JP6288610B2 - 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 at least the lift amount of an exhaust valve and an intake valve.

  Conventionally, an internal EGR system that raises the temperature of the mixed gas in the combustion chamber by opening the exhaust valve during a predetermined period during the intake stroke to reversely flow the burned gas (internal EGR gas) from the exhaust port to the combustion chamber. Is known (see, for example, Patent Document 1).

JP 2008-051017 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, and in a low load region, compression self-ignition (“CI (Compression Ignition)” or “HCCI (Homogeneous-) Technology that performs spark ignition (SI (Spark Ignition)) in a high load region has been developed. In such an engine (hereinafter referred to as “HCCI engine” as appropriate), the exhaust valve is opened not only in the exhaust stroke but also in the intake stroke from the viewpoint of increasing the temperature in the cylinder in the low load region. By executing the opening, the internal EGR gas is reintroduced into the cylinder. Further, in the HCCI engine, in the low load region, as the engine load increases, the ratio of internal EGR gas reintroduced into the cylinder (internal EGR rate) is decreased, thereby causing the premature increase due to the increase in the cylinder temperature. I try to avoid ignition.

  In the HCCI engine, when the internal EGR rate is decreased as the engine load increases as described above, the internal EGR rate is continuously changed within a desired range according to the engine load from the viewpoint of improving fuel efficiency and emission. It is desirable to make it. Here, as a method of changing the internal EGR rate, a method of performing control to change the lift amount and / or opening / closing timing of the exhaust valve and / or the intake valve using a variable valve mechanism is conceivable. As described above, when changing the lift amount and / or opening / closing timing of the exhaust valve and / or the intake valve, if priority is given to continuously changing the internal EGR rate in accordance with the engine load, a pumping loss occurs and the fuel consumption is reduced. It may get worse. Therefore, it can be said that it is necessary to perform control to change the internal EGR rate in consideration of generation of pumping loss.

  The present invention has been made to solve the above-described problems of the prior art, and in an engine that opens the exhaust valve twice in a predetermined low load region and reintroduces the internal EGR gas into the cylinder. An object of the present invention is to provide an engine control device that can appropriately ensure controllability of an internal EGR rate while suppressing the occurrence of a pumping loss.

In order to achieve the above object, the present invention provides an engine control device including an intake valve for introducing intake air into a cylinder and a cylinder provided with an exhaust valve for discharging exhaust gas from the cylinder. An exhaust valve comprising: a first exhaust valve having a predetermined exhaust effective area in the intake stroke; and a second exhaust valve having an exhaust effective area smaller than the exhaust effective area of the first exhaust valve in the intake stroke; The exhaust side variable valve mechanism that changes at least the lift amount of the engine and the exhaust side so that the exhaust valve is opened in the intake stroke in addition to the exhaust stroke when the engine operating state is within a predetermined region on the low load side Control means for controlling the variable valve mechanism and reintroducing exhaust gas into the cylinder as internal EGR gas, the control means being in a first operating region on the low load side in a predetermined region. In The exhaust side variable valve mechanism is controlled so that both the first exhaust valve and the second exhaust valve of the exhaust valve are opened in the intake stroke, and the engine operating state is the first operation in a predetermined region. When the engine is in the second operating region on the higher load side than the region, the exhaust side variable valve mechanism is controlled so that only the first exhaust valve of the exhaust valve is opened in the intake stroke, and the engine operating state is The exhaust-side variable valve mechanism is controlled so that only the second exhaust valve of the exhaust valve is opened during the intake stroke when it is in the third operation region on the higher load side than the second operation region in the predetermined region. and further includes an intake side variable valve mechanism for at least changing the lift amount of the intake valve, the intake side variable valve mechanism is also controlled by the control means, the control means, the ratio of the internal EGR gas in accordance with an increase in engine load The first exhaust valve and the second exhaust valve of the exhaust valve depend on whether the operating state of the engine belongs to the first operating region, the second operating region, or the third operating region so as to continuously decrease within a predetermined range. The exhaust side variable valve mechanism is controlled so as to switch the valve to be opened in the intake stroke among the exhaust valves, and the intake side variable valve mechanism is controlled so that the lift amount of the intake valve increases as the engine load increases. When the engine load increases, the region to which the engine operating state belongs is switched from the first operation region to the second operation region, and the valve that opens in the intake stroke is changed from both the first exhaust valve and the second exhaust valve. When switching to only the first exhaust valve, and the region to which the engine operating state belongs is switched from the second operation region to the third operation region, and the valve to be opened in the intake stroke is the first exhaust valve. When the engine is switched to the second exhaust valve, the intake side variable valve mechanism is controlled so that the lift amount of the intake valve is once reduced and then the lift amount of the intake valve is increased. The ratio of the internal EGR gas is continuously reduced .

