JP2020197166A - Supercharging system - Google Patents

Abstract

To provide a supercharging system including superchargers provided in parallel, for estimating exhaust pressure P4 of an exhaust manifold.SOLUTION: The supercharging system includes primary and secondary superchargers including turbines 32, 42 to be driven by exhaust gas from an engine and variable nozzle mechanisms 35, 45 for adjusting the flow speed of exhaust gas to the turbines 32, 42, respectively, for supercharging intake air to the engine, and a control device for switching a supercharging mode from one of a single supercharging mode in which air supercharged by the primary supercharger is supplied to the engine and a twin supercharging mode in which air supercharged by the primary and secondary superchargers is supplied to the engine, to the other. The control device, before switching from the single supercharging mode to the twin supercharging mode, switches to a run-up mode to supply air supercharged by the secondary supercharger to the primary supercharger while supplying the exhaust gas to the secondary supercharger, uses a common estimated equation for estimating P4 in the three modes to calculate the P4, and controls the engine using the P4.SELECTED DRAWING: Figure 7

Description

This disclosure relates to a supercharging system, and particularly to a supercharging system having a plurality of superchargers connected in parallel.

Conventionally, in an engine equipped with a series sequential turbo provided with a bypass valve provided in a path for bypassing a high-pressure stage turbine in the exhaust path, the opening area ratio between the bypass valve and the turbine, intake pressure and exhaust gas flow rate. There was a technique for estimating the exhaust pressure of an exhaust manifold (see, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2016-79810

However, since the technique of Patent Document 1 is a technique relating to a series sequential turbo, it is difficult to estimate the exhaust pressure of the exhaust manifold in an engine equipped with a parallel sequential turbo by using the technique of Patent Document 1.

FIG. 13 is a diagram showing the relationship between the fuel injection amount of the engine equipped with the parallel sequential turbo and the exhaust pressure of the exhaust manifold. With reference to FIG. 13, in an engine equipped with a parallel sequential turbo, when switching between single supercharging and twin supercharging at an equal supercharging pressure, switching is performed in the hiss region shown in the figure. In this case, since the exhaust pressure P4 of the exhaust manifold differs between the single supercharging and the twin supercharging, the pumping loss changes, so that the torque generated by the engine has a step. In order to eliminate this torque step, it is corrected by the fuel injection amount. Therefore, it is necessary to estimate the exhaust pressure P4 of the exhaust manifold.

This disclosure was made in order to solve the above-mentioned problems, and the purpose of the disclosure is to provide a supercharging system capable of estimating the exhaust pressure of the exhaust manifold in a supercharging system equipped with a supercharger in parallel. Is to provide.

The supercharging system according to this disclosure includes a first turbine driven by exhaust discharged from the engine and a first variable nozzle mechanism that adjusts the flow velocity of the exhaust flowing into the first turbine according to the opening degree, and is supplied to the engine. Includes a first turbocharger that supercharges intake air, a second turbocharger driven by exhaust from the engine, and a second variable nozzle mechanism that adjusts the flow velocity of the exhaust air flowing into the second turbine according to the opening degree. , The second supercharger that supercharges the intake air to the engine, the single supercharge mode in which the supercharged air is supplied to the engine in the first supercharger, and the supercharged air in the first supercharger. A control device for switching the supercharging mode from one of the twin supercharging mode in which the supercharged air in the second supercharger and the supercharged air is supplied to the engine to the other is provided.

The control device supplies the air supercharged by the second supercharger to the first supercharger while supplying exhaust to the second supercharger before switching from the single supercharge mode to the twin supercharge mode. Switch to the run-up operation mode, calculate the exhaust pressure of the exhaust manifold using a common estimation formula that estimates the exhaust pressure of the exhaust manifold in the single supercharging mode, twin supercharging mode and run-up operation mode, and calculate the exhaust manifold The engine is controlled using the pressure of the exhaust.

Preferably, the controller calculates the exhaust pressure of the exhaust manifold by substituting the pressure of the exhaust merging after the first turbine and the second turbine into the estimation formula.

Preferably, it further comprises an exhaust gas recirculation device having a return path that recirculates a part of the engine exhaust as the engine intake.

More preferably, the control device calculates the exhaust pressure of the exhaust manifold by substituting the exhaust pressure of the exhaust gas merging after the first turbine and the second turbine and the exhaust pressure of the return path into the estimation formula.

More preferably, the exhaust gas recirculation device includes a valve provided in the return path to regulate the amount of exhaust returned. The estimation formula is constructed from the nozzle formula and the conservation of mass law for each of the first variable nozzle mechanism, the second variable nozzle mechanism and the valve.

Preferably, the control device specifies the ratio of the exhaust flow rate distributed to each of the first variable nozzle mechanism and the second variable nozzle mechanism from the opening area ratio of the first variable nozzle mechanism and the second variable nozzle mechanism, and the engine. Exhaust distributed to each of the first variable nozzle mechanism and the second variable nozzle mechanism based on the ratio of the exhaust flow rate discharged from the first variable nozzle mechanism and the exhaust flow rate distributed to each of the first variable nozzle mechanism and the second variable nozzle mechanism. The first variable nozzle mechanism is determined from the exhaust flow rate that is specified and distributed to each of the specified first variable nozzle mechanism and the second variable nozzle mechanism, and the opening degree of each of the first variable nozzle mechanism and the second variable nozzle mechanism. And the effective opening area of the second variable nozzle mechanism is specified, and the effective opening area of each of the specified first variable nozzle mechanism and the second variable nozzle mechanism is substituted into the estimation formula to calculate the exhaust pressure of the exhaust manifold.

According to this disclosure, it is possible to provide a supercharging system capable of estimating the exhaust pressure of the exhaust manifold in a supercharging system including a supercharger in parallel.

It is a figure which shows an example of the schematic structure of the engine in this embodiment. It is a figure for demonstrating the operation of the supercharging system in the single supercharging mode. It is a figure for demonstrating the operation of the supercharging system in the approach mode. It is a figure for demonstrating the operation of the supercharging system in the twin supercharging mode. It is a figure which shows the outline of the exhaust flow of the engine in a single supercharging mode. It is a figure which shows that the φ function can be approximated to a straight line. It is a figure which shows the outline of the exhaust flow of the engine in the approach mode. It is a figure which shows the outline of the flow of the exhaust gas to the variable nozzle mechanism of a primary supercharger and a secondary supercharger. It is a figure which shows the relationship between the opening area ratio of the variable nozzle mechanism of a primary supercharger and a secondary supercharger, and the ratio of the amount of gas passing through each. It is a figure which shows the outline of the exhaust flow of the engine in the twin supercharging mode. It is a figure which shows the outline of the method of calculating the opening degree of a variable nozzle mechanism so that the exhaust pressure of an exhaust manifold does not exceed the constraint value. It is a flowchart which shows the flow of the VN opening degree calculation processing during approach running in this embodiment. It is a figure which shows the relationship between the fuel injection amount of the engine equipped with a parallel sequential turbo, and the exhaust pressure of an exhaust manifold.

Hereinafter, embodiments of this disclosure will be described with reference to the drawings. In the following description, the same parts are designated by the same reference numerals. Their names and functions are the same. Therefore, detailed explanations about them are not repeated.

[About the configuration of the supercharging system]
FIG. 1 is a diagram showing an example of a schematic configuration of an engine 1 in this embodiment. With reference to FIG. 1, the engine 1 is mounted on the vehicle, for example, as a drive source for traveling. In this embodiment, the case where the engine 1 is a diesel engine will be described as an example, but it may be, for example, a gasoline engine.

The engine 1 includes banks 10A and 10B, an air cleaner 20, an intercooler 25, intake manifolds 28A and 28B, a primary supercharger 30, a secondary supercharger 40, and an exhaust manifold 50A and 50B (hereinafter, "exhaust manifold"). Also referred to as), an exhaust treatment device 81, and a control device 200. The engine 1 further includes an exhaust gas recirculation device (EGR device) including an EGR (Exhaust Gas Recirculation) cooler 71 and an EGR valve 72.

