Control device for an internal combustion engine

Abstract

Control device (200) for an internal combustion engine (100) for controlling an internal combustion engine (100) with: a motor body (1), a variable compression ratio mechanism (A) which is configured to change a mechanical compression ratio of the engine body (1); and an intake system (3) configured to recirculate exhaust gas discharged from a combustion chamber (11) of the engine body (1) to an intake passage (30) of the engine body (1), wherein the control device (200) has a compression ratio control part which is configured to control the variable compression ratio mechanism (A) such that the mechanical compression ratio becomes a target compression ratio, wherein the compression ratio control part is configured to set the target compression ratio to a lower value when exhaust gas is recirculated on a low-load side of the engine in a predetermined operating range than when exhaust gas is not recirculated, in order to set an effective compression ratio to a lower value when the exhaust gas is recirculated on the low-load side of the engine in the predetermined operating range than when the exhaust gas is not recirculated.

Description

Technical background

[0001] The present disclosure relates to a control device for an internal combustion engine. State of the art

[0002] JP 2003 - 314 318 A discloses a conventional control device for an internal combustion engine, which is configured to lower a compression ratio to effect exhaust gas recirculation on a high-load side of the engine and to increase the compression ratio to effect exhaust gas recirculation on a low-load side of the engine.

[0003] Further prior art is known from US 2011 / 0 290 218 A1, which discloses a spark-ignition internal combustion engine equipped with a variable valve timing mechanism capable of changing the valve closing time after bottom dead center and with an exhaust gas recirculation mechanism that allows a portion of the exhaust gas to flow back into a combustion chamber as exhaust gas recirculation. Furthermore, the amount of exhaust gas recirculation is reduced only in the range where the valve closing time is on the side that is retarded with respect to a specific closing time, and this reduction increases the further the valve closing time is on the retarded side. Additionally, an effective compression ratio is maintained constant within a specific range.

[0004] JP 2012 - 225 199 A relates to an internal combustion engine with spark ignition, a variable compression ratio mechanism, a variable valve mechanism, and an ignition timing adjustment device, configured to perform control such that the combustibility of fuel in the combustion chamber decreases. The engine has a load threshold associated with an ignition timing to stabilize the combustibility of the fuel in the combustion chamber, and control is performed to maintain the ignition timing at a constant, fixed ignition point within a load range below the load threshold. When control is performed, during which the combustibility of the fuel in the combustion chamber decreases, the fixed mechanical compression ratio is reduced, and the fixed valve closing timing is also advanced.The load threshold value associated with the ignition timing is defined based on a decrease in the fixed mechanical compression ratio and a lead angle of the fixed valve closing time. An effective compression ratio is kept constant within a specific range.

[0005] Furthermore, DE 11 2009 004 735 B4 discloses a spark-ignition internal combustion engine with a variable compression ratio mechanism that can change the mechanical compression ratio, a variable valve timing mechanism that can control the closing time of an intake valve, and an EGR mechanism that can introduce a portion of the exhaust gas into a combustion chamber as EGR gas via the EGR line. In the spark-ignition internal combustion engine, the mechanical compression ratio is increased during low-load operation compared to high-load operation. The higher the EGR rate, the higher the actual compression ratio is set. Summary of Revelation

[0006] If the engine load decreases from a low-load state where exhaust gas is recirculated, it is necessary to fully close the EGR valve to stop exhaust gas recirculation and ensure combustion stability. However, even after the EGR valve is fully closed, exhaust gas remaining in an EGR passage on the downstream side of the valve will briefly enter the cylinders. Therefore, when exhaust gas recirculation is stopped from the recirculation state, combustion can become temporarily unstable in the aforementioned conventional control device of an internal combustion engine.

[0007] The present disclosure was created with a focus on such a problem and has the task of preventing combustion from becoming unstable when exhaust gas recirculation is stopped.

[0008] To solve the aforementioned problem, according to one aspect of the present disclosure, a control device for an internal combustion engine is provided for controlling an internal combustion engine which is equipped with an engine body, a variable compression ratio mechanism configured to change the mechanical compression ratio of the engine body, and an intake system configured to recirculate exhaust gas discharged from a combustion chamber of the engine body to an intake passage of the engine body. The control device has a compression ratio control element configured to control the variable compression ratio mechanism such that the mechanical compression ratio becomes a target compression ratio.Furthermore, the compression ratio control section is configured to set the target compression ratio to a lower value when exhaust gas is recirculated on a low-load side of the engine in a predetermined operating range than when exhaust gas is not recirculated, in order to set an effective compression ratio to a lower value when exhaust gas is recirculated on the low-load side of the engine in the predetermined operating range than when exhaust gas is not recirculated.

[0009] According to this aspect of the present disclosure, it is possible to prevent combustion from becoming unstable by stopping exhaust gas recirculation. Brief description of drawings Fig. Figure 1 is a schematic view of the configuration of an internal combustion engine and an electronic control unit controlling the internal combustion engine. Fig. Figure 2 is a cross-sectional view of the engine body of an internal combustion engine. Fig. Figure 3 is a disassembled perspective view of a variable compression ratio mechanism. Fig. 4A is a view that explains the operation of a variable compression ratio mechanism. Fig. 4B is a view that explains the operation of a variable compression ratio mechanism. Fig. 4C is a view that explains the operation of a variable compression ratio mechanism. Fig. 5 is a view which specifies a target compression ratio tε on to the EGR gas injection time and a target compression ratio tε off to the EGR gas non-injection time according to an engine load at a specific engine speed of this embodiment. Fig. Figure 6 is a flowchart that explains a compression ratio control according to a first embodiment of the present disclosure. Fig. Figure 7 is a target EGR rate calculation image to calculate a target EGR rate tRe based on an engine operating condition. Fig. Figure 8 is a timing diagram that explains the operation of a compression ratio control according to the first embodiment of the present disclosure. Fig. 9 is a view which explains the content of a compression ratio control according to a second embodiment of the present disclosure. Fig. Figure 10 is a flowchart which explains a compression ratio control according to the second embodiment of the present disclosure. Fig. 11 is a view which presents a method for correcting a target compression ratio tε offexplained at the time when no EGR gas is introduced. Fig. Figure 12 is a timing diagram which explains the operation of a compression ratio control according to the second embodiment of the present disclosure. Fig. 13 is a view which explains a compression ratio control according to the second embodiment of the present disclosure. Fig. Figure 14 is a timing diagram which explains the operation of a control of an inlet valve closing time according to a modification of the second embodiment of the present disclosure. Description of embodiments

[0010] The embodiments of the present disclosure are explained in detail below with reference to the drawings. It should be noted that identical individual elements are designated by the same reference symbols in the following explanation. First embodiment

[0011] Fig. Figure 1 is a schematic view of the configuration of an internal combustion engine 100 and an electronic control unit 200, which controls the internal combustion engine 100 according to a first embodiment of the present disclosure. Fig. Figure 2 is a cross-sectional view of an engine body 1 of the internal combustion engine 100.

[0012] The internal combustion engine 100 is provided with an engine body 1 which has a number of cylinders 10, a fuel supply system 2, an intake system 3 and an exhaust system 4.