In the present invention configured as described above, the first to third predetermined regions in which the exhaust valve is opened (that is, opened twice) and the internal EGR gas is reintroduced into the cylinder in the intake stroke in addition to the exhaust stroke. In the first operation region on the low load side, both the first and second exhaust valves are opened twice, and the lift amount is relatively large in the second operation region on the higher load side than the first operation region. Only the first exhaust valve having the opening is opened twice, and only the second exhaust valve having a relatively small lift amount is opened twice in the third operation region on the higher load side than the second operation region. Thereby, controllability of the proportion of internal EGR gas (internal EGR rate) can be improved while suppressing the occurrence of pumping loss. Specifically, the internal EGR rate can be appropriately changed according to the engine load in a predetermined region where the internal EGR gas is used.
In addition, according to the present invention, since an operation mode in which only one of the first and second exhaust valves is opened twice is applied, compared to a configuration in which both of the two exhaust valves are always opened twice, The internal EGR gas can be distributed more uniformly in the cylinder, and the advance angle of the combustion center of gravity when the engine load increases can be suppressed. Therefore, it is possible to expand the predetermined region in which the internal EGR gas is used to the high load side while suppressing an increase in combustion noise due to the advance of the combustion center of gravity accompanying an increase in engine load.
Further, according to the present invention, the internal EGR rate can be appropriately reduced in accordance with an increase in engine load, and the controllability of the internal EGR rate can be improved. In particular, the internal EGR rate can be appropriately and continuously reduced within a desired range as the engine load increases.
In addition, according to the present invention, the lift amount of the intake valve is temporarily reduced at the time of switching described above (specifically, when the operation mode of the exhaust valve is switched), so that continuity in the change of the internal EGR rate is ensured. It is possible to appropriately suppress the disappearance, that is, the occurrence of a step in the change in the internal EGR rate.

  In the present invention, it is preferable that the second exhaust valve has a lift amount in the intake stroke smaller than that of the first exhaust valve, so that an effective exhaust area in the intake stroke is smaller than that of the first exhaust valve.

In the present invention, preferably, in the engine described above, premixed compression self-ignition combustion is performed when the engine operating state is within a predetermined region, and spark ignition combustion is performed when the engine operating state is outside the predetermined region. Done.
According to the present invention configured as described above, the exhaust valve is controlled via the exhaust-side variable valve mechanism as described above when the operating state of the engine is within a predetermined region where premixed compression self-ignition combustion is performed. Thus, the controllability of the internal EGR rate can be improved, so that the ignitability and stability of the premixed compression self-ignition combustion can be appropriately ensured on the low load side of the predetermined region, and the predetermined region On the high load side, pre-ignition can be appropriately suppressed. Further, by suppressing the advance angle of the combustion center of gravity when the engine load increases, the operating range in which the premixed compression self-ignition combustion is performed using the internal EGR can be expanded to the high load side.

  According to the engine control apparatus of the present invention, in an engine in which the exhaust valve is opened twice in a predetermined low load region and the internal EGR gas is reintroduced into the cylinder, the occurrence of the pumping loss is suppressed and the internal EGR is suppressed. The controllability of the rate can be ensured appropriately.

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 schematic side view which shows the exhaust valve by embodiment of this invention. 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. In embodiment of this invention, it is explanatory drawing about the exhaust effective area required in order to satisfy | fill the request | requirement range of an internal EGR rate. It is a figure which shows the lift curve of the exhaust valve and intake valve by embodiment of this invention. It is explanatory drawing about the range of the realizable internal EGR rate obtained by the comparative example. It is explanatory drawing about the range of the realizable internal EGR rate obtained by embodiment of this invention. It is explanatory drawing about the control method performed in order to change an internal EGR rate in 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 apparatus according to an embodiment of the present invention is applied. FIG. 2 shows a schematic side view of an exhaust valve according to an embodiment of the present invention. FIG. 3 is a block diagram showing an engine control apparatus according to an 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. Specifically, two exhaust valves 22 are provided for each cylinder 18. As shown in FIG. 2, the exhaust valve 22 includes an exhaust valve 22a having a lift amount indicated by a symbol L1 and an exhaust valve 22b having a lift amount indicated by a symbol L2 (the lift amounts L1 and L2 are the valve amounts). Is the distance in the direction of motion away from the valve seat surface). In this case, the lift amount L1 of the exhaust valve 22a is configured to be larger than the lift amount L2 of the exhaust valve 22b (L1> L2). Further, these exhaust valves 22a and 22b have substantially the same valve diameter. The exhaust valve 22a corresponds to the “first exhaust valve” in the present invention, and the exhaust valve 22b corresponds to the “second exhaust valve” in the present invention.