A plurality of cylinders 12A are formed in the bank 10A. A plurality of cylinders 12B are formed in the bank 10B. A piston (not shown) is housed in each of the cylinders 12A and 12B, and a combustion chamber (a space for burning fuel) is formed by the top of the piston and the inner wall of the cylinder. The volume of the combustion chamber is changed by sliding the piston in each of the cylinders 12A and 12B. Injectors (not shown) are provided in the cylinders 12A and 12B, and during the operation of the engine 1, the timing and amount of fuel set by the control device 200 are injected into the cylinders 12A and 12B. .. The injection amount and timing of the fuel injected from each injector are set by the control device 200, for example, from the engine rotation speed NE, the intake air amount Ga, the accelerator pedal depression amount, the vehicle speed, and the like.

The pistons of the cylinders 12A and 12B are connected to a common crankshaft (not shown) via a connecting rod. When fuel burns in each cylinder 12A and 12B in a predetermined order, the piston slides in each cylinder 12A and 12B, and the vertical movement of the piston is converted into the rotational movement of the crankshaft via the connecting rod. ..

The primary turbocharger 30 is a turbocharger including a compressor 31 and a turbine 32. The compressor 31 of the primary supercharger 30 is provided in the intake passage of the engine 1 (that is, the passage from the air cleaner 20 to the intake manifolds 28A and 28B). The turbine 32 of the primary supercharger 30 is provided in the exhaust passage of the engine 1 (that is, the passage from the exhaust manifolds 50A and 50B to the exhaust treatment device 81).

The compressor wheel 33 is rotatably housed in the compressor 31. A turbine wheel 34 and a variable nozzle mechanism 35 are provided in the turbine 32. The turbine wheel 34 is rotatably housed in the turbine 32. The compressor wheel 33 and the turbine wheel 34 are connected by a rotating shaft 36 and rotate integrally. The compressor wheel 33 is rotationally driven by the exhaust energy (exhaust energy) supplied to the turbine wheel 34.

The variable nozzle mechanism 35 changes the flow velocity of the exhaust gas that operates the turbine 32. The variable nozzle mechanism 35 is arranged on the outer peripheral side of the turbine wheel 34, and by rotating a plurality of nozzle vanes (not shown) that guide the exhaust gas supplied from the exhaust inlet to the turbine wheel 34, and each of the plurality of nozzle vanes. It includes a drive device (not shown) that changes the gap between adjacent nozzle vanes (this gap is referred to as the VN opening in the following description). The variable nozzle mechanism 35 changes the VN opening degree by rotating the nozzle vane using a drive device in response to the control signal VN1 from the control device 200, for example.

The secondary supercharger 40 is a turbocharger including a compressor 41 and a turbine 42. In this embodiment, the secondary turbocharger 40 has the same structure and size as the primary turbocharger 30. The compressor 41 of the secondary supercharger 40 is provided in parallel with the compressor 31 in the intake passage of the engine 1 to supercharge the intake air of the engine 1. The turbine 42 of the secondary supercharger 40 is provided in parallel with the turbine 32 in the exhaust passage of the engine 1.

The compressor wheel 43 is rotatably housed in the compressor 41. A turbine wheel 44 and a variable nozzle mechanism 45 are provided in the turbine 42. The turbine wheel 44 is rotatably housed in the turbine 42. The compressor wheel 43 and the turbine wheel 44 are connected by a rotating shaft 46 and rotate integrally. The compressor wheel 43 is rotationally driven by the exhaust energy supplied to the turbine wheel 44.

Since the variable nozzle mechanism 45 has the same configuration as the variable nozzle mechanism 35, the detailed description thereof will not be repeated. The variable nozzle mechanism 45 changes the VN opening degree by, for example, rotating the nozzle vane using a drive device in response to the control signal VN2 from the control device 200.

The air cleaner 20 removes foreign matter from the air sucked from the intake port (not shown). One end of the intake pipe 23 is connected to the air cleaner 20. The other end of the intake pipe 23 branches and is connected to one end of the intake pipe 21 and one end of the intake pipe 22.

The other end of the intake pipe 21 is connected to the intake inlet of the compressor 31 of the primary supercharger 30. One end of the intake pipe 37 is connected to the intake outlet of the compressor 31 of the primary supercharger 30. The other end of the intake pipe 37 is connected to the intercooler 25. The compressor 31 supercharges the air sucked through the intake pipe 21 by the rotation of the compressor wheel 33 and supplies the air to the intake pipe 37.

The other end of the intake pipe 22 is connected to the intake inlet of the compressor 41 of the secondary supercharger 40. One end of the intake pipe 47 is connected to the intake outlet of the compressor 41 of the secondary supercharger 40. The other end of the intake pipe 47 is connected to a connecting portion C3 in the middle of the intake pipe 37. The compressor 41 supercharges the air sucked through the intake pipe 22 by the rotation of the compressor wheel 43 and supplies the air to the intake pipe 47.

A first control valve 62 is provided in the middle of the intake pipe 47. The first control valve 62 is, for example, a normally-off VSV (negative pressure switching valve) that is ON (open) / OFF (closed) controlled in response to the control signal CV1 from the control device 200.

Further, one end of the return pipe 48 is connected to the connection portion C4 located on the upstream side (compressor 41 side) of the first control valve 62 in the intake pipe 47. Further, the other end of the reflux pipe 48 is connected to the intake pipe 21. The return pipe 48 is a passage for returning at least a part of the air flowing through the intake pipe 47 to the upstream side of the compressor 31 of the primary supercharger 30. The air that has returned to the intake pipe 21 through the return pipe 48 is supplied to the compressor 31.

A second control valve 64 is provided in the middle of the return pipe 48. The second control valve 64 is, for example, a normally-off solenoid valve (solenoid valve) that is ON (open) / OFF (closed) controlled according to the control signal CV2 from the control device 200.

The air supercharged by the compressor 31 and the air supercharged by the compressor 41 and passed through the first control valve 62 are supplied to the connection portion C3. These airs merge at the connection portion C3 and flow into the intercooler 25.

The intercooler 25 is configured to cool the inflowing air. The intercooler 25 is, for example, an air-cooled or water-cooled heat exchanger. One end of the intake pipe 27A and one end of the intake pipe 27B are connected to the intake outlet of the intercooler 25 via the diesel throttle 68. The opening degree of the diesel throttle 68 is adjustable by using an electric actuator, and the flow rate of intake air is adjusted according to a control signal from the control device 200. The other end of the intake pipe 27A is connected to the intake manifold 28A. The other end of the intake pipe 27B is connected to the intake manifold 28B.

The intake manifolds 28A and 28B are connected to intake ports (not shown) of cylinders 12A and 12B in banks 10A and 10B, respectively. On the other hand, the exhaust manifolds 50A and 50B are connected to the exhaust ports (not shown) of the cylinders 12A and 12B in the banks 10A and 10B, respectively.

Exhaust gas (gas after combustion) discharged from the combustion chambers of the cylinders 12A and 12B to the outside of the cylinder through the exhaust port is discharged to the outside via the exhaust passage of the engine 1. The exhaust passage includes exhaust manifolds 50A and 50B, exhaust pipes 51A and 51B, connection portions C1, exhaust pipes 52A, 52B, 53A and 53B, and connection portions C2. One end of the exhaust pipe 51A is connected to the exhaust manifold 50A. One end of the exhaust pipe 51B is connected to the exhaust manifold 50B. The other end of the exhaust pipe 51A and the other end of the exhaust pipe 51B merge once at the connection portion C1 and then branch off and are connected to one end of the exhaust pipe 52A and one end of the exhaust pipe 52B.

The other end of the exhaust pipe 52A is connected to the exhaust inlet of the turbine 32. One end of the exhaust pipe 53A is connected to the exhaust outlet of the turbine 32. The other end of the exhaust pipe 52B is connected to the exhaust inlet of the turbine 42. One end of the exhaust pipe 53B is connected to the exhaust outlet of the turbine 42.

A third control valve 66 is provided in the middle of the exhaust pipe 52B. The third control valve 66 is, for example, a Normalion VSV (negative pressure switching valve) that is ON (open) / OFF (closed) controlled according to the control signal CV3 from the control device 200.

The other end of the exhaust pipe 53A and the other end of the exhaust pipe 53B merge at the connection portion C2 and are connected to the exhaust treatment device 81. The exhaust treatment device 81 is composed of, for example, an SCR catalyst, an oxidation catalyst, a PM removal filter, or the like, and purifies the exhaust gas flowing from the exhaust pipe 53A and the exhaust pipe 53B.

