JP2017180353A - Control device of engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control device of an engine capable improving efficiency in compression self combustion by properly controlling an amount of fresh air in the control device of the engine implementing compression self combustion.SOLUTION: A control device of an engine 1 includes an intake valve 21, and an intake variable valve mechanism 71 for controlling an opening/closing timing of the intake valve 21. The intake variable valve mechanism 71 includes a cam 71d rotated in synchronization with rotation of a crank shaft 15, a pressure chamber 71c in which an engine oil is charged and an oil pressure of the engine oil is changed by motion of the cam 71d, and a solenoid valve 71b connected to the pressure chamber 71c and controlling the oil pressure acting on the intake valve 21 by being opened and closed. The intake variable valve mechanism 71 controls the solenoid valve 71b to retard an opening timing of the intake valve 21 in an intake stroke in accordance with lowering of load on the engine 1 in compression self combustion.SELECTED DRAWING: Figure 7

Description

  The present invention relates to an engine control device.

  2. Description of the Related Art Conventionally, in an engine control device, a technique for improving the engine operating efficiency particularly in a compression self-combustion operation region by appropriately controlling the timing of opening and closing of an intake valve and an exhaust valve of an engine is known. (For example, Patent Document 1).

JP 2009-174432 A

  As a means for controlling the opening and closing of the intake and exhaust valves of the engine, the valve is opened and closed at regular intervals according to the shape of the cam crest provided on the cam surface and at a constant lift. A so-called mechanical valve mechanism that opens and closes by an amount and a variable valve mechanism that can be opened and closed by a predetermined lift amount at a predetermined timing are known.

  By the way, in recent years, for the purpose of improving fuel efficiency and exhaust emission performance, it is often used properly depending on the engine combustion state in accordance with the operating state of the engine. Specifically, in such control, in the low load operation region of the engine, control by compression self-combustion is performed, thereby improving fuel efficiency and improving exhaust emission performance. Then, spark ignition combustion using an ignition plug is performed to prevent engine misfire. Among these, when control by compression self-combustion is performed, the fuel is self-combusted basically by a temperature increase corresponding to a decrease in the volume in the cylinder of the engine. Therefore, during the control by the compression self-combustion, it is necessary to keep the temperature in the cylinder of the engine at a high temperature before the intake stroke starts. And in order to keep the temperature in the cylinder of the engine at a high temperature, so-called internal EGR that keeps the temperature in the cylinder by keeping the high temperature burned gas generated in the combustion stroke immediately before the start of the intake stroke in the cylinder. (Exhaust Gas Recirculation) control is used.

  When internal EGR control is performed, the temperature in the cylinder can be kept high by keeping EGR gas in the cylinder before the intake stroke starts. However, in order to perform compression self-combustion, Therefore, it is required to keep the ratio of fresh air newly introduced to the EGR gas and EGR gas remaining in the cylinder appropriately.

Accordingly, the present invention has been made to solve the above-described problems, and in an engine control apparatus that performs compression self-combustion, the efficiency of compression self-combustion is improved by appropriately controlling the amount of fresh air. It is an object of the present invention to provide an engine control device that can perform the above-mentioned.

  In order to solve the above-described problems, the present invention is an engine control apparatus that performs compression self-combustion by compressing the inside of a cylinder in a predetermined low-load operation region in a state where burned gas exists in the cylinder. An intake valve provided at an intake port of a cylinder of the engine for opening and closing the intake port, and an intake variable valve mechanism for controlling the opening and closing timing of the intake valve, the intake variable valve mechanism Is connected to the pressure chamber, the cam that rotates in synchronization with the rotation of the crankshaft, the engine oil filled therein, and the oil pressure of the engine oil changes by the operation of the cam, and opens and closes And a hydraulic valve that controls the hydraulic pressure applied to the intake valve, and the intake variable valve mechanism is configured to perform an intake stroke as the engine load is lower during the compression self-combustion. Serial to control the hydraulic valve so as to slow down the time when the intake valve opens.

