JP4957651B2 - Intake control device for internal combustion engine - Google Patents

Description

  The present invention relates to an intake control device for an internal combustion engine represented by a vehicle diesel engine. In particular, the present invention relates to a measure for optimizing the charging efficiency in a device provided with means for changing the charging efficiency of intake air into a cylinder.

  As is well known in the art, in a diesel engine (hereinafter sometimes simply referred to as an engine) used as an automobile engine, fuel injection is performed according to engine speed, accelerator operation amount, cooling water temperature, intake air temperature, and the like. Fuel injection control is performed to adjust the fuel injection timing and fuel injection amount from a valve (hereinafter also referred to as an injector).

  Further, as a technique for solving the shortage of engine driving force, the following Patent Document 1 proposes correcting the target engine speed. Specifically, the technique disclosed in Patent Document 1 is based on the maximum amount of fuel depending on the intake air amount and the engine speed when a driving force shortage occurs due to the supercharging delay of the supercharger. Set the injection amount. Further, a torque that can be generated is calculated based on the maximum fuel injection amount. Then, the fuel pressure increase correction is performed so that the maximum injection amount is obtained.

In recent years, as a kind of turbocharger applied to a diesel engine or the like, for example, as disclosed in Patent Document 2 below, a variable displacement turbocharger having a variable capacity turbine side is known. In this type of turbocharger, a nozzle vane (also referred to as a movable vane) is provided in the exhaust gas flow path of the turbine housing so that the flow area of the exhaust gas flow path is variable. And, for example, by rotating the nozzle vane when the engine is running at a low speed to reduce the flow area (throat area), the flow rate of the exhaust gas is increased, thereby obtaining a high boost pressure from the engine low speed range. Can be done. Further, Patent Document 2 discloses that a target boost pressure is set according to the steady operation and transient operation of the engine.
JP 2001-73823 A JP 2001-82158 A

  Conventional diesel engines may not be able to respond quickly to the driver's acceleration request due to vehicle running resistance or the like. This will be specifically described below.

  FIG. 17 is a diagram illustrating an engine operating state in which the horizontal axis represents the engine speed and the vertical axis represents the engine torque. Tmax in FIG. 17 indicates the maximum torque line. That is, the engine uses the inside of this maximum torque line as the operable region.

  Consider the case of traveling on an uphill road in a state where the engine speed is relatively low (for example, 1000 rpm). When an acceleration request is generated from the driver and the amount of depression of the accelerator pedal increases, the fuel pressure increases accordingly, and the engine torque also increases. However, when the slope of the uphill road is relatively large, the engine speed does not increase in a situation where the running resistance and engine torque on the uphill road are balanced, and as a result, the current transmission gear stage cannot be accelerated. It will be. That is, in order for the vehicle to accelerate, the engine torque needs to be higher than the running resistance. However, in a situation where the running resistance is high such as traveling on an uphill road, the vehicle may not be able to accelerate.

  Referring to FIG. 17, if the amount of depression of the accelerator pedal increases during traveling on an uphill road in the driving state indicated by the point X in the figure, the fuel pressure rises and the engine torque rises to increase the point Y in the figure. It becomes the state of. Thus, when moving from the point X to the point Y, the engine rotational speed does not increase due to the traveling resistance on the uphill road, and only the engine torque increases as the fuel pressure increases. This point Y is a point on the maximum torque line Tmax. That is, in the operating state indicated by this point Y, the limit point of the torque that can be output at the current engine speed has been reached, so that the engine torque cannot be increased unless the engine speed increases. Therefore, no further increase in torque can be expected at the current engine speed, and it is impossible to increase the engine speed due to running resistance due to the uphill road. For this reason, it will fall into the situation where neither a torque increase nor an engine speed increase can be performed. If it falls into such a driving | running state, it becomes impossible to respond to a driver | operator's acceleration request.

  In order to solve this problem, the inventor of the present invention can not expect an increase in torque because the operating state of the engine has reached the maximum torque line, and cannot increase an engine speed due to running resistance or the like. In this case, it has been proposed to increase the engine speed and the engine torque by forcibly increasing the fuel pressure and increasing the heat generation rate per unit time in the cylinder. That is, it has proposed a control that enables a vehicle to be accelerated rapidly by such an increase in engine speed and engine torque.

  The inventor of the present invention has further studied the control for increasing the fuel pressure in this way. In order to optimize the charging efficiency by finding that when the fuel pressure is changed, the optimum value of the charging efficiency of the intake air into the cylinder is also different from the state before the fuel pressure is changed. The control action of was examined.

  The present invention has been made in view of such points, and an object of the present invention is to provide an optimal charging efficiency corresponding to a change in fuel pressure for an internal combustion engine provided with a means for changing the charging efficiency of intake air. An object of the present invention is to provide an intake control device for an internal combustion engine that can be obtained.

-Principle of solving the problem-
The solution principle of the present invention taken in order to achieve the above object is that when a control operation in which the fuel pressure temporarily rises is performed, the intake air is charged into the cylinder according to the increase in the fuel pressure. The efficiency is changed to an optimum value, so that in addition to the torque increase accompanying the increase in the fuel pressure, the torque is increased by optimizing the charging efficiency.

-Solution-
Specifically, the present invention is premised on an intake control device for an internal combustion engine provided with a variable charging efficiency mechanism for changing the charging efficiency of intake air supplied toward a cylinder of the compression ignition type internal combustion engine. When the fuel pressure increase operation for temporarily increasing the fuel pressure is executed for the intake control device of the internal combustion engine, the larger the fuel pressure increase amount, the larger the intake charging efficiency set by the variable charging efficiency mechanism. There is provided a charging efficiency changing means for setting a large increase amount .

  In this case, as an example of the fuel pressure increasing operation, when the acceleration request from the vehicle driver is generated, the internal combustion engine speed reaches the maximum torque at the current internal combustion engine speed, and There is an operation of temporarily increasing the fuel pressure until the rotational speed of the internal combustion engine increases when the engine does not increase. The fuel pressure increasing operation is an operation for increasing the combustion speed in the cylinder by temporarily increasing the fuel pressure.

Due to these specific matters, for example, when traveling on an uphill road, the operating state of the internal combustion engine reaches the maximum torque at the current internal combustion engine speed, and the internal combustion engine speed does not increase due to running resistance. The fuel pressure is temporarily increased until the internal combustion engine speed increases. This increase in fuel pressure can increase the amount of increase in heat generation rate per unit time at the beginning of combustion in the cylinder (increase the inclination angle of the heat generation rate waveform) and obtain the same injection amount. The injection period can be shortened and the combustion period can be shortened (decrease in the heat generation rate can be set at an early timing). That is, the phase of the heat release rate waveform can be shortened with respect to the degree of advance of the crank angle (the heat release rate lowering timing can be shifted to the advance side). In addition, the peak value of the heat generation rate (the maximum value of the heat generation rate waveform) can be obtained high. As described above, by temporarily increasing the fuel pressure, it is possible to bring the heat generation rate waveform closer to an ideal waveform suitable for the vehicle acceleration request required by the driver. When the fuel pressure increasing operation for temporarily increasing the fuel pressure is executed in this way, the charging efficiency changing means controls the above charging efficiency variable mechanism to set a large increase amount of the intake charging efficiency accordingly. To do. This is the case where the fuel pressure is changed, the maximum torque of the internal combustion engine is the charging efficiency is a value different from that obtained by changing the charging efficiency accordingly, the internal combustion engine in accordance with the fuel pressure after the change This is the control operation for obtaining the maximum torque of. Thereby, optimization of filling efficiency can be achieved.
In addition, the larger the fuel pressure increase amount, the larger the increase amount of the charging efficiency of the intake air, so that the acceleration operation of the vehicle by the increase of the fuel pressure can be performed quickly and reliably, and the driver's acceleration request can be accurately met. It becomes possible to meet.

  Specific examples of the structure of the filling efficiency variable mechanism include the following. In other words, the charging efficiency variable mechanism changes the flow area of the gas flowing toward the turbine wheel by changing the opening degree of the nozzle vane that is provided in the supercharger and that can be opened and closed by the variable nozzle vane mechanism. Thus, the charging efficiency of intake air is changed by changing the supercharging pressure.

  Further, as the charging efficiency changing means, a vehicle driver's acceleration request is generated from the light load operation region of the internal combustion engine in which EGR for recirculating part of the exhaust gas from the exhaust system of the internal combustion engine to the intake system is executed. Thus, when the fuel pressure increasing operation is executed when the operation range of the internal combustion engine in which EGR is not executed is changed, the intake charging efficiency set by the variable charging efficiency mechanism is changed. .