One end of the return path 73 of the exhaust gas recirculation device is connected to the confluence of the exhaust pipe 51A and the exhaust pipe 51B. The other end of the return path 73 is connected to the EGR cooler 71. The EGR cooler 71 is configured to cool the inflowing exhaust gas. The EGR cooler 71 is, for example, an air-cooled or water-cooled heat exchanger. One end of the return path 74 is connected to the outlet of the EGR cooler 71 via the EGR valve 72. The EGR valve 72 is a flow rate adjusting valve that adjusts the opening degree according to the control signal CV4 from the control device 200. The other end of the return path 74 is connected to the confluence of the intake pipe 27A and the intake pipe 27B.

The operation of the engine 1 is controlled by the control device 200. The control device 200 includes a CPU (Central Processing Unit) that performs various processes, a memory that includes a ROM (Read Only Memory) that stores programs and data, a RAM (Random Access Memory) that stores the processing results of the CPU, and the like. Includes input / output ports (neither shown) for exchanging information with the outside. Various sensors (for example, an air flow meter 102, a first pressure sensor 106, a second pressure sensor 108, a temperature sensor 114, a third pressure sensor 118, etc.) are connected to the input port. Devices to be controlled (for example, a plurality of injectors, variable nozzle mechanisms 35 and 45, first control valve 62, second control valve 64, third control valve 66, EGR valve 72, etc.) are connected to the output port. To.

The control device 200 controls various devices so that the engine 1 is in a desired operating state based on signals from each sensor and device, as well as maps and programs stored in memory. Note that various controls are not limited to software processing, but can also be processed by dedicated hardware (electronic circuits). Further, the control device 200 has a built-in timer circuit (not shown) for measuring the time.

The air flow meter 102 detects the intake air amount Ga. The air flow meter 102 transmits a signal indicating the detected intake air amount Ga to the control device 200.

The first pressure sensor 106 detects the pressure (hereinafter, referred to as the first boost pressure) Pp at the connection portion C3 of the intake pipe 37. The first pressure sensor 106 transmits a signal indicating the detected first boost pressure Pp to the control device 200.

The second pressure sensor 108 detects the pressure at the connection portion C4 of the intake pipe 47 (hereinafter, referred to as the second boost pressure Ps). The second pressure sensor 108 transmits a signal indicating the second boost pressure Ps to the control device 200.

The third pressure sensor 118 detects the pressure in the intake manifolds 28A and 28B (hereinafter, referred to as the intake manifold pressure Pim). The third pressure sensor 118 transmits a signal indicating the intake manifold pressure Pim to the control device 200.

The temperature sensor 114 detects the pressure (hereinafter referred to as the exhaust manifold gas temperature T4) in the exhaust manifold 50 (typically, the exhaust manifold 50B). The temperature sensor 114 transmits a signal indicating the exhaust manifold temperature T4 to the control device 200.

In this embodiment, the "supercharging system" is configured by the primary supercharger 30, the secondary supercharger 40, and the control device 200.

The control device 200 has a single supercharging mode in which supercharging is performed only by the primary supercharger 30 (primary turbo) by controlling the first control valve 62, the second control valve 64, and the third control valve 66, and the primary. It is configured to be able to execute switching control for switching from one of the twin supercharging mode in which supercharging is performed by both the supercharger 30 (primary turbo) and the secondary supercharger 40 (secondary turbo) to the other. Further, when switching from the single supercharging mode to the twin supercharging mode, the control device 200 executes the operation in the approach mode in which the supercharging pressure by the secondary supercharger 40 is raised to a certain level or more from the single supercharging mode. After that, the supercharging mode is switched to the twin supercharging mode.

Hereinafter, the operation of the supercharging system in each of the single supercharging mode, the approaching mode, and the twin supercharging mode will be described with reference to FIGS. 2, 3, and 4.

<About single supercharging mode>
The control device 200 operates the supercharging system in the single supercharging mode when a predetermined execution condition is satisfied. The predetermined execution condition includes, for example, a condition that the operating state of the engine 1 based on the engine rotation speed NE and the intake air amount Ga is a low load operating state. When the supercharging mode is the single supercharging mode, the control device 200 closes (off state) the first control valve 62, the second control valve 64, and the third control valve 66.

FIG. 2 is a diagram for explaining the operation of the supercharging system in the single supercharging mode. As shown by the arrows in FIG. 2, the exhaust gas flowing through the exhaust manifolds 50A and 50B flows to the turbine 32 of the primary supercharger 30 via the exhaust pipe 52A, and flows to the exhaust treatment device 81 via the exhaust pipe 53A. It flows. The exhaust supplied to the turbine 32 rotates the turbine wheel 34, and the compressor wheel 33 rotates as the turbine wheel 34 rotates.

The air sucked from the air cleaner 20 flows to the compressor 31 via the intake pipe 23 and the intake pipe 21. The intake air discharged from the compressor 31 flows to the intercooler 25 via the intake pipe 37. The intake air flowing through the intercooler 25 branches into the intake pipes 27A and 27B and flows into each of the intake manifolds 28A and 28B.

<About run-up mode>
The control device 200 switches from the single supercharging mode to the twin supercharging mode, for example, when the supercharging mode is the single supercharging mode and the rotation speed of the primary supercharger 30 exceeds the threshold value. Determine that there is a request.

When there is a request for switching from the single supercharging mode to the twin supercharging mode, the control device 200 executes the run-up mode before switching to the twin supercharging mode. That is, the control device 200 puts both the second control valve 64 and the third control valve 66 in the open state (on state) and closes the first control valve 62 (off state).

FIG. 3 is a diagram for explaining the operation of the supercharging system in the approach mode. As shown by the arrows in FIG. 3, the exhaust gas flowing through the exhaust manifolds 50A and 50B once merges at the connection portion C1 and then branches into the exhaust pipes 52A and 52B, and the turbines of the primary supercharger 30 and the secondary supercharger 40. It flows through both 32 and 42, and flows to the exhaust treatment device 81 via the exhaust pipes 53A and 53B.

The exhaust supplied to the turbine 32 rotates the turbine wheel 34, and the compressor wheel 33 rotates as the turbine wheel 34 rotates. The exhaust supplied to the turbine 42 rotates the turbine wheel 44, and the compressor wheel 43 rotates as the turbine wheel 44 rotates.

The air sucked from the air cleaner 20 branches from the intake pipe 23 to the intake pipes 21 and 22, and flows to both the compressors 31 and 41. The intake air discharged from the compressor 31 flows to the intercooler 25 via the intake pipe 37. The intake air discharged from the compressor 41 flows from the intake pipe 47 to the reflux pipe 48 via the connection portion C4, and flows from the reflux pipe 48 to the compressor 31 via the intake pipe 21.

The intake air flowing through the intercooler 25 branches into the intake pipes 27A and 27B and flows into each of the intake manifolds 28A and 28B. In the approach mode, the rotation speed of the secondary supercharger 40 is increased while supercharging the intake air flowing through the intercooler 25 by the primary supercharger 30. As the rotation speed of the secondary supercharger 40 increases, the pressure of the intake air discharged from the compressor 41 of the secondary supercharger 40 increases.

<About twin supercharging mode>
The control device 200 operates the supercharging system in the twin supercharging mode at the timing when the supercharging capacity of the secondary supercharger 40 becomes sufficiently high in the approach mode. When the supercharging mode is the twin supercharging mode, the control device 200 sets the first control valve 62 in the open state (on state) and the second control valve 64 in the closed state (off state).

FIG. 4 is a diagram for explaining the operation of the supercharging system in the twin supercharging mode. In the run-up mode, the intake air discharged from the compressor 41 of the secondary supercharger 40 flows from the middle of the intake pipe 47 to the intake pipe 21 via the return pipe 48, whereas in the twin supercharge mode. In, as shown by the arrow in FIG. 4, the intake air discharged from the compressor 41 of the secondary supercharger 40 flows from the intake pipe 47 to the intercooler 25 via the intake pipe 37.

The exhaust and intake flows other than the above are the same as the exhaust and intake flows in the run-up mode. Therefore, the detailed explanation will not be repeated.

