JP2016011588A - Reciprocating piston engine valve gear control unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a configuration capable of ensuring a large quantity of internal EGR gas.SOLUTION: An intake valve drive mechanism (VVL 71) opens an intake valve 21 so that a lift shelf part 213 is present on a valve opening side of a lift curve 212, and an exhaust valve drive mechanism (VVL 73) opens an exhaust valve 22 so that a lift shelf part 223 is present on a valve closing side of a lift curve 222. The intake valve drive mechanism (VVT 72) and the exhaust valve drive mechanism (VVT 74) are configured to regulate a quantity of EGR gas by changing a phase of opening/closing timing of the intake valve 21 and a phase of opening/closing timing of the exhaust valve 22, and to locate both the lift shelf part 213 of the intake valve 21 and the lift shelf part 223 of the exhaust valve 22 at a top dead center of a piston 14 when the opening timing of the intake valve 21 is set to the most advanced position and the closing timing of the exhaust valve 22 to the most retarded position, respectively.

Description

  The technology disclosed herein relates to a valve control device for a reciprocating piston engine.

  For example, in Patent Document 1, in a premixed compression auto-ignition engine, an exhaust valve opened during an exhaust stroke is opened again during an intake stroke, whereby a part of the exhaust gas discharged to the exhaust port is released into the cylinder. The so-called exhaust valve is opened twice. This engine adjusts the amount of exhaust gas introduced into the cylinder (that is, the amount of internal EGR gas) by changing the phase of the opening / closing timing of the exhaust valve. By adjusting the amount of internal EGR gas introduced into the cylinder, the temperature in the cylinder is adjusted, and as a result, the timing of self-ignition can be controlled.

  Patent Document 2 describes a compression self-ignition gasoline engine in which a part of exhaust gas is introduced into a cylinder by opening the exhaust valve twice, as in Patent Document 1. In this engine, the valve lift curve of the exhaust valve that opens during the exhaust stroke and the valve lift curve of the exhaust valve that opens during the intake stroke are from the advance side to the retard side across the exhaust top dead center. It is described to be continuous. As a result, when the piston descends after exhaust top dead center, at least the exhaust valve is opened, so that the pump loss is reduced and fuel efficiency is improved.

JP 2008-51017 A JP 2012-188949 A

  By the way, in an engine in which an air-fuel mixture in a cylinder is burned by controlled auto ignition (CAI) or compression ignition (CI), a large amount is used to improve ignitability in an operation region where the load is low. It is necessary to introduce the internal EGR gas into the cylinder. For example, as described in Patent Document 2, it is advantageous for increasing the amount of exhaust gas introduced into the cylinder to keep the exhaust valve open from the exhaust stroke to the intake stroke. . However, in this configuration, the lift amount of the exhaust valve when the piston reaches top dead center is limited to a predetermined amount or less in order to avoid interference with the upper surface of the piston. For this reason, it is difficult to further increase the amount of internal EGR gas.

  To stabilize CAI combustion, it is also effective to increase the geometric compression ratio. However, when the geometric compression ratio is increased, the distance between the upper surface of the piston and the ceiling surface of the combustion chamber (that is, the lower surface of the cylinder head) when the piston reaches top dead center is shortened. Therefore, the lift amount of the exhaust valve when the piston is near top dead center must be further reduced. In an engine having a high geometric compression ratio, it is difficult to ensure a sufficient amount of internal EGR gas.

  The technology disclosed herein has been made in view of the above points, and an object thereof is to realize a configuration capable of securing a large amount of internal EGR gas.

  The technology disclosed herein relates to a valve control device for a reciprocating piston engine, and this device is configured to be inserted into the cylinder and reciprocate within the cylinder. A piston, an intake valve configured to open and close an intake port for sucking gas into the cylinder, an exhaust valve configured to open and close an exhaust port for exhausting gas from the cylinder, and open and close the intake valve An intake valve drive mechanism configured to drive, and an exhaust valve drive mechanism configured to open and close the exhaust valve.

  Then, the intake valve drive mechanism maintains the open state of the intake valve with respect to the progress of the crank angle on the valve opening side of the lift curve having a peak during the intake stroke with a lift amount lower than the peak. The intake valve is opened so as to have a lift shelf, and the exhaust valve drive mechanism has a lift amount lower than the peak on the valve closing side of the lift curve having a peak during the exhaust stroke. The exhaust valve is opened so that the valve opening state is maintained with respect to the crank angle, and the intake valve drive mechanism and the exhaust valve drive mechanism And adjusting the internal EGR gas amount by changing the opening / closing timing of the exhaust valve, when the opening timing of the intake valve is advanced most and the closing timing of the exhaust valve is delayed most, Lift of the intake valve Parts and lift ledge of the exhaust valve are both being configured to be positioned top dead center of the piston.

  According to this configuration, the lift curve of the intake valve has the lift shelf on the valve opening side. In the lift shelf, the intake valve is kept open with a predetermined lift amount with respect to the progress of the crank angle. Therefore, after the intake valve is opened, the intake shelf is kept in the open state after the valve is opened. The valve closes through a peak in the process. The lift curve of the exhaust valve has a lift shelf on the valve closing side. Therefore, after the exhaust valve has opened, after passing through a peak during the exhaust stroke, the exhaust valve maintains the valve open state at the lift shelf and closes.

  By opening the intake valve during the exhaust stroke, a part of the exhaust gas in the cylinder is discharged to the intake port, and the exhaust gas is reintroduced into the cylinder together with fresh air. Further, by opening the exhaust valve during the intake stroke, part of the exhaust gas discharged to the exhaust port during the exhaust stroke is reintroduced into the cylinder during the intake stroke.

  The amount of exhaust gas introduced into the cylinder (that is, the amount of internal EGR gas) depends on the area of the lift curve of the intake valve that opens during the exhaust stroke and the area of the lift curve of the exhaust valve that opens during the intake stroke Related to. The larger the area, the greater the amount of exhaust gas introduced into the cylinder. In a conventional configuration in which part of the exhaust gas is introduced into the cylinder by opening the exhaust valve twice, the amount of exhaust gas introduced into the cylinder depends on the area of the lift curve of the exhaust valve that opens during the intake stroke. Is determined.

  On the other hand, in the above-described configuration, by providing the lift shelf on the lift curve of the exhaust valve, the area of the lift curve of the exhaust valve that opens during the intake stroke increases, and in addition, the lift curve of the intake valve By providing a lift shelf, the area of the lift curve of the intake valve that opens during the exhaust stroke is increased. Therefore, this configuration is advantageous in increasing the maximum amount of internal EGR gas compared to the conventional configuration in which the exhaust valve is opened twice.

  In the above configuration, when the opening timing of the intake valve is advanced most and the closing timing of the exhaust valve is retarded most, both the lift shelf of the intake valve and the lift shelf of the exhaust valve are It is configured to be located at the top dead center. As a configuration for changing the opening / closing timing of the intake valve and the exhaust valve, it is possible to employ a hydraulic or electric variable valve timing mechanism that changes the rotational phase of the camshaft with respect to the crankshaft. However, it is not limited to these structures.

  The lift amount of the lift shelf of the intake valve and the lift amount of the lift shelf of the exhaust valve are limited to avoid interference with the upper surface of the piston located at the top dead center. However, since the lift shelves are provided for both the intake valve and the exhaust valve, a large amount of internal EGR gas can be secured even if the lift amount of the lift shelves is small. This ensures a large amount of internal EGR gas especially when the geometric compression ratio of the engine body is high and the distance between the piston upper surface and the combustion chamber ceiling surface is short when the piston is located at the top dead center. This is advantageous. Therefore, since this engine can achieve both a large amount of internal EGR gas and a high geometric compression ratio, the engine is suitable for self-ignition combustion.

  Here, from the viewpoint of securing a large amount of internal EGR gas, the lift amount of the lift shelves of the intake valve and the exhaust valve is preferably set to the maximum lift amount as long as interference with the piston upper surface is avoided. However, it is not limited to the maximum lift amount. In addition, the lift amount of the lift shelf of the intake valve and the exhaust valve is preferably the maximum lift amount and should be constant with the progress of the crank angle, but the lift amount is increased or decreased with the progress of the crank angle. May be. Furthermore, the lift amount of the lift shelf may be the same for the intake valve and the exhaust valve, or may be different from each other. For example, the lift amount of the lift shelf of the intake valve and the lift amount of the lift shelf of the exhaust valve may not be the same due to the shape of the upper surface of the piston, the use of an offset crank, or the like.

