JP6308228B2 - Engine control device - Google Patents

Description

  The present invention relates to an engine control device, and more particularly to an engine control device that controls a variable valve mechanism that changes the opening / closing timing and / or lift amount of an intake valve.

  Conventionally, a variable valve mechanism that changes the opening / closing timing and / or the lift amount of an exhaust valve or an intake valve is known. For example, in Patent Document 1, an exhaust valve is opened at the beginning of the intake stroke, that is, an overlap period in which both the exhaust valve and the intake valve are open is formed at the beginning of the intake stroke. A technique for controlling the exhaust VVT is disclosed. In this technique, the negative pressure of the exhaust pulsation generated in the cylinder performing the exhaust stroke is used to scavenge another cylinder performing the intake stroke.

JP 2013-185446 A

By the way, in recent years, from the viewpoint of improving fuel consumption and emission, a high compression ratio is applied as a geometric compression ratio of the engine. -Charge Compression Ignition))), and a technology that performs spark ignition (SI (Spark Ignition)) in the high load region has been developed. In such a high compression ratio engine, during spark ignition operation, in order to suppress the occurrence of abnormal combustion, pre-ignition that the air-fuel mixture self-ignites before the normal combustion start timing triggered by spark ignition is suppressed. Therefore, combustion injection is performed in the latter half of the compression stroke.
Here, in the conventional high compression ratio engine, in the high load region where spark ignition is performed, the temperature on the intake side is high, and relatively high temperature intake air tends to be introduced into the cylinder. If the intake air temperature is high in this way, the possibility of pre-ignition increases. Therefore, it is considered that the pre-ignition can be more effectively suppressed by reducing the intake air temperature introduced into the cylinder.

  The present invention has been made to solve the above-mentioned problems of the prior art, and effectively controls the intake valve opening / closing period during the exhaust stroke to effectively control the intake air temperature introduced into the cylinder. An object of the present invention is to provide an engine control apparatus that can reduce the charging efficiency and improve the charging efficiency.

In order to achieve the above object, the present invention provides a cylinder provided with an intake valve for introducing intake air into the cylinder and an exhaust valve for discharging exhaust gas from the cylinder, and opening / closing timing of the intake valve, And a variable valve mechanism for changing the lift amount . In a first operating region where the engine load is less than a predetermined value, the air-fuel mixture containing fuel is compressed and self-ignited, and the load is higher than that in the first operating region. opening the second operating region, a control apparatus for an engine fuel mixture Ru forced ignition containing fuel, in the first or the second operating region of the engine, the intake valve even in the exhaust stroke in addition to the intake stroke so as to have a variable valve timing control means for controlling the variable valve mechanism, the variable valve mechanism control means is a second operating region for forcibly igniting the air-fuel mixture and der engine speed is below a predetermined rotational speed If, in the exhaust stroke of the engine, based on the timing of the primary negative pressure wave of the exhaust pulsation is generated that occurs when the exhaust valve is opened, the higher the rotational speed of the engine, the intake valve is opened in the exhaust stroke The timing and the closing timing of the intake valve are retarded .

According to the present invention configured as described above, when the double opening control for opening the intake valve in the exhaust stroke in addition to the intake stroke is executed, it occurs when the exhaust valve is opened in the exhaust stroke. Since the opening timing of the intake valve during the exhaust stroke is set based on the timing when the exhaust pulsation becomes negative pressure, it is possible to improve the scavenging effect of flowing the exhaust gas out of the cylinder and flowing the intake air into the cylinder it can. As a result, the efficiency of filling air into the cylinder (volumetric efficiency) can be improved, and as a result, the output torque from the engine can be improved. In addition, by improving the above scavenging effect, it is possible to reduce the temperature on the intake side by blowing gas from the intake side to the exhaust side via the cylinder. As a result, the intake temperature introduced into the cylinder in the intake process can be reduced, and pre-ignition can be appropriately suppressed.
Also, the intake valve is appropriately opened in accordance with the timing at which the exhaust pulsation becomes negative pressure, which changes according to the engine speed, and the intake valve is adjusted in accordance with the timing at which the exhaust pulsation changes from negative pressure to positive pressure. It can be closed properly. Moreover, the scavenging effect can be further improved by using a primary negative pressure wave having large energy. Further, in a high compression ratio engine that operates by switching between compression self-ignition and forced ignition according to the operation region, the above-described intake valve is controlled in the operation region at a low rotation speed and high load, and the scavenging effect is obtained. Thus, it is possible to appropriately improve the charging efficiency, and it is possible to reduce the intake air temperature and suppress the pre-ignition.

In the present invention, preferably, the variable valve mechanism control means sets the closing timing of the intake valve that is opened during the exhaust stroke based on the timing at which the exhaust pulsation changes from negative pressure to positive pressure.
According to the present invention thus configured, the intake valve can be closed when the exhaust pulsation is at a positive pressure, and the exhaust gas blowback from the exhaust side to the intake side can be suppressed. it can.