[About the premise of this embodiment]
Conventionally, in an engine 1 equipped with two turbochargers as shown in FIGS. 1 to 4, when switching between single supercharging and twin supercharging at an equal supercharging pressure, the hiss region shown in FIG. 13 has been conventionally used. Switch with. In this case, since the exhaust pressures P4 of the exhaust manifolds 50A and 50B are different between the single supercharging and the twin supercharging, the pumping loss changes, so that the torque generated by the engine 1 has a step. In order to eliminate this torque step, it is corrected by the fuel injection amount. Therefore, it is necessary to estimate the exhaust pressure P4 of the exhaust manifolds 50A and 50B.

Therefore, in this embodiment, the control device 200 is supercharged by the secondary supercharger 40 while supplying exhaust to the secondary supercharger 40 before switching from the single supercharging mode to the twin supercharging mode. The exhaust manifold is switched to the run-up mode in which air is supplied to the primary supercharger 30, and the exhaust manifold is estimated using a common estimation formula for estimating the exhaust pressure P4 of the exhaust manifolds 50A and 50B in the single supercharging mode, the twin supercharging mode and the run-up mode. The exhaust pressure P4 of the exhaust manifolds 50A and 50B is calculated, and the engine is controlled using the calculated exhaust pressure P4 of the exhaust manifolds 50A and 50B. Thereby, the exhaust pressure P4 of the exhaust manifolds 50A and 50B can be estimated in the supercharging system including the supercharger in parallel.

Further, conventionally, some superchargers having a turbine and a compressor are provided with an electric motor for assisting the driving force of the compressor by the turbine. In such a turbocharger, when there is a discrepancy between the target supercharging pressure and the actual supercharging pressure, the drive of the compressor is assisted by the electric motor, so that the nozzle vane is suddenly increased in order to increase the driving force of the turbine. It was designed to suppress sudden fluctuations in the exhaust pressure of the exhaust manifold by avoiding opening it.

By using this technology, it is possible to suppress abrupt fluctuations in the exhaust pressure of the exhaust manifold even in a supercharging system equipped with two turbochargers. However, if the turbocharger is equipped with an electric motor that is an additional configuration in this way, the cost will increase in order to equip the supercharger, it will be necessary to secure a space for mounting the electric motor, and the electric motor will be installed. The weight of the vehicle increases due to the weight of the vehicle. Further, if the exhaust pressure of the exhaust manifold becomes too high, each part of the engine may be damaged.

Therefore, in this embodiment, the control device 200 is supercharged by the secondary supercharger 40 while supplying exhaust to the secondary supercharger 40 before switching from the single supercharging mode to the twin supercharging mode. The run-up mode is switched to supply air to the primary supercharger 30, and at the start of the run-up mode, the exhaust manifold 50A is opened from the opening degree of the variable nozzle mechanism 35 of the primary supercharger 30 and the variable nozzle mechanism 45 of the secondary supercharger 40. Using an estimation formula that estimates the exhaust pressure P4 of the exhaust manifolds 50A and 50B, the opening degrees of the variable nozzle mechanisms 35 and 45 are specified and variable so that the exhaust pressure P4 of the exhaust manifolds 50A and 50B does not exceed the constraint value. The opening degree of each of the nozzle mechanisms 35 and 45 is controlled so as to have a specified opening degree. Thereby, in the supercharging system including the supercharger in parallel, the exhaust pressure P4 of the exhaust manifolds 50A and 50B can be prevented from becoming too high without providing an additional configuration.

[About the derivation of the estimation formula of the exhaust pressure of the exhaust manifold]
First, the derivation of a common estimation formula for estimating the exhaust pressure P4 of the exhaust manifolds 50A and 50B in the single supercharging mode, the twin supercharging mode, and the approaching mode will be described.

FIG. 5 is a diagram showing an outline of the exhaust flow of the engine 1 in the single supercharging mode. With reference to FIG. 5, in the single supercharging mode, the exhaust gas discharged from the engine 1 through the exhaust manifolds 50 (50A, 50B) is on the side of the primary supercharger 30 and the side of the exhaust gas recirculation device. It branches into and flows.

Here, for valves, nozzles, etc., the state of the nozzle can be expressed by the nozzle formula shown by the mathematical formula (1) by the energy conservation law, the momentum conservation law, and the equation of state. In addition, μA: effective opening area, Pus: nozzle upstream pressure, Pds: nozzle downstream pressure, Tus: nozzle upstream temperature, R: gas constant.

Further, the φ function included in the mathematical formula (1) is a function showing the characteristics of the ease of flow of the nozzle, and is represented by the following mathematical formula (2). Κ: Specific heat ratio of exhaust gas.

FIG. 6 is a diagram showing that the φ function can be approximated to a straight line. With reference to FIG. 6, the φ function of the equation (2) can be approximated to a straight line as shown by the equation (3), depending on the approximate value of Pds / Pus. It should be noted that a and b: constants.

Returning to FIG. 5, the flow rate mout per unit time of the exhaust flowing out from the exhaust manifold 50 is the flow rate Gcyl per unit time of the air flowing into the cylinders 12A and 12B and the fuel per unit time to the cylinders 12A and 12B. Is the sum of the injection amount and Gf. That is, the following mathematical formula (4) is obtained.

Further, the flow rate mout per unit time of the exhaust flowing out from the exhaust manifold 50 flows to the side of the exhaust recirculation device and the flow rate mVN per unit time of the exhaust flowing to the side of the primary supercharger 30 according to the mass preservation law. It is the sum of the flow rate mEGR per unit time of exhaust gas. That is, the following mathematical formula (5) is obtained.

If the nozzle type is specified for the exhaust flowing to the EGR valve 72 on the side of the exhaust gas recirculation device, the following mathematical formula (6) is obtained. In addition, μAEGR: effective opening area of EGR valve 72, P4: exhaust pressure of exhaust manifold, T4: exhaust temperature of exhaust manifolds 50A and 50B, Pim: intake pressure of intake manifold, a, b: constant. The effective opening area μAEGR of the EGR valve 72 can be specified by using a two-dimensional map showing the relationship between the actual opening of the EGR valve 72 and the effective opening area μAEGR for each gas amount mEGR passing through the EGR valve 72. This two-dimensional map is stored in advance in the ROM of the control device 200.

If the nozzle type is specified for the exhaust gas flowing through the variable nozzle mechanism 35 of the turbine 32 on the side of the primary supercharger 30, the following mathematical formula (7) is obtained. In addition, μAVN: effective opening area of variable nozzle mechanism 35, P6: pressure after turbine, c, d: constant. The effective opening area μAVN of the variable nozzle mechanism 35 shall be specified by using a two-dimensional map showing the relationship between the actual opening of the variable nozzle mechanism 35 and the effective opening area μAVN for each amount of gas mVN passing through the variable nozzle mechanism 35. Can be done. This two-dimensional map is stored in advance in the ROM of the control device 200.

When P4 is arranged based on the mathematical formulas (4) to (7), it becomes the estimation formula of P4 shown by the following mathematical formula (8).

In the single supercharging mode, the exhaust pressure P4 of the exhaust manifold 50 can be calculated using the estimation formula of the formula (8). In addition, μAEGR and μAVN can be specified by the above-mentioned method. Gcyl is an estimated cylinder inflow gas amount that can be calculated by using, for example, the boost pressure and the rotation speed of the engine 1 as arguments, and can be basically calculated using the relationship obtained by the experiment. Gf can be specified by a known method from the rotation speed of the engine 1, the injection amount of fuel, and the like. T4 and Pim can be identified by signals from the temperature sensor 114 and the third pressure sensor 118, respectively. The post-turbine pressure P6 can be estimated from a pre-specified correlation with atmospheric pressure. Although the post-turbine pressure P6 is an estimated value here, the pressure P6 is not limited to this and may be detected by a pressure sensor.

Next, the derivation of the estimation formula for estimating the exhaust pressure P4 of the exhaust manifolds 50A and 50B in the approach mode will be described.

FIG. 7 is a diagram showing an outline of the exhaust flow of the engine 1 in the approach mode. With reference to FIG. 7, in the run-up mode, the exhaust gas discharged from the engine 1 through the exhaust manifolds 50 (50A, 50B) is directed to the primary supercharger 30 side and the exhaust gas recirculation device side. In addition, it branches to the side of the secondary supercharger 40 and flows.

