JP7059949B2 - Supercharging system - Google Patents

Description

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

Conventionally, there has been a supercharging system having two superchargers connected in parallel (see, for example, Patent Document 1). In the supercharging system of Patent Document 1, a single supercharging mode in which one supercharger supercharges the engine intake and a twin supercharging in which two superchargers supercharge the engine intake according to the load of the engine are used. Switch to the supply mode.

In the low speed range, the single supercharging mode is used in which only the primary turbocharger is driven. This is to improve the responsiveness of the supercharging pressure with one supercharger in the speed range where the exhaust energy is small. In the high-speed range, the twin supercharging mode for driving the primary supercharger and the secondary supercharger is used. This is to realize a high supercharging pressure with two superchargers in the speed range where the exhaust energy is large.

Japanese Unexamined Patent Publication No. 2009-250191

Patent Document 1 discloses a characteristic technique for switching from a single supercharging mode to a twin supercharging mode. However, Patent Document 1 does not disclose a characteristic technique for switching from the twin supercharging mode to the single supercharging mode. As described above, conventionally, a characteristic technique for switching from the twin supercharging mode to the single supercharging mode has not been considered so much. In a commonly used technique, the twin supercharging mode is switched to the single supercharging mode according to the engine speed and the load (fuel injection amount).

FIG. 14 is a diagram for explaining switching from the conventional twin supercharging mode to the single supercharging mode. FIG. 14A shows a change in the rotational speed of the engine. FIG. 14B shows changes in the fuel injection amount. FIG. 14C shows the change in boost pressure. At time T1, the engine speed gradually starts to decrease due to the accelerator being off or the like, and the fuel injection amount is sharply cut. Therefore, the target boost pressure determined by the engine speed and the fuel injection amount also drops sharply. However, there is a delay in the decrease in the actual boost pressure, and the actual boost pressure gradually decreases, so there is a discrepancy between the target boost pressure and the actual boost pressure determined by the engine speed and fuel injection amount. Occurs. Therefore, switching from the twin supercharging mode to the single supercharging mode according to the engine speed and fuel injection amount corresponds to the transient state where the engine speed and fuel injection amount are changing. Can not.

This disclosure is made to solve the above-mentioned problems, and the purpose is a supercharging system capable of appropriately switching from the twin supercharging mode to the single supercharging mode even in a transient situation. 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 gas 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 in the first supercharger is supplied to the engine, and the supercharged air in the first supercharger. It is provided with 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.

The control device of the first variable nozzle mechanism and the second variable nozzle mechanism required for the first supercharger and the second supercharger to obtain the target supercharging pressure when the twin supercharging mode is switched to. The target opening is calculated from the state quantities of the intake path and the exhaust path, and when the calculated target opening is out of the controllable range, the supercharging mode is switched to the single supercharging mode.

Preferably, the control device uses a simulation formula based on the physical laws of the intake path and the exhaust path of the engine as the calculation formula for calculating the target opening degree.

Preferably, the control device uses the state quantities of the intake path and the exhaust path when calculating the target opening degree as the state quantities of the intake path before branching to the first turbocharger and the second turbocharger, respectively. And, the state quantity of the exhaust path after merging from the first supercharger and the second supercharger is used.

Preferably, the first supercharger and the second supercharger are of the same model. The control device regards the first supercharger and the second supercharger as one supercharger, calculates one target opening degree, and uses the calculated one target opening degree as the first variable nozzle mechanism and the second. The target opening of the variable nozzle mechanism is set.

Preferably, the control device switches the supercharging mode to the single supercharging mode when the calculated target opening degree is out of the controllable range for a predetermined time.

More preferably, the first turbocharger includes a first compressor that supercharges the intake air to the engine. The supercharging system further includes a storage unit for storing data showing a compressor map showing the characteristics of the first compressor. The compressor map includes a first axis of the amount of air sucked into the first compressor of the first turbocharger and a second axis of the pressure ratio of the discharge pressure to the suction pressure of the first compressor.

