WO2009150790A1

WO2009150790A1 - Intake control apparatus of internal combustion engine

Info

Publication number: WO2009150790A1
Application number: PCT/JP2009/002286
Authority: WO
Inventors: Mitsuhiro Nada
Original assignee: Toyota Motor Corp
Current assignee: Toyota Motor Corp
Priority date: 2008-06-10
Filing date: 2009-05-25
Publication date: 2009-12-17
Anticipated expiration: 2010-12-10
Also published as: JP4793408B2; JP2009299474A

Abstract

In one embodiment, with respect to a common rail diesel engine to which an EGR apparatus and a variable capacity turbocharger has been applied, for each EGR ratio, as an intake filling efficiency that is set by the nozzle vane opening degree of a variable nozzle vane mechanism, adapted values that approximately maximize an intake charging efficiency are acquired by an automatic adaptation apparatus and a filling efficiency setting map is stored in a ROM, and the nozzle vane opening degree of the variable nozzle vane mechanism is controlled according to the filling efficiency setting map. The automatic adaptation apparatus, in a state with the nozzle vane opening degree fixed, obtains an EGR ratio where maximum torque is obtained while changing the EGR ratio, and acquires the nozzle vane opening degree at this time as an adapted value that corresponds to the present EGR ratio.

Description

[Title established by the ISA under Rule 37.2] INTAKE CONTROL APPARATUS OF INTERNAL COMBUSTION ENGINE

The present invention relates to an intake control apparatus of an internal combustion engine represented by a diesel engine for use in a vehicle, and an automatic adaptation apparatus of an internal combustion engine for acquiring an adapted value as a control value of that intake control apparatus. Specifically, the present invention relates to a measure for achieving optimization of an intake efficiency in an apparatus provided with a means of recirculating part of an exhaust gas in an intake system, and a means that allows varying of a filling efficiency of intake into a cylinder.

As is commonly known in the conventional technology, in a diesel engine (below, also referred to simply as an engine) used as an automobile engine, complicated control is performed in order for engine characteristics such as exhaust gas characteristics, fuel consumption characteristics, stable combustion characteristics, power characteristics, and so forth to satisfy various demands.

Specifically, adapted values of various control parameters such as an optimal fuel injection amount according to the operating state of the engine determined based on the revolutions or load of the engine are set in advance as a control map, and this control map is stored in an electronic control unit for engine control (engine ECU). The engine ECU performs engine control by referring to the adapted values in the control map.

In this type of engine, in order to achieve an improvement in exhaust emissions, an exhaust gas recirculation (EGR) apparatus that recirculates part of an exhaust gas in an intake path is provided (for example, see below PTL 1). This EGR apparatus is provided with an EGR path in which an engine exhaust path and intake path are in communication with each other, and an EGR valve provided in the EGR path. By adjusting the opening degree of the EGR valve, the amount (EGR amount) of exhaust gas that is recirculated from the exhaust path to the intake path via the EGR path is adjusted to set an EGR ratio in the intake gas to a target EGR ratio that has been set in advance. When part of the exhaust gas is returned to the intake path by the EGR apparatus in this way, the combustion temperature of the air-fuel mixture is reduced, so production of nitrogen oxide (NOx) in a combustion chamber is suppressed, and as a result exhaust emissions are improved.

Also, recently, as one type of turbocharger applied in a diesel engine or the like, for example as disclosed in below PTL 2, a variable capacity turbocharger is known in which a turbine side is made to have a variable capacity. In this type of turbocharger, in an exhaust gas flow path of a turbine housing, nozzle vanes (also referred to as movable vanes) whereby the flow path area (throat area) of this exhaust gas flow path is made variable are disposed. For example, by turning the nozzle vanes when engine revolutions are low to reduce the flow path area, the flow rate of the exhaust gas is increased, and thus it is possible to obtain a high charging pressure from a low engine speed range.

JP 2006-266159A JP 2000-110628A

Incidentally, in an engine in which the above-described EGR apparatus and a variable capacity turbocharger are both installed, up to now, the relationship between the EGR ratio set by the EGR apparatus and the intake filling efficiency set by the variable capacity turbocharger has not been quantified.

That is, there have not yet been any proposals related to optimization of the intake filling efficiency by the variable capacity turbocharger for a case in which the EGR ratio has been adjusted (for example, adjustment to an increased EGR ratio accompanying an increased NOx exhaust amount) by the EGR apparatus in response to demands for improvement of exhaust emissions. Specifically, there have not been any proposals with respect to a technical idea for, in an engine in which this EGR apparatus and variable capacity turbocharger are installed, in a circumstance in which the engine torque changes with a change in the EGR ratio, obtaining maximum engine torque.

The present invention provides, for an internal combustion engine provided with a means of recirculating part of an exhaust gas in an intake system, and a means that allows varying of a filling efficiency of intake into a cylinder, an intake control apparatus and an automatic adaptation apparatus of the internal combustion engine that can obtain an optimal intake efficiency.

- Principles of Solution -
The principles of the solution of the present invention are as follows. That is, by obtaining an intake filling efficiency at which maximum torque of an internal combustion engine is obtained for various values of an exhaust recirculation ratio, optimization of the relationship between the exhaust recirculation ratio and the intake filling efficiency is achieved, and thus it is possible to obtain torque of the internal combustion engine that is always near the maximum torque, even when the exhaust recirculation ratio has changed.

- Solving Means -
The intake control apparatus of an internal combustion engine according to the present invention is an intake control apparatus of an internal combustion engine provided with a filling efficiency varying unit that allows varying of a filling efficiency of intake gas that is supplied into a cylinder of the internal combustion engine; and an exhaust recirculation ratio varying unit that recirculates exhaust of the internal combustion engine to an intake system and allows varying of that recirculation ratio, the intake control apparatus being provided with a storage unit that respectively stores, for each of the exhaust recirculation ratios varied by the exhaust recirculation ratio varying unit, as an adapted value, a control value of the filling efficiency varying unit at which the torque of the internal combustion engine becomes approximately maximum; and a filling efficiency control unit that, during operation of the internal combustion engine, reads from the storage unit a control value as the adapted value of the filling efficiency varying unit that corresponds to the exhaust recirculation ratio that has been set by the exhaust recirculation ratio varying unit, and controls the filling efficiency varying unit based on that control value.

During operation of the internal combustion engine, the exhaust recirculation ratio varying unit is controlled such that the exhaust recirculation ratio becomes an appropriate value, due to demands for improvement of exhaust emissions. A control value (adapted value) of the filling efficiency varying unit that has been stored in advance corresponding to the exhaust recirculation ratio that has been set in this case is read from the storage unit, and the filling efficiency varying unit is controlled based on this control value. This control value of the filling efficiency varying unit that has been stored in advance is obtained, for each exhaust recirculation ratio, as a value at which the intake filling efficiency where the torque of the internal combustion engine becomes approximately maximum is obtained. Therefore, this control value (adapted value) of the filling efficiency varying unit that has been obtained in advance is appropriately obtained in order to maximize the operating efficiency of the internal combustion engine, and by controlling the filling efficiency varying unit based on this control value, it is possible to maintain an approximately maximum intake efficiency. As a result, even while achieving an improvement in exhaust emissions, it is possible to obtain approximately maximum torque in the present operating state of the internal combustion engine (at the present exhaust recirculation ratio).

The following is a specific example of the configuration of the above filling efficiency varying unit and filling efficiency control unit. The filling efficiency varying unit is provided in a supercharger, and changes a charging pressure by changing a flow path area of gas that flows towards a turbine wheel by changing a nozzle vane opening degree that can be driven open/closed with a variable nozzle vane mechanism, thus changing the intake filling efficiency. The filling efficiency control unit, during operation of the internal combustion engine, controls the variable nozzle vane mechanism in order to set the nozzle vane opening degree, based on the control value used as the adapted value that corresponds to the exhaust recirculation ratio.

In the case of this configuration, the nozzle vane opening degree is used as the control value (adapted value) of the filling efficiency varying unit that has been obtained in advance according to the exhaust recirculation ratio. By setting the nozzle vane opening degree according to this control value, it is possible to realize an intake filling efficiency at which it is possible to obtain approximately maximum torque in the present operating state of the internal combustion engine.

In the above storage unit, control values of the filling efficiency varying unit that have been obtained in the following manner, for example, are stored. That is, an operation in which, in a state in which the control value of the filling efficiency varying unit has been fixed, the torque of the internal combustion engine is measured while the exhaust recirculation ratio is changed by the exhaust recirculation ratio varying unit is executed for a plurality of control values of the filling efficiency varying unit to obtain an intake filling efficiency at which approximately maximum torque is obtained at the same exhaust recirculation ratio, and each control value of the filling efficiency varying unit for obtaining that filling efficiency is stored as an adapted value of the filling efficiency varying unit that corresponds to that exhaust recirculation ratio.