[0013] The engine body 1 burns fuel within combustion chambers 11 formed in the cylinders 10 (see Fig. 2) to generate, for example, the power needed to drive a vehicle, etc. The engine body 1 has a spark plug 15 for each cylinder, which faces a combustion chamber 11 of the cylinder 10.

[0014] As in Fig. As shown in Figure 2, the engine body 1 further comprises a pair of inlet valves 81 and a pair of exhaust valves 91 for each cylinder and is provided with an inlet valve actuating device 8 for driving the opening and closing actions of the inlet valves 81 and an exhaust valve actuating device 9 for driving the opening and closing actions of the exhaust valves 91. The inlet valve actuating device 8 according to the present disclosure is configured to control the opening and closing times of an inlet valve 81 to any desired time by driving the opening and closing actions of the inlet valves 81 via an inlet camshaft 82 and providing a variable valve actuating mechanism B at one end of the inlet camshaft 82, which changes a relative phase angle of the inlet camshaft 82 with respect to a crankshaft 14 by means of a hydraulic control.

[0015] Within each cylinder 10, a piston 12 is held, which absorbs combustion pressure and moves back and forth within the cylinder 10. The piston 12 is connected to the crankshaft 14 by a connecting rod 13. The crankshaft 14 converts the reciprocating motion of the piston 12 into a rotational motion.

[0016] Furthermore, according to the present embodiment, the engine body 1 has a variable compression ratio mechanism A at a connecting part between the cylinder block 2 and a crankcase 4. The variable compression ratio mechanism A, according to the present embodiment, changes the relative positions of the cylinder block 2 and the crankcase 4 in the direction of a cylinder axis line in order to change the volume of a combustion chamber 11 when the piston 12 is positioned at top dead center. A relative position sensor 211 is attached to the connecting part between the cylinder block 2 and the crankcase 4 to determine the relative position relationship between the cylinder block 2 and the crankcase 4. This relative position sensor 211 outputs a signal indicating a change in the gap between the cylinder block 2 and the crankcase 4.The output signal of the relative position sensor 211 is input into an electronic control unit 200 via an associated analog-to-digital converter 207. The electronic control unit 200 determines the mechanical compression ratio of the engine block 1 based on the output signal of the relative position sensor 211. Details of the variable compression ratio mechanism A are described with reference to [reference missing]. Fig. 3 and Fig. 4C explained.

[0017] Returning to Fig. 1 has the fuel supply system 2 fuel injectors 20 one of a design with electronic control, a supply pipe 21, a supply pump 22, a fuel tank 23 and a pressure pipe 24.

[0018] Each cylinder 10 is equipped with a fuel injector 20, which is positioned centrally on the top of the combustion chamber 11 such that it is located next to the spark plug 15 and faces the combustion chamber 11 of cylinder 10. The opening time (injection quantity) and opening time (injection timing) of the fuel injector 20 are modified by control signals from the electronic control unit 200. When the fuel injector 20 is open, fuel is injected directly from the fuel injector 20 into the interior of the combustion chamber 11.

[0019] Supply pipe 21 is connected to fuel tank 23 via pressure pipe 24. A supply pump 22 is located in the center of fuel pipe 24 to pressurize the fuel stored in fuel tank 23 and supply it to supply pipe 21. Supply pipe 21 temporarily stores the high-pressure fuel pumped by supply pump 22. When fuel injector 20 opens, the high-pressure fuel stored in supply pipe 21 is injected directly into combustion chamber 11 by fuel injector 20.

[0020] The supply pump 22 is configured to vary its output quantity. The output quantity of the supply pump 22 is changed by a control signal from the electronic control unit 200. By controlling the output quantity of the supply pump 22, the fuel pressure within the supply line 21, i.e., the injection pressure of the fuel injectors 20, is controlled.

[0021] The intake system 3 is a system for directing intake air into the combustion chambers 11 and is configured to modify the state of the intake air (intake pressure, intake temperature, and EGR (exhaust gas recirculation) gas quantity) received in the combustion chambers 11. The intake system 3 has an intake passage 30, an intake manifold 31, and an EGR passage 32.

[0022] The intake passage 30 is connected at one end to an air cleaner 34 and at the other end to an intake manifold 31a of the intake manifold 31. In the intake passage 30, starting from the upstream side, an air flow meter 212, a compressor 71 of an exhaust gas turbocharger 7, an intercooler 35, and a throttle valve 36 are provided in sequence.

[0023] The airflow meter 212 determines the flow of air which flows through the interior of the intake passage 30 and is finally taken into the cylinders 10 (hereinafter referred to as "intake quantity").

[0024] The compressor 71 has a compressor housing 71a and a compressor wheel 71b, which is arranged inside the compressor housing 71a. The compressor wheel 71b is driven by a coaxially attached turbine wheel 72b of the exhaust gas turbocharger 7 to rotate, compressing the intake flowing into the compressor housing 71a and expelling it.

[0025] The charge air cooler 35 is a heat exchanger for cooling the intake air, which is compressed by the compressor 71 and brought to a high temperature, e.g. by outside cooling air, coolant, etc.

[0026] The throttle valve 36 changes the cross-sectional area of ​​the intake passage 30 in order to adjust the amount of intake air introduced into the intake manifold 31a. The throttle valve 36 is driven by a throttle actuator 36a to open and close, and then a throttle sensor 213 determines the degree of opening (throttle opening degree).

[0027] The intake manifold 31 is connected to an inlet port 16 formed on the engine body 1 (see Fig. 2) and distributes the intake flowing from the intake passage 30 through the inlet port 16 evenly to the cylinders 10. On the intake collector 31a of the intake manifold 31, an intake pressure sensor 214 for determining the pressure of the intake taken into the cylinders (intake pressure) and an intake temperature sensor 215 for determining the temperature of the intake taken into the cylinders (intake temperature) are provided.

[0028] The EGR passage 32 is a passage connecting the exhaust passage 42 and the intake passage 30, allowing a portion of the exhaust gas discharged from the cylinders 10 to be recirculated to the intake passage 30 by means of the pressure differential, and enabling the exhaust gas recirculated to the intake passage 30 to ultimately be recirculated to the cylinders 10. The exhaust gas flowing into the EGR passage 32 is hereinafter referred to as the "EGR gas". The EGR passage 32 contains, in sequence from the upstream side, an EGR cooler 37 and an EGR valve 38.

[0029] The EGR cooler 37 is a heat exchanger to cool EGR gas, e.g., by means of outside cooling air, cooling water, etc.

[0030] The EGR valve 38 is a solenoid valve that allows the opening degree to be adjusted continuously or in stages. This opening degree is controlled by the electronic control unit 200 according to the engine operating conditions. By controlling the opening degree of the EGR valve 38, the flow of EGR gas, which is recirculated to the intake manifold 31a, is adjusted.

[0031] The exhaust system 4 is a system to drain the exhaust gas from the cylinders and is equipped with an exhaust manifold 41, an exhaust passage 42 and an exhaust aftertreatment apparatus 43.

[0032] The exhaust manifold 41 is connected to an exhaust port 17 formed on the engine body 1 (see Fig. 2) The exhaust gas discharged from cylinders 10 is introduced together into the exhaust passage 42.