When the control device is switched to the twin supercharging mode, if the calculated target opening is out of the controllable range for a predetermined time, the pressure in the compressor map stored in the storage unit is not maintained. When it is shown that the operating point specified by the ratio and the amount of air is below a predetermined line on the compressor map, the supercharging mode is switched to the single supercharging mode.

According to this disclosure, it is possible to provide a supercharging system capable of appropriately switching from the twin supercharging mode to the single supercharging mode even in a transitional situation.

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 flowchart which shows an example of the flow of the switching process to the single supercharging mode in this embodiment. It is 1st figure for demonstrating the physical formula of a supercharger. It is the 2nd figure for demonstrating the physical formula of a supercharger. It is a figure for demonstrating the example of the change of the target VN opening degree calculated by the physical formula. It is a figure which shows an example of the compressor operation map which shows the relationship between the intake air amount of the compressor of a primary supercharger, and the pressure ratio before and after a compressor. It is a figure for demonstrating the change of supercharging pressure by re-acceleration when the operating point of a compressor operation map reaches the switching line L1 and when it does not reach it. It is a figure for demonstrating the difference of the operating point by the accelerator opening in a steady state on a compressor operation map. It is a figure for demonstrating the difference of supercharging pressure in re-acceleration for each accelerator opening after deceleration. It is a figure for demonstrating the calculation of the target VN opening degree in the modification. It is a figure for demonstrating the switching from the conventional twin supercharging mode to the single supercharging mode.

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 turbocharger 30, a secondary turbocharger 40, and an exhaust manifold 50A and 50B (hereinafter referred to as "exhaust manifolds"). Also referred to as), an exhaust treatment device 81, and a control device 200.

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. An injector (not shown) is provided in each of 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 speed NE, the intake air amount Qin, 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. By burning fuel in each cylinder 12A, 12B in a predetermined order, the piston slides in each cylinder 12A, 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 turbocharger 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 turbocharger 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 each of the plurality of nozzle vanes (not shown) and the plurality of nozzle vanes that guide the exhaust gas supplied from the exhaust inlet to the turbine wheel 34. 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 the drive device in response to the control signal VN1 from the control device 200, for example.

The secondary turbocharger 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 turbocharger 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 rotating the nozzle vane using the drive device in response to the control signal VN2 from the control device 200, for example.

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 is branched and 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 turbocharger 30. One end of the intake pipe 37 is connected to the intake outlet of the compressor 31 of the primary turbocharger 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 turbocharger 40. One end of the intake pipe 47 is connected to the intake outlet of the compressor 41 of the secondary turbocharger 40. The other end of the intake pipe 47 is connected to a connection 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 according 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 return 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 turbocharger 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) whose ON (open) / OFF (closed) control is performed 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 air 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 the intake ports (not shown) of the cylinders 12A and 12B in the 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 an exhaust manifold 50A, 50B, an exhaust pipe 51A, 51B, a connection portion C1, an exhaust pipe 52A, 52B, 53A, 53B, and a connection portion 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.

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, 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, etc.) are connected to the output port.

The control device 200 controls various devices so that the engine 1 is in a desired operating state based on the signals from each sensor and the device, and the map and the program stored in the memory. It should be noted that various controls are not limited to processing by software, but can also be processed by dedicated hardware (electronic circuit). 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 Qin. The air flow meter 102 transmits a signal indicating the detected intake air amount Qin to the control device 200.

The engine speed sensor 104 detects the engine speed NE. The engine rotation speed sensor 104 transmits a signal indicating the detected engine rotation speed NE 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.

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 modes 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 increased 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 speed NE and the intake air amount Qin is a low load operating state. When the supercharging mode is the single supercharging mode, the control device 200 closes (offs) 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 arrow in FIG. 2, the exhaust gas flowing through the exhaust manifolds 50A and 50B flows to the turbine 32 of the primary turbocharger 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 with the rotation of the turbine wheel 34.

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 puts the first control valve 62 in the closed state (off state).

