JP2017015038A - Control device, control method and control program of internal combustion engine, and internal combustion engine system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control device of an internal combustion engine capable of improving heat efficiency by stabilizing combustion even when an air-fuel mixture is kept in a lean state.SOLUTION: An ECU 100 makes a valve gear 70 have a negative overlap period during which both of an intake valve 15 and an exhaust valve 16 are closed in an exhaust stroke and an intake stroke, so that self-ignition occurs on an air-fuel mixture in a combustion chamber 17 in a compression stroke, when a load of an engine 1 is in a prescribed low load region. The ECU 100 ignites an ignition plug 31 at a prescribed period after the period during which the self-ignition occurs.SELECTED DRAWING: Figure 13

Description

  The present invention relates to a control device, a control method, a control program, and an internal combustion engine system for a spark ignition type internal combustion engine that ignites an air-fuel mixture in a combustion chamber with a spark plug.

  Patent Document 1 discloses a spark ignition type internal combustion engine that ignites an air-fuel mixture in a combustion chamber with a spark plug. Further, Patent Document 1 discloses a technique in which lean combustion is performed by setting the air-fuel ratio to a lean state in which the air-fuel ratio is larger than the stoichiometric air-fuel ratio.

Japanese Patent Application Laid-Open No. 2015-072003

  When lean combustion is performed in an internal combustion engine, thermal efficiency is generally improved. However, in the lean state, an initial flame cannot be formed and a fire may be lost. Further, even when the initial flame is formed, the flame propagation speed is slow and partial combustion may occur. Such misfire or partial combustion hinders improvement in thermal efficiency due to lean combustion.

  The present invention provides an internal combustion engine control device, control method, control program, and internal combustion engine system that can stabilize combustion and improve thermal efficiency even when the air-fuel mixture is in a lean state.

The control device for an internal combustion engine according to the present invention is a control device for a spark ignition type internal combustion engine that ignites an air-fuel mixture in a combustion chamber with a spark plug.
The internal combustion engine
An intake valve, an exhaust valve, and a valve operating mechanism configured to open and close the intake valve and the exhaust valve and to change at least the opening timing of the exhaust valve among the intake valve and the exhaust valve.
The control device includes load detection means for detecting a load of the internal combustion engine,
A valve mechanism control means for controlling the operation of the valve mechanism;
Ignition control means for controlling the ignition timing of the spark plug.
The valve mechanism control means controls the valve mechanism so that when the load is in a predetermined low load region, self-ignition occurs in the air-fuel mixture in the combustion chamber during the compression stroke, the intake valve and the aforementioned valve during the exhaust stroke or the intake stroke. Creates a negative overlap condition where both exhaust valves are closed.
The ignition control means ignites the spark plug at a predetermined timing after the timing at which self-ignition occurs.

The internal combustion engine control method of the present invention is a spark ignition type internal combustion engine control method in which an air-fuel mixture in a combustion chamber is ignited by a spark plug.
The internal combustion engine
An intake valve, an exhaust valve, and a valve operating mechanism configured to open and close the intake valve and the exhaust valve and to change at least the opening timing of the exhaust valve among the intake valve and the exhaust valve.
The control method is
A valve mechanism control process for controlling the operation of the valve mechanism;
An ignition control step for controlling the ignition timing of the spark plug.
In the valve mechanism control process, when the load of the internal combustion engine is in a predetermined low load region, the valve mechanism is evacuated in the exhaust stroke or the intake stroke so that self-ignition occurs in the air-fuel mixture in the combustion chamber in the compression stroke. A negative overlap condition is generated in which both the valve and the exhaust valve are closed.
In the ignition control step, the spark plug is ignited at a predetermined timing after the timing at which self-ignition occurs.

  The control program for an internal combustion engine of the present invention causes a computer to function as a control device for the internal combustion engine.