  Of the valve systems that drive the intake valve 21 and the exhaust valve 22, respectively, on the exhaust side, the operation modes of a plurality of exhaust valves 22 provided for each cylinder 18 are "normal mode" and "special mode". For example, a hydraulically operated variable valve lift mechanism (see FIG. 3; hereinafter referred to as VVL (Variable Valve Lift)) 71 and a phase variable mechanism capable of changing the rotational phase of the exhaust camshaft with respect to the crankshaft 15. (Hereinafter referred to as VVT (Variable Valve Timing)) 75.

  Although detailed illustration of the configuration of the VVL 71 on the exhaust side 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 it includes a lost motion mechanism that selectively transmits an operating state of one of the first and second cams to the exhaust valve 22. 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 operating state of the second cam is When transmitting to the exhaust valve 22, the exhaust valve 22 is operated in a “special mode” that opens twice during the exhaust stroke and also opens 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. Such a VVL 71 corresponds to the “exhaust side variable valve mechanism” in the present invention. An electromagnetically driven valve system that drives the exhaust valve 22 by an electromagnetic actuator may be employed. On the other hand, the VVT 75 may employ a hydraulic, electromagnetic, or mechanical known structure as appropriate, and the detailed structure is not shown. The exhaust valve 22 can continuously change its valve opening timing and valve closing timing within a predetermined range by the VVT 75.

  As shown in FIG. 3, VVL 74 and VVT 72 are provided on the intake side in the same manner as the exhaust side valve train system provided with VVL 71 and VVT 75. Unlike the VVL 71 on the exhaust side, the intake-side VVL 74 is configured so that the lift amount of the intake valve 21 can be changed continuously. The VVL 74 corresponds to the “intake side variable valve mechanism” in the present invention. On the other hand, as with the VVT 75 on the exhaust side, the intake side VVT 72 may employ 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.

  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 that purify harmful components in the exhaust. 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 an EGR passage for returning a part of the exhaust to the intake passage 30. 50 is connected. 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 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 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 a “control unit” in the present invention.

[Operation area]
Next, with reference to FIG. 4, an operation region of the engine 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 economy and exhaust emission performance, the engine 1 is not ignited by the spark plug 25 in an operation region (hereinafter referred to as “HCCI region”) R1 where the engine load is relatively low. Then, compression ignition combustion is performed by premixed compression self-ignition (Homogeneous-Charge Compression Ignition: HCCI). However, as the load on the engine 1 increases, in the compression ignition combustion, the combustion becomes too steep and causes problems such as combustion noise. Therefore, in this engine 1, in the operation region (hereinafter referred to as "SI region") R2 where the engine load is relatively high, compression ignition combustion is stopped and forced ignition combustion (here, sparks) using the spark plug 25 is performed. Switch to ignition combustion (Spark Ignition: SI). As described above, the engine 1 is configured to switch between the HCCI mode in which the premixed compression self-ignition combustion is performed and the SI mode in which the spark ignition combustion is performed in accordance with the operation state of the engine 1, in particular, the load of the engine 1. ing. However, the boundary line for mode switching is not limited to the illustrated example.

  As shown in FIG. 4, the HCCI region R1 in which the engine 1 is operated in the HCCI mode includes a first operation region R11 on the low load side and a second operation region on the higher load side than the first operation region R11. R12 is divided into a third operation region R13 on the higher load side than the second operation region R12. Although details will be described later, it is provided for each cylinder 18 depending on whether the operating state of the engine 1 is in the first operating region R11, the second operating region R12, or the third operating region R13 in the HCCI region R1. The operation modes of the two exhaust valves 22a and 22b are switched.

[Control Method According to this Embodiment]
Next, in the embodiment of the present invention, the contents of control performed on the exhaust valve 22 (exhaust valves 22a and 22b) via the VVL 71 as the exhaust side variable valve mechanism will be specifically described. As described above, in the present embodiment, in the HCCI region R1, the PCM 10 performs a so-called double opening of exhaust so that the exhaust valve 22 opens during the exhaust stroke and also during the intake stroke. The VVL 71 is controlled to operate in the mode, and the internal EGR gas is reintroduced into the cylinder.

  First, the exhaust effective area required to satisfy the required range of the internal EGR rate will be described with reference to FIG. FIG. 5 shows the effective intake area on the horizontal axis and the effective exhaust area on the vertical axis. Further, in FIG. 5, the internal EGR rate is represented by grayscale shading. Specifically, the internal EGR rate increases as the color becomes lighter, and the internal EGR rate decreases as the color becomes darker.