In the present invention, preferably, the variable valve mechanism control means sets the valve opening timing of the intake valve during the exhaust stroke based on the valve opening timing of the exhaust valve.
According to the present invention configured as described above, the intake valve can be appropriately opened in accordance with the timing at which the exhaust pulsation becomes negative pressure, which changes according to the opening timing of the exhaust valve.

In the present invention, preferably, the variable valve mechanism control means sets the valve opening timing of the intake valve during the exhaust stroke so that the lift amount of the intake valve is maximized at the timing when the negative pressure wave peak occurs in the exhaust pulsation. Set.
According to the present invention configured as described above, the opening of the intake valve during the exhaust stroke is performed so that the timing at which the negative pressure wave peak (peak timing) coincides with the timing at which the lift amount of the intake valve becomes maximum. Since the valve timing is set, the energy of the negative pressure wave can be utilized to the maximum, and the scavenging effect can be further improved.

  In the present invention, preferably, the engine has a plurality of cylinders each having an intake valve and an exhaust valve, and the variable valve mechanism control means determines the valve opening timing of the intake valve during the exhaust stroke. Therefore, it is preferable to set based on the timing at which the exhaust pulsation generated when the exhaust valve of one cylinder having the intake valve is opened becomes negative pressure.

In the present invention, preferably, the variable valve mechanism control means retards the closing timing of the intake valve that is opened during the exhaust stroke as the opening timing of the exhaust valve is retarded, and the engine speed increases. The higher the valve timing, the later the closing timing of the intake valve that is opened during the exhaust stroke.
According to the present invention configured as above, the intake valve is appropriately adjusted in accordance with the timing at which the exhaust pulsation changes from negative pressure to positive pressure, which changes according to the opening timing of the exhaust valve and the engine speed. It can be closed.

  According to the engine control apparatus of the present invention, it is possible to appropriately control the opening / closing period of the intake valve during the exhaust stroke, effectively reducing the intake air temperature introduced into the cylinder, and improving the charging efficiency. Can be made.

1 is a schematic configuration diagram of an engine to which an engine control device according to an embodiment of the present invention is applied. It is a block diagram which shows the electrical structure regarding the control apparatus of the engine by embodiment of this invention. It is explanatory drawing of the driving | operation area | region of the engine by embodiment of this invention. It is explanatory drawing about operation | movement of an intake valve and an exhaust valve in the area | region where an engine speed is relatively low in the 2nd operation area | region by embodiment of this invention. It is explanatory drawing about the basic concept of the control method of the intake valve by embodiment of this invention. It is explanatory drawing about the difference in the timing which a primary negative pressure wave generate | occur | produces in an exhaust pulsation by the difference in engine speed. It is a figure which shows the relationship between an engine speed and the crank angle which the primary negative pressure wave in an exhaust pulsation generate | occur | produces. It is a flowchart which shows the control processing of the intake valve by embodiment of this invention.

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

[Device configuration]
FIG. 1 shows a schematic configuration of an engine (engine body) 1 to which an engine control device according to an embodiment of the present invention is applied, and FIG. 2 is a block diagram showing the engine control device according to the embodiment of the present invention. .

  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 (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.

  Of the valve systems that drive the intake valve 21 and the exhaust valve 22, respectively, on the exhaust side, the operation mode of the exhaust valve 22 is switched between a normal mode and a special mode, for example, a hydraulically operated variable valve lift mechanism (FIG. 2). (Hereinafter referred to as VVL (Variable Valve Lift)) 71 and a phase variable mechanism (hereinafter referred to as VVT (Variable Valve Timing)) 75 capable of changing the rotational phase of the exhaust camshaft with respect to the crankshaft 15. , Is provided. Although detailed illustration of the configuration of the VVL 71 is omitted, for example, two types of cams having different cam profiles, a first cam having one cam peak and a second cam having two cam peaks, and A cam shifting mechanism that selectively transmits the operating state of one of the first and second cams to the exhaust valve 22 is configured. In this example, when the operating state of the first cam is transmitted to the exhaust valve 22, the exhaust valve 22 operates in the normal mode in which the valve is opened only once during the exhaust stroke, whereas the operation of the second cam is performed. When the state is transmitted to the exhaust valve 22, the exhaust valve 22 is operated in a special mode in which the exhaust valve 22 is opened during the exhaust stroke and is also opened during the intake stroke so that the exhaust is opened twice. . The normal mode and the special mode of the VVL 71 are switched according to the operating state of the engine. Specifically, the special mode is used in the control related to the internal EGR. An electromagnetically driven valve system that drives the exhaust valve 22 by an electromagnetic actuator may be employed.

