JP4479502B2 - Multistage supercharging system for internal combustion engine and control method thereof - Google Patents

Description

  The present invention relates to a multistage supercharging system for an internal combustion engine and a control method therefor.

Conventionally, a multi-stage turbocharging system for an internal combustion engine in which a high-pressure turbocharger and a low-pressure turbocharger having different maximum capacities are arranged in series is known. In this type of system, in order to properly use the high-pressure turbocharger and the low-pressure turbocharger appropriately, a bypass passage that bypasses the turbine of the high-pressure turbocharger is provided and the flow rate of the exhaust gas to the bypass passage is adjusted. A device provided with an exhaust bypass valve has been proposed (see, for example, Patent Document 1 and Patent Document 2). Further, there is known a device that efficiently operates an engine brake by narrowing the nozzle opening area of the turbine when the internal combustion engine is decelerated (see, for example, Patent Document 3). In addition, Patent Documents 4 to 7 exist as prior art documents related to the present invention.
JP 2001-140653 A JP 2001-329849 A No. 03-020511 Japanese Patent Laid-Open No. 08-114156 JP 2000-274289 A Japanese Utility Model Publication No. 01-021147 Japanese Utility Model Publication No. 01-162051

  In these documents, in the multistage turbocharging system in which variable capacity turbochargers equipped with movable vanes are connected in multiple stages, the opening degree of each movable vane and the opening degree of the exhaust bypass valve are controlled respectively. It does not disclose how to increase effectiveness.

  Therefore, the present invention provides a multistage turbocharger system in which turbochargers having movable vanes are connected in multiple stages, and the multistage for an internal combustion engine capable of increasing the effectiveness of engine braking by controlling the opening of each movable vane. An object is to provide a supercharging system and a control method thereof.

A control method for a first multistage supercharging system for an internal combustion engine according to the present invention includes a variable capacity high pressure turbocharger having a movable vane, and a downstream of an exhaust passage from a turbine of the high pressure turbocharger. And a variable displacement low-pressure turbocharger having a movable vane and having a compressor disposed upstream of the compressor of the high-pressure turbocharger and having a movable vane. A control method applied to a multistage supercharging system for an internal combustion engine comprising a supercharger, wherein the pressure of the intake passage is increased so that the intake air temperature rises during deceleration of the internal combustion engine, The movable vane of the high-pressure turbocharger so that the pressure of the exhaust passage is higher than the pressure of the intake passage, and the difference between the pressure of the exhaust passage and the pressure of the intake passage is enlarged. By controlling the opening and the opening of the movable vanes of the low pressure turbocharger respectively, solving the problems described above (claim 1).

The difference between the pressure in the pressure and the intake passage of the exhaust passage is expanded, a piston of an internal combustion engine to push the exhaust during the exhaust stroke at a greater force than the force received from the intake at the time of the intake stroke, it is possible to increase the pumping loss . Further, by increasing the intake air temperature, the heat that escapes from the intake air to the internal combustion engine during the compression stroke and the expansion stroke can be increased, and the cooling loss of the internal combustion engine can be increased. Therefore, the effectiveness of engine braking can be enhanced by increasing the pumping loss and cooling loss of the internal combustion engine in this way.

In the first control method for a multistage turbocharging system for an internal combustion engine of the present invention, the exhaust passage includes a bypass passage that bypasses the turbine of the high-pressure turbocharger, an inflow of exhaust gas to the bypass passage, and An exhaust bypass valve capable of switching prohibition, and at the time of deceleration of the internal combustion engine, the higher the intake air amount of the internal combustion engine, the closer the movable vane of the low pressure turbocharger is set to the closed side and the high pressure turbo When the movable vane of the supercharger is set to the open side, and the intake air amount of the internal combustion engine is equal to or larger than the determined intake air amount set based on the maximum capacity of the high-pressure turbocharger, the bypass passage The exhaust bypass valve is switched so that exhaust gas flows in. If the intake air amount of the internal combustion engine is less than the determined intake air amount, the exhaust gas to the bypass passage is Even switches the exhaust bypass valve so that flow of is prohibited good (claim 2).

  According to this aspect, when the amount of intake air is small at the time of deceleration of the internal combustion engine, the movable vane of the high-pressure turbocharger is controlled to the closed side, so that the exhaust passage on the upstream side of the turbine of the high-pressure turbocharger The pressure difference between the exhaust passage pressure and the intake passage pressure can be increased. Further, by controlling the movable vane to the closed side, the number of revolutions of the high-pressure turbocharger can be increased, so that the pressure in the intake passage can be increased and the intake air temperature can be increased. Further, by increasing the rotational speed of the high-pressure turbocharger in this way, the internal combustion engine can be supercharged quickly during reacceleration. At this time, since the movable vanes of the low-pressure turbocharger are controlled to the opening side, an increase in the pressure of the exhaust passage on the downstream side of the turbine of the high-pressure turbocharger is suppressed. Thereby, since the reduction | decrease of the pressure difference before and behind the turbine of a high pressure turbocharger can be suppressed, the fall of the rotation speed of a high pressure turbocharger can be suppressed.

  On the other hand, if the amount of intake air is large during deceleration of the internal combustion engine, the movable vane of the low-pressure turbocharger is controlled to the closed side, so the pressure in the exhaust passage upstream of the turbine of the low-pressure turbocharger is increased. Thus, the difference between the pressure in the exhaust passage and the pressure in the intake passage can be increased. Further, by controlling the movable vane on the closing side, the number of revolutions of the low-pressure turbocharger can be increased to increase the pressure in the intake passage, thereby increasing the intake air temperature. At this time, since the movable vane of the high-pressure turbocharger is controlled to the open side, an increase in the rotation speed of the high-pressure turbocharger can be suppressed. Furthermore, when the intake air amount is greater than or equal to the determined intake air amount, the exhaust bypass valve is switched so that the exhaust flows into the bypass passage, so that over-rotation of the high-pressure turbocharger can be prevented. Thus, by controlling the opening degree of each movable vane and the opening degree of the exhaust bypass valve, it is possible to prevent over-rotation of the high-pressure turbocharger while enhancing the effectiveness of the engine brake.

According to the first control method for a multistage supercharging system for an internal combustion engine of the present invention, a throttle valve for adjusting an intake air amount is provided in the intake passage, and a part of the exhaust gas is recirculated from the exhaust passage to the intake passage. An EGR passage, and an EGR valve that is provided in the EGR passage and adjusts the amount of exhaust gas recirculated to the intake passage. When the internal combustion engine is decelerated, the throttle valve is opened and the EGR valve is fully opened. It may be controlled to close ( Claim 3 ). By opening the throttle valve during deceleration of the internal combustion engine, intake air can be introduced into the internal combustion engine without reducing the pressure in the intake passage. Further, by controlling the EGR valve to be fully closed, the gas flow between the exhaust passage and the intake passage can be cut off, and the pressure difference between the pressure in the exhaust passage and the pressure in the intake passage can be maintained. Furthermore, by closing the EGR valve, the number of revolutions of each turbo can be increased, so that the pressure in the intake passage can be increased.