  In the present invention, when a control operation for temporarily increasing the fuel pressure of the compression ignition type internal combustion engine is performed, the charging efficiency of the intake air into the cylinder becomes an optimum value according to the increase of the fuel pressure. Has been changed. For this reason, in addition to the torque increase accompanying the increase in the fuel pressure, the torque increase is also performed by optimizing the charging efficiency, so that the operation efficiency of the internal combustion engine and the acceleration performance of the vehicle can be improved. .

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the present embodiment, a case where the present invention is applied to a common rail in-cylinder direct injection multi-cylinder (for example, in-line 4-cylinder) diesel engine (compression self-ignition internal combustion engine) mounted on an automobile will be described.

-Engine configuration-
First, a schematic configuration of a diesel engine (hereinafter simply referred to as an engine) according to the present embodiment will be described. FIG. 1 is a schematic configuration diagram of an engine 1 and its control system according to the present embodiment. FIG. 2 is a cross-sectional view showing the combustion chamber 3 of the diesel engine and its periphery.

  As shown in FIG. 1, the engine 1 according to the present embodiment is configured as a diesel engine system having a fuel supply system 2, a combustion chamber 3, an intake system 6, an exhaust system 7 and the like as main parts.

  The fuel supply system 2 includes a supply pump 21, a common rail 22, an injector (fuel injection valve) 23, a shutoff valve 24, a fuel addition valve 26, an engine fuel passage 27, an addition fuel passage 28, and the like.

  The supply pump 21 pumps fuel from the fuel tank, makes the pumped fuel high pressure, and supplies it to the common rail 22 via the engine fuel passage 27. The common rail 22 has a function as a pressure accumulation chamber that holds (accumulates) the high-pressure fuel supplied from the supply pump 21 at a predetermined pressure, and distributes the accumulated fuel to the injectors 23. The injector 23 includes a piezoelectric element (piezo element) therein, and is configured by a piezo injector that is appropriately opened to supply fuel into the combustion chamber 3. Details of the fuel injection control from the injector 23 will be described later.

  The supply pump 21 supplies a part of the fuel pumped from the fuel tank to the fuel addition valve 26 via the addition fuel passage 28. The added fuel passage 28 is provided with the shutoff valve 24 for shutting off the added fuel passage 28 and stopping fuel addition in an emergency.

  The fuel addition valve 26 is configured so that the fuel addition amount to the exhaust system 7 becomes a target addition amount (addition amount that makes the exhaust A / F become the target A / F) by an addition control operation by the ECU 100 described later. In addition, it is constituted by an electronically controlled on-off valve whose valve opening timing is controlled so that the fuel addition timing becomes a predetermined timing. That is, a desired fuel is injected and supplied from the fuel addition valve 26 to the exhaust system 7 (from the exhaust port 71 to the exhaust manifold 72) at an appropriate timing.

  The intake system 6 includes an intake manifold 63 connected to an intake port 15a formed in the cylinder head 15 (see FIG. 2), and an intake pipe 64 constituting an intake passage is connected to the intake manifold 63. Further, an air cleaner 65, an air flow meter 43, and a throttle valve 62 are arranged in this intake passage in order from the upstream side. The air flow meter 43 outputs an electrical signal corresponding to the amount of air flowing into the intake passage via the air cleaner 65.

  The exhaust system 7 includes an exhaust manifold 72 connected to an exhaust port 71 formed in the cylinder head 15, and exhaust pipes 73 and 74 constituting an exhaust passage are connected to the exhaust manifold 72. In addition, a maniverter (exhaust gas purification device) 77 including a NOx storage catalyst (NSR catalyst: NOx Storage Reduction catalyst) 75 and a DPNR catalyst (Diesel Particle-NOx Reduction catalyst) 76, which will be described later, is disposed in the exhaust passage. Yes. Hereinafter, the NSR catalyst 75 and the DPNR catalyst 76 will be described.

The NSR catalyst 75 is an NOx storage reduction catalyst. For example, alumina (Al ₂ O ₃ ) is used as a support, and potassium (K), sodium (Na), lithium (Li), cesium (Cs), for example, is supported on this support. Alkali metal such as barium (Ba), alkaline earth such as calcium (Ca), rare earth such as lanthanum (La) and yttrium (Y), and noble metal such as platinum (Pt) were supported. It has a configuration.

The NSR catalyst 75 occludes NOx in a state where a large amount of oxygen is present in the exhaust gas, has a low oxygen concentration in the exhaust gas, and a large amount of reducing component (for example, an unburned component (HC) of the fuel). In the existing state, NOx is reduced to NO ₂ or NO and released. NO NOx released as NO ₂ or NO, the N ₂ is further reduced due to quickly reacting with HC or CO in the exhaust. Further, HC and CO are oxidized to H ₂ O and CO ₂ by reducing NO ₂ and NO. That is, by appropriately adjusting the oxygen concentration and HC component in the exhaust gas introduced into the NSR catalyst 75, HC, CO, and NOx in the exhaust gas can be purified. In the present embodiment, the oxygen concentration and HC component in the exhaust gas can be adjusted by the fuel addition operation from the fuel addition valve 26.

  On the other hand, the DPNR catalyst 76 is, for example, a porous ceramic structure carrying a NOx storage reduction catalyst, and PM in the exhaust gas is collected when passing through the porous wall. Further, 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 becomes rich, the stored NOx is reduced and released. Further, the DPNR catalyst 76 carries a catalyst that oxidizes and burns the collected PM (for example, an oxidation catalyst mainly composed of a noble metal such as platinum).

  Here, the structure of the combustion chamber 3 of a diesel engine and its peripheral part is demonstrated using FIG. As shown in FIG. 2, a cylinder block 11 constituting a part of the engine body is formed with a cylindrical cylinder bore 12 for each cylinder (four cylinders), and a piston 13 is formed inside each cylinder bore 12. Is accommodated so as to be slidable in the vertical direction.

  The combustion chamber 3 is formed above the top surface 13 a of the piston 13. That is, the combustion chamber 3 is defined by the lower surface of the cylinder head 15 attached to the upper part of the cylinder block 11 via the gasket 14, the inner wall surface of the cylinder bore 12, and the top surface 13 a of the piston 13. A cavity 13 b is formed in a substantially central portion of the top surface 13 a of the piston 13, and this cavity 13 b also constitutes a part of the combustion chamber 3.

  The piston 13 has a small end portion 18a of a connecting rod 18 connected by a piston pin 13c, and a large end portion of the connecting rod 18 is connected to a crankshaft that is an engine output shaft. As a result, the reciprocating movement of the piston 13 in the cylinder bore 12 is transmitted to the crankshaft via the connecting rod 18, and the engine output is obtained by rotating the crankshaft. Further, a glow plug 19 is disposed toward the combustion chamber 3. The glow plug 19 functions as a start-up assisting device that is heated red when an electric current is applied immediately before the engine 1 is started and a part of the fuel spray is blown onto the glow plug 19 to promote ignition and combustion.

  The cylinder head 15 is formed with the intake port 15a for introducing air into the combustion chamber 3 and the exhaust port 71 for exhausting exhaust gas from the combustion chamber 3, and intake air for opening and closing the intake port 15a. An exhaust valve 17 that opens and closes the valve 16 and the exhaust port 71 is provided. The intake valve 16 and the exhaust valve 17 are disposed to face each other with the cylinder center line P interposed therebetween. That is, the engine 1 is configured as a cross flow type. The cylinder head 15 is provided with the injector 23 that directly injects fuel into the combustion chamber 3. The injector 23 is disposed at a substantially upper center of the combustion chamber 3 in a standing posture along the cylinder center line P, and injects fuel introduced from the common rail 22 toward the combustion chamber 3 at a predetermined timing. It has become.

  Furthermore, as shown in FIG. 1, the engine 1 is provided with a supercharger (turbocharger) 5. The turbocharger 5 includes a turbine wheel 52c and a compressor wheel 52b that are connected via a turbine shaft 52a. The compressor wheel 52b is disposed facing the inside of the intake pipe 64, and the turbine wheel 52c is disposed facing the inside of the exhaust pipe 73. For this reason, the turbocharger 5 performs a so-called supercharging operation in which the compressor wheel 52b is rotated using the exhaust flow (exhaust pressure) received by the turbine wheel 52c to increase the intake pressure. The turbocharger 5 in this embodiment is a variable nozzle type (variable capacity type) turbocharger, and is provided with a variable nozzle vane mechanism (not shown in FIG. 1) on the turbine wheel 52c side. The variable nozzle vane mechanism is opened. By adjusting the degree, the supercharging pressure of the engine 1 can be adjusted. A specific configuration of the variable nozzle vane mechanism will be described later.