[0033] At the exhaust passage 42, a turbine 72 of the exhaust gas turbocharger 7 and an exhaust gas aftertreatment apparatus 43 are provided in a sequence starting from the upstream side.

[0034] The turbine 72 is equipped with a turbine housing 72a and the turbine wheel 72b arranged inside the turbine housing 72a. The turbine wheel 72b is driven to rotate by the energy of the exhaust gas flowing into the turbine housing 72a and drives the compressor wheel 71b, which is attached coaxially to it.

[0035] The exhaust aftertreatment apparatus 43 is an apparatus or device to clean the exhaust gas and then release it into the outside air, and is equipped with various types of exhaust gas cleaning catalysts to remove harmful substances and a filter to trap harmful substances, etc.

[0036] The electronic control unit 200 has a digital computer which is equipped with components connected to each other by a bidirectional bus 201, such as a ROM (read-only memory) 202, a RAM (working memory) 203, a CPU (microprocessor) 204, an input port 205 and an output port 206.

[0037] In addition to the output signals of the aforementioned relative position sensor 211, throttle sensor 212, air flow meter 213, intake pressure sensor 214, intake air temperature sensor 215, etc., output signals from a water temperature sensor 216 for determining the temperature of the coolant for cooling the engine block 1 (hereinafter referred to as the "coolant temperature"), etc., are input to input terminal 205 via associated analog-to-digital converters 207. Furthermore, the output voltage of a load sensor 217 is input to input terminal 205 via an associated analog-to-digital converter 207 to generate an output voltage proportional to the amount of depressurization of an accelerator pedal 220 (hereinafter referred to as the "accelerator depressor"). Furthermore, the output signal of a crankshaft angle sensor 218 is input at the input terminal 205 as a signal for calculating the engine speed, etc., which is triggered every time the crankshaft 14 of the engine body 1 rotates by, for example,Rotating by 15°, it generates an output pulse. In this way, output signals from various sensor types are inputted to the input terminal 205, which are necessary for controlling the combustion engine 100.

[0038] At the output terminal 206, the fuel injectors 20 or spark plugs 15, the variable compression ratio mechanism A, the variable valve actuation mechanism B and other control parts are electrically connected to each other by means of corresponding driver circuits 208.

[0039] The electronic control unit 200 outputs control signals from the output terminal 206 to control the control parts and controls the combustion engine 100 based on the output signals of the various sensor types entered at the input terminal 205.

[0040] Fig. Figure 3 is a disassembled perspective view of the variable compression ratio mechanism A according to the present embodiment.

[0041] As in Fig. As shown in Figure 3, a plurality of spaced-apart projections 50 are formed on the lower part of the two side walls of the cylinder block 2. Cam insertion holes 51 with a round cross-section are formed on these projections.

[0042] On the other hand, a plurality of spaced-apart projections 52, which fit between the associated projections 50, are formed on the upper surface of the crankcase 4. Cam insertion holes 53 with a round cross-section are also formed on these projections 52.

[0043] Furthermore, the variable compression ratio mechanism A has a pair of camshafts 54 and 55. Round cams 58 are attached to the camshafts 54 and 55 to rotate within the cam mounting holes 53 with predetermined gaps. These round cams 58 are coaxial with the axes of rotation of the camshafts 54 and 55. On the other hand, eccentrics 57 extend along the two sides of the round cams 58 (see Fig. 4A to Fig. 4C), which are arranged eccentrically with respect to the axes of rotation of the camshafts 54 and 55. Separate round cams 56 are attached to the eccentrics 57 to enable eccentric rotation. As in Fig. Figure 3 shows these round cams 56 attached to the two sides of the round cams 58. These round cams 56 are inserted into the corresponding cam insertion holes 51 in such a way that they can rotate in them.

[0044] Worm gears 63 and 64 are attached to individual end sections of the camshafts 54 and 55, which mesh with a pair of worms 61 and 62 provided on a camshaft 60. The pair of worms 61 and 62 have opposite directions of rotation to allow the camshafts 54 and 55 to rotate in opposite directions. The camshaft 60 is rotated by the motor 65. By operating the motor 65 to rotate the camshafts 54 and 55 in opposite directions, the volumes of the combustion chambers 11 are adjusted when the pistons 12 are positioned at top dead center, as shown in Fig. 3A to Fig. Figure 3C shows, modified. A cam rotation angle sensor 221 is mounted on the camshaft 55, which generates an output signal indicating the rotation angle of the camshaft 55. The output signal of the cam rotation angle sensor 221 is input into the electronic control unit 200 via the associated analog-to-digital converter 207. The following is described with reference to Fig. 4A to Fig. 4C explains the operation of the variable compression ratio mechanism A.

[0045] Fig. 4a to Fig. 4C are views that explain the operation of the variable compression ratio mechanism A.

[0046] Fig. 4A is a view of the state in which the volume of a combustion chamber 11, when the piston 12 is positioned at top dead center, is maximized by the variable compression ratio mechanism A, i.e., the state in which the mechanical compression ratio is minimized. Fig. 4B is a view of the state in which the volume of a combustion chamber 11, when the piston 12 is positioned at a top dead center, is brought by the variable compression ratio mechanism A into a state between the maximum and the minimum, i.e., the state in which the mechanical compression ratio is one between the minimum and the maximum. Fig. 4C is a view of the state in which the volume of a combustion chamber 11, when the piston 12 is positioned at top dead center, is minimized by the variable compression ratio mechanism A, i.e., the state in which the mechanical compression ratio is maximized.

[0047] If the round cams 58 attached to the camshafts 54 starting from the in Fig. 4A state shown, as indicated by the arrows in Fig. As shown in Figure 4A, when rotated in opposite directions, the eccentrics 57 move away from each other, so that the round cams 56 within the cam insertion holes 51 rotate in directions opposite to the round cams 58. As shown in Fig. As shown in Figure 4B, the positions of the eccentrics 57 change from upper positions to positions at intermediate heights. When the round cams 58, as shown in Figure 4B, are in the upper positions, the positions of the eccentrics 57 change from upper positions to positions at intermediate heights. Fig. As shown in 4C, the eccentrics 57 are rotated in the directions indicated by the arrows and reach their lowest positions next.

[0048] It should be noted that Fig. 4A to Fig. 4C shows the positional relationship between a center “a” of a round cam 58, a center “b” of an eccentric 57 and a center “c” of a round cam 56 in their corresponding states.

[0049] As a comparison of Fig. 4A to Fig. As explained in Figure 4C, the relative position of the crankcase 4 and the cylinder block 2 is determined by the distance between the center “a” of the round cams 58 and the center “c” of the round cams 56. The greater the distance between the center “a” of the round cams 58 and the center “c” of the round cams 56, the further the cylinder block 2 moves away from the crankcase 4. That is, the variable compression ratio mechanism A according to the present embodiment changes the relative position between the crankcase 4 and the cylinder block 2 by means of a crank mechanism utilizing the rotating cams. When the cylinder block 2 separates from the crankcase 4, the volumes of the combustion chambers 11 increase when the pistons 12 are positioned at top dead center.In this way it is possible to change the volumes of the combustion chambers 11 when the pistons 12 are positioned at top dead center by rotating the camshafts 54 and 55.

