging efficiency improving means for providing a valve overlap period in which the intake valve opening period and the exhaust valve opening period overlap, and matching the timing at which the pulsation of the exhaust pressure becomes a valley with the valve overlap period;
It is characterized by providing.

The third invention is the second invention, wherein
Each of the small supercharger and the large supercharger is a turbocharger having a turbine operated by exhaust gas,
The turbine of the large supercharger is disposed downstream of the turbine of the small supercharger.

Moreover, 4th invention is set in 3rd invention,
The supercharger switching means is
A small turbine bypass passage for bypassing the turbine of the small supercharger and passing exhaust gas;
A small turbine bypass passage opening / closing valve for opening and closing the small turbine bypass passage;
Including
The small turbine bypass passage on-off valve is closed in the small turbocharger use region, and the small turbine bypass passage on-off valve is opened in the large supercharger use region.

The fifth invention is the fourth invention, wherein
The supercharger switching means is
A large turbine bypass passage for bypassing the turbine of the large supercharger and passing exhaust gas;
A large turbine bypass passage opening / closing valve for opening and closing the large turbine bypass passage;
Further including
In the small turbocharger use region, the small turbine bypass passage on / off valve is closed and the large turbine bypass passage on / off valve is opened, and in the large supercharger use region, the small turbine bypass passage on / off valve is opened and the large turbocharger is opened. The turbine bypass passage on-off valve is closed.

  According to the first invention, when the exhaust pressure level is low, the exhaust pressure is made lower than the intake pressure in the valve overlap period by matching the timing when the pulsation of the exhaust pressure becomes a valley with the valve overlap period. Therefore, the charging efficiency (torque) can be improved by utilizing the scavenging effect. Therefore, in the first invention, when the exhaust pressure level is low, the first operating region in which the supercharger is not substantially used is expanded and the supercharger is used, compared with the case where the exhaust pressure level is high. The second operation area is reduced. As a result, the benefits of improved charging efficiency (torque increase) due to the scavenging effect that does not adversely affect fuel consumption can be enjoyed in a wider area, and the use area of the turbocharger that increases pump loss or mechanical loss is narrowed. be able to. For this reason, both fuel consumption improvement and torque increase can be achieved. Further, when the exhaust pressure level is high and the improvement of charging efficiency (torque increase) due to the scavenging effect cannot be expected, the use range of the supercharger can be expanded. Thereby, even if it is a case where an exhaust pressure level is high, the fall of a torque can be suppressed reliably.

  According to the second invention, when the exhaust pressure level is low, the exhaust pressure is made lower than the intake pressure in the valve overlap period by matching the timing when the pulsation of the exhaust pressure becomes a valley with the valve overlap period. Therefore, the charging efficiency (torque) can be improved by utilizing the scavenging effect. Therefore, in the second invention, when the exhaust pressure level is low, compared with the case where the exhaust pressure level is high, the use range of the small supercharger capable of improving the charging efficiency (torque increase) by the scavenging effect is expanded, and the large Reduce the turbocharger usage area. As a result, the benefits of improved charging efficiency due to the scavenging effect that does not adversely affect fuel consumption can be enjoyed in a wider area, and the use area of large turbochargers that increase pump loss or mechanical loss can be reduced. . For this reason, both fuel consumption improvement and torque increase can be achieved. In addition, when the exhaust pressure level is high and improvement in charging efficiency (torque increase) due to the scavenging effect cannot be expected, the use range of the large turbocharger that can obtain a high supercharging pressure can be expanded. Thereby, even if it is a case where an exhaust pressure level is high, the fall of a torque can be suppressed reliably.

  In the third invention, the turbine of the large turbocharger is disposed downstream of the turbine of the small turbocharger. When a large turbocharger is used, the exhaust path to the turbine becomes long and the exhaust system volume increases. For this reason, the pulsation of the exhaust pressure becomes weak, and an improvement in charging efficiency (torque increase) due to the scavenging effect cannot be expected. On the other hand, when the small turbocharger is used, the exhaust system volume is reduced and the pulsation of the exhaust pressure can be increased. Therefore, if the exhaust pressure level is low, the charging efficiency can be improved by the scavenging effect. According to the third invention, when the exhaust pressure level is low, the charging efficiency can be improved by the scavenging effect, and the usage area of the small turbocharger with low pump loss is expanded. can do. Further, when the exhaust pressure level is high and the improvement of the charging efficiency due to the scavenging effect cannot be expected, the use range of the large turbocharger that can obtain a high supercharging pressure can be expanded. Thereby, even if it is a case where an exhaust pressure level is high, the fall of a torque can be suppressed reliably.