  The VVT 75 may employ a hydraulic, electromagnetic, or mechanical structure as appropriate, and illustration of the detailed structure is omitted. The exhaust valve 22 can continuously change its valve opening timing and valve closing timing within a predetermined range by the VVT 75. Further, the lift amount and the operation timing of the exhaust valve 22 provided in each of the plurality of cylinders 18 may be controlled by the VVL 71 and the VVT 75 separately for each cylinder 18.

  The execution of the internal EGR is not realized only by opening the exhaust valve 22 twice as described above. For example, the internal EGR control may be performed by opening the intake valve 21 twice or by opening the intake valve twice, or by providing a negative overlap period in which both the intake valve 21 and the exhaust valve 22 are closed in the exhaust stroke or the intake stroke. Internal EGR control that causes the fuel gas to remain in the cylinder 18 may be performed.

  As shown in FIG. 2, a VVL 74 and a VVT 72 are provided on the intake side in the same manner as the valve system on the exhaust side provided with the VVL 71 and the VVT 75. The intake side VVL 74 is different from the exhaust side VVL 71. For example, the VVL 74 on the intake side includes two types of cams having different cam profiles, a large lift cam that relatively increases the lift amount of the intake valve 21 and a small lift cam that relatively decreases the lift amount of the intake valve 21. A cam shifting mechanism that selectively transmits an operating state of one of the large lift cam and the small lift cam to the intake valve 21 is included. In this example, when the VVL 74 is transmitting the operating state of the large lift cam to the intake valve 21, the intake valve 21 is opened with a relatively large lift amount and the valve opening period is also long. On the other hand, when the VVL 74 is transmitting the operating state of the small lift cam to the intake valve 21, the intake valve 21 is opened with a relatively small lift amount and the valve opening period is also shortened. The large lift cam and the small lift cam are set to be switched at the same valve closing timing or valve opening timing.

As with the VVT 75 on the exhaust side, the intake-side VVT 72 may adopt a known hydraulic, electromagnetic, or mechanical structure as appropriate, and the detailed structure is not shown. The valve opening timing and the valve closing timing of the intake valve 21 can also be continuously changed within a predetermined range by the VVT 72. Further, the lift amount and the operation timing of the intake valve 21 provided in each of the plurality of cylinders 18 may be controlled by the VVL 74 and the VVT 72 separately for each cylinder 18. Note that, instead of applying the VVL 74 to the intake side, only the VVT 72 may be applied and only the valve opening timing and the valve closing timing of the intake valve 21 may be changed.
VVT 72 and VVL 74 correspond to the “variable valve mechanism” in the present invention.

  In addition, for each cylinder 18, an injector 67 that directly injects fuel into the cylinder 18 (direct injection) is attached to the cylinder head 12. 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. 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 SW1, SW2, and 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 determines the state of the engine 1 and the vehicle by performing various calculations based on these detection signals, and in response to this, (direct injection) injector 67, spark plug 25, intake valve side VVT72 and VVL74. Control signals are output to the VVT 75 and VVL 71 on the exhaust valve side, the fuel supply system 62, and actuators of various valves (throttle valve 36, EGR valve 511). Thus, the PCM 10 operates the engine 1. Although details will be described later, the PCM 10 corresponds to an engine control device in the present invention. In particular, the PCM 10 functions as “variable valve mechanism control means” in the present invention.

[Operation area]
Next, with reference to FIG. 3, the operating region of the engine according to the embodiment of the present invention will be described. FIG. 3 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.

[Control of intake and exhaust valves]
Next, a specific example of control of the intake valve 21 and the exhaust valve 22 according to the embodiment of the present invention will be described with reference to FIG. FIG. 4 shows the intake valve 21 and the exhaust valve 22 in the second operation region R12 in which SI operation is performed, particularly in the region R13 (see FIG. 3) in which the engine speed is relatively low in the second operation region R12. Shows the operation. FIG. 4 shows the crank angle in the horizontal direction and the lift amounts of the intake valve 21 and the exhaust valve 22 in the vertical direction. Specifically, a broken line graph G11 indicates the operation of the exhaust valve 22 according to the crank angle, and a solid line graph G12 indicates the operation of the intake valve 21 according to the crank angle.

  As shown in the graph G12 in FIG. 4, in the present embodiment, in the low speed region R13 in the second operation region R12, the intake valve 21 is opened during the intake stroke and also opened during the exhaust stroke. Perform a double-open. In this case, in the exhaust stroke, both the intake valve 21 and the exhaust valve 22 are open. As described above, such double opening of the intake valve 21 is performed by the PCM 10 via the VVT 72 and VVL 74 (hereinafter, simply referred to as “intake side variable valve mechanism” as appropriate), This is realized by controlling the valve closing timing and the lift amount. In particular, in the present embodiment, the PCM 10 performs control to change the valve opening period of the intake valve 21 during the exhaust stroke. By doing so, the scavenging effect in the cylinder (the effect of expelling the exhaust gas from the cylinder and filling the cylinder with the intake air) is improved.