Because the control values (adapted values) of the filling efficiency varying unit that have been obtained in this way are stored in the storage unit, a control value is obtained such that the relationship of the exhaust recirculation ratio and the intake filling efficiency is adapted to the actual internal combustion engine (actual engine), so it is possible to reliably obtain the working effects described above.

The following is an example of a configuration of an automatic adaptation apparatus for automatically acquiring, for each exhaust recirculation ratio, a control value of the filling efficiency varying unit at which the torque of the internal combustion engine becomes maximum. That is, the invention provides an automatic adaptation apparatus of an internal combustion engine provided with a filling efficiency varying unit that allows varying of a filling efficiency of intake gas that is supplied into a cylinder, and an exhaust recirculation ratio varying unit that recirculates exhaust to an intake system and allows varying of that recirculation ratio, the automatic adaptation apparatus being for obtaining, for each exhaust recirculation ratio varied by the exhaust recirculation ratio varying unit, as a control value of the filling efficiency varying unit, an adapted value where the torque of the internal combustion engine becomes approximately maximum; the automatic adaptation apparatus, in a state in which the control value of the filling efficiency varying unit has been fixed, executing an operation of measuring the torque of the internal combustion engine while the exhaust recirculation ratio is changed by the exhaust recirculation ratio varying unit, for a plurality of control values of the filling efficiency varying unit, to obtain an intake filling efficiency at which approximately maximum torque is obtained at the same exhaust recirculation ratio, thus automatically acquiring a control value of the filling efficiency varying unit for obtaining that filling efficiency as an adapted value that corresponds to that exhaust recirculation ratio.

Thus, it is possible to automatically acquire an adapted value of the intake filling efficiency that corresponds to the exhaust recirculation ratio, and with this adapted value it is possible to obtain approximately maximum torque as the torque of the internal combustion engine. As a result, the need for acquiring an appropriate adapted value in trial and error, and the need for a great deal of time to acquire that adapted value, is eliminated, so it is possible to achieve increased efficiency of the adaptation operation and improved reliability of the adapted value.

The following is an example of a configuration for controlling operation of the internal combustion engine using a control value (adapted value) acquired by the automatic adaptation apparatus as described above. That is, the invention provides an intake control apparatus of an internal combustion engine provided with a filling efficiency varying unit that allows varying of a filling efficiency of intake gas that is supplied into a cylinder of the internal combustion engine; and an exhaust recirculation ratio varying unit that recirculates exhaust of the internal combustion engine to an intake system and allows varying of that recirculation ratio, the intake control apparatus being provided with a storage unit that stores each adapted value that has been obtained by an automatic adaptation apparatus that, in a state in which the control value of the filling efficiency varying unit has been fixed, executes an operation of measuring the torque of the internal combustion engine while the exhaust recirculation ratio is changed by the exhaust recirculation ratio varying unit, for a plurality of control values of the filling efficiency varying unit, to obtain an intake filling efficiency at which approximately maximum torque is obtained at the same exhaust recirculation ratio, thus automatically acquiring a control value of the filling efficiency varying unit for obtaining that filling efficiency as an adapted value that corresponds to that exhaust recirculation ratio; and a filling efficiency control unit that, during operation of the internal combustion engine, reads from the storage unit an adapted value of the filling efficiency varying unit that corresponds to the exhaust recirculation ratio that has been set by the exhaust recirculation ratio varying unit according to a target NOx amount, and controls the filling efficiency varying unit based on that adapted value.

Thus, it is possible to control operation of the above internal combustion engine by effectively using the adapted value acquired by the automatic adaptation apparatus, so an improvement in the utility of the invention can be achieved.

In the present invention, for an internal combustion engine provided with a filling efficiency varying unit that allows varying of the filling efficiency of intake gas supplied into cylinders of the internal combustion engine, and an exhaust recirculation ratio varying unit that allows varying of the recirculation ratio of exhaust gas in an intake system, an intake filling efficiency is obtained at which maximum torque of the internal combustion engine is obtained for various exhaust recirculation ratios, thus achieving optimization of the relationship between the exhaust recirculation ratio and the intake filling efficiency. Therefore, even when the exhaust recirculation ratio has changed, it is possible to always maintain approximately maximum intake efficiency, and so even while achieving an improvement in exhaust emissions, it is possible to obtain approximately maximum torque in the present operating state of the internal combustion engine.

Fig. 1 is a schematic configuration diagram of an engine and a control system of that engine according to an embodiment. Fig. 2 is a cross-sectional view that shows a combustion chamber of a diesel engine and parts in the vicinity of that combustion chamber. Fig. 3 is cross-sectional view along a center axis of a turbine shaft in a turbocharger. Fig. 4 is a cross-sectional view that shows an enlarged view of a turbine wheel of the turbocharger and parts in the vicinity of that turbine wheel. Fig. 5 is a front view of a variable nozzle vane mechanism in a state in which a large nozzle vane opening degree has been set. Fig. 6 is a rear view of the variable nozzle vane mechanism in a state in which the large nozzle vane opening degree has been set. Fig. 7 is a front view of the variable nozzle vane mechanism in a state in which a small nozzle vane opening degree has been set. Fig. 8 is a rear view of the variable nozzle vane mechanism in a state in which the small nozzle vane opening degree has been set. Fig. 9 is a block diagram that shows the configuration of a control system of an ECU or the like. Fig. 10 is a waveform diagram that shows the state of change of a heat production rate during an expansion stroke. Fig. 11 shows EGR ratio contour lines. Fig. 12 shows the relationship between filling efficiency and engine torque when the EGR ratio is 0%. Fig. 13 shows curves that indicate the change in engine torque and EGR ratio contour lines when the EGR ratio has been changed while a nozzle vane opening degree is fixed. Fig. 14 shows the configuration of a system for performing automatic adaptation that acquires adapted values of the EGR ratio and the intake filling efficiency. Fig. 15 is a flowchart that shows a procedure for performing automatic adaptation of the EGR ratio and the intake filling efficiency. Fig. 16 shows equal EGR ratio lines, equal VN opening degree lines, and equal EGR valve opening degree lines.

Following is a description of an embodiment of the invention based on the drawings. In the present embodiment, a case will be described in which the invention is applied to a common rail in-cylinder direct injection multi-cylinder (for example, inline four-cylinder) diesel engine (compression self-igniting internal combustion engine) mounted in an automobile.

- Engine Configuration -
First, the overall configuration of a diesel engine (referred to below as simply the engine) according to the present embodiment will be described. Fig. 1 is a schematic configuration diagram of an engine 1 and a control system of the engine 1 according to this embodiment. Fig. 2 is a cross-sectional view that shows a combustion chamber 3 of the diesel engine and parts in the vicinity of the combustion chamber 3.

As shown in Fig. 1, the engine 1 according to this embodiment is configured as a diesel engine system having a fuel supply system 2, combustion chambers 3, an intake system 6, an exhaust system 7, and the like as its main portions.

The fuel supply system 2 is provided with a supply pump 21, a common rail 22, injectors (fuel injection valves) 23, a cutoff valve 24, a fuel addition valve 26, an engine fuel path 27, an added fuel path 28, and the like.

The supply pump 21 draws fuel from a fuel tank, and after putting the drawn fuel under high pressure, supplies that fuel to the common rail 22 via the engine fuel path 27. The common rail 22 has a function as an accumulation chamber where high pressure fuel supplied from the supply pump 21 is held (accumulated) at a predetermined pressure, and this accumulated fuel is distributed to each injector 23. The injectors 23 are configured from piezo injectors within which a piezoelectric element (piezo element) is provided, and supply fuel by injection into the combustion chambers 3 by appropriately opening a valve. The details of control of fuel injection from the injectors 23 will be described later.

Also, the supply pump 21 supplies part of the fuel drawn from the fuel tank to the fuel addition valve 26 via the added fuel path 28. In the added fuel path 28, the aforementioned cutoff valve 24 is provided in order to stop fuel addition by cutting off the added fuel path 28 during an emergency.

The fuel addition valve 26 is configured from an electronically controlled opening/closing valve whose valve opening period is controlled with an addition control operation by an ECU 100 described later such that the amount of fuel added to the exhaust system 7 becomes a target addition amount (an addition amount such that exhaust A/F becomes target A/F), or such that a fuel addition timing becomes a predetermined timing. That is, a desired amount of fuel from the fuel addition valve 26 is supplied by injection to the exhaust system 7 (to an exhaust manifold 72 from exhaust ports 71) at an appropriate timing.

The intake system 6 is provided with an intake manifold 63 connected to an intake port 15a formed in a cylinder head 15 (see Fig. 2), and an intake tube 64 that comprises an intake path is connected to the intake manifold 63. Also, in this intake path, an air cleaner 65, an airflow meter 43, and a throttle valve 62 are disposed in order from the upstream side. The airflow meter 43 outputs an electrical signal according to the amount of air that flows into the intake path via the air cleaner 65.