  Furthermore, as the opening / closing timing of the intake valve is changed by the intake valve driving mechanism, the phase of the lift shelf is changed, so the area of the lift curve of the intake valve that opens during the exhaust stroke is changed. As the opening / closing timing of the exhaust valve is changed by the exhaust valve driving mechanism, the phase of the lift shelf is changed, so that the area of the lift curve of the exhaust valve that opens during the intake stroke is changed. Therefore, this configuration adjusts the internal EGR gas amount by both changing the opening / closing timing of the intake valve by the intake valve driving mechanism and changing the opening / closing timing of the exhaust valve by the exhaust valve driving mechanism. It becomes possible to do. The internal EGR gas amount is adjusted corresponding to the operating state of the engine.

  Here, in general, in the configuration in which the opening / closing timing of the intake valve or the exhaust valve is changed by changing the rotational phase of the camshaft relative to the crankshaft by hydraulic pressure or electricity, the time required for the change (that is, the phase change speed) Are constrained by the configuration of the drive mechanism (ie, hardware limitations). For example, in response to changes in the operating state of the engine due to the driver's accelerator operation, even if the internal EGR gas amount is to be reduced or increased, the conventional exhaust valve opening / closing timing changes the opening / closing timing of the exhaust valve. Since the internal EGR gas amount is changed only by this, a relatively long time is required for the change of the internal EGR gas amount due to the hardware limit related to the phase change of the exhaust valve. As a result, in the conventional configuration, the responsiveness of changes in the operating state of the engine to the driver's accelerator operation is reduced.

  On the other hand, in the above configuration, when the internal EGR gas amount is adjusted, the opening / closing timings of both the intake valve and the exhaust valve are changed. For this reason, the phase change amounts on the intake valve side and the exhaust valve side can be combined, and the phase change amount can be almost doubled compared to the conventional method. The time required to change to the target internal EGR gas amount is almost ½ of the conventional configuration even if the hardware limit is the same as the conventional one. As a result, the responsiveness of the change in the operating state of the engine with respect to the driver's accelerator operation is significantly increased as compared with the conventional configuration.

  Each of the intake valve drive mechanism and the exhaust valve drive mechanism controls the opening timing of the intake valve when the operating state of the engine body is in a predetermined low load region and the air-fuel mixture in the cylinder self-ignites and burns. The internal EGR gas amount may be maximized by advancing the most and delaying the closing timing of the exhaust valve the most.

  As described above, this configuration can increase the maximum amount of internal EGR gas. Therefore, the ignitability and / or stability of self-ignition combustion is improved by introducing a large amount of internal EGR gas into the cylinder in a low load region where the ignitability and / or stability of self-ignition combustion is reduced.

  The intake valve drive mechanism may adjust the opening / closing timing of the intake valve so that the closing timing of the intake valve is in a range of 30 ° before bottom dead center to 70 ° CA after bottom dead center.

  The exhaust valve drive mechanism may adjust the opening / closing timing of the exhaust valve so that the opening timing of the exhaust valve is in a range of 70 ° before bottom dead center to 30 ° CA after bottom dead center. .

  The opening timing of the intake valve may be set in a range of 100 ° to 40 ° CA before top dead center when the opening is most advanced. The closing timing of the exhaust valve may be set in a range of 40 ° to 100 ° CA after top dead center when the exhaust valve is most retarded.

  The opening timing of the intake valve when set to the most advanced side and the closing timing of the exhaust valve when set to the most retarded side are respectively the required maximum internal EGR gas amount (in other words, the maximum internal EGR gas amount). And an adjustment range between the minimum internal EGR gas amount and the above range.

  As described above, according to the valve control device for the above-described reciprocating piston engine, interference with the piston can be avoided by providing the lift shelf in each of the lift curve of the intake valve and the lift curve of the exhaust valve. However, it is possible to secure a large amount of internal EGR gas and shorten the response time for adjusting the internal EGR gas amount.

It is the schematic which shows the structure of an engine. It is a block diagram concerning control of an engine. (A) Exhaust valve and intake valve lift curves in normal mode and special mode, (b) Exhaust valve and intake valve lift curves in special mode, (c) Exhaust valve in special mode 4 is an example of phase change of a lift curve of an intake valve. It is a diagram which illustrates the valve opening period (working angle) of an intake valve and an exhaust valve, and the variation | change_quantity of a phase. It is an example (the lower figure) of the lift curve of an exhaust valve and an intake valve in the conventional composition, and an example of change of intake pressure, exhaust pressure, and in-cylinder pressure. (A) A part of the p-v diagram of the engine in the conventional configuration, (b) A part of the p-v diagram of the engine in the present configuration. It is a figure which illustrates the operation control map of an engine. It is a figure which illustrates the relationship of the EGR rate with respect to the level of engine load. In the conventional configuration, when the engine load increases, (a) change in the phase of the opening / closing timing of the exhaust valve, (b) change in gas composition in the cylinder, (c) change in fuel amount, and (d) change in pump loss. And (e) a change in the phase of the opening / closing timing of the exhaust valve, (f) a change in the phase of the opening / closing timing of the intake valve, and (g) in the cylinder, when the engine load increases in this configuration. It is each time chart which illustrates the change of a gas composition, (h) Change of fuel amount, and (i) Change of pump loss.

  Hereinafter, an embodiment of a valve control device for a reciprocating piston engine will be described with reference to the drawings. The following description of preferred embodiments is exemplary.

(Entire engine configuration)
1 and 2 show a schematic configuration of an engine (engine body) 1. The engine 1 is a gasoline engine that is mounted on a vehicle and supplied with a fuel containing at least gasoline. The engine 1 includes a cylinder block 11 provided with a plurality of cylinders 18 (only one cylinder is shown in FIG. 1, but four cylinders are provided in series, for example), and the cylinder block 11 is arranged on the cylinder block 11. The cylinder head 12 is provided, and an oil pan 13 is provided below the cylinder block 11 and stores lubricating oil. A piston 14 connected to the crankshaft 15 via a connecting rod 142 is fitted in each cylinder 18 so as to be able to reciprocate. On the upper surface of the piston 14, a cavity 141 like a reentrant type in a diesel engine is formed. The cavity 141 is opposed to an injector 67 described later when the piston 14 is positioned near the compression top dead center. The cylinder head 12, the cylinder 18 and the piston 14 having the cavity 141 define a combustion chamber. The shape of the combustion chamber is not limited to the shape illustrated. For example, the shape of the cavity 141, the upper surface shape of the piston 14, the shape of the ceiling portion of the combustion chamber, and the like can be changed as appropriate.

  The gasoline engine 1 is set to a relatively high geometric compression ratio of 15 or more for the purpose of improving the theoretical thermal efficiency and stabilizing combustion by compression autoignition described later. The geometric compression ratio may be set as appropriate in the range of about 15 to 20, and may be 18, for example.

  The cylinder head 12 is formed with an intake port 16 and an exhaust port 17 for each cylinder 18. The intake port 16 and the exhaust port 17 include an intake valve 21 and an exhaust valve that open and close the opening on the combustion chamber side. 22 are arranged respectively.

  Among the valve systems that drive the intake valve 21 and the exhaust valve 22, respectively, on the intake side, a variable mechanism that switches the operation mode of the intake valve 21 between a normal mode and a special mode (see FIG. 2; hereinafter, VVL (Variable 71) (referred to as ValveLift) and a phase variable mechanism (hereinafter referred to as VVT (Variable ValveTiming)) 72 capable of changing the rotation phase of the intake camshaft with respect to the crankshaft 15. The normal mode and the special mode have different cam profiles. A drive mechanism of the intake valve 21 is configured including the VVL 71 and the VVT 72. On the exhaust side, a VVL 73 that switches the operation mode of the exhaust valve 22 between a normal mode and a special mode and a VVT 74 that can change the rotation phase of the exhaust camshaft with respect to the crankshaft 15 are provided. Yes. A drive mechanism for the exhaust valve 22 is configured including the VVL 73 and the VVT 74. Details of the structure of the drive mechanism of the intake valve 21 and the exhaust valve 22 will be described later.

  In addition, an injector 67 that directly injects fuel into the cylinder 18 is attached to the cylinder head 12 for each cylinder 18. The injector 67 is arranged so that its nozzle hole faces the combustion chamber from the center portion of the ceiling surface of the combustion chamber. The injector 67 directly injects an amount of fuel corresponding to the operation state of the engine 1 at an injection timing set according to the operation state of the engine 1 into the combustion chamber. In this example, the injector 67 is a multi-hole injector having a plurality of nozzle holes, although detailed illustration is omitted. Thereby, the injector 67 injects the fuel so that the fuel spray spreads radially from the center position of the combustion chamber. At the timing when the piston 14 is positioned near the compression top dead center, the fuel spray injected radially from the central portion of the combustion chamber flows along the wall surface of the cavity 141 formed on the upper surface of the piston. It can be paraphrased that the cavity 141 is formed so that the fuel spray injected at the timing when the piston 14 is located near the compression top dead center is contained therein. This combination of the multi-hole injector 67 and the cavity 141 is an advantageous configuration for shortening the mixture formation period and the combustion period after fuel injection. In addition, the injector 67 is not limited to a multi-hole injector, and may be an outside-opening type injector.