[0050] It should be noted that the in Fig. 2 and Fig. Figure 3 shows a variable compression ratio mechanism A as an example. For instance, this could also be one with an upper joint, one end of which is connected to a piston by a piston pin, a lower joint which is connected to the other end of the upper joint and a crankpin of the crankshaft, a camshaft which is substantially parallel to the crankshaft, and a camshaft in which one end is connected to the camshaft in order to oscillate around it, and in which another end is connected to the lower joint and configured to rotate the camshaft by an engine in order to change the top dead center position of the piston and to change the mechanical compression ratio.

[0051] As in the present embodiment, in the case of an internal combustion engine 110, which has a variable compression ratio mechanism A and an intake system 3 configured to recirculate EGR gas to the cylinders, it is possible to reduce the oxygen concentration in the combustion chambers 11 and lower the combustion temperature by recirculating the EGR gas to the cylinders 10. Therefore, during the EGR gas injection time, when EGR gas is recirculated to the cylinders 10, it is possible to suppress the occurrence of knocking, compared to the EGR gas non-injection time, when EGR gas is not recirculated to the cylinders 10.

[0052] By recirculating the EGR gas to cylinders 10, it is possible to operate the engine block 1 in a state where the mechanical compression ratio is increased compared to the EGR gas non-injection time. This improves thermal efficiency and thus fuel economy. Furthermore, recirculating the EGR gas reduces the flow of fresh air through throttle valve 36 by precisely this amount, necessitating an increase in the throttle opening to supply the required air volume to cylinders 10. This reduces pumping losses, further improving thermal efficiency and fuel economy.

[0053] On the other hand, combustion can become unstable due to the drop in oxygen concentration in the combustion chambers 11 if EGR gas is recirculated to the cylinders 10.

[0054] For this reason, in the present embodiment, the recirculation of the EGR gas is stopped in a part of the operating range on the engine's low-load side, in which the fuel injection quantity is relatively small and combustion becomes slightly unstable.

[0055] If the engine operating condition changes and switches from an operating range in which the EGR gas is recirculated to cylinders 10 (hereinafter referred to as an "EGR gas inlet range") to an operating range on the engine's low-load side in which EGR gas is not recirculated to cylinders 10 (hereinafter referred to as an "EGR gas non-inlet range"), the EGR valve 38 is controlled such that the EGR opening degree becomes zero (is completely closed). However, even after the EGR valve 38 is completely closed, EGR gas remaining in the EGR passage 32 on the downstream side of the EGR valve 38 is briefly introduced into cylinders 10.When switching from an EGR gas injection area to an EGR gas non-injection area on the engine's low-load side, unnecessary EGR gas is temporarily injected into cylinder 10 in an EGR gas non-injection area, resulting in unstable combustion and, in the worst case, misfires.

[0056] One method for stabilizing combustion is increasing the mechanical compression ratio. Increasing the mechanical compression ratio makes it possible to raise the temperature of the air-fuel mixture in the combustion chambers 11 at the time of ignition (near top dead center), thereby improving the ignitability of the air-fuel mixture and potentially also increasing the combustion rate.

[0057] To ensure the stability of combustion when switching from an EGR gas injection range to an EGR gas non-injection range on the engine's low-load side, the variable compression ratio mechanism A is controlled in the present embodiment to avoid increasing the mechanical compression ratio to the maximum value during the EGR gas injection period, but rather to set the EGR ratio to a relatively low value under knock-suppressing conditions and to increase the mechanical compression ratio during the EGR gas non-injection period.Because of this, it is possible to increase the mechanical compression ratio when switching from an EGR gas injection range to an EGR gas non-injection range on the engine's low-load side, and it is therefore possible to prevent combustion from becoming unstable, even when EGR gas is temporarily injected into cylinder 10 during an EGR gas non-injection range on the engine's low-load side.

[0058] Fig. 5 is a view which shows a target compression ratio (solid line Y1) tε on the EGR gas injection time of the present embodiment at a specific engine speed and a target compression ratio (dashed line) tε off The EGR non-induction time is shown according to the engine load. As shown in Fig. As shown in Figure 5, in the present embodiment the range in which the engine load is lower than a predetermined first load KL1 and the range in which it corresponds to a predetermined second load KL2 or more are EGR gas non-injection ranges, while the range in which it is the first load KL1 to less than the second load KL2 is an EGR gas injection range.

[0059] It should be noted that the dashed line X1 in Fig. 5 an upper threshold compression ratio (hereinafter referred to as an “upper threshold compression ratio for the prevention of misfires”) ε lim shows which can prevent combustion from becoming unstable and misfires from occurring at the EGR gas introduction time by increasing the mechanical compression ratio to the maximum compression ratio ε maxis increased when the engine load changes from the state in an EGR gas injection range, in which continuous operation with a constant engine load is carried out at a certain engine speed (state in which an EGR rate is controlled to a target EGR rate), and switches to an EGR gas non-injection range.

[0060] As in Fig. Figure 5 shows the target compression ratio tε in an operating range on the engine's low-load side. on to the EGR gas injection time on the upper threshold compression ratio to prevent misfires ε lim set and the target compression ratio tε off to the EGR gas non-injection time to the maximum compression ratio ε max set. That is, in an operating range on the engine's low-load side, the target compression ratio tε is set. onto a smaller value than the target compression ratio tε during the EGR gas injection time off The EGR gas non-injection time is set. Because of this, it is possible to increase the mechanical compression ratio when the engine switches from an EGR gas induction range to an EGR gas non-injection range on the low-load side, thus preventing unstable combustion.

[0061] In the high-load operating range of the engine, it is necessary to reduce the mechanical compression ratio along with the increase in engine load to prevent knocking. For this reason, in the high-load operating range of the engine, the target compression ratio tε is reduced when the engine load is increased. on The EGR gas injection time is gradually reduced from the upper threshold compression ratio to prevent misfires ε limlowered, while the target compression ratio tε off The EGR gas non-injection time also gradually depends on the maximum compression ratio ε. max is lowered. As explained above, at this time, during the EGR gas injection time, it is possible to suppress knocking better than during the EGR gas non-injection time, and it is therefore possible to operate the engine block 1 in a state in which the mechanical compression ratio is set higher than during the EGR gas non-injection time. For this reason, the target compression ratio tε on The EGR gas injection time in an operating range on the engine's high-load side is set to a higher value than the target compression ratio tε. off to the EGR gas non-injection time.

[0062] Fig. Figure 6 is a flowchart that explains a compression ratio control according to the present embodiment.

[0063] In step S1, the electronic control unit 200 reads the engine load determined by the load sensor 217 and the engine speed calculated based on the output signal of the crankshaft angle sensor 218, and determines the engine operating state. Furthermore, the electronic control unit 200 reads the coolant temperature determined by the water temperature sensor 216.

[0064] In step S2, the electronic control unit 200 assesses whether the cooling water temperature is at or above a predetermined EGR gas inlet permissible water temperature Tth. If the cooling water temperature is at or above the EGR gas inlet permissible water temperature Tth, the electronic control unit 200 proceeds to step S3. Conversely, if the cooling water temperature is lower than the EGR gas inlet permissible water temperature Tth, the electronic control unit 200 proceeds to step S8.