  According to the present invention configured as described above, during the compression self-combustion, the intake variable valve mechanism can delay the opening time of the intake valve during the intake stroke as the engine load decreases. When performing compression self-combustion, when the engine load is low, the amount of fresh air flowing into the cylinder is limited by delaying the opening time of the intake valve in the intake stroke, thereby reducing the amount of burned gas in the cylinder. The relative amount can be increased. Thereby, the temperature in a cylinder can be maintained and the efficiency of compression self-combustion can be improved.

  In the present invention, it is preferable that the variable intake valve operating mechanism adjusts the hydraulic valve so that the intake valve opens earlier in the intake stroke as the engine load increases during the compression self-combustion. Control.

  According to the present invention configured as described above, when the load on the engine is high, the amount of fresh air flowing into the cylinder is ensured by increasing the timing of opening the intake valve in the intake stroke, and the burned in the cylinder The relative amount of gas can be reduced. Thereby, an appropriate engine output according to a high engine load can be obtained.

  In the present invention, preferably, the burned gas present in the cylinder is provided in an exhaust port of the cylinder of the engine in an intake stroke, thereby opening the exhaust valve for opening and closing the exhaust port. It was introduced into the cylinder.

  In the present invention, preferably, the burnt gas existing in the cylinder is provided in an exhaust port of the cylinder of the engine in an exhaust stroke, and an exhaust valve for opening and closing the exhaust port is kept closed. By doing so, it remains in the cylinder.

  In the present invention, it is preferable that the timing of closing the intake valve in the intake stroke is constant regardless of the load of the engine.

  In this case, it is preferable that the timing for closing the intake valve is determined in advance according to the engine speed.

  According to the present invention configured as described above, the timing for closing the intake valve is made constant regardless of the load of the engine, so that the timing for closing the intake valve is made constant regardless of the timing for opening the intake valve in the intake stroke. can do. Thereby, the required fresh air filling amount can be accurately realized.

1 is a schematic configuration diagram of an engine according to an embodiment of the present invention. It is a schematic side view of an intake side variable valve mechanism applied to an intake valve in an engine according to an embodiment of the present invention. It is a control block diagram of the engine by the embodiment of the present invention. It is explanatory drawing of the driving | operation area | region of the engine by embodiment of this invention. It is explanatory drawing of the basic operation | movement of an intake valve and an intake valve in the 1st operation area | region by embodiment of this invention. It is explanatory drawing about the characteristic of the intake side variable valve mechanism by embodiment of this invention. It is explanatory drawing about operation | movement of the intake valve and exhaust valve by embodiment of this invention.

  Hereinafter, an engine according to an embodiment of the present invention will be described with reference to the accompanying drawings.

[Engine configuration]
First, the configuration of an engine according to an embodiment of the present invention will be described with reference to FIGS. 1 to 3. FIG. 1 is a schematic configuration diagram of an engine according to an embodiment of the present invention, and FIG. 2 is a schematic side view (partially) of an exhaust side variable valve mechanism applied to an intake valve of the engine according to an embodiment of the present invention. FIG. 3 is a control block diagram of the engine according to the embodiment of the present invention.

  As shown in FIG. 1, the engine 1 is a gasoline engine that is mounted on a vehicle and supplied with fuel containing at least gasoline. The engine 1 includes a cylinder block 11 provided with a plurality of cylinders 18 (in FIG. 1, only one cylinder is illustrated, but four cylinders are provided in series, for example), and the cylinder block 11 is disposed 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. A cavity 141 like a reentrant type in a diesel engine is formed on the top surface of the piston 14. 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 19. The shape of the combustion chamber 19 is not limited to the shape illustrated. For example, the shape of the cavity 141, the top surface shape of the piston 14, the shape of the ceiling portion of the combustion chamber 19, and the like can be changed as appropriate.

  The 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 the compression ignition combustion described later. In addition, what is necessary is just to set a geometric compression ratio suitably in the range of about 15-20.

  The cylinder head 12 is provided with an intake port 16 and an exhaust port 17 for each cylinder 18. The intake port 16 and the exhaust port 17 have an intake valve 21 and an exhaust for opening and closing the opening on the combustion chamber 19 side. Each valve 22 is disposed. Specifically, as shown in FIG. 2, two intake ports 16 are formed for each cylinder 18, and an intake valve 21 (21 a, 21 b) is disposed in each of the intake ports 16, and two intake ports 16 are provided. An exhaust port 17 is formed, and an exhaust valve 22 (22a, 22b) is disposed in each of the exhaust ports 17.

