Internal combustion engine

Abstract

To provide an internal combustion engine that appropriately performs combustion during a switching operation of a variable valve train in the internal combustion engine including the variable valve train.SOLUTION: An internal combustion engine 1 includes: a variable valve train for changing opening / closing timing of an intake valve; a main combustion chamber 40; an auxiliary combustion chamber 42; a first ignition plug 61 disposed in the main combustion chamber 40; a second ignition plug 62 disposed in the auxiliary combustion chamber 42; and a control device 50 that controls the first ignition plug 61 and the second ignition plug 62. The control device 50 switches an ignition form to either of SI ignition by using the first ignition plug 61, JET ignition by using the second ignition plug 62 or SI+JET ignition by using the first ignition plug 61 and the second ignition plug 62 along with change of the opening / closing timing of the intake valve by using the variable valve train.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an internal combustion engine that is equipped with a spark plug disposed in a main combustion chamber and a spark plug disposed in an auxiliary combustion chamber, and that is also equipped with a variable valve mechanism. [Background technology]

[0002] Conventionally, there is known a technique relating to an internal combustion engine having an ignition plug arranged in a main combustion chamber and an ignition plug arranged in a pre-combustion chamber. For example, Patent Document 1 describes an internal combustion engine having an ignition plug arranged in a main combustion chamber and an ignition plug arranged in a pre-combustion chamber, in which ignition occurs in the pre-combustion chamber when the engine is warmed up and in the main combustion chamber when the engine is cold, and by performing ignition timing retard control after startup, the exhaust temperature is quickly raised immediately after startup, and an exhaust purification catalyst provided in the exhaust passage is quickly activated. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2023-030452 A Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, an increasing number of internal combustion engines are equipped with variable valve mechanisms that variably control the opening and closing timing of the intake valves. In such internal combustion engines equipped with variable valve mechanisms, changing the opening and closing timing of the intake valves significantly changes the intake air flow within the cylinder. Therefore, in an internal combustion engine that is capable of switching ignition modes as in Patent Document 1 and is equipped with a variable valve mechanism, there is a demand for achieving appropriate combustion that takes into account changes in the intake air flow in the cylinder due to the operation of the variable valve mechanism.

[0005] The present invention has been made in view of the above problems, and its object is to provide an internal combustion engine that is equipped with a variable valve mechanism for the intake valve and is capable of switching ignition modes, and that is capable of performing appropriate combustion when the variable valve mechanism is switched. [Means for solving the problem]

[0006] In order to achieve the above object, an internal combustion engine of the present invention includes a main combustion chamber filled with a mixture of air and fuel, an auxiliary combustion chamber communicating with the main combustion chamber via a plurality of communication holes, a first ignition plug disposed in the main combustion chamber for igniting the mixture in the main combustion chamber, a second ignition plug disposed in the auxiliary combustion chamber for igniting the mixture in the auxiliary combustion chamber, and a variable valve mechanism for changing the opening and closing timing of an intake valve, and further includes a control device for controlling the ignition type and ignition timing of the first ignition plug and the second ignition plug based on the operating state of the internal combustion engine, and a second ignition form in which only the second spark plug is ignited, and the control device changes the ignition form from one of the first ignition form and the second ignition form, which are set based on the operating state of the internal combustion engine, to the other, and retards the ignition timing, when the variable valve mechanism changes the closing timing of the intake valve so that it crosses bottom dead center within a single ignition region, which is an operating region of the internal combustion engine in which the first ignition form or the second ignition form is applied. [Effects of the Invention]