The first control method for a multi-stage turbocharging system for an internal combustion engine according to the present invention acquires an exhaust purification catalyst provided in the exhaust passage downstream of the turbine of the low-pressure turbocharger and the temperature of the exhaust purification catalyst. Catalyst temperature acquisition means; and fuel supply stop means for stopping fuel supply to the internal combustion engine when the internal combustion engine is decelerated. The temperature acquired by the catalyst temperature acquisition means during deceleration of the internal combustion engine is the exhaust gas. When it is determined that the temperature is higher than a predetermined temperature set in advance according to the activation temperature range of the purification catalyst, the throttle valve is controlled to be fully opened and the EGR valve is closed, while the catalyst temperature is acquired when the internal combustion engine is decelerated. When it is determined that the temperature acquired by the means is equal to or lower than the predetermined temperature, the throttle valve is controlled to be fully closed, the EGR valve is opened, and the high pressure Bo of movable vanes of the supercharger opening and the opening of the movable vanes of the low pressure turbocharger may be controlled to the closing side, respectively (claim 4).

  According to this aspect, since the fuel supply to the internal combustion engine is stopped when the internal combustion engine is decelerated, the temperature of the exhaust gas decreases. When the deceleration continues for a long time and the exhaust gas having a low temperature continues to flow into the exhaust purification catalyst, the temperature of the exhaust purification catalyst may fall below the lower limit value of the activation temperature range of the exhaust purification catalyst. Therefore, when the temperature of the exhaust purification catalyst is equal to or lower than a predetermined temperature set in accordance with this activation temperature range, the throttle valve is fully closed to reduce the amount of intake air and the amount of gas flowing into the exhaust purification catalyst. . Furthermore, the exhaust gas is returned from the exhaust passage to the intake passage by opening the EGR valve, and the opening degree of the movable vane of the low pressure turbocharger and the opening degree of the movable vane of the high pressure turbocharger are respectively controlled to the closed side. Thus, the amount of exhaust gas flowing into the exhaust purification catalyst is reduced. Thus, by controlling the opening degree of the throttle valve, the EGR valve, and each movable vane, it is possible to suppress a decrease in the temperature of the exhaust purification catalyst when the internal combustion engine is decelerated, and to suppress the deterioration of exhaust emission.

In this embodiment, the catalyst temperature acquiring means may be estimated temperature of the exhaust purification catalyst based on the intake air amount of the internal combustion engine during the operating state and deceleration of the internal combustion engine before the deceleration (claim 5 ). During deceleration of the internal combustion engine, the temperature of the exhaust gas increases as the temperature of the turbine of the high-pressure turbocharger, the temperature of the turbine of the low-pressure turbocharger, and the temperature of the exhaust passage increase, and as the intake air amount decreases. Become. The temperature of each turbine and the temperature of the exhaust passage change according to the operating state of the internal combustion engine before deceleration. For example, when the internal combustion engine is operated at a high load, it is more than when the internal combustion engine is operated at a low load. In addition, the temperature of each turbine and the temperature of the exhaust passage are increased. Based on such a relationship, the temperature of the exhaust gas during deceleration is estimated from the operating state of the internal combustion engine before deceleration and the intake air amount during deceleration, and the temperature of the exhaust purification catalyst into which the exhaust gas flows is estimated. Thus, the temperature of the exhaust purification catalyst can be acquired without providing a new sensor by estimating the temperature of the exhaust purification catalyst based on the operating state and the intake air amount in the internal combustion engine before deceleration.

A second control method for a multi-stage turbocharging system for an internal combustion engine according to the present invention includes a variable capacity high pressure turbocharger having a movable vane and a downstream of an exhaust passage from a turbine of the high pressure turbocharger. A low-pressure turbocharger having a maximum capacity different from that of the high-pressure turbocharger, and an exhaust passage in the exhaust passage. The invention is applied to a multistage supercharging system for an internal combustion engine provided with a bypass passage that bypasses the turbine of the high-pressure turbocharger and an exhaust bypass valve that adjusts the flow rate of exhaust gas that passes through the bypass passage A control method, wherein when the internal combustion engine is decelerated, the opening degree of the movable vane of the high-pressure turbocharger and the pumping loss and the cooling loss of the internal combustion engine are increased. By controlling the opening degree of the exhaust bypass valve respectively, to solve the problems described above (claim 6).

  According to the second control method of the present invention, when the internal combustion engine is decelerated, the opening degree of the movable vane and the exhaust bypass valve of the high-pressure turbocharger are controlled to reduce the pumping loss and cooling loss of the internal combustion engine. Since each of them is increased, the effectiveness of engine braking can be increased as in the first control method.

A first multistage supercharging system for an internal combustion engine according to the present invention includes a variable capacity high pressure turbocharger having a movable vane, and a turbine disposed downstream of an exhaust passage from the turbine of the high pressure turbocharger. And a variable displacement low-pressure turbocharger having a compressor disposed upstream of the compressor of the high-pressure turbocharger and having a movable vane and having a maximum capacity different from that of the high-pressure turbocharger And the opening degree of the movable vane of the high-pressure turbocharger so that the pumping loss and the cooling loss of the internal combustion engine respectively increase when the internal combustion engine is decelerated. and a control means for controlling the opening of the movable vanes of the low pressure turbocharger respectively, wherein, during deceleration of the internal combustion engine, so that the intake air temperature rises The high pressure turbocharger is configured to increase the pressure of the intake passage and to increase the pressure of the exhaust passage higher than the pressure of the intake passage and to increase the difference between the pressure of the exhaust passage and the pressure of the intake passage. by controlling the machine of the movable vane opening and the opening of the movable vanes of the low pressure turbocharger respectively, solving the problems described above (claim 7).

  According to the first multistage supercharging system for an internal combustion engine of the present invention, when the internal combustion engine is decelerated, the control means determines the opening degree of the movable vane of the high pressure turbocharger and the opening degree of the movable vane of the low pressure turbocharger. Since the pumping loss and the cooling loss of the internal combustion engine are respectively increased by controlling them, the effectiveness of the engine brake can be enhanced.

  The first multistage supercharging system for an internal combustion engine according to the present invention can include the following aspects in order to realize the preferable aspect of the control method of the present invention described above.