  A fuel tank (not shown) and the injector 67 are connected to each other by a fuel supply path. A fuel supply system 62 including a fuel pump 63 and a common rail 64 and capable of supplying fuel to the injector 67 at a relatively high fuel pressure is interposed on the fuel supply path. The fuel pump 63 pumps fuel from the fuel tank to the common rail 64, and the common rail 64 can store the pumped fuel at a relatively high fuel pressure. When the injector 67 is opened, the fuel stored in the common rail 64 is injected from the injection port of the injector 67. Here, although not shown, the fuel pump 63 is a plunger type pump and is driven by the engine 1. The fuel supply system 62 configured to include this engine-driven pump enables the fuel with a high fuel pressure of 30 MPa or more to be supplied to the injector 67. The fuel pressure may be set to about 120 MPa at the maximum. The pressure of the fuel supplied to the injector 67 is changed according to the operating state of the engine 1. The fuel supply system 62 is not limited to this configuration.

  A spark plug 25 for forcibly igniting the air-fuel mixture in the combustion chamber is also attached to the cylinder head 12. In this example, the spark plug 25 is disposed through the cylinder head 12 so as to extend obliquely downward from the exhaust side of the engine 1. The tip of the spark plug 25 is disposed facing the cavity 141 of the piston 14 located at the compression top dead center.

  As shown in FIG. 1, an intake passage 30 is connected to one side of the engine 1 so as to communicate with the intake port 16 of each cylinder 18. On the other hand, an exhaust passage 40 for discharging burned gas (exhaust gas) from the combustion chamber of each cylinder 18 is connected to the other side of the engine 1.

  An air cleaner 31 that filters intake air is disposed at the upstream end of the intake passage 30. A surge tank 33 is disposed near the downstream end of the intake passage 30. The intake passage 30 on the downstream side of the surge tank 33 is an independent passage branched for each cylinder 18, and the downstream end of each independent passage is connected to the intake port 16 of each cylinder 18.

  Between the air cleaner 31 and the surge tank 33 in the intake passage 30, a water-cooled intercooler / warmer 34 that cools or heats the air and a throttle valve 36 that adjusts the amount of intake air to each cylinder 18 are arranged. It is installed. An intercooler bypass passage 35 that bypasses the intercooler / warmer 34 is also connected to the intake passage 30. The intercooler bypass passage 35 is connected to an intercooler for adjusting the flow rate of air passing through the passage 35. A bypass valve 351 is provided. Adjusting the temperature of fresh air introduced into the cylinder 18 by adjusting the ratio between the passage flow rate of the intercooler bypass passage 35 and the passage flow rate of the intercooler / warmer 34 through the opening degree adjustment of the intercooler bypass valve 351. Is possible. It should be noted that the intercooler / warmer 34 and its associated members can be omitted.

  The upstream portion of the exhaust passage 40 is constituted by an exhaust manifold having an independent passage branched for each cylinder 18 and connected to the outer end of the exhaust port 17 and a collecting portion where the independent passages gather. A direct catalyst 41 and an underfoot catalyst 42 are connected downstream of the exhaust manifold in the exhaust passage 40 as exhaust purification devices for purifying harmful components in the exhaust gas. Each of the direct catalyst 41 and the underfoot catalyst 42 includes a cylindrical case and, for example, a three-way catalyst disposed in a flow path in the case. The engine 1 does not include a NOx purification catalyst.

  A portion between the surge tank 33 and the throttle valve 36 in the intake passage 30 and a portion upstream of the direct catalyst 41 in the exhaust passage 40 are used for returning a part of the exhaust gas to the intake passage 30. They are connected via a passage 50. The EGR passage 50 includes a main passage 51 in which an EGR cooler 52 for cooling the exhaust gas with engine coolant is disposed, and an EGR cooler bypass passage 53 for bypassing the EGR cooler 52. ing. The main passage 51 is provided with an EGR valve 511 for adjusting the amount of exhaust gas recirculated to the intake passage 30, and the EGR cooler bypass passage 53 has a flow rate of exhaust gas flowing through the EGR cooler bypass passage 53. An EGR cooler bypass valve 531 for adjustment is provided.

  The engine 1 is controlled by a powertrain control module (hereinafter referred to as PCM) 10. The PCM 10 includes a microprocessor having a CPU, a memory, a counter timer group, an interface, and a path connecting these units. This PCM 10 constitutes a controller.

As shown in FIGS. 1 and 2, detection signals from various sensors SW <b> 1 to SW <b> 16 are input to the PCM 10. The various sensors include the following sensors. That is, on the downstream side of the air cleaner 31, the air flow sensor SW 1 that detects the flow rate of fresh air, the intake air temperature sensor SW 2 that detects the temperature of fresh air, and the downstream side of the intercooler / warmer 34, and the intercooler / warmer 34. A second intake air temperature sensor SW3 for detecting the temperature of fresh air after passing through the EGR gas temperature sensor SW4, which is disposed in the vicinity of the connection portion of the EGR passage 50 with the intake passage 30 and detects the temperature of the external EGR gas. An intake port temperature sensor SW5 that is attached to the intake port 16 and detects the temperature of the intake air just before flowing into the cylinder 18, and an in-cylinder pressure sensor SW6 that is attached to the cylinder head 12 and detects the pressure in the cylinder 18. The exhaust passage 40 is disposed in the vicinity of the connection portion of the EGR passage 50, and the exhaust temperature and the exhaust respectively. Exhaust temperature sensor SW7 and exhaust pressure sensor SW8 for detecting a force, and is disposed on the upstream side of the direct catalyst 41, the linear O ₂ sensor SW9, direct catalyst 41 and underfoot catalyst 42 for detecting the oxygen concentration in the exhaust gas The lambda O ₂ sensor SW10 that detects the oxygen concentration in the exhaust gas, the water temperature sensor SW11 that detects the temperature of the engine coolant, the crank angle sensor SW12 that detects the rotation angle of the crankshaft 15, and the vehicle An accelerator opening sensor SW13 for detecting an accelerator opening corresponding to an operation amount of an accelerator pedal (not shown), intake-side and exhaust-side cam angle sensors SW14, SW15, and a common rail 64 of the fuel supply system 62 are attached. The fuel pressure sensor SW16 detects the fuel pressure supplied to the injector 67. The

  The PCM 10 performs various calculations based on these detection signals to determine the state of the engine 1 and the vehicle, and accordingly, the injector 67, the spark plug 25, the VVL 71 and VVT 72 on the intake valve side, and the exhaust valve side Control signals are output to the actuators of the VVL 73 and VVT 74, the fuel supply system 62, and various valves (throttle valve 36, intercooler bypass valve 351, EGR valve 511, EGR cooler bypass valve 531). Thus, the PCM 10 operates the engine 1.

(Configuration of valve drive mechanism)
Although the detailed illustration of the structure of the VVL 71 on the intake side is omitted, the operating state of the two types of first and second cams having different cam profiles and one of the first and second cams is shown. A lost motion mechanism that selectively transmits to the intake valve 21 is included. The first cam is a cam profile having one cam peak so as to be a lift curve 211 indicated by a solid line in FIG. 3A, and the second cam is a lift curve 212 indicated by a broken line in FIG. Thus, it is a cam profile which has the lift shelf part 213 which maintains a lift substantially constant with respect to advance of a crank angle on the valve opening side in the lift curve 212. Note that the cam profile shown in FIG. 3 is an example.

  When the lost motion mechanism is transmitting the operating state of the first cam to the intake valve 21, as illustrated by the solid line in FIG. 3A, the intake valve 21 is opened and then the crank angle advances. After the lift amount gradually increases and reaches a predetermined peak at least during the intake stroke, the lift amount gradually decreases as the crank angle progresses, and the operation is performed in the normal mode in which the valve is closed as it is. On the other hand, when the loft motion mechanism is transmitting the operating state of the second cam to the intake valve 21, as illustrated by a broken line in FIG. 3A, the intake valve 21 opens during, for example, the exhaust stroke. After the valve operation, while maintaining a predetermined lift amount in the lift shelf 213, the piston 14 reaches the top dead center and reaches the intake stroke, and the lift amount is increased again as the crank angle progresses to reach a predetermined peak. After that, as the crank angle progresses, the lift amount gradually becomes smaller and the valve operates in a special mode. The normal mode and the special mode of the VVL 71 are switched according to the operating state of the engine 1. Specifically, the special mode is used when the internal EGR gas is introduced into the cylinder 18, and the normal mode is used at other times. In the following description, operating the VVL 71 in the normal mode is referred to as “turning off the VVL 71”, and operating the VVL 71 in the special mode and performing internal EGR is referred to as “turning on the VVL 71”. There is.