  The effective intake area corresponds to an amount obtained by multiplying the area of the flow path through which the gas passes through the intake valve 21 and the volumetric flow rate of the gas. The effective exhaust area passes through the exhaust valve 22. This corresponds to an amount obtained by multiplying the area of the flow path by the volume flow rate of the gas. More specifically, the effective intake area and the effective exhaust area are amounts obtained by integrating the product of the flow area and the volume flow rate change rate with the crank angle for the valve opening periods of the intake valve 21 and the exhaust valve 22, respectively. Further, the intake effective area uniquely corresponds to the lift amount of the intake valve 21 (hereinafter referred to as “intake valve lift amount” as appropriate), and is an amount that changes in accordance with the change in the intake valve lift amount. In addition, the exhaust effective area uniquely corresponds to the lift amount of the exhaust valve 22 (hereinafter referred to as “exhaust valve lift amount” as appropriate), and is an amount that changes in accordance with the change in the exhaust valve lift amount. .

  In FIG. 5, graphs G11 and G12 show contour lines of the internal EGR rate, respectively. Specifically, the graph G11 shows the upper limit (for example, 75%) in the range of the required internal EGR rate for the internal EGR gas to be reintroduced into the cylinder in the HCCI region R1, and the graph G12 The lower limit value (for example, 25%) in the range of the internal EGR rate of the request is shown. On the other hand, the graph G13 is a boundary line where a pumping loss occurs, and shows that a pumping loss occurs when the effective intake area and the effective exhaust area located below the graph G13 are applied.

  In the present embodiment, a range of the effective exhaust area is applied such that the required internal EGR rate range is realized while preventing a pumping loss. In this case, the range of the effective exhaust area is made as narrow as possible. This is because the intake-side VVL 74 is configured so that the lift amount of the intake valve 21 can be continuously changed. Therefore, the intake-side VVL 74 greatly changes the lift amount of the intake valve 21, that is, changes the intake effective area. This is intended to minimize the range in which the effective exhaust area is changed by taking a large range. Then, from the graphs G11, G12, and G13 described above, the range indicated by the symbol R3 in FIG. 5 is obtained as the range of the effective exhaust area to be applied.

  Here, in the present embodiment, the PCM 10 according to the first operation region R11, the second operation region R12, and the third operation region R13 in the HCCI region R1 in realizing the desired exhaust effective area range R3. (Refer to FIG. 4) The operation modes of the two exhaust valves 22a and 22b provided for each cylinder 18 are switched. Specifically, (1) “both valve operation mode” in which both the exhaust valves 22a and 22b are operated in a special mode and both the exhaust valves 22a and 22b are opened twice over the intake stroke and the exhaust stroke. (2) Of the exhaust valves 22a and 22b, only the exhaust valve 22a having the larger lift amount is operated in the special mode, and only the exhaust valve 22a is opened twice over the intake stroke and the exhaust stroke. Among the valves 22a and 22b, the exhaust valve 22b having the smaller lift amount is operated in the normal mode and is opened only once during the exhaust stroke, and (3) the exhaust valve 22a. 22b, only the exhaust valve 22b having the smaller lift amount is operated in the special mode, and only the exhaust valve 22b is opened twice over the intake stroke and the exhaust stroke, and the exhaust valve 22a, 22b The exhaust valve 22a having the larger valve amount is operated in the normal mode, and the “second one-valve operation mode” in which the valve is opened only once during the exhaust stroke is switched and applied in the HCCI region R1, so that the desired The exhaust effective area range R3 is realized.

  In the present embodiment, the PCM 10 executes the double valve operation mode in the first operation region R11, executes the first single valve operation mode in the second operation region R12, and the second single valve in the third operation region R13. Run the operating mode. In other words, in this embodiment, the operation region to which the both-valve operation mode is applied is defined as the first operation region R11, the operation region to which the first one-valve operation mode is applied is defined as the second operation region R12, and the second The operation region to which the single valve operation mode is applied is defined as a third operation region R13.

  According to the above-described embodiment, since both the exhaust valves 22a and 22b are opened twice in the double valve operation mode, the exhaust effective area in the intake stroke becomes the largest. In the first single valve operation mode, the lift amount Since only the exhaust valve 22a having a larger value is opened twice, the effective exhaust area in the intake stroke is smaller than that in the double valve operation mode. In the second single valve operation mode, only the exhaust valve 22b having a smaller lift amount is used. Since it is opened twice, the effective exhaust area in the intake stroke is smaller than in the first one-valve operation mode. Therefore, according to the present embodiment, since the two-valve operation mode, the first one-valve operation mode, and the second one-valve operation mode are switched in this way, both the two exhaust valves 22 are always opened twice. (A configuration in which both valve operation modes are always executed), two exhaust valves 22 having the same lift amount, and a two-valve operation mode in which both the two exhaust valves 22 are opened twice and two exhaust valves 22 Compared with a configuration in which only one side is switched to a one-valve operation mode in which only one is opened (hereinafter, this configuration is referred to as a “comparative example” as appropriate), a range of possible exhaust effective areas is widened.