  Note that, in the region where the engine speed is higher than the region R13 in the second operation region R12, the PCM 10 does not open the intake valve 21 as described above twice. In this case, the PCM 10 opens the intake valve 21 once so that both the intake valve 21 and the exhaust valve 22 are open from the latter half of the exhaust stroke to the first half of the intake stroke (that is, so as to form an overlap period). Control to open only.

[Control by this embodiment]
Next, the details of control performed on the intake valve 21 via the intake side variable valve mechanism in the embodiment of the present invention will be described more specifically. As described above, in the present embodiment, the PCM 10 opens the intake valve 21 during the intake stroke and also during the exhaust stroke in the low rotation speed region R13 in the second operation region R12. The opening is executed, and control is performed to change the valve opening period of the intake valve 21 during this exhaust stroke. Specifically, the PCM 10 sets the valve opening timing of the intake valve 21 during the exhaust stroke based on the timing when the exhaust pulsation generated when the exhaust valve 22 opens after the expansion stroke (combustion stroke) becomes negative pressure. To do.

  With reference to FIG. 5, the basic concept of the control method of the intake valve 21 according to the embodiment of the present invention will be specifically described. In FIG. 5, the abscissa indicates the crank angle, and the ordinate indicates the pressure of the exhaust pulsation and the intake pulsation. Specifically, in FIG. 5, a graph G21 shows exhaust pulsation according to the crank angle, and a graph G22 shows intake pulsation according to the crank angle. These exhaust pulsation and intake pulsation are generated in the same cylinder 18, that is, due to the operation (combustion cycle) in a cylinder 18 different from the one cylinder 18 of interest. (The same shall apply hereinafter). Further, in FIG. 5, with respect to the graphs G21 and G22 showing the exhaust pulsation and the intake pulsation, the operation of the exhaust valve 22 according to the crank angle (graph G23) and the operation of the intake valve 21 according to the crank angle ( Graph G24) is shown superimposed.

  As shown in the graph G21 in FIG. 5, it can be seen that a relatively large exhaust pulsation occurs after the exhaust valve 22 is opened at the crank angle T14. In the expansion stroke (combustion stroke), the gas expands in the cylinder. In this stroke, the pressure of the gas in the cylinder is high, and when the exhaust valve 22 is opened in this state, the gas vigorously flows. By flowing out to the exhaust side (blowdown), a relatively large exhaust pulsation is generated. This exhaust pulsation is a wave (pressure wave) corresponding to the flow of exhaust gas, and is propagated in pressure from the inside of the cylinder to the exhaust side. Specifically, the exhaust pulsation changes between a positive pressure and a negative pressure by oscillating like a wave (see symbols A11, A12, and A13). Here, “negative pressure” means a state where the pressure of exhaust pulsation is lower than the pressure of intake pulsation (see graph G22), that is, a state where the pressure on the exhaust side is lower than the pressure on the intake side. “Positive pressure” means a state where the pressure of the exhaust pulsation is larger than the pressure of the intake pulsation, that is, a state where the pressure on the exhaust side is higher than the pressure on the intake side.

  More specifically, the exhaust pressure pulsation positive pressure wave (primary positive pressure wave) indicated by reference numeral A11 and the exhaust pulsation negative pressure wave indicated by reference numeral A12 (primary negative pressure wave) are caused by the blowdown described above. . On the other hand, the positive pressure wave and the negative pressure wave after the secondary, such as the positive pressure wave of the exhaust pulsation indicated by the symbol A13, are generated by the wave caused by blowdown colliding with the inner wall in the path through which the exhaust gas passes. It corresponds to the reflected wave. The primary positive pressure wave and the negative pressure wave mean a positive pressure wave and a negative pressure wave that are generated first (first time) after the exhaust valve 22 is opened, respectively. Each of them means a positive pressure wave and a negative pressure wave generated after the exhaust valve 22 is opened for the second time and thereafter.

  In this embodiment, exhaust gas is discharged from the cylinder by using negative pressure due to exhaust pulsation, that is, a state where the pressure on the intake side is higher than that on the exhaust side, and intake air flows into the cylinder. In order to obtain the scavenging effect, the intake valve 21 opens during a period in which the exhaust pulsation is negative, that is, the period in which the exhaust pulsation is negative and the valve opening period of the intake valve 21 overlap. Thus, the opening / closing timing of the intake valve 21 is controlled via the intake side variable valve mechanism. More specifically, the PCM 10 corresponds to the valve opening timing T11 (crank angle of the intake valve 21 during the exhaust stroke, based on the timing at which a primary negative pressure wave (see symbol A12) is generated in the exhaust pulsation. Set). That is, the PCM 10 controls the intake side variable valve mechanism so that the intake valve 21 is opened when the primary negative pressure wave is generated. This is because the primary negative pressure wave has a larger amplitude (that is, energy) than the secondary and subsequent negative pressure waves. Therefore, when the intake valve 21 is opened when the primary negative pressure wave is generated. This is because a large scavenging effect can be obtained. Further, as described above, since the negative pressure wave after the second order corresponds to the reflected wave, it is difficult to estimate the timing at which it occurs, whereas the primary negative pressure wave is blown down. This is because the occurrence timing can be accurately estimated and the intake valve 21 can be easily controlled.