  According to the fourth aspect of the present invention, the small turbine bypass passage on-off valve is closed in the small turbocharger use region, and the small turbine bypass passage on-off valve is opened in the large supercharger use region. The turbocharger and the large turbocharger can be switched smoothly and reliably.

  According to the fifth aspect of the invention, the small turbine bypass passage opening / closing valve is closed and the large turbine bypass passage opening / closing valve is opened in the small turbocharger usage region, and the small turbine bypass passage opening / closing valve is opened in the large turbocharger usage region. By closing the large turbine bypass passage on-off valve, the small turbocharger and the large turbocharger can be switched smoothly and reliably with a simple structure. Further, when the small turbocharger is used, the exhaust pressure can be made to flow by bypassing the turbine of the large turbocharger, so that the back pressure can be lowered. For this reason, when the scavenging effect during the valve overlap period is used to improve the charging efficiency (torque), the differential pressure between the intake pressure and the exhaust pressure can be sufficiently increased, so that the scavenging effect is more reliably achieved. Obtainable.

  Embodiments of the present invention will be described below with reference to the drawings. In addition, the same code | symbol is attached | subjected to the element which is common in each figure, and the overlapping description is abbreviate | omitted.

Embodiment 1 FIG.
[Description of system configuration]
FIG. 1 is a diagram for explaining a system configuration according to the first embodiment of the present invention. The system shown in FIG. 1 includes a four-cycle diesel engine 10. It is assumed that the diesel engine 10 is mounted on a vehicle and used as a power source. The exhaust gas discharged from each cylinder of the diesel engine 10 is collected by the exhaust manifold 12 and flows into the exhaust passage 14. In addition, although the diesel engine 10 of this embodiment is an inline 4-cylinder type, the number of cylinders and cylinder arrangement | positioning of a diesel engine in this invention are not limited to this.

  The diesel engine 10 of the present embodiment includes a small turbocharger 16 and a large turbocharger 18 having a larger capacity (suitable for high flow rate) than the small turbocharger 16. As will be described later, in the diesel engine 10, the small turbocharger 16 is used in the operation region on the relatively low rotation / low load side, and the large turbocharger 18 is used in the operation region on the relatively high rotation / high load side. Is done.

  The turbine 18 a of the large turbocharger 18 is disposed on the downstream side of the turbine 16 a of the small turbocharger 16. That is, the exhaust passage 14 immediately below the exhaust manifold 12 is connected to the inlet of the turbine 16 a of the small turbocharger 16. The exhaust passage 17 extending from the outlet of the turbine 16 a of the small turbocharger 16 is connected to the inlet of the turbine 18 a of the large turbocharger 18.

  The exhaust passage 14 on the upstream side of the turbine 16 a of the small turbocharger 16 and the exhaust passage 17 on the downstream side are connected by a small turbine bypass passage 20. In the middle of the small turbine bypass passage 20, an on-off valve 22 that opens and closes this passage is installed.

  In addition, the upstream exhaust passage 17 and the downstream exhaust passage 19 of the turbine 18 a of the large turbocharger 18 are connected by a large turbine bypass passage 24. In the middle of the large turbine bypass passage 24, an on-off valve 26 for opening and closing the passage is installed.

  In the middle of the exhaust passage 19 on the downstream side of the turbine 18 a of the large turbocharger 18, an exhaust filter 28 for capturing particulate matter in the exhaust gas (hereinafter represented by “PM (Particulate Matter)”). Is provided. Although illustration is omitted, an exhaust purification catalyst may be provided upstream or downstream of the exhaust filter 28. Further, the exhaust filter 28 may carry a catalyst component.

  In the vicinity of the exhaust filter 28, a differential pressure sensor 30 for detecting a differential pressure between the upstream pressure and the downstream pressure of the exhaust filter 28 is installed. As PM accumulates in the exhaust filter 28 and the ventilation resistance of the exhaust filter 28 increases, the differential pressure detected by the differential pressure sensor 30 increases. Therefore, the PM accumulation amount (degree of clogging) in the exhaust filter 28 can be detected by the differential pressure sensor 30. When the amount of accumulated PM (the degree of clogging) in the exhaust filter 28 exceeds a predetermined reference value, PM regeneration control for burning and removing the PM collected in the exhaust filter 28 is performed. In PM regeneration control, unburned fuel is circulated through the exhaust passage 14 by a method such as post-injection or exhaust system fuel addition, and the unburned fuel is burned by the exhaust filter 28 so that the exhaust filter 28 has a temperature of about 600 ° C., for example. Keep it hot.