FIG. 3 is a diagram for explaining the operation of the supercharging system in the run-up mode. As shown by the arrow 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 to 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 with the rotation of the turbine wheel 34. The exhaust supplied to the turbine 42 rotates the turbine wheel 44, and the compressor wheel 43 rotates with the rotation of the turbine wheel 44.

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 run-up 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 run-up 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 turbocharger 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.

[Conventional issues]
In the technique often used in the past, the twin supercharging mode is switched to the single supercharging mode according to the rotation speed of the engine and the load (fuel injection amount). As described in FIG. 14 above, switching from the twin supercharging mode to the single supercharging mode according to the engine rotation speed and the fuel injection amount changes the engine rotation speed and the fuel injection amount. It cannot handle transient conditions.

[Regarding control in this embodiment]
Therefore, in this embodiment, the control device 200 is a variable nozzle required for the primary supercharger 30 and the secondary supercharger 40 to obtain the target supercharging pressure when the twin supercharging mode is switched to. The target opening of the mechanism 35 and the variable nozzle mechanism 45 is calculated from the state quantities of the intake path and the exhaust path, and when the calculated target opening is out of the controllable range, the supercharging mode is switched to the single supercharging mode. .. This makes it possible to appropriately switch from the twin supercharging mode to the single supercharging mode even in a transitional situation.

Further, in this embodiment, the memory of the control device 200 stores data showing a compressor map showing the characteristics of the first compressor. The compressor map includes a first axis of the amount of air sucked into the first compressor of the first turbocharger and a second axis of the pressure ratio of the discharge pressure to the suction pressure of the first compressor. When the control device 200 is switched to the twin supercharging mode, the operating point specified by the pressure ratio and the amount of air in the compressor map stored in the memory is below the predetermined line on the compressor map. If indicated, switch the supercharging mode to single supercharging mode. This makes it possible to appropriately switch from the twin supercharging mode to the single supercharging mode even in a transitional situation.

Specifically, the following processing is executed in order to execute such control. FIG. 5 is a flowchart showing an example of the flow of the switching process to the single supercharging mode in this embodiment. With reference to FIG. 5, the control device 200 determines whether or not the supercharging mode flag has a value indicating the twin supercharging mode (step S101). The supercharging mode flag is a flag indicating the currently controlled supercharging mode, and is a value indicating one of the single supercharging mode, the twin supercharging mode, and the run-up mode as the controlled supercharging mode. Can be taken.

If it is determined that the supercharging mode flag does not indicate that the turbocharging mode is in the twin supercharging mode (NO in step S101), the control device 200 returns the process to be executed to the process of the caller of this process.

When it is determined that the supercharging mode flag indicates that the turbocharging mode is in the twin supercharging mode (YES in step S101), the control device 200 calculates the target VN opening degree from the state quantity of each part using the physical formula of the supercharger. (Step S112). The state quantities of the intake path and the exhaust path when calculating the target VN opening are the state quantities of the intake path before branching to the primary turbocharger 30 and the secondary turbocharger 40, respectively, and the primary turbocharger. The state quantity of the exhaust path after merging from 30 and the secondary turbocharger 40 is used.

FIG. 6 is a first diagram for explaining the physical formula of the turbocharger. In the physical formula of the turbocharger with reference to FIG. 6, first, the target compressor rear pressure P3 is calculated from the target diesel throttle front pressure and the intercooler pressure loss. The target diesel throttle front pressure is the target pressure between the diesel throttle 68 and the intercooler 25. The intercooler pressure loss is the pressure loss due to the intercooler 25. The target compressor post-pressure P3 is calculated by adding the intercooler pressure loss to the target diesel throttle pre-pressure (hereinafter referred to as “target D slot pre-pressure”).

Next, the target compressor work is calculated from the target post-compressor pressure P3, the fresh air amount Ga, the intake air temperature Tha, and the pre-compressor pressure P2 using the mathematical formula (1). Cpa: constant temperature specific heat (0.24), k: specific heat ratio of air (1.4). The intake air amount Ga is specified according to the detection signal from the air flow meter 102.