Basically, the generation timing of the primary negative pressure wave is determined according to the valve opening timing T14 of the exhaust valve 22. Specifically, as the valve opening timing T14 of the exhaust valve 22 is retarded, the generation timing of the primary negative pressure wave is delayed, in other words, as the valve opening timing T14 of the exhaust valve 22 is advanced, the primary negative pressure wave is delayed. The generation timing of the pressure wave is advanced. Further, the degree of change in the generation timing of the primary negative pressure wave according to the valve opening timing T14 of the exhaust valve 22 substantially corresponds to the speed of sound. Therefore, the relationship between the valve opening timing T14 of the exhaust valve 22 and the generation timing of the primary negative pressure wave and the peak timing of the primary negative pressure wave are obtained in advance from experiments and simulations, and such a relationship is obtained. Based on this, the PCM 10 may set the valve opening timing T11 of the intake valve 21 in accordance with the actual valve opening timing T14 of the exhaust valve 22.
Although details will be described later, the generation timing of the primary negative pressure wave and the peak timing of the primary negative pressure wave in the exhaust pulsation are affected not only by the valve opening timing T14 of the exhaust valve 22, but also by the engine speed. Therefore, it is preferable to set the valve opening timing T11 of the intake valve 21 during the exhaust stroke based on both the valve opening timing T14 of the exhaust valve 22 and the engine speed.

  Further, in the present embodiment, the PCM 10 is configured so that the lift amount of the intake valve 21 is maximized at the timing (peak timing) T13 when the peak of the primary negative pressure wave occurs in the exhaust pulsation, that is, the peak of the primary negative pressure wave. The valve opening timing T11 of the intake valve 21 during the exhaust stroke is set so that the timing T13 coincides with the timing at which the lift amount of the intake valve 21 becomes maximum. By doing so, the scavenging effect is effectively improved by making maximum use of the negative pressure due to the primary negative pressure wave in the exhaust pulsation. Further, in the present embodiment, the PCM 10 is based on the timing at which the exhaust pulsation changes from negative pressure to positive pressure, that is, based on the timing at which the primary negative pressure wave switches to the secondary positive pressure wave (see symbol A13). The closing timing T12 of the intake valve 21 opened at is set. Specifically, the PCM 10 controls the valve closing timing of the intake valve 21 via the intake side variable valve mechanism so that the intake valve 21 is not opened when the exhaust pulsation is positive pressure. By doing so, exhaust gas blowback from the exhaust side to the intake side is suppressed.

  Next, with reference to FIG.6 and FIG.7, the relationship between an engine speed and the generation | occurrence | production timing of the negative pressure wave in exhaust pulsation is demonstrated. FIG. 6 is a diagram for explaining a difference in timing (crank angle) at which a primary negative pressure wave is generated in exhaust pulsation due to a difference in engine speed, and FIG. 7 is a graph showing engine speed (horizontal axis) and exhaust gas. It is a figure which shows the relationship with the crank angle (vertical axis | shaft) in which the primary negative pressure wave in a pulsation generate | occur | produces.

  In each of FIGS. 6A to 6C, the horizontal axis represents the crank angle, and the vertical axis represents the exhaust pulsation pressure and the intake pulsation pressure. FIG. 6A is a view similar to FIG. 5 and shows an exhaust pulsation or the like at a relatively low engine speed (for example, 1000 rpm). In FIG. 6A, elements denoted by the same reference numerals as those in FIG. 5 have the same meaning. FIG. 6B shows an exhaust pulsation at an engine speed (for example, 2000 rpm) higher than that in FIG. Specifically, in FIG. 6B, the graph G31 shows the exhaust pulsation according to the crank angle, the graph G32 shows the intake pulsation according to the crank angle, and the graph G33 shows the crank angle. The graph G34 shows the operation of the intake valve 21 according to the crank angle. FIG. 6C shows the exhaust pulsation at a higher engine speed (for example, 3000 rpm) than FIG. 6B. Specifically, in FIG. 6C, the graph G41 shows the exhaust pulsation according to the crank angle, the graph G42 shows the intake pulsation according to the crank angle, and the graph G43 shows the crank angle. The graph G44 shows the operation of the intake valve 21 according to the crank angle.