  An intake pipe 64 of the intake system 6 is provided with an intercooler 61 for forcibly cooling the intake air whose temperature has been raised by supercharging in the turbocharger 5. The throttle valve 62 provided further downstream than the intercooler 61 is an electronically controlled on-off valve whose opening degree can be adjusted steplessly. It has a function of narrowing down the area and adjusting (reducing) the supply amount of the intake air.

  Further, the engine 1 is provided with an exhaust gas recirculation passage (EGR passage) 8 that connects the intake system 6 and the exhaust system 7. The EGR passage 8 is configured to reduce the combustion temperature by recirculating a part of the exhaust gas to the intake system 6 and supplying it again to the combustion chamber 3, thereby reducing the amount of NOx generated. In addition, the EGR passage 8 is opened and closed steplessly by electronic control, and the exhaust gas passing through the EGR passage 8 (recirculating) is cooled by an EGR valve 81 that can freely adjust the exhaust flow rate flowing through the passage. An EGR cooler 82 is provided.

-Turbocharger 5-
Next, the turbocharger (variable capacity turbocharger) 5 and the variable nozzle vane mechanism (filling efficiency variable mechanism) 9 provided in the turbocharger 5 will be described.

  FIG. 3 is a cross-sectional view of the turbocharger 5 along the axis of the turbine shaft 52a, and FIG. 4 is an enlarged cross-sectional view of the turbine wheel 52c and its periphery. FIG. 5 is a front view of the variable nozzle vane mechanism 9 (a view of the variable nozzle vane mechanism 9 viewed from the compressor wheel 52b side), and shows a state where the nozzle vane opening is set large. Further, FIG. 6 is a rear view of the variable nozzle vane mechanism 9 (a view of the variable nozzle vane mechanism 9 viewed from the side opposite to the compressor wheel 52b side), and shows a state in which the nozzle vane opening is set large.

  The turbocharger 5 is configured as a variable capacity type (variable nozzle type) turbocharger. As shown in FIG. 3, the turbocharger 5 includes a housing 51, a turbine shaft 52a rotatably accommodated in the housing 51, and the turbine shaft. The compressor wheel 52b attached to one end side (right side in FIG. 3) of 52a and the turbine wheel 52c attached to the other end side (left side in FIG. 3) of the turbine shaft 52a are provided. The turbine shaft 52a, the compressor wheel 52b, and the turbine wheel 52c constitute a turbine 52 that is a rotating body.

  The housing 51 is configured by integrally assembling a compressor housing 51a, a center housing (bearing housing) 51b, and a turbine housing 51c. That is, the compressor housing 51a and the turbine housing 51c are assembled on both sides of the center housing 51b.

  The compressor housing 51a has a shape capable of taking in air from the central portion (axial center portion) and discharging it to the outside.

  The compressor wheel 52b accommodated in the compressor housing 51a is fixed to the turbine shaft 52a by a lock nut 52d, and rotates integrally with the turbine shaft 52a. The compressor wheel 52b is provided with a plurality of compressor blades. When the compressor wheel 52b rotates, the air is accelerated and compressed radially outward by centrifugal force by the compressor blade. For this reason, when air is introduced into the central portion of the compressor housing 51a, the air is compressed by the compressor blades of the rotating compressor wheel 52b, and the compressed air is discharged to the intake pipe 64 toward the intake manifold 63. It has come to be.

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

  The center housing 51b is disposed at a substantially central portion in the axial direction of the turbocharger 5. The center housing 51b is provided with a thrust bearing 52f. The thrust bearing 52f is a bearing for receiving a load in the thrust direction of the turbine shaft 52a, and is lubricated by oil or the like.

  The center housing 51b is provided with a floating bearing 52g for holding the rotation of the turbine shaft 52a. The floating bearing 52g holds the load in the radial direction of the turbine shaft 52a. An oil film is interposed between the floating bearing 52g and the turbine shaft 52a so that the floating bearing 52g does not directly contact the turbine shaft 52a. Further, an oil film is also present between the floating bearing 52g and the center housing 51b so 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, the variable nozzle vane mechanism 9 will be described. The 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 includes a unison ring 92 housed in the link chamber 91 and a plurality of arms 93, 93,... That are located on the inner peripheral side of the unison ring 92 and partially engage with the unison ring 92. (See FIG. 5), a nozzle plate (NV plate) 94 (see FIG. 4) disposed so as to contact the turbine housing 51c in the turbocharger axial direction, and the plurality of arms 93, 93, Are provided with a main arm 95 for driving... And a vane shaft 97 connected to the arm 93 for driving the nozzle vane 96. The vane shaft 97 is rotatably supported by the nozzle plate 94, and each arm 93 and each nozzle vane 96 are connected to each other in an integral manner.

  Further, in the present embodiment, the turbine housing 51c is configured by integrally assembling two members, a main body 51c-a made of cast metal and a plate 51c-b made of sheet metal (see FIG. 4). The weight is reduced.

  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 an arrangement space for the nozzle vane 96 is formed between the housing plate 51e and the nozzle plate 94. That is, an exhaust gas flow path is formed between the nozzle plate 94 and the housing plate 51e, and the nozzle vane 96 is disposed in the flow path. For this reason, the nozzle plate 94 and the housing plate 51 e are disposed on both sides of the nozzle vane 96 in the rotational axis direction so as to face the end face of the nozzle vane 96. The gap between the nozzle plate 94 and the end face of the nozzle vane 96, and the gap between the housing plate 51e and the end face of the nozzle vane 96 (these gaps are referred to as nozzle side clearance) are within a range in which the sliding resistance does not increase. It is preferable to make it as small as possible so that the exhaust gas flows only in the exhaust gas flow path formed between the nozzle vanes 96 and 96 (to reduce the leakage of exhaust gas from the nozzle side clearance).

  The variable nozzle vane mechanism 9 is a mechanism for adjusting the rotation angle (rotation posture) of the plurality of (for example, 12) nozzle vanes 96, 96,... Disposed at equal intervals on the outer peripheral side of the turbine blade. Yes, when the drive link 95a connected to the main arm 95 is rotated by a predetermined angle, the turning force is applied to the main arm 95, the unison ring 92, the arms 93, 93, ..., the vane shafts 97, 97, Are transmitted to the nozzle vanes 96, 96,... Via the nozzle vanes 96, 96,.

  Specifically, the drive link 95a is rotatable around a drive shaft 95b. The drive shaft 95b is pivotally coupled to the drive link 95a and the main arm 95. For this reason, if the drive shaft 95b rotates with the rotation of the drive link 95a, this rotational force is transmitted to the main arm 95. An inner peripheral end of the main arm 95 is fixed to the drive shaft 95 b, and an outer peripheral end is engaged with the unison ring 92. For this reason, when the main arm 95 rotates around the drive shaft 95b, this turning force is transmitted to the unison ring 92. The outer peripheral side ends of the arms 93, 93,... Are fitted to the inner peripheral surface of the unison ring 92. When the unison ring 92 is rotated, this rotational force is transmitted to the arms 93, 93,. Specifically, the unison ring 92 is disposed so as to be slidable in the circumferential direction with respect to the nozzle plate 94, and a plurality of recesses 92a, 92a,. And the end portions on the outer peripheral side of the arms 93, 93,. The arms 93, 93,... Can rotate around the vane shaft 97, and the rotation of the arms 93 is transmitted to the vane shaft 97. Since the vane shaft 97 is connected to the nozzle vane 96, the nozzle vane 96 rotates together with the vane shaft 97 and the arm 93.

  The turbine housing 51c is provided with a turbine housing vortex chamber. Exhaust gas is supplied to the turbine housing vortex chamber, and the flow of the exhaust gas rotates the turbine wheel 52c. At this time, as described above, the rotational positions of the nozzle vanes 96, 96,... Are adjusted, and the rotational angle is set to adjust the flow rate and flow velocity of the exhaust from the turbine housing vortex chamber to the exhaust turbine chamber. It is possible to do. This makes it possible to adjust the supercharging performance. For example, the nozzle vanes 96, 96,... Are reduced so as to reduce the flow area (throat area) between the nozzle vanes 96, 96,. If the rotational position of... Is adjusted, the flow rate of the exhaust gas increases, and a high boost pressure can be obtained from the engine low speed range.