  An exhaust-side variable valve mechanism 72 is attached to the exhaust valve 22 (see FIGS. 3 and 4). The exhaust-side variable valve mechanism 72 changes the opening / closing timing of the exhaust valve 22 so as to change the exhaust valve. 22 is operated. Further, an intake side variable valve mechanism 71 is attached to the intake valve 21 (see FIG. 4), and the intake side variable valve mechanism 71 changes the opening / closing timing and / or the lift amount of the intake valve 21. .

  As shown in FIG. 2, an intake side variable valve mechanism 71 applied to the intake valve 21 includes an oil supply path 71a through which engine oil supplied from the outside passes, and a three-way valve provided on the oil supply path 71a. As a solenoid valve 71b (corresponding to a hydraulic valve), and a pressure chamber 71c filled with engine oil supplied from the oil supply passage 71a via the solenoid valve 71b. In this case, when the solenoid valve 71b is open, the oil supply passage 71a and the pressure chamber 71c are in fluid communication, and engine oil is supplied from the oil supply passage 71a to the pressure chamber 71c (in FIG. 2). Arrow A11). The solenoid valve 71b is opened when not energized, and closes when energized. More specifically, the solenoid valve 71b is maintained in a closed state by being energized. Note that a check valve (not shown) is provided on the oil supply passage 71a upstream of the solenoid valve 71b.

  Further, the intake side variable valve mechanism 71 swings by a cam 71d provided on the intake camshaft 23 to which the rotation of the crankshaft 15 is transmitted via a timing belt and the like, and a force transmitted from the cam 71d. The roller finger follower 71e is connected to the pressure chamber 71c, and is operated by the roller finger follower 71e to have a pump unit 71f that raises the pressure (hydraulic pressure) of the engine oil in the pressure chamber 71c. In addition, the intake side variable valve mechanism 71 is connected to the pressure chamber 71c via the solenoid valve 71b, and operates to open the intake valve 21 by the hydraulic pressure in the pressure chamber 71c. And a valve spring 71h for applying a force for maintaining the closed state of the intake valve 21 when the 71g is not operating. In this case, when the solenoid valve 71b is closed, the fluid communication between the oil supply passage 71a and the pressure chamber 71c is interrupted, and the pressure chamber 71c and the brake unit 72g are in fluid communication with each other. The hydraulic pressure in 71c acts on the brake unit 71g (see arrow A12 in FIG. 2).

  The operation of the intake side variable valve mechanism 71 for opening the intake valve 21 will be specifically described. While the cam 71d rotates in synchronization with the intake camshaft 23, when the cam crest (in other words, the cam lobe) formed on the cam 71d contacts the roller finger follower 71e, the cam crest causes the roller finger follower 71e to move. Push in. Thereby, the roller finger follower 71e urges the pump unit 71f, and the pump unit 71f operates so as to compress the engine oil in the pressure chamber 71c, whereby the hydraulic pressure in the pressure chamber 71c increases. At this time, when the solenoid valve 71b is closed, the raised hydraulic pressure in the pressure chamber 71c acts on the brake unit 71g, and the brake unit 71g urges the intake valve 21, whereby the intake valve 21 is lifted. That is, the intake valve 21 is opened.

  Basically, the intake valve 21 can be opened by closing the solenoid valve 71b at some timing while the cam crest formed on the cam 71d is acting on the roller finger follower 71e. Therefore, the valve opening timing of the intake valve 21 can be changed by changing the timing for switching the solenoid valve 71b from the open state to the closed state. In the present embodiment, a cam crest is formed at a predetermined position on the cam 71d so that the intake valve 21 can be opened in the intake stroke.

