JP2014139425A - Internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress torque difference at a time of switching a high-pressure-stage turbocharger to/from a low-pressure-stage turbocharger.SOLUTION: An internal combustion engine 1 according to the present invention includes: a fuel battery 4; a low-pressure-stage turbocharger 3L that includes a low-pressure-stage turbine 3LT and a low-pressure-stage compressor 3LC; a high-pressure-stage turbocharger 3H that includes a high-pressure-stage turbine 3HT and a high-pressure-stage compressor 3HC; a first exhaust path 27A connecting the fuel battery 4 to an exhaust passage 6 upstream of the high-pressure-stage turbine 3HT; a second exhaust path 27B connecting the fuel cell 4 to the exhaust passage 6 between the high-pressure-stage turbine 3HT and the low-pressure-stage turbine 3LT; and exhaust-path switching means 28, 100 for switching the first exhaust path to/from the second exhaust path. If an operating state of the internal combustion engine is in a transition range B between an operating range of the high-pressure-stage turbocharger 3H and that of the low-pressure-stage turbocharger 3L, the exhaust-path switching means 28, 100 switches the first exhaust path 27A to the second exhaust path 27B.

Description

  The present invention relates to an internal combustion engine, and more particularly to an internal combustion engine provided with a fuel cell and a multistage turbocharging system.

  Internal combustion engines with a multi-stage turbocharging system are known. In particular, as a multistage turbocharger system, a two-stage sequential turbosystem in which two turbochargers, a low-pressure turbocharger and a high-pressure turbocharger, are connected in series is known. For example, Patent Literature 1 discloses a turbocharged engine having a large turbocharger and a small turbocharger. In a large turbocharger, a clutch is provided on a connecting shaft that connects a compressor and a turbine, and an electric motor for assisting the rotation of the compressor is provided on a connecting shaft closer to the compressor than the clutch.

JP 2011-58400 A

  By the way, it is conceivable to combine a fuel cell with an internal combustion engine equipped with a multistage turbocharging system. However, this causes the following problems.

  In general, in a multi-stage turbocharger system, a low-speed region of an internal combustion engine is handled by a high-pressure stage turbocharger, and a high-speed region of the internal combustion engine is handled by a low-pressure stage turbocharger. When switching between these turbochargers, there is a problem that a step difference in engine torque occurs and drivability is impaired.

  In order to cope with this problem, it is conceivable to reduce the size difference between the high-pressure turbocharger and the low-pressure turbocharger. However, when the fuel cells are combined, it may be difficult to reduce the size difference. In such a case, it becomes difficult to eliminate the problem of the torque step described above.

  Accordingly, the present invention was created in view of the above circumstances, and one object of the present invention is an internal combustion engine capable of suppressing a torque step at the time of switching between a high-pressure turbocharger and a low-pressure turbocharger. To provide an institution.

According to one aspect of the invention,
Comprising a fuel cell, a low-pressure stage turbocharger having a low-pressure stage turbine and a low-pressure stage compressor, and a high-pressure stage turbocharger having a high-pressure stage turbine and a high-pressure stage compressor,
In the exhaust passage, the low-pressure stage turbine is disposed on the downstream side of the high-pressure stage turbine, and in the intake passage, the high-pressure stage compressor is disposed on the downstream side of the low-pressure stage compressor,
A first exhaust passage that connects the fuel cell and the exhaust passage upstream of the high-pressure turbine, and a first exhaust passage that connects the fuel cell and the exhaust passage between the high-pressure turbine and the low-pressure turbine. Two exhaust paths, and an exhaust path switching means for switching the first and second exhaust paths,
When the operating state of the internal combustion engine is in a transition region between the operating region of the high-pressure stage turbocharger and the operating region of the low-pressure stage turbocharger, the exhaust passage switching means is the second exhaust passage. An internal combustion engine characterized by switching to is provided.

  Here, the “turbine” strictly means a turbine wheel housed in the turbine housing of the turbine. Thus, in the case of “an exhaust passage upstream of the turbine”, this includes a passage portion in the turbine housing located upstream or inlet of the turbine wheel. The same applies to the “exhaust passage on the downstream side of the turbine”.

  Similarly, “compressor” refers strictly to a compressor wheel housed within the compressor housing of the compressor. Therefore, in the case of “an intake passage on the downstream side of the compressor”, this includes a passage portion in the compressor housing located on the downstream side or the outlet side of the compressor wheel. The same applies to the “intake passage on the upstream side of the compressor”.

  The “exhaust passage between the high-pressure turbine and the low-pressure turbine” is synonymous with “the exhaust passage downstream of the high-pressure turbine and upstream of the low-pressure turbine”. Accordingly, this includes a passage portion in the high-pressure turbine housing located downstream or outlet of the high-pressure turbine wheel and a passage portion in the low-pressure turbine housing located upstream or inlet of the low-pressure turbine wheel. And are included. It will be understood that “the intake passage between the low-pressure compressor and the high-pressure compressor” is interpreted in the same way.

Preferably, the internal combustion engine has a first air supply path connecting the fuel cell and the intake passage downstream of the high pressure compressor, and between the fuel cell, the low pressure compressor and the high pressure compressor. A second air supply path that connects the intake passage, and an air supply path switching means that switches between the first and second air supply paths,
When the operating state of the internal combustion engine is in the transition region, the air supply path switching means switches to the first air supply path.