The exhaust system 7 is provided with the exhaust manifold 72 connected to the exhaust ports 71 formed in the cylinder head 15, and

exhaust tubes

73 and 74 that constitute an exhaust path are connected to the exhaust manifold 72. Also, in this exhaust path, a maniverter (exhaust purification apparatus) 77 is disposed that is provided with a NOx storage catalyst (NSR catalyst: NOx Storage Reduction catalyst) 75 and a DPNR catalyst (Diesel Particulate-NOx Reduction catalyst) 76, described later. Following is a description of the NSR catalyst 75 and the DPNR catalyst 76.

The NSR catalyst 75 is a storage reduction NOx catalyst, and is configured using alumina (Al₂O₃) as a support, with, for example, an alkali metal such as potassium (K), sodium (Na), lithium (Li), or cesium (Cs), an alkaline earth element such as barium (Ba) or calcium (Ca), a rare earth element such as lanthanum (La) or Yttrium (Y), and a precious metal such as platinum (Pt) supported on this support.

The NSR catalyst 75, in a state in which a large amount of oxygen is present in the exhaust, stores NOx, and in a state in which the oxygen concentration in the exhaust is low and a large amount of a reduction component (for example, an unburned component (HC) of fuel) is present, reduces NOx to NO₂ or NO and releases the resulting NO₂ or NO. NOx that has been released as NO₂ or NO is further reduced due to quickly reacting with HC or CO in the exhaust and becomes N₂. Also, by reducing NO₂ or NO, HC and CO themselves are oxidized and thus become H₂O and CO₂. In other words, by appropriately adjusting the oxygen concentration or the HC component in the exhaust introduced to the NSR catalyst 75, it is possible to purify HC, CO, and NOx in the exhaust. In the configuration of the present embodiment, adjustment of the oxygen concentration or the HC component in the exhaust can be performed with an operation to add fuel from the aforementioned fuel addition valve 26.

On the other hand, in the DPNR catalyst 76, a NOx storage reduction catalyst is supported on a porous ceramic structure, for example, and PM in exhaust gas is captured when passing through a porous wall. When the air-fuel ratio of the exhaust gas is lean, NOx in the exhaust gas is stored in the NOx storage reduction catalyst, and when the air-fuel ratio is rich, the stored NOx is reduced and released. Furthermore, a catalyst that oxidizes/burns the captured PM (for example, an oxidization catalyst whose main component is a precious metal such as platinum) is supported on the DPNR catalyst 76.

Here, the combustion chamber 3 of the diesel engine and parts in the vicinity of the combustion chamber 3 will be described with reference to Fig. 2. As shown in Fig. 2, in a cylinder block 11 that constitutes part of the main body of the engine, a cylindrical cylinder bore 12 is formed in each cylinder (each of four cylinders), and a piston 13 is housed within each cylinder bore 12 such that the piston 13 can slide in the vertical direction.

The aforementioned combustion chamber 3 is formed on the top side of a top face 13a of the piston 13. More specifically, the combustion chamber 3 is partitioned by a lower face of the cylinder head 15 installed on top of the cylinder block 11 via a gasket 14, an inner wall face of the cylinder bore 12, and the top face 13a of the piston 13. A cavity 13b is concavely provided in approximately the center of the top face 13a of the piston 13, and this cavity 13b also constitutes part of the combustion chamber 3.

A small end 18a of a connecting rod 18 is linked to the piston 13 by a piston pin 13c, and a large end of the connecting rod 18 is linked to a crank shaft that is an engine output shaft. Thus, back and forth movement of the piston 13 within the cylinder bore 12 is transmitted to the crank shaft via the connecting rod 18, and engine output is obtained due to rotation of this crank shaft. Also, a glow plug 19 is disposed facing the combustion chamber 3. The glow plug 19 glows due to the flow of electrical current immediately before the engine 1 is started, and functions as a starting assistance apparatus whereby ignition and combustion are promoted due to part of a fuel spray being blown onto the glow plug.

In the cylinder head 15, the intake port 15a that introduces air to the combustion chamber 3 and the exhaust port 71 that discharges exhaust gas from the combustion chamber 3 are respectively formed, and an intake valve 16 that opens/closes the intake port 15a and an exhaust valve 17 that opens/closes the exhaust port 71 are disposed. The intake valve 16 and the exhaust valve 17 are disposed facing each other on either side of a cylinder center line P. That is, this engine 1 is configured as a cross flow-type engine. Also, the injector 23 that injects fuel directly into the combustion chamber 3 is installed in the cylinder head 15. The injector 23 is disposed in approximately the center above the combustion chamber 3, in an erect orientation along the cylinder center line P, and injects fuel introduced from the common rail 22 toward the combustion chamber 3 at a predetermined timing.

Furthermore, as shown in Fig. 1, a turbocharger 5 is provided in the engine 1. This turbocharger 5 is provided with a turbine wheel 52c and a compressor wheel 52b that are linked via a turbine shaft 52a. The compressor wheel 52b is disposed facing the inside of the intake tube 64, and the turbine wheel 52c is disposed facing the inside of the exhaust tube 73. Thus the turbocharger 5 uses exhaust flow (exhaust pressure) received by the turbine wheel 52c to rotate the compressor wheel 52b, thereby performing a so-called turbocharging operation that increases the intake pressure. In this embodiment, the turbocharger 5 is a variable nozzle-type (variable capacity) turbocharger, in which a variable nozzle vane mechanism (not shown in Fig. 1) is provided on the turbine wheel 52c side, and by adjusting the opening degree of this variable nozzle vane mechanism it is possible to adjust the turbocharging pressure of the engine 1. The specific configuration of this variable nozzle vane mechanism is described below.

An intercooler 61 for forcibly cooling intake air heated due to charging with the turbocharger 5 is provided in the intake tube 64 of the intake system 6. The throttle valve 62 provided on the downstream side from the intercooler 61 is an electronically controlled opening/closing valve whose opening degree is capable of stepless adjustment, and has a function to constrict the area of the channel of intake air under predetermined conditions, and thus adjust (reduce) the supplied amount of intake air.

Also, the engine 1 is provided with an exhaust gas recirculation path (EGR path) 8 that connects the intake system 6 and the exhaust system 7. The EGR path 8 decreases the combustion temperature by appropriately recirculating part of the exhaust to the intake system 6 and resupplying that exhaust to the combustion chamber 3, thus reducing the amount of NOx produced. Also, provided in the EGR path 8 are an EGR valve (exhaust recirculation ratio varying unit) 81 that by being opened/closed continuously under electronic control is capable of freely adjusting the amount of exhaust flow that flows through the EGR path 8, and an EGR cooler 82 for cooling exhaust that passes through (recirculates through) the EGR path 8.

- Turbocharger 5 -
Next is a description of the above turbocharger (variable capacity turbocharger) 5, and a variable nozzle vane mechanism (filling efficiency varying unit) 9 provided in the turbocharger 5.

Fig. 3 is a cross-sectional view of the turbocharger 5 along a center axis of the turbine shaft 52a, and Fig. 4 is a cross-sectional view that shows an enlarged view of the turbine wheel 52c and parts in the vicinity of that turbine wheel 52c. Fig. 5 is a front view of the variable nozzle vane mechanism 9 (viewing the variable nozzle vane mechanism 9 from the side of the compressor wheel 52b), and shows a state in which a large nozzle vane opening degree has been set. Fig. 6 is a rear view of the variable nozzle vane mechanism 9 (viewing the variable nozzle vane mechanism 9 from the opposite side as the compressor wheel 52b), and shows a state in which the large nozzle vane opening degree has been set.

The turbocharger 5 is configured as a variable capacity (variable nozzle type) turbocharger, and as shown in Fig. 3, is provided with a housing 51, the turbine shaft 52a rotatably housed in this housing 51, the compressor wheel 52b attached to one end (the right end in Fig. 3) of the turbine shaft 52a, and the turbine wheel 52c attached to the other end (the left end in Fig. 3) of the turbine shaft 52a. A turbine 52, which is a rotating body, is configured with the turbine shaft 52a, the compressor wheel 52b, and the turbine wheel 52c.

The housing 51 is configured with a compressor housing 51a, a center housing (bearing housing) 51b, and a turbine housing 51c combined as a single body. That is, the compressor housing 51a and the turbine 51c are attached to respective ends of the center housing 51b, which is in the middle.

The compressor housing 51a has a shape such that it is possible to take in air from the center portion (center axis portion) and release that air to the outside.

Also, the compressor wheel 52b housed in the compressor housing 51a is fixed to the turbine shaft 52a by a lock nut 52d, and rotates as a single body with the turbine shaft 52a. A plurality of compressor blades are provided in the compressor wheel 52b, and when the compressor wheel 52b rotates, air is accelerated and compressed by the compressor blades to the outside in the radial direction by centrifugal force. Therefore, when air is introduced to the center portion of the compressor housing 51a, the air is compressed by the compressor blades of the compressor wheel 52b that rotates, and this compressed air is discharged in the intake tube 64 towards the intake manifold 63.