  The exhaust-side variable valve mechanism 72 has the same configuration as the intake-side variable valve mechanism 71, and the cam of the exhaust-side variable valve mechanism 72 can open the exhaust valve 22 during the exhaust stroke. A cam crest is formed at a predetermined position above. Further, as will be described later, when the exhaust valve 22 is opened during the intake stroke to open the exhaust twice, an additional cam crest is formed at a predetermined position of the exhaust-side variable valve mechanism 72. ing. Such double opening of the exhaust is performed when burnt gas (internal EGR gas) is caused to flow backward from the exhaust port 17 to the combustion chamber 19 and reintroduced.

  Referring to FIG. 1 again, the cylinder head 12 is provided with an injector 67 for direct injection of fuel into the cylinder 18 for each cylinder 18 (direct injection). The injector 67 is disposed so that its nozzle hole faces the inside of the combustion chamber 19 from the central portion of the ceiling surface of the combustion chamber 19. The injector 67 directly injects an amount of fuel into the combustion chamber 19 at an injection timing set according to the operating state of the engine 1 and according to the operating state of the engine 1. 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 19. 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 19 flows along the wall surface of the cavity 141 formed on the top 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 open valve 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.

  An ignition plug 25 for forcibly igniting the air-fuel mixture in the combustion chamber 19 (specifically, spark ignition) 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 19 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, and a throttle valve 36 that adjusts the amount of intake air to each cylinder 18 is disposed downstream thereof. 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.

  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.

  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. The main passage 51 is provided with an EGR valve 511 for adjusting the recirculation amount of the exhaust gas to the intake passage 30.

  The engine 1 is controlled by a powertrain control module (hereinafter referred to as “PCM”) 10 as control means. 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 3, detection signals of various sensors SW1, SW2, SW4 to SW18 are input to the PCM 10. Specifically, on the downstream side of the air cleaner 31, the PCM 10 includes a detection signal of an air flow sensor SW 1 that detects a flow rate of fresh air, a detection signal of an intake air temperature sensor SW 2 that detects the temperature of fresh air, and an EGR passage 50. The detection signal of the EGR gas temperature sensor SW4 that is disposed in the vicinity of the connection portion with the intake passage 30 and detects the temperature of the external EGR gas, and the intake air that is attached to the intake port 16 and immediately before flowing into the cylinder 18 The detection signal of the intake port temperature sensor SW5 for detecting the temperature, the detection signal of the in-cylinder pressure sensor SW6 attached to the cylinder head 12 and detecting the pressure in the cylinder 18, and the vicinity of the connection portion of the EGR passage 50 in the exhaust passage 40 And the detection signals of the exhaust temperature sensor SW7 and the exhaust pressure sensor SW8 that detect the exhaust temperature and the exhaust pressure, respectively. And it is disposed on the upstream side of the direct catalyst 41, disposed between the detection signal of the linear O ₂ sensor SW9 for detecting the oxygen concentration in the exhaust gas, the direct catalyst 41 and underfoot catalyst 42 and the exhaust A detection signal of a lambda O ₂ sensor SW10 that detects the oxygen concentration of the engine, a detection signal of a water temperature sensor SW11 that detects the temperature of engine cooling water, a detection signal of a crank angle sensor SW12 that detects the rotation angle of the crankshaft 15, A detection signal of an accelerator opening sensor SW13 that detects an accelerator opening corresponding to an operation amount of an accelerator pedal (not shown) of the vehicle, detection signals of intake side and exhaust side cam angle sensors SW14 and SW15, and a fuel supply system A fuel pressure sensor S that is attached to the common rail 64 of 62 and detects the fuel pressure supplied to the injector 67. 16 a detection signal of a detection signal of the hydraulic sensor SW17 for detecting the oil pressure of the engine 1, and the detection signal of the oil temperature sensor SW18 for detecting the oil temperature of the engine 1, are input.

  The PCM 10 performs various calculations based on these detection signals to determine the state of the engine 1 and the vehicle, and in response to this, (direct injection) injector 67, spark plug 25, intake side variable valve mechanism 71 Control signals are output to the exhaust side variable valve mechanism 72, the fuel supply system 62, and the actuators of various valves (throttle valve 36, EGR valve 511). Thus, the PCM 10 operates the engine 1. In particular, in this embodiment, the PCM 10 outputs a control signal to the solenoid valve 71b of the intake side variable valve mechanism 71 (specifically, supplies a voltage or current to the solenoid valve 71b), and the solenoid valve 71b. The control for changing the opening / closing timing of the intake valve 21 is executed by switching the opening / closing of the.