The nozzle type for the exhaust flowing to the EGR valve 72 on the side of the exhaust gas recirculation device is the same as the above-mentioned formula (6). As in the case of the single supercharging mode described above, the exhaust gas flowing through the variable nozzle mechanism 35 of the turbine 32 on the side of the primary turbocharger 30 and the exhaust gas flowing through the variable nozzle mechanism 45 of the turbine 42 on the side of the secondary turbocharger 40. If the nozzle formula is specified for each of the above, the following formulas (9) and (10) are obtained. It should be noted that μAVN1, μAVN2: effective aperture areas of the variable nozzle mechanisms 35 and 45, c, d, e, f: constants.

Further, the flow rate mout per unit time of the exhaust gas flowing out from the exhaust manifold 50 is determined by the flow rate mVN1 per unit time of the exhaust gas flowing to the primary supercharger 30 side and the secondary supercharger 40 side according to the mass preservation law. It is the sum of the flow rate mVN2 per unit time of the flowing exhaust gas and the flow rate mEGR per unit time of the exhaust gas flowing to the side of the exhaust gas recirculation device. That is, the following mathematical formula (11) is obtained.

When P4 is arranged based on the mathematical formula (4), the mathematical formula (6), and the mathematical formula (9) to the mathematical formula (11), it becomes the estimation formula of P4 shown by the following mathematical formula (12).

The effective opening area μAEGR of the EGR valve 72 can be specified as in the case of the single supercharging mode.

The effective opening areas μAVN1 and μAVN2 of the variable nozzle mechanisms 35 and 45 are the actual opening and effective opening areas μAVN1 and μAVN2 of the variable nozzle mechanisms 35 and 45 for each of the gas amounts mVN1 and mVN2 passing through the variable nozzle mechanisms 35 and 45, respectively. It can be specified using a two-dimensional map showing the relationship with. This two-dimensional map is stored in advance in the ROM of the control device 200. Since the pressures P4 and P6 before and after the variable nozzle mechanisms 35 and 45 are the same, c = e and d = f.

FIG. 8 is a diagram showing an outline of the flow of exhaust gas to the variable nozzle mechanisms 35 and 45 of the primary supercharger 30 and the secondary supercharger 40. With reference to FIG. 8, in the run-up mode, the gas amounts mWN1 and mVN2 passing through the variable nozzle mechanisms 35 and 45, respectively, cannot be specified. Therefore, the effective opening areas μAVN1 and μAVN2 of the variable nozzle mechanisms 35 and 45 cannot be specified.

FIG. 9 is a diagram showing the relationship between the opening area ratio of the variable nozzle mechanisms 35 and 45 of the primary supercharger 30 and the secondary supercharger 40 and the ratio of the amount of gas passing through each of them. With reference to FIG. 9, the plot shows the experimental results. The opening area ratio of the variable nozzle mechanisms 35 and 45 of the primary supercharger 30 and the secondary supercharger 40 (opening area of the variable nozzle mechanism 35 / opening area of the variable nozzle mechanism 45) has a range of use normally used. In this registered area, the opening area ratios of the variable nozzle mechanisms 35 and 45 of the primary supercharger 30 and the secondary supercharger 40 and the ratio of the amount of gas passing through each (mVN1 / mVN2) are shown in FIG. It can be approximated to a proportional relationship.

Further, the opening areas of the variable nozzle mechanisms 35 and 45 and their respective openings have a one-to-one relationship. Therefore, since the opening degrees of the variable nozzle mechanisms 35 and 45 can be specified, the opening areas of the variable nozzle mechanisms 35 and 45 can be specified. Therefore, the ratio of the amount of gas passing through each of the variable nozzle mechanisms 35 and 45 can be specified from the opening area ratio. As a result, since the total amount of gas passing through the variable nozzle mechanisms 35 and 45 can be specified, the respective gas amounts mVN1 and mVN2 can be specified, and from the gas amounts mVN1 and mVN2 and the actual opening of the variable nozzle mechanisms 35 and 45. , Effective opening area μAVN1 and μAVN2 can be specified. As a result, the exhaust pressure P4 of the exhaust manifolds 50A and 50B can be estimated using the mathematical formula (12).

Next, the derivation of the estimation formula for estimating the exhaust pressure P4 of the exhaust manifolds 50A and 50B in the twin supercharging mode will be described. FIG. 10 is a diagram showing an outline of the exhaust flow of the engine in the twin supercharging mode. With reference to FIG. 10, in the twin supercharging mode, the opening degrees of the variable nozzle mechanisms 35 and 45 of the primary supercharger 30 and the secondary supercharger 40 are the same. Therefore, the gas amounts mVN1 and mVN2 (= mVN1) passing through each can be specified, and the effective opening areas μAVN1 and μAVN2 (= μAVN1) can be obtained from the gas amounts mVN1 and mVN2 and the actual opening degrees of the variable nozzle mechanisms 35 and 45. Can be identified. As a result, the exhaust pressure P4 of the exhaust manifolds 50A and 50B can be estimated using the mathematical formula (12).

In the single supercharging mode, since the third control valve 66 is closed, the flow rate of the exhaust gas passing through the turbine 42 of the secondary supercharger 40 is 0. Therefore, in the formula (12), μAVN2 = 0. By setting, it becomes the same as the mathematical formula (8).

That is, the exhaust pressure P4 of the exhaust manifolds 50A and 50B in the single supercharging mode, the twin supercharging mode, and the approaching mode can be estimated by using the common mathematical formula (12). Therefore, in the single supercharging mode, the twin supercharging mode, and the approaching mode, the exhaust pressure P4 of the exhaust manifolds 50A and 50B is increased without using different estimation formulas and without adding parts such as special sensors. It can be estimated accurately. Then, in the control of the engine 1, the exhaust pressure P4 of the exhaust manifolds 50A and 50B can be used.

In addition, in the single supercharging mode, twin supercharging mode, and run-up mode, a common two-dimensional map showing the relationship between the actual opening degree of the EGR valve 72 and the effective opening area μAEGR for each gas amount mEGR passing through the EGR valve 72 is provided. Can be used. Therefore, it is possible to reduce the man-hours for preparing the two-dimensional map for the EGR valve 72 for each of the single supercharging mode, the twin supercharging mode, and the approaching mode.

Further, in the single supercharging mode, the twin supercharging mode, and the approaching mode, the relationship between the actual opening degree of the variable nozzle mechanism 35, 45 for each gas amount mVN passing through the variable nozzle mechanism 35, 45 and the effective opening area μAVN is shown. A common 2D map can be used. Therefore, it is possible to reduce the man-hours for preparing the two-dimensional maps for the variable nozzle mechanisms 35 and 45 for each of the single supercharging mode, the twin supercharging mode, and the approaching mode.

As a result, the accuracy of estimating the pumping loss can be improved, so that the accuracy of correcting the fuel injection amount for eliminating the step in the torque generated by the engine 1 due to the change in the pumping loss is improved. As a result, drivability can be improved not only in the single supercharging mode but also in the twin supercharging mode and the approaching mode.

[Modified example of deriving the estimation formula of the exhaust pressure of the exhaust manifold]
(1) In the above-described embodiment, the engine 1 is a V-type engine having two banks or a horizontally opposed engine. However, the present invention is not limited to this, and other types of engines such as an in-line engine may be used.

(2) In the above-described embodiment, an exhaust gas recirculation device is provided. However, the present invention is not limited to this, and the exhaust gas recirculation device may not be provided. In this case, the terms related to the exhaust gas recirculation device such as the formula (12) are deleted.

[Regarding the control of the variable nozzle mechanism using the exhaust pressure estimation formula of the exhaust manifold]
Next, the control of the variable nozzle mechanisms 35 and 45 using the estimation formula of the exhaust pressure P4 of the exhaust manifolds 50A and 50B in the approach mode will be described.

Variable nozzle mechanism of the primary turbocharger 30 to increase the pressure of the exhaust manifolds 50A and 50B in order to prevent the boost pressure step due to the work reduction of the turbocharger when controlled from the single supercharger mode to the approach mode. 35 uses the closed side. However, as a trade-off, at the time of sudden acceleration, the exhaust pressure P4 of the exhaust manifolds 50A and 50B in the approach mode may increase and exceed the constraint value.