That is, in the first internal combustion engine supercharger system of the present invention, before Symbol exhaust passage, a bypass passage bypassing the turbine of the high-pressure turbocharger, inlet and exhaust gas to the bypass passage An exhaust bypass valve capable of switching prohibition, and the control means sets the movable vane of the low-pressure turbocharger to the closed side as the intake air amount of the internal combustion engine increases when the internal combustion engine decelerates And when the movable vane of the high-pressure turbocharger is set to the open side, and the intake air amount of the internal combustion engine is equal to or greater than the determined intake air amount set based on the maximum capacity of the high-pressure turbocharger Switches the exhaust bypass valve so that exhaust gas flows into the bypass passage, and if the intake air amount of the internal combustion engine is less than the determined intake air amount, It may be switched to the exhaust bypass valve so the inflow of exhaust gas into the passage is prohibited (claim 8). By thus controlling the opening degree of the movable vanes, because the pumping loss and cooling loss of the engine can be increased respectively, can be enhanced effectiveness of engine braking.

The first multistage supercharging system for an internal combustion engine according to the present invention is provided with a throttle valve for adjusting an intake air amount in the intake passage, and an EGR passage for recirculating a part of exhaust gas from the exhaust passage to the intake passage. An EGR valve that is provided in the EGR passage and adjusts an amount of exhaust gas recirculated to the intake passage, and the control means opens the throttle valve and decelerates the EGR valve when the internal combustion engine is decelerated. May be controlled to be fully closed ( claim 9 ). Further, an exhaust purification catalyst provided in the exhaust passage downstream of the turbine of the low-pressure turbocharger, catalyst temperature acquisition means for acquiring the temperature of the exhaust purification catalyst, and the internal combustion engine when the internal combustion engine is decelerated Fuel supply stop means for stopping the fuel supply, and the control means presets the temperature acquired by the catalyst temperature acquisition means during deceleration of the internal combustion engine according to the activation temperature range of the exhaust purification catalyst When it is determined that the temperature is higher than the predetermined temperature, the throttle valve is controlled to be fully opened and the EGR valve is closed, while the temperature acquired by the catalyst temperature acquisition means when the internal combustion engine is decelerated is equal to or lower than the predetermined temperature. Is determined, the throttle valve is controlled to be fully closed, the EGR valve is opened, and the opening degree of the movable vane of the high-pressure turbocharger is increased. It may be used to control the degree of opening of the movable vanes of the low pressure turbocharger to the closing side, respectively (claim 10). In this case, the catalyst temperature acquiring means may be estimated temperature of the exhaust purification catalyst based on the intake air amount of the internal combustion engine during the operating state and deceleration of the internal combustion engine before the deceleration (claim 11) .

A second multi-stage turbocharging system for an internal combustion engine according to the present invention includes a variable capacity high-pressure turbocharger having a movable vane, and a turbine disposed downstream of an exhaust passage from the turbine of the high-pressure turbocharger. And a compressor disposed upstream of the intake passage from the compressor of the high-pressure turbocharger, the low-pressure turbocharger having a maximum capacity different from that of the high-pressure turbocharger, and provided in the exhaust passage, A multi-stage supercharging system for an internal combustion engine, comprising: a bypass passage that bypasses the turbine of the high-pressure turbocharger; and an exhaust bypass valve that adjusts a flow rate of exhaust gas that passes through the bypass passage. The opening degree of the movable vane of the high-pressure turbocharger and the opening degree of the exhaust bypass valve so that the pumping loss and the cooling loss of the internal combustion engine respectively increase during deceleration of By that it comprises a control means for controlling each of solving the problems described above (claim 12).

  According to the second multistage supercharging system for an internal combustion engine of the present invention, when the internal combustion engine is decelerated, the control means controls the opening of the movable vane and the opening of the exhaust bypass valve of the high-pressure turbocharger. The pumping loss and the cooling loss of the engine are respectively increased, so that the effectiveness of the engine brake at the time of deceleration can be enhanced.

  As described above, according to the present invention, the opening degree of the movable vane of the low-pressure turbocharger, the opening degree of the movable vane of the high-pressure turbocharger, and the opening degree of the exhaust bypass valve are determined during deceleration of the internal combustion engine. Since the pumping loss and the cooling loss of the internal combustion engine are increased by controlling each of them, the effectiveness of the engine brake can be enhanced.

(First embodiment)
FIG. 1 is an overall configuration diagram showing a first embodiment in which a multistage supercharging system of the present invention is applied to a diesel engine (hereinafter abbreviated as an engine) 1 as an internal combustion engine. The engine 1 is mounted on a vehicle as a driving power source, and includes an intake manifold 2 and an exhaust manifold 3. An intake passage 4 is connected to the intake manifold 2, and an exhaust passage 5 is connected to the exhaust manifold 3. The By connecting in this way, the intake manifold 2 forms part of the intake passage 4, and the exhaust manifold 3 forms part of the exhaust passage 5. A turbine 6a of a high pressure turbocharger (hereinafter abbreviated as high pressure TC) 6 is provided in the exhaust passage 5, and a turbine of a low pressure turbocharger (hereinafter abbreviated as low pressure TC) 7 is provided downstream of the turbine 6a. 7a is provided. The intake passage 4 is provided with a compressor 7b having a low pressure TC7, and a compressor 6b having a high pressure TC6 is provided downstream of the compressor 7b. The turbine 6a and the compressor 6b of the high pressure TC 6 are connected to each other via a common rotating shaft 6c so that the turbine 6a and the compressor 6b can rotate together. Similarly, the turbine 7a and the compressor 7b of the low pressure TC 7 are connected to each other via a common rotating shaft 7c so that the turbine 7a and the compressor 7b can rotate integrally.

  Each of the high pressure TC6 and the low pressure TC7 is a variable capacity turbocharger, and the maximum capacity of the low pressure TC7 is larger than the maximum capacity of the high pressure TC6. A plurality of movable vanes 6d are arranged at the inlet of the turbine 6a of the high pressure TC6, and a variable nozzle VN is configured by the plurality of movable vanes 6d. The variable nozzle VN can change the opening area (opening degree of the movable vane) by changing the inclination of the plurality of movable vanes 6d. The low pressure TC 7 is provided with a movable vane 7d similarly to the high pressure TC 6, and this movable vane 7d also has the same function as the movable vane 6d. As is well known, by controlling the opening degree of the movable vane 6d to the closed side, it is possible to increase the supercharging pressure and increase the pressure in the exhaust passage 3 upstream of the turbine 6a, and conversely, the movable vane 6d. The back pressure of the engine 1 can be reduced by controlling the opening of the engine 1 to the open side. Similarly, the movable vane 7d can increase the supercharging pressure by controlling the opening degree to the closed side, and can increase the pressure in the exhaust passage 3 upstream of the turbine 7a, and the opening degree is controlled to the opening side. Thus, the back pressure of the engine 1 can be reduced. Hereinafter, a state in which the opening degree of the movable vane 6d and the movable vane 7d is changed to the most closed side is referred to as a fully closed state, and a state in which the opening degree of the movable vane 6d and the movable vane 7d is changed to the most open side is fully opened. This is called a state. Since the mechanism for operating the movable vane 6d and the movable vane 7d may be the same as a known mechanism, the details are omitted.