  From such a viewpoint, in the present embodiment, the lift amounts L1 and L2 of the exhaust valves 22a and 22b are set so that a desired exhaust effective area range R3 is appropriately realized. Specifically, the sum of the lift amount L1 and the lift amount L2 is determined so that the upper limit value of the desired exhaust effective area range R3 is appropriately realized, and the lower limit of the desired exhaust effective area range R3 is determined. The lift amounts L1 and L2 of the exhaust valves 22a and 22b are set by determining the smaller lift amount L2 so that the value is appropriately realized.

  Next, the lift curves of the exhaust valve 22 and the intake valve 21 applied in the embodiment of the present invention will be described with reference to FIG. FIG. 6 shows a specific example of lift curves of the exhaust valve 22 and the intake valve 21 according to the present embodiment. In FIG. 6, the abscissa indicates the crank angle, and the ordinate indicates the lift amount of the exhaust valve 22 (exhaust valves 22 a and 22 b) and the intake valve 21.

  In FIG. 6, a graph G21 shows the lift curve of the exhaust valve 22a having the larger lift amount of the exhaust valves 22a and 22b. The exhaust valve 22a is opened twice over the intake stroke and the exhaust stroke. I understand that. The lift curve G21 of the exhaust valve 22a is applied in the first operation region R11 and the second operation region R12 in the HCCI region R1 in which the exhaust valve 22a is operated in the special mode, that is, the both valve operation mode and This is applied in the first single valve operation mode. The graph G22 shows the lift curve of the exhaust valve 22b having the smaller lift amount of the exhaust valves 22a and 22b, and the exhaust valve 22b is opened twice over the intake stroke and the exhaust stroke. I understand. The lift curve G22 of the exhaust valve 22b is applied in the first operation region R11 and the third operation region R13 in the HCCI region R1 in which the exhaust valve 22b is operated in a special mode. This is applied in the second single valve operation mode.

  On the other hand, the graph G23 shows the lift curve of the intake valve 21, and it can be seen that the intake valve 21 is opened in the intake stroke. The lift curve G23 of the intake valve 21 is applied in the HCCI region R1. In FIG. 6, only one lift curve G23 of the intake valve 21 is shown, but as described above, the lift amount of the intake valve 21 is continuously changed by the VVL 74. There are a plurality of lift curves having different lift amounts.

  Next, the range of the internal EGR rate that can be realized when the lift amount of the intake valve 21 is changed while switching the operation mode of the exhaust valve 22 will be described with reference to FIGS. 7 and 8.

  FIG. 7 is an explanatory diagram of the range of realizable internal EGR rates obtained by the comparative example described above. In the comparative example, two exhaust valves 22 having the same lift amount are used, and both of the two exhaust valves 22 are opened twice, and only one of the two exhaust valves 22 (which one of the exhaust valves 22 is selected). Switch between the one-valve operation mode that opens twice. Further, in the comparative example, as the lift amount of the exhaust valve 22, an amount between the lift amount L1 of the exhaust valve 22a and the lift amount L2 of the exhaust valve 22b according to the present embodiment is applied. Hereinafter, the lift amount of the exhaust valve 22 according to the comparative example is appropriately expressed as “L3” (L1> L3> L2).

  The upper graph in FIG. 7 shows the relationship between the intake valve lift amount and the internal EGR rate, and the lower graph in FIG. 7 shows the intake valve lift amount and PMEP (Pumping Mean Effective Pressure) that is the pump loss average effective pressure. Shows the relationship. The symbol “PL” in the lower graph of FIG. 7 indicates the pressure corresponding to the pumping loss. As shown in the lower graph of FIG. 7, in the comparative example, in a range not lower than the pumping loss PL, The intake valve lift amount is changed for each of the double valve operation mode and the single valve operation mode. Then, according to the comparative example, as shown in the upper graph of FIG. 7, the range of the internal EGR rate indicated by the symbol R41 is realized in the dual valve operation mode, and the internal EGR rate indicated by the symbol R42 is realized in the single valve operation mode. A range is realized. In this case, in the comparative example, the internal EGR rate in the range indicated by the symbol R43 cannot be realized by the above-described pumping loss PL. Therefore, according to the comparative example, there is an internal EGR rate range R43 that cannot be realized even if the intake valve lift amount is changed while switching the operation mode of the exhaust valve 22, so the internal EGR rate is continuously increased. Cannot be changed.