Therefore, in this embodiment, as shown below, the pressure P4 in the approach mode is estimated from the physical state of each part before entering the approach mode by using the estimation formula of the pressure P4, and the pressure P4 is restricted. A method of calculating the opening degree of the variable nozzle mechanism 35 that can prevent the value from being exceeded will be described.

FIG. 11 is a diagram showing an outline of a method of calculating the opening degree of the variable nozzle mechanisms 35 and 45 so that the exhaust pressure P4 of the exhaust manifolds 50A and 50B does not exceed the constraint value. With reference to FIG. 11, first, a provisional value is set as the VN opening degree of the variable nozzle mechanism 35 of the primary turbocharger 30. Further, in this embodiment, the VN opening degree of the variable nozzle mechanism 45 of the secondary turbocharger 40 in the approach mode is a fixed opening degree (= controlled fully closed (minimum controllable opening degree)).

As shown in FIG. 9, the opening areas of the variable nozzle mechanisms 35 and 45 and their respective openings have a one-to-one relationship. Further, the ratio of the opening areas of the variable nozzle mechanisms 35 and 45 of the primary supercharger 30 and the secondary supercharger 40 and the ratio of the amount of gas passing through each (mVN1 / mVN2) have a proportional relationship from FIG. Can be approximated. Thereby, the ratio of the amount of gas passing through each of the variable nozzle mechanisms 35 and 45 can be specified from the VN opening degree. The total value of the amount of gas passing through the variable nozzle mechanisms 35 and 45 at this time is the value of the amount of gas passing through the variable nozzle mechanism 35 immediately before the approach mode switching. Thereby, the gas amounts G4_1st and G4_2nd passing through the variable nozzle mechanisms 35 and 45 can be calculated.

Relationship between the actual opening of the variable nozzle mechanism 35 and the effective opening area μAVN for each gas amount mVN passing through the variable nozzle mechanism 35 from the VN opening degree of the variable nozzle mechanism 35 of the primary turbocharger 30 and the amount of gas passing through G4_1st. The effective opening area μAVN1 can be specified by using the two-dimensional map showing.

Similarly, from the VN opening degree and the passing gas amount G4_2nd of the variable nozzle mechanism 45 of the secondary turbocharger 40, the actual opening degree and the effective opening area μAVN of the variable nozzle mechanism 45 for each gas amount mVN passing through the variable nozzle mechanism 45. The effective opening area μAVN2 can be specified by using a two-dimensional map showing the relationship with.

The estimated value of P4 can be calculated by substituting μAVN1 and μAVN2, and other sensor values and estimated values into the estimation formula of the exhaust pressure P4 of the exhaust manifolds 50A and 50B shown in the equation (12). When the estimated value of P4 exceeds the criteria (constraint value) of P4, the VN opening degree of the variable nozzle mechanism 35 of the primary turbocharger 30 is changed to the open side, and the estimated value of P4 is calculated again. By this iterative calculation, the VN opening degree of the variable nozzle mechanism 35 which is closer to the criterion and less than the criterion is found, and the command value of the VN opening degree of the variable nozzle mechanism 35 in the approach mode is set, so that the approach mode is in progress. P4 is controlled.

FIG. 12 is a flowchart showing the flow of the run-up VN opening degree calculation process in this embodiment. This run-up VN opening degree calculation process is called and executed at predetermined intervals from the higher-level process. With reference to FIG. 12, the control device 200 determines whether or not the supercharging mode flag has been changed from the value indicating the single supercharging mode to the value indicating the approaching mode (step S111). If it is determined that the change has not been made (NO in step S111), the control device 200 returns the process to be executed to the process higher than the caller of this process.

When it is determined that the supercharging mode flag has been changed from the value indicating the single supercharging mode to the value indicating the approaching mode (YES in step S111), the control device 200 determines the intake manifold pressure Pim, the turbine rear pressure P6, and each cylinder. The flow rate Gcyl of the air flowing into the 12A and 12B per unit time and the fuel injection amount Gf per unit time of the cylinders 12A and 12B are specified (step S112).

Next, a temporary value of the VN opening degree of the variable nozzle mechanism 35 of the primary supercharger 30 is set as the base opening degree (step S113). The base opening is the optimum opening determined by the work and efficiency of the turbine. On the closed side from this opening, the boost pressure step deteriorates and the performance deteriorates. Therefore, the upper limit opening of the VN opening in the approach mode is considered as the base opening.

Next, the control device 200 calculates the gas amounts G4_1st and G4_2nd passing through the variable nozzle mechanisms 35 and 45 by the method described with reference to FIG. 11 (step S114), and the exhaust manifolds 50A and 50B shown in the mathematical formula (12). The estimated pressure P4 is calculated using the estimation formula of the exhaust pressure P4 (step S115).

Then, the control device 200 determines whether or not the calculation of the pressure P4 in step S115 is the specified time (step S121). If it is determined that it is not the specified time (NO in step S121), the control device 200 determines whether or not the calculation of the pressure P4 in step S115 is the first time (step S122).

When it is determined that the calculation of the pressure P4 is the first time (YES in step S122), the control device 200 determines whether or not the estimated P4 is less than the constraint value of P4 (step S123). When it is determined that the calculation of the pressure P4 is not the first time (NO in step S122), and when it is determined that the estimated P4 is equal to or greater than the constraint value of P4 (YES in step S123), the control device 200 determines the primary supercharging. The temporary value of the VN opening degree of the variable nozzle mechanism 35 of the machine 30 is updated (step S124), and the processing from step S114 is repeated.

Table 1 is an example for explaining the update of the VN temporary value. In the first update of the provisional value of the VN opening, the VN opening is set to the most open side (40%). In the subsequent update, the VN opening degree is set to the value between the calculation of P4 two times before and the calculation of P4 last time (center in this embodiment).

Then, regarding the estimated pressure P4 corresponding to each of the VN opening of the previous time, the previous VN opening, and the current VN opening, the estimated pressure P4 corresponding to the VN opening of the previous time and the current VN opening are supported. When a constraint value (400 kPa in this embodiment) is included between the estimated pressure and P4, the value between the VN opening before the previous time and the VN opening this time (center in this embodiment) is set. , The next VN opening degree, and a constraint value (400 kPa in this embodiment) is included between the estimated pressure P4 corresponding to the previous VN opening degree and the estimated pressure P4 corresponding to the current VN opening degree. If so, the value between the previous VN opening degree and the current VN opening degree (center in this embodiment) is defined as the next VN opening degree.

For example, if the VN opening degree at the time of the calculation of P4 two times before is 80% and the VN opening degree at the time of the calculation of P4 last time is 40%, the VN opening degree is set to (80 + 40) / 2 = 60%. Then, the estimated P4 = 430 kPa for the VN opening 80% two times before, the estimated P4 = 280 kPa for the previous VN opening 40%, and the estimated P4 = 310 kPa for the current VN opening 60%, so the constraint value. Since 400 kPa is considered to be a value between the VN opening of 80% two times before and the VN opening of 60% this time, the median value between the VN opening of 80% of the previous time and the VN opening of 60% this time. (80 + 60) / 2 = 70% is set as the next VN opening degree.

By updating the VN opening degree in this way, the difference between the VN opening degree at the time of the seventh calculation of P4 and the VN opening degree at the time of the eighth calculation of P4 becomes less than 1.00%. In this embodiment, when the difference in VN opening degree is less than 1.00%, it is considered that the difference in estimated P4 is not so much, and 8 times is set as the specified time.

Then, the estimated P4 is calculated in step S115 with respect to the updated temporary value of the VN opening degree. Control when it is determined that the calculation of the pressure P4 is the specified time (YES in step S121), and when it is determined that the calculation is the first time and the estimated P4 is less than the constraint value of P4 (YES in step S123). The device 200 sets the command opening degree of the VN opening degree of the variable nozzle mechanism 35 of the primary supercharger 30 in the approach mode as a temporary value used in the calculation at that time (step S125). After that, the control device 200 returns the process to be executed to a process higher than the caller of this process.

In the approach mode, the control device 200 controls the opening degree of the variable nozzle mechanism 35 of the primary supercharger 30 so as to have the calculated command opening degree.