  An air cleaner 34 is provided near the inlet of the intake passage 32 of the diesel engine 10. The intake passage 32 is branched downstream of the air cleaner 34 into a first passage 32a and a second passage 32b. The compressor 16b of the small turbocharger 16 is disposed in the middle of the first passage 32a, and the compressor 18b of the large turbocharger 18 is disposed in the middle of the second passage 32b. The first passage 32 a and the second passage 32 b are joined again on the downstream side of the compressors 16 b and 18 b and connected to the intercooler 36. An intake passage 32 on the downstream side of the intercooler 36 is connected to an intake manifold 38.

  The air sucked through the air cleaner 34 is compressed by the compressor 16 b of the small turbocharger 16 or the compressor 18 b of the large turbocharger 18, cooled by the intercooler 36, and passed through the intake manifold 38 to each cylinder. Flow into.

  The system of the present embodiment further includes an ECU (Electronic Control Unit) 50. The ECU 50 includes various sensors such as the above-described on-off valves 22 and 26, the differential pressure sensor 30, and an accelerator position sensor 40 that detects the depression amount (accelerator opening) of an accelerator pedal of a vehicle on which the diesel engine 10 is mounted. The actuator is electrically connected. The ECU 50 controls the operating state of the diesel engine 10 by operating each actuator according to a predetermined program based on the output of each sensor.

  FIG. 2 is a view showing a cross section of one cylinder of the diesel engine 10 in the system shown in FIG. Hereinafter, the diesel engine 10 of the present embodiment will be further described. The cylinder of the diesel engine 10 is provided with an injector 42 that directly injects fuel into the cylinder. The injector 42 of each cylinder is connected to a common rail (not shown). The common rail stores high-pressure fuel pressurized by a supply pump (not shown). Then, fuel is supplied from the common rail to the injector 42 of each cylinder.

  A crank angle sensor 46 for detecting the rotation angle of the crankshaft 44 is attached in the vicinity of the crankshaft 44 of the diesel engine 10. The ECU 50 can calculate the engine speed based on the signal from the crank angle sensor 46.

  The diesel engine 10 also includes an exhaust VVT mechanism (exhaust variable valve operating device) 58 that makes the valve timing of the exhaust valve 56 variable. The exhaust VVT mechanism 58 of the present embodiment can increase or decrease the phase of the valve opening period of the exhaust valve 56 by changing the phase of the camshaft that drives the exhaust valve 56. That is, according to the exhaust VVT mechanism 58, the exhaust valve opening timing (Exhaust Valve Open: EVO) and the exhaust valve closing timing (Exhaust Valve Close: EVC) are continuously advanced or retarded while the valve opening period remains constant. You can do it. The exhaust VVT mechanism 58 is connected to the ECU 50.

The exhaust variable valve operating apparatus according to the present invention is not limited to the exhaust VVT mechanism 58. That is, the exhaust variable valve operating apparatus according to the present invention may have any configuration as long as it can change at least the opening timing of the exhaust valve 56 continuously or stepwise. Things can also be used.
(1) A working angle variable mechanism that changes the opening timing of the exhaust valve 56 together with the working angle (valve opening period) by interposing a swing cam or the like between the exhaust valve 56 and the camshaft.
(2) A mechanism that allows the exhaust valve 56 to be opened and closed at an arbitrary time by rotationally driving a cam for opening the exhaust valve 56 by an electric motor.
(3) A mechanism (electromagnetically driven valve) that can open and close at any time by driving the exhaust valve 56 by electromagnetic force.

  In the configuration of FIG. 2, the diesel engine 10 further includes an intake VVT mechanism (intake variable valve operating device) 54 that makes the valve timing of the intake valve 52 variable, but in the present invention, the intake valve 52 is opened. The valve characteristic may be fixed. That is, in the present invention, the intake valve 52 may be driven by a normal valve mechanism without providing the intake VVT mechanism 54.

[Features of Embodiment 1]
(Supercharger switching control)
In general, in an internal combustion engine equipped with a turbocharger, the turbine does not operate effectively in the low-revolution / low-load operation region where the exhaust energy is small, resulting in torque shortage, fuel consumption deterioration, response deterioration (so-called turbo lag), etc. There is a problem that it is easy.

  On the other hand, in the diesel engine 10 of the present embodiment, the small turbocharger 16 is used in the operation region on the low rotation / low load side where the exhaust energy is small, and the operation region on the high rotation / high load side where the exhaust energy is large. A turbocharger 18 is used. Since the small turbocharger 16 has a smaller capacity than the large turbocharger 18, it operates effectively even with a small exhaust energy. For this reason, in the diesel engine 10 of the present embodiment, supercharging can be performed satisfactorily even in the operation region on the low rotation and low load side, and characteristics such as torque, fuel consumption, and responsiveness can be sufficiently improved. . This point will be further described with reference to FIG.