  The drive link 95a of the variable nozzle vane mechanism 9 is connected to a motor rod 95c. The motor rod 95c is a rod-like member and is connected to a variable nozzle controller (not shown). The variable nozzle controller is connected to a direct current motor (DC motor) as an actuator. When the direct current motor rotates, the rotational force is transmitted to the motor rod 95c via a gear mechanism and a worm mechanism. As the drive link 95a rotates with the movement of the rod 95c, the nozzle vanes 96, 96,... Rotate as described above.

  As shown in FIGS. 5 and 6, when the motor rod 95c is pulled in the direction of the arrow X in the figure, the unison ring 92 rotates in the direction of the arrow X1 in the figure, and as shown in FIG. ,... Rotate in the counterclockwise direction in FIG.

  7 and 8 show a state in which the nozzle vane opening is set small, FIG. 7 is a front view of the variable nozzle vane mechanism 9 (a diagram corresponding to FIG. 5), and FIG. 8 is a back view of the variable nozzle vane mechanism 9. FIG. 7 is a diagram (corresponding to FIG. 6). As shown in these drawings, when the motor rod 95c is pushed in the direction of arrow Y in the figure, the unison ring 92 rotates in the direction of arrow Y1 in the figure, and as shown in FIG. 8, each nozzle vane 96, 96,. By rotating in the clockwise direction in the figure, the nozzle vane opening is set small.

  A pin 94a (see FIG. 5) is inserted into the nozzle plate 94, and a roller 94b is fitted into the pin 94a. The roller 94b guides the inner peripheral surface of the unison ring 92. Thereby, the unison ring 92 is held by the roller 94b and can rotate in a predetermined direction. A spacer bolt 51d is attached to the turbine housing 51c (see FIG. 4). Further, a cooling water passage W through which cooling water for cooling the turbocharger 5 flows is formed in the center housing 51b.

-Sensors-
Various sensors are attached to each part of the engine 1, and signals related to the environmental conditions of each part and the operating state of the engine 1 are output.

  For example, the air flow meter 43 outputs a detection signal corresponding to the flow rate of intake air (intake air amount) upstream of the throttle valve 62 in the intake system 6. The intake air temperature sensor 49 is disposed in the intake manifold 63 and outputs a detection signal corresponding to the temperature of the intake air. The intake pressure sensor 48 is disposed in the intake manifold 63 and outputs a detection signal corresponding to the intake air pressure. The A / F (air-fuel ratio) sensor 44 outputs a detection signal that continuously changes in accordance with the oxygen concentration in the exhaust gas downstream of the manipulator 77 of the exhaust system 7. Similarly, the exhaust temperature sensor 45 outputs a detection signal corresponding to the temperature of the exhaust gas (exhaust temperature) downstream of the manipulator 77 of the exhaust system 7. The rail pressure sensor 41 outputs a detection signal corresponding to the fuel pressure stored in the common rail 22. The throttle opening sensor 42 detects the opening of the throttle valve 62.

-ECU-
As shown in FIG. 9, the ECU 100 includes a CPU 101, a ROM 102, a RAM 103, a backup RAM 104, and the like. The ROM 102 stores various control programs, maps that are referred to when the various control programs are executed, and the like. The CPU 101 executes various arithmetic processes based on various control programs and maps stored in the ROM 102. The RAM 103 is a memory that temporarily stores calculation results of the CPU 101, data input from each sensor, and the like. The backup RAM 104 is a nonvolatile memory that stores data to be saved when the engine 1 is stopped, for example. Memory.

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

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

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

  The fuel injection pressure for executing these fuel injections is determined by the internal pressure of the common rail 22. As the common rail internal pressure, generally, the target value of the fuel pressure supplied from the common rail 22 to the injector 23, that is, the target rail pressure, increases as the engine load (engine load) increases and the engine speed (engine speed) increases. It will be expensive. That is, when the engine load is high, the amount of air sucked into the combustion chamber 3 is large. Therefore, a large amount of fuel must be injected from the injector 23 into the combustion chamber 3, and therefore the injection from the injector 23 is performed. The pressure needs to be high. Further, when the engine speed is high, the injection period is short, so the amount of fuel injected per unit time must be increased, and therefore the injection pressure from the injector 23 needs to be increased. . Thus, the target rail pressure is generally set based on the engine load and the engine speed. A specific method for setting the target value of the fuel pressure will be described later.

  As for the fuel injection parameters in the fuel injection such as the pilot injection and the main injection, the optimum values vary depending on the temperature conditions of the engine 1 and the intake air.

  For example, the ECU 100 adjusts the fuel discharge amount of the supply pump 21 so that the common rail pressure becomes equal to the target rail pressure set based on the engine operating state, that is, the fuel injection pressure matches the target injection pressure. To measure. Further, the ECU 100 determines the fuel injection amount and the fuel injection form based on the engine operating state. Specifically, the ECU 100 calculates the engine rotation speed based on the detection value of the crank position sensor 40 and obtains the depression amount (accelerator opening) to the accelerator pedal based on the detection value of the accelerator opening sensor 47. The total fuel injection amount (the sum of the injection amount in the pre-injection and the injection amount in the main injection, which will be described later) is determined based on the engine speed and the accelerator opening.

-Fuel injection mode-
Hereinafter, an outline of each operation of the pilot injection, pre-injection, main injection, after-injection, and post-injection in this embodiment will be described.

(Pilot injection)
Pilot injection is an injection operation in which a small amount of fuel is injected in advance prior to main injection (main injection) from the injector 23. That is, after the pilot injection is performed, the fuel injection is temporarily interrupted, and the compressed gas temperature (in-cylinder temperature) is sufficiently increased until the main injection is started to reach the fuel self-ignition temperature. This ensures good ignitability of the fuel injected in the main injection. That is, the pilot injection function in this embodiment is specialized for preheating in the cylinder. That is, the pilot injection in the present embodiment is an injection operation (preheating fuel supply operation) for preheating the gas in the combustion chamber 3.

Specifically, in the present embodiment, in order to optimize the distribution of the spray and the local concentration, the injection rate is set to the minimum injection rate (for example, the injection amount per injection 1.5 mm ³ ), and a plurality of pilots are performed. By executing the injection, the total pilot injection amount necessary for the pilot injection is ensured.

  In addition, the interval of the pilot injection that is divided and injected in this way is determined by the responsiveness of the injector 23 (speed of opening and closing operation). In the present embodiment, it is set to 200 μs, for example. The pilot injection interval is not limited to this value.

(Pre-injection)
The pre-injection is an injection operation (torque generating fuel supply operation) for suppressing the initial combustion speed by the main injection and leading to stable diffusion combustion, and is also called sub-injection. Specifically, in the present embodiment, the total injection amount (the injection amount in the pre-injection and the total injection amount for obtaining the required torque determined according to the operating state such as the engine speed, the accelerator operation amount, the coolant temperature, the intake air temperature, etc. The pre-injection amount is set to 10% with respect to the injection amount in the main injection).

In this case, when the total injection amount is less than 15 mm ³ , the injection amount in the pre-injection is less than the minimum limit injection amount (1.5 mm ³ ) of the injector 23, so the pre-injection is not executed. become. In this case, the fuel injection in the pre-injection may be performed by the minimum limit injection amount (1.5 mm ³ ) of the injector 23. On the other hand, when the total injection amount of the pre-injection is required to be at least twice the minimum limit injection amount of the injector 23 (for example, 3 mm ³ or more), it is necessary for this pre-injection by executing a plurality of pre-injections. The total injection amount is secured. Thereby, the ignition delay of the pre-injection can be suppressed, the initial combustion speed by the main injection can be surely suppressed, and the stable diffusion combustion can be led.

(Main injection)
The main injection is an injection operation (torque generation fuel supply operation) for generating torque of the engine 1. Specifically, in the present embodiment, the pre-injection from the total combustion injection amount for obtaining the required torque determined according to the operating state such as the engine speed, the accelerator operation amount, the cooling water temperature, the intake air temperature and the like. It is set as an injection amount obtained by subtracting the injection amount.

  The pre-injection and main injection control processes described above will be briefly described below. First, a total fuel injection amount that is the sum of the injection amount in the pre-injection and the injection amount in the main injection is calculated with respect to the torque request value of the engine 1. That is, the total fuel injection amount is calculated as an amount for generating the torque required for the engine 1.