A seal ring collar 52e is disposed adjacent to the compressor wheel 52b. The seal ring collar 52e has a shape that surrounds the turbine shaft 52a.

The center housing 51b is disposed in approximately the center portion in the center axis direction of the turbocharger 5. A thrust bearing 52f is provided in the center housing 51b. This thrust bearing 52f is a bearing for bearing the load of the turbine shaft 52a in the thrust direction, and is lubricated with oil or the like.

A floating bearing 52g for retaining rotation of the turbine shaft 52a is provided in the center housing 51b. This floating bearing 52g retains a load in the radial direction of the turbine shaft 52a. An oil film exists between the floating bearing 52g and the turbine shaft 52a, such that the floating bearing 52g does not directly contact the turbine shaft 52a. Further, an oil film also exists between the floating bearing 52g and the center housing 51b, such that the floating bearing 52g does not directly contact the center housing 51b. The floating bearing 52g is positioned by a retainer ring 52h.

Next is a description of the variable nozzle vane mechanism 9. This variable nozzle vane mechanism 9 is disposed in a link chamber 91 formed between the center housing 51b and the turbine housing 51c.

The variable nozzle vane mechanism 9 is provided with a unison ring 92 housed in the link chamber 91, a plurality of arms 93 that are positioned on the inner circumferential side of the unison ring 92, part of which engage with the unison ring 92 (see Fig. 5), a nozzle plate (NV plate) 94 disposed so as to contact the turbine housing 51c in the center axis direction of the turbocharger (see Fig. 4), a main arm 95 for driving the plurality of arms 93, and vane shafts 97 that are connected to the arms 93 and drive nozzle vanes 96. The vane shafts 97 are rotatably supported by the nozzle plate 94, and are coupled to each of the arms 93 and the nozzle vanes 96 such that they turn as a single body.

Also, in the present embodiment, the turbine housing 51c is configured by combining two members into a single body, specifically a main body portion 51c-a formed of cast metal and a plate portion 51c-b formed of plate metal (see Fig. 4), thus achieving reduced weight.

Also, a housing plate 51e is attached to the turbine housing 51c. The housing plate 51e is disposed at a position facing the nozzle plate 94, and a space for disposing the nozzle vanes 96 is formed between the housing plate 51e and the nozzle plate 94. That is, an exhaust gas flow path is formed between the housing plate 51e and the nozzle plate 94, and the nozzle vanes 96 are disposed in this flow path. Therefore, the nozzle plate 94 and the housing plate 51e are positioned on both sides in the direction of the turning axis of the nozzle vanes 96, and disposed facing the end faces of the nozzle vanes 96. It is preferable that a gap between the nozzle plate 94 and an end face of the nozzle vanes 96, and a gap between the housing plate 51e and an end face of the nozzle vanes 96 (these gaps referred to as a nozzle side clearance), are made as small as possible in a range that sliding resistance does not become large, such that exhaust gas only flows in the exhaust gas flow path formed between the nozzle vanes 96 (such that there is little leakage of exhaust gas from the nozzle side clearance).

The variable nozzle vane mechanism 9 is a mechanism for adjusting a turn angle (turning attitude) of the plurality (for example, 12) of nozzle vanes 96 disposed at equal intervals on the outer circumference side of the turbine blades. In the variable nozzle vane mechanism 9, by a drive link 95a connected to the main arm 95 being turned by a predetermined angle, this turning force is transmitted to the nozzle vanes 96 via the main arm 95, the unison ring 92, the arms 93, and the vane shafts 97, so that the nozzle vanes 96 turn in unison.

Specifically, the drive link 95a is capable of turning around a drive shaft 95b. The drive shaft 95b is linked to the drive link 95a and the main arm 95 such that they turn as a single body. Therefore, when the drive shaft 95b turns along with turning of the drive link 95a, this turning force is transmitted to the main arm 95. The end of the main arm 95 on the inner circumferential side is fixed to the drive shaft 95b, and the end on the outer circumferential side is engaged with the unison ring 92. Therefore, when the main arm 95 turns around the drive shaft 95b, this turning force is transmitted to the unison ring 92. The end of the arms 93 on the outer circumferential side fits together with the inner circumferential face of the unison ring 92, and when the unison ring 92 turns, this turning force is transmitted to the arms 93. Specifically, the unison ring 92 is disposed so as to be capable of sliding in the circumferential direction relative to the nozzle plate 94, and the ends of the main arm 95 and the arms 93 on the outer circumferential side are fitted together with each of a plurality of recessions 92a provided on the inner circumferential edge of the unison ring 92. The arms 93 are capable of turning around the vane shafts 97, and turning of the arms 93 is transmitted to the vane shafts 97. The vane shafts 97 are linked to the nozzle vanes 96, so the nozzle vanes 96 turn together with the vane shafts 97 and the arms 93.

A turbine housing vortex chamber is provided in the turbine housing 51c. Exhaust gas is supplied to the turbine housing vortex chamber, and the flow of this exhaust gas rotates the turbine wheel 52c. At this time, as described above, the turning position of the nozzle vanes 96 is adjusted, and by setting that turn angle, it is possible to adjust the flow amount and flow rate of exhaust from the turbine housing vortex chamber towards an exhaust turbine chamber. Thus, it is possible to adjust charging performance, and for example, by adjusting the turn position of the nozzle vanes 96 such that the flow path area (throat area) between the nozzle vanes 96 is reduced when engine revolutions are low, the flow rate of exhaust gas is increased, so it is possible to obtain high charging pressure from a low engine speed range.

Also, the drive link 95a of the variable nozzle vane mechanism 9 is connected to a motor rod 95c. The motor rod 95c is a bar-shaped member, and is connected to an unshown variable nozzle controller. The variable nozzle controller is connected as an actuator to a direct current motor (DC motor), and due to this direct current motor rotating, that rotational force is transmitted to the motor rod 95c via a gear mechanism, a worm mechanism, and so forth, and due to the drive link 95a turning along with this movement of the motor rod 95c, as described above, the nozzle vanes 96 turn.

As shown in Fig. 5, by pulling the motor rod 95c in the direction of arrow X in Fig. 5, the unison ring 92 turns in the direction of arrow X1 in Fig. 5, so as shown in Fig. 6, the nozzle vanes 96 turn in the counterclockwise direction in Fig. 6, and thus a large nozzle vane opening degree is set.

Figs. 7 and 8 show a state in which a small nozzle vane opening degree has been set, with Fig. 7 being a front view (corresponding to Fig. 5) of the variable nozzle vane mechanism 9, and Fig. 8 being a rear view (corresponding to Fig. 6) of the variable nozzle vane mechanism 9. As shown in Figs. 7 and 8, by pushing the motor rod 95c in the direction of arrow Y in Fig. 7, the unison ring 92 turns in the direction of arrow Y1 in Fig. 7, so as shown in Fig. 8, the nozzle vanes 96 turn in the clockwise direction in Fig. 8, and thus the small nozzle vane opening degree is set.

Pins 94a (see Fig. 5) are inserted into the nozzle plate 94, and rollers 94b are fitted to these pins 94a. The rollers 94b guide the inner circumferential face of the unison ring 92. Thus, the unison ring 92 can turn in a predetermined direction while held by the rollers 94b. Also, a spacer bolt 51d is attached to the turbine housing 51c (see Fig. 4). Further, inside of the center housing 51b, a coolant water path W is formed through which coolant water for cooling the turbocharger 5 flows.

- Sensors -
Various sensors are installed in respective parts of the engine 1, and these sensors output signals related to environmental conditions of the respective parts and the operating state of the engine 1.

For example, the above airflow meter 43 outputs a detection signal according to an intake air flow amount (intake air amount) on the upstream side of the throttle valve 62 within the intake system 6. An intake temperature sensor 49 is disposed in the intake manifold 63, and outputs a detection signal according to the temperature of intake air. An intake pressure sensor 48 is disposed in the intake manifold 63, and outputs a detection signal according to the intake air pressure. An A/F (air-fuel ratio) sensor 44 outputs a detection signal that continuously changes according to the oxygen concentration in exhaust on the downstream side of the maniverter 77 of the exhaust system 7. An exhaust temperature sensor 45 likewise outputs a detection signal according to the temperature of exhaust gas (exhaust temperature) on the downstream side of the maniverter 77 of the exhaust system 7. A rail pressure sensor 41 outputs a detection signal according to the pressure of fuel accumulated in the common rail 22. A throttle opening degree sensor 42 detects the opening degree of the throttle valve 62.

- ECU -
As shown in Fig. 9, the ECU 100 is provided with a CPU 101, a ROM 102, a RAM 103, a backup RAM 104, and the like. In the ROM 102, various control programs, maps that are referred to when executing those various control programs, and the like are stored. The CPU 101 executes various computational processes based on the various control programs and maps stored in the ROM 102. The RAM 103 is a memory that temporarily stores data resulting from computation with the CPU 101 or data that has been input from the respective sensors, and the backup RAM 104, for example, is a nonvolatile memory that stores that data or the like to be saved when the engine 1 is stopped.