[Operation area]
Next, with reference to FIG. 4, an operation region of the engine 1 according to the embodiment of the present invention will be described. FIG. 4 shows an example of the operation control map of the engine 1. For the purpose of improving fuel consumption and exhaust emission performance, the engine 1 does not perform ignition by the spark plug 25 in the first operating region R11, which is a low load region where the engine load is relatively low. Performs compression ignition combustion by ignition. However, as the load on the engine 1 increases, in this compression ignition combustion, the combustion becomes too steep and combustion noise is generated, and it becomes difficult to control the ignition timing (prone to misfire and the like). It is in). Therefore, in this engine 1, in the second operating region R12, which is a high load region where the engine load is relatively high, forced ignition combustion (here, spark ignition combustion) using the spark plug 25 is used instead of compression ignition combustion. To do. As described above, the engine 1 performs a CI (Compression Ignition) operation for performing an operation by compression ignition combustion and an SI (for performing an operation by spark ignition combustion) according to the operation state of the engine 1, particularly, the load of the engine 1. It is configured to switch between (Spark Ignition) driving.

  Here, with reference to FIG. 5, basic operations of the intake valve 21 and the exhaust valve 22 (particularly, the exhaust valve 21 to which the intake-side variable valve mechanism 71 is applied) in the first operation region R11 in which the CI operation is performed. explain. FIG. 5 shows the crank angle on the horizontal axis and the lift amount of the valve on the vertical axis. A solid line graph G11 shows the operation of the exhaust valve 22 according to the crank angle, and broken line graphs G12 and G13 show the operation of the intake valve 21 according to the crank angle. As shown in FIG. 5, in the first operation region R11 in which the CI operation is performed, the exhaust side variable valve mechanism 72 opens the exhaust valve 22 during the exhaust stroke and opens the exhaust valve during the intake stroke. The opening is performed twice, and the internal EGR gas having a relatively high temperature is introduced into the cylinder 18. By doing so, during the CI operation, the compression end temperature in the cylinder 18 is increased to improve the ignitability and stability of the compression ignition combustion. Further, in the intake stroke, the opening timing of the intake valve 21 is controlled by the intake side variable valve mechanism 71 and operates at the timing shown in the graph G12 or the graph G13, for example, according to the engine load.

[Operation of intake valve]
Next, the operation of the intake valve 21 according to the embodiment of the present invention will be specifically described.

  First, the characteristics of the exhaust-side variable valve mechanism 71 that operates the intake valve 21 will be described with reference to FIG.

  6A shows the operation (lift curve) of the intake valve 21 when the intake valve 21 is opened at a relatively early time t11 by the intake variable valve mechanism 71. FIG. Below (a), the open / close state of the solenoid valve 71b of the intake side variable valve mechanism 71 when the intake valve 21 is operated in this way is shown. For example, the valve opening timing t11 is the valve opening timing when the valve opening timing of the intake valve 21 is advanced to the maximum by the intake side variable valve mechanism 71 (hereinafter referred to as “maximum advance timing” as appropriate). is there. On the other hand, in FIG. 6 (b), the intake air is shown at a relatively late time t12, specifically at a time t12 delayed from the valve opening time t11 shown in FIG. 6 (a) (see arrow A21). The operation (lift curve) of the intake valve 21 when the intake valve 21 is opened by the side variable valve mechanism 71 is shown. The lower part of FIG. The open / close state of the solenoid valve 71b of the intake side variable valve mechanism 71 at the time of the intake is shown. Further, on the upper part of FIG. 6B, the lift curve shown in the upper part of FIG.

  Comparing FIG. 6A and FIG. 6B, it can be seen that the lift amount of the intake valve 21 decreases when the opening timing of the intake valve 21 is retarded (see arrow A22). It can also be seen that the lift amount integrated value of the intake valve 21 corresponding to the area indicated by the symbol Ar2 is smaller than the lift amount integrated value of the intake valve 21 corresponding to the area indicated by the symbol Ar1. The reason why the lift amount and the lift amount integrated value become smaller when the opening timing of the intake valve 21 is retarded in this way is as follows.