  On the other hand, FIG. 8 is an explanatory diagram of the range of internal EGR rates that can be achieved, obtained by the embodiment of the present invention. Similarly to FIG. 7, FIG. 8 shows the relationship between the intake valve lift amount and the internal EGR rate, and the lower graph shows the relationship between the intake valve lift amount and PMEP. Also in the present embodiment, as shown in the lower graph of FIG. 8, the intake valve lift amount for each of the double valve operation mode, the first single valve operation mode, and the second single valve operation mode within a range that does not fall below the pumping loss PL. To change. Then, according to the present embodiment, as shown in the upper graph of FIG. 8, the internal EGR rate indicated by the symbol R5 as a whole by the double valve operation mode, the first single valve operation mode, and the second single valve operation mode. A range of is realized. In the internal EGR rate range R5 according to this embodiment, there is no internal EGR rate range R43 that cannot be realized by the pumping loss PL as in the comparative example. Therefore, according to the present embodiment, the internal EGR rate can be changed appropriately and continuously within the range R5 by changing the intake valve lift amount while switching the operation mode of the exhaust valve 22.

  Further, in the comparative example, the one-valve operation mode is performed by the exhaust valve 22 having the lift amount L3, whereas in the present embodiment, the exhaust valve 22b having the lift amount L2 smaller than the lift amount L3 is used. Since the second one-valve operation mode is implemented, the lower limit value of the realizable internal EGR rate range is smaller than that of the comparative example. That is, according to the present embodiment, the lower range of the realizable internal EGR rate is expanded as compared with the comparative example.

  Next, with reference to FIG. 9, a specific control method performed to change the internal EGR rate in the embodiment of the present invention will be described. In FIG. 9, as in FIG. 5, the horizontal axis represents the effective intake area (which uniquely corresponds to the intake valve lift amount), and the vertical axis represents the effective exhaust area (which uniquely corresponds to the exhaust valve lift amount). Show. Elements having the same reference numerals as those in FIG. 5 have the same meaning. The expression for the internal EGR rate is the same as in FIG.

  Here, as can be seen from FIG. 8 described above, when switching between the two-valve operation mode and the first one-valve operation mode at a certain intake valve lift amount, the intake valve lift amount is determined in the both-valve operation mode. Since the internal EGR rate when set to 1 and the internal EGR rate when the intake valve lift amount is set in the first one-valve operation mode are basically different, the continuity of the change in the internal EGR rate during this switching is It is not ensured, that is, there is a step in the change of the internal EGR rate. This step in the internal EGR rate similarly occurs when switching between the first single valve operation mode and the second single valve operation mode. Therefore, in the present embodiment, the PCM 10 cooperates with the control for switching the operation mode of the exhaust valve 22 to suppress the step in the change in the internal EGR rate that occurs at the time of switching the operation mode, and lifts the intake valve 21. Control to change the amount.

  Details of the control for changing the intake valve lift amount in cooperation with switching of the operation mode of the exhaust valve 22 will be described with reference to FIG. In FIG. 9, the range indicated by the symbol R61 can be realized by changing the intake valve lift amount when the double valve operation mode is applied (that is, when both the exhaust valves 22a and 22b are operated in the special mode). This is a range of the internal EGR rate. Further, the range indicated by the symbol R62 can be realized by changing the intake valve lift amount when the first single valve operation mode is applied (that is, when only the larger exhaust valve 22a is operated in the special mode). This is a range of the internal EGR rate. The range indicated by the symbol R63 can be realized by changing the intake valve lift amount when the second one-valve operation mode is applied (that is, when only the smaller exhaust valve 22b is operated in the special mode). This is a range of the internal EGR rate. These internal EGR rate ranges R61, R62, and R63 are basically determined in accordance with the effective exhaust area (corresponding to the exhaust valve lift amount) and the boundary line G13 where the pumping loss occurs.

  In the present embodiment, the PCM 10 cooperates with the switching of the operation mode of the exhaust valve 22 based on the above-described internal EGR rate ranges R61, R62, and R63 as shown by the arrow A1 in FIG. Change the lift amount. Specifically, for example, when the engine load increases in a state where the engine operation state is in the first operation region R11, the PCM 10 operates the exhaust valve 22 in the dual valve operation mode, specifically, the exhaust valve The VVL 74 is controlled so as to gradually increase the lift amount of the intake valve 21 while controlling the VVL 71 so that both the 22a and the exhaust valve 22b are operated in the special mode (see reference numeral A11). When the engine load increases and the engine operating state is switched from the first operation region R11 to the second operation region R12, the PCM 10 switches from the both-valve operation mode to the first one-valve operation mode. The VVL 71 is controlled so as to switch the exhaust valve 22b from the special mode to the normal mode while maintaining the exhaust valve 22a in the special mode, and the VVL 74 is controlled so as to temporarily reduce the lift amount of the intake valve 21 (see reference A12). ). Specifically, the PCM 10 reduces the lift amount of the intake valve 21 along the contour line of the internal EGR rate in order to maintain the internal EGR rate during this switching.