[0007] According to the internal combustion engine of the present invention, when the intake valve closing timing is changed by the variable valve mechanism so that it crosses bottom dead center, knocking caused by high pressure inside the cylinder is avoided by retarding, and by switching the ignition type, power reduction or excessive combustion is suppressed, allowing combustion to be carried out appropriately when the variable valve mechanism is switched. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic configuration diagram of an internal combustion engine according to an embodiment. [Figure 2] FIG. 2 is an explanatory diagram schematically showing a cylinder. [Figure 3] 3 is an example of a map for setting an ignition type corresponding to an operating state of an internal combustion engine. [Figure 4] 4 is an example of a map for setting the operation of a variable valve mechanism in relation to the operating state of an internal combustion engine. [Figure 5] 10A and 10B are explanatory diagrams of an embodiment of switching of ignition modes accompanying switching of a variable valve mechanism in a single ignition region. [Figure 6] 10A and 10B are explanatory diagrams of another embodiment of the switching of the ignition mode accompanying the switching of the variable valve mechanism in the single ignition region. [Figure 7] 5A and 5B are schematic diagrams showing other examples of the positions of the first and second spark plugs. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. (Internal combustion engine) FIG. 1 is a schematic diagram of an internal combustion engine 1 according to an embodiment of the present invention. The internal combustion engine 1 is, for example, a gasoline engine mounted on a vehicle for driving the vehicle. The internal combustion engine 1 includes an internal combustion engine main body 10 (hereinafter referred to as "main body 10") and a control device 50. In an intake passage 5 of the main body 10, an air cleaner 6, an intercooler 7, and a throttle valve 8 are provided upstream of the intake port 2 of each cylinder 30 along the flow of intake air. Meanwhile, in an exhaust passage 11 of the main body 10, an upstream exhaust purification catalyst 12 and a downstream exhaust purification catalyst 13 are provided along the flow of exhaust gas from the exhaust port 3 of each cylinder 30.

[0010] The main body 10 is also provided with a turbocharger 15 and an EGR system 16. The turbocharger 15 rotates a turbine (not shown) using exhaust gas flowing through the exhaust passage 11, and supplies compressed air to the intake side by rotating a compressor (not shown) connected to the turbine. The EGR system 16 includes an EGR passage 20 that connects the exhaust passage 11 and the intake passage 5, an EGR valve 21 that changes the flow area of ​​the EGR passage 20, and an EGR cooler 22 that cools the exhaust gas passing through the EGR passage 20.

[0011] 2 is an explanatory diagram that schematically shows a cylinder 30. The cylinder 30 is composed of a cylinder head 34, a cylinder block 36, and a piston 37 that is slidably disposed within the cylinder block 36 via a cylindrical cylinder liner (not shown). The cylinder head 34 is provided with an intake port 2 and an exhaust port 3 corresponding to each cylinder 30, and each intake port 2 is provided with an intake valve 32 (intake valve) that can be opened and closed, and each exhaust port 3 is provided with an exhaust valve 33 that can be opened and closed.

[0012] The cylinder 30 is provided with a main combustion chamber 40, which is a space surrounded by the cylinder head 34, cylinder block 36, and piston 37. In the main body 10 of this embodiment, an injector (not shown) serving as a fuel injection device is provided in the intake port 2, and an air-fuel mixture mixed with air in the intake port 2 is supplied into the main combustion chamber 40. Note that the main body 10 may also be provided with a direct injection injector that injects fuel directly into the main combustion chamber. A first spark plug 61 that ignites the air-fuel mixture in the main combustion chamber 40 is provided at the top of the main combustion chamber 40 (i.e., in the cylinder head 34).

[0013] Also, within the main combustion chamber 40, there is provided an auxiliary combustion chamber 42, which is a space separated by a partition wall 44 attached to the cylinder block 36. A plurality of communication holes 46 are formed in the partition wall 44. As a result, the main combustion chamber 40 and the auxiliary combustion chamber 42 are in communication via the plurality of communication holes 46, and the air-fuel mixture within the main combustion chamber 40 flows into the auxiliary combustion chamber 42. A second ignition plug 62 is disposed within the auxiliary combustion chamber 42, and ignites the air-fuel mixture that flows in from the main combustion chamber 40.

[0014] When the first spark plug 61 ignites the air-fuel mixture in the main combustion chamber 40 (hereinafter referred to as "SI ignition"), as shown by the dashed dotted line in the figure, the flame F1 propagates from the first spark plug 61 toward the exhaust port 3 due to the flow of the air-fuel mixture in the main combustion chamber 40. In this way, stable ignition can be achieved by directly igniting the air-fuel mixture filled in the main combustion chamber 40.