  As described above, in the intake side variable valve mechanism 71, when the cam crest formed on the cam 71d is in contact with the roller finger follower 71e, the cam crest pushes the roller finger follower 71e, so that the pump The hydraulic pressure in the pressure chamber 71c is increased by the unit 71f. Thus, when the cam crest of the cam 71d acts on the roller finger follower 71e, if the solenoid valve 71b is closed, the raised hydraulic pressure in the pressure chamber 71c acts on the intake valve 21 via the brake unit 71g. As a result, the intake valve 21 is opened.

  Here, the hydraulic pressure in the pressure chamber 72c increases when the cam crest of the cam 72d starts to act on the roller finger follower 72e, but decreases after increasing to some extent. Therefore, when the solenoid valve 72b is closed at an initial predetermined timing when the cam crest of the cam 72d starts to act on the roller finger follower 72e, the pressure of the high pressure chamber increases from a relatively early time. The valve opening speeds up, and after that, the valve lifts in accordance with the movement of the pump unit pushed by the cam crest, so that the lift amount and the lift amount integrated value become the largest (see FIG. 6A). In this case, the valve opening timing of the exhaust valve 22 that maximizes the lift amount and the lift amount integral value of the exhaust valve 22 is defined as the maximum advance valve opening timing of the exhaust valve 22. On the other hand, if the valve closing timing of the solenoid valve 72b is retarded from such maximum advance valve opening timing, the pressure increase in the high pressure chamber becomes relatively slow and the opening of the exhaust valve 22 becomes slow. Then, the lift amount and the lift amount integrated value that are lifted in accordance with the movement of the pump unit that is pushed in by the cam crest thereafter are also reduced (see FIG. 6B). As described above, the exhaust-side variable valve mechanism 72 can change the opening / closing timing of the exhaust valve 22, but as shown in FIG. 6, the exhaust-side variable valve mechanism 72 opens and closes the exhaust valve 22. When the timing is changed, the lift amount of the exhaust valve 22 also changes. Therefore, it can be said that the exhaust side variable valve mechanism 72 can change the lift amount in addition to the opening / closing timing of the exhaust valve 22.

  The lift amount integral value of the intake valve 21 substantially corresponds to the amount of fresh air introduced into the cylinder 18 at high rotation, and roughly corresponds to the pumping loss when introducing the same fresh air amount at low rotation. . Therefore, by controlling the timing for closing the solenoid valve 1b of the intake side variable valve mechanism 71, the amount of fresh air introduced into the cylinder 18 and the pumping loss generated at that time can be controlled.

  FIG. 7 shows the relationship between the lift amount of the intake valve and the exhaust valve and the crank angle during CI operation. In FIG. 7, a solid line graph G <b> 21 indicates the operation of the exhaust valve 22, and broken line graphs G <b> 22 to G <b> 25 indicate the operation of the intake valve 21. As shown in FIG. 7, in the exhaust valve 22, the lift amount increases and the valve opening amount increases in the exhaust stroke, and after the lift amount reaches the maximum value, the valve opening amount decreases. The lift amount of the exhaust valve 22 once increases in the intake stroke, and so-called exhaust is opened twice. As a result, the burned gas exhausted from the cylinder 18 in the exhaust stroke is returned to the cylinder 18 as internal EGR gas.

  On the other hand, the intake valve 21 operates according to the lift curve of any of graphs G22 to G25, for example, according to the engine load. The graphs G22 to G25 have different lift start timings, and the lift start timing of the intake valve 21 is controlled by controlling the lift start timing of the intake valve 21 to be, for example, any one of the timings t1 to t4. The amount and lift amount integral value can be controlled.