  Here, the cam profile of the second cam in the VVL 71 on the intake side will be described in more detail with reference to FIGS. FIG. 3B corresponds to the lift curve of the intake valve 21 when the phase of the opening timing of the intake valve 21 is set to the most retarded side, and the solid line in FIG. This corresponds to the lift curve of the intake valve 21 when the timing phase is set to the most advanced side. As described above, the second cam is configured to have the lift shelf 213 on the valve opening side of the lift curve 212. Here, the valve opening side in the lift curve 212 corresponds to the valve opening side when the both sides sandwiching the peak in the lift curve 212 are divided into the valve opening side and the valve closing side. As indicated by a solid line in FIG. 3C, when the phase of the opening timing of the intake valve 21 is advanced by the VVT 72, the lift shelf 213 is positioned at least in the second half of the exhaust stroke. The “second half” here corresponds to the second half when the exhaust stroke is divided into the first half and the second half. Accordingly, a part of the exhaust gas in the cylinder 18 is discharged to the intake port 16 during the exhaust stroke. The exhaust gas discharged to the intake port 16 is introduced into the cylinder 18 together with fresh air as the intake valve 21 opens during the intake stroke. Thus, a part of the exhaust gas substantially remains in the cylinder 18 (that is, internal EGR control).

  The lift amount of the lift shelf 213 is set to a lift amount lower than the peak of the lift curve 212. As indicated by a solid line in FIG. 3C, when the phase of the opening / closing timing of the intake valve 21 is advanced by the VVT 72, the lift shelf 213 may be located at the top dead center. Therefore, in this embodiment, the lift amount of the lift shelf 213 is set to be the maximum lift amount Linmax as long as it does not interfere with the upper surface of the piston 14 located at the top dead center (see FIG. 3B). ). In this way, the maximum amount of internal EGR can be set as large as possible. For example, the lift amount of the lift shelf 213 can be appropriately set within a range of 1/2 or less with respect to the lift amount at the peak of the lift curve 212. In order to set the maximum amount of internal EGR as large as possible, it is desirable that the lift amount of the lift shelf 213 be constant at the maximum lift amount Linmax. However, the lift amount of the lift shelf 213 may be changed so as to be slightly increased or slightly decreased within a range in which the lift amount is substantially maintained with respect to the progress of the crank angle. You may let them. It can be said that the lift shelf 213 is a portion where the rate of change of the lift amount becomes a predetermined value or less with respect to the progress of the crank angle. The change in the lift amount in the lift shelf 213 may be continuous or stepwise with respect to the progress of the crank angle.

  Further, the length of the lift shelf 213 (that is, the length of the crank angle in the traveling direction) can satisfy the required maximum internal EGR gas amount based on the maximum lift amount Linmax that can be set. Set to Here, as shown by a solid line in FIG. 3C, the most retarded position of the lift shelf 213 is set to be located at the top dead center when the opening timing of the intake valve 21 is advanced most. The Therefore, in order to increase the internal EGR gas amount in order to satisfy the required maximum internal EGR gas amount, the length of the lift shelf 213 is extended to the advance side. As a result, the opening timing of the intake valve 21 is set to the advance side. Further, as the length of the lift shelf 213 is extended to the advance side, the phase change amount of the opening / closing timing of the intake valve 21 is also increased.

  As with the intake side described above, the exhaust-side VVL 73 is not shown in detail in its configuration, but any of two types of first and second cams having different cam profiles, and the first and second cams. A lost motion mechanism for selectively transmitting the operating state of one of the cams to the exhaust valve 22 is configured. The first cam is a cam profile having one cam peak so as to be a lift curve 221 indicated by a solid line in FIG. 3A, and the second cam is a lift curve 222 indicated by a broken line in FIG. Thus, it is a cam profile which has the lift shelf part 223 which maintains a lift substantially constant with advance of a crank angle on the valve opening side in the lift curve 222. Note that the cam profile shown in FIG. 3 is an example.

  When the lost motion mechanism of the VVL 73 on the exhaust side transmits the operating state of the first cam to the exhaust valve 22, the exhaust valve 22 is opened after the valve is opened as illustrated by the solid line in FIG. As the angle progresses, the lift amount gradually increases. At least after reaching a predetermined peak during the exhaust stroke, the lift amount gradually decreases as the crank angle progresses, and the valve operates in the normal mode in which the valve is closed as it is. On the other hand, when the loft motion mechanism is transmitting the operating state of the second cam to the exhaust valve 22, as illustrated by a broken line in FIG. 3A, the exhaust valve 22 is opened during the exhaust stroke, for example. After the valve operation, the lift amount gradually increases as the crank angle progresses, and after reaching a predetermined peak during the exhaust stroke, the piston 14 reaches top dead center while maintaining the predetermined lift amount in the lift shelf 223. Then, the intake stroke is reached, and thereafter, the lift amount gradually decreases as the crank angle advances, and the valve operates in a special mode in which the valve is closed. The normal mode and the special mode of the VVL 73 are switched according to the operating state of the engine 1. Specifically, the special mode is used when the internal EGR gas is introduced into the cylinder 18, and the normal mode is used at other times. In the following description, operating the VVL 73 in the normal mode is referred to as “turning off the VVL 73”, and operating the VVL 73 in the special mode and performing internal EGR is referred to as “turning on the VVL 73”. There is.

  The cam profile of the second cam in the exhaust VVL 73 is different from the cam profile of the second cam in the intake VVL 71, as illustrated in FIGS. The lift shelf 223 is configured. The valve closing side here corresponds to the valve closing side when the both sides of the peak in the lift curve 222 are divided into the valve opening side and the valve closing side. 3B corresponds to the lift curve of the exhaust valve 22 when the closing timing phase of the exhaust valve 22 is set to the most advanced side, and the solid line in FIG. 3C indicates the exhaust valve 22. This corresponds to the lift curve of the exhaust valve 22 when the phase of the closing timing is set to the most retarded angle side. As shown by a solid line in FIG. 3C, when the phase of the closing timing of the exhaust valve 22 is retarded by the VVT 74, the lift shelf 223 is positioned at least in the first half of the intake stroke. The “first half” here corresponds to the first half when the intake stroke is divided into the first half and the second half. Therefore, part of the exhaust gas discharged to the exhaust port 17 during the exhaust stroke is returned to the cylinder 18 as the exhaust valve 22 opens during the intake stroke. Thus, a part of the exhaust gas substantially remains in the cylinder 18 (that is, internal EGR control).

  Also on the exhaust side, the lift amount of the lift shelf 223 is set to a lift amount lower than the peak of the lift curve 222. In this embodiment, the lift of the lift shelf 213 is based on the same design concept as the intake side. The amount is set to be the maximum lift amount Lexmax as long as it does not interfere with the upper surface of the piston 14 located at the top dead center (see FIG. 3B). In this way, the maximum amount of internal EGR can be set as large as possible. For example, the lift amount of the lift shelf 223 can be appropriately set within a range of 1/2 or less with respect to the lift amount at the peak of the lift curve 222. In the example disclosed here, the lift amount Lexmax of the lift shelf 223 in the lift curve 222 of the exhaust valve 22 is set to be the same as the lift amount Linmax of the lift shelf 213 in the lift curve 212 of the intake valve 21. However, the lift amount Lexmax and the lift amount Linmax may not be the same. For example, the lift amount of the lift shelf 213 of the intake valve 21 and the lift amount of the lift shelf 223 of the exhaust valve 22 may not be made the same due to the shape of the upper surface of the piston 14 or the use of an offset crank. Can happen.

  The lift amount of the lift shelf 223 of the exhaust valve 22 is preferably constant with respect to the progress of the crank angle, but the lift amount is within a range in which the lift amount is substantially maintained with respect to the progress of the crank angle. It may be changed so as to be slightly increased, or may be changed so that the lift amount is slightly reduced. The change in the lift amount may be continuous or stepwise with respect to the progress of the crank angle.

  Further, the length of the lift shelf 223 (that is, the length of the crank angle in the traveling direction) can satisfy the required maximum internal EGR gas amount based on the settable maximum lift amount Lexmax. Is set to Here, as shown by a solid line in FIG. 3C, the most advanced angle position of the lift shelf 223 is set to be located at the top dead center when the closing timing of the exhaust valve 22 is most retarded. . Therefore, in order to increase the internal EGR gas amount in order to satisfy the required maximum internal EGR gas amount, the length of the lift shelf 213 is extended to the retard side. As a result, the closing timing of the exhaust valve 22 is set to the retard side. Further, as the length of the lift shelf 223 is extended to the retard side, the phase change amount of the opening / closing timing of the exhaust valve 22 also increases.