  FIG. 3 is a diagram illustrating the supercharging characteristics of the small turbocharger 16 and the large turbocharger 18. As shown in the figure, the small turbocharger 16 generates a higher supercharging pressure than the large turbocharger 18 in the low exhaust energy side (low rotation, low load side) region. In contrast, in the region on the high exhaust energy side, the supercharging pressure of the small turbocharger 16 reaches a peak. On the other hand, the supercharging pressure of the large turbocharger 18 increases as the exhaust energy increases. Therefore, by operating the small turbocharger 16 in the region on the low exhaust energy side and operating the large turbocharger 18 in the region on the high exhaust energy side, a high supercharging pressure can be obtained in the entire region.

  The exhaust energy on the horizontal axis in FIG. 3 is determined by the amount, temperature, and pressure of the exhaust gas, and is a value that increases as the engine speed increases with high rotation. Further, the supercharging characteristic of the small turbocharger 16 in FIG. 3 is obtained when the charging efficiency improvement control described later is not executed.

  Hereinafter, an operation region in which the small turbocharger 16 is operated is referred to as a “small turbo use region”, and an operation region in which the large turbocharger 18 is operated is referred to as a “large turbo use region”. The ECU 50 stores a map that defines a small turbo usage area and a large turbo usage area. Then, the ECU 50 calculates the rotational speed and load of the diesel engine 10 from the detection signals of the crank angle sensor 46 and the accelerator position sensor 40, and when the operating point defined by the rotational speed and load is in the small turbo use region. Uses the small turbocharger 16 and executes the supercharger switching control using the large turbocharger 18 when the operating point is in the large turbo use region.

  In the small turbo usage region, the open / close valve 22 provided in the small turbine bypass passage 20 is closed and the open / close valve 26 provided in the large turbine bypass passage 24 is opened. In this state, the exhaust gas from the exhaust manifold 12 first flows into the turbine 16a of the small turbocharger 16 to operate the turbine 16a. The exhaust gas flow path exiting the turbine 16 a is divided into a turbine 18 a of the large turbocharger 18 and a large turbine bypass passage 24 because the on-off valve 26 is open. However, most of the exhaust gas exiting the turbine 16a flows into the large turbine bypass passage 24 having a small ventilation resistance. For this reason, the turbine 18a of the large turbocharger 18 does not substantially operate. In this way, the small turbocharger 16 mainly operates in the small turbo usage region.

  On the other hand, in the large turbo usage region, the open / close valve 22 provided in the small turbine bypass passage 20 is opened, and the open / close valve 26 provided in the large turbine bypass passage 24 is closed. In this state, since the on-off valve 22 is open, the flow path of the exhaust gas flowing in from the exhaust manifold 12 is divided into the turbine 16 a of the small turbocharger 16 and the small turbine bypass passage 20. However, most of the exhaust gas from the exhaust manifold 12 flows into the small turbine bypass passage 20 having a low ventilation resistance. For this reason, the turbine 16a of the small turbocharger 16 does not substantially operate. The exhaust gas that has passed through the small turbine bypass passage 20 and has flowed into the exhaust passage 17 then flows into the turbine 18a of the large turbocharger 18 to operate the turbine 18a. In this way, the large turbocharger 18 mainly operates in the large turbo usage region.

(Filling efficiency improvement control)
In addition, the system of the present embodiment uses a scavenging effect in a valve overlap period (near intake and exhaust top dead center) where the valve opening period of the exhaust valve 56 and the valve opening period of the intake valve 52 overlap. The filling efficiency improvement control for improving the filling efficiency η _{v of} 10 can be executed. FIG. 4 is a diagram for explaining the filling efficiency improvement control.

  The exhaust pressure (exhaust manifold pressure) pulsates (fluctuates) as the exhaust gas is intermittently discharged from the exhaust valve 56 of each cylinder. The broken line waveform in FIG. 4 indicates the pulsation of the exhaust pressure when the exhaust VVT mechanism 58 is controlled so that the exhaust valve opening timing becomes the base timing. As shown in this waveform, when the exhaust valve opening timing is controlled to be the base timing, the exhaust pressure pulsation valley timing is the intake valve opening timing (Intake Valve Open: IVO). It is the time before.

  On the other hand, the solid line waveform in FIG. 4 shows the pulsation of the exhaust pressure when the exhaust VVT mechanism 58 is controlled so that the exhaust valve opening timing is later than the base timing. As the exhaust valve opening timing is delayed, the timing at which the exhaust gas is discharged to the exhaust port is delayed. Therefore, the waveform (phase) of the exhaust pressure shifts to the right in FIG. Therefore, by appropriately setting the amount by which the exhaust valve opening timing is delayed, as shown in FIG. 4, the timing of the valley of the pulsation of the exhaust pressure can be matched with the valve overlap period. In the charging efficiency improvement control, as described above, the exhaust valve pulsation valley timing is controlled to coincide with the valve overlap period by delaying the exhaust valve opening timing from the base.