Next, the target turbine work is calculated using the mathematical formula (2) from the target compressor work and the total turbo efficiency ηtot. The total turbo efficiency ηtot is calculated by the control device 200 from the state quantity using a known calculation formula.

Next, the target exhaust manifold pressure is calculated using the mathematical formula (3) from the target turbine work, the exhaust manifold gas temperature T4, the turbo post-turbo pressure P6, and the turbine passing gas amount Ga + Gf. Cpg: constant pressure specific heat (0.26), K: specific heat ratio of exhaust gas (1.33). The mass flow rate Gf of the injected fuel is calculated from the fuel injection amount calculated by the control device 200 for fuel injection.

FIG. 7 is a second diagram for explaining the physical formula of the turbocharger. With reference to FIG. 7, a constraint guard is applied to the target exhaust manifold pressure P4. In this constraint guard, if the target exhaust manifold pressure P4 is higher than the limit exhaust manifold pressure, P4 is set as the limit exhaust manifold pressure. The limit exhaust manifold pressure is predetermined as a value at which the oil seal of the valve stem of the exhaust valve does not blow through or the exhaust valve does not open.

Then, the target effective opening area μA is calculated from the target exhaust pressure P4, the exhaust gas temperature T4, the turbo post-turbo pressure P6, and the turbine passing gas amount Ga + Gf using the nozzle formula of the equation (4). It should be noted that A: the actual opening area, μA: the target effective opening area, R: the gas constant (287), and a, b: P6 / P4, which are predetermined constants.

Next, the target VN opening degree is calculated from the calculated target effective opening area μA by using the opening degree characteristic map showing the relationship between the VN opening degree and the effective opening area.

Returning to FIG. 5, the control device 200 determines whether or not the calculated target VN opening degree is out of the controllable range (step S113). Due to the structure of the nozzle vane, the VN opening cannot be controlled to a completely closed state (100%) or a completely open state (0%). Therefore, the controllable range of the VN opening degree is, for example, a range of 10% to 96%. When it is determined that the calculated target VN opening degree is out of this controllable range (YES in step S113), the control device 200 continues the state in which the target VN opening degree is out of the controllable range for a predetermined period. Whether or not it is determined (step S114).

If it is determined that the system has continued for a predetermined period (YES in step S114), the control device 200 changes the supercharging mode flag to a value indicating the single supercharging mode (step S117), and performs the process of this process. Return to the caller's processing. As a result, the mode is switched to the single supercharging mode.

FIG. 8 is a diagram for explaining an example of a change in the target VN opening degree calculated by a physical formula. With reference to FIG. 8, as shown in FIG. 8 (B), when the accelerator is turned off and the fuel injection amount is drastically reduced, the engine is shown in FIG. 8 (A). The rotation speed of 1 gradually decreases. As a result, the target D slot front pressure, which is determined by the rotation speed of the engine 1 and the fuel injection amount, also drops sharply, and the target boost pressure (= target compressor post-pressure P3) also drops sharply. Along with this, the target VN opening for judgment calculated by the above physical formula also decreases, but when the target boost pressure exceeds the actual boost pressure at time T1, the target VN opening for judgment increases. Turn to. After that, the supercharging mode is switched from the twin supercharging mode to the single supercharging mode at the continuous time T2 for a predetermined period in a state where the target VN opening degree exceeds the predetermined value of the upper limit on the closing side of the controllable range.

Returning to FIG. 5, it is determined that the calculated target VN opening degree is not out of the controllable range (NO in step S113), or the calculated target VN opening degree is out of the controllable range. If it is determined that the period is not continued (NO in step S114), the control device 200 determines that the intake air amount Ga of the primary supercharger 30 is the post-compressor pressure P3 with respect to the pre-compressor pressure P2 of the primary supercharger 30. It is determined whether or not the pressure ratio is equal to or less than the threshold value calculated from the pressure ratio (step S115).