  The mechanism for changing the lift characteristics of the valve so as to switch between the normal mode and the special mode on each of the intake side and the exhaust side is not limited to the switching between the first cam and the second cam described above. A hydraulically driven valve system that controls the opening and closing of the intake valve 21 and the exhaust valve 22 by controlling the supply and discharge of hydraulic pressure may be employed. Further, an electromagnetically driven valve system that drives the opening and closing of the intake valve 21 and the exhaust valve 22 by an electromagnetic actuator may be employed.

  The intake-side and exhaust-side VVTs 72 and 74 may adopt a known hydraulic or electric structure as appropriate, and illustration of the detailed structure is omitted. In this embodiment, electric VVTs 72 and 74 are employed in order to increase the phase change speed.

  FIG. 4 is a diagram showing an example of the valve opening period (working angle) of the intake valve 21 and the exhaust valve 22 and the phase change amount. In the example of FIG. 4, the intake valve 21 is changed by the electric VVT 72 so that the closing timing (IVC) is in the range of 30 ° before the bottom dead center to 70 ° after the bottom dead center. When the closing timing of the intake valve 21 is set to the most advanced angle phase, a lift curve shown by a solid line in FIG. 3C is obtained, and when the closing timing of the intake valve 21 is set to the most retarded angle phase, FIG. The lift curve indicated by the broken line in FIG. 4 is obtained, and the closing timing of the intake valve 21 is continuously changed during that time (see the arrow in the figure). In the example of FIG. 4, the exhaust valve 22 is changed by the electric VVT 74 so that the opening timing (EVO) is in a range from 70 ° before the bottom dead center to 30 ° after the bottom dead center. When the opening timing of the exhaust valve 22 is set to the most advanced angle phase, the lift curve shown by the broken line in FIG. 3C is obtained, and when the opening timing of the exhaust valve 22 is set to the most retarded angle phase, FIG. The opening curve of the exhaust valve 22 is continuously changed during the lift curve indicated by the solid line (see the arrow in the figure). As indicated by the solid line in FIG. 3C, the top dead center is sandwiched when the opening timing of the intake valve 21 is set to the most advanced phase and the closing timing of the exhaust valve 22 is set to the most retarded phase. On both sides, the overlap between the opening timing of the intake valve 21 and the opening timing of the exhaust valve 22 becomes the largest (that is, the valve overlap amount is maximum, see FIG. 4), and the exhaust gas introduced into the cylinder 18 The amount is maximized. On the other hand, when the opening timing of the intake valve 21 is set to the most retarded phase and the closing timing of the exhaust valve 22 is set to the most advanced phase, as shown by the broken line in FIG. On both sides, the overlap between the opening timing of the intake valve 21 and the opening timing of the exhaust valve 22 is minimized, and the amount of exhaust gas introduced into the cylinder 18 is minimized. In order to minimize the amount of exhaust gas here, the amount of exhaust gas introduced into the cylinder 18 becomes substantially zero, that is, the amount of internal EGR gas becomes substantially zero. Including. When the internal EGR gas amount is changed from large to small, the phase of the opening timing of the intake valve 21 is changed to the retard direction, and the phase of the closing timing of the exhaust valve 22 is changed to the advance direction. Conversely, when the internal EGR gas amount is changed from small to large, the phase of the opening timing of the intake valve 21 is changed to the advance direction, and the phase of the closing timing of the exhaust valve 22 is changed to the retard direction. As will be described in detail later by changing the phases of both the intake valve 21 and the exhaust valve 22, the configuration of the valve operating system disclosed herein is compared with the conventional configuration in which the exhaust valve 22 is opened twice. Thus, there is an advantage that the speed of changing the amount of internal EGR gas from large to small or from small to large becomes high.

  As described above, in this configuration, by providing the lift shelf 213 on the intake valve 21 and the lift shelf 223 on the exhaust valve 22, the maximum internal EGR gas amount can be set to a relatively large amount. Become.

  In the configuration of the conventional valve operating system, as illustrated by a solid line or a broken line in the lower diagram of FIG. 5, the exhaust valve 22 that opens during the exhaust stroke remains open until the intake stroke. The internal EGR control was performed by opening twice. If the internal EGR gas amount is increased when the exhaust valve 22 is opened twice, it is necessary to increase the lift amount of the exhaust valve 22 that opens during the intake stroke (that is, the lift amount at the restart valve). The lift amount when the exhaust valve 22 is restarted cannot be increased so much in order to avoid interference with the piston 14 located at the top dead center. In particular, the engine 1 has a high geometric compression ratio as described above (geometric compression ratio ε = 15 or more, for example, 18), and the piston 14 when the piston 14 reaches top dead center. The distance between the upper surface of the combustion chamber and the ceiling surface of the combustion chamber is short. For this reason, if it is going to avoid interference with piston 14, the lift amount at the time of the restart valve of exhaust valve 22 must be made small. In the conventional configuration, it is difficult to increase the maximum amount of internal EGR gas due to the structure of the engine 1. It is possible to perform internal EGR control by opening the intake valve 21 that opens during the intake stroke twice, that is, the so-called intake valve 21 that opens during the exhaust stroke. Similarly to the double opening of the exhaust valve 22, the lift amount of the intake valve 21 that opens during the exhaust stroke (that is, the lift amount at the time of preceding valve opening) interferes with the piston 14 located at the top dead center. It is difficult to increase the maximum amount of internal EGR gas because it cannot be made so large to avoid.

  On the other hand, in the configuration described above, the lift shelf 213 is provided in the lift curve 212 of the intake valve 21, and the lift shelf 223 is provided in the lift curve 222 of the exhaust valve 22. The lift amount of the lift shelf 213 of the intake valve 21 is limited to avoid interference with the piston 14, and the lift amount of the lift shelf 223 of the exhaust valve 22 is also avoided to avoid interference with the piston 14. Although limited, by providing the lift shelves 213 and 223 in both valves 21 and 22, even if the lift amounts of the lift shelves 213 and 223 are relatively small, the intake valves 21 and the exhaust valves 22 Only one of them can increase the maximum amount of internal EGR compared to the conventional configuration in which the opening is performed twice. This is particularly the case in an engine having a high geometric compression ratio and a short distance between the top surface of the piston 14 and the ceiling surface of the combustion chamber when the piston 14 reaches top dead center, as described above. It will be advantageous in securing.

  In addition, this configuration is more advantageous than the conventional double opening configuration of the exhaust valve 22 in terms of reducing pump loss. The upper diagram of FIG. 5 shows the pressure change (broken line) in the cylinder 18 and the pressure on the intake side when the lift curve of the exhaust valve 22 shown by the solid line and the lift curve of the intake valve 21 shown by the alternate long and short dashed line in the lower diagram of FIG. A change (one-dot chain line) and a pressure change (solid line) on the exhaust side are illustrated. In the conventional configuration in which the exhaust valve 22 is opened twice, the exhaust valve 22 depends on the phase of the closing timing. The intake valve 21 may be opened in the middle period of the intake stroke. In this case, both the intake valve 21 and the exhaust valve 22 are substantially closed during the intake stroke in which the piston 14 descends. Therefore, as shown by the arrows in the upper diagram of FIG. The pressure increases (see ΔP1). Particularly, in the middle of the intake stroke, the descending speed of the piston 14 is the highest, and the volume change in the cylinder 18 per unit time is large. For this reason, as shown in the p-v diagram of FIG. 6A, negative work increases and pump loss tends to increase.

  On the other hand, in this configuration, the lift curve of the intake valve 21 and the lift curve of the exhaust valve 22 are set so as to be line-symmetric with respect to the top dead center. As shown, when the intake valve 21 and the exhaust valve 22 both close (or substantially close), the timing is set near the top dead center. Since the descending speed of the piston 14 is low near the top dead center, the negative pressure in the cylinder 18 does not increase, and the volume change in the cylinder 18 per unit time is small. For this reason, as shown in the p-v diagram shown in FIG. 6B, pump loss hardly occurs.