On the other hand, the alternate long and short dash line in FIG. 4 indicates the intake pressure (intake manifold pressure). As shown in FIG. 4, the intake pressure is substantially constant regardless of the crank angle. For this reason, if the timing of the trough of the exhaust pressure pulsation coincides with the valve overlap period by executing the filling efficiency improvement control, the intake pressure can be made higher than the exhaust pressure in the valve overlap period. For this reason, when the intake valve 52 is opened, the burned gas in the cylinder can be quickly expelled to the exhaust port by the fresh air flowing into the cylinder from the intake valve 52. In this way, a high scavenging effect can be obtained, and the burned gas in the cylinder can be smoothly and reliably replaced with fresh air. As a result, the residual gas can be sufficiently reduced, and the amount of fresh air filled in the cylinder can be increased accordingly. That is, the charging efficiency η _v can be increased, and the torque of the diesel engine 10 can be increased.

  In the system of the present embodiment, the effect of the charging efficiency improvement control as described above can be sufficiently obtained when the small turbocharger 16 is used. On the other hand, in the state where the large turbocharger 18 is used, the effect of the above-described charging efficiency improvement control cannot be sufficiently obtained. The reason is as follows.

  The pulsation of the exhaust pressure becomes stronger (the amplitude becomes smaller) as the volume of the exhaust manifold 12 and the space communicating with the exhaust manifold 12 (hereinafter collectively referred to as “exhaust system volume”) is smaller. This is because the smaller the exhaust system volume, the higher the exhaust manifold pressure when exhaust gas is discharged from the exhaust valve 56, and the lower the exhaust manifold pressure in the latter stage of the exhaust stroke. Conversely, the larger the exhaust system volume, the weaker the exhaust pressure pulsation (the smaller the amplitude).

  In the state where the small turbocharger 16 is used, the on-off valve 20 is closed, so that the exhaust gas does not flow through the small turbine bypass passage 20. The exhaust pressure wave is reflected at the inlet of the turbine 16 a of the small turbocharger 16. For this reason, since the exhaust system volume reaches the inlet of the turbine 16a of the small turbocharger 16, the exhaust system volume becomes small. Therefore, the amplitude of the pulsation of the exhaust pressure becomes large, and the exhaust pressure at the valley of the pulsation becomes sufficiently low. For this reason, since the differential pressure between the intake pressure and the exhaust pressure can be sufficiently increased during the valve overlap period, the scavenging effect is sufficiently exhibited, and the charging efficiency and torque can be sufficiently improved.

  On the other hand, when the large turbocharger 18 is used, the on-off valve 20 is opened, so that the exhaust passage 17 communicates with the exhaust manifold 12 via the small turbine bypass passage 20. In this case, the pressure wave of the exhaust is reflected at the inlet of the turbine 18 a of the large turbocharger 18. For this reason, the exhaust system volume is up to the inlet of the turbine 18a of the large turbocharger 18. Therefore, the small turbine bypass passage 20 and the exhaust passage 17 are added to the exhaust system volume, and the exhaust system volume is expanded. As a result, the amplitude of the pulsation of the exhaust pressure is reduced, the exhaust pressure at the valley of the pulsation is not lowered, and the differential pressure between the intake pressure and the exhaust pressure cannot be sufficiently increased during the valve overlap period. For this reason, the scavenging effect is not sufficiently exhibited, and the filling efficiency and the torque cannot be sufficiently improved.

  As described above, in the present embodiment, when the small turbocharger 16 is used, the air amount and the torque can be increased by the charging efficiency improvement control. However, in order for the effect of the filling efficiency improvement control to occur, the exhaust pressure needs to be sufficiently lower than the intake pressure during the valve overlap period. For this reason, when the exhaust pressure level (average exhaust pressure) increases due to clogging of the exhaust filter 28, the exhaust pressure is not sufficiently lower than the intake pressure during the valve overlap period, and the charging efficiency is improved. The effectiveness of the control is reduced.

  That is, under the situation where the PM accumulation amount of the exhaust filter 28 increases and the ventilation resistance of the exhaust filter 28 increases, the waveform of the exhaust pressure as shown in FIG. 4 increases in the pressure increasing direction (upward in FIG. 4). shift. For this reason, even if the timing of the pulsation valley of the exhaust pressure is matched with the valve overlap period, the intake pressure cannot be made sufficiently lower than the exhaust pressure or the exhaust pressure is larger than the intake pressure. It becomes. In such a case, since the scavenging effect is hardly exhibited, the air amount and torque cannot be sufficiently increased.