FIG. 9 is a diagram showing an example of a compressor operation map showing the relationship between the intake air amount of the compressor 31 of the primary turbocharger 30 and the pressure ratio before and after the compressor 31. With reference to FIG. 9, the compressor operation map is a map showing an operating region of the compressor 31 with the intake air amount and the pressure ratio of the compressor 31 of the primary turbocharger 30 as parameters. The horizontal axis and the vertical axis of this map show the intake air amount and the pressure ratio of the compressor 31, respectively. The intake air amount of the compressor 31 can be estimated from, for example, the intake air amount detected by the air flow meter 102.

The "surge line" (dashed-dotted line) indicates a boundary line with a surge region where surging is likely to occur in the primary turbocharger 30. The "equal rotation speed line" (fine solid line) is a group of lines connecting operating points having the same rotation speed of the compressor 31 for each rotation speed of the compressor 31. The rotation speed of the compressor 31 becomes higher as the amount of intake air of the compressor 31 is larger and the pressure ratio is larger. Further, the rotation speed of the compressor 31 becomes higher as the engine rotation speed is higher in the single supercharging mode.

The "switching line L2" (thick solid line) is a line in which switching from the single supercharging mode to the twin supercharging mode is performed. During acceleration, the operating point of the compressor 31 moves along the operating line shown in FIG. 9, and when it reaches the switching line L2, it is switched to the approach mode in the preparatory stage for switching from the single supercharging mode to the twin supercharging mode, and then. , Switch to twin supercharging mode.

The "switching line L1" (thick solid line) is a line in which the twin supercharging mode is switched to the single supercharging mode. At the time of deceleration, the operating point of the compressor 31 moves along the operating line shown in FIG. 9, and when the switching line L1 is reached, the twin supercharging mode is switched to the single supercharging mode.

Returning to FIG. 5, when the operating point reached the switching line L1, the intake air amount Ga of the primary turbocharger 30 became equal to or less than the threshold value calculated from the pressure ratio of the primary turbocharger 30 (step S115). The control device 200 changes the supercharging mode flag to a value indicating the single supercharging mode (step S117), and returns the process to be executed to the process of the caller of this process. As a result, the mode is switched to the single supercharging mode.

On the other hand, when it is determined that the operating point has not reached the switching line L1 and the intake air amount Ga is not equal to or less than the threshold value calculated from the pressure ratio of the primary turbocharger 30 (NO in step S115), the control device The 200 returns the process of leaving the supercharging mode flag to the value indicating the twin supercharging mode (step S116) to the process of the caller of this process.

FIG. 10 is a diagram for explaining a change in boost pressure during reacceleration between the case where the operating point of the compressor operation map reaches the switching line L1 and the case where the operating point does not reach the switching line L1. With reference to FIG. 10, as shown in FIG. 10 (A), when the accelerator opening is reduced from 100% to 20%, the target boost pressure suddenly increases as shown in FIG. 10 (B). Can be lowered to. However, as shown in FIG. 10B, the actual boost pressure gradually decreases.

When determining the switching from the twin supercharging mode to the single supercharging mode according to the rotation speed of the engine 1 and the fuel injection amount as in the conventional case, the single supercharging pressure is suddenly lowered at the time T1. Switch to supercharging mode. When re-accelerating immediately after switching, the responsiveness of the boost pressure is poor because the target boost pressure deviates from the actual boost pressure.

On the other hand, in this embodiment, when the operating point of the compressor operation map falls below the switching line L1 (time T3 in FIG. 10), the twin supercharging mode is switched to the single supercharging mode. As shown by the thick broken line in FIG. 10 (I), when the accelerator opening is set to 100% and the vehicle is re-accelerated at the time T2 immediately before the time T3, the operating point is before the switching line L1 is reached. Even if the feeding mode remains, the responsiveness of the boost pressure is good.