  As described above, the cam profiles of the intake valve 21 and the exhaust valve 22 are not limited to the illustrated example. In particular, in the second cam, the lift amounts Linmax and Lexmax of the lift shelves 213 and 223 and the lengths of the lift shelves 213 and 223 are changed according to the maximum amount of internal EGR required for the engine 1. For example, assuming that the lift amount of the lift shelves 213 and 223 is set to the maximum lift amount, when the engine 1 is required to have a large maximum amount of internal EGR, the intake valve 21 and the exhaust valve 22 are opened. When the length of the lift shelf is set to be relatively long so that the overlap amount of the period is as large as possible, and the required maximum amount of internal EGR is not so large, the opening period of the intake valve 21 and the exhaust valve 22 The length of the lift shelf is set to be relatively short so that the amount of overlap does not become so large. Further, the adjustment range of the internal EGR gas amount (that is, the difference between the maximum amount and the minimum amount of the internal EGR) is also determined according to the set maximum amount of the internal EGR, and accordingly, the intake valve 21 is adjusted accordingly. The phase change amount and the phase change amount of the exhaust valve 22 are set. That is, when the required maximum amount of internal EGR is large, the adjustment range of the internal EGR gas amount is also increased, so that the phase change amount of the intake valve 21 and the phase change amount of the exhaust valve 22 are both increased and required. When the maximum amount of internal EGR is not so large, the adjustment range of the internal EGR gas amount is not so large, so the phase change amount of the intake valve 21 and the phase change amount of the exhaust valve 22 are relatively small. In the example of FIG. 4, the phase change amount of the intake valve 21 is 100 ° CA, and the phase change amount of the exhaust valve 22 is also 100 ° CA. For example, the phase change amount of the intake valve 21 may be set in a range of 40 to 100 ° CA. Similarly, the phase change amount of the exhaust valve 22 is set in a range of 40 to 100 ° CA, for example. Also good. As a result, when the internal EGR gas amount is maximized (in other words, when the opening timing of the intake valve 21 is advanced most and the closing timing of the exhaust valve 22 is delayed most), the intake valve 21 The opening timing (IVO) is set in the range of 100 to 40 ° CA before top dead center, and the closing timing (EVC) of the exhaust valve 22 is set in the range of 40 ° to 100 ° CA after top dead center. Good.

(Engine operation control)
FIG. 7 shows an example of the operation control map of the engine 1. In order to improve fuel efficiency and exhaust emission performance, the engine 1 is controlled ignition (CAI) without performing ignition by the spark plug 25 in a low load region where the engine load is relatively low. To burn. In the example of FIG. 7, a region lower than the combustion switching load indicated by a solid line corresponds to a self-ignition region (CAI) in which CAI combustion is performed.

  As the load on the engine 1 increases, in CAI combustion, the combustion becomes too steep, causing problems such as combustion noise. Therefore, in the engine 1, in a high load region where the engine load is relatively high, the CAI combustion is stopped and the combustion is switched to the combustion by forced ignition (here, spark ignition (SI)) using the spark plug 25. In the example of FIG. 7, a region equal to or greater than the combustion switching load indicated by a solid line corresponds to a spark ignition region (SI) in which spark ignition combustion is performed. Thus, the engine 1 is configured to switch between the CAI mode and the SI mode in accordance with the operating state of the engine 1, in particular, the load of the engine 1. However, the boundary line for mode switching is not limited to the illustrated example.

  FIG. 8 shows a change in the EGR rate (that is, a change in the gas composition in the cylinder 18) with respect to the load of the engine 1 when the engine speed is constant at a predetermined speed on the low speed side. Hereinafter, the change in the gas composition in the cylinder 18 will be described in order from the low load side to the high load side.

(From minimum load to a specific load _{T 1)}
Low-load region to a certain load T ₁ corresponds to a low load region of the CAI mode, in order to improve the ignitability and stability of the CAI combustion, introducing a relatively high temperature hot EGR gas into the cylinder 18 . As described above, this is because both the intake-side and exhaust-side VVLs 71 and 73 are turned on and the internal EGR gas is introduced into the cylinder 18. The introduction of hot EGR gas increases the compression end temperature in the cylinder 18 (that is, the temperature in the cylinder 18 when the piston 14 reaches compression top dead center), and the ignitability and stability of CAI combustion in a low load range. To increase.

In the CAI mode, the internal EGR gas amount is adjusted while the throttle valve 36 is kept fully open. This is advantageous for reducing pump loss. Further, in the low load region to a certain load _{T 1,} the EGR rate is set to maximum EGR rate _{r max.} As described below, in certain load above T ₁ of the load area, in accordance with the load of the engine 1 becomes higher, when it is set continuously low EGR rate, the load of the engine 1 than the specific load T ₁ is low, the engine Regardless of the level of the load of 1, the EGR rate is made constant at the maximum EGR rate r _max . Limiting the EGR rate to the maximum EGR rate r _max means that if the EGR rate is made higher than that and a large amount of exhaust gas is introduced into the cylinder 18, the specific heat ratio of the gas in the cylinder 18 becomes low. Thus, even if the gas temperature at the start of compression is high, the compression end temperature is conversely lowered.

That is, the exhaust gas contains a large amount of triatomic molecules such as CO ₂ and H ₂ O, and has a higher specific heat ratio than air containing nitrogen (N ₂ ) and oxygen (O ₂ ). Therefore, when the EGR rate is increased and the exhaust gas introduced into the cylinder 18 increases, the specific heat ratio of the gas in the cylinder 18 decreases.

Since the exhaust gas temperature is higher than fresh air, the higher the EGR rate, the higher the temperature in the cylinder 18 at the start of compression. However, the higher the EGR rate, the lower the specific heat ratio of the gas. Therefore, even if compression is performed, the temperature of the gas does not increase so much. As a result, the compression end temperature becomes the highest at a predetermined EGR rate r _max , and EGR Even if the rate is increased, the compression end temperature is lowered.

Therefore, in this engine 1, the compression end temperature is set to the highest becomes EGR rate to a maximum EGR rate _{r max.} Then, when the load of the engine 1 is lower than the specific loads T ₁ sets the EGR rate to a maximum EGR rate r _max, by the compression end temperature is avoided lowered. The maximum EGR rate r _max may be set to 50 to 90%. The maximum EGR rate r _max may be set as high as possible as long as a high compression end temperature can be secured, and is preferably 70 to 90%. In this engine 1, the geometric compression ratio is set to a high compression ratio of 15 or more so that a high compression end temperature can be obtained. Thus, in the engine 1 configured to ensure the highest possible compression end temperature, the maximum EGR rate r _max may be set to about 80%, for example. Setting the maximum EGR rate r _max as high as possible is advantageous in reducing the unburned loss of the engine 1. That is, since the unburned loss tends to increase when the load on the engine 1 is low, setting the EGR rate as high as possible when the load on the engine 1 is lower than the specified load T ₁ It is extremely effective for improvement.

Thus in this engine 1, when the load of the engine 1 is lower than the specific loads T ₁ also, by ensuring a high compression end temperature, thereby ensuring the ignition performance and combustion stability of CAI combustion.

In the region lower than the specific loads T _1, specifically, as shown by the solid line in FIG. 3 (c), is set to the most advance side of the opening timing of the phase of the intake valve 21 to turn on the VVL 71, Similarly, the phase of the closing timing of the exhaust valve 22 with the VVL 73 turned on is set to the most retarded side. Thus, the amount of internal EGR gas introduced into the cylinder 18 is maximized. As described above, this configuration is effective in setting the maximum internal EGR gas amount high (that is, increasing the maximum EGR rate) in the engine 1 having a high geometric compression ratio.

Further, in the region lower than this particular load T _1, within a period of at least the intake stroke until the first half of the compression stroke, the injector 67 injects fuel into the cylinder 18. As a result, a homogeneous air-fuel mixture is formed in the cylinder 18.

(From a particular load _{T 1} to a predetermined load _{T 2)}
In the region from a particular load T ₁ to a predetermined load T _2, it is larger than the excess air ratio λ of the mixture 1. Therefore, the amount of fresh air introduced into the cylinder 18 is greater than the line of λ≈1 indicated by the one-dot chain line in FIG. 8, and the amount of exhaust gas introduced into the cylinder 18 (in this case, the amount of internal EGR gas) is It is less than the line of λ≈1. The excess air ratio λ of the air-fuel mixture is preferably made to be lean at least 2.4. Making the air-fuel mixture lean is advantageous for improving the fuel efficiency by improving the thermal efficiency, and by making the excess air ratio λ 2.4 or more, the generation of RawNOx is suppressed. This makes it possible to ensure the exhaust emission performance in the engine 1 that does not include the NOx purification catalyst. Note that the predetermined load T _2, between the switching load T ₃ to be described later, is provided a section for gradually changing the excess air ratio λ of the gas mixture.

In the region above a certain load T _1, since the fuel injection amount in accordance with the load of the engine 1 is increased to increase the excess air ratio lambda, in maintaining the so 2.4 above, as described above, the required fresh air amount The amount of hot EGR gas gradually decreases with the increase. When the load on the engine 1 is low, the temperature in the cylinder 18 at the start of compression is increased by increasing the amount of hot EGR gas introduced, and accordingly, the compression end temperature is increased to increase the ignitability of compression self-ignition and the compression. This is advantageous in increasing the stability of auto-ignition combustion. On the other hand, when the load on the engine 1 increases, the temperature state in the cylinder 18 increases. Therefore, even if the amount of hot EGR gas introduced is small, the ignitability and stability of compression self-ignition can be ensured.