  As described above, the air amount characteristics when the small turbocharger 16 is used and when the large turbocharger 18 is used are as shown in FIG. The solid line graph in FIG. 5 is the air amount characteristic when the small turbocharger 16 is used when the exhaust pressure level is high (when the PM accumulation amount of the exhaust filter 28 is large), and the broken line graph in FIG. Fig. 5 is an air amount characteristic when the small turbocharger 16 is used when the exhaust pressure level is low (when the PM accumulation amount of the exhaust filter 28 is small), and the one-dot chain line graph in Fig. 5 shows the large turbocharger. This is an air amount characteristic when the machine 18 is used.

  As described above, when the small turbocharger 16 is used, when the exhaust pressure level is low, the effect of the charging efficiency improvement control is sufficiently exhibited, whereas when the exhaust pressure level is high, the charging efficiency is improved. The control effect is difficult to be demonstrated. Therefore, as can be seen from FIG. 5, when the small turbocharger 16 is used, the air amount and torque can be increased when the exhaust pressure level is low compared to when the exhaust pressure level is high.

  On the other hand, when the large turbocharger 18 is used, as described above, the effect of the charging efficiency improvement control is hardly obtained. For this reason, the air quantity characteristics when the large turbocharger 18 is used are the same whether the exhaust pressure level is high or low.

  In the supercharger switching control, the optimum point for switching from the state where the small turbocharger 16 is used to the state where the large turbocharger 18 is used is a point where the air quantity characteristics of both are reversed. Therefore, the optimum switching point when the exhaust pressure level is high is a point A where the solid line and the alternate long and short dash line intersect in FIG. On the other hand, the optimum switching point when the exhaust pressure level is low is a point B where the broken line and the alternate long and short dash line intersect in FIG. As can be seen from FIG. 5, the point B (optimal switching point when the exhaust pressure level is low) is higher than the point A (optimal switching point when the exhaust pressure level is high). It is on the rotating high load side. Thus, when the exhaust pressure level is low, the optimum supercharger switching point is shifted to the high rotation high load side as compared with the case where the exhaust pressure level is high. For this reason, when the exhaust pressure level is low, it is ideal to shift the switching point between the small turbocharger 16 and the large turbocharger 18 to the high rotation and high load side as compared with the case where the exhaust pressure level is high. It is.

  FIG. 6 is a map used by the ECU 50 in the present embodiment to realize the above ideal. The solid line in FIG. 6 is a line connecting the optimum supercharger switching points when the exhaust pressure level is high. When the ECU 50 detects that the exhaust pressure level is higher than a predetermined determination level, the ECU 50 detects that the low rotation and low load side is the small turbo use region and the high rotation and high load side is the large turbo, with the solid line in FIG. As a use area, supercharger switching control is executed.

  On the other hand, the broken line in FIG. 6 is a line connecting optimum turbocharger switching points when the exhaust pressure level is low. When it is detected that the exhaust pressure level is lower than the above judgment level, the ECU 50 uses the low-revolution / low-load side as a small turbo use area and the high-revolution / high load side as a large turbo, with the broken line in FIG. As a region, supercharger switching control is executed.

  That is, in the present embodiment, when the exhaust pressure level is lower than the determination level, the small turbo use area is expanded and the large turbo use area is reduced as compared with the case where the exhaust pressure level is higher than the determination level. Thus, whether the exhaust pressure level is high or low, the small turbocharger 16 and the large turbocharger 16 are large at the optimum switching point, that is, the point at which the transient air amount can be maximized. The turbocharger 18 can be switched.

  On the other hand, unlike the present invention, when the supercharger switching line is always constant, the transient air amount cannot be maximized. For example, in FIG. 5, assuming that the turbocharger is switched at the optimum switching point when the exhaust pressure level is low, that is, when the charging efficiency can be improved due to the scavenging effect, the exhaust pressure level is high, the air amount is The route changes from C to point A to point B. For this reason, compared with the case where it switches to the small turbocharger 16 at the point B which is the original optimum switching point, a transient decrease in the air amount is caused by the area represented by the triangle ABC in FIG. . On the other hand, according to the control of the present embodiment, since the use of the small turbocharger 16 is continued up to the point B, the benefit of the charging efficiency improvement control can be obtained up to the point B. As a result, the amount of air changes along the path from point C to point B. That is, it is possible to avoid a transient decrease in the air amount.