Further, as shown by the thick solid line in FIG. 10 (II), when the accelerator opening is re-accelerated at time T4 after switching to the single supercharging mode at time T3, the operating point is the switching line. Since it has fallen below L1, reacceleration is started in the single supercharging mode, so that the responsiveness of the supercharging pressure is good. After that, at time T5, when the rotation speed of the compressor 31 increases to some extent in the single supercharging mode and the intake air amount increases, the supercharging pressure is switched to the approach mode for switching to the twin supercharging mode. Can be raised.

FIG. 11 is a diagram for explaining the difference in operating points depending on the accelerator opening degree in a steady state on the compressor operation map. With reference to FIG. 11, the accelerator opening degree is indicated by A1% to A5%, and is A1> A2> A3> A4> A5. In the compressor operation map, the larger the accelerator opening is in steady state, the more the operating point moves in the upper right direction where the intake air amount and the pressure ratio P3 / P2 are higher. The operating point of the accelerator opening A3% is on the switching line L1. The operating point of the accelerator opening A4% is a position below the switching line L1.

FIG. 12 is a diagram for explaining the difference in boost pressure in re-acceleration for each accelerator opening after deceleration. With reference to FIG. 12, as shown in FIG. 12 (A), when the vehicle is re-accelerated from the accelerator opening A4% at time T1 in the twin supercharging mode, the post-compressor pressure P3 is shown by the thick solid line. Rise. When the accelerator opening A4% is re-accelerated at time T1 after switching to the single supercharging mode, the post-compressor pressure P3 increases as shown by the thick broken line. As shown in FIG. 12A, when reaccelerating from the accelerator opening A4%, the responsiveness of the supercharging pressure is better after switching to the single supercharging mode than in the twin supercharging mode. Is good.

As shown in FIG. 12B, when the vehicle is re-accelerated from the accelerator opening A3% at time T1 in the twin supercharging mode, the post-compressor pressure P3 increases as shown by the thick solid line. When the accelerator opening A3% is re-accelerated at time T1 after switching to the single supercharging mode, the post-compressor pressure P3 increases as shown by the thick broken line. As shown in FIG. 12B, when reaccelerating from the accelerator opening A3%, the responsiveness of the supercharging pressure is almost the same after switching to the single supercharging mode and in the twin supercharging mode. equal.

As shown in FIGS. 12A and 12B, the post-compressor pressure P3 is increased when the accelerator opening is re-accelerated in the single supercharging mode in both cases of accelerator opening A3% and A4%. After rising to some extent, the second control valve 64 is switched to the open state, and after the run-up mode is set, the first control valve 62 is switched to the open state, so that the twin supercharging mode is switched.

From the results shown in FIG. 12, when the speed falls below the constant rotation speed line passing through the operating point of the accelerator opening A3% in the steady state, switching to the single supercharging mode improves the responsiveness of the supercharging pressure. The constant rotation speed line can be defined as the switching line L1.

[Modification example]
(1) In the above-described embodiment, as described with reference to FIGS. 6 and 7, the target VN opening degree is calculated by using the post-compressor pressure P3 calculated from the pre-D slot pressure as it is. FIG. 13 is a diagram for explaining the calculation of the target VN opening degree in the modified example. With reference to FIG. 13, in this case, as shown in FIG. 13 (A), when the accelerator opening is increased, the actual boost pressure gradually increases as shown in FIG. 12 (B). However, the target boost pressure is raised sharply. As a result, as shown in FIG. 13C, when the target VN opening degree is calculated by the physical formula described with reference to FIGS. 6 and 7, the target VN opening degree is suddenly calculated as a value on the closing side. As a result, the determination of the target VN opening degree in step S113 of FIG. 5 becomes unstable.

In order to deal with such a situation, as shown in FIG. 13D, the target boost pressure that has been subjected to the tampering treatment may be used for calculating the target VN opening degree. This makes it possible to stabilize the determination of the target VN opening degree.