[0015] On the other hand, when the second spark plug 62 ignites the air-fuel mixture in the auxiliary combustion chamber 42 (hereinafter referred to as "JET ignition"), flame F2 is injected from the auxiliary combustion chamber 42 through the multiple communication holes 46 into the main combustion chamber 40, as shown by the dashed line in the figure. As a result, flame F2 can be quickly propagated within the main combustion chamber 40, accelerating combustion and ultimately improving the thermal efficiency of the main body 10. Furthermore, when both SI ignition and JET ignition are performed, flame F2 from JET ignition can burn unburned fuel that was not ignited by SI ignition. Furthermore, flame F2 from JET ignition can push flame F1 generated by SI ignition to the vicinity of the cylinder wall, thereby also burning unburned fuel that remained near the cylinder wall in the previous cycle. By promoting the combustion of unburned fuel in this way, knocking can be suppressed.

[0016] The auxiliary combustion chamber 42 and the plurality of communication holes 46 are positioned so that the injection direction of the flame F2 is generally along the extension direction of the face of the piston 37 facing the main combustion chamber 40 (a direction perpendicular to the sliding direction of the piston 37). This makes it possible to prevent the flame F2 from damaging the piston 37. The size and number of the plurality of communication holes 46 may be set according to the cylinder volume. In this embodiment, the plurality of communication holes 46 are formed side by side in the depth direction of FIG. 2.

[0017] The main body 10 configured as described above is controlled by a control device 50 (FIG. 1). The control device 50 is composed of an output device, memory devices (ROM, RAM, non-volatile RAM, etc.), a central processing unit (CPU), etc. The control device 50 acquires information such as the crank angle, intake air volume, exhaust temperature, and EGR gas volume from various sensors provided in the main body 10, and appropriately controls the throttle valve 8, EGR valve 21, turbocharger 15, the amount of fuel injected from an injector (not shown), intake valve 32, exhaust valve 33, first spark plug 61, second spark plug 62, etc. based on the acquired information.

[0018] The supercharger 15 is in the supercharging region when the load T (output torque, charging efficiency, etc.) of the internal combustion engine 1 is equal to or greater than a predetermined value T1, and is in the natural aspiration region when the load T is less than the predetermined value T1. (Ignition method control) The control device 50 switches the ignition mode based on the operating state of the internal combustion engine 1 (for example, the rotation speed Ne and the load T).

[0019] For example, as shown in Figure 3, in the supercharging region where the rotation speed Ne of the internal combustion engine 1 is below a predetermined rotation speed Ne1 and the load T is equal to or greater than a predetermined value T1, only JET ignition is used out of SI ignition and JET ignition. JET ignition promotes high-speed combustion and enables the generation of high torque, while SI ignition is not used because the rotation speed is in the low to medium rotation range, suppressing excessive combustion and improving fuel economy.

[0020] In the naturally aspirated region where the rotation speed Ne of the internal combustion engine 1 is less than a predetermined rotation speed Ne1 and the load T is less than a predetermined value T1, only SI ignition is performed out of SI ignition and JET ignition. SI ignition ensures reliable ignition even in the low rotation speed region, and JET ignition is not performed, thereby improving fuel economy. In the high rotational speed range where the rotational speed Ne of the internal combustion engine 1 is equal to or greater than a predetermined rotational speed Ne1, both SI ignition and JET ignition are performed. This enables combustion suited to high rotational speeds, and particularly in the supercharging range, combustion is suitable for high output, i.e., high rotational speed and high torque. In the supercharging range of this high rotational speed range, SI ignition is performed at an earlier timing than JET ignition. As a result, when the flame is injected into the main combustion chamber by JET ignition, combustion in the main combustion chamber has already begun by SI ignition, reducing the shock of flame injection in JET ignition. In addition, in the naturally aspirated range of this high rotational speed range, JET ignition is performed at an earlier timing than SI ignition. As a result, JET ignition injects a flame into the main combustion chamber to assist ignition in the combustion chamber, and JET ignition stabilizes combustion.