The CPU 101, the ROM 102, the RAM 103, and the backup RAM 104 are connected to each other via a bus 107, and are connected to an input interface 105 and an output interface 106 via the bus 107.

The rail pressure sensor 41, the throttle opening degree sensor 42, the airflow meter 43, the A/F sensor 44, the exhaust temperature sensor 45, the intake pressure sensor 48, and the intake temperature sensor 49 are connected to the input interface 105. Further, a water temperature sensor 46 that outputs a detection signal according to the coolant water temperature of the engine 1, an accelerator opening degree sensor 47 that outputs a detection signal according to the amount that an accelerator pedal is depressed, a crank position sensor 40 that outputs a detection signal (pulse) each time that an output shaft (crankshaft) of the engine 1 rotates a fixed angle, and the like are connected to the input interface 105. On the other hand, the aforementioned injectors 23, fuel addition valve 26, throttle valve 62, EGR valve 81, variable nozzle vane mechanism 9 (above variable nozzle controller) and the like are connected to the output interface 106.

The ECU 100 executes various control of the engine 1 based on the output of the various sensors described above. Furthermore, the ECU 100 controls pilot injection, pre-injection, main injection, after-injection, and post-injection as control of fuel injection of the injectors 23.

The fuel injection pressure when executing these modes of fuel injection is determined by the internal pressure of the common rail 22. As the common rail internal pressure, ordinarily, the target value of the fuel pressure supplied from the common rail 22 to the injectors 23, i.e., the target rail pressure, is set to increase as the engine load increases, and as the engine revolutions increase. That is, when the engine load is high, a large amount of air is sucked into the combustion chamber 3, so the injectors 23 are required to inject a large amount of fuel into the combustion chamber 3, and therefore it is necessary to set a high injection pressure from the injectors 23. Also, when the engine revolutions are high, the period during which injection is possible is short, so it is necessary to inject a large amount of fuel per unit time, and therefore it is necessary to set a high injection pressure from the injectors 23. In this way, the target rail pressure is ordinarily set based on the engine load and the engine revolutions.

The optimum values of fuel injection parameters for fuel injection such as the above pilot injection, main injection, and the like differ according to temperature conditions of the engine 1, intake air, and the like.

For example, the ECU 100 adjusts the amount of fuel discharged by the supply pump 21 such that the common rail pressure becomes the same as the target rail pressure set based on the engine operating state, i.e., such that the fuel injection pressure matches the target injection pressure. Also, the ECU 100 determines the fuel injection amount and the form of fuel injection based on the engine operating state. Specifically, the ECU 100 calculates an engine rotational speed based on the value detected by the crank position sensor 40 and obtains an amount of accelerator pedal depression (accelerator opening degree) based on the value detected by the accelerator opening degree sensor 47, and determines the total fuel injection amount (total of the injection amount in pre-injection and the injection amount in main injection, described below) based on the engine rotational speed and the accelerator opening degree.

- Setting of Target Fuel Pressure -
Next is a description of a technical idea when setting target fuel pressure in the present embodiment.

In the diesel engine 1, it is important to achieve the demands of improving exhaust emissions by decreasing the amount of NOx produced, reducing combustion noise during a combustion stroke, and insuring adequate engine torque. The inventors of the present invention, noting that as a method of achieving these demands together, it is effective to appropriately control the state of change of the heat production ratio in the cylinder during a combustion stroke (state of change expressed by a heat production ratio waveform), established the method of setting a target fuel pressure described below as a method of controlling the state of change of the heat production ratio.

The solid line in Fig. 10 indicates an ideal heat production ratio waveform for combustion of the fuel that has been injected in main injection, with the crank angle shown on the horizontal axis and the heat production ratio shown on the vertical axis. TDC in Fig. 10 indicates the crank angle position that corresponds to the compression top dead center of the piston 13. With this heat production ratio waveform, for example, combustion of the fuel that has been injected in main injection is started from the compression top dead center (TDC) of the piston 13, the heat production ratio reaches a maximum value (peak value) at a predetermined piston position after the compression top dead center (for example, at the time of 10 degrees after the compression top dead center (ATDC 10 degrees), and combustion of the fuel that has been injected in main injection ends at a predetermined piston position after the compression top dead center (for example, at the time of 25 degrees after the compression top dead center (ATDC 25 degrees). By causing combustion of the air-fuel mixture to be performed in this sort of heat production ratio change state, for example, combustion is completed for 50% of the air-fuel mixture within the cylinder at the time of 10 degrees after the compression top dead center (ATDC 10 degrees). That is, in an expansion stroke, about 50% of the total heat production amount is produced by the time of ATDC 10 degrees, and thus it is possible to cause the engine 1 to operate at high heat efficiency.

The waveform indicated by the single-dotted line in Fig. 10 is a heat production ratio waveform for combustion of the fuel that has been injected in pre-injection. With this waveform, diffusion combustion is realized in which the fuel that has been injected in main injection is stable. For example, a heat amount of 10J is produced by combustion of the fuel that has been injected in this pre-injection. This heat amount is not limited to the value in this example. For example, this heat amount is appropriately set according to the above total fuel injection amount. Also, although not shown, pilot injection is also performed prior to pre-injection, and thus the temperature within the cylinder is adequately increased, so that ignition of the fuel injected in main injection is well-insured.

Also, the waveform indicated by a dashed double-dotted line H1 in Fig. 10 is a heat production rate waveform in the case where the fuel injection pressure has been set higher than the appropriate value, and as shown by this waveform, the combustion speed and peak value are both too high, and there is concern regarding an increase in combustion noise and the NOx production amount. On the other hand, the waveform indicated by a dashed double-dotted line H2 in Fig. 10 is a heat production rate waveform in the case where the fuel injection pressure has been set lower than the appropriate value, and as shown by this waveform, the combustion speed is low and the timing at which the peak appears is shifted a large amount toward the side of a later angle, and so there is concern that it will be impossible to ensure sufficient engine throttle.

As described above, the technique for setting the target fuel pressure according to the present embodiment is based on the technical idea that combustion efficiency is improved by optimizing the changing state of the heat production rate (optimizing the heat production rate waveform).

- Filling Efficiency Setting Method -
One feature of the present embodiment is the method whereby the opening degree of the nozzle vanes 96 in the above turbocharger 5 is determined. Specifically, for the EGR ratio that is set by the opening degree of the EGR valve 81, an opening degree of the nozzle vanes 96 is obtained, in advance, such that an intake filling efficiency corresponding thereto is obtained. More specifically, the relationship of the EGR ratio and the intake filling efficiency is converted to a map and stored in the ROM (storage unit) 102. That is, an intake filling efficiency to be used as a target, corresponding to the EGR ratio, is read from the map (below, referred to as a filling efficiency setting map), and the variable nozzle vane mechanism 9 is controlled (filling efficiency is controlled) so as to obtain that filling efficiency.

Fig. 11 shows an example of the relationship between the EGR ratio that is set by the opening degree of the EGR valve 81, the intake filling efficiency that is set by the opening degree of the nozzle vanes 96, and the engine torque that is produced (shows EGR ratio contour lines (below, also referred to as equal EGR ratio lines). In this way, even for identical EGR ratios, if the intake filling efficiency is different (if the opening degree of the nozzle vanes 96 is different), the obtained engine torque also is different. In the filling efficiency setting map, an intake filling efficiency corresponding to each EGR ratio is stored such that the maximum engine torque on each curve is obtained. For example, when the EGR ratio is 0% (EGR valve 81 completely closed), Pa in Fig. 11 is obtained as the filling efficiency, when the EGR ratio is 5%, Pb in Fig. 11 is obtained as the filling efficiency, when the EGR ratio is 10%, Pc in Fig. 11 is obtained as the filling efficiency, when the EGR ratio is 15%, Pd in Fig. 11 is obtained as the filling efficiency, and when the EGR ratio is 20%, Pe in Fig. 11 is obtained as the filling efficiency. When the EGR ratio is an EGR ratio that is not stored in this map, an interpolation calculation by the CPU 101 is used to calculate a filling efficiency for that EGR ratio such that maximum engine torque is obtained. Thus, the relationship of the EGR ratio and the intake filling efficiency for obtaining maximum engine torque is stored in advance in the filling efficiency setting map.

Next is a specific description of the method for acquiring the intake filling efficiency at which maximum engine torque is obtained corresponding to each EGR ratio as described above.