  The exhaust passage 5 is disposed downstream of the bypass passage 8 for bypassing the turbine 6a of the high pressure TC 6, the exhaust bypass valve 9 for adjusting the flow rate of the exhaust gas guided to the bypass passage 8, and the turbine 7a of the low pressure TC 7. An exhaust purification catalyst 10 is provided. In the intake passage 4, an air cleaner 11 for filtering the intake air, an air flow meter 12 that outputs a signal corresponding to the amount of intake air, and a first intercooler 13 for cooling the intake air heated by the compressor 7 b of the low pressure TC 7. And a second intercooler 14 for cooling the intake air heated by the compressor 6b of the high pressure TC 6 and a throttle valve 15 for adjusting the intake air amount. The exhaust passage 5 and the intake passage 4 are connected by an EGR passage 16, and an EGR valve 17 is provided in the EGR passage 16.

  The opening degree of the movable vane 6d, the opening degree of the movable vane 7d, and the opening degree of the exhaust bypass valve 9 are controlled by an engine control unit (ECU) 20, respectively. The ECU 20 includes a microprocessor and peripheral devices such as ROM and RAM necessary for its operation, and is a well-known computer unit that controls the operating state of the engine 1. The ECU 20 controls the opening degree of the throttle valve 15 to control the intake air amount. The amount of exhaust gas to be recirculated is adjusted by adjusting the opening degree of the EGR valve 17. The ECU 20 controls the operation of a fuel injection valve (not shown) for supplying fuel into the cylinder of the engine 1. For example, when the ECU 20 determines that the engine 1 is in a deceleration state, the ECU 20 stops the fuel supply to the engine 1. Thus, by stopping the fuel supply to the engine 1 during deceleration, the ECU 20 functions as the fuel supply stop means of the present invention. In order to acquire information to be referred to when controlling these devices, the ECU 20 has, for example, a signal from the air flow meter 12 and a signal from the accelerator opening sensor 21 that outputs a signal corresponding to an accelerator opening (not shown). Is entered.

  FIG. 2 shows a movable vane opening control routine executed by the ECU 20 to control the opening of the movable vane 6d, the opening of the movable vane 7d, and the opening of the exhaust bypass valve 9. By executing the control routine of FIG. 2, the ECU 20 functions as the control means of the present invention. The control routine of FIG. 2 is repeatedly executed at a predetermined cycle while the engine 1 is operating.

  In the control routine of FIG. 2, the ECU 20 first determines in step S11 whether or not the engine 1 is in a decelerating state. The determination of the deceleration state is performed based on, for example, the accelerator opening and the rotational speed of the engine 1, the rotational speed of the engine 1 exceeds a predetermined rotational speed (for example, 1400 rpm), and the accelerator opening sensor 21 is referred to. It is determined that the vehicle is decelerating when the accelerator opening obtained in step S is 0% (that is, the accelerator is not depressed). If it is determined that the engine 1 is not in a deceleration state, the current control routine is terminated. On the other hand, when it is determined that the engine 1 is in a decelerating state, the process proceeds to step S12, and the ECU 20 refers to the output signal of the air flow meter 12 and acquires the intake air amount. In the next step S13, the ECU 20 controls the opening degree of the movable vane 6d, the opening degree of the movable vane 7d, and the opening degree of the exhaust bypass valve 9 so as to be adjusted to the opening degree set by the setting method described later. . Thereafter, the current control routine is terminated.

  The opening degree of the movable vane 6d, the opening degree of the movable vane 7d, and the opening degree of the exhaust bypass valve 9 are set based on, for example, the map shown in FIG. FIG. 3 is a map showing an example of the relationship between the intake air amount during deceleration of the engine 1, the opening degree of the movable vane 6d, the opening degree of the movable vane 7d, and the opening degree of the exhaust bypass valve 9. In FIG. 3, line A is an example of the relationship between the intake air amount and the opening of the movable vane 6d, line B is an example of the relationship between the intake air amount and the opening of the movable vane 7d, and line C is the intake. An example of the relationship between the air amount and the opening degree of the exhaust bypass valve 9 is shown. These relationships are obtained in advance by experiments or numerical calculations, and are stored as a map in the ROM of the ECU 20. As shown in FIG. 3, when the intake air amount is small, the opening degree of the movable vane 6d is set to the closed side, and the opening degree of the movable vane 7d is set to the open side. On the other hand, when the intake air amount is large, the opening degree of the movable vane 6d is set on the open side, and the opening degree of the movable vane 7d is set on the closing side. That is, as the intake air amount increases, the movable vane 6d is set to the open side, and the movable vane 7d is set to the closed side. As shown in FIG. 3, the exhaust bypass valve 9 is closed when the intake air amount is less than the determined intake air amount Ga, and is opened when the intake air amount is greater than or equal to the determined intake air amount Ga. The determination intake air amount Ga is set based on, for example, the maximum capacity of the high pressure TC 6, so that the rotation speed of the high pressure TC 6 does not exceed the allowable upper limit rotation speed when the movable vane 6 d is fully opened, that is, the high pressure TC 6 does not over-rotate. Set to

  When the amount of intake air is small when the engine 1 is decelerated, the pressure of the exhaust manifold 3 is increased more than the pressure of the intake manifold 2 by setting the movable vane 6d of the high pressure TC 6 to the closed side. And the pressure of the exhaust manifold 3 can be increased. Therefore, the pumping loss of the engine 1 can be increased. Further, the number of revolutions of the high pressure TC 6 can be increased and the pressure of the intake passage 4 can be increased. At this time, since the movable vane 7d of the low pressure TC7 is set on the open side, an increase in pressure in the exhaust passage 5 downstream of the turbine 6a can be suppressed. Thereby, since the reduction | decrease of the difference of the upstream pressure of the turbine 6a and a downstream pressure is suppressed, the fall of the rotation speed of the high voltage | pressure TC6 is suppressed. Further, since the exhaust bypass valve 9 is closed, all exhaust gas can be introduced into the turbine 6a of the high pressure TC6. Thus, the cooling loss of the engine 1 can be increased by increasing the pressure in the intake passage 4. Further, by maintaining the pressure of the exhaust manifold 3 at a high level, exhaust gas can be quickly introduced into the turbine 6a at the time of re-acceleration, and the engine 1 can be supercharged quickly, so that the acceleration performance of the engine 1 can be improved. it can.