  The lift start times t1 to t4 are values determined in advance according to the engine load. The lower the engine load, the slower the time, and the higher the engine load, the earlier the time. That is, when the engine load is low, it is required to increase the amount of EGR gas in the cylinder 18 relative to the amount of fresh air and maintain the temperature in the cylinder 18. Accordingly, when the load on the engine is low, the lift start timing of the intake valve 21 is delayed, for example, by setting the timing t4, so that fresh air corresponding to the lift amount integral value of the curve drawn by the graph G25 is stored in the cylinder 18. Can be introduced. Thereby, the relative amount of EGR gas in the cylinder 18 increases, and the temperature in the cylinder 18 can be maintained.

  Further, when the engine load is high, it is required to reduce the amount of EGR gas in the cylinder 18 with respect to the amount of fresh air to obtain an appropriate engine output corresponding to the high engine load. Therefore, when the engine load is high, the lift start timing of the intake valve 21 is advanced, for example, by the timing t1, so that fresh air corresponding to the lift amount integrated value of the curve drawn by the graph G22 is stored in the cylinder 18. Can be introduced.

  Even if the lift start timing is any of timings t1 to t4, the lift amount of the intake valve 21 is controlled by controlling the timing at which the solenoid valve 71b of the intake side variable valve mechanism 71 is closed. It is preferable to control to be zero at t5. The time t5 is a value determined according to the engine speed, regardless of the engine load, and is set, for example, when a certain crank angle is reached from the start of the intake stroke.

  Thus, according to the embodiment of the present invention, when the compression self-combustion control is performed, the intake variable valve mechanism 71 delays the opening time of the intake valve 21 during the intake stroke as the load of the engine 1 is lower. Can do. Then, by delaying the opening timing of the intake valve 21 in the intake stroke, the amount of fresh air flowing into the cylinder 18 can be limited and the relative amount of EGR gas in the cylinder 18 can be increased. Thereby, the temperature in the cylinder 18 can be maintained and the efficiency of compression self-combustion can be improved.

  In the above-described embodiment, control is performed to return the EGR gas exhausted from the cylinder 18 once into the cylinder 18 by so-called twice opening of the exhaust. However, during the exhaust stroke, the intake valve 21 and the exhaust valve 22 are controlled. The burned gas may be held in the cylinder 18 by performing so-called intake / exhaust negative overlap (NVO) control that keeps both the valves closed. In this case as well, the efficiency of compression self-combustion can be increased by determining the opening timing of the intake valve 21 during the intake stroke according to the engine load.

1 engine 10 PCM
18 cylinder 21 intake valve 22 exhaust valve 25 spark plug 67 injector 71 intake side variable valve mechanism 72b solenoid valve 72c pressure chamber 72d cam

Claims (6)

In a predetermined low-load operation region, an engine control device that performs compression self-combustion by compressing the inside of a cylinder in a state where burned gas exists in the cylinder,
An intake valve provided at the intake of a cylinder of the engine for opening and closing the intake;
An intake variable valve mechanism for controlling the opening and closing timing of the intake valve,
The intake variable valve mechanism is
A cam that rotates in synchronization with the rotation of the rank shaft;
A pressure chamber in which engine oil is filled, and the oil pressure of the engine oil is changed by the operation of the cam;
A hydraulic valve that is connected to the pressure chamber and controls the hydraulic pressure applied to the intake valve by opening and closing;
In the compression self-combustion, the intake variable valve mechanism controls the hydraulic valve such that the lower the engine load, the later the opening timing of the intake valve in the intake stroke.   2. The variable intake valve operating mechanism according to claim 1, wherein, during the compression self-combustion, the hydraulic valve is controlled such that the higher the engine load, the earlier the opening timing of the intake valve in the intake stroke. Engine control device.   The burned gas existing in the cylinder is introduced into the cylinder by opening an exhaust valve provided at the exhaust port of the cylinder of the engine in the intake stroke for opening and closing the exhaust port. The engine control device according to claim 1 or 2.   In the exhaust stroke, the burned gas existing in the cylinder remains in the cylinder by keeping the exhaust valve provided at the exhaust port of the engine cylinder for opening and closing the exhaust port closed. The engine control device according to claim 1, wherein the control device is an engine.   5. The engine control device according to claim 1, wherein the timing of closing the intake valve in the intake stroke is constant regardless of the load of the engine. 6.   The engine control device according to claim 5, wherein the timing for closing the intake valve is determined in advance according to the engine speed.

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