[0065] In step S3, the electronic control unit 200 assesses whether the operating range is within an EGR gas injection range, i.e., whether the engine load is between a first load KL1 and a second load KL2. The electronic control unit 200 proceeds to step S4 if the operating range is within an EGR gas injection range. Conversely, the electronic control unit 200 proceeds to step S8 if the operating range is within an EGR gas non-injection range. It should be noted that in the present embodiment, the threshold values ​​used to determine whether the operating range is within an EGR gas injection range—i.e., the values ​​of the first load KL1 and the second load KL2—are set to constant (fixed values). However, the value of the first load KL1 or the second load KL2 can also be set, for example, to change according to the engine speed.

[0066] In step S4, the electronic control unit 200 refers to a target EGR rate calculation image from Fig. 7, which was prepared in advance by experiments etc., and calculates the target EGR rate tRe [%] based on the engine operating condition.

[0067] In step S5, the electronic control unit 200 controls the opening degree of the EGR valve 38 in such a way that the EGR rate becomes a target EGR rate tRe.

[0068] In step S6, the electronic control unit 200 refers to the aforementioned scheme from Fig. 5 and calculates a target compression ratio tε on to the EGR initiation time based on engine load. It should be noted that a number of schemes according to Fig. 5 is prepared for different engine speeds. From these, the electronic control unit 200 selects the optimal scheme corresponding to the engine speed and then calculates the target compression ratio tε. on to the EGR initiation time based on engine load.

[0069] In step S7, the electronic control unit 200 controls the variable compression ratio mechanism A such that the mechanical compression ratio is the target compression ratio tε on to the EGR induction time.

[0070] In step S8, the electronic control unit 200 sets the target EGR rate to 0 [%].

[0071] In step S9, the electronic control unit 200 controls the EGR valve 38 in such a way that the EGR rate becomes the target EGR rate tRe, i.e., the opening degree of the EGR valve 38 is completely closed.

[0072] In step S10, the electronic control unit 200 refers to the aforementioned scheme from Fig. 5 (optimal scheme corresponding to engine speed) and calculates the target compression ratio tε off to the EGR non-introduction time based on engine load.

[0073] In step S11, the electronic control unit 200 controls the variable compression ratio mechanism A such that the mechanical compression ratio at the EGR non-initiation time is the target compression ratio tε off becomes.

[0074] Fig. Figure 8 is a timing diagram that explains the operation of a compression ratio control according to the present embodiment. In the diagram shown in Fig. In the example shown in Figure 8, the cooling water temperature Tw is lower than the EGR gas injection permissible water temperature Tth from time t0 to time t5. Therefore, from time t0 to time t5, the electronic control unit 200 sets the target EGR rate tRe to 0 [%], completely closes the EGR valve 38, and controls the variable compression ratio mechanism A such that the mechanical compression ratio during the EGR gas non-injection time is the target compression ratio tε. off becomes.

[0075] In particular, continuous operation with a constant engine load is carried out from time t0 to time t1 in an EGR gas non-injection range. For this reason, the electronic control unit 200 calculates the target compression ratio tε. off the EGR non-initiation time is based on the engine load. In the present embodiment, the target compression ratio tε offto the EGR non-injection time in the EGR gas non-injection range to the maximum compression ratio ε max The mechanical compression ratio is adjusted so that it reaches its maximum compression ratio ε from time t0 to time t1. max is controlled.

[0076] If the accelerator pedal is pressed down further at time t1 to accelerate, the engine load increases and the operation switches to an EGR gas injection range on the engine's high-load side; however, by time t5, the target compression ratio tε off The EGR gas non-injection time is calculated based on the engine load. As a result, with an increase in engine load, the target compression ratio tε decreases from time t2 onwards. off to the EGR gas non-injection time of the maximum compression ratio ε maxand thus the electronic control unit 200 controls the variable compression ratio mechanism A in such a way that the mechanical compression ratio at the EGR gas non-injection time is this reduced target compression ratio tε off reached.

[0077] Furthermore, at time t3, the acceleration ends and the accelerator pedal is released, thus reducing the engine load. Along with this, the mechanical compression ratio drops to its maximum compression ratio ε. max reset. From time t4 to time t6, continuous operation with a constant engine load is carried out in an EGR gas injection range on the engine's low-load side.

[0078] At this time, up to time t5, the cooling water temperature Tw is lower than the EGR gas inlet permissible water temperature Th, thus the target compression ratio tε offThe EGR gas non-injection time is calculated based on the engine load, and the mechanical compression ratio is based on the maximum compression ratio ε. max held.

[0079] Furthermore, if at time t5 the coolant temperature Tw becomes the EGR gas inlet permissible water temperature Tth or higher, the engine body 1 is operated in an EGR gas inlet range on the engine low-load side, so that the electronic control unit 200 calculates the target EGR rate tRe according to the engine operating condition and controls the EGR valve 38 such that the EGR rate becomes the target EGR rate tRe.

[0080] Furthermore, the electronic control unit 200 controls the target compression ratio tε on the EGR gas injection time is based on the engine load. In the present embodiment, the target compression ratio tε onto the EGR gas injection time in an EGR gas injection area on the engine's low-load side to an upper threshold compression ratio for the prevention of misfires ε lim set to a value lower than the maximum compression ratio ε max For this reason, the electronic control unit 200 controls the variable compression ratio mechanism A in such a way that the mechanical compression ratio at time t5 is the upper threshold compression ratio to prevent misfires ε. lim reached, and reduces the mechanical compression ratio from the maximum compression ratio ε max on the upper swelling compression ratio for the prevention of misfires ε lim .

[0081] If the engine body 1 is operated in a condition in which the mechanical compression ratio is higher than the upper threshold compression ratio to prevent misfires ε limIf the EGR gas inlet is set to a higher value, it is possible here, in an EGR gas inlet area on the engine's low-load side, to increase the flow of recirculated EGR gas by precisely the amount by which the mechanical compression ratio is increased (i.e., it is possible to set the target EGR rate tRe to a higher value). For this reason, it is possible to reduce pumping losses, so from a fuel-saving perspective, it is considered advantageous to set the mechanical compression ratio in an EGR gas inlet area on the engine's low-load side higher than the upper threshold compression ratio to prevent misfires ε. lim to adjust.

[0082] However, if at time t6 the accelerator pedal is released for a delay and the engine load continues to decrease, and at time t7 the operation switches to an EGR gas non-injection range, the target EGR rate tRe is set to 0 [%] and the EGR valve 38 closes completely. Even after the EGR valve 38 is completely closed, at this time the EGR gas remaining in the EGR passage 32 on the downstream side of the EGR valve 38 is briefly injected into cylinder 10. That is, a time delay occurs until the actual EGR rate rRe (hereinafter referred to as the "actual EGR rate") reaches the target EGR rate tRe. For this reason, from time t7 to time t8 in the EGR gas non-injection range, EGR gas is temporarily introduced into cylinder 10, and combustion becomes unstable.