  On the other hand, when the intake air amount is large when the engine 1 is decelerated, the movable vane 7d of the low pressure TC 7 is controlled to the closed side, so that the pressure in the exhaust passage 5 upstream of the turbine 7a of the low pressure TC 7 is increased. Can do. Therefore, the difference between the pressure of the intake manifold 2 and the pressure of the exhaust manifold 3 can be expanded, and the pumping loss of the engine 1 can be increased. Further, since the rotational speed of the low pressure TC 7 can be increased by controlling the movable vane 7d to the closed side, the pressure of the intake manifold 2 is increased to increase the intake air temperature, and the cooling loss of the engine 1 is increased. be able to. At this time, since the movable vane 6d of the high pressure TC6 is controlled to open, an increase in the rotational speed of the high pressure TC6 can be suppressed. Further, when the intake air amount is equal to or larger than the determination intake air amount Ga, the exhaust bypass valve 9 is opened, so that the amount of exhaust gas flowing into the turbine 6a of the high pressure TC 6 can be reduced to prevent the high pressure TC 6 from over-rotating. .

  As described above, when the engine 1 is decelerated, the opening degree of the movable vane 6d, the opening degree of the movable vane 7d, and the opening degree of the exhaust bypass valve 9 are controlled according to the intake air amount, and the pumping loss of the engine 1 is reduced. In addition, since the cooling loss is increased, the effectiveness of the engine brake of the engine 1 can be enhanced. Further, since the pressure of the exhaust manifold 3 is increased, the engine 1 can be supercharged quickly during reacceleration. Therefore, the acceleration performance of the engine 1 can be improved.

  FIG. 4 shows a modification of the movable vane opening degree control routine of FIG. In FIG. 4, the same processes as those in FIG. 2 are denoted by the same reference numerals, and the description thereof is omitted. The control routine of FIG. 4 is also repeatedly executed at a predetermined cycle while the engine 1 is operating.

  In the control routine of FIG. 4, the ECU 20 performs the same processing as in the control routine of FIG. 2 until step S13. In the subsequent step S21, the ECU 20 opens the throttle valve 15 and controls the EGR valve 17 to be fully closed. Thereafter, the current control routine is terminated.

  According to the control routine of FIG. 4, the gas flow between the intake passage 4 and the exhaust passage 5 is cut off by controlling the EGR valve 17 to be fully closed when the engine 1 is decelerated, and the pressure of the intake manifold 2 and the exhaust gas are exhausted. A difference from the pressure of the manifold 3 can be maintained. Therefore, the pumping loss of the engine 1 is not reduced. By controlling the EGR valve 17 to be fully closed, it is possible to increase the amount of exhaust gas introduced to the turbine 6a of the high pressure TC6 and the turbine 7a of the low pressure TC7. The pressure of the intake manifold 3 can be increased. Further, by opening the throttle valve 15, intake air can be guided to the engine 1 without reducing the pressure in the intake passage 2. Therefore, the cooling loss of the engine 1 can be increased. Thus, by suppressing the reduction of the pumping loss of the engine 1 and increasing the cooling loss, the effectiveness of the engine brake can be strengthened.

  FIG. 5 shows another modification of the movable vane opening degree control routine of FIG. In FIG. 5, the same processes as those in FIG. 2 are denoted by the same reference numerals, and the description thereof is omitted. The control routine of FIG. 5 is also repeatedly executed at a predetermined cycle while the engine 1 is operating.

  In the control routine of FIG. 5, the ECU 20 performs the same processing as in the control routine of FIG. 2 until step S13. In subsequent step S31, the ECU 20 determines whether or not the temperature of the exhaust gas flowing into the exhaust purification catalyst 10 is lower than a predetermined determination temperature. Since the temperature of the exhaust purification catalyst 10 changes according to the temperature of the exhaust gas flowing into the exhaust purification catalyst 10, in this process, is the exhaust gas temperature used to determine whether the temperature of the exhaust purification catalyst 10 is in the catalyst activation temperature range? Judge whether or not. The temperature of the exhaust gas flowing into the exhaust purification catalyst 10 may be acquired by providing, for example, a temperature sensor that outputs a signal corresponding to the temperature of the exhaust gas in the exhaust passage 5, or a temperature estimation routine of FIG. You may make ECU20 perform and may acquire. The predetermined determination temperature is set according to the catalyst activation temperature range of the exhaust purification catalyst 10, and the temperature of the exhaust purification catalyst 10 is not lowered below the lower limit value of the catalyst activation temperature range by the exhaust gas when the engine 1 is decelerated. The temperature of the exhaust gas is set. Since the catalyst activation temperature range varies depending on the type of the exhaust purification catalyst 10 and the like, the predetermined determination temperature is appropriately set according to the exhaust purification catalyst 10.

  When it is determined that the temperature of the exhaust gas is lower than the predetermined determination temperature, the process proceeds to step S32, and the ECU 20 controls the throttle valve 15 to a fully closed state. In subsequent step S33, the ECU 20 opens the EGR valve 17. In the next step S34, the ECU 20 controls the movable vane 6d of the high pressure TC6 and the movable vane 7d of the low pressure TC7 to be fully closed. In the subsequent step S35, the ECU 20 closes the exhaust bypass valve 9. Thereafter, the current control routine is terminated. On the other hand, when it is determined that the temperature of the exhaust gas is higher than the predetermined determination temperature, the process proceeds to step S36, and the ECU 20 controls the throttle valve 15 to be fully opened. In subsequent step S37, the ECU 20 closes the EGR valve 17. Thereafter, the current control routine is terminated.

  Since the fuel is not supplied to the engine 1 when the engine 1 is decelerated, the temperature of the exhaust gas decreases. When the deceleration continues for a long time, the temperature of the exhaust manifold 3, the turbine 6a, and the turbine 7a is lowered due to the effect of the temperature reduction of the exhaust gas, so that the temperature of the gas flowing into the exhaust purification catalyst 10 is reduced, and the exhaust purification catalyst. The temperature of 10 decreases. Therefore, as explained above, in the control routine of FIG. 5, when the temperature of the exhaust gas is lower than the predetermined determination temperature, the throttle valve 15 is controlled to be fully closed to reduce the intake air amount and the exhaust gas amount. Decrease. Further, by opening the EGR valve 17, the exhaust gas is returned from the exhaust passage 5 to the intake passage 4 via the EGR passage 16, and the amount of exhaust gas flowing into the exhaust purification catalyst 10 is reduced. Further, the movable vane 6d of the high pressure CT 6 and the movable vane 7d of the low pressure TC 7 are controlled to be fully closed, and the exhaust bypass valve 9 is closed, thereby reducing the amount of exhaust gas flowing into the turbine 6a, the turbine 7a, and the exhaust purification catalyst 10. Decrease. In this way, by reducing the amount of exhaust gas flowing into the exhaust purification catalyst 10, the temperature reduction of the exhaust purification catalyst 10 can be suppressed. Therefore, deterioration of exhaust emission can be suppressed.