The internal combustion engine system of the present invention includes a spark ignition type internal combustion engine that ignites an air-fuel mixture in a combustion chamber with a spark plug and a control device that controls the internal combustion engine.
The internal combustion engine
An intake valve, an exhaust valve, and a valve operating mechanism configured to open and close the intake valve and the exhaust valve and to change at least the opening timing of the exhaust valve of the intake valve and the exhaust valve;
The control device
A valve mechanism control means for controlling the operation of the valve mechanism;
Ignition control means for controlling the ignition timing of the spark plug, and
The valve mechanism control means controls the valve mechanism so that the air-fuel mixture in the combustion chamber is self-ignited during the compression stroke when the load of the internal combustion engine is in a predetermined low load region. Create a negative overlap condition where both the valve and the exhaust valve are closed,
The ignition control means ignites the spark plug at a predetermined timing after the timing at which self-ignition occurs.

  According to the present invention, in the spark ignition engine, when the load is in a predetermined low load region, a negative overlap state is generated in which both the intake valve and the exhaust valve are closed in the exhaust stroke or the intake stroke, In the compression stroke, self-ignition occurs in the air-fuel mixture in the combustion chamber, and then the spark plug is ignited. According to the inventor's knowledge, when the load is in a predetermined low load region, when the air-fuel mixture is in a lean state by causing self-ignition as a negative overlap state and then igniting with a spark plug However, it is possible to stabilize the combustion and improve the thermal efficiency.

1 is a diagram illustrating a configuration of an engine system according to Embodiment 1. FIG. It is a figure which shows the main specifications of the engine utilized in experiment. It is a figure which shows the setting conditions of the NVO period in experiment and simulation. It is a figure which shows the characteristic of MBT with respect to an air fuel ratio (A / F). It is a figure which shows the characteristic of the fluctuation rate of the illustration average effective pressure with respect to an air fuel ratio (A / F) and the illustration average effective pressure. It is a figure which shows the characteristic of the illustration thermal efficiency with respect to an air fuel ratio (A / F). It is a figure which shows the characteristic of the heat release rate with respect to a crank angle. It is a figure which shows the characteristic of MBF2-50% period with respect to an air fuel ratio. It is a figure which shows the characteristic of the internal EGR rate with respect to the length of an NVO period, and the characteristic of the in-cylinder temperature just before ignition with respect to an NVO period (340 degree CA). It is a figure (Log-PV diagram) which shows the pressure of gas with respect to the volume of the combustion chamber in a cylinder. It is a figure which shows the characteristic of the illustration thermal efficiency with respect to a torque (engine load), a net thermal efficiency, and a fuel consumption rate. It is a figure which shows the appropriate range of the heat release rate in the case of performing NVO driving | operation in a spark ignition type engine. It is a figure explaining an example of valve opening timing control in each operation mode of an engine. It is a figure which shows the characteristic of the heat release rate with respect to the crank angle for demonstrating optimal combustion. It is a figure which shows the example of combustion when the optimal combustion is not acquired. 3 is a flowchart showing a flow of control by the engine control apparatus of the first embodiment. It is a figure which shows the structure of an ion current sensor. It is a figure which shows the structure of the engine system which concerns on Embodiment 3. FIG. 6 is a flowchart showing a flow of combustion control by the engine control apparatus of Embodiment 3. FIG. 6 is a diagram showing a configuration of an engine ignition system according to a fourth embodiment. 6 is a flowchart showing a flow of control by an engine control apparatus according to a fourth embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

1. Configuration FIG. 1 is a diagram illustrating a configuration of an engine system according to the first embodiment. The engine system is, for example, deployed in an automobile, and includes an engine 1 (internal combustion engine) and an engine control device 100 (ECU (Engine Control Unit), hereinafter referred to as “ECU 100”) that controls the operation of the engine 1. .

  The engine 1 includes an engine body 10, a fuel supply system 20, an ignition system 30, an intake passage 40, an exhaust passage 50, an exhaust recirculation passage 60, a valve mechanism 70, and the like.