  As shown by reference signs A12, A21, and A22 in FIGS. 6A, 6B, and 6C, it can be seen that the higher the engine speed, the later the generation timing of the primary negative pressure wave in the exhaust pulsation. In other words, it can be seen that the crank angle at which the primary negative pressure wave is generated shifts to the retard side. Here, referring to FIG. 7, the relationship between the engine speed and the crank angle at which the primary negative pressure wave is generated in the exhaust pulsation is linear. Specifically, the crank angle at which the primary negative pressure wave is generated changes linearly according to the engine speed. This is because, since the exhaust pulsation is propagated by pressure almost at the speed of sound, the propagation speed is substantially constant. On the other hand, when the engine speed changes, the time required for one cycle changes (when the engine speed increases, 1). This is due to the change in the relationship between the crank angle and the time.

  Therefore, in the present embodiment, the PCM 10 sets the valve opening timing of the intake valve 21 during the exhaust stroke based on the engine speed. Specifically, according to the linear relationship between the engine speed and the crank angle at which the primary negative pressure wave is generated as shown in FIG. 7, the PCM 10 increases the opening timing of the intake valve 21 as the engine speed increases. Is controlled (see valve opening timings T11, T21, and T31 in FIGS. 6A to 6C) to control the intake side variable valve mechanism. In this case, as described above, the generation timing of the primary negative pressure wave is also affected by the valve opening timing T14 of the exhaust valve 22 (FIG. 6 illustrates the case where the valve opening timing T14 is fixed). Sets the opening timing of the intake valve 21 during the exhaust stroke based on both the engine speed and the opening timing T14 of the exhaust valve 22. Specifically, the PCM 10 retards the opening timing of the intake valve 21 as the engine speed increases and as the opening timing T14 of the exhaust valve 22 retards. For example, a map in which the opening timing of the intake valve 21 to be set in accordance with the engine speed and the opening timing T14 of the exhaust valve 22 is created in advance, and the PCM 10 refers to such a map. Thus, the intake valve 21 is set at the valve opening timing corresponding to the current engine speed and the valve opening timing T14 of the exhaust valve 22. Further, when the opening timing of the intake valve 21 is retarded according to the engine speed and the opening timing T14 of the exhaust valve 22 in this way, naturally, the PCM 10 also delays the closing timing of the intake valve 21. Horn. That is, the PCM 10 delays the closing timing of the intake valve 21 as the engine speed is higher and the opening timing T14 of the exhaust valve 22 is retarded (in FIGS. 6A to 6C). Valve closing timings T12, T22, T32).

  Here, as described above, the valve opening timing of the intake valve 21 is controlled only in the low speed region R13 in the second operating region R12 (see FIG. 3) based on the timing at which the exhaust pulsation becomes negative pressure. The reason for doing this is as follows. As the engine speed increases, the generation timing of the primary negative pressure wave in the exhaust pulsation is delayed (see symbols A12, A21, and A22 in FIGS. 6A to 6C), but when the engine speed increases to some extent. The primary negative pressure wave is not generated during the exhaust stroke. Further, when the engine speed increases, the primary negative pressure wave in the exhaust pulsation becomes gentle. Therefore, in the present embodiment, the valve opening timing of the intake valve 21 is controlled based on the timing at which the exhaust pulsation becomes negative in the region where the engine speed is higher than the low speed region R13 in the second operating region R12. I decided not to do it. In the region where the engine speed is higher than the low speed region R13, the PCM 10 does not execute the twice opening control of the intake valve 21, and the intake valve 21 and the exhaust valve 22 over the second half of the exhaust stroke and the first half of the intake stroke. Are controlled to open the intake valve 21 only once (valve overlap).

  Next, with reference to FIG. 8, the control process of the intake valve 21 according to the embodiment of the present invention will be specifically described. FIG. 8 is a flowchart showing a control process of the intake valve 21 according to the embodiment of the present invention. This control process is repeatedly executed by the PCM 10 at a predetermined cycle.

  First, in step S1, the PCM 10 acquires the engine speed and the opening timing of the exhaust valve 22 based on detection signals from the crank angle sensor SW12 and the cam angle sensor SW15.

  Next, in step S2, the PCM 10 is based on the relationship between the engine speed and the generation timing (crank angle) of the primary negative pressure wave with respect to the opening timing of the exhaust valve 22, which is obtained and stored in advance by experiments and simulations. For example, the generation timing of the primary negative pressure wave corresponding to the engine speed acquired in step S1 and the opening timing of the exhaust valve 22 is obtained on the basis of the relationship as shown in FIG.

  Next, in step S3, the PCM 10 acquires the engine speed and the cycle of the primary negative pressure wave corresponding to the engine speed. The cycle of the primary negative pressure wave also depends on the engine speed (specifically, the cycle becomes longer as the engine speed increases), and the relationship between the engine speed and the cycle of the primary negative pressure wave is also It is obtained and memorized in advance by experiments and simulations. The PCM 10 acquires the period of the primary negative pressure wave corresponding to the current engine speed based on the relationship between the engine speed and the primary negative pressure wave period thus stored.