  In this CAI region, the amount of hot EGR gas introduced corresponding to the load of the engine 1 is adjusted, as described above, by the phase of the opening timing of the intake valve 21 when the VVLs 71 and 73 are turned on and the closing of the exhaust valve 22, respectively. This is done by adjusting the phase of the time. That is, when the EGR rate is changed from high to low as the load of the engine 1 increases, the phase of the opening timing of the intake valve 21 is changed in the retarded direction and the phase of the closing timing of the exhaust valve 22 is advanced. Change direction. Conversely, when the EGR rate is changed from low to high as the load on the engine 1 decreases, the phase of the opening timing of the intake valve 21 is changed to the advance direction and the phase of the closing timing of the exhaust valve 22 is delayed. The angle is changed (see the arrow in FIG. 3C).

(From the predetermined load _{T 2} to the switching load _{T 3)}
The predetermined load T ₂ or more load regions in the CAI mode, i.e., in the high load side region in the CAI mode, sets the air-fuel ratio of the mixture to the stoichiometric air-fuel ratio (λ ≒ 1). As a result, a three-way catalyst can be used, and exhaust emission performance can be ensured.

In this high-load region, the temperature state in the cylinder 18 is further increased, so hot EGR gas was introduced into the cylinder 18 while maintaining the air-fuel ratio of the air-fuel mixture at the theoretical air-fuel ratio (λ≈1). In this case, the temperature state in the cylinder 18 becomes too high and abnormal combustion such as pre-ignition occurs, or the pressure rise (dP / dθ) in the cylinder 18 becomes steep during CAI combustion, causing a problem of combustion noise. There is a risk that. Therefore, in the region from the predetermined load _{T 2} to switch the load _{T 3,} together with the hot EGR gas is introduced cooled EGR gas into the cylinder 18. The cooled EGR gas is basically an external EGR gas cooled by passing through the EGR cooler 52. The external EGR gas that bypasses the EGR cooler 52 may be included in the cooled EGR gas. Thus, by introducing the cooled EGR gas into the cylinder 18, it is avoided that the temperature state in the cylinder 18 becomes too high, which is advantageous for avoiding abnormal combustion and combustion noise. In the CAI mode, unlike the SI mode described later, there is no restriction on the EGR rate related to combustion stability. Therefore, it is possible to make the EGR rate as high as possible while setting the excess air ratio λ of the air-fuel mixture to substantially 1.

Even during the period from the predetermined load T ₂ to switch the load T _3, adjustment of the introduction amount of the hot EGR gas corresponding to the load of the engine 1, the opening timing of the phase of the intake valve 21 respectively turn on the VVL71,73, This is performed by adjusting the phase of the closing timing of the exhaust valve 22.

Threshold engine load _{T 3} relates to switching between the CAI mode and SI-mode, the SI mode in the switching load _{T 3} or more high-load side. In the CAI mode, as described above, the VVLs 71 and 73 on the intake side and the exhaust side are respectively turned on to introduce the internal EGR gas (that is, hot EGR gas) into the cylinder 18, while in the SI mode, the intake side Then, the VVLs 71 and 73 on the exhaust side are turned off, and the introduction of the internal EGR gas is stopped. Therefore, by switching the load _{T 3} as the boundary, VVL71,73 off of the intake side and exhaust side is switched.

(From the switching load _{T 3} up to a maximum load _{T max)}
Region of a load higher than the switching load T ₃ corresponds to SI mode. In this SI region, as described above, only the cooled EGR gas is introduced into the cylinder 18.

  In the SI mode, basically, the opening of the throttle valve 36 is kept fully open, and the opening of the EGR valve 511 is changed according to the engine load. Thus, in the SI mode, the EGR rate is set to the maximum under the condition that the air-fuel ratio of the air-fuel mixture is set to the theoretical air-fuel ratio (λ≈1). This is advantageous for reducing pump loss. In addition, setting the air-fuel ratio of the air-fuel mixture to the stoichiometric air-fuel ratio makes it possible to use a three-way catalyst. Specifically, the EGR valve 511 gradually closes as the engine load increases, and closes at the fully open load. This is advantageous in improving controllability because the gas composition in the cylinder 18 is continuously changed when the engine load changes continuously.

In SI combustion, if the amount of exhaust gas introduced into the cylinder 18 is too large, the combustion stability is lowered. Therefore, there is a maximum EGR rate (that is, an EGR limit) that can be set in SI combustion. As described above, since the air-fuel ratio of the air-fuel mixture is set to the stoichiometric air-fuel ratio (λ≈1), the EGR rate changes continuously according to the engine load level, and when the engine load is low in the SI mode, the fuel amount and less, by fresh air amount is reduced, although the EGR rate can be high, from the switching load T ₃ to a predetermined load T _4, the EGR rate is limited to EGR limit. Thus, during the threshold engine load T ₃ to a predetermined load T ₄ it is, the EGR rate becomes constant at EGR limit, thus, when the EGR rate is limited by the EGR limit, the stoichiometric air-fuel ratio of the mixture (lambda In setting ≈1), the amount of fresh air introduced into the cylinder 18 must be reduced. Here, the amount of fresh air introduced into the cylinder 18 is reduced by delaying the closing timing of the intake valve 21 after the intake bottom dead center. Note that fresh air introduced into the cylinder 18 can be reduced by controlling the opening degree of the throttle valve 36, for example, instead of controlling the closing timing of the intake valve 21. However, controlling the closing timing of the intake valve 21 is advantageous in reducing pump loss.

(Adjustment of internal EGR gas amount accompanying changes in engine load)
As described above, in the CAI mode, the internal EGR gas amount is changed according to the engine load. Here, in this configuration, as described above, the phase of the opening / closing timing of the intake valve 21 in which the VVL 71 is turned on is adjusted by the VVT 72 on the intake side, and the exhaust valve 22 in which the VVL 73 is turned on by the VVT 74 on the exhaust side. In order to adjust the internal EGR gas amount by adjusting the phase of the opening / closing timing of the exhaust valve 22, for example, in the conventional configuration in which the exhaust valve 22 is opened twice, only the phase of the opening / closing timing of the exhaust valve 22 is adjusted. There is an advantage that the responsiveness related to the adjustment of the internal EGR gas amount becomes high. This point will be described with reference to the time chart of FIG.

The figures of the left side of FIG. 9, in the conventional configuration in which the open-twice of the exhaust valve 22, the load of the engine 1 is, from a predetermined initial load between the T ₁ through T ₂ shown in FIG. 8, T ₂ through T (A) phase change of the exhaust valve 22, (b) change in gas composition in the cylinder 18, (c) change in fuel amount, and (d) pump loss when rising to a predetermined target load between ₃ Each change is shown. The horizontal axis of each figure is time. In the conventional configuration in which the exhaust valve 22 is opened twice, the internal EGR gas amount is changed from r ₀ at the initial load to the target load by changing the phase of the exhaust valve 22 from Pex ₀ to Pex ₁ to the advance side. up of _{r 1,} it becomes less and less. The speed of changing the phase of the exhaust valve 22, that is, the slope of the straight line in the time chart of FIG. 9A corresponds to the drive speed of the VVT 74 of the exhaust valve 22 (in other words, the hardware limit).

As the internal EGR gas amount decreases, the air amount in the cylinder 18 increases (see FIG. 5B). Further, as the load on the engine 1 increases, the amount of fuel gradually increases (see (c) in the figure). The pump loss is relatively high when the phase of the exhaust valve 22 is set to Pex ₀ on the retard side, but gradually decreases as the phase of the exhaust valve 22 advances from that state. Thus, when the phase of the exhaust valve 22 reaches a predetermined phase, the pump loss becomes the lowest, and the pump loss gradually increases as the phase of the exhaust valve 22 further advances toward Pex _1. (See (d) in the figure).

  In the illustrated example, since the load of the engine 1 reaches the switching load from the lean to the stoichiometric air-fuel ratio in the middle of reaching the target, as shown in FIG. It switches from the fuel amount which concerns on this to the fuel amount which concerns on a theoretical air fuel ratio. Even after the fuel amount is changed, the change in the opening timing of the exhaust valve 22 is continued, so that the internal EGR gas amount gradually decreases while the external EGR gas enters the cylinder 18 as shown in FIG. be introduced.