[0021] When the load T of the internal combustion engine 1 is 0 or less, this is a fuel cut region in which fuel supply is stopped, and this is a region in which friction of the internal combustion engine 1 is applied to the vehicle's driving powertrain, and ignition is not performed. (variable valve mechanism) The internal combustion engine 1 of this embodiment is equipped with a variable valve mechanism 70 that variably controls the opening and closing timing of the intake valve 32. The variable valve mechanism 70 includes a first variable valve mechanism 71 that continuously variably controls the valve lift of the intake valve 32 and varies the phase to vary the valve opening period (the interval between the valve opening and closing periods), for example, and a second variable valve mechanism 72 (variable valve timing mechanism) that continuously variably controls the phase of the intake cam to vary both the valve opening and closing periods, for example, and these mechanisms can be independently controlled by the control device 50. Note that the first variable valve mechanism 71 is configured to advance the valve closing period, thereby retarding the valve opening period and shortening the valve opening period. Therefore, by appropriately controlling these two variable valve mechanisms 71 and 72, it is possible to independently change the valve opening period and the valve closing period.

[0022] The control device 50 switches the operation of the variable valve mechanism 70 based on the operating state of the internal combustion engine 1 (for example, the rotation speed Ne and the load T). The internal combustion engine 1 of this embodiment is a Miller cycle engine that achieves high compression by switching the closing timing of the intake valve 32 between early closing, which is earlier than bottom dead center BDC, and late closing, which is later than bottom dead center BDC.

[0023] 4, in range A where the internal combustion engine 1 is in a high-load low-speed range (a higher-load low-speed range than range B described later), the control device 50 sets the opening timing of the intake valve 32 earlier than top dead center TDC and the closing timing later than bottom dead center BDC to increase the overlap with the exhaust valve 33. This increases the scavenging effect and ensures the output torque.

[0024] In region B, which is a high load region where the rotation speed Ne of the internal combustion engine 1 is lower than a predetermined rotation speed Ne2 and the load T is equal to or higher than a predetermined value T2, the opening timing of the intake valve 32 is set earlier than top dead center TDC and the closing timing is set later than bottom dead center BDC, thereby providing a medium overlap with the exhaust valve 33. This adjusts the total EGR amount, reduces pumping loss, and improves fuel efficiency.

[0025] In the high load region C where the rotation speed Ne of the internal combustion engine 1 is equal to or higher than a predetermined rotation speed Ne2 and the load T is equal to or higher than a predetermined value T2, the opening timing of the intake valve 32 is set to be substantially the same as top dead center TDC and the closing timing is set to be later than bottom dead center BDC, thereby reducing the overlap with the exhaust valve 33. This reduces residual gas in the cylinder and improves operation in the high rotation speed region. In the idling range D, the valve opening timing is set to approximately the same as top dead center, and the valve closing timing is set to approximately the same as bottom dead center (BDC), reducing the overlap with the exhaust valve 33. This improves combustion stability.

[0026] In the E region where the rotation speed Ne of the internal combustion engine 1 is lower than a predetermined rotation speed Ne2 and the load T is lower than a predetermined value T2, the opening timing of the intake valve 32 is set earlier than top dead center TDC and the closing timing is set earlier than bottom dead center BDC, thereby providing a medium overlap with the exhaust valve 33. This adjusts the total EGR amount and reduces pumping loss. In the G region where the load T of the internal combustion engine 1 is equal to or less than 0, the opening timing of the intake valve 32 is set to be approximately the same as top dead center TDC, and the closing timing is set to be later than bottom dead center BDC, thereby suppressing scavenging and suppressing a drop in the temperature of the exhaust purification catalysts 12, 13.

[0027] The control device 50 is provided with a map for the first variable valve mechanism 71 and a map for the second variable valve mechanism 72. In each map, the load T and rotation speed Ne of the internal combustion engine 1 are divided into three stages: low, medium, and high, and 3 x 3 = 9 types of control target values ​​are stored. Furthermore, the control target values ​​read from these two maps are subjected to bottom dead center crossing avoidance processing to set each control target value.