[0083] If the engine body 1 is ultimately operated in the state in which the mechanical compression ratio in an EGR gas inlet area of ​​the engine's low-load side is increased so that it is higher than the upper threshold compression ratio for the prevention of misfires ε lim If the engine switches to an EGR gas non-injection range on the low-load side, there are no other means to ensure combustion stability, and in the worst case, misfires will occur.

[0084] In the present embodiment, the mechanical compression ratio in an EGR gas inlet area is thus reduced to the upper threshold compression ratio to prevent misfires ε. limlimited, while at time t7, when the engine switches from an EGR gas injection range to an EGR gas non-injection range on the low-load side, the mechanical compression ratio reaches the maximum compression ratio ε max This can be increased. Therefore, it is possible to ensure the stability of combustion when switching from an EGR gas injection range to an EGR gas non-injection range.

[0085] According to the embodiment described above, an electronic control unit 200 (control device) is provided to control an internal combustion engine 100 comprising an engine body 1, a variable compression ratio mechanism A configured to change the mechanical compression ratio of the engine body 1, and an intake system 3 configured to recirculate exhaust gases discharged from combustion chambers 11 of the engine body 1 to an intake passage 30 of the engine body 1. The electronic control unit 200 (control device) is provided with a compression ratio control element that controls the variable compression ratio mechanism A such that the mechanical compression ratio becomes the target compression ratio.

[0086] Furthermore, the compression ratio control section is configured to set the target compression ratio to a lower value when exhaust gas is recirculated on the engine's low-load side within a predetermined operating range, compared to when exhaust gas is not recirculated.

[0087] When exhaust gas recirculation is stopped, starting from the state in which exhaust gas is recirculated on the low-load side of the engine, the target compression ratio changes from a relatively low value to a high value, and the mechanical compression ratio is increased by the variable compression ratio mechanism A. For this reason, it is possible to prevent combustion from becoming unstable temporarily due to EGR gas being introduced into cylinder 10, which remains in the EGR passage 32 even after exhaust gas recirculation is stopped.

[0088] Furthermore, according to the present embodiment, the compression ratio control part is also configured to set the target compression ratio to a higher value when exhaust gas is recirculated on the high-load side of the engine in a predetermined operating range than when exhaust gas is not recirculated.

[0089] Therefore, in an operating range on the high-load side of the engine where knocking occurs relatively easily, it is possible to implement exhaust gas recirculation to suppress knocking. Simultaneously, the mechanical compression ratio increases over time when exhaust gas recirculation is stopped to power the engine block. By increasing the mechanical compression ratio over time when exhaust gas recirculation is stopped in this way, it is possible to improve thermal efficiency and thus fuel economy. Furthermore, pumping losses can also be reduced, further improving thermal efficiency and fuel economy. Second embodiment

[0090] Next, a second embodiment of the present disclosure is explained. The present embodiment differs from the first embodiment with respect to the content of the compression ratio control at the point where the target compression ratio tε on The EGR gas injection time is corrected based on the actual EGR rate rRe. The following explanation focuses on this point of distinction.

[0091] Fig. Figure 9 is a view which explains the content of the compression ratio control according to the present embodiment.

[0092] In the first embodiment mentioned above, the control device has the scheme provided for each engine speed consisting of Fig. 5 referred to and the target compression ratio tε on to the EGR gas injection time or the target compression ratio tε offThe EGR gas non-injection time is calculated based on the engine load. Furthermore, it has the target compression ratio tε. on to the EGR gas injection time on the engine's low-load side to an upper threshold compression ratio to prevent misfires ε lim limited to prevent a misfire during a delay.

[0093] Here, in Fig. 5 and Fig. 9, is the upper threshold compression ratio for the prevention of misfires, indicated by the dashed line X1 ε lim the upper limit of the mechanical compression ratio to the EGR gas introduction time, which makes it possible to prevent misfires by limiting the mechanical compression ratio to the maximum compression ratio ε maxThe increase occurs when the engine load changes from a state in which continuous operation of a constant engine load at a specific engine speed is carried out in an EGR gas injection range (state in which the actual EGR rate is controlled to the target EGR rate), and switches to an EGR gas non-injection range on the engine low-load side.

[0094] When the engine switches from the EGR gas non-injection range on the low-load or high-load side to the EGR gas injection range, the EGR valve 38 opens and EGR gas is introduced into cylinder 10. However, there is a time delay until the actual EGR rate rRe increases and reaches the target EGR rate tRe. Therefore, the amount of EGR gas introduced into cylinder 10 is temporarily lower than the target amount until the actual EGR rate rRe reaches the target EGR rate tRe. Furthermore, the amount of EGR gas present in the EGR passage 32 on the downstream side of the EGR valve 38 is also lower compared to the time of continuous operation.

[0095] Even if the engine load continues to decrease and the engine switches to a low-load EGR gas injection range, the amount of EGR gas injected into cylinder 10 will therefore be temporarily lower compared to the period of steady-state operation, before the actual EGR rate rRe increases and reaches the target EGR rate tRe. This means that during the transition period, until the actual EGR rate rRe increases and reaches the target EGR rate tRe, the system is more resistant to misfires than when switching from the period of steady-state operation to the low-load EGR gas injection range after the actual EGR rate rRe reaches the target EGR rate tRe.

[0096] As shown by the dashed line X2 in Fig. As shown in Figure 9, when switching from an EGR gas non-injection range to the EGR gas injection range on the engine low-load side or the engine high-load side, until the actual EGR rate rRe increases and the target EGR rate tRe is reached, the upper threshold compression ratio to prevent misfires ε lim higher than the upper threshold compression ratio to prevent misfires ε lim at the time of continuous operation, which is shown by the dashed line X1. Furthermore, the temporarily increased upper threshold compression ratio for the prevention of misfires reaches ε lim the upper swelling compression ratio for the prevention of misfires ε lim at the time of steady operation, as shown by the dashed line X1, when the actual EGR rate rRe increases and the target EGR rate tRe is reached.

[0097] Furthermore, the target compression ratio tε onat the EGR gas injection time, as in Fig. 5 and Fig. 9 shown by the solid line, is the optimal mechanical compression ratio at which knocking and misfires are avoided and fuel economy is optimized in a state of steady operation at a constant engine load and a specific engine speed.

[0098] As explained above, the amount of EGR gas introduced into each cylinder 10 is temporarily lower than the target amount when switching from an EGR gas non-injection range to an EGR gas injection range, until the actual EGR rate rRe reaches the target EGR rate tRe. During this transition period, until the actual EGR rate rRe increases and reaches the target EGR rate tRe, the cylinder environment is therefore one in which knocking occurs more easily than during steady operation after the actual EGR rate rRe reaches the target EGR rate tRe.

[0099] As seen through the solid line Y2 in Fig. As shown in Figure 9, on the high-load side of the engine, during a transition from an EGR gas non-injection range to an EGR gas injection range until the actual EGR rate rRe increases and the target EGR rate tRe is reached, the optimal mechanical compression ratio is temporarily lower than the target compression ratio tε. on The EGR gas injection time is adjusted during steady-state operation, as shown by the solid line Y1. Furthermore, as shown by the dashed line X2, the upper threshold compression ratio ε is adjusted on the engine's low-load side to prevent misfires. lim higher, and thus the optimal mechanical compression ratio becomes temporarily higher than the target compression ratio tε. onThe EGR gas injection time during continuous operation is shown by the solid line Y1. Furthermore, the optimal mechanical compression ratio reaches the target compression ratio tε. on at the EGR gas injection time, as shown by the solid line Y1, when the actual EGR rate rRe increases, the target EGR rate tRe is reached.