  On the other hand, in FIG. 5, assuming that the turbocharger is switched at the optimum switching point when the exhaust pressure level is high, that is, when the charging efficiency cannot be improved due to the scavenging effect, the exhaust pressure level is low. Changes as point A → point D → point B. For this reason, compared with the case where it switches to the large turbocharger 18 at the point A which is the original optimum switching point, the transient air amount is reduced by the area represented by the triangle ABD in FIG. On the other hand, according to the control of the present embodiment, by switching to the large turbocharger 18 at the point A, the supercharging by the large turbocharger 18 can be started early. As a result, insufficient improvement of the charging efficiency using the scavenging effect can be compensated for by supercharging by the large turbocharger 18, and the air amount changes along the path from point A to point B. That is, it is possible to avoid a transient decrease in the air amount as described above.

  By the way, when the turbocharger is operated, the pump loss of the internal combustion engine generally increases. This increase in pump loss acts in the direction of worsening the fuel consumption of the internal combustion engine. In the system of the present embodiment, the pump loss is smaller in the state where the small turbocharger 16 is used than in the state where the large turbocharger 18 is used. For this reason, it is more advantageous to use the small turbocharger 16 from the viewpoint of fuel consumption. On the other hand, the charging efficiency improvement control using the scavenging effect does not adversely affect the fuel consumption.

  As described above, according to the present embodiment, when the exhaust pressure level is lower than the determination level, that is, when the charging efficiency improvement control using the scavenging effect is effective, the small turbocharger with better fuel efficiency is provided. The use area of the machine 18 can be expanded, and the benefits of filling efficiency improvement control can be enjoyed in a wider range. For this reason, fuel consumption can be reduced sufficiently.

  Regarding the detection method of the exhaust pressure level, in the present embodiment, utilizing the fact that there is a correlation between the differential pressure before and after the exhaust filter 28 detected by the differential pressure sensor 30 and the exhaust pressure level, The exhaust pressure level can be calculated from the differential pressure detected by the differential pressure sensor 30. In the present invention, the method of detecting the exhaust pressure level is not limited to the above method. For example, a sensor for detecting the exhaust manifold pressure is provided, and the exhaust pressure level (average exhaust pressure) is determined from the detection value of the sensor. You may make it calculate.

  In the example shown in FIG. 6, the supercharger switching line (the boundary between the small turbo use area and the large turbo use area) is changed in two stages according to the level of the exhaust pressure level. The supercharger switching line may be changed in multiple stages or continuously according to the exhaust pressure level.

  Further, in this embodiment, when the small turbocharger 16 is used, the exhaust gas can be allowed to flow by bypassing the turbine 18a of the large turbocharger 18, so that the back pressure can be lowered. . For this reason, when the scavenging effect during the valve overlap period is used to improve the charging efficiency (torque), the differential pressure between the intake pressure and the exhaust pressure can be sufficiently increased, so that the scavenging effect is more reliably achieved. Obtainable. On the other hand, in this invention, the structure which is not provided with the large turbine bypass channel 24 and the on-off valve 26 which opens and closes this may be sufficient. In the case where the large turbine bypass passage 24 and the on-off valve 26 are not provided, in the small turbo usage region, the exhaust gas after the energy is recovered by the turbine 16a of the small turbocharger 16 (that is, the exhaust gas having a small exhaust energy). Will flow into the turbine 18a of the large turbocharger 18, the large turbocharger 18 will not operate effectively, and the small turbocharger 16 will mainly operate. Further, even in the case where the large turbine bypass passage 24 and the on-off valve 26 are not provided, a variable nozzle (not shown) that makes the inlet area of the turbine 18a of the large turbocharger 18 variable in the small turbo use region. It is also possible to obtain an effect that is relatively close to the case where there is the large turbine bypass passage 24 by reducing the back pressure by a method such as opening).

  Moreover, although this embodiment demonstrated the case where this invention was applied to control of a diesel engine (compression ignition internal combustion engine), this invention is not limited to control of a diesel engine, and is a spark ignition internal combustion engine. It is also possible to apply to control.

  In the present embodiment, the case where the supercharger is a turbocharger has been described. However, the present invention also applies to a case where the supercharger is a mechanical supercharger driven by the output shaft of the internal combustion engine. Applicable. When a small supercharger and a large supercharger are provided as in the system of this embodiment, even if one is a mechanical supercharger and the other is a turbocharger, both are mechanical superchargers. It may be a feeder.

  Further, in the present embodiment, a system including a small supercharger and a large supercharger has been described as an example. However, in the present invention, there is one supercharger, and supercharging is performed in an operation region on a low rotation / low load side. It is also applicable to a system that uses a supercharger in the operating region on the high rotation high load side without using a machine.