  Preferably, when the operating state of the internal combustion engine is in an operating region of the high-pressure turbocharger, the exhaust path switching means switches to the first exhaust path, and the air supply path switching means Switch to the air supply path.

  Preferably, when the operating state of the internal combustion engine is in an operating region of the low-pressure stage turbocharger, the exhaust passage switching means switches to the second exhaust passage, and the air supply passage switching means Switch to the air supply path.

  According to the present invention, an excellent effect is exhibited that a torque step can be suppressed when switching between a high-pressure turbocharger and a low-pressure turbocharger.

It is the schematic which shows the structure of embodiment of this invention. It is a figure which shows the map of an engine operation area | region. FIG. 6 is a diagram showing the flow of air, engine exhaust, and FC exhaust when the rotational speed and load belong to region A. FIG. 6 is a diagram showing the flow of air, engine exhaust, and FC exhaust when the rotation speed and load belong to region C. FIG. 6 is a diagram showing the flow of air, engine exhaust, and FC exhaust when the rotational speed and load belong to region B.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  As shown in FIG. 1, an internal combustion engine (engine) 1 includes an engine body 2, a plurality (two) of turbochargers, that is, a low-pressure turbocharger 3L and a high-pressure turbocharger 3H, and a fuel cell. 4. The engine 1 may be either a spark ignition type internal combustion engine (gasoline engine) or a compression ignition type internal combustion engine (diesel engine). In this embodiment, the engine 1 is a spark ignition type internal combustion engine. The engine 1 is mounted on a vehicle (automobile) (not shown).

  Hereinafter, the low-pressure turbocharger is also referred to as “LP turbo”, and the high-pressure turbocharger is also referred to as “HP turbo”. The low pressure stage is also expressed as “LP”, the high pressure stage as “HP”, and the fuel cell as “FC”.

  The engine body 2 includes basic engine components such as a cylinder block, a cylinder head, a crankcase, an oil pan, a head cover, a piston, a connecting rod, a crankshaft, a camshaft, and an intake / exhaust valve. The engine body 2 includes a plurality of (four) cylinders, and a fuel injection injector 41 and a spark plug 42 are provided in each cylinder.

  An intake passage 5 and an exhaust passage 6 are connected to the engine body 2, and a low-pressure turbocharger 3 </ b> L and a high-pressure turbocharger 3 </ b> H are provided in series so as to straddle the intake passage 5 and the exhaust passage 6. Yes. As is well known, the high-pressure turbocharger 3H is provided on the near side and the low-pressure turbocharger 3L is provided on the far side with respect to the engine body 2.

  The low-pressure stage turbocharger 3L and the high-pressure stage turbocharger 3H constitute a multistage turbocharger system, particularly a two-stage sequential turbosystem. In the exhaust passage 6, a high-pressure turbine 3HT of the high-pressure turbocharger 3H is disposed on the upstream side, and a low-pressure turbine 3LT of the low-pressure turbocharger 3L is disposed on the downstream side thereof. In addition, in the intake passage 5, a low-pressure stage compressor 3LC of the low-pressure turbocharger 3L is arranged upstream, and a high-pressure stage compressor 3LC of the high-pressure turbocharger 3H is arranged downstream thereof. Yes.

  Hereinafter, the low-pressure turbine is also referred to as “LP turbine”, the high-pressure turbine as “HP turbine”, the low-pressure compressor as “LP compressor”, and the high-pressure compressor as “HP compressor”. Further, “upstream side” and “downstream side” refer to the upstream side and the downstream side in the flow direction of intake air or exhaust gas as indicated by arrows in the figure.

  In the intake passage 5, an air flow meter 7 for detecting the amount of intake air is provided upstream of the low-pressure compressor 3LC, and an intercooler 8 and an electronically controlled throttle valve 9 are provided downstream of the high-pressure compressor 3HC. It is provided in series. An air cleaner (not shown) is provided at the upstream end of the intake passage 5.

  In the exhaust passage 6, an exhaust purification catalyst 10 is provided on the downstream side of the low-pressure stage turbine 3LT. Although only one exhaust purification catalyst 10 is shown in the figure, a plurality of exhaust purification catalysts 10 may be provided. In the present embodiment, the exhaust purification catalyst 10 is composed of a three-way catalyst. However, the type of the exhaust purification catalyst 10 is arbitrary.

  An LP turbine bypass passage 11 that bypasses the low-pressure stage turbine 3LT is provided in parallel with the exhaust passage 6. The LP turbine bypass passage 11 is branched from the exhaust passage 6 on the downstream side of the high-pressure stage turbine 3HT and on the upstream side of the low-pressure stage turbine 3LT, and enters the exhaust passage 6 on the downstream side of the low-pressure stage turbine 3LT and the upstream side of the exhaust purification catalyst 10. Merged. A waste gate valve 12 is provided in the LP turbine bypass passage 11.

  A variable vane or variable nozzle (VN) 13 is provided at the inlet of the high-pressure turbine 3HT in the exhaust passage 6. An HP turbine bypass passage 14 that bypasses the high-pressure turbine 3HT is provided in parallel with the exhaust passage 6. The HP turbine bypass passage 14 is branched from the exhaust passage 6 at the position of the exhaust manifold 18 on the upstream side of the variable nozzle 13, and the exhaust passage 6 is downstream of the high-pressure turbine 3 HT and upstream of the branch position of the LP turbine bypass passage 11. To join. An HP turbine bypass valve 19 is provided in the HP turbine bypass passage 14.