For example, if the VN opening at the time of calculation of P4 two times before the specified time is 77.5% and the VN opening at the time of calculation of P4 one time before the specified time is 78.75, the VN opening at the specified time is 78.75. Is updated to (77.5 + 78.75) /2≈78.13%. Then, the estimated P4 = 390 kPa for the VN opening degree 77.5% two times before the specified time, the estimated P4 = 410 kPa for the VN opening degree 78.75% one time before the specified time, and the VN opening degree 78.13 for the specified time. Since the estimated P4 = 402 kPa, the constraint value of 400 kPa is considered to be a value between the VN opening degree of 77.5% two times before the specified time and the VN opening degree of 78.13% of the specified time. Since the constraint value of 400 kPa is considered to correspond to the VN opening degree between 77.5% and 78.13%, the command opening degree is 77.5%, which corresponds to the estimated P4 = 390 kPa that does not exceed the constraint value.

As a result, the exhaust pressure P4 of the exhaust manifolds 50A and 50B can be increased as much as possible within a range that does not exceed the constraint value. Therefore, as shown by the mathematical formula (13), the turbine work increases, the compressor work increases, and the decrease in the boost pressure Pp of the primary supercharger 30 can be suppressed.

Cpg: constant pressure specific heat (= 0.26), κ: specific heat ratio of exhaust (1.33), G4: flow rate of exhaust passing through supercharger, T4: exhaust temperature of exhaust manifolds 50A and 50B, P4: exhaust manifold 50A , 50B pressure, P6: pressure after turbine.

By repeatedly calculating the estimated P4 while updating the temporary value of the VN opening in this way, the step of the VN opening becomes smaller, and it is possible to calculate to the required accuracy in which the VN opening can be controlled. Moreover, it is possible to calculate the estimated P4 that is closer to the constraint value of P4 and less than the constraint value. As a result, the VN opening degree of the variable nozzle mechanism 35 of the primary supercharger 30 is feed-forward (F / F) controlled by using the estimated P4 calculated from the physical quantity in the single supercharging mode immediately before the approach mode. The third control valve 66 is opened, and the exhaust pressure P4 of the exhaust manifolds 50A and 50B can be controlled when the approach mode in which the flow rate of the exhaust gas to the turbine 42 of the secondary supercharger 40 increases is entered.

As a result, by controlling the exhaust pressures P4 of the exhaust manifolds 50A and 50B in the approach mode, the boost pressure step at the time of switching to the approach mode can be minimized regardless of the operation. Can be done. Therefore, the boost pressure step can be reduced without adding parts such as a special sensor, and the exhaust pressure P4 of the exhaust manifolds 50A and 50B can be prevented from exceeding the constraint value. In addition, drivability can be improved, and reliability of control of the engine 1 can be ensured.

[Modification example in control of variable nozzle mechanism]
(1) Although the control in the approach mode has been described here, the control of the variable nozzle mechanism described above can also be used in the single supercharging mode and the twin supercharging mode.

(2) Here, the VN opening degree of the variable nozzle mechanism 45 of the secondary supercharger 40 is set to the fixed opening degree on the most closed side. However, the present invention is not limited to this, and the VN opening degree of the variable nozzle mechanism 45 of the secondary supercharger 40 may be a fixed opening degree different from the most closed side, or the VN opening degree of the variable nozzle mechanism 35 of the primary supercharger 30 may be set. It may be calculated in the same manner as the opening degree.

(3) Here, the optimum pressure of the exhaust of the exhaust manifolds 50A and 50B and the variable nozzle mechanism 35 of the primary supercharger 30 corresponding to the optimum pressure by the optimization method described with reference to FIGS. 11 and 12 are used. The optimum VN opening degree of is calculated. However, the present invention is not limited to this, and the optimum pressure of the exhaust manifolds 50A and 50B and the optimum VN opening degree of the variable nozzle mechanism 35 may be optimized by other methods.

[Summary]
(1-1) As shown in FIGS. 1 to 4, the supercharging system adjusts the flow velocity between the turbine 32 driven by the exhaust discharged from the engine 1 and the exhaust flowing into the turbine 32 according to the opening degree. The primary supercharger 30, which includes a variable nozzle mechanism 35 and supercharges the intake air to the engine 1, the turbine 42 driven by the exhaust discharged from the engine 1, and the flow velocity of the exhaust flowing into the turbine 42 are opened. A secondary supercharger 40 that supercharges the intake air to the engine 1 and a single supercharge mode in which the supercharged air in the primary supercharger 30 is supplied to the engine 1 including a variable nozzle mechanism 45 adjusted by , The supercharging mode is set from one of the twin supercharging mode in which the supercharged air in the primary supercharger 30 and the supercharged air in the secondary supercharger 40 are supplied to the engine 1. A control device 200 for switching is provided.

As shown in FIGS. 5 to 10, the control device 200 is supercharged by the secondary supercharger 40 while supplying exhaust to the secondary supercharger 40 before switching from the single supercharging mode to the twin supercharging mode. It is shown by the formula (12) for estimating the exhaust pressure P4 of the exhaust manifolds 50A and 50B in the single supercharging mode, the twin supercharging mode and the approaching mode by switching to the approach mode in which the generated air is supplied to the primary supercharger 30. The exhaust pressure P4 of the exhaust manifolds 50A and 50B is calculated using a common estimation formula, and the engine is controlled using the calculated exhaust pressure P4 of the exhaust manifolds 50A and 50B. Thereby, the exhaust pressure P4 of the exhaust manifolds 50A and 50B can be estimated in the supercharging system including the supercharger in parallel.

(1-2) As shown in FIGS. 5 to 10, the control device 200 calculates the exhaust pressure P6 merged after the turbine 32 of the primary supercharger 30 and the turbine 42 of the secondary supercharger 40. Substituting into the estimation formula shown in (12), the exhaust pressure P4 of the exhaust manifolds 50A and 50B is calculated. Thereby, the pressures P4 of the exhaust manifolds 50A and 50B can be calculated from the identifiable post-turbine pressure P6.

(1-3) As shown in FIGS. 1 to 4, an exhaust gas recirculation device having return paths 73 and 74 for refluxing a part of the exhaust gas of the engine 1 as the intake air of the engine 1 is further provided. As a result, the exhaust pressure P4 of the exhaust manifolds 50A and 50B can be estimated even when the exhaust recirculation device capable of improving the efficiency of the engine 1 is provided.

(1-4) As shown in FIGS. 5 to 10, in the control device 200, the exhaust pressure P6 and the return path merged after the turbine 32 of the primary supercharger 30 and the turbine 42 of the secondary supercharger 40. The exhaust pressure Pim of the exhaust manifolds 73 and 74 is calculated by substituting the exhaust pressure Pim of 73 and 74 into the estimation formula shown by the equation (12). Thereby, the pressures P4 of the exhaust manifolds 50A and 50B can be calculated from the identifiable post-turbine pressure P6 and the exhaust pressure Pim of the return passages 73 and 74 of the exhaust gas recirculation device.

(1-5) As shown in FIGS. 1 to 4, the exhaust gas recirculation device includes an EGR valve 72 provided in the return passages 73 and 74 to adjust the amount of exhaust gas returned. As shown in FIGS. 5 to 10, the estimation formula shown by the mathematical formula (12) is the variable nozzle mechanism 35 of the primary supercharger 30, the variable nozzle mechanism 45 of the secondary supercharger 40, and the EGR valve 72. It is constructed from the nozzle formulas and mass conservation rules of formulas (9), formulas (10) and formulas (6) for each.

(1-6) As shown in FIGS. 7 to 9, the control device 200 has an opening area ratio (variable nozzle mechanism) of the variable nozzle mechanism 35 of the primary supercharger 30 and the variable nozzle mechanism 45 of the secondary supercharger 40. The ratio of the exhaust flow rate (mVN1 / mVN2) distributed to each of the variable nozzle mechanism 35 and the variable nozzle mechanism 45 is specified from the opening area of 35 / the opening area of the variable nozzle mechanism 45), and the exhaust flow rate discharged from the engine. , And the exhaust flow rate distributed to each of the first variable nozzle mechanism and the second variable nozzle mechanism from the ratio of the exhaust flow rate distributed to each of the first variable nozzle mechanism and the second variable nozzle mechanism (mVN1 / mVN2). mVN1 and mVN2 are specified, and the exhaust flow rate mVN1 and mVN2 distributed to each of the specified first variable nozzle mechanism and second variable nozzle mechanism, and the opening degree of each of the first variable nozzle mechanism and the second variable nozzle mechanism. The effective opening areas μAVN1 and μAVN2 of the first variable nozzle mechanism and the second variable nozzle mechanism are specified, and the effective opening areas μAVN1 and μAVN2 of the specified first variable nozzle mechanism and the second variable nozzle mechanism, respectively, are calculated by the mathematical formula (12). Substituting into the estimation formula shown, the exhaust pressure P4 of the exhaust manifold is calculated.