  The torque request value of the engine 1 is determined according to the operating state of the engine speed, the amount of accelerator operation, the coolant temperature, the intake air temperature, and the like, and the usage status of the auxiliary machinery and the like. For example, the higher the engine speed (the engine speed calculated based on the detection value of the crank position sensor 40), the more the accelerator operation amount (the accelerator pedal depression amount detected by the accelerator opening sensor 47). The larger the value (the larger the accelerator opening), the higher the required torque value of the engine.

  After the total fuel injection amount is calculated in this way, the ratio (split rate) of the injection amount in the pre-injection with respect to the total fuel injection amount is set. That is, the pre-injection amount is set as an amount divided by the above-described division ratio with respect to the total fuel injection amount. This division ratio (pre-injection amount) is obtained as a value that achieves both “suppression of fuel ignition delay by main injection” and “suppression of the peak value of the heat generation rate of combustion by main injection”. By suppressing these, it is possible to reduce the combustion noise and the amount of NOx generated while securing a high engine torque. In the present embodiment, the division ratio is set to 10%.

(After spray)
After injection is an injection operation for increasing the exhaust gas temperature. Specifically, in this embodiment, after-injection is performed at a timing at which most of the combustion energy of the fuel supplied by this after-injection is obtained as exhaust heat energy without being converted into engine torque. I have to. Also in this after injection, similarly to the case of the pilot injection described above, the after injection is performed by performing a plurality of after injections with the minimum injection rate (for example, the injection amount per injection 1.5 mm ³ ). Therefore, the necessary total after injection amount is secured.

(Post injection)
The post-injection is an injection operation for directly introducing fuel into the exhaust system 7 to increase the temperature of the manipulator 77. For example, when the accumulated amount of PM trapped in the DPNR catalyst 76 exceeds a predetermined amount (for example, detected by detecting a differential pressure before and after the manipulator 77), post injection is performed. .

-Setting of target fuel pressure-
One of the features of this embodiment is a method for setting a target fuel pressure. Specifically, when the driver makes an acceleration request to increase the amount of depression of the accelerator pedal, the engine speed does not increase with the engine torque reaching the maximum torque at the current engine speed. In this case, a control operation for temporarily increasing the fuel pressure until the engine speed increases (hereinafter referred to as fuel pressure increase control) is executed. For example, when driving on an uphill road, the engine is in a situation where the running resistance on the uphill road is balanced with the engine torque even though the driver has requested acceleration to increase the amount of depression of the accelerator pedal. This is a control operation for temporarily increasing the fuel pressure when the rotational speed does not increase. Before specifically describing the fuel pressure increase control, first, a basic setting method and a fuel pressure setting map of the target fuel pressure will be described.

(Basic target pressure setting method)
In the diesel engine 1, it is important to simultaneously satisfy various requirements such as improvement of exhaust emission by reducing the amount of NOx generated, reduction of combustion noise during the combustion stroke, and sufficient securing of engine torque. The inventor of the present invention can appropriately control the change state of the heat generation rate in the cylinder during the combustion stroke (change state represented by the heat generation rate waveform) as a method for simultaneously satisfying these requirements. Focusing on the effectiveness, we found a target fuel pressure setting method as described below as a method for controlling the change state of the heat generation rate.

  The solid line in FIG. 10 shows an ideal heat generation rate waveform related to combustion of fuel injected by main injection, with the horizontal axis representing the crank angle and the vertical axis representing the heat generation rate. TDC in the figure indicates the crank angle position corresponding to the compression top dead center of the piston 13. As this heat generation rate waveform, for example, combustion of fuel injected by main injection is started from the compression top dead center (TDC) of the piston 13, and a predetermined piston position after the compression top dead center (for example, compression top dead center). The heat generation rate reaches a maximum value (peak value) at 10 ° (at the time of ATDC 10 °), and a predetermined piston position after compression top dead center (for example, 25 ° after compression top dead center (ATDC 25 °)). The combustion of the fuel injected in the main injection ends at the time). If combustion of the air-fuel mixture is performed in such a state of change in heat generation rate, for example, 50% of the air-fuel mixture in the cylinder burns at 10 ° (ATDC 10 °) after compression top dead center. Completed status. That is, about 50% of the total heat generation amount in the expansion stroke is generated by ATDC 10 °, and the engine 1 can be operated with high thermal efficiency.

  In addition, the waveform shown with a dashed-dotted line in FIG. 10 has shown the heat release rate waveform which concerns on combustion of the fuel injected by the said pre-injection. Thereby, stable diffusion combustion of the fuel injected by the main injection is realized. For example, the amount of heat of 10 J is generated by the combustion of the fuel injected by this pre-injection. This value is not limited to this. For example, it is appropriately set according to the total fuel injection amount. Although not shown, pilot injection is also performed prior to the pre-injection, thereby sufficiently increasing the in-cylinder temperature and ensuring good ignitability of the fuel injected in the main injection.

  Further, the waveform indicated by a two-dot chain line α in FIG. 10 is a heat generation rate waveform when the fuel injection pressure is set higher than an appropriate value, and both the combustion speed and the peak value are too high, and the combustion This is a state in which there is a concern about an increase in sound and an increase in the amount of NOx generated. On the other hand, the waveform indicated by the two-dot chain line β in FIG. 10 is a heat release rate waveform when the fuel injection pressure is set lower than the appropriate value, and the timing at which the combustion speed is low and the peak appears is greatly retarded. There is a concern that sufficient engine torque cannot be ensured by shifting to.

  As described above, the target fuel pressure setting method according to the present embodiment is a technical idea that the combustion efficiency is improved by optimizing the change state of the heat generation rate (optimization of the heat generation rate waveform). It is based on. And in order to implement | achieve it, the setting of the target fuel pressure according to the fuel pressure setting map which is mentioned later is performed.

(Fuel pressure setting map)
FIG. 11 is a fuel pressure setting map that is referred to when the target fuel pressure is determined in the present embodiment. This fuel pressure setting map is stored in the ROM 102, for example. In this fuel pressure setting map, the horizontal axis is the engine speed, and the vertical axis is the engine torque. Further, Tmax in FIG. 11 indicates a maximum torque line.

  As a feature of this fuel pressure setting map, an equal fuel injection pressure line (equal fuel injection pressure region) indicated by A to L in the figure is an equal power line (etc.) of output (power) obtained from the rotational speed and torque of the engine 1. Assigned to the output area. That is, in this fuel pressure setting map, the equal power line and the equal fuel injection pressure line are set to substantially coincide.

  Specifically, a curve A in FIG. 11 is a line with an engine output of 10 kW, and a line with 30 MPa is allocated as the fuel injection pressure. Hereinafter, similarly, the curve B is a line with an engine output of 20 kW, and a line of 45 MPa is allocated to this as a fuel injection pressure. Curve C is a line with an engine output of 30 kW, and a line of 60 MPa is allocated to this as a fuel injection pressure. Curve D is a line with an engine output of 40 kW, and a line of 75 MPa is allocated to this as fuel injection pressure. Curve E is a line with an engine output of 50 kW, and a line of 90 MPa is allocated to this as fuel injection pressure. Curve F is a line with an engine output of 60 kW, and a line of 105 MPa is assigned to this as the fuel injection pressure. A curve G is a line with an engine output of 70 kW, and a line of 120 MPa is assigned to this as a fuel injection pressure. A curve H is a line having an engine output of 80 kW, and a line of 135 MPa is allocated as the fuel injection pressure. Curve I is a line with an engine output of 90 kW, and a line of 150 MPa is allocated as the fuel injection pressure. Curve J is a line with an engine output of 100 kW, and a line of 165 MPa is allocated to this as the fuel injection pressure. A curve K is a line with an engine output of 110 kW, and a line of 180 MPa is assigned to this as a fuel injection pressure. A curve L is a line having an engine output of 120 kW, and a line of 200 MPa is allocated as the fuel injection pressure. These values are not limited to this, and are set as appropriate according to the performance characteristics of the engine 1 and the like. Further, the relationship between the engine output and the fuel injection pressure between the above-mentioned lines is obtained by a known interpolation calculation or the like.

  Each of the lines A to L is set such that the ratio of the change amount of the fuel injection pressure with respect to the change amount of the engine output becomes smaller as the engine speed is in the low rotation region. That is, the interval between the lines is set wider in the low rotation region than in the high rotation region. The intervals between the lines may be set evenly.

  In accordance with the fuel pressure setting map created in this way, a target fuel pressure suitable for the operating state of the engine 1 is set, and the supply pump 21 is controlled.