(2) In the above-described embodiment, the primary supercharger 30 and the secondary supercharger 40 are provided in the intake passage of the engine 1, but the primary supercharger 30 is provided in the intake passage of the engine 1. In addition to the 30 and the secondary turbocharger 40, for example, an EGR (Exhaust Gas Recirculation) gas inlet of an intake throttle valve or an exhaust recirculation device may be provided.

(3) In the above-described embodiment, the engine 1 has been described using a V-type 6-cylinder engine as an example, but may be, for example, an engine having another cylinder layout (for example, in-line type or horizontal type).

(4) In the above-described embodiment, the supercharging system has been described as having two superchargers, but it may have three or more superchargers.

(5) Disclosure of a supercharging system including a primary supercharger 30, a secondary supercharger 40, and a control device 200, disclosure of an internal combustion engine such as an engine 1, internal combustion of an engine 1 or the like, according to the above-described embodiment. It can be regarded as disclosure of a control device such as an engine ECU 100, disclosure of a control method by such a control device, or disclosure of an internal combustion engine system including such an internal combustion engine and a control device.

[effect]
(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 step S112, step S113, step S117, FIG. 6 and FIG. 7 of FIG. 5, when the control device 200 is switched to the twin supercharging mode, the primary supercharger 30 and the secondary supercharger 30 are used. The target VN opening degree of the variable nozzle mechanism 35 and the variable nozzle mechanism 45 required for 40 to obtain the target boost pressure is calculated from the state quantities of the intake path and the exhaust path, and the calculated target VN opening degree can be controlled. If it is out of range, the supercharging mode is switched to the single supercharging mode.

This makes it possible to appropriately switch from the twin supercharging mode to the single supercharging mode even in a transitional situation. Further, in the conventional control using the engine rotation speed and injection amount, a correction map is used for environmental changes, but in this disclosure, the target VN opening degree used for the determination is calculated by a physical formula. The need for environmental correction can be eliminated. In addition, it is possible to reduce the trouble of creating a correction map.

(1-2) As shown in FIGS. 6 and 7, the control device 200 uses a simulation formula based on the physical laws of the intake path and the exhaust path of the engine 1 as a calculation formula for calculating the target VN opening degree. Use. As a result, the target VN opening degree for determination can be appropriately calculated.

(1-3) The control device 200 uses the intake path before branching to the primary turbocharger 30 and the secondary turbocharger 40 as the state quantities of the intake path and the exhaust path when calculating the target VN opening degree, respectively. And the state amount of the exhaust path after merging from the primary supercharger 30 and the secondary supercharger 40 are used. As a result, the target VN opening degree for determination can be appropriately calculated.

(1-4) As shown in FIGS. 1 to 4, the primary turbocharger 30 and the secondary turbocharger 40 have the same model. The control device 200 considers the primary supercharger 30 and the secondary supercharger 40 as one supercharger, calculates one target VN opening degree, and uses the calculated one target VN opening degree as the variable nozzle mechanism 35, Determined as the target VN opening degree of 45. This makes it possible to simplify the calculation of the target VN opening degree and the control of the supercharging mode.

(1-5) As shown in step S114 of FIG. 5, when the calculated target VN opening degree is out of the controllable range for a predetermined period of time, the control device 200 singles the supercharging mode. Switch to feed mode. This makes it possible to prevent hunting for switching the supercharging mode.

(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. A primary supercharger 30 including a variable nozzle mechanism 35 and a compressor 31 that supercharges intake air to the engine 1, a turbocharger 42 driven by exhaust gas discharged from the engine 1, and a flow velocity of exhaust water flowing into the turbine 42. A single turbocharger 40 that supercharges the intake air to the engine 1 and a single turbocharger 40 that supercharges the air supercharged in the primary supercharger 30 are supplied to the engine 1. One of the supercharging mode and 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 is supercharged to the other. It includes a control device 200 for switching the supply mode and a memory for storing data showing a compressor operation map showing the characteristics of the compressor 31. As shown in FIG. 9, the compressor operation map shows the first axis of the intake air amount sucked into the compressor 31 of the primary turbocharger 30 and the pressure ratio P3 / P2 of the discharge pressure to the suction pressure of the compressor 31. Includes 2 axes.