[0028] In this embodiment, the predetermined rotation speed Ne2, which is a control threshold for the variable valve mechanism 70, is the same as the predetermined rotation speed Ne1, which is the ignition direction control threshold. The predetermined value T2, which is a control threshold for the variable valve mechanism 70, may be the same as the predetermined value T1, which is the ignition direction control threshold, or may be a value different from the predetermined value T1. Furthermore, in the control of the variable valve mechanism 70 described above, the threshold value between region B and region E is the predetermined value T2, which is the load on the internal combustion engine 1. However, the variable valve mechanism 70 may also be switched using the rotation speed Ne of the internal combustion engine 1 as the threshold value. For example, when the rotation speed Ne of the internal combustion engine 1 is less than a predetermined rotation speed Ne3, the intake valve 32 may be closed early, earlier than bottom dead center BDC, and when the rotation speed Ne is equal to or greater than the predetermined rotation speed Ne3, the intake valve 32 may be closed late, later than bottom dead center BDC. In this case, the predetermined rotation speed Ne3 corresponds to the predetermined rotation speed of the present invention. (Control during transition of operating range) Furthermore, in this embodiment, in a region where the rotational speed of the internal combustion engine 1, in which either SI ignition or JET ignition is performed, is less than a predetermined rotational speed Ne1, if the closing timing of the intake valve 32 changes to cross the bottom dead center BDC as the operating region of the internal combustion engine 1 changes, and bottom dead center crossing avoidance processing is performed, the ignition type set based on the load T and rotational speed Ne of the internal combustion engine 1 is changed, and a retard processing is performed to retard the ignition timing.

[0029] For example, as shown in Figure 5, in the region where SI ignition is performed, in internal combustion engine 1, the closing timing of intake valve 32 is set to early closing, earlier than bottom dead center BDC, when the rotation speed is less than a predetermined rotation speed Ne3, and the closing timing of intake valve 32 is set to late closing, later than bottom dead center BDC, when the rotation speed is equal to or greater than the predetermined rotation speed Ne3, when there is a transition (transition) from the early closing region to the late closing region or from the late closing region to the early closing region within the SI ignition region, as shown in a and b in Figure 5, SI ignition is not maintained, but JET ignition is temporarily performed at the time of switching.

[0030] Furthermore, when the valve shifts from the early closing region to the late closing region, or from the late closing region to the early closing region, within the JET ignition region as shown in c and d in Figure 5, JET ignition is not maintained, but SI ignition is temporarily performed at the time of switching. When the SI ignition region transitions from the early closing region to the late closing region as shown in Figure 5a, or when the SI ignition region transitions from the late closing region to the early closing region as shown in Figure 5b, the closing timing of the intake valve 32 approaches bottom dead center (BDC), resulting in high compression inside the cylinder. To prevent knocking due to high compression, the ignition timing is retarded. Furthermore, in this embodiment, temporary JET ignition is performed to compensate for the power reduction caused by the retard and suppress power fluctuations.

[0031] To explain in more detail, internal combustion engines have MBT ignition timing, which is the ignition timing at which output torque is maximized. For example, at low to medium loads in the naturally aspirated region, the MBT ignition timing is retarded relative to the knock ignition timing. Therefore, when the intake valve 32 closing timing is shifted to cross bottom dead center (BDC), the actual compression ratio increases near bottom dead center (BDC), making knocking more likely. In this case, if the MBT ignition timing is more advanced than the ignition timing that causes knocking, it must be retarded to prevent knocking. Because the SI ignition region is approximately the naturally aspirated region, the intake air volume filling the cylinder is lower than the boost pressure. In an internal combustion engine with specifications that optimize the nozzle hole shape and diameter of the auxiliary combustion chamber 42, primarily in a supercharged state, the actual compression ratio increases from a state in which fuel supply to the auxiliary combustion chamber 42 is low in the naturally aspirated region, making it easier to force the fuel mixture into the auxiliary combustion chamber 42, temporarily enabling JET ignition. Therefore, when the closing timing of the intake valve 32 is changed to cross bottom dead center (BDC) in the SI ignition region as described above, by temporarily performing JET ignition, the power loss that occurs when the MBT ignition timing is retarded to an ignition timing that does not cause knocking can be compensated for by the high-speed combustion of JET ignition.

[0032] When the JET ignition region transitions from the early closing region to the late closing region as shown in Figure 5c, or when the JET ignition region transitions from the late closing region to the early closing region as shown in Figure 5d, the closing timing of the intake valve 32 approaches bottom dead center (BDC), as described above, resulting in high compression within the cylinder. When the JET ignition region becomes highly compressed, there is a risk that the power of the JET ignition may become excessive. Therefore, in this embodiment, by further temporarily performing SI ignition, excessive combustion within the cylinder can be suppressed, thereby suppressing vibrations, etc.