  The temperature of the exhaust gas flowing into the exhaust purification catalyst 10 has a correlation with the temperature of the exhaust manifold 3, the temperature of the turbine 6a of the high pressure TC6, and the temperature of the turbine 7a of the low pressure TC7. For example, when the engine 1 is decelerated, that is, when fuel is not supplied to the engine 1, the temperature of the exhaust gas is determined according to the heat received from the exhaust manifold 3, the turbine 6a, and the turbine 7a. On the other hand, when the engine 1 is not decelerated, that is, when fuel is supplied to the engine 1, the temperature of the exhaust manifold 3, the temperature of the turbine 6a, and the temperature of the turbine 7a are determined according to the heat received from the exhaust gas. Therefore, the temperature of the exhaust gas can be estimated based on the temperature of the exhaust manifold 3, the temperature of the turbine 6a, and the temperature of the turbine 7a. FIG. 6 shows an exhaust gas temperature estimation routine executed by the ECU 20 to estimate the exhaust gas temperature using this relationship. In FIG. 6, the same processes as those in FIG. 2 are denoted by the same reference numerals, and description thereof is omitted. The estimation routine of FIG. 6 is repeatedly executed at a predetermined cycle while the engine 1 is operating. By executing the estimation routine of FIG. 6, the ECU 20 functions as the catalyst temperature acquisition means of the present invention.

  In the estimation routine of FIG. 6, the ECU 20 first determines in step S11 whether or not the engine 1 is in a decelerating state. When it is determined that the vehicle is decelerating, the process proceeds to step S12 to acquire the intake air amount. In subsequent step S41, the ECU 20 estimates the temperature of the exhaust manifold 3, the temperature of the turbine 6a of the high pressure TC6, and the temperature of the turbine 7a of the low pressure TC7 based on the acquired intake air amount. These temperatures are estimated by the following method, for example. Here, a method for estimating the temperature of the exhaust manifold 3 is shown as an example. The temperature of the turbine 6a and the temperature of the turbine 7a can also be estimated by a method similar to this method. The temperature of the exhaust manifold 3 is estimated based on the previously estimated temperature of the exhaust manifold 3 and the temperature change of the exhaust manifold 3 since the previous estimation. When the engine 1 is decelerated, the temperature of the exhaust manifold 3 greatly decreases as the amount of exhaust gas increases. Since the amount of exhaust gas has a correlation with the amount of intake air, a relationship between the amount of intake air and the temperature change of the exhaust manifold 3 is obtained in advance by experiments or the like, and this relationship is stored in the ROM of the ECU 20 as a map. Let me. The temperature of the exhaust manifold 3 since the previous estimation is obtained with reference to this map. The temperature of the exhaust manifold 3 estimated this time can be estimated by adding the temperature change of the exhaust manifold 3 to the temperature of the exhaust manifold 3 estimated last time.

  The temperature of the turbine 6a and the temperature of the turbine 7a can also be estimated by a method similar to this method. Note that the temperature of the turbine 6a and the temperature of the turbine 7a also greatly decrease as the amount of exhaust gas increases, that is, as the amount of intake air increases. Therefore, the temperature change of the turbine 6a, the temperature change of the turbine 7a, A relationship with the intake air amount is obtained, and this relationship is stored in the ECU 20 as a map.

  In the next step S42, the ECU 20 estimates the temperature of the exhaust gas flowing into the exhaust purification catalyst 10. Thereafter, the current estimation routine is terminated. The temperature of the exhaust gas changes according to the temperature of the exhaust manifold 3, the temperature of the turbine 6a, and the temperature of the turbine 7a. For example, as the temperature of the exhaust manifold 3 increases, the amount of heat that the exhaust gas receives from the exhaust manifold 3 increases, so the temperature of the exhaust gas increases. Further, the temperature of the exhaust gas has the same relationship with the temperature of the turbine 6a and the temperature of the turbine 7a. Therefore, the relationship between the temperature of the exhaust manifold 3, the temperature of the turbine 6a, and the temperature of the turbine 7a and the exhaust gas temperature during deceleration is obtained in advance through experiments and stored in the ROM of the ECU 20 as a map. The temperature of the exhaust gas is estimated with reference.

  On the other hand, if it is determined that the vehicle is not in the deceleration state, the process proceeds to step S43, where the ECU 20 acquires an integrated value of the amount of fuel supplied to the engine 1 (hereinafter abbreviated as an integrated supply amount). The ECU 20 calculates the amount of fuel to be supplied from the fuel injection valve to the engine 1 in order to control the operation of the fuel injection valve. The supply amount integrated value is, for example, such that the amount of fuel to be supplied is such that the temperature of the exhaust manifold 3, the temperature of the turbine 6a, and the temperature of the turbine 7a at the time when the estimation routine of FIG. 6 is executed can be estimated. It is a value integrated for a predetermined time.

  In the next step S44, the ECU 20 estimates the temperature of the exhaust manifold 3, the temperature of the turbine 6a of the high pressure TC6, and the temperature of the turbine 7a of the low pressure TC7 based on the acquired supply amount integrated value. Thereafter, the current estimation routine is terminated. As is well known, when the engine 1 is operated at a high load, the amount of fuel supplied to the engine 1 is large, so the temperature of the exhaust gas is high. On the other hand, when the engine 1 is operated at a low load, the amount of fuel supplied to the engine 1 is small, so the temperature of the exhaust gas is low. In this way, the amount of fuel supplied to the engine 1 changes according to the operating state, and the temperature of the exhaust gas changes. Further, as described above, when the fuel is supplied to the engine 1, the temperature of the exhaust manifold 3, the temperature of the turbine 6a, and the temperature of the turbine 7a are determined according to the heat received from the exhaust gas. Is also related to the integrated supply amount. Therefore, the relationship between the temperature of the exhaust manifold 3, the temperature of the turbine 6a, the temperature of the turbine 7a, and the integrated supply amount is obtained in advance through experiments and stored in the ECU 20 as a map. In step S44, the temperature of the exhaust manifold 3, the temperature of the turbine 6a, and the temperature of the turbine 7a are estimated with reference to this map.

  As described above, in the estimation routine of FIG. 6, the temperature of the exhaust gas flowing into the exhaust purification catalyst 10 is estimated with reference to the integrated supply amount value and the intake air amount. Therefore, it is necessary to newly provide a temperature sensor. Absent. The physical quantity acquired in step S43 is not limited to the supply amount integrated value. For example, various physical quantities that can determine the operating state of the engine 1 such as an integrated value of the intake air amount may be used.

(Second embodiment)
FIG. 7 is an overall configuration diagram showing a second embodiment of a diesel engine to which the multistage turbocharging system of the present invention is applied. In FIG. 7, the same reference numerals are given to the portions common to FIG. This embodiment is different from the first embodiment in that the low pressure TC7 does not include a movable vane. Therefore, when the engine 1 is decelerated, the ECU 20 controls the opening degree of the movable vane 6d of the high pressure TC 6 and the opening degree of the exhaust bypass valve 9 to increase the pumping loss and the cooling loss of the engine 1. FIG. 8 shows a movable vane opening degree control routine executed by the ECU 20 to control the opening degree of the movable vane 6d and the opening degree of the exhaust bypass valve 9. The control routine of FIG. 8 is repeatedly executed at a predetermined cycle while the engine 1 is operating. In FIG. 8, the same processes as those in FIG. 2 are denoted by the same reference numerals, and description thereof is omitted.