As shown in steps S115 and S117 of FIG. 5, when the control device 200 is switched to the twin supercharging mode, the pressure ratio P3 / P2 and the intake air amount are displayed in the compressor operation map stored in the memory. When it is shown that the operating point specified by is below the switching line L1 on the compressor operation map, the supercharging mode is switched to the single supercharging mode.

This makes it possible to appropriately switch from the twin supercharging mode to the single supercharging mode even in a transitional situation. In addition, in the conventional control using the engine speed and injection amount, a correction map was used for environmental changes, but in this disclosure, since the judgment is made using the compressor operation map, it is necessary to correct the environment. Can be eliminated. In addition, it is possible to reduce the trouble of creating a correction map.

(2-2) As shown in FIGS. 11 and 12, the switching line L1 has a pressure ratio in the twin supercharging mode rather than the single supercharging mode when the fuel injection is restarted in the engine 1. This is the boundary between the region where the rise is fast and the region where the pressure ratio rises faster in the single supercharging mode than in the twin supercharging mode. This makes it possible to appropriately set the switching line L1.

(2-3) As shown in FIG. 9, the switching line L1 is a line having a constant rotation speed during steady running of the primary turbocharger 30.

It is also planned that the embodiments disclosed this time will 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 set forth by the claims rather than the description of the embodiments described above, and is intended to include all modifications within the meaning and scope of the 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 Supercharger, 48 Recirculation Pipe, 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, 81 Exhaust treatment device, 102 Airflow meter, 104 Engine rotation speed sensor, 106 1st pressure sensor, 108 2nd 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 the opening degree, and supercharges the intake air to the engine. 1 supercharger and
It includes a second turbine driven by the 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. With the second supercharger,
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 for switching the supercharging mode from one of the twin supercharging modes supplied to the engine to the other.
The control device has the first variable nozzle mechanism and the first variable nozzle mechanism required for the first supercharger and the second supercharger to obtain a target supercharging pressure when the twin supercharging mode is switched to. 2 The target opening of the variable nozzle mechanism is calculated from the state quantities of the intake path and the exhaust path, and when the calculated target opening is out of the controllable range, the supercharging mode is switched to the single supercharging mode. Salary system. The supercharging system according to claim 1, wherein the control device uses a simulation formula based on the physical laws of the intake path and the exhaust path of the engine as a calculation formula for calculating the target opening degree. The control device has, as the state quantities of the intake path and the exhaust path when calculating the target opening degree, the state quantities of the intake path before branching to the first supercharger and the second supercharger, respectively. The supercharging system according to claim 1, wherein the state quantity of the exhaust path after merging from the first supercharger and the second supercharger is used. The first supercharger and the second supercharger are of the same model and have the same model.
The control device regards the first supercharger and the second supercharger as one supercharger, calculates one target opening degree, and uses the calculated target opening degree as the first variable nozzle. The supercharging system according to claim 1, wherein the mechanism and the target opening degree of the second variable nozzle mechanism are set. The supercharging system according to claim 1, wherein the control device switches the supercharging mode to the single supercharging mode when the calculated target opening degree is out of the controllable range for a predetermined time. The first supercharger includes a first compressor that supercharges the intake air to the engine.
Further, a storage unit for storing data showing a compressor map showing the characteristics of the first compressor is provided.
The compressor map includes a first axis of the amount of air sucked into the first compressor of the first turbocharger and a second axis of the pressure ratio of the discharge pressure to the suction pressure of the first compressor.
When the control device is switched to the twin supercharging mode, if the calculated target opening degree is out of the controllable range for the predetermined time, the control device is stored in the storage unit. The single supercharging mode is switched to the single supercharging mode when it is shown that the operating point specified by the pressure ratio and the air amount in the compressor map is below a predetermined line on the compressor map. The supercharging system according to 5.

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