Next, in step S4, the PCM 10 obtains the peak timing of the primary negative pressure wave based on the generation timing of the primary negative pressure wave acquired in step S2 and the period of the primary negative pressure wave acquired in step S3. For example, the PCM 10 obtains a timing obtained by adding a time corresponding to a half cycle of the primary negative pressure wave to the generation timing of the primary negative pressure wave as the peak timing of the primary negative pressure wave.
If the relationship between the engine speed and the opening timing of the exhaust valve 22 and the peak timing of the primary negative pressure wave is obtained and stored in advance, the processing for obtaining the peak timing of the primary negative pressure wave as described above. It is not necessary to perform.

  Next, in step S5, the PCM 10 sets the valve opening timing of the intake valve 21 during the exhaust stroke based on the peak timing of the primary negative pressure wave obtained in step S4. Specifically, the PCM 10 maximizes the lift amount of the intake valve 21 at the peak timing of the primary negative pressure wave, that is, the timing at which the peak timing of the primary negative pressure wave and the lift amount of the intake valve 21 become maximum. Is set so that the intake valve 21 opens during the exhaust stroke.

  Next, in step S6, the PCM 10 controls the intake side variable valve mechanism so that the intake valve 21 opens at the valve opening timing set in step S5.

[Function and effect]
Next, functions and effects of the engine control apparatus according to the embodiment of the present invention will be described.

  According to the present embodiment, when performing double opening control for opening the intake valve 21 in the exhaust stroke in addition to the intake stroke, the exhaust pulsation generated when the exhaust valve 22 is opened in the exhaust stroke is detected. Since the opening timing of the intake valve 21 during the exhaust stroke is set based on the negative pressure timing, it is possible to improve the scavenging effect of flowing the exhaust gas out of the cylinder and flowing the intake air into the cylinder. Thereby, the filling efficiency (volumetric efficiency) of air into the cylinder can be improved, and as a result, the output torque from the engine 1 can be improved. In addition, by improving the scavenging effect, it is possible to lower the temperature on the intake side by blowing gas from the intake side to the exhaust side via the cylinder 18. For example, it is estimated that the temperature of the high-temperature gas in the cylinder is received by the intake valve 21, so that the gas temperature in the vicinity of the valve back of the intake valve 21 and the like is considerably increased. (In other words, cooling and heat insulation effects of the intake valve 21 can be obtained). As a result, the intake temperature introduced into the cylinder in the intake process can be reduced, and pre-ignition can be appropriately suppressed.

  In this embodiment, since the valve opening timing of the intake valve 21 during the exhaust stroke is set based on the timing at which the primary negative pressure wave is generated in the exhaust pulsation, the primary negative pressure wave having large energy can be used. The scavenging effect can be further improved. Further, in the present embodiment, the valve opening timing of the intake valve 21 during the exhaust stroke is set so that the lift amount of the intake valve 21 is maximized at the timing when the primary negative pressure wave peak occurs in the exhaust pulsation. The energy of the primary negative pressure wave can be utilized to the maximum, and the scavenging effect can be further improved.

  Further, in the present embodiment, the higher the engine speed, the more retarded the opening timing of the intake valve 21 during the exhaust stroke, so that the exhaust pulsation, which changes according to the engine speed, matches the timing when the exhaust pulsation becomes negative pressure. Thus, the intake valve 21 can be appropriately opened. In this case, by using the timing at which the primary negative pressure wave is generated in the exhaust pulsation, this timing changes linearly according to the engine speed (see FIG. 7), so that the intake valve 21 can be easily controlled. It becomes possible. Furthermore, in this embodiment, since the valve opening timing of the intake valve 21 during the exhaust stroke is set based on the valve opening timing of the exhaust valve 22, the exhaust pulsation that changes according to the valve opening timing of the exhaust valve 22 is negative. The intake valve 21 can be appropriately opened in accordance with the timing when the pressure is reached.

  In the present embodiment, since the closing timing of the intake valve 21 opened during the exhaust stroke is set based on the timing at which the exhaust pulsation changes from negative pressure to positive pressure, the exhaust pulsation is positive pressure. Sometimes the intake valve 21 can be closed, and exhaust gas blowback from the exhaust side to the intake side can be suppressed. In this case, the higher the engine speed, the retarded the closing timing of the intake valve 21 opened during the exhaust stroke, so the exhaust pulsation that changes according to the engine speed changes from negative pressure to positive pressure. The intake valve 21 can be appropriately closed according to the timing.