[0033] More specifically, in the supercharging region, the amount of air intake into the cylinder is large and the actual compression ratio tends to be high. If the specifications (volume, number of injection holes, hole diameter) of the pre-combustion chamber 42 are tailored to the use of early or late closing of the intake valve 32, and the actual compression ratio is temporarily increased near bottom dead center (BDC) in the jet ignition region, which is substantially the same as the supercharging region, as described above, the increased fuel supplied to the pre-combustion chamber 42 and the high pressure state during compression could result in excessive jet ignition power. Therefore, when the closing timing of the intake valve 32 is changed to cross bottom dead center (BDC) in the SI ignition region, SI ignition is temporarily used to suppress excessively powerful jet ignition.

[0034] Furthermore, when starting the internal combustion engine 1, the control device 50 may set the closing timing of the intake valve 32 to bottom dead center (BDC) as in the above-described region D, and may set the ignition mode to JET ignition, thereby improving ignition performance at the time of starting. As described above, the internal combustion engine 1 of this embodiment has a first spark plug 61 that ignites the mixture in the main combustion chamber 40 and a second spark plug 62 that ignites the mixture in the auxiliary combustion chamber 42, and is capable of switching between ignition modes such as SI ignition by the first spark plug 61, JET ignition by the second spark plug 62, and SI+JET ignition by both the first spark plug 61 and the second spark plug 62.

[0035] The internal combustion engine 1 further includes a variable valve mechanism 70, which is capable of switching and controlling the opening and closing timing of the intake valve 32. The variable valve mechanism 70 enables the intake valve 32 to be closed early, that is, earlier than the bottom dead center, or late, that is, later than the bottom dead center. Generally, in an internal combustion engine, early closing of the intake valve reduces the amount of blocked air at low engine speeds and increases the amount of blocked air as the engine speed increases. In other words, as described below, late closing has advantages in the low engine speed range, as opposed to the high engine speed range where it has advantages. Such disadvantages at high engine speeds can be eliminated by canceling early closing through retarding operation using a variable valve mechanism or by forcing intake air into the cylinder through supercharging (however, this will increase intake pressure loss). Early closing also increases the time the cylinder is sealed, increasing the compression ratio and achieving a temperature rise effect through adiabatic expansion.

[0036] On the other hand, by closing the intake valve late, the amount of blowback is large at low engine speeds, and decreases as the engine speed increases. This is suitable for internal combustion engines that require more intake air as the engine speed increases, and can improve power output. At low engine speeds, losses such as pump loss can be suppressed, and at high engine speeds, the air pressure time can be extended. Note that as the intake valve closing timing becomes later at the most retarded angle, starting performance deteriorates, so there is a limit to how far the valve can be retarded. In addition, the combustion temperature decreases, which can suppress the generation of NOx.

[0037] In this embodiment, the ignition mode and the variable valve mechanism 70 are switched based on the operating state of the internal combustion engine 1, for example, the load T and rotation speed Ne of the internal combustion engine 1. Moreover, the region below the predetermined rotation speed Ne1 is a single ignition region in which the ignition mode is set to either SI ignition or JET ignition. In the single ignition region, if the operating conditions change, for example, if changes in the load T and the rotational speed Ne cause the variable valve mechanism 70 to switch the closing timing of the intake valve 32 between early closing (earlier than bottom dead center) and late closing (later than bottom dead center), i.e., if the closing timing of the intake valve 32 is changed so that it crosses bottom dead center, the ignition mode will switch from SI ignition or JET ignition, which are set based on the load T and the rotational speed Ne, to the other, and the ignition timing will be retarded.

[0038] This allows for appropriate combustion by switching the ignition mode in response to the temporary rise in in-cylinder pressure that occurs when the closing timing of the intake valve 32 is changed so as to straddle bottom dead center. As described above, there are advantages and disadvantages to both early and late closing of the intake valve 32, and the operating ranges of the internal combustion engine 1 in which the advantages are realized are different. However, by switching the ignition mode in accordance with when switching between early and late closing of the intake valve 32, the advantages of both early and late closing can be obtained while minimizing the disadvantages.