  In the present embodiment, the small turbocharger 16 is the “small supercharger” in the second invention, and the large turbocharger 18 is the “supercharger” and the second in the first invention. In the “large turbocharger” in the invention of the present invention, the small turbo use area is in the “first operation area” in the first invention and the “small turbocharger use area” in the second invention. Corresponds to the “second operating region” in the first invention and the “large turbocharger use region” in the second invention, respectively. Further, the “supercharger switching means” in the first and second aspects of the present invention is obtained when the ECU 50 switches between the usage state of the small turbocharger 16 and the usage state of the large turbocharger 18 according to the map shown in FIG. By determining whether the exhaust pressure level calculated from the differential pressure detected by the differential pressure sensor 30 is higher or lower than a predetermined determination level, the “exhaust pressure level determining means” in the first and second inventions By changing the supercharger switching line in the map shown in FIG. 6 on the basis of the exhaust pressure level, the “region changing means” in the first and second inventions causes the exhaust VVT so that scavenging occurs during the valve overlap period. The “filling efficiency improving means” in the first and second inventions by controlling the mechanism 58 (further, if necessary, the intake VVT mechanism 54), respectively. It has been realized.

It is a figure for demonstrating the system configuration | structure of Embodiment 1 of this invention. It is a figure which shows the cross section of one cylinder of the diesel engine in the system of Embodiment 1 of this invention. It is a figure which shows each supercharging characteristic of a small turbocharger and a large turbocharger. It is a figure for demonstrating filling efficiency improvement control. It is a figure which shows the air quantity characteristic at the time of use of a small turbocharger and a large turbocharger. It is a map which shows a small turbo use area and a large turbo use area.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Diesel engine 12 Exhaust manifold 14, 17, 19 Exhaust passage 16 Small turbocharger 16a Turbine 16b Compressor 18 Large turbocharger 18a Turbine 18b Compressor 20 Small turbine bypass passage 22 Open / close valve 24 Large turbine bypass passage 26 Open / close valve 28 Exhaust filter 30 Differential pressure sensor 32 Intake passage 34 Air cleaner 36 Intercooler 38 Intake manifold 50 ECU
52 Intake Valve 54 Intake VVT Mechanism 56 Exhaust Valve 58 Exhaust VVT Mechanism

Claims (5)

A turbocharger,
Supercharger switching means that does not substantially operate the supercharger in the first operation region, and operates the supercharger in the second operation region on the high rotation high load side from the first operation region; ,
Exhaust pressure level determining means for determining whether the exhaust pressure level is lower than a predetermined level;
When the exhaust pressure level is lower than the predetermined level, compared with a case where the exhaust pressure level is higher than the predetermined level, region changing means for expanding the first operating region and reducing the second operating region;
A charging efficiency improving means for providing a valve overlap period in which the intake valve opening period and the exhaust valve opening period overlap, and matching the timing at which the pulsation of the exhaust pressure becomes a valley with the valve overlap period;
A control device for an internal combustion engine, comprising: A small turbocharger,
A large supercharger having a larger capacity than the small supercharger;
The supercharger that mainly operates the small supercharger in the small supercharger use region, and that mainly operates the large supercharger in the large supercharger use region on the high rotation and high load side from the small supercharger use region. Switching means;
Exhaust pressure level determining means for determining whether the exhaust pressure level is lower than a predetermined level;
Region change means for expanding the small supercharger use region and reducing the large supercharger use region when the exhaust pressure level is lower than the predetermined level, compared to when the exhaust pressure level is higher than the predetermined level When,
A charging efficiency improving means for providing a valve overlap period in which the intake valve opening period and the exhaust valve opening period overlap, and matching the timing at which the pulsation of the exhaust pressure becomes a valley with the valve overlap period;
A control device for an internal combustion engine, comprising: Each of the small supercharger and the large supercharger is a turbocharger having a turbine operated by exhaust gas,
The control device for an internal combustion engine according to claim 2, wherein the turbine of the large supercharger is disposed downstream of the turbine of the small supercharger. The supercharger switching means is
A small turbine bypass passage for bypassing the turbine of the small supercharger and passing exhaust gas;
A small turbine bypass passage opening / closing valve for opening and closing the small turbine bypass passage;
Including
4. The internal combustion engine according to claim 3, wherein the small turbine bypass passage on-off valve is closed in the small supercharger use region, and the small turbine bypass passage on-off valve is opened in the large supercharger use region. Control device. The supercharger switching means is
A large turbine bypass passage for bypassing the turbine of the large supercharger and passing exhaust gas;
A large turbine bypass passage opening / closing valve for opening and closing the large turbine bypass passage;
Further including
In the small turbocharger use region, the small turbine bypass passage on / off valve is closed and the large turbine bypass passage on / off valve is opened, and in the large supercharger use region, the small turbine bypass passage on / off valve is opened and the large turbocharger is opened. 5. The control device for an internal combustion engine according to claim 4, wherein the turbine bypass passage on-off valve is closed.

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