  The exhaust manifold 18 constitutes the most upstream part of the exhaust passage 6 and is attached to the cylinder head of the engine body 2 to join exhaust gases from the cylinders.

  An HP compressor bypass passage 20 that bypasses the high-pressure compressor 3HC is provided in parallel with the intake passage 5. The HP compressor bypass passage 20 is branched from the intake passage 5 downstream of the low-pressure compressor 3LC and upstream of the high-pressure compressor 3HC, and joins the intake passage 5 downstream of the high-pressure compressor 3HC and upstream of the intercooler 8. Is done. An HP compressor bypass valve 21 is provided in the HP compressor bypass passage 20.

  An EGR device 44 is provided for circulating a part of exhaust gas (referred to as engine exhaust) from the engine body 2 to the intake side. The EGR device 44 includes an EGR passage 45, an EGR cooler 46, and an EGR valve 47. The EGR passage 45 connects the exhaust manifold 18 and the intake manifold 47. The EGR cooler 46 and the EGR valve 47 are provided in the EGR passage 45 in this order from the upstream side.

  The intake manifold 47 constitutes the most downstream portion of the intake passage 5 and is attached to the cylinder head of the engine body 2 to distribute and supply intake air to each cylinder.

  An electric fuel pump 22 is provided to supply fuel to the injector 41 of each cylinder of the engine body 2. The fuel pump 22 sends fuel to the delivery pipe 23, and the fuel accumulated in the delivery pipe 23 is directly injected into the cylinder from the injector 41 of each cylinder. Thus, although the engine of this embodiment is a direct injection type, the injection method is not particularly limited, and may be a port injection type.

  In order to supply fuel to the fuel cell 4, an electric FC fuel pump 15 is provided. Between the FC fuel pump 15 and the fuel cell 4, an FC fuel metering valve 16 for adjusting the fuel supply amount to the fuel cell 4 is provided. As described above, in this embodiment, the fuel pump is provided separately for the injector and for the fuel cell, but may be shared.

  In addition, a battery 17 for supplying electric power to each electrical component of the vehicle and an electric motor, that is, a starter motor 48 for cranking the engine body 2 for starting or starting the engine body 2 are provided. Although the kind of the battery 17 is arbitrary, in this embodiment, it is a general lead acid battery. The starter motor 48 appropriately rotates the crankshaft of the engine body 2.

  An air supply path 25 is provided to extract air from the intake passage 5 and supply it to the fuel cell 4. An air supply control valve 26 is provided in the air supply path 25. The air supply passage 25 is branched from the intake passage 5 on the downstream side of the high-pressure compressor 3HC and the upstream side of the intercooler 8, and is connected to the air supply control valve 26, and the HP compressor bypass valve 21 A second air passage 32 branched from the upstream HP compressor bypass passage 20 and connected to the air supply control valve 26, and a third air passage 33 connecting the air supply control valve 26 and the fuel cell 4 are included. A branch position of the first air passage 31 in the intake passage 5 is indicated by a reference symbol P1, and a branch position of the second air passage 32 in the HP compressor bypass passage 20 is indicated by a reference symbol P2. In particular, in the intake passage 5, the branch position P <b> 1 of the first air passage 31 is downstream of the joining position of the HP compressor bypass passage 20.

  The first air passage 31 and the third air passage 33 constitute a first air supply passage 25A that connects the fuel cell 4 and the intake passage 5 on the downstream side of the high-pressure compressor 3HC. Further, a portion from the upstream end to the branch position P2 in the HP compressor bypass passage 20, the second air passage 32, and the third air passage 33 are provided between the fuel cell 4, the low-pressure compressor 3LC, and the high-pressure compressor 3HC. A second air supply path 25B connecting the intake passage 5 is configured. The air supply path 25 includes a first air supply path 25A and a second air supply path 25B. In the present embodiment, the downstream portion of the first supply passage 25 </ b> A and the second supply passage 25 </ b> B is commonly formed by the third air passage 33 on the downstream side of the supply control valve 26 or on the fuel cell 4 side. Has been. However, it is naturally possible to form these separately.

  The air supply control valve 26 is a valve for switching a supply source of air (also referred to as FC air) supplied to the fuel cell 4. In the case of this embodiment, the air supply control valve 26 is constituted by a single three-way valve, and is installed at the joining position of the first air passage 31 and the second air passage 32. However, the type and installation position are arbitrary. For example, when the first air supply path 25A and the second air supply path 25B are formed completely separately, an air supply control valve is formed by a two-way valve individually provided in the air supply paths 25A and 25B. It doesn't matter.

  Next, an exhaust passage 27 is provided to supply or discharge exhaust gas (referred to as FC exhaust) from the fuel cell 4 to the exhaust passage 6. An exhaust control valve 28 is provided in the exhaust path 27. The exhaust passage 27 extends from the first exhaust passage 34 that connects the fuel cell 4 and the exhaust control valve 28, the second exhaust passage 35 that extends from the exhaust control valve 28 and joins the exhaust manifold 18, and the exhaust control valve 28. And a third exhaust passage 36 joined to the exhaust passage 6 downstream of the joining position of the HP turbine bypass passage 14 and upstream of the branching position of the LP turbine bypass passage 11. A joining position of the third exhaust passage 36 in the exhaust passage 6 is indicated by a symbol Q.