[0039] For example, in the low load range as described above, if the closing timing of the intake valve 32 is changed so that it crosses the bottom dead center, SI ignition is switched to JET ignition. However, in a Miller cycle engine such as the internal combustion engine 1 of this embodiment, knocking is likely to occur when the intake valve 32 closes at bottom dead center. Therefore, ignition retard is performed to slow combustion in the cylinder, but the EGR amount must be reduced to ensure combustibility. However, there is a time lag in reducing the EGR amount, which may result in insufficient combustion performance.

[0040] In this embodiment, when the closing timing of the intake valve 32 is changed to cross bottom dead center in the low load range where the load T is less than a predetermined value T1, ignition retardation is performed and SI ignition is switched to JET ignition, thereby compensating for slow combustion in the cylinder without reducing the EGR amount and improving combustion performance. Also, as shown in FIG. 6, even in an internal combustion engine 1 that switches between SI ignition and JET ignition based on the load T of the internal combustion engine 1 in the single ignition region, if the closing timing of the intake valve 32 is changed so as to cross the bottom dead center, the ignition timing may be retarded while switching from one of SI ignition and JET ignition, which are set based on the load T and the rotational speed Ne, to the other.

[0041] For example, if the load T of the internal combustion engine 1 is less than a predetermined value T2, the intake valve 32 is closed early, and if the load T is equal to or greater than the predetermined value T2, the intake valve 32 is closed late, and the predetermined value T2 is set to be smaller than the predetermined value T1, which is the threshold for switching between SI ignition and JET ignition, then when there is a transition from the early-closing region to the late-closing region within the SI ignition region as shown in a of Figure 6, or when there is a transition from the late-closing region to the early-closing region within the SI ignition region as shown in b of Figure 6, JET ignition can be temporarily performed to cover the output reduction due to retarding and suppress output fluctuations.

[0042] More specifically, similar to the cases a and b in Figure 5 above, the power loss caused by retarding the ignition timing can be compensated for by the high-speed combustion of jet ignition. Furthermore, in the cases a and b in Figure 6, the operating range shifts in the direction of the load change. Therefore, during slight transient operation, such as when reducing output torque for fine adjustment, the frequency of crossing the normally closed state (when the closing timing of the intake valve 32 is near bottom dead center BDC) may increase even if hysteresis is set. By using jet ignition to compensate for the reduction in output torque caused by retarding the ignition timing as described above, the linearity of the output torque when the closing timing of the intake valve 32 crosses bottom dead center BDC can be compensated for, thereby reducing the sense of discomfort felt by the driver.

[0043] The internal combustion engine 1 has a first variable valve mechanism 71 and a second variable valve mechanism 72 as the variable valve mechanism 70, each of which can be independently controlled. This allows the opening and closing timings of the intake valve 32 to be changed independently. In this embodiment, by switching the ignition mode according to the changes in the opening and closing timings of the intake valve 32, it is possible to more precisely perform ignition appropriately in response to changes in the flow state of intake air in the cylinder.

[0044] Although the description of the embodiment has been completed above, the aspects of the present invention are not limited to this embodiment, and the detailed structure of the internal combustion engine 1 may be changed as appropriate. For example, in the above embodiment, the variable valve mechanism 70 switches the opening and closing timing of the intake valve 32 based on the load T and rotation speed Ne of the internal combustion engine 1, but the present invention can also be applied to an internal combustion engine that switches the opening and closing timing of the intake valve 32 based on conditions other than the load T and rotation speed Ne of the internal combustion engine 1.

[0045] For example, in an internal combustion engine in which the intake valve 32 is basically set to late closing, later than bottom dead center BDC, and the intake valve 32 is set to early closing, earlier than bottom dead center BDC, during warm-up operation or when performing temperature rise control such as regeneration of a DPF or the like provided in the exhaust passage 11, when switching from early closing to late closing after temperature rise control ends, the ignition timing may be retarded and switched from one of SI ignition and JET ignition, which are set based on other operating conditions of the internal combustion engine. This allows appropriate ignition when switching the intake valve opening / closing timing, as in the above embodiment.