(2-1) As shown in FIGS. 1 to 4, the supercharging system adjusts the flow velocity between the turbine 32 driven by the exhaust discharged from the engine 1 and the exhaust flowing into the turbine 32 according to the opening degree. The primary supercharger 30, which includes a variable nozzle mechanism 35 and supercharges the intake air to the engine 1, the turbine 42 driven by the exhaust discharged from the engine 1, and the flow velocity of the exhaust flowing into the turbine 42 are opened. A secondary supercharger 40 that supercharges the intake air to the engine 1 and a single supercharge mode in which the supercharged air in the primary supercharger 30 is supplied to the engine 1 including a variable nozzle mechanism 45 adjusted by , The supercharging mode is set from one of the twin supercharging mode in which the supercharged air in the primary supercharger 30 and the supercharged air in the secondary supercharger 40 are supplied to the engine 1. A control device 200 for switching is provided.

As shown in FIGS. 11 and 12, the control device 200 is supercharged by the secondary supercharger 40 while supplying exhaust to the secondary supercharger 40 before switching from the single supercharging mode to the twin supercharging mode. It is switched to the approach mode in which the generated air is supplied to the primary supercharger 30, and at the start of the approach mode, the variable nozzle mechanism 35 of the primary supercharger 30 and the variable nozzle mechanism 45 of the secondary supercharger 40 are exhausted from their respective openings. Using an estimation formula that estimates the exhaust pressure P4 of the manifolds 50A and 50B, the opening degrees of the variable nozzle mechanisms 35 and 45 are specified so that the exhaust pressure P4 of the exhaust manifolds 50A and 50B does not exceed the constraint value. , The opening degree of each of the variable nozzle mechanisms 35 and 45 is controlled so as to have a specified opening degree. Thereby, in the supercharging system including the supercharger in parallel, the exhaust pressure P4 of the exhaust manifolds 50A and 50B can be prevented from becoming too high without providing an additional configuration.

(2-2) As shown in FIG. 11, the control device 200 specifies the VN opening degree of the variable nozzle mechanism 45 of the secondary supercharger 40 as the opening degree on the most closed side among the controllable opening degree. This makes it easier to calculate the VN opening degree of the variable nozzle mechanism 35 of the primary turbocharger 30.

(2-3) As shown in FIGS. 11 and 12, the control device 200 includes a first opening degree of the variable nozzle mechanism 35 of the primary supercharger 30 and a second opening degree on the opening side of the first opening degree. The first pressure, the second pressure, and the third pressure, which are the pressures of the exhausts of the exhaust manifolds 50A and 50B corresponding to the third opening between the first opening and the second opening, are calculated, and the first pressure is calculated. If a limit value is included between the pressure and the third pressure, the third opening corresponding to the third pressure is changed to a new second opening, and the limit is set between the third pressure and the second pressure. If a value is included, the third opening corresponding to the third pressure is changed to a new first opening, the difference between the first opening and the third opening, and the third opening and the second opening. The opening degree corresponding to the largest pressure among the first pressure, the second pressure, and the third pressure when the difference between the pressure and the pressure is less than the predetermined value is specified as the VN opening degree of the variable nozzle mechanism 35. To do. Thereby, the optimum VN opening degree can be efficiently specified.

Each of the embodiments disclosed this time is also planned to be implemented in combination as appropriate. And it should be considered that the embodiments disclosed this time are exemplary in all respects and not restrictive. The scope of the present disclosure is indicated by the scope of claims rather than the description of the embodiment described above, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

1 engine, 10A, 10B bank, 12A, 12B cylinder, 20 air cleaner, 21,22,23,27A, 27B, 37,47 intake pipe, 25 intercooler, 28A, 28B intake manifold, 30 primary supercharger, 31, 41 Compressor, 32,42 Turbine, 33,43 Compressor wheel, 34,44 Turbine wheel, 35,45 Variable nozzle mechanism, 36,46 Rotating shaft, 40 Secondary turbocharger, 48 Recirculation pipe, 50, 50A, 50B Exhaust manifold , 51A, 51B, 52A, 52B, 53A, 53B Exhaust pipe, 62 1st control valve, 64 2nd control valve, 66 3rd control valve, 68 Diesel throttle, 71 EGR cooler, 72 EGR valve, 73,74 Circulation path , 81 Exhaust gas recirculation device, 102 Air flow meter, 106 1st pressure sensor, 108 2nd pressure sensor, 114 temperature sensor, 118 3rd pressure sensor, 200 control device.

Claims (6)

A first turbine driven by exhaust gas discharged from the engine and a first variable nozzle mechanism that adjusts the flow velocity of the exhaust gas flowing into the first turbine according to an opening degree to supercharge the intake air to the engine. 1 supercharger and
It includes a second turbine driven by exhaust gas discharged from the engine and a second variable nozzle mechanism that adjusts the flow velocity of the exhaust gas flowing into the second turbine according to the opening degree, and supercharges the intake air to the engine. The second supercharger and
The single supercharging mode in which the supercharged air in the first supercharger is supplied to the engine, the air supercharged in the first supercharger and the air supercharged in the second supercharger. Is equipped with a control device that switches the supercharging mode from one of the twin supercharging modes supplied to the engine to the other.
The control device
Before switching from the single supercharging mode to the twin supercharging mode, the air supercharged by the second supercharger is supplied to the first supercharger while supplying exhaust gas to the second supercharger. Switch to the run-up operation mode,
The exhaust pressure of the exhaust manifold is calculated using a common estimation formula for estimating the exhaust pressure of the exhaust manifold in the single supercharging mode, the twin supercharging mode, and the approaching operation mode.
A supercharging system that controls the engine using the calculated exhaust pressure of the exhaust manifold. The supercharging system according to claim 1, wherein the control device calculates the exhaust pressure of the exhaust manifold by substituting the pressure of the exhaust gas merged after the first turbine and the second turbine into the estimation formula. .. The supercharging system according to claim 1, further comprising an exhaust gas recirculation device having a reflux path for returning a part of the exhaust gas of the engine as intake air of the engine. The control device calculates the exhaust pressure of the exhaust manifold by substituting the exhaust pressure of the exhaust gas merging after the first turbine and the second turbine and the exhaust pressure of the recirculation path into the estimation formula. Item 3. The supercharging system according to item 3. The exhaust gas recirculation device includes a valve provided in the return path to adjust the amount of exhaust returned.
The supercharging system according to claim 3, wherein the estimation formula is constructed from the nozzle formula and the law of conservation of mass for each of the first variable nozzle mechanism, the second variable nozzle mechanism, and the valve. The control device
From the opening area ratio of the first variable nozzle mechanism and the second variable nozzle mechanism, the ratio of the exhaust flow rate distributed to each of the first variable nozzle mechanism and the second variable nozzle mechanism is specified.
From the ratio of the exhaust flow rate discharged from the engine and the exhaust flow rate distributed to each of the first variable nozzle mechanism and the second variable nozzle mechanism, the first variable nozzle mechanism and the second variable nozzle mechanism Identify the exhaust flow rate to be distributed to each,
The first variable nozzle mechanism is based on the exhaust flow rate distributed to each of the specified first variable nozzle mechanism and the second variable nozzle mechanism, and the opening degree of each of the first variable nozzle mechanism and the second variable nozzle mechanism. And the effective opening area of the second variable nozzle mechanism was specified.
The supercharging system according to claim 1, wherein the effective opening area of each of the specified first variable nozzle mechanism and the second variable nozzle mechanism is substituted into the estimation formula to calculate the exhaust pressure of the exhaust manifold.

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