  The engine body 10 includes a cylinder block 11, a piston 12, a piston rod 13, a crankshaft 14, an intake valve 15, and an exhaust valve 16. A combustion chamber 17 is formed by the cylinder block 11 and the piston 12. The piston 12 slides in the cylinder bore inside the cylinder block 11. The piston rod 13 converts the linear motion of the piston 12 into the rotational motion of the crankshaft 14. A pressure sensor 18 and a crank position sensor 19 are attached to the cylinder block 11. The pressure sensor 18 outputs a signal indicating the pressure of the gas in the combustion chamber 17. The crank position sensor 19 outputs a signal indicating a rotation angle (crank angle) based on the rotation position of the crankshaft 14 when the piston 12 is at top dead center (TDC).

  The intake valve 15 opens and closes a communication portion that connects the combustion chamber 17 of the engine body 10 and the intake passage 40. The exhaust valve 16 opens and closes a communication portion that connects the combustion chamber 17 of the engine body 10 and the intake passage 40.

  The valve mechanism 70 includes an intake side valve mechanism 71 that opens and closes the intake valve 15 and an exhaust side valve mechanism 72 that opens and closes the exhaust valve 16. The exhaust side valve mechanism 72 is a variable valve timing control mechanism (VVT (Variable Valve Timing-control)) that makes the valve opening timing (valve opening timing) of the exhaust valve 16 variable, and the valve lift amount of the exhaust valve 16 is variable. And a variable valve lift control mechanism (VVL (Variable Valve Lift-control). Well-known ones can be used as these mechanisms, and detailed description thereof is omitted. The variable valve timing control mechanism of this embodiment is A so-called negative overlap (Negative Valve-overlap, hereinafter referred to as “NVO” as appropriate) that closes both the intake valve 15 and the exhaust valve 16 in the exhaust stroke or the intake stroke is configured to be realized.

  In the intake passage 40, an air cleaner 41, an intake flow rate sensor 42, and a throttle valve 43 are arranged in this order from the upstream side. The air cleaner 41 contains a filter element therein, and filters the fresh air to be sucked by the filter element. The intake flow rate sensor 42 outputs a signal indicating the flow rate of fresh air flowing into the intake passage 40 from the outside. The throttle valve 43 is controlled in opening based on an opening signal output from the ECU 100, and adjusts the flow rate of fresh air flowing through the intake passage 40.

  A silencer (not shown) is disposed in the exhaust passage 50.

  The exhaust gas recirculation passage 60 is a passage connecting the exhaust passage 50 and the intake passage 40, and recirculates exhaust gas from the exhaust passage 50 to the intake passage 40 (external EGR). An exhaust gas recirculation valve 61 is disposed on the exhaust gas recirculation passage 60. The exhaust gas recirculation valve 61 is controlled in opening degree based on an opening degree signal output from the ECU 100 and adjusts the amount of exhaust gas to be recirculated.

  The fuel supply system 20 includes an injector 21, a fuel pump 22, and a fuel tank 23, and supplies the fuel in the fuel tank 23 to the injector 21 through the fuel pump 22. The injector 21 is disposed so that the fuel injection port faces the intake passage 40 and injects combustion into the intake passage 40 based on a combustion injection signal output from the ECU 100.

  The ignition system 30 includes an ignition plug 31, an ignition coil 32, and an igniter 33. When the igniter 33 receives an ignition signal output from the ECU 100, a high voltage is generated by the ignition coil 32 and a spark is generated from the ignition plug 31. Is generated.

  The ECU 100 includes a control unit, a storage unit, a signal interface, and the like, and inputs or outputs various signals to and from each sensor and each actuator. The storage unit stores various data such as a program for realizing various functions of the ECU 100 and an operation region map described later. A control part is comprised by CPU, MPU, or FPGA, for example. The ECU 100 realizes various functions by the control unit performing arithmetic processing based on the program and various data. The function of the ECU 100 may be realized by cooperation of hardware such as a control unit and a storage unit and software, or may be realized only by hardware (electronic circuit).

  The ECU 100 includes at least a signal indicating the crank angle output from the crank position sensor 19, a signal indicating the combustion pressure output from the pressure sensor 18, and a signal indicating the depression amount output from the accelerator pedal module 80 provided in the vehicle. And various actuators are controlled based on these signals. Generally, the depression amount with respect to the accelerator pedal module 80 substantially corresponds to the magnitude of the engine load (torque), and the ECU 100 uses the signal indicating the depression amount as a signal indicating the engine load to control combustion of the engine ( Operation control).