  Specifically, when both the engine speed and the engine torque increase (see arrow I in FIG. 11), and when the engine speed increases at a constant engine speed (see arrow II in FIG. 11), In addition, the fuel injection pressure is increased in any case where the engine torque is constant and the engine speed increases (see arrow III in FIG. 11). This ensures a fuel injection amount suitable for the intake air amount when the engine torque (engine load) is high, and increases the fuel injection amount per unit time when the engine speed is high, which is required in a short period of time. A fuel injection amount can be secured. For this reason, regardless of the engine output and the engine speed, it is possible to always realize the combustion mode with an ideal heat generation rate waveform as shown by the solid line in FIG. 10, and to reduce the NOx generation amount. Various requirements such as improvement of exhaust emission, reduction of combustion noise during combustion stroke, and sufficient securing of engine torque can be combined.

  On the other hand, even if the engine speed and the engine torque change, if the engine output has not changed before and after the change (see arrow IV in FIG. 11), the fuel injection pressure should not be changed. Maintain the proper value of the fuel injection pressure set up to. In other words, the fuel injection pressure is not changed when the engine operating state changes along the equal fuel injection pressure line (corresponding to the equal power line), and the combustion mode with the ideal heat release rate waveform described above is used. To continue. In this case, it is possible to continuously satisfy various requirements such as improvement of exhaust emission by reducing the amount of NOx generated, reduction of combustion noise during the combustion stroke, and sufficient securing of engine torque.

  As described above, in the fuel pressure setting map in the present embodiment, there is a unique correlation between the output (power) of the engine 1 and the fuel injection pressure (common rail pressure), and the engine speed and engine torque are In a situation where the engine output changes due to at least one change, fuel injection can be performed at an appropriate fuel pressure accordingly, and conversely, the engine output does not change even if the engine speed or engine torque changes In the situation, the fuel pressure is not changed from the proper value that has been set. This makes it possible to bring the heat generation rate change state closer to the ideal state over substantially the entire engine operation region. Also, as shown in this fuel pressure setting map, having a unique correlation between the output (power) of the engine 1 and the fuel injection pressure (common rail pressure) is a systematic fuel pressure common to various engines. Since a setting method is constructed, it is possible to simplify the creation of a fuel pressure setting map for setting an appropriate fuel injection pressure according to the operating state of the engine 1.

  Further, as described above, in the fuel pressure setting map according to the present embodiment, the ratio of the change amount of the fuel injection pressure to the change amount of the engine output is set so as to become smaller as the engine speed is in the low rotation region. For this reason, in the low rotation region of the engine 1, the change in the fuel injection pressure is gradual, and a sudden increase in the combustion pressure in the cylinder in this operating state can be avoided to suppress the generation of vibration and noise associated with combustion. . On the other hand, in the high rotation region of the engine 1, for example, the fuel injection pressure is greatly changed as the torque increases, so that the required output can be quickly obtained and the response of the engine 1 can be obtained satisfactorily. be able to.

-Filling efficiency setting map-
FIG. 12 is a charging efficiency setting map that is referred to when the opening degree of the nozzle vanes 96, 96,... In the turbocharger 5 is determined in the present embodiment. This filling efficiency setting map is stored in the ROM 102, for example. In this charging efficiency setting map, the horizontal axis represents the engine speed, and the vertical axis represents the engine torque. That is, the map is used to obtain the opening degree of the nozzle vanes 96, 96,... (Filling efficiency determined by the opening degree) suitable for the current engine operating state according to the engine speed and the engine torque. Further, Tmax in FIG. 12 indicates a maximum torque line. Further, the hatched area in FIG. 12 is an EGR area where the EGR valve 81 is opened and a part of the exhaust gas is recirculated to the intake system 6, and the other areas are non-EGR where the EGR valve 81 is closed. (No EGR) area.

  This filling efficiency setting map indicates that the nozzle vanes 96, 96,... Have the maximum intake supercharging efficiency (the highest point of the intake supercharging efficiency) according to the operating state of the engine 1 (engine speed, engine torque). The degree of opening is acquired. That is, the filling efficiency setting map stores the appropriate values of the nozzle vanes 96, 96,.

  Specifically, the highest point of the intake supercharging efficiency referred to here is the nozzle vane 96 when the throttle valve 62 is fully opened and the fuel injection amount, fuel injection pattern, and fuel injection pressure into the cylinder are substantially constant. , 96,..., 96,..., And when the engine torque changes accordingly, the engine torque reaches its maximum value. That is, the opening at which the opening degree of the nozzle vanes 96, 96,... At the time when the engine torque reaches the maximum value is the maximum supercharging efficiency in the operating state (engine speed, engine torque) of the engine 1 at that time. The value of the opening is written in the charging efficiency setting map as an appropriate value in the engine operating state. This will be specifically described below.

  FIG. 13 shows the amount of fuel injected into the cylinder, fuel injection pattern (pre-injection and main injection timings, intervals, etc.) under certain engine operating conditions (the throttle valve 62 is fully opened in the non-EGR region). This shows a change in engine torque when the opening degree of the nozzle vanes 96, 96,... Is changed in a state where the fuel injection pressure is substantially constant. The horizontal axis in FIG. 13 is the filling efficiency determined by the opening degree of the nozzle vanes 96, 96,... The filling efficiency increases as the opening degree of the nozzle vanes 96, 96,. Further, the vertical axis in FIG. 13 is the engine torque.

  Here, as a specific example of the case where the fuel injection amount into the cylinder, the fuel injection pattern, and the fuel injection pressure are substantially constant, the fuel injection amount and the fuel injection pattern are, for example, those of the fuel injected by the pre-injection. The timing at which the heat generation rate due to combustion is maximized, the timing at which combustion of fuel injected by main injection is started, and the timing at which the piston 13 reciprocating in the cylinder reaches compression top dead center substantially coincide with each other. There is a case where the injection timing and the injection amount of the pre-injection and the main injection are fixed. As for the fuel injection pressure, the equal fuel injection pressure region (equal fuel injection pressure line) is allocated to the equal output region (equal power line) of the output (power) obtained from the engine speed and engine torque as described above. In addition (see FIG. 11), there is a case where the fuel injection pressure is set to be set according to the output of the engine 1.

  As shown in FIG. 13, when the opening degree of the nozzle vanes 96, 96,... Is large (the throat area is large: the filling efficiency is low), the opening degree is gradually decreased (the filling efficiency is gradually increased). The amount of conversion of the exhaust gas from heat energy to rotational energy in the turbocharger 5 gradually increases, and the engine torque increases accordingly (see the charging efficiency range I in FIG. 13). However, when the opening degree of the nozzle vanes 96, 96,... Is reduced in this way, the exhaust energy increases, that is, exhaust gas exhaustion worsens. It gets bigger. And the balance between the amount of increase in rotational energy (energy amount contributing to efficiency improvement) by reducing the opening degree of the nozzle vanes 96, 96,... And the amount of increase in exhaust energy (energy amount leading to deterioration in efficiency). As the increase amount of the exhaust energy increases, the supercharging efficiency decreases and the engine torque decreases (see the charging efficiency range II in FIG. 13). Therefore, a point (a boundary point between the charging efficiency ranges I and II) where the increased amount of rotational energy and the increased amount of exhaust energy are balanced is obtained as the maximum point of supercharging efficiency.

  The opening (adapted value) of the nozzle vanes 96, 96,..., Which is the maximum point of the supercharging efficiency obtained in this way, is determined for each operating state of the engine and obtained on the coordinates (horizontal axis). .. Is plotted on the coordinates with the engine speed as the vertical axis and the engine torque as the vertical axis), and the filling efficiency setting map shown in FIG. 12 is obtained by connecting the nozzle vanes 96, 96,. It is. In this filling efficiency setting map, lines indicated by a to i (each line indicated by a broken line) are a set of points where the opening degree of the nozzle vanes 96, 96,... Is the same (a set of points having the same filling efficiency). This is an equal filling efficiency line (equal filling efficiency region). That is, on this equal charging efficiency line, the opening degree of the nozzle vanes 96, 96,... For obtaining the maximum point of supercharging efficiency is the same.

  In other words, this equal charging efficiency line is a set of points at which the supercharging efficiency of the turbocharger 5 is maximized, and the nozzle vane 96 corresponding to the equal charging efficiency line selected based on the rotational speed and torque of the engine 1. , 96,... Can be set to maximize the supercharging efficiency of the turbocharger 5.