  Thereafter, when the engine load increases in a state where the engine operating state is in the second operation region R12, the PCM 10 operates the exhaust valve 22 in the first one-valve operation mode, specifically, the exhaust valve 22a. The VVL 74 is controlled so as to gradually increase the lift amount of the intake valve 21 while controlling the VVL 71 so as to operate in the special mode and the exhaust valve 22b in the normal mode (see reference A13). When the engine load increases and the engine operating state is switched from the second operation region R12 to the third operation region R13, the PCM 10 switches from the first one-valve operation mode to the second one-valve operation mode, Specifically, the VVL 71 is controlled so that the exhaust valve 22a is switched from the special mode to the normal mode and the exhaust valve 22b is switched from the normal mode to the special mode, and the VVL 74 is controlled so as to temporarily reduce the lift amount of the intake valve 21. (See reference A14). Specifically, the PCM 10 reduces the lift amount of the intake valve 21 along the contour line of the internal EGR rate in order to maintain the internal EGR rate during this switching. Thereafter, when the engine load increases in a state where the engine operating state is in the third operation region R13, the PCM 10 operates the exhaust valve 22 in the second one-valve operation mode, specifically, the exhaust valve 22a. The VVL 74 is controlled so as to gradually increase the lift amount of the intake valve 21 while controlling the VVL 71 so as to operate in the normal mode and the exhaust valve 22b in the special mode (see reference A15).

  Note that when the engine load decreases in the HCCI region R1, the PCM 10 performs the control in a flow reverse to the above-described control. Also in this case, the PCM 10 changes the lift amount of the intake valve 21 in cooperation with the switching of the operation mode of the exhaust valve 22, as indicated by an arrow A1 in FIG.

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

  In the present embodiment, the HCCI region R1 is divided into first to third operation regions R11, R12, R13, and both the exhaust valve 22a and the exhaust valve 22b are opened twice in the first operation region R11 on the low load side, In the second operation region R12 on the higher load side than the first operation region R11, only the exhaust valve 22a having a relatively large lift amount is opened twice, and the third operation region R13 on the higher load side than the second operation region R12. Then, only the exhaust valve 22b having a relatively small lift amount is opened twice. Thereby, controllability of the internal EGR rate can be improved while suppressing the occurrence of pumping loss. Specifically, in the HCCI region R1, the internal EGR rate can be appropriately changed according to the engine load.

  Further, according to the present embodiment, the operation mode (the first one-valve operation mode and the second one-valve operation mode) in which only one of the exhaust valves 22a and 22b is opened twice is applied. Compared with the configuration in which both of the two are always opened twice, the internal EGR gas can be distributed more uniformly in the cylinder, and the advance angle of the combustion center of gravity when the engine load increases can be suppressed. Therefore, it is possible to expand the HCCI region R1 using the internal EGR gas to the high load side while suppressing an increase in combustion noise due to the advance of the combustion center of gravity accompanying an increase in engine load.

  Further, according to the present embodiment, in the HCCI region R1, the control for switching the operation mode of the exhaust valve 22 and the control for changing the lift amount of the intake valve 21 so that the internal EGR rate decreases as the engine load increases. Therefore, the internal EGR rate can be appropriately reduced as the engine load increases.

  In particular, according to the present embodiment, when the engine load increases in the HCCI region R1, depending on which of the first operation region R11, the second operation region R12, and the third operation region R13 the engine operating state belongs to. Thus, control is performed to switch the valve to be opened twice between the exhaust valve 22a and the exhaust valve 22b, and control is performed to increase the lift amount of the intake valve 21 in accordance with an increase in engine load. Accordingly, the internal EGR rate can be decreased continuously (more specifically, linearly) within a desired range.

  In particular, according to the present embodiment, the engine load increases, the region to which the engine operating state belongs is switched from the first operation region R11 to the second operation region R12, and the valves that are opened twice are the exhaust valve 22a and the second valve. When switching from both of the two exhaust valves 22b to only the exhaust valve 22a, and the region to which the engine operating state belongs is switched from the second operating region R12 to the third operating region R13, and the valve to be opened twice is switched from the exhaust valve 22a. When switching to the exhaust valve 22b, control is performed so that the lift amount of the intake valve 21 is once reduced. Therefore, continuity in the change of the internal EGR rate is not ensured at the time of the switching, that is, there is a step difference in the change of the internal EGR rate. Can be appropriately suppressed.