[0100] In this way, the optimal mechanical compression ratio, at which knocking and misfires are avoided while fuel economy is optimized, changes temporarily in accordance with the actual EGR rate when switching from an EGR gas non-injection range to an EGR gas injection range, until the actual EGR rate rRe increases and the target EGR rate tRe is reached.

[0101] Thus, the present embodiment corrects as long as the target compression ratio tε onThe EGR gas injection time is based on the actual EGR rate rRe until the actual EGR rate rRe increases and the target EGR rate tRe is reached. A compression ratio control based on the present embodiment is explained below.

[0102] Fig. Figure 10 is a flowchart explaining a compression ratio control according to the present embodiment, which is carried out by the electronic control unit 200. It should be noted that the processing from step S1 to step S11 in Fig. 10 performs a similar processing to the first embodiment, so the explanation is omitted here.

[0103] In step S21, the electronic control unit 200 assesses whether the time is a transition period in which the operation changes from an EGR gas non-injection range to an EGR gas injection range, until the actual EGR rate rRe increases and the target EGR rate tRe is reached.

[0104] In particular, the electronic control unit 200 estimates the actual EGR rate rRe during the transition period and assesses whether the difference ΔRe between the target EGR rate tRe and the actual EGR rate rRe is a predetermined value α or greater. It should be noted that the estimation method for the actual EGR rate rRe can be a suitably selected method from various known methods; however, the present embodiment assesses the actual EGR rate rRe based on the engine operating conditions, the intake pressure, etc. Furthermore, the predetermined value α is a value that can be freely set and at which it can be assessed whether the actual EGR rate rRe reaches the target EGR rate tRe if the difference ΔRe is lower than the predetermined value α, i.e., a value at which it can be assessed whether the difference ΔRe between the actual EGR rate rRe and the target EGR rate tRe is sufficiently small and it is the time of continuous operation.The electronic control unit 200 continues processing step S23 if the difference ΔRe is a predetermined value α or greater. Conversely, the electronic control unit 200 continues processing step S6 if the difference ΔRe is less than the predetermined value α.

[0105] In step S22, the electronic control unit 200 calculates the corrected target compression ratio tε on ' to the EGR gas injection time based on the actual EGR rate rRe. In the present embodiment, the electronic control unit 200 corrects the aforementioned scheme from Fig. 5 based on the actual EGR rate rRe and refers to the corrected scheme to determine the corrected target compression ratio tε on ' to calculate the EGR gas injection time based on the engine load.

[0106] In particular, the electronic control unit 200 corrects, as in Fig. 11 shown, the scheme from Fig. 5 such that the corrected target compression ratio tε on ' at the EGR gas injection time the target compression ratio tε off The EGR gas non-injection time is reached when the actual EGR rate rRe is zero [%] immediately after the EGR valve 38 opens.

[0107] Furthermore, together with the increase in the actual EGR rate rRe, the scheme from Fig. 5 as in Fig. 11 shown by arrow Z, corrected such that the correction ends when the actual EGR rate rRe becomes the target EGR rate tRe (that the corrected target compression ratio tε on ' at the EGR gas injection time the target compression ratio tε on (at the time of EGR gas injection during continuous operation).

[0108] This means that until the actual EGR rate rRe reaches the target EGR rate tRe, the scheme is executed. Fig. 5 corrected such that the corrected target compression ratio tε is achieved on the engine's low-load side on The longer the EGR gas injection time becomes, the lower the actual EGR rate rRe is compared to the target compression ratio tε. on at the EGR gas injection time during continuous operation. Furthermore, the scheme consists of Fig. 5 corrected such that the corrected target compression ratio tε is achieved on the high-load side of the engine. on The lower the actual EGR rate rRe is compared to the target compression ratio tε, the lower the EGR gas injection time becomes. on at the time of EGR gas injection during a period of continuous operation.

[0109] In step S23, the electronic control unit 200 controls the variable compression ratio mechanism A such that the mechanical compression ratio at the EGR gas injection time is the corrected target compression ratio tε on ' becomes.

[0110] Fig. 12 is a timing diagram that explains the operation of a compression ratio control according to the present embodiment, in particular a timing diagram of the time in which, as in Fig. Figure 13 shows that the engine load drops from a fourth load KL4 in an EGR gas non-injection area on the engine high load side to a third load KL3 of an EGR gas injection area.

[0111] From time t0 to time t1, the accelerator pedal is depressed sharply for acceleration. During the EGR gas non-injection phase on the high-load side of the engine, continuous operation with a constant engine load (fourth load KL4) is maintained.

[0112] At time t1, acceleration ends and the accelerator pedal is released, thus reducing the engine load. If, at time t2, the engine load falls below the second load KL2, the electronic control unit 200 calculates the target EGR rate tRe according to the engine operating state and controls the EGR valve 38 so that the actual EGR rate rRe becomes the target EGR rate tRe. As a result, the EGR valve 38 opens. Starting from time t2, the actual EGR rate rRe gradually increases to the target EGR rate tRe. At time t5, the actual EGR rate rRe reaches the target EGR rate tRe.

[0113] In the present embodiment, the corrected target compression ratio tε is applied from time t2 to time t5. on ' calculated based on the actual EGR rate for the EGR gas injection time.

[0114] In particular, from time t2 to time t3 the actual EGR rate rRe becomes zero, so that the corrected target compression ratio tε on' to the EGR gas injection time the target compression ratio tε off which corresponds to the EGR gas non-injection time. As in Fig. 12 and Fig. Figure 13 shows the corrected target compression ratio tε. on 'The EGR gas injection time is set to ε1. Along with the increase in the actual EGR rate, the corrected target compression ratio tε is also adjusted. on 'The EGR gas injection time is successively set to ε2, ε5, ε4 and ε3, for example, and the variable compression ratio mechanism A is controlled in such a way that the mechanical compression ratio is the set corrected target compression ratio tε on ' at the EGR gas injection time.

[0115] At this time up to time t4, when the upper limit of the mechanical compression ratio is determined by the upper threshold compression ratio to prevent misfires ε limWhen limited, the corrected target compression ratio tε is used. on ' to the EGR gas injection time. Furthermore, the corrected target compression ratio tε applies from time t4 onwards. on ' to the EGR gas injection time.

[0116] At time t5, when the actual EGR rate rRe reaches the target EGR rate tRe, and subsequently, the variable compression ratio mechanism A is controlled such that the mechanical compression ratio reaches the target compression ratio tε. on The EGR gas injection time will occur during a period of steady operation.

[0117] The electronic control unit 200 (control device) according to the present embodiment described above has an exhaust gas recirculation control section that controls the intake system 3 such that the EGR rate becomes the target EGR rate tRe, and an actual recirculation rate estimator section that estimates an actual EGR rate rRe. Furthermore, the compression ratio control section is configured to correct the target compression ratio based on the actual EGR rate rRe until the actual EGR rate rRe increases and reaches the target EGR rate tRe when exhaust gas recirculation is initiated.