  Specifically, the curve a in FIG. 12 is a line with a nozzle vane opening degree of 90%, the nozzle vane opening degree is set to be smaller by 10% from the curve b toward the curve i, and the curve i has a nozzle vane opening degree of 10%. It has become a line. These values are not limited to this, and are set as appropriate according to the performance characteristics of the engine 1 and the like.

  In accordance with the charging efficiency setting map created in this way, the opening control of the nozzle vanes 96, 96,... During the operation of the engine 1 according to the present embodiment uses the charging efficiency of intake air suitable for the operating state of the engine 1. The variable nozzle vane mechanism 9 is controlled to set the opening degree of the nozzle vanes 96, 96,... So as to obtain the filling efficiency from the filling efficiency setting map.

  In this way, by setting the opening degree of the nozzle vanes 96, 96,..., The intake supercharging efficiency can be maximized in any engine operating state, and the engine 1 can be operated with high efficiency. As a result, the fuel consumption rate can be greatly improved.

  Further, as described above, in the filling efficiency setting map in the present embodiment, a unique correlation is provided among the engine speed, the engine torque, and the nozzle vane opening (filling efficiency). This makes it possible to maintain high supercharging efficiency over substantially the entire engine operation region. Also, as shown in this charging efficiency setting map, having a unique correlation among the engine speed, engine torque, and nozzle vane opening is a systematic intake control method common to various engines. Since it is constructed, it is possible to simplify the creation of a charging efficiency setting map for setting an appropriate intake amount according to the operating state of the engine 1.

-Fuel pressure increase control-
Next, fuel pressure increase control, which is one of the features that characterize the present embodiment, will be described in detail. As described above, in this fuel pressure increase control, when the driver requests acceleration to increase the amount of depression of the accelerator pedal, the engine speed reaches the maximum torque at the current engine speed. This is a control operation for temporarily increasing the fuel pressure until the engine speed increases when the engine does not increase.

  Specifically, a case where a driver's acceleration request is generated during traveling on an uphill road with a relatively low engine speed will be described with reference to FIG.

  While driving on an uphill road in the driving state indicated by point X in FIG. 11 (for example, the engine speed is about 1000 rpm and the engine torque is about 100 Nm), the driver is required to accelerate and the amount of depression of the accelerator pedal is large. Then, the fuel pressure rises and the engine torque rises to the state of point Y in the figure (engine torque is about 250 Nm). Thus, when moving from the point X to the point Y, the engine rotational speed does not increase due to the traveling resistance on the uphill road, and only the engine torque increases as the fuel pressure increases. This point Y is a point on the maximum torque line Tmax. That is, in the operating state indicated by this point Y, the limit point of the torque that can be output at the current engine speed has been reached, so that the engine torque cannot be increased unless the engine speed increases.

  Thus, when it is recognized that the engine torque reaches the maximum torque at the current engine speed and the engine speed does not increase, in this embodiment, the engine speed is Increase fuel pressure temporarily until it rises.

  Specifically, the amount of change in the accelerator opening detected by the accelerator opening sensor 47 is compared with the amount of change in the engine speed calculated based on the detected value of the crank position sensor 40, and the accelerator opening is detected. If the engine speed hardly changes despite the increase in the engine speed, it is determined that the engine speed has not increased because the engine operating state has reached the maximum torque line. When such a situation continues for a predetermined time (for example, 1 sec), fuel pressure increase control is started, and the fuel pressure is temporarily increased. For example, the common rail pressure is increased by increasing the flow rate of the fuel supplied from the supply pump 21 to the common rail 22, thereby increasing the fuel injection pressure into the cylinder. More specifically, the amount of fuel discharged to the common rail 22 is increased by limiting the amount of fuel returned to the fuel tank by controlling a pressure control valve (not shown) provided near the discharge port of the supply pump 21. To temporarily increase the common rail pressure. In the state shown in FIG. 11, the engine operating state is controlled to move toward the point Z by increasing the fuel pressure to about 90 MPa from the state where the fuel pressure is set at about 55 MPa at the point Y.

  An example of the change of the heat release rate waveform in the combustion chamber 3 in this case is shown in FIG. The two-dot chain line in FIG. 14 is a heat release rate waveform in the state of point Y, that is, the state where the fuel pressure is set to about 55 MPa. Further, the solid line in FIG. 14 is a heat release rate waveform in the state of point Z, that is, in a state where the fuel pressure is set to about 90 MPa.

  Here, the target value of fuel pressure at the start of fuel pressure increase control (about 90 MPa in the above case) will be described. The target value of the fuel pressure is set according to the driver's acceleration request. That is, the larger the accelerator pedal depression amount (accelerator opening), the higher the fuel pressure target value is set. Specifically, the power line in FIG. 11 is selected so that power (engine output) corresponding to the amount of depression of the accelerator pedal is obtained, and the fuel injection pressure assigned to the power line is set as the target fuel pressure. It is set up. That is, when the target value is set to about 90 MPa as described above, the power required for the engine (engine output) is about 50 kW. Since the target value of the fuel pressure is set in this way, the higher the driver's acceleration request, the higher the acceleration during vehicle acceleration, and the vehicle is accelerated at an acceleration according to the driver's acceleration request. To be able to.

  By increasing the fuel injection pressure as described above, the amount of increase in heat generation rate per unit time at the beginning of combustion in the cylinder can be increased (the inclination angle of the heat generation rate waveform can be increased) and the same. The injection period for obtaining the injection amount can be shortened and the combustion period can be shortened (decrease in the heat generation rate can be set at an early timing). That is, the phase of the heat release rate waveform can be shortened with respect to the degree of advance of the crank angle (the heat release rate lowering timing can be shifted to the advance side). In addition, the peak value of the heat generation rate (the maximum value of the heat generation rate waveform) can be obtained high. In this way, by temporarily increasing the fuel pressure, it becomes possible to bring the heat generation rate waveform closer to an ideal waveform suitable for the vehicle acceleration requirement requested by the driver, and the amount of intake air Further, calculation processing such as engine speed and the like is not necessary, so that the vehicle can be quickly accelerated as the engine speed increases and the engine torque increases.

  In the heat generation rate waveform shown in FIG. 14, the injection start timing of the main injection is set to the advance side (for example, BTDC 5 °) from the compression top dead center (TDC) of the piston 13, and the maximum value of the heat generation rate is set. The (peak value) is obtained slightly on the retard side (for example, near ATDC 5 °) from the compression top dead center (TDC).

  The fuel pressure increase control is continued until the driver's acceleration request is canceled, for example, when the accelerator pedal depression amount is reduced to a predetermined amount. That is, when the driver's acceleration request is canceled, the temporary increase of the fuel pressure is canceled, and the normal fuel pressure setting operation (the fuel pressure (engine speed and engine according to the fuel pressure setting map shown in FIG. 11) The fuel pressure is determined according to the torque (setting operation).

  By performing the fuel pressure increase control as described above, the fuel pressure is temporarily increased even when the engine operating state reaches the maximum torque line and the engine speed does not increase. Thus, the heat generation rate waveform can be brought close to an ideal waveform suitable for the vehicle acceleration request required by the driver. For this reason, it is possible to quickly accelerate the vehicle as the engine speed increases and the engine torque increases, and the acceleration performance of the vehicle can be improved.

-Filling efficiency change operation-
The most characteristic feature of this embodiment resides in the charging efficiency changing operation that is executed in accordance with the start of the fuel pressure increase control described above. Hereinafter, the filling efficiency changing operation will be described.

  When the fuel pressure is temporarily increased by the fuel pressure increase control, a charging efficiency changing operation for increasing the charging efficiency of the intake air is started in conjunction therewith. Specifically, the variable nozzle vane mechanism 9 is controlled so as to reduce the opening degree of the nozzle vanes 96, 96,. As a result, the flow velocity of the exhaust gas flowing toward the turbine wheel 52c increases, the amount of conversion of the exhaust gas from thermal energy to rotational energy increases, and the engine torque increases (by the charging efficiency changing means). Intake charging efficiency change operation).