Fig. 12 shows the change in engine torque when changing the opening degree of the nozzle vanes 96, in a state with the fuel injection amount into the cylinder, the fuel injection pattern (such as the timing or interval of injection in pre-injection and main injection), and the fuel injection pressure approximately fixed, in a state in which the EGR ratio is 0% (the EGR valve 81 is fully closed) and the throttle valve 62 is fully open. In Fig. 12, the horizontal axis indicates the filling efficiency determined by the opening degree of the nozzle vanes 96, and the filling efficiency increases as smaller opening degrees of the nozzle vanes 96 are set. The vertical axis in Fig. 12 indicates the engine torque.

Here, as a specific example of a case where the fuel injection amount into the cylinder, the fuel injection pattern, and the fuel injection pressure are approximately fixed, with respect to the fuel injection amount and the fuel injection pattern, the injection timing and injection amount in pre-injection and main injection are fixed such that, for example, the timing at which the heat production ratio from combustion of fuel injected in pre-injection becomes maximum, the timing at which combustion of fuel injected in main injection is started, and the timing at which the piston 13 that moves back and forth in the cylinder reaches the compression top dead center approximately match each other. As for the fuel injection pressure, for example, an equal fuel injection pressure region (equal fuel injection pressure line) is allocated to an equal output region (equal power line) of the output (power) obtained from the engine revolutions and the engine torque, and the fuel injection pressure is fixed to a fuel injection pressure set corresponding to output of the engine 1.

As shown in Fig. 12, from a state in which the opening degree of the nozzle vanes 96 is large (the above throttle area is large: low filling efficiency), when that opening degree is successively reduced (when the filling efficiency is successively increased), the amount of conversion of exhaust gas from heat energy to rotation energy in the turbocharger 5 is successively greater, and this is accompanied by an increase in engine torque (see filling efficiency range I in Fig. 12). However, when the opening degree of the nozzle vanes 96 has been reduced in this way, exhaust energy increases, i.e., exhaust escape worsens, and this becomes a major factor in worsening of the charging efficiency. As for the balance of the amount of rotation energy increase (amount of energy that contributes to efficiency improvement) due to reducing the opening degree of the nozzle vanes 96 and the amount of exhaust energy increase (amount of energy leading to efficiency worsening), when the amount of increase in exhaust energy is greater, the charging efficiency decreases (see filling efficiency range II in Fig. 12). Accordingly, the point where the amount of rotation energy increase and the amount of exhaust energy increase are balanced (point at border of the filling efficiency ranges I and II) is obtained as the point of maximum charging efficiency. That is, the intake filling efficiency at point A in Fig. 12 is acquired as the intake filling efficiency where maximum engine torque is obtained when the EGR ratio is 0%.

On the other hand, when the EGR ratio is other than 0%, the method for acquiring the maximum engine torque is as follows.

First, a state is established in which the opening degree of the nozzle vanes 96 is fixed at some predetermined value, and in this state the EGR ratio is changed. For example, while increasing the EGR ratio in steps of 5%, 10%, 15%, 20%, the engine torque at each EGR ratio is obtained. Point A1 in Fig. 13 indicates the engine torque in a case where the EGR ratio is set to 0% when the opening degree of the nozzle vanes 96 has been set to 80% (VN closing degree 20%). Point A2 indicates the engine torque in a case where the EGR ratio has been set to 5%, point A3 indicates the engine torque in a case where the EGR ratio has been set to 10%, point A4 indicates the engine torque in a case where the EGR ratio has been set to 15%, and point A5 indicates the engine torque in a case where the EGR ratio has been set to 20%. Also, curve A in Fig. 13 is a curve in which each of the above points A1, A2, A3, A4, and A5 are joined, that is, an equal VN opening degree line at a VN closing degree 20%.

Afterward, the opening degree of the nozzle vanes 96 is changed (for example, changing in the closing direction) by a predetermined opening degree (for example, 20%) from the above fixed value, and in a state with this new opening degree fixed, the EGR ratio is changed. In this case, same as above, while increasing the EGR ratio in steps of 5%, 10%, 15%, 20%, the engine torque at each EGR ratio is obtained. Point B1 in Fig. 13 indicates the engine torque in a case where the EGR ratio is set to 0% for the above fixed (fixed as a new fixed value) opening degree (VN closing degree 40%) of the nozzle vanes 96. Point B2 indicates the engine torque in a case where the EGR ratio has been set to 5%, point B3 indicates the engine torque in a case where the EGR ratio has been set to 10%, point B4 indicates the engine torque in a case where the EGR ratio has been set to 15%, and point B5 indicates the engine torque in a case where the EGR ratio has been set to 20%. Also, curve B in Fig. 13 is a curve in which each of the above points B1, B2, B3, B4 and B5are joined, that is, an equal VN opening degree line at a VN closing degree 40%.

Afterward, the opening degree of the nozzle vanes 96 is again changed from the above fixed value by a predetermined opening degree (for example, 20%), and in a state in which this new opening degree has been fixed, the EGR ratio is changed. In this case as well, same as above, respective engine torques are obtained while increasing the EGR ratio in steps of 5%, 10%, 15%, 20%. Point C1 in Fig. 13 indicates the engine torque in a case where the EGR ratio is set to 0% for the above fixed (fixed as a new fixed value) opening degree (VN closing degree 60%) of the nozzle vanes 96. Point C2 indicates the engine torque in a case where the EGR ratio has been set to 5%, point C3 indicates the engine torque in a case where the EGR ratio has been set to 10%, point C4 indicates the engine torque in a case where the EGR ratio has been set to 15%, and point C5 indicates the engine torque in a case where the EGR ratio has been set to 20%. Also, curve C in Fig. 13 is a curve in which each of the above points C1, C2, C3, C4 and C5 are joined, that is, an equal VN opening degree line at a VN closing degree 60%.

Below, respective engine torques are likewise obtained while changing the EGR ratio with respect to each of a case where the VN closing degree has been set to 80%, and a case where the VN closing degree has been set to 100%.

Point D1 in Fig. 13 indicates the engine torque in a case where the EGR ratio is set to 0% when the VN closing degree has been set to 80%. Point D2 indicates the engine torque in a case where the EGR ratio has been set to 5%, point D3 indicates the engine torque in a case where the EGR ratio has been set to 10%, point D4 indicates the engine torque in a case where the EGR ratio has been set to 15%, and point D5 indicates the engine torque in a case where the EGR ratio has been set to 20%. Also, curve D in Fig. 13 is a curve in which each of the above points D1, D2, D3, D4 and D5 are joined, that is, an equal VN opening degree line at a VN closing degree 80%.

Point E1 in Fig. 13 indicates the engine torque in a case where the EGR ratio is set to 0% when the VN closing degree has been set to 100%. Point E2 indicates the engine torque in a case where the EGR ratio has been set to 5%, point E3 indicates the engine torque in a case where the EGR ratio has been set to 10%, point E4 indicates the engine torque in a case where the EGR ratio has been set to 15%, and point E5 indicates the engine torque in a case where the EGR ratio has been set to 20%. Also, curve E in Fig. 13 is a curve in which each of the above points E1, E2, E3, E4 and E5 are joined, that is, an equal VN opening degree line at a VN closing degree 100%.

After obtaining points in this way, equal EGR ratio lines (equal NOx lines) are obtained by connecting points where the EGR ratio is the same. Specifically, an equal EGR ratio line (the curve shown by a fine solid line in Fig. 13) where the EGR ratio is 5% is obtained by smoothly connecting the above-described points A2, B2, C2, D2, and E2. An equal EGR ratio line (the curve shown by a broken line in Fig. 13) where the EGR ratio is 10% is obtained by smoothly connecting the above-described points A3, B3, C3, D3, and E3. An equal EGR ratio line (the curve shown by a single-dotted chained line in Fig. 13) where the EGR ratio is 15% is obtained by smoothly connecting the above-described points A4, B4, C4, D4, and E4. An equal EGR ratio line (the curve shown by a double-dotted chained line in Fig. 13) where the EGR ratio is 20% is obtained by smoothly connecting the above-described points A5, B5, C5, D5, and E5. The curve shown by a thick solid line in Fig. 13 (the curve connecting points A1, B1, C1, D1, and E1) is an equal EGR ratio line where the EGR ratio is 0%.

In this way it is possible to acquire the line map (line map showing the relationship of EGR ratio, intake filling efficiency, and engine torque: equal NOx lines) shown in Fig. 11. By converting to a map the intake filling efficiency (filling efficiency Pa when the EGR ratio is 0%, filling efficiency Pb when the EGR ratio is 5%, filling efficiency Pc when the EGR ratio is 10%, filling efficiency Pd when the EGR ratio is 15%, and filling efficiency Pe when the EGR ratio is 20%) where the maximum engine torque is obtained at each EGR ratio (each equal NOx line), the above filling efficiency setting map can be obtained from which it is possible to obtain an optimal intake filling efficiency for each of the above EGR ratios.

The following can be performed as the method for setting the opening degree of the nozzle vanes 96 and the opening degree of the EGR valve 81, which are the actual control subjects.