  The first exhaust passage 34 and the second exhaust passage 35 constitute a first exhaust passage 27A that connects the fuel cell 4 and the exhaust passage 6 on the upstream side of the high-pressure turbine 3HT. Further, the first exhaust passage 34 and the third exhaust passage 36 constitute a second exhaust passage 27B that connects the fuel cell 4 and the exhaust passage 6 between the high-pressure turbine 3HT and the low-pressure turbine 3LT. The exhaust path 27 includes a first exhaust path 27A and a second exhaust path 27B. In the present embodiment, on the upstream side of the exhaust control valve 28 or the fuel cell 4 side, the upstream side portion of the first exhaust path 27A and the second exhaust path 27B is formed in common by the first exhaust path 34. . However, it is naturally possible to form these separately.

  The exhaust control valve 28 is a valve for switching the supply destination of the FC exhaust discharged from the fuel cell 4. In the case of this embodiment, the exhaust control valve 28 is constituted by a single three-way valve, and is installed at a branch position between the second exhaust passage 35 and the third exhaust passage 36. However, the type and installation position are arbitrary. For example, when the first exhaust path 27A and the second exhaust path 27B are formed completely separately, the exhaust control valve may be formed by a two-way valve provided individually in the exhaust paths 27A and 27B. .

  In the case of the present embodiment, the first exhaust passage 34 is configured to send exhaust gas from the air electrode (cathode) 4A and the fuel electrode (anode) 4B of the fuel cell 4 to the downstream side after merging. .

  In order to control the engine 1 and the vehicle, an electronic control unit (ECU) 100 as a control device or a control unit is provided. The ECU 100 includes a CPU, a storage device such as a ROM and a RAM, an A / D converter, an input / output interface, and the like. Various programs, data, maps, and the like are stored in the storage device, and the ECU 100 executes various controls by executing these programs.

  The ECU 100 inputs various signals from the crank angle sensor 51, the accelerator opening sensor 52, and other various sensors and switches in addition to the air flow meter 7 described above. The ECU 100 also includes the above-described injector 41, spark plug 42, throttle valve 9, waste gate valve 12, variable nozzle 13, EGR valve 47, starter motor 48, fuel pump 22, HP turbine bypass valve 19, HP compressor bypass valve 21, Control signals are output to the FC fuel pump 15, the FC fuel metering valve 16, the air supply control valve 26, and the exhaust control valve 28, respectively, to control them.

  Based on the signal from the air flow meter 7, the ECU 100 detects an intake air amount that is the amount of intake air per unit time, that is, an intake flow rate. The ECU 100 detects the load of the engine 1 based on at least one of the accelerator opening detected by the accelerator opening sensor 52 and the intake air amount detected by the air flow meter 7.

  The ECU 100 detects the crank angle itself and the rotational speed of the engine 1 based on the crank pulse signal from the crank angle sensor 51. Here, “the number of rotations” means the number of rotations per unit time and is synonymous with the rotation speed. In the present embodiment, it means rpm per minute.

  Here, the fuel cell 4 will be described in detail. As is well known, the fuel cell 4 generates power by an electrochemical reaction between air and fuel (hydrogen). The fuel cell 4 of this embodiment is a solid oxide type or a solid electrolyte type (SOFC), but other types of fuel cells such as a solid polymer type (PEFC), a phosphoric acid type (PAFC), and a molten carbonate type. (MCFC) can also be used.

The fuel cell 4 is mainly composed of a cell stack formed by stacking a plurality of cells composed of an air electrode 4A, a fuel electrode 4B, and an electrolyte sandwiched between these electrodes with a separator interposed therebetween. Oxygen O ₂ contained in the air sent from the intake passage 5 is substantially supplied to the air electrode 4A. Hydrogen H ₂ obtained by reforming liquid fuel (in this embodiment, gasoline) is substantially supplied to the fuel electrode 4B. Carbon monoxide CO may be supplied to the fuel electrode. In this case, carbon dioxide CO ₂ is discharged after the reaction. The main component of the exhaust gas from the fuel cell 4 is water vapor.

Compared to other types of fuel cells, the advantages of using SOFC are as follows.
(1) Since the operating temperature is relatively high at 450 to 1000 ° C. and close to the engine exhaust temperature, high-temperature FC exhaust can be used for driving the turbine.
(2) Since the operating temperature is high, the fuel can be reformed inside, the reformer can be omitted, and the liquid fuel can be directly supplied.
(3) Power generation efficiency is relatively high (45 to 65%) and compact.

  In the case of this embodiment, the fuel cell 4 functions as a power generation device for charging the battery 17 as a main power source or an auxiliary power source for assisting the main power source. Therefore, unlike a general engine, the engine 1 of the present embodiment does not include a generator or an alternator that is mechanically driven by a crankshaft. A fuel cell 4 is provided in place of the alternator. By omitting the mechanical generator in this way, it is possible to reduce engine mechanical loss and improve fuel efficiency. However, an embodiment in which the fuel cell 4 is used in combination with a mechanical generator and an embodiment in which the fuel cell 4 is used for other purposes such as power are possible.