[0118] In particular, the compression ratio control unit corrects the target compression ratio so that it becomes higher in a predetermined operating range on the engine's low-load side the lower the actual EGR rate rRe is with respect to the target EGR rate tRe, and corrects the target compression ratio so that it becomes lower in a predetermined operating range on the engine's high-load side.

[0119] Therefore, during the transition period, when switching from an EGR gas non-injection range to an EGR gas injection range, until the actual EGR rate rRe increases and the target EGR rate tRe is reached, it is possible to control the mechanical compression ratio to the optimal mechanical compression ratio, at which knocking and misfires are avoided and fuel savings are optimized.

[0120] It should be noted that, as a modification of the second embodiment, the following effects can be achieved by correcting the target intake valve closing time (hereinafter referred to as "IVC") based on the actual EGR rate rRe, and furthermore by controlling the variable valve actuation mechanism B such that the IVC becomes a target IVC according to the engine operating condition.

[0121] This means that if the target IVC is calculated based on the engine operating condition and the variable valve actuation mechanism B is controlled such that the IVC becomes the target IVC, the IVC which yields the optimal amount of intake at the time of steady operation (when the actual EGR rate rRe is controlled to the target EGR rate tRe) is set as the target IVC.

[0122] For this reason, when switching from an EGR gas non-injection range to an EGR gas injection range, the EGR gas quantity will be temporarily insufficient if the IVC is finally set to the target IVC during steady operation, after the actual EGR rate rRe reaches the target EGR rate tRe, but before the actual EGR rate rRe reaches the target EGR rate tRe. As a result, the intake air volume (fresh air volume) will be exactly the amount by which EGR gas was not injected, and knocking may occur temporarily.

[0123] If the variable compression ratio mechanism A and the variable valve actuation mechanism B are controlled according to the engine operating condition, then during the transition period, when changing from an EGR gas non-injection range to an EGR gas injection range until the actual EGR rate rRe increases and the target EGR rate tRe is reached, even if only the target value of the mechanical compression ratio is corrected based on the actual EGR rate rRe, knocking is likely to occur.

[0124] If the IVC (Integrated Control Valve) is finally set to the target IVC during steady operation, after the actual EGR rate rRe reaches the target EGR rate tRe, then, furthermore, when switching from an EGR gas injection range to an EGR gas non-injection range, the amount of EGR gas will be temporarily excess before the actual EGR rate rRe drops and reaches the target EGR rate tRe (= zero). As a result, the amount of intake air (fresh air) will ultimately be exceeded by exactly the amount of EGR gas that was injected in excess, and engine power may decrease.

[0125] Thus, the present embodiment corrects the target IVC based on the actual EGR rate rRe and controls the variable compression ratio mechanism A and the variable valve actuation mechanism B sequentially. As a result, it is possible to suppress the occurrence of knocking and a drop in engine power.

[0126] Fig. Figure 14 is a timing diagram illustrating the operation of an intake valve closing timing control system according to a modification of the second embodiment. Apart from the operation of the intake valve closing timing, the diagram also includes... Fig. 14 the establishments of the time diagram are the same as those in Fig. 12.

[0127] If the target IVC is calculated based on the engine operating condition and the variable valve actuation mechanism B is controlled such that the actual IVC becomes the target IVC, the IVC at which the amount of intake becomes optimal in the state in which the mechanical compression ratio and the actual EGR rate rRe are controlled to their target values ​​is set as the target IVC, as explained above.

[0128] If, at time t2, the operation changes from an EGR gas non-injection range to an EGR gas injection range, and if the actual IVC is ultimately adjusted to the optimal target IVC during a period of steady operation after the actual EGR rate rRe reaches the target EGR rate tRe, then, as described in Fig. 14 (F) shown by the dashed line P, at a time before time t5, at which the actual EGR rate rRe reaches the target EGR rate tRe (in which in Fig. In example 14, the amount of intake (fresh air quantity) is finally exceeded by exactly the amount of EGR gas that was not introduced, and knocking may occur temporarily.

[0129] By using the IVC, as in Fig.As shown in Figure 14 (F) by the solid line, the actual EGR rate rRe is controlled according to which it is possible to adjust this to an IVC corresponding to the actual EGR rate rRe and a mechanical compression ratio, thereby suppressing knocking. In particular, during the transition period (time t2 to time t5), when the actual EGR rate is low, the target IVC is corrected such that the delay from bottom dead center increases in order to reduce the intake volume by exactly the amount of EGR gas that was introduced during steady-state operation. Furthermore, the target IVC is corrected such that the delay from bottom dead center gradually decreases as the actual EGR rate approaches the target EGR rate.

[0130] The foregoing describes embodiments of the present disclosure; however, the foregoing embodiments only show some application examples of the present disclosure and are not intended to limit the technical scope of the present disclosure to the specific configurations of the embodiments.

Claims

[1] Control device (200) for an internal combustion engine (100) for controlling an internal combustion engine (100) with: a motor body (1), a variable compression ratio mechanism (A) which is configured to change a mechanical compression ratio of the engine body (1); and an intake system (3) configured to recirculate exhaust gas discharged from a combustion chamber (11) of the engine body (1) to an intake passage (30) of the engine body (1), wherein the control device (200) has a compression ratio control part which is configured to control the variable compression ratio mechanism (A) such that the mechanical compression ratio becomes a target compression ratio, wherein the compression ratio control part is configured to set the target compression ratio to a lower value when exhaust gas is recirculated on a low-load side of the engine in a predetermined operating range than when exhaust gas is not recirculated, in order to set an effective compression ratio to a lower value when the exhaust gas is recirculated on the low-load side of the engine in the predetermined operating range than when the exhaust gas is not recirculated. [2] Control device (200) for an internal combustion engine (100) according to claim 1, wherein the compression ratio control part is configured to set the target compression ratio to a high value when exhaust gas is recirculated at a predetermined operating range on a high-load side of the engine, rather than when exhaust gas is not recirculated. [3] Control device (200) for an internal combustion engine (100) according to claim 1 or 2, further comprising: an exhaust gas recirculation control unit configured to control the intake system (3) such that an exhaust gas recirculation rate becomes a target recirculation rate; and a part that estimates an actual recirculation rate, which is configured to estimate an actual exhaust gas recirculation rate, wherein the compression ratio control part is configured to correct the target compression rate based on the actual recirculation rate, and wherein the compression ratio control part is configured to correct the target compression ratio based on the actual recirculation rate until the exhaust gas recirculation rate increases to reach the target recirculation rate when exhaust gas recirculation is started. [4] Control device (200) for an internal combustion engine (100) according to claim 3, wherein the compression ratio control part is configured to: to correct the target compression ratio such that it becomes higher on the engine's low-load side within a predetermined operating range when the actual recirculation rate is lower than the target recirculation rate; and to correct the target compression ratio so that it becomes lower in a predetermined operating range on the high-load side of the engine when the actual recirculation rate is lower than the target recirculation rate.

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