First, as the method for setting the opening degree of the nozzle vanes 96, an intake filling efficiency corresponding to the EGR ratio determined by the opening degree of the EGR valve 81 adjusted in order to reduce the NOx amount to an allowable range is read from the above filling efficiency setting map. Control of the variable nozzle vane mechanism 9 is performed in order to set the opening degree of the nozzle vanes 96 such that this filling efficiency can be obtained (control operation of filling efficiency varying unit by filling efficiency control unit). Then, adapting the relationship of the filling efficiency and the engine torque obtained from the above filling efficiency setting map to Fig. 13, by performing interpolation calculation or the like on each of the equal VN opening degree lines (above curves a, b, g, d, and e) in Fig. 13, the opening degree of the nozzle vanes 96 for obtaining the above filling efficiency is calculated. That is, each of the above equal VN opening degree lines are also stored in the map, and the VN opening degree for obtaining the target filling efficiency (the filling efficiency that has been obtained from Fig. 13) is derived from these stored equal VN opening degree lines. In this way, the above filling efficiency setting map and equal VN opening degree line map are stored in the ROM (storage unit) 102. For example, when point Z in Fig. 13 has been given as an adaptation control point, by performing interpolation calculation between the equal VN opening degree lines b and g, a VN closing degree of 55%, for example, is set as the opening degree of the nozzle vanes 96.

Next is a description of the specific operation of setting the opening degree of the EGR valve 81 in order to obtain the EGR ratio in this case. Fig. 16 shows equal EGR valve opening degree lines, in addition to the above equal EGR ratio lines and equal VN opening degree lines a, b, g, d, and e. Adapting the EGR ratio to be controlled to Fig. 16, by performing interpolation calculation or the like on each of the equal EGR valve opening degree lines in Fig. 16, the opening degree of the EGR valve 81 for obtaining the above EGR ratio is calculated. For example, when point Z in Fig. 16 has been given as an adaptation control point, by performing interpolation calculation between the equal EGR valve opening degree line where the EGR valve opening degree is 20% and the equal EGR valve opening degree line where the EGR valve opening degree is 40%, an opening degree of 22%, for example, is set as the opening degree of the EGR valve 81.

Due to the opening degree of the nozzle vanes 96 and the opening degree of the EGR valve 81 being set in this way, in any engine operating state, it is possible to optimize the relationship of the EGR ratio and the intake filling efficiency, so the intake charging efficiency can be maximized, and thus the engine 1 can be operated at high efficiency. Therefore, it is possible to achieve both higher engine output and a large improvement in the rate of fuel consumption.

Also, as described above, in the filling efficiency setting map in the present embodiment, there is a unique relationship between EGR ratio, engine torque, and nozzle vane opening degree (intake filling efficiency). Thus, it is possible to maintain a high charging efficiency throughout all engine operating ranges. Also, by causing the map to have a unique relationship between engine revolutions, engine torque, a nozzle vane opening degree (intake filling efficiency), as in this filling efficiency setting map, a systematic intake control method shared by various engines is constructed, so it is possible to simplify creation of a filling efficiency setting map for setting an intake amount that is appropriate for the operating state of the engine 1.

- Filling Efficiency Automatic Adaptation Apparatus -
Next is a description of a filling efficiency automatic adaptation apparatus (automatic adaptation tool) used for acquiring an optimal value (adapted value) of the opening degree of the nozzle vanes 96 as described above. Specifically, the above filling efficiency setting map is created from adapted values of each engine operating state that have been acquired with this filling efficiency automatic adaptation apparatus.

Ordinarily, in control of an automobile engine, various control parameters such as the fuel injection timing are determined according to the operating state of the engine, such as the engine speed and the engine load. Respective control parameters in respective operating states are adapted in advance such that various engine characteristics like exhaust emissions characteristics and fuel consumption characteristics satisfy demands.

This sort of control parameter adaptation, conventionally, is performed by repeated trial and error on an engine bench. That is, the output shaft of a vehicle-mounted engine and a dynamo meter are linked with a rotating drive shaft, and by absorbing the load torque of the vehicle-mounted engine as a test torque with the dynamo meter, a state in which the vehicle-mounted engine is operated while mounted in a vehicle is virtually created. Various engine characteristic values such as the amount of nitrogen oxide exhaust, the amount of consumed fuel, and the like are measured while adjusting control parameters in various operating states, and optimal values of the control parameters are acquired as adapted values. For adaptation of the control parameters in this way, trial and error as well as an accompanying great deal of time are necessary.

Such circumstances are the same when determining the intake filling efficiency. That is, also when determining the opening degree of the nozzle vanes 96, conventionally, trial and error as well as an accompanying great deal of time are necessary. The filling efficiency automatic adaptation apparatus in the present embodiment automatically determines this filling efficiency. This is specifically described below.

Fig. 14 shows a system configuration for performing the automatic filling efficiency adaptation. As shown in Fig. 14, a state in which the engine 1 is virtually mounted in a vehicle is produced by a dynamo meter 110 absorbing output torque of the engine 1. Also, a measurement apparatus 120 measures exhaust gas characteristics and the like of the engine 1, and measures rotational velocity of the crank shaft of the engine 1. Further, an automatic adaptation apparatus 130 configured using an adaptation computer has a function of operating the dynamo meter 110, and also a function of appropriately setting the operation amount of various actuators of the above supply pump 21, injectors 23, variable nozzle vane mechanism 9, and so forth, and using that operating amount to operate the actuators via the above ECU 100. With the automatic adaptation apparatus 130, based on the results of measurement with the measurement apparatus 120, the above adaptations, including filling efficiency, are performed.

The operation for performing the above automatic adaptation of filling efficiency is performed as described below. Fig. 15 is a flowchart that shows the procedure for performing this automatic adaptation of filling efficiency. The routine in Fig. 15 is executed for each type of engine, thus acquiring an optimal value (adapted value) of the relationship of the EGR ratio and the intake filling efficiency for that engine, and this value is contributed to creation of a filling efficiency setting map appropriate for that engine.

In the automatic adaptation operation described below, the minimum value (initial value) of the EGR ratio is 5%, the EGR ratio is changed in steps of 5%, and the opening degree of the nozzle vanes 96 is changed in steps of 20%. Also, when starting the automatic adaptation operation, the value of the below variable i is '1'. The relationship of this variable i and the set opening degree of the nozzle vanes 96 is shown in the table in Fig. 15. That is, the automatic adaptation operation is performed while reducing the set opening degree of the nozzle vanes 96 in six steps of a predetermined opening degree (20%). The amount of change of the set opening degree and the number of steps are not limited to those in this example. Also, although not a limitation, as described above, the automatic adaptation operation may be performed while changing the EGR ratio in steps, with 0% as the minimum value of the EGR ratio, or while increasing the set opening degree of the nozzle vanes 96 in steps of a predetermined opening degree.

When the filling efficiency automatic adaptation operation is started, first, in Step ST1, the opening degree (set opening degree i) of the nozzle vanes 96 is set. When starting this automatic adaptation, the opening degree (VNi=VN1) of the nozzle vanes 96 is set to the maximum opening degree (100%). Then, the routine moves to Step ST2, in which the opening degree of the EGR valve 81 is operated. When starting this operation, the opening degree of the EGR valve 81 is set so as to produce a target EGR ratio of 5% as an initial value. Then, in Step ST3, a determination is made of whether or not the opening degree of the EGR valve 81 has been set to an opening degree at which the target EGR ratio (REGTRT) is obtained, and operation of the opening degree of the EGR valve 81 is continued until the target EGR ratio is obtained.

Then, when the opening degree of the EGR valve 81 is set to an opening degree at which the target EGR ratio (REGTRT) is obtained, so the actual EGR ratio (REGRi) becomes equal to the target EGR ratio (REGTRT) and thus a Yes determination is made in Step ST3, the routine moves to Step ST4, and the engine torque at the present time is measured (DATAi (=DATA1) is measured).

Then, in Step ST5, a determination is made of whether or not the present target EGR ratio has reached the maximum EGR ratio (maximum EGR ratio among the EGR ratios that are changed in the automatic adaptation operation: for example EGR ratio 20%). The EGR ratio is 5% when starting operation of the opening degree of the EGR valve 81, so the maximum EGR ratio has not been reached, and so a No determination is made in Step ST5 and the routine moves to Step ST6. In Step ST6, 5% is added to the present target EGR ratio, the value of the target EGR ratio is updated to the new target EGR ratio (REGRT), and the routine returns to above Step ST2, in which the opening degree of the EGR valve 81 is operated such that the updated target EGR ratio is obtained. Then, in Step ST3, when the opening degree of the EGR valve 81 is set to an opening degree such that the target EGR ratio is obtained, in Step ST4, the engine torque at the present time is measured (DATAi is measured).

In this way, the engine torque is measured while increasing the target EGR ratio in 5% steps in a state in which the opening degree of the nozzle vanes 96 is fixed, and the measured data is recorded.