  Next, a multistage turbocharging system will be described. The high-pressure stage turbocharger 3H is smaller or smaller in diameter than the low-pressure stage turbocharger 3L. The low-pressure stage turbocharger 3L is mainly used for the low engine speed range with the high-pressure stage turbocharger 3H, and the high-speed area turbocharger 3L. It comes to take charge in. When the engine speed increases from the idle speed, first, the rotation of the small high-pressure turbocharger 3H starts up, and supercharging by the high-pressure turbocharger 3H is executed. As a result, a high engine torque can be obtained even in a low rotation range. The high-pressure turbocharger 3H has a better supercharging response than the low-pressure turbocharger 3L, and can improve the turbo lag in the emission mode range and the normal range.

  The emission mode region refers to an engine operation region used when the vehicle is operated in accordance with an emission mode (JC08 or the like) defined by the laws and regulations of each country. Further, the normal range refers to an engine operating range that is used during general driving of the vehicle. Each of these is a region from a low rotation / low load of the engine to a middle rotation / medium load, and is a region where the high-pressure turbocharger 3H mainly works.

  Thereafter, when the engine speed further increases, the rotation of the relatively large low-pressure turbocharger 3L starts up, and supercharging by the low-pressure turbocharger 3L is executed. As a result, a high engine torque can be generated in a high rotation range. Since the low-pressure stage turbocharger 3L is large, it can accept a large amount of exhaust gas in a high rotation range.

  In order to realize such an operation, the HP turbine bypass valve 19 and the HP compressor bypass valve 21 are generally controlled by the ECU 100 as follows. When the engine speed increases from the idle speed, the HP turbine bypass valve 19 and the HP compressor bypass valve 21 are first controlled to be fully closed. Then, the entire amount of engine exhaust is supplied to the HP turbine 3HT without bypassing the HP turbine 3HT. As a result, the rotation of the HP turbine 3HT and then the HP compressor 3HC is started, and supercharging by the HP turbo 3H is performed.

  At this time, the exhaust gas that has passed through the HP turbine 3HT is supplied to the LP turbine 3LT. At this time, much of the exhaust gas energy (pressure energy and thermal energy) has already been consumed. Few. And the amount of work of the LP compressor 3LC is inevitably small. The HP compressor 3HC will supercharge the intake air slightly increased in pressure by the LP compressor 3LC.

  The low speed region where the HP turbine bypass valve 19 and the HP compressor bypass valve 21 are fully closed is a region where supercharging is executed substantially only by the HP turbo 3H. This region is referred to as the HP turbo 3H operating region.

  Thereafter, when the engine speed increases, the HP turbine bypass valve 19 and the HP compressor bypass valve 21 are gradually opened. Then, the amount of engine exhaust that bypasses the HP turbine 3HT increases, the work amount of the HP turbine 3HT decreases, and at the same time, the work amount of the LP turbine 3LT increases. Accordingly, the work amount of the HP compressor 3HC decreases, and at the same time, the work amount of the LP compressor 3LC increases.

  The intermediate rotation region in which the HP turbine bypass valve 19 and the HP compressor bypass valve 21 are at an intermediate opening is a region where supercharging is executed by both the HP turbo 3H and the LP turbo 3L. This area is called a transition area.

  Thereafter, when the engine speed further increases, the HP turbine bypass valve 19 and the HP compressor bypass valve 21 are controlled to be fully opened. Then, almost all of the engine exhaust bypasses the HP turbine 3HT and is supplied to the LP turbine 3LT. At this time, since the inlet pressure and the outlet pressure of the HP turbine 3HT are substantially equal, the HP turbine 3HT substantially does not work.

  Along with this, the LP compressor 3LC starts supercharging in earnest. Almost all of the air discharged from the LP compressor 3LC is guided to the engine body side, bypassing the HP compressor 3HC. At this time, the HP compressor 3HC substantially does not work.

  The high rotation region where the HP turbine bypass valve 19 and the HP compressor bypass valve 21 are fully opened is a region where supercharging is performed substantially only by the LP turbo 3L. This region is referred to as the LP turbo 3L operating region.

  As in the case of a normal single turbo that is not a multi-stage type, in the operation region of the LP turbo 3L, when the supercharging pressure reaches a predetermined upper limit pressure, the waste gate valve 12 is opened and the supercharging pressure limiting control is executed. In the operating region of the HP turbo 3H, the opening degree of the variable nozzle 13 is controlled according to the engine operating state, and the inlet pressure of the HP turbine 3HT is controlled. In order to increase the pressure in the exhaust manifold 18 during EGR execution, the opening degree of the variable nozzle 13 may be reduced.

  Now, the engine 1 according to the present embodiment including the multi-stage turbocharging system (3L, 3H) and the fuel cell 4 uses the intake air passage 5 on the downstream side of the HP compressor 3HC or the LP compressor 3LC as the air supplied to the fuel cell 4. It is configured to extract from. That is, the HP compressor 3HC or the LP compressor 3LC is shared with the engine body 2 as an air source for the fuel cell 4, and a part of the intake air whose pressure is increased by these compressors is extracted and supplied to the fuel cell 4. Therefore, it is not necessary to provide a separate air source such as a motor compressor for supplying air to the fuel cell, and the complexity of the apparatus and the increase in cost can be avoided.

  Further, the engine 1 of the present embodiment is configured to supply exhaust gas discharged from the fuel cell 4 to the exhaust passage 6 on the upstream side of the HP turbine 3HT or the LP turbine 3LT. Thereby, the FC exhaust can be effectively used for driving the HP turbine 3HT or the LP turbine 3LT.