Thus, when the phase of the exhaust valve 22 reaches Pex ₁ at time t ₁ , the internal EGR gas amount reaches r ₁ corresponding to the target load of the engine 1. Thus, in order to change the load of the engine 1 from the initial load to the target load, it is necessary to change the internal EGR gas amount introduced into the cylinder 18 from the initial r ₀ to the target r ₁ . In the conventional configuration in which the exhaust valve 22 is opened twice, only the phase of the exhaust valve 22 is changed and the internal EGR gas amount is adjusted, so that the phase change amount of the exhaust valve 22 is large (Pex ₁ -Pex ₀ ), Since the state of the engine 1 changes to a state corresponding to the target load, a relatively long time from time t0 to t1 is required. This leads to a decrease in acceleration performance, for example.

  In contrast, in this configuration, as described above, the amount of internal EGR gas introduced into the cylinder 18 is adjusted by changing both the phase of the intake valve 21 and the phase of the exhaust valve 22. The right diagram of FIG. 9, similar to the left diagram, shows (e) phase change of the exhaust valve 22 and (f) phase change of the intake valve 21 when the load of the engine 1 increases from the initial load to the target load. (G) Changes in the gas composition in the cylinder 18, (h) changes in the fuel amount, and (i) changes in the pump loss are shown.

As described above, in this configuration, the internal EGR gas amount is reduced by changing the phase of the exhaust valve 22 from Pex ₀ to the advance side and changing the phase of the intake valve 21 from Pin ₀ to the retard side. initially gradually become less from r ₀ at the time of load. The phase change speed of the exhaust valve 22 corresponds to the drive speed of the VVT 74 of the exhaust valve 22 (that is, the hardware limit), and the phase change speed of the intake valve 21 is the drive speed of the VVT 72 of the intake valve 21 (that is, the hardware speed). 9 (e), the slope of the straight line in the time chart of FIG. 9 (e) is the same as the slope of the straight line in the time chart of FIG. 9 (a). In addition, regarding the change of the phase of the intake valve 21, the slope of the straight line in the time chart of FIG. 10F is the same as the slope of the straight line related to the phase change of the exhaust valve 22, although positive and negative are opposite.

  In this way, even if the hardware limits of the intake-side VVT 71 and the exhaust-side VVT 73 are the same as in the prior art, in this configuration, the phases of both the intake valve 21 and the exhaust valve 22 are changed. The rate of change of the amount of internal EGR gas introduced into the interior is higher than in the conventional configuration in which only the phase of the exhaust valve 22 is changed. That is, as shown in FIG. 9 (g), the slope of the change of the internal EGR gas amount with respect to time becomes steeper than in the conventional configuration.

Phase change amount of the exhaust valve 22, the change amount in the conventional configuration _(Pe x1 -Pex ₀₎ approximately half of _(Pex 2 -Pex ₀₎ becomes and, the phase change amount of the intake valve 21, the phase change amount of the exhaust valve 22 the same level if the _(Pin 1 -Pin _0), the internal EGR gas amount is changed from _{r 0} at initial load _{r 1} corresponding to the target load (see time t2). In other words, in this configuration, the phase change amount of the exhaust valve 22 required for changing to the target load can be reduced (specifically, about half) compared to the conventional configuration. The time required to change the load of 1 to the target load is shorter than that of the conventional configuration (specifically, approximately half the time). Thus, as compared with the conventional configuration, the target internal EGR gas amount can be changed in a short time, and as a result, the responsiveness related to the change in the load of the engine 1 is enhanced.

  When the load of the engine 1 decreases from the high load side to the low load side, the reverse is true. In this case, too, the target internal EGR gas amount can be achieved in a short time compared to the conventional configuration. Since it is possible to change, the responsiveness which concerns on the change of the load of the engine 1 increases.

  Here, in this configuration, as shown in FIG. 9G, the phase of the opening / closing timing of the intake valve 21 is retarded after the air-fuel ratio of the air-fuel mixture is switched from lean to the stoichiometric air-fuel ratio. The amount of fresh air introduced into the cylinder 18 can be reduced (see also the one-dot chain line in FIG. 8). Therefore, as shown in FIG. 9 (h), the fuel injection amount is set to be small so that the stoichiometric air-fuel ratio is maintained in accordance with a decrease in the amount of fresh air introduced into the cylinder 18.

  Regarding the pump loss, in this configuration, when the amount of internal EGR gas is large (time t0), as illustrated by the solid line in FIG. 3C, the intake valve 21 and / Alternatively, since the valve opening amount of the exhaust valve 22 can be maintained relatively large, the pump loss is reduced as compared with the conventional configuration, and after the time t2 when the phase change of the intake valve 21 and the exhaust valve 22 is completed. Then, it becomes possible to avoid an increase in pump loss (see FIG. 9 (i)). Thus, in this configuration, the pump loss can be reduced as compared with the conventional configuration as a whole when the load of the engine 1 changes from the initial load to the target load.

  The technique disclosed here is not limited to application to the engine configuration described above. For example, the operation control map shown in FIG. 7 is an exemplification, and various other maps can be provided.

  In addition, the exhaust passage is provided with only a three-way catalyst, but it is provided with a NOx purification catalyst, so that the excess air ratio λ is smaller than 2.4 and larger than 1.0, and A / F can be operated with Lean. May be.

  Furthermore, the technology disclosed herein can be applied to a diesel engine. In a diesel engine in which a large amount of internal EGR gas is introduced with a reduced geometric compression ratio, as described above, the maximum amount of internal EGR gas is increased, and the response of changes in internal EGR gas amount is increased. It is beneficial to increase In a diesel engine, the geometric compression ratio may be set to 12 or more, for example.

1 Engine (Engine body)
14 Piston 16 Intake port 17 Exhaust port 18 Cylinder 21 Intake valve 22 Exhaust valve 71 VVL (Intake valve drive mechanism)
72 VVT (Intake valve drive mechanism)
73 VVL (exhaust valve drive mechanism)
74 VVT (exhaust valve drive mechanism)
212 Lift curve 213 (intake side) Lift shelf 222 (intake side) Lift curve 223 (Exhaust side) lift shelf 213

Claims (6)

An engine body having a cylinder;
A piston fitted into the cylinder and configured to reciprocate within the cylinder;
An intake valve configured to open and close an intake port for sucking gas into the cylinder;
An exhaust valve configured to open and close an exhaust port for exhausting gas from within the cylinder;
An intake valve drive mechanism configured to open and close the intake valve;
An exhaust valve drive mechanism configured to open and close the exhaust valve,
The intake valve drive mechanism has a lift shelf on a valve opening side of a lift curve having a peak during an intake stroke, and a valve opening state of the intake valve is maintained with respect to a crank angle with a lift amount lower than the peak. Opening the intake valve to have a portion,
The exhaust valve drive mechanism has a lift shelf on a valve closing side of a lift curve having a peak during an exhaust stroke, in which the valve opening state of the exhaust valve is maintained with respect to the crank angle with a lift amount lower than the peak. Opening the exhaust valve to have a portion,
The intake valve drive mechanism and the exhaust valve drive mechanism adjust the internal EGR gas amount by changing the opening / closing timing of the intake valve and the opening / closing timing of the exhaust valve, respectively, and adjust the opening timing of the intake valve. The intake valve lift shelf and the exhaust valve lift shelf are both positioned at the top dead center of the piston when the valve is advanced most and the exhaust valve closing time is retarded most. A reciprocating valve engine control device for a reciprocating piston engine. In the valve operating control device of the reciprocating piston engine according to claim 1,
Each of the intake valve drive mechanism and the exhaust valve drive mechanism controls the opening timing of the intake valve when the operating state of the engine body is in a predetermined low load region and the air-fuel mixture in the cylinder self-ignites and burns. A valve operating control device for a reciprocating piston engine that makes the internal EGR gas amount maximum by advancing the most and delaying the closing timing of the exhaust valve the most. In the valve operating control device of the reciprocating piston engine according to claim 1 or 2,
The intake valve drive mechanism operates a reciprocating piston engine that adjusts the opening / closing timing of the intake valve so that the closing timing of the intake valve is in a range of 30 ° before bottom dead center to 70 ° CA after bottom dead center. Valve control device. In the valve operating control apparatus of the reciprocating piston engine of any one of Claims 1-3,
The exhaust valve drive mechanism operates a reciprocating piston engine that adjusts the opening / closing timing of the exhaust valve so that the opening timing of the exhaust valve is in the range of 70 ° before bottom dead center to 30 ° CA after bottom dead center. Valve control device. In the valve operating control apparatus of the reciprocating piston engine of any one of Claims 1-4,
A valve operating control device for a reciprocating piston engine, wherein the opening timing of the intake valve is set in a range of 100 ° to 40 ° CA before top dead center when the intake valve is most advanced. In the valve operating control apparatus of the reciprocating piston engine of any one of Claims 1-5,
A valve operating control device for a reciprocating piston engine, wherein the closing timing of the exhaust valve is set within a range of 40 ° to 100 ° CA after top dead center when the timing is most retarded.

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