  In the control routine of FIG. 8, the ECU 20 performs the same processing as in the control routine of FIG. 2 until step S12. In subsequent step S51, the ECU 20 controls the opening degree of the movable vane 6d and the opening degree of the exhaust bypass valve 9 based on the acquired intake air amount and a map shown in FIG. Thereafter, the current control routine is terminated. FIG. 9 shows an example of the relationship between the opening of the movable vane 6d, the opening of the exhaust bypass valve 9, and the intake air amount. In FIG. 9, line D shows an example of the relationship between the intake air amount and the opening degree of the movable vane 6d, and line E shows an example of the relationship between the intake air amount and the opening degree of the exhaust bypass valve 9. . These relationships are obtained in advance by experiments or the like and stored in the ROM of the ECU 20 as a map. As shown in FIG. 9, when the amount of intake air is small when the engine 1 is decelerated, the opening of the movable vane 6d is set to the closed side, so that the pressure of the exhaust manifold 3 is increased and the pressure of the intake manifold 2 is increased. And the pressure of the exhaust manifold 3 can be increased. Therefore, the pumping loss of the engine 1 can be increased. Further, by setting the opening degree of the movable vane 6d to the closed side, the rotational speed of the high pressure TC 6 can be increased, the intake air temperature can be increased, and the cooling loss of the engine 1 can be increased. Further, since the pressure of the exhaust manifold 3 can be maintained at a high level, the number of revolutions of the high pressure TC 6 can be quickly increased during re-acceleration, and the engine 1 can be supercharged quickly. Therefore, the acceleration performance of the engine 1 can be improved. On the other hand, when the intake air amount is large at the time of deceleration, the opening degree of the movable vane 6d is set to the open side, so that an increase in the rotation speed of the high pressure TC6 can be suppressed. Further, since the exhaust bypass valve 9 is opened when the intake air amount is greater than or equal to the determined intake air amount Ga, the excessive rotation of the high pressure TC 6 can be prevented by reducing the amount of exhaust gas introduced into the turbine 6 a of the high pressure TC 6. Can do.

  As described above, according to the second embodiment of the present invention, the opening degree of the movable vane 6d of the high pressure TC 6 and the opening degree of the exhaust bypass valve 9 are controlled in accordance with the intake air amount at the time of deceleration. Since the pumping loss and the cooling loss of 1 can be increased, the effectiveness of the engine brake can be enhanced. In the second embodiment, as in the first embodiment, the throttle valve 15 may be opened and the EGR valve 17 may be fully closed during deceleration. Thus, by controlling the throttle valve 15 and the EGR valve 17 respectively, the pumping loss and the cooling loss of the engine 1 can be further increased. Further, the opening degree of the throttle valve 15, the opening degree of the EGR valve 17, and the opening degree of the exhaust bypass valve 9 may be controlled according to the temperature of the exhaust gas flowing into the exhaust purification catalyst 10. In this case, the temperature reduction of the exhaust purification catalyst 10 can be suppressed.

  The present invention is not limited to the above embodiment, and may be implemented in various forms. For example, the opening degree of the movable vane of the high pressure TC, the opening degree of the movable vane of the low pressure TC, and the opening degree of the bypass valve during engine deceleration may be changed according to the engine speed.

The figure which shows the whole structure of 1st embodiment of the diesel engine to which the multistage supercharging system of this invention was applied. The flowchart which shows the movable vane opening degree control routine which ECU performs. The figure which shows an example of the relationship between the amount of intake air at the time of deceleration, the opening degree of the movable vane of high pressure TC, the opening degree of the movable vane of low pressure TC, and the opening degree of a bypass valve. The flowchart which shows the modification of the movable vane opening degree control routine which ECU performs. The flowchart which shows the other modification of the movable vane opening degree control routine which ECU performs. The flowchart which shows the exhaust gas temperature estimation routine which ECU performs. The figure which shows the whole structure of 2nd embodiment of the diesel engine to which the multistage supercharging system of this invention was applied. The flowchart which shows the movable vane opening degree control routine which ECU of FIG. 7 performs. The figure which shows an example of the relationship between the amount of intake air at the time of deceleration, the opening degree of the movable vane of high pressure TC, and the opening degree of a bypass valve.

Explanation of symbols

1 Diesel engine (internal combustion engine)
4 Intake passage 5 Exhaust passage 6 High-pressure turbocharger (high-pressure turbocharger)
6a Turbine 6b Compressor 6d Movable vane 7 Low pressure turbocharger (low pressure turbocharger)
7a Turbine 7b Compressor 7d Movable vane 8 Bypass passage 9 Exhaust bypass valve 10 Exhaust purification catalyst 15 Throttle valve 16 EGR passage 17 EGR valve 20 Engine control unit (control means, catalyst temperature acquisition means, fuel supply stop means)

Claims (12)