  By the way, as described above, in the multistage turbocharger system as in the present embodiment, when the turbocharger is switched from the HP turbo 3H to the LP turbo 3L as the engine speed increases, there is a difference in engine torque. There is a problem that occurs and impairs drivability. A similar problem may occur when the turbocharger is switched in the reverse direction as the engine speed decreases. The reason why this torque step occurs is mainly because the LP turbo 3L is larger than the HP turbo 3H and the rotation speed and supercharging pressure are difficult to rise.

  In order to cope with this problem, it is conceivable to reduce the size difference between the HP turbo 3H and the LP turbo 3L. However, when the fuel cell 4 is provided as in this embodiment, it is relatively difficult to reduce the size difference. That is, in the operating region of the LP turbo 3L, FC air is extracted from the downstream side of the LP compressor 3LC, but the LP turbo 3L must be enlarged in order to supplement the extracted air and maintain the same engine output. I must. Therefore, it is difficult to reduce the size difference.

  Recently, downsizing of the engine, that is, reduction of the engine body 2 has been progressing. Under such circumstances, the LP turbo 3L tends to increase in size in order to ensure the necessary engine output. This is also the reason why it is difficult to reduce the size difference.

  Therefore, in order to suppress a torque step at the time of switching between the HP turbo 3H and the LP turbo 3L, in the present embodiment, the following control is executed.

  FIG. 2 shows a map of the engine operation region defined by the engine speed and load. This map is created in advance based on an actual machine test or the like and stored in the ECU 100 in advance. The ECU 100 performs switching control between the HP turbo 3H and the LP turbo 3L according to this map, specifically, the opening control of the HP turbine bypass valve 19 and the HP compressor bypass valve 21. At the same time, the ECU 100 performs supply / exhaust control for the fuel cell 4 according to this map, specifically, switching control of the supply control valve 26 and the exhaust control valve 28.

  As shown in FIG. 2, the entire operation region of the engine is divided into a plurality of (three) regions. Region A is the low rotation region described above, and is the operating region of the HP turbo 3H. A region C is the above-described high rotation region, and is an operation region of the LP turbo 3L. Region B is a medium rotation region or transition region between region A and region C as described above. The region A and the region B are partitioned by a predetermined boundary line L1, and the region C and the region B are partitioned by a predetermined boundary line L2. Compared to the regions A and C, the region B has a relatively narrow rotational speed width.

  In the area B, the area A and the area C are divided by a rotation speed area that is approximately half of the maximum rotation speed. The boundary lines L1 and L2 are substantially parallel to each other, and have such characteristics that the load rapidly decreases as the rotational speed increases. That is, as the rotational speed increases, the region A, the region B, and the region C are sequentially shifted at an earlier timing as the load increases.

  The ECU 100 compares the detected actual rotational speed and load with the map, and controls the HP turbine bypass valve 19, the HP compressor bypass valve 21, the air supply control valve 26, and the exhaust control valve 28 as described below for each region. . In the following description, it is assumed that the fuel cell 4 is operating or generating power.

  When the detected actual rotational speed and load belong to the region A, the flow of air, engine exhaust, and FC exhaust is as shown in FIG. At this time, the ECU 100 controls the HP turbine bypass valve 19 and the HP compressor bypass valve 21 to be fully closed. Then, the engine exhaust is supplied to the HP turbine 3HT, the HP turbine 3HT is rotationally driven, the HP compressor 3HC supercharges the intake air, and supercharging is executed substantially only by the HP turbo 3H.

  At this time, the ECU 100 switches the air supply control valve 26 so that the third air passage 33 is connected to or communicates only with the first air passage 31. That is, the ECU 100 switches the air supply path 25 to the first air supply path 25A. Then, air is extracted from the downstream side of the HP compressor 3 HC, and this air passes through the first air passage 31, the air supply control valve 26 and the third air passage 33 in order, and is supplied to the fuel cell 4.

  At this time, the ECU 100 switches the exhaust control valve 28 so that the first exhaust passage 34 is connected to or communicates only with the second exhaust passage 35. That is, the ECU 100 switches the exhaust path 27 to the first exhaust path 27A. Then, the FC exhaust discharged from the fuel cell 4 sequentially passes through the first exhaust passage 34, the exhaust control valve 28 and the second exhaust passage 35, and is supplied or discharged to the exhaust manifold 18. This supplied or exhausted FC exhaust can be effectively used for rotational driving of the HP turbine 3HT.

  Of course, the ECU 100 operates the FC fuel pump 15 to open the FC fuel metering valve 16. As described above, air and fuel are supplied to the fuel cell 4, and the fuel cell 4 performs power generation. Hereinafter, description of the point of fuel supply is abbreviate | omitted.

  Next, when the detected actual rotational speed and load belong to region C, the flow of air, engine exhaust, and FC exhaust is as shown in FIG. At this time, the ECU 100 controls the HP turbine bypass valve 19 and the HP compressor bypass valve 21 to fully open. Then, after the engine exhaust gas passes through the HP turbine bypass passage 14, it is supplied to the LP turbine 3LT to drive the LP turbine 3LT to rotate. Then, the LP compressor 3LC supercharges the intake air, and the intake air passes through the HP compressor bypass passage 20 and is then supplied to the intake passage 5 on the downstream side of the HP compressor 3HC. As a result, supercharging is executed substantially only by the LP turbo 3L.