[Modification]
In the above-described embodiment, the exhaust valve 22a is set to the lift amount L1, and the exhaust valve 22b is set to the lift amount L2. That is, the fixed lift amounts L1 and L2 are applied to the exhaust valves 22a and 22b. However, in another example, the VVL 71 may be configured so that the lift amount of the exhaust valves 22a and 22b can be continuously changed.

  In the above-described embodiment, the exhaust effective area is different between the exhaust valve 22a and the exhaust valve 22b by making the lift amount L1 of the exhaust valve 22a different from the lift amount L2 of the exhaust valve 22b. There is no limit to doing it. In another example, the exhaust valve 22a and the exhaust valve 22b may have different exhaust effective areas of the exhaust valves 22a and 22b by changing the valve diameter, the diameter of the throat portion, and the like.

  In the above-described embodiment, the engine 1 having two exhaust valves 22a and 22b for each cylinder 18 is shown. However, the present invention can also be applied to an engine having three or more exhaust valves 22 for each cylinder 18. It is. Even in that case, the exhaust valves 22 may be configured so that the effective exhaust areas are different.

1 engine 10 PCM
18 cylinder 21 intake valve 22 exhaust valve 22a exhaust valve (first exhaust valve)
22b Exhaust valve (second exhaust valve)
25 Spark plug 67 Injector 71 VVL (exhaust side variable valve mechanism)
74 VVL (Intake side variable valve mechanism)
72, 75 VVT

Claims (3)

An engine control device including a cylinder provided with an intake valve for introducing intake air into a cylinder and an exhaust valve for discharging exhaust gas from the cylinder,
An exhaust valve comprising: a first exhaust valve having a predetermined exhaust effective area in the intake stroke; and a second exhaust valve having an exhaust effective area smaller than the exhaust effective area of the first exhaust valve in the intake stroke;
An exhaust side variable valve mechanism for changing at least the lift amount of the exhaust valve;
When the operating state of the engine is within a predetermined region on the low load side, the exhaust side variable valve mechanism is controlled to open the exhaust valve not only in the exhaust stroke but also in the intake stroke, thereby Control means for reintroducing gas into the cylinder;
Have
The control means includes
When the operating state of the engine is in the first operating region on the low load side in the predetermined region, both the first exhaust valve and the second exhaust valve of the exhaust valve are opened in the intake stroke. To control the exhaust side variable valve mechanism,
When the operating state of the engine is in the second operating region on the higher load side than the first operating region in the predetermined region, only the first exhaust valve of the exhaust valve is opened in the intake stroke. To control the exhaust side variable valve mechanism,
When the operating state of the engine is in the third operating region on the higher load side than the second operating region in the predetermined region, only the second exhaust valve of the exhaust valve is opened in the intake stroke. to, and controls the exhaust side variable valve mechanism,
An intake side variable valve mechanism for changing at least the lift amount of the intake valve, and the intake side variable valve mechanism is also controlled by the control means;
The control means includes
The engine operating state is any of the first operating region, the second operating region, and the third operating region so that the ratio of the internal EGR gas continuously decreases within a predetermined range as the engine load increases. The exhaust side variable valve mechanism is controlled so as to switch a valve to be opened in the intake stroke among the first exhaust valve and the second exhaust valve of the exhaust valve according to The intake side variable valve mechanism is controlled so that the lift amount of the intake valve increases in accordance with the increase,
As the engine load increases, the region to which the engine operating state belongs is switched from the first operation region to the second operation region, and valves that are opened in the intake stroke are connected to the first exhaust valve and the second exhaust valve. When switching to only the first exhaust valve from both, and the region to which the engine operating state belongs is switched from the second operation region to the third operation region, and the valve that opens in the intake stroke is the first exhaust valve. When switching from the first exhaust valve to the second exhaust valve, the intake side variable valve mechanism is controlled so as to temporarily reduce the lift amount of the intake valve and then increase the lift amount of the intake valve, thereby A control apparatus for an engine, characterized in that the ratio of the internal EGR gas is continuously decreased in accordance with the increase .   2. The second exhaust valve according to claim 1, wherein a lift amount in an intake stroke is smaller than that of the first exhaust valve, and thereby an effective exhaust area in the intake stroke is smaller than that of the first exhaust valve. Engine control device. 2. The engine according to claim 1, wherein premixed compression self-ignition combustion is performed when the engine operating state is within the predetermined region, and spark ignition combustion is performed when the engine operating state is outside the predetermined region. Or the control apparatus of the engine of 2 .