[0046] Furthermore, the first spark plug 61 is arranged at the top of the main combustion chamber 40 (i.e., the cylinder head 34), and the auxiliary combustion chamber 42 is provided in the cylinder block 36 and the second spark plug 62 is arranged therein; however, as shown in FIG. 7, the auxiliary combustion chamber 42 may be provided at the top of the main combustion chamber 40 and the second spark plug 62 may be arranged therein, and the first spark plug 61 may be arranged in the cylinder block 36. In addition, in the above embodiment, the variable valve mechanism 70 includes a first variable valve mechanism 71 and a second variable valve mechanism 72, but any variable valve mechanism that changes at least one of the opening and closing timings of the intake valve 32 may be used.

[0047] Furthermore, the internal combustion engine of the present invention can be widely applied to internal combustion engines for driving vehicles mounted on gasoline engine vehicles, hybrid vehicles, or plug-in hybrid vehicles (PHEVs) that can be externally charged or externally powered, or to other uses. The present invention can be widely applied to internal combustion engines having spark plugs in the auxiliary combustion chamber and the main combustion chamber, respectively, and having a variable valve mechanism. [Explanation of symbols]

[0048] 1. Internal combustion engine 30, 300 cylinders 32 Intake valve (intake valve) 40 Main combustion chamber 42 Auxiliary combustion chamber 50 Control device 61 No. 1 spark plug 62 No. 2 spark plug 70 Variable valve mechanism 71 First variable valve mechanism 72 Second variable valve mechanism

Claims

1. a main combustion chamber filled with an air-fuel mixture; an auxiliary combustion chamber communicating with the main combustion chamber via a plurality of communication holes; a first spark plug disposed in the main combustion chamber and configured to ignite the air-fuel mixture in the main combustion chamber; a second spark plug disposed in the auxiliary combustion chamber and configured to ignite the air-fuel mixture in the auxiliary combustion chamber; An internal combustion engine equipped with a variable valve mechanism that changes the opening and closing timing of an intake valve, a control device that controls the ignition type and ignition timing of the first spark plug and the second spark plug based on an operating state of the internal combustion engine, a first ignition mode in which only the first spark plug of the first and second spark plugs ignites, and a second ignition mode in which only the second spark plug ignites, the control device changes the ignition type from one of the first ignition type and the second ignition type, which are set based on the operating state of the internal combustion engine, to the other, and retards the ignition timing, when the variable valve mechanism changes the closing timing of the intake valve so that it crosses bottom dead center within a single ignition region, which is an operating region of the internal combustion engine in which the first ignition type or the second ignition type is applied.

2. Equipped with a supercharger, the control device, in the single ignition region, sets the second ignition type in a supercharging region by the supercharger and sets the first ignition type in a natural aspiration region, an early closing region, which is an operating region of the internal combustion engine in which the closing timing of the intake valve is set earlier than the bottom dead center by the variable valve mechanism, and a late closing region, which is an operating region of the internal combustion engine in which the closing timing of the intake valve is set later than the bottom dead center by the variable valve mechanism; 2. The internal combustion engine according to claim 1, wherein the variable valve mechanism switches between the early-closing region and the late-closing region in the single ignition region.

3. 3. The internal combustion engine according to claim 2, wherein the control device sets the valve to the early closing region in the single ignition region when the engine is in a low rotation range below a predetermined rotation speed of the internal combustion engine, and sets the valve to the late closing region when the engine is in a high rotation range above the predetermined rotation speed of the internal combustion engine.

4. 3. The internal combustion engine according to claim 2, wherein the control device sets the valve to the early closing region in the single ignition region when the engine is in a low load region below a predetermined value, and sets the valve to the late closing region when the engine is in a high load region above the predetermined value.

5. a third ignition mode in which both the first spark plug and the second spark plug are ignited; The internal combustion engine according to claim 2 , wherein the control device selects the third ignition mode in a rotational speed range higher than the single ignition region.

6. 6. The internal combustion engine according to claim 1, wherein the control device controls the variable valve mechanism so that the intake valve closes at bottom dead center when the internal combustion engine is started, and also selects the second ignition mode.

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