  At this time, the ECU 100 switches the air supply control valve 26 so that the third air passage 33 is connected to or communicates only with the second air passage 32. That is, the ECU 100 switches the air supply path 25 to the second air supply path 25B. Then, air is extracted from the downstream side of the LP compressor 3LC and the upstream side of the HP compressor 3HC, and this air is upstream of the HP compressor bypass passage 20, the second air passage 32, the air supply control valve 26, and the third air passage. Then, the fuel cell 4 is supplied to the fuel cell 4 sequentially.

  At this time, the ECU 100 switches the exhaust control valve 28 so that the first exhaust passage 34 is connected to or communicates only with the third exhaust passage 36. That is, the ECU 100 switches the exhaust path 27 to the second exhaust path 27B. Then, the FC exhaust discharged from the fuel cell 4 sequentially passes through the first exhaust passage 34, the exhaust control valve 28, and the third exhaust passage 36, and is supplied to the exhaust passage 6 between the HP turbine 3HT and the LP turbine 3LT. Or it is discharged. The supplied or discharged FC exhaust can be effectively used for the rotational drive of the LP turbine 3LT.

  By the way, when the detected actual rotational speed and load belong to the transition region B, the flows of air, engine exhaust, and FC exhaust are as shown in FIG. At this time, the ECU 100 controls the HP turbine bypass valve 19 and the HP compressor bypass valve 21 to an intermediate opening between fully closed and fully opened. Then, the engine exhaust in the exhaust manifold 18 is supplied to both the HP turbine 3HT and the LP turbine 3LT, and both are rotationally driven. The intake air boosted by the LP compressor 3LC that is rotationally driven by the LP turbine 3LT is partially supplied to the HP compressor 3HC, and the remaining part passes through the HP compressor bypass passage 20 (that is, bypasses the HP compressor 3HC). It is supplied to the intake passage 5 on the downstream side of the HP compressor 3HC. Thereby, supercharging is executed by both the HP turbo 3H and the LP turbo 3L.

  At this time, the ECU 100 controls the HP turbine bypass valve 19 and the HP compressor bypass valve 21 so that the opening degree of the HP turbine bypass valve 19 and the HP compressor bypass valve 21 increases as at least one of the rotational speed and the load increases. Thereby, as at least one of the rotational speed and the load increases, the work of the LP turbo 3L is gradually increased and the work of the HP turbo 3H is gradually decreased, so that the transition between the region A and the region C is as smooth as possible. Can be done.

  However, even if such turbo switching control is performed, there is still room for improvement in eliminating the torque step when transitioning between region A and region C. Therefore, in the present embodiment, the following control is executed.

  That is, as shown in FIG. 5, the ECU 100 switches the air supply control valve 26 so that the third air passage 33 is connected or communicated only to the first air passage 31 as in the case of the region A. That is, the ECU 100 switches the air supply path 25 to the first air supply path 25A.

  Further, as in the region C, the ECU 100 switches the exhaust control valve 28 so that the first exhaust passage 34 is connected or communicated only with the third exhaust passage 36. That is, the ECU 100 switches the exhaust path 27 to the second exhaust path 27B. Then, the FC exhaust discharged from the fuel cell 4 sequentially passes through the first exhaust passage 34, the exhaust control valve 28, and the third exhaust passage 36, and is supplied to the exhaust passage 6 between the HP turbine 3HT and the LP turbine 3LT. Or it is discharged.

  In particular, the supplied or exhausted FC exhaust can be used to rotationally drive the LP turbine 3LT and thus the LP compressor 3LC to give them rotation. Specifically, when the rotational speed and load pass from the region A through the region B to the region C, the FC turbine exhausts the LP turbine 3LT and then the LP compressor 3LC in the region B before the transition to the region C. A given rotation can be provided. Therefore, it is possible to increase the rotational speed and its rising speed in the LP turbo 3L, as well as the supercharging pressure and its rising speed, and to suppress or reduce the torque step.

  By suppressing this torque step, it becomes possible to employ a large LP turbo 3L compared to the HP turbo 3H, and the size difference between the two can be relatively enlarged. And it becomes suitable for the engine 1 equipped with the fuel cell 4 like this embodiment, and can respond easily to engine downsizing.

  Further, the air supply path 25 is switched to the first air supply path 25A, and the FC air is extracted from the intake passage 5 on the downstream side of the HP compressor 3HC, in particular, on the downstream side of the merging position of the HP compressor bypass passage 20. The air discharged from the compressor 3HC and the air discharged from the LP compressor 3LC can be extracted together as FC air, and air can be stably supplied to the fuel cell 4.

  However, in the region B, the work amount of the LP turbo 3L is gradually increased and the work amount of the HP turbo 3H is gradually decreased as at least one of the rotational speed and the load increases. Therefore, it is also preferable to control the opening degree of the air supply control valve 26 in accordance with this characteristic. That is, as at least one of the rotational speed and the load increases, the opening degree on the second air passage 32 side (second air supply passage 25B side) becomes closer to the first air passage 31 side (first air supply passage 25A side). The air supply control valve 26 is controlled so as to gradually increase with respect to the opening. As a result, even in a relatively narrow region B, it is possible to continue extracting FC air from an appropriate position in accordance with the operating characteristics of both turbos.