When the target EGR ratio has reached the maximum EGR ratio, and so a Yes determination is made in Step ST5, the target EGR ratio is returned to 5% (Step ST7), then the routine moves to Step ST8 and an examination end determination (automatic adaptation operation end determination) is performed. In this examination end determination, a determination is made of whether or not the measurement of engine torque (measurement of DATAi) when the opening degree of the nozzle vanes 96 has been set to a predetermined opening degree (for example, opening degree 20%) is completed. In this routine, the maximum value of the variable i is '6', so in Step ST8, a determination is made of whether or not the variable i has exceeded '6' (corresponding to a 20% opening degree of the nozzle vanes 96).

When the variable i has not exceeded '6', the routine moves to Step ST9, in which '1' is added to the variable i, and then the routine returns to Step ST1. Here, in Step ST1, the set opening degree of the nozzle vanes 96 is reduced 20%, and in a state in which the opening degree of the nozzle vanes 96 has been fixed, same as above, the engine torque is measured (DATAi is measured) while changing the EGR ratio.

When the variable i exceeds '6', and so a Yes determination has been made in Step ST8, the routine moves to Step ST10, and as shown in Fig. 11, equal EGR ratio lines (equal NOx lines: EGR ratio contour lines) are created by joining points where the EGR ratio is the same. In Fig. 11, equal EGR ratio lines where the EGR ratio is 0%, 5%, 10%, and 20% are shown, but in the automatic adaptation operation in the flowchart described above, equal EGR ratio lines where the EGR ratio is 5%, 10%, 15%, and 20% are created.

Thus, an intake filling efficiency that obtains maximum engine torque is obtained for each of the equal EGR ratio lines, and by converting this to a map, the above filling efficiency setting map in which it is possible to obtain the optimal opening degree of the nozzle vanes 96 for each of the EGR ratios is obtained.

The above is a filling efficiency automatic adaptation operation for creating a filling efficiency setting map.

In this way, with the present embodiment, it is possible to automatically adapt to the filling efficiency (opening degree of the nozzle vanes 96) where the charging efficiency becomes maximum, eliminating the need for acquiring an adapted value in trial and error, and the need for a great deal of time to acquire that adapted value, so it is possible to achieve increased efficiency of the adaptation operation.

- Other Embodiments -
In the embodiment described above, a case was described in which the present invention is applied to an in-line four-cylinder diesel engine mounted in an automobile. The present invention is not limited to use in an automobile, and is applicable also to engines used in other applications. Also, there is no particular limitation with respect to the number of cylinders or the engine format (classified as an in-line engine, V-type engine, and so forth). Furthermore, the present invention is also applicable to a gasoline engine.

Also, in the above embodiment, the maniverter 77 is provided with the NSR catalyst 75 and the DPNR catalyst 76, but a maniverter provided with the NSR catalyst 75 and a DPF (Diesel Particulate Filter) may also be used.

Also, in the above embodiment, a filling efficiency setting map is created using adapted values that have been acquired with the filling efficiency automatic adaptation apparatus 130, and from this filling efficiency setting map, an intake filling efficiency appropriate for the present engine operating state is read to set the opening degree of the nozzle vanes 96. The present invention is not limited thereto; a scheme may also be adopted in which a filling efficiency setting map is created using adapted values for each of various engine operating states through experimentation and simulation, and the opening degree of the nozzle vanes 96 is set using this filling efficiency setting map.

Further, the automatic adaptation apparatus 130 according to the present invention is not limited to an automatic adaptation apparatus used as an automatic adaptation tool that acquires filling efficiency adapted values; the automatic adaptation apparatus can also be used as a simulation/forecasting tool for simulating engine operating states.

The present invention may be embodied in various other forms without departing from the spirit or essential characteristics thereof. The embodiments disclosed in this application are to be considered in all respects as illustrative and not limiting. The scope of the invention is indicated by the appended claims rather than by the foregoing description, and all modifications or changes that come within the meaning and range of equivalency of the claims are intended to be embraced therein.

This application claims priority on Japanese Patent Application No. 2008-151230 filed in Japan on June 10, 2008, the entire contents of which are herein incorporated by reference. Furthermore, the entire contents of references cited in the present description are herein specifically incorporated by reference.

1 Engine (internal combustion engine)
5 Turbocharger (supercharger)
52c Turbine wheel
6 Intake system
81 EGR valve (exhaust gas recirculation ratio varying unit)
9 Variable nozzle vane mechanism (filling efficiency varying unit)
96 Nozzle vane
102 ROM (storage unit)
130 Automatic adaptation apparatus

Claims

An intake control apparatus of an internal combustion engine provided with a filling efficiency varying unit that allows varying of a filling efficiency of intake gas that is supplied into a cylinder of the internal combustion engine; and an exhaust recirculation ratio varying unit that recirculates exhaust of the internal combustion engine to an intake system and allows varying of that recirculation ratio, the intake control apparatus comprising:
a storage unit that respectively stores, for each of the exhaust recirculation ratios varied by the exhaust recirculation ratio varying unit, as an adapted value, a control value of the filling efficiency varying unit at which the torque of the internal combustion engine becomes approximately maximum; and
a filling efficiency control unit that, during operation of the internal combustion engine, reads from the storage unit a control value as the adapted value of the filling efficiency varying unit that corresponds to the exhaust recirculation ratio that has been set by the exhaust recirculation ratio varying unit, and controls the filling efficiency varying unit based on that control value.
The intake control apparatus of an internal combustion engine according to claim 1, wherein:
the filling efficiency varying unit is provided in a supercharger, and changes a charging pressure by changing a flow path area of gas that flows towards a turbine wheel by changing a nozzle vane opening degree that can be driven open/closed with a variable nozzle vane mechanism, thus changing the intake filling efficiency; and
the filling efficiency control unit, during operation of the internal combustion engine, controls the variable nozzle vane mechanism in order to set the nozzle vane opening degree, based on the control value used as the adapted value that corresponds to the exhaust recirculation ratio.
The intake control apparatus of an internal combustion engine according to claim 1 or 2, wherein:
as for each control value used as an adapted value of the filling efficiency varying unit that is stored in the storage unit, an operation in which, in a state in which the control value of the filling efficiency varying unit has been fixed, the torque of the internal combustion engine is measured while the exhaust recirculation ratio is changed by the exhaust recirculation ratio varying unit is executed for a plurality of control values of the filling efficiency varying unit to obtain an intake filling efficiency at which approximately maximum torque is obtained at the same exhaust recirculation ratio, and each control value of the filling efficiency varying unit for obtaining that filling efficiency is stored as an adapted value that corresponds to that exhaust recirculation ratio.
An automatic adaptation apparatus of an internal combustion engine provided with a filling efficiency varying unit that allows varying of a filling efficiency of intake gas that is supplied into a cylinder, and an exhaust recirculation ratio varying unit that recirculates exhaust to an intake system and allows varying of that recirculation ratio, the automatic adaptation apparatus being for obtaining, for each exhaust recirculation ratio varied by the exhaust recirculation ratio varying unit, as a control value of the filling efficiency varying unit, an adapted value where the torque of the internal combustion engine becomes approximately maximum;
the automatic adaptation apparatus, in a state in which the control value of the filling efficiency varying unit has been fixed, executing an operation of measuring the torque of the internal combustion engine while the exhaust recirculation ratio is changed by the exhaust recirculation ratio varying unit, for a plurality of control values of the filling efficiency varying unit, to obtain an intake filling efficiency at which approximately maximum torque is obtained at the same exhaust recirculation ratio, thus automatically acquiring a control value of the filling efficiency varying unit for obtaining that filling efficiency as an adapted value that corresponds to that exhaust recirculation ratio.
An intake control apparatus of an internal combustion engine provided with a filling efficiency varying unit that allows varying of a filling efficiency of intake gas that is supplied into a cylinder of the internal combustion engine; and an exhaust recirculation ratio varying unit that recirculates exhaust of the internal combustion engine to an intake system and allows varying of that recirculation ratio, the intake control apparatus comprising:
a storage unit that stores each adapted value that has been obtained by an automatic adaptation apparatus that, in a state in which the control value of the filling efficiency varying unit has been fixed, executes an operation of measuring the torque of the internal combustion engine while the exhaust recirculation ratio is changed by the exhaust recirculation ratio varying unit, for a plurality of control values of the filling efficiency varying unit, to obtain an intake filling efficiency at which approximately maximum torque is obtained at the same exhaust recirculation ratio, thus automatically acquiring a control value of the filling efficiency varying unit for obtaining that filling efficiency as an adapted value that corresponds to that exhaust recirculation ratio; and
a filling efficiency control unit that, during operation of the internal combustion engine, reads from the storage unit an adapted value of the filling efficiency varying unit that corresponds to the exhaust recirculation ratio that has been set by the exhaust recirculation ratio varying unit according to a target NOx amount, and controls the filling efficiency varying unit based on that adapted value.