In the above description, it has been described that the engine 1 according to the present embodiment is applied with a high compression ratio engine set to a relatively high geometric compression ratio. Since the distance between the top surface of the piston and the lower surface of the cylinder head at the top dead center can be made so that the volume in the cylinder when located near the top dead center is considerably reduced, the cylinder is configured to be short. Therefore, if the intake valve 21 and the exhaust valve 22 are opened near the top dead center, they may come into contact with the top surface of the piston. Therefore, the intake valve 21 and the exhaust valve 22 should not be opened near the top dead center. ing. In some cases, a valve recess may be provided on the top surface of the piston so that the intake valve 21 and the exhaust valve 22 can be opened near the top dead center.
When the control according to this embodiment is applied to such a high compression ratio engine, in this embodiment, the intake valve 21 is opened in the first half of the exhaust stroke away from the top dead center. Even in a high compression ratio engine configured to shorten the distance between the piston top surface and the cylinder head bottom surface, the opened intake valve 21 does not contact the piston top surface. Therefore, the control according to this embodiment can be appropriately applied to a high compression ratio engine in which a valve recess is not provided on the piston top surface (of course, it can also be applied to an engine in which a valve recess is provided on the piston top surface. In addition, when the control according to this embodiment is applied to a high compression ratio engine, it is not necessary to separately provide a valve recess on the piston top surface.

  The technique described in Patent Document 1 described above also uses the negative pressure in the exhaust pulsation as in the present embodiment, but in this embodiment, the negative pressure generated in the same cylinder is used. On the other hand, in the technique described in Patent Document 1, negative pressure generated in other cylinders is used. The technique described in Patent Document 1 is configured such that the distance between the top surface of the piston and the bottom surface of the cylinder head near the top dead center is shortened in order to open the intake valve 21 near the top dead center. It cannot be basically applied to a high compression ratio engine. This is because the opened intake valve 21 tends to contact the top surface of the piston.

[Modification]
In the above-described embodiment, the opening timing of the intake valve 21 during the exhaust stroke is set based on the timing at which the primary negative pressure wave is generated in the exhaust pulsation, but this is not limitative. In another example, the valve opening timing of the intake valve 21 during the exhaust stroke may be set based on the timing at which secondary negative pressure waves (preferably secondary negative pressure waves) are generated in the exhaust pulsation. In this case, since the negative pressure wave after the secondary is a reflected wave of the wave caused by blowdown, the timing at which the negative pressure wave after the secondary is generated is considered in consideration of the location where the exhaust gas is reflected in the exhaust path. It may be estimated. In addition, since the secondary and subsequent negative pressure waves move at a sound velocity corresponding to the exhaust gas temperature, it is preferable to estimate the timing at which the secondary and subsequent negative pressure waves occur in consideration of this.

1 engine 10 PCM
18 cylinder 21 intake valve 22 exhaust valve 25 spark plug 67 injector 71, 74 VVL
72, 75 VVT

Claims (6)

Comprising a cylinder exhaust valve is provided for discharging the intake valve and the exhaust for introducing intake air into the cylinder from the cylinder, a variable valve mechanism for changing the opening and closing timing and lift amount of the intake valve, an engine In the first operating region where the load is less than a predetermined value, the mixture containing fuel is compressed and self-ignited, and in the second operating region where the load is higher than the first operating region, the mixture containing fuel is forced. a control apparatus for an engine Ru was ignited,
Variable valve mechanism control means for controlling the variable valve mechanism so as to open the intake valve not only in the intake stroke but also in the exhaust stroke in the first or second operation region of the engine;
The variable valve mechanism control means is the second operating region in which the air-fuel mixture is forcibly ignited and the engine speed is equal to or lower than a predetermined speed when the exhaust valve is opened during the exhaust stroke of the engine. Based on the timing at which the primary negative pressure wave of the exhaust pulsation generated in the engine is generated, the higher the engine speed, the more the opening timing of the intake valve and the closing timing of the intake valve during the exhaust stroke are retarded. An engine control device characterized by that.   2. The engine control according to claim 1, wherein the variable valve mechanism control means sets a closing timing of the intake valve that is opened during an exhaust stroke based on a timing at which the exhaust pulsation changes from a negative pressure to a positive pressure. apparatus. The engine control apparatus according to claim 1 or 2 , wherein the variable valve mechanism control means sets the opening timing of the intake valve during an exhaust stroke based on the opening timing of the exhaust valve. The variable valve mechanism control means sets the valve opening timing of the intake valve during the exhaust stroke so that the lift amount of the intake valve is maximized at the timing when a negative pressure wave peak occurs in the exhaust pulsation. The engine control device according to any one of claims 1 to 3 . The engine has a plurality of cylinders each including the intake valve and the exhaust valve,
The variable valve mechanism control means is configured to detect the opening timing of the intake valve during an exhaust stroke when the exhaust valve of one cylinder having the intake valve among the plurality of cylinders is opened. The engine control device according to any one of claims 1 to 4 , wherein the engine control device is set based on a timing at which the pulsation becomes negative pressure. The variable valve mechanism control means retards the closing timing of the intake valve opened during the exhaust stroke as the opening timing of the exhaust valve is retarded, and increases the exhaust stroke as the engine speed increases. The engine control device according to any one of claims 1 to 5 , wherein the closing timing of the intake valve that has been opened is retarded.

Images