  By the way, in the engine 1 of this embodiment, the fuel cell 4 can be operated independently. Here, the self-sustained operation of the fuel cell 4 refers to the supply of air to the fuel cell 4 by rotating the turbine and compressor of the HP turbo 3H and the LP turbo 3L with the exhaust gas of the fuel cell 4 while the engine body 2 is stopped. The state in which the fuel cell 4 continues to operate or generate electric power by performing the fuel supply together. In this self-sustained operation, when the engine body 2 is stopped, the remaining amount of the battery falls below a predetermined threshold value, or the amount of discharge from the battery increases above the predetermined threshold value due to the use of an electric load, and power generation by the fuel cell 4 is required It is done when it becomes.

  For example, when the fuel cell 4 is operated autonomously using the HP turbo 3L, the ECU 100 switches the air supply path 25 to the first air supply path 25A and the exhaust path 27 to the first exhaust as shown in FIG. Switch to road 27A. Then, the HP turbine 3HT is driven by FC exhaust, the air from the HP compressor 3HC is supplied to the fuel cell 4, and the FC fuel pump 15 is also operated, and the FC fuel metering valve 16 is opened. The ECU 100 controls the HP turbine bypass valve 19 and the HP compressor bypass valve 21 to be fully closed. Since the HP turbine bypass valve 19 and the HP compressor bypass valve 21 are fully closed when the engine is stopped, this state is maintained during the autonomous operation of the fuel cell 4.

  In order to start the self-sustaining operation, the HP turbo 3H must be initially moved. This is performed by the ECU 100 turning on the starter motor 48 for a short time and causing the engine body 2 to perform a motoring operation.

  Although detailed description is omitted, the self-sustained operation of the fuel cell 4 using the LP turbo 3L is also possible.

  As can be understood from the above description, in the present embodiment, the ECU 100 and the exhaust control valve 28 constitute an exhaust path switching means, and the ECU 100 and the air supply control valve 26 constitute an air supply path switching means.

  Although the embodiment of the present invention has been described in detail above, various other embodiments of the present invention are conceivable. For example, the use and type of the internal combustion engine are arbitrary and may be other than those for automobiles.

  The present invention includes all modifications, applications, and equivalents included in the spirit of the present invention defined by the claims. Therefore, the present invention should not be construed as being limited, and can be applied to any other technique belonging to the scope of the idea of the present invention.

1 Internal combustion engine
2 Engine body 3L Low-pressure turbocharger (LP turbo)
3LT Low pressure turbine (LP turbine)
3LC Low-pressure compressor (LP compressor)
3H High-pressure turbocharger (HP turbo)
3HT High-pressure turbine (HP turbine)
3HC high-pressure compressor (HP compressor)
4 Fuel cell (FC)
5 Intake passage 6 Exhaust passage 14 HP turbine bypass passage 15 FC fuel pump 16 FC fuel metering valve 17 Battery 19 HP turbine bypass valve 20 HP compressor bypass passage 21 HP compressor bypass valve 25 Supply passage 25A First supply passage 25B Second air passage 26 Air supply control valve 27 Exhaust passage 27A First exhaust passage 27B Second exhaust passage 28 Exhaust control valve 31 First air passage 32 Second air passage 33 Third air passage 34 First exhaust passage 35 Second exhaust passage 36 Third exhaust passage 51 Crank angle sensor 52 Accelerator opening sensor 100 Electronic control unit (ECU)

Claims (4)

Comprising a fuel cell, a low-pressure stage turbocharger having a low-pressure stage turbine and a low-pressure stage compressor, and a high-pressure stage turbocharger having a high-pressure stage turbine and a high-pressure stage compressor,
In the exhaust passage, the low-pressure stage turbine is disposed on the downstream side of the high-pressure stage turbine, and in the intake passage, the high-pressure stage compressor is disposed on the downstream side of the low-pressure stage compressor,
A first exhaust passage that connects the fuel cell and the exhaust passage upstream of the high-pressure turbine, and a first exhaust passage that connects the fuel cell and the exhaust passage between the high-pressure turbine and the low-pressure turbine. Two exhaust paths, and an exhaust path switching means for switching the first and second exhaust paths,
When the operating state of the internal combustion engine is in a transition region between the operating region of the high-pressure stage turbocharger and the operating region of the low-pressure stage turbocharger, the exhaust passage switching means is the second exhaust passage. An internal combustion engine characterized by switching to A first air supply path connecting the fuel cell and the intake passage on the downstream side of the high pressure compressor, and the intake passage between the fuel cell, the low pressure compressor and the high pressure compressor are connected. A second air supply path, and an air supply path switching means for switching the first and second air supply paths,
2. The internal combustion engine according to claim 1, wherein when the operating state of the internal combustion engine is in the transition region, the air supply path switching unit switches to the first air supply path. When the operating state of the internal combustion engine is in an operating region of the high-pressure turbocharger, the exhaust path switching means switches to the first exhaust path, and the air supply path switching means switches to the first air supply path. The internal combustion engine according to claim 2, wherein the internal combustion engine is switched to. When the operating state of the internal combustion engine is in the operating region of the low-pressure turbocharger, the exhaust path switching means switches to the second exhaust path, and the air supply path switching means switches to the second air supply path. The internal combustion engine according to claim 2 or 3, wherein the internal combustion engine is switched to.

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