A variable capacity high-pressure turbocharger having a movable vane; a turbine disposed downstream of an exhaust passage from a turbine of the high-pressure turbocharger; and an upstream of an intake passage from a compressor of the high-pressure turbocharger And a variable displacement low-pressure turbocharger that has a movable vane and has a maximum capacity different from that of the high-pressure turbocharger, and is applied to a multistage supercharging system for an internal combustion engine. Control method,
When the internal combustion engine is decelerated, the pressure of the intake passage is increased so that the intake air temperature rises, the pressure of the exhaust passage is higher than the pressure of the intake passage, and the pressure of the exhaust passage and the intake passage over multistage for internal combustion engine you and controls each difference is movable vanes of the high-pressure turbocharger to expand the opening and the opening of the movable vanes of the low-pressure turbocharger and pressure Supply system control method. The exhaust passage is provided with a bypass passage that bypasses the turbine of the high-pressure turbocharger, and an exhaust bypass valve that can switch between inflow and prohibition of exhaust gas into the bypass passage,
When the internal combustion engine decelerates, the larger the intake air amount of the internal combustion engine, the closer the movable vane of the low-pressure turbocharger is set to the closed side and the movable vane of the high-pressure turbocharger is set to the open side, and When the intake air amount of the internal combustion engine is greater than or equal to a determined intake air amount set based on the maximum capacity of the high-pressure turbocharger, the exhaust bypass valve is switched so that exhaust gas flows into the bypass passage, 2. The exhaust bypass valve according to claim 1, wherein when the intake air amount of the internal combustion engine is less than the determined intake air amount, the exhaust bypass valve is switched so that the inflow of exhaust gas to the bypass passage is prohibited. A control method of a multistage supercharging system for an internal combustion engine. A throttle valve for adjusting the amount of intake air is provided in the intake passage;
An EGR passage that recirculates a part of the exhaust gas from the exhaust passage to the intake passage, and an EGR valve that is provided in the EGR passage and adjusts the amount of exhaust gas recirculated to the intake passage,
3. The control method for a multistage supercharging system for an internal combustion engine according to claim 1 or 2 , wherein when the internal combustion engine is decelerated, the throttle valve is opened and the EGR valve is controlled to be fully closed. An exhaust purification catalyst provided in the exhaust passage downstream of the turbine of the low-pressure turbocharger, catalyst temperature acquisition means for acquiring the temperature of the exhaust purification catalyst, and fuel to the internal combustion engine during deceleration of the internal combustion engine Fuel supply stopping means for stopping supply,
When it is determined that the temperature acquired by the catalyst temperature acquisition means during deceleration of the internal combustion engine is higher than a predetermined temperature set in advance according to the activation temperature range of the exhaust purification catalyst, the throttle valve is fully opened. When the EGR valve is closed and the temperature acquired by the catalyst temperature acquisition means during deceleration of the internal combustion engine is determined to be lower than the predetermined temperature, the throttle valve is controlled to be fully closed and the EGR is controlled. The internal combustion engine according to claim 3, wherein the valve is opened, and the opening degree of the movable vane of the high-pressure turbocharger and the opening degree of the movable vane of the low-pressure turbocharger are controlled to be closed. Control method for multi-stage turbocharging system. The catalyst temperature acquiring means, according to claim 4, characterized in that for estimating the temperature of the exhaust purification catalyst based on the intake air amount of the internal combustion engine during the operating state and deceleration of the internal combustion engine before decelerating A control method of a multistage supercharging system for an internal combustion engine. A variable capacity high-pressure turbocharger having a movable vane; a turbine disposed downstream of an exhaust passage from a turbine of the high-pressure turbocharger; and an upstream of an intake passage from a compressor of the high-pressure turbocharger A low-pressure turbocharger having a maximum capacity different from that of the high-pressure turbocharger, a bypass passage provided in the exhaust passage and bypassing the turbine of the high-pressure turbocharger, An exhaust bypass valve for adjusting the flow rate of exhaust gas passing through the bypass passage, and a control method applied to a multistage supercharging system for an internal combustion engine,
The opening degree of the movable vane and the opening degree of the exhaust bypass valve of the high-pressure turbocharger are respectively controlled so that the pumping loss and the cooling loss of the internal combustion engine are increased when the internal combustion engine is decelerated. Control method for a multistage supercharging system for an internal combustion engine. A variable capacity high-pressure turbocharger having a movable vane; a turbine disposed downstream of an exhaust passage from a turbine of the high-pressure turbocharger; and an upstream of an intake passage from a compressor of the high-pressure turbocharger A variable capacity low-pressure turbocharger having a compressor and a movable vane each having a maximum capacity different from that of the high-pressure turbocharger. ,
When the internal combustion engine is decelerated, the opening degree of the movable vane of the high pressure turbocharger and the opening degree of the movable vane of the low pressure turbocharger are controlled so that the pumping loss and the cooling loss of the internal combustion engine respectively increase. a control means for,
The control means increases the pressure of the intake passage so that the intake air temperature increases when the internal combustion engine is decelerated, the pressure of the exhaust passage is higher than the pressure of the intake passage, and the pressure of the exhaust passage And the opening of the movable vane of the high-pressure turbocharger and the opening of the movable vane of the low-pressure turbocharger are controlled so that the difference between the pressure of the intake passage and the pressure of the intake passage increases. Multistage supercharging system. The exhaust passage is provided with a bypass passage that bypasses the turbine of the high-pressure turbocharger, and an exhaust bypass valve that can switch between inflow and prohibition of exhaust gas into the bypass passage,
When the internal combustion engine is decelerated, the control means sets the movable vane of the low-pressure turbocharger to the closed side as the intake air amount of the internal combustion engine increases, and opens the movable vane of the high-pressure turbocharger to the open side And when the intake air amount of the internal combustion engine is equal to or larger than a determined intake air amount set based on the maximum capacity of the high-pressure turbocharger, the exhaust gas flows into the bypass passage. switching the bypass valve, when the intake air amount of the internal combustion engine is less than the determination amount of intake air and switches the exhaust bypass valve so the inflow of exhaust gas into the bypass passage is inhibited claimed Item 8. The multistage turbocharging system for an internal combustion engine according to Item 7 . A throttle valve for adjusting the amount of intake air is provided in the intake passage;
An EGR passage that recirculates a part of the exhaust gas from the exhaust passage to the intake passage, and an EGR valve that is provided in the EGR passage and adjusts the amount of exhaust gas recirculated to the intake passage,
9. The multistage supercharging system for an internal combustion engine according to claim 7 , wherein the control means opens the throttle valve and controls the EGR valve to be fully closed when the internal combustion engine is decelerated. An exhaust purification catalyst provided in the exhaust passage downstream of the turbine of the low-pressure turbocharger, catalyst temperature acquisition means for acquiring the temperature of the exhaust purification catalyst, and fuel to the internal combustion engine during deceleration of the internal combustion engine Fuel supply stopping means for stopping supply,
When the control means determines that the temperature acquired by the catalyst temperature acquisition means during deceleration of the internal combustion engine is higher than a predetermined temperature set in advance according to the activation temperature range of the exhaust purification catalyst, the throttle The throttle valve is fully closed when it is determined that the temperature acquired by the catalyst temperature acquisition means during the deceleration of the internal combustion engine is lower than the predetermined temperature while the valve is controlled to be fully open and the EGR valve is closed. claim controls open the EGR valve, further wherein the controller controls the movable vanes of the high pressure turbocharger opening and the opening of the movable vanes of the low pressure turbocharger to the closing side, respectively 9 A multi-stage turbocharging system for an internal combustion engine as described in 1. The catalyst temperature acquiring means, according to claim 10, wherein estimating the temperature of the exhaust purification catalyst based on the intake air amount of the internal combustion engine during the operating state and deceleration of the internal combustion engine before decelerating Multistage supercharging system for internal combustion engines. A variable capacity high-pressure turbocharger having a movable vane; a turbine disposed downstream of an exhaust passage from a turbine of the high-pressure turbocharger; and an upstream of an intake passage from a compressor of the high-pressure turbocharger A low-pressure turbocharger having a maximum capacity different from that of the high-pressure turbocharger, a bypass passage provided in the exhaust passage and bypassing the turbine of the high-pressure turbocharger, An exhaust bypass valve that adjusts the flow rate of exhaust gas that passes through the bypass passage, and a multi-stage turbocharging system for an internal combustion engine,
Control means for respectively controlling the opening degree of the movable vane and the opening degree of the exhaust bypass valve of the high-pressure turbocharger so that the pumping loss and the cooling loss of the internal combustion engine respectively increase during deceleration of the internal combustion engine. A multi-stage turbocharging system for an internal combustion engine.

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