  Points X, Y, and Z in FIG. 12 correspond to points X, Y, and Z in FIG. 11, and the amount of depression of the accelerator pedal by the driver increases to increase the fuel pressure (FIGS. 11 and FIG. 12 and the change in charging efficiency when the fuel pressure is temporarily increased by the fuel pressure increase control (from point Y to point Z in FIGS. 11 and 12). Migration operation). In particular, in this case, the EGR region (relatively light load operation region) in which the EGR is executed by an increase in fuel pressure (transition operation from point X to point Y) accompanying an increase in the accelerator pedal depression amount. To the non-EGR area where EGR is not executed. FIG. 15 is a diagram showing the relationship between the charging efficiency of intake air and the engine torque. The curve indicated by a broken line in FIG. 15 indicates the charging efficiency at the fuel pressure at point Y in FIGS. 11 and 12 and the engine. The relationship with torque is shown. A curve indicated by a solid line in FIG. 15 indicates the relationship between the charging efficiency and the engine torque at the fuel pressure (fuel pressure at the point Z in FIG. 11) set by the fuel pressure increase control. The reason why the engine torque changes as the charging efficiency is changed as shown in FIG. 15 has already been described with reference to FIG. 13 and will not be described here.

  As shown in FIG. 15, when the fuel pressure is changed, the optimum value of the charging efficiency (the value of the charging efficiency at which the maximum torque is obtained) is also different from the state before the fuel pressure is changed. That is, when the fuel pressure at the point Y in FIG. 11 is changed to the fuel pressure at the point Z (the fuel pressure is increased), the characteristic indicated by the broken line in FIG. 15 changes to the characteristic indicated by the solid line. In consideration of this point, in the present embodiment, when the fuel pressure is temporarily increased by the fuel pressure increase control, the nozzle vanes 96, 96,... Are set so as to obtain the charging efficiency at which the maximum torque is obtained at the increased fuel pressure. The variable nozzle vane mechanism 9 is controlled so as to reduce the opening degree. That is, the opening degree of the nozzle vanes 96, 96,... Is set so that the charging efficiency at the point Y1 corresponding to the maximum torque on the broken line in FIG. Has been. Then, when the fuel pressure increase control is started and the fuel pressure state is increased, the nozzle vanes 96, 96, 96, 96, 96, 96, 96, 96, 96, 96, 96, 96, Is set (the opening is set small). As a result, the engine torque increases from Ty in FIG. 15 to Tz.

  FIG. 16 is a diagram illustrating the relationship between the fuel pressure increase amount and the filling efficiency increase amount set corresponding to the increase in the fuel efficiency when performing the charging efficiency changing operation. As shown in FIG. 16, the larger the fuel pressure increase amount, the larger the charging efficiency increase amount is set.

  As described above, in the present embodiment, when the fuel pressure is temporarily increased by the fuel pressure increase control, the nozzle vanes 96, 96,... The charging efficiency is changed to reduce the opening. As a result, in addition to the torque increase associated with the increase in fuel pressure by the fuel pressure increase control, the torque increase is also performed by optimizing the charging efficiency, so that the charging efficiency can be optimized so that a high engine torque can be obtained. Can be planned.

-Other embodiments-
In the embodiment described above, the case where the present invention is applied to an in-line four-cylinder diesel engine mounted on an automobile has been described. The present invention is applicable not only to automobiles but also to engines used for other purposes. Further, the number of cylinders and the engine type (separate type engine, V-type engine, etc.) are not particularly limited.

  In the above-described embodiment, the NSR catalyst 75 and the DPNR catalyst 76 are provided as the manipulator 77. However, the manifold 77 may be provided with an NSR catalyst 75 and a DPF (Diesel Particle Filter).

  Moreover, in the said embodiment, the equal fuel injection pressure line was allocated to the equal power line over the whole engine operation area | region. The present invention is not limited to this, and a region where the equal fuel injection pressure line does not coincide with the equal power line may be provided in a part of the engine operation region (for example, in the vicinity of the maximum torque line Tmax).

  In the above-described embodiment, the fuel pressure target value at the start of the fuel pressure increase control is assigned to the power line in FIG. 11 so that power (engine output) corresponding to the amount of depression of the accelerator pedal can be obtained. The obtained fuel injection pressure was set as the target fuel pressure. The present invention is not limited to this, and in order to further improve the acceleration performance of the vehicle, the fuel injection pressure higher than the fuel injection pressure assigned to the power line in FIG. 11 corresponding to the depression amount of the accelerator pedal is targeted. The fuel pressure may be set.

In the above-described embodiment, the above charging efficiency changing operation is executed along with the fuel pressure increasing operation that is executed when an acceleration request is made to the driver and the amount of depression of the accelerator pedal is increased during traveling on an uphill road. Explained when to do. The present invention is not limited to this, and when the fuel pressure is increased due to other factors, the charging efficiency changing operation may be executed accordingly. For example, in situations where the engine torque with the increase in EGR amount is decreased, when the fuel pressure increase operation is performed to increase the engine torque, it may be performed to the charging efficiency change operation.

It is a schematic block diagram of the engine which concerns on embodiment, and its control system. It is sectional drawing which shows the combustion chamber of a diesel engine, and its peripheral part. It is sectional drawing along the axial center of the turbine shaft in a turbocharger. It is sectional drawing which expands and shows the turbine wheel of a turbocharger, and its peripheral part. It is a front view of the variable nozzle vane mechanism in the state where the nozzle vane opening degree was set large. It is a rear view of the variable nozzle vane mechanism in a state where the nozzle vane opening degree is set to be large. It is a front view of the variable nozzle vane mechanism in the state where the nozzle vane opening degree was set small. It is a rear view of the variable nozzle vane mechanism in the state where the nozzle vane opening degree was set small. It is a block diagram which shows the structure of control systems, such as ECU. It is a wave form diagram which shows the change state of the heat release rate at the time of an expansion stroke. It is a figure which shows a fuel pressure setting map. It is a figure which shows a filling efficiency setting map. It is a figure which shows the relationship between the charging efficiency in a certain engine operating state, and an engine torque. It is a wave form diagram which shows the change state of the heat release rate before and at the time of execution of fuel pressure increase control. The relationship between the charging efficiency and the engine torque, the relationship between the charging efficiency at the fuel pressure before the start of the fuel pressure increase control and the engine torque is indicated by a broken line, and the charging efficiency at the fuel pressure after the start of the fuel pressure increase control and the engine torque It is a figure which shows this relationship with a continuous line. FIG. 6 is a diagram showing a relationship between a fuel pressure increase amount and a filling efficiency increase amount set corresponding thereto when executing a charging efficiency changing operation. It is a figure which shows the relationship between the engine speed for demonstrating operation | movement when an engine driving | running state reaches the maximum torque line, and an engine torque.

Explanation of symbols

1 engine (internal combustion engine)
3 Combustion chamber 23 Injector (fuel injection valve)
47 Accelerator opening sensor 5 Turbocharger (supercharger)
52c Turbine wheel 9 Variable nozzle vane mechanism (Filling efficiency variable mechanism)
96 nozzle vanes

Claims (5)

In an intake air control apparatus for an internal combustion engine provided with a charging efficiency variable mechanism that varies a charging efficiency of intake air supplied toward a cylinder of a compression ignition type internal combustion engine,
When the fuel pressure increase operation for temporarily increasing the fuel pressure is executed, the larger the fuel pressure increase amount, the larger the increase amount of the intake charging efficiency set by the variable charging efficiency mechanism is set. An intake control device for an internal combustion engine, characterized by comprising means. The intake control apparatus for an internal combustion engine according to claim 1,
The fuel pressure increasing operation is a situation in which the internal combustion engine torque does not increase in a state in which the internal combustion engine torque reaches the maximum torque at the current internal combustion engine speed when an acceleration request from the vehicle driver is generated. An intake control device for an internal combustion engine, wherein the fuel pressure is temporarily increased until the internal combustion engine speed increases. The intake control apparatus for an internal combustion engine according to claim 1 or 2,
The intake control device for an internal combustion engine, wherein the fuel pressure increasing operation is an operation for increasing the combustion speed in the cylinder by temporarily increasing the fuel pressure. The intake control device for an internal combustion engine according to claim 1, 2, or 3,
The charging efficiency variable mechanism is provided in the supercharger and changes the flow area of the gas flowing toward the turbine wheel by changing the opening degree of the nozzle vane that can be opened and closed by the variable nozzle vane mechanism. An intake air control apparatus for an internal combustion engine, wherein the intake air charging efficiency is changed by changing a supercharging pressure. The intake control device for an internal combustion engine according to any one of claims 1 to 4,
The charging efficiency changing means is a vehicle driver's acceleration request from the light load operation region of the internal combustion engine in which EGR for recirculating a part of the exhaust gas from the exhaust system of the internal combustion engine to the intake system is performed. When the operation is shifted to the operating range of the internal combustion engine that does not execute the above, when the fuel pressure increase operation is executed, the intake charging efficiency set by the variable charging efficiency mechanism is changed. An intake control device for an internal combustion engine.

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