2. The subject of this invention, etc. are demonstrated before demonstrating the specific control of this embodiment.

2-1. Problem As described in the section of the problem to be solved by the invention, when lean combustion is performed in an internal combustion engine, the thermal efficiency is generally improved. However, in the lean state, an initial flame cannot be formed and a fire may be lost. Further, even when the initial flame is formed, the flame propagation speed is slow and partial combustion may occur. Such misfire or partial combustion hinders improvement in thermal efficiency due to lean combustion.

  Therefore, an object of the present invention is to provide an engine control device that can stabilize combustion and improve thermal efficiency even when the air-fuel mixture is in a lean state.

  In order to cope with this problem, the inventors of the present application have made extensive studies and obtained knowledge about a technology based on an engine that performs combustion by spark ignition (SI) (SI combustion). Specifically, in each combustion cycle, combustion by spark ignition is performed, and both the intake valve 15 and the exhaust valve 16 are closed in the exhaust stroke or intake stroke before the spark ignition to generate a negative overlap state, In the compression stroke, combustion (CI combustion) by self-ignition (CI) is generated. In other words, after combustion by self-ignition (CI combustion) is generated in the compression stroke, combustion by spark ignition is further performed. The inventor of the present application verified the combustion characteristics and the like in the case of performing such combustion control through experiments and simulations, and studied conditions for obtaining optimum combustion. Hereinafter, the examination results will be described.

2-2. Main Specifications and Valve Timing of Test Engine FIG. 2 is a diagram showing the main specifications of the engine used in the experiment. The engine used is an engine with 3 cylinders, 658cc displacement, 11 compression ratio, 64.0mm bore diameter, 68.2mm stroke, and port injection.

  FIG. 3 is a diagram showing the setting conditions of the NVO period in the experiment and simulation. In this evaluation, the valve opening timing of the intake valve 15 was not changed with respect to the so-called positive overlap (Positive Valve-overlap, hereinafter referred to as “PVO” as appropriate), and only the valve opening timing of the exhaust valve 16 was changed. . In PVO, the maximum lift amount of the intake valve 15 and the exhaust valve 16 is 7.6 mm, and the valve opening period is 210 ° CA. In NVO, the maximum lift amount of the exhaust valve 16 is 2.6 mm, and the valve opening period is 90 ° CA. The valve opening timing is changed while maintaining the maximum lift amount and the valve opening period. There are four types of NVO periods: 26 ° CA, 43 ° CA, 60 ° CA, and 77 ° CA. Moreover, the positive overlap period in PVO was set to 2 ° CA. Hereinafter, the state in which the NVO period is set to 26 ° CA, 43 ° CA, 66 ° CA, 77 ° CA will be referred to as NVO 26, NVO 43, NVO 60, and NVO 77 as appropriate. A state where the PVO period is set to 2 ° CA is appropriately referred to as PVO2.

2-3. FIG. 4A is a diagram showing MBT characteristics with respect to the air-fuel ratio (hereinafter referred to as “A / F” where appropriate). MBT (minimum advance for the best torque) is an ignition timing at which the torque becomes maximum when only the ignition timing is changed under the same conditions such as engine speed and intake air amount. FIG. 4A shows the characteristics of the advance amount (° CA) of the MBT with respect to the compressed TDC. 4B is a graph showing characteristics of an indicated mean effective pressure (IMEP) and a variation rate of the indicated mean effective pressure with respect to the air-fuel ratio (A / F). F is a graph showing the characteristics of the indicated thermal efficiency with respect to F) The measurement conditions are an engine speed of 1000 rpm, a throttle opening (hereinafter referred to as “TVO”) of 10%, and an ignition timing of MBT.

  As shown in FIG. 4A, the advance amount (° CA) of the MBT with respect to the compressed TDC increases as the air-fuel ratio increases. Further, the advance amount (° CA) of the MBT with respect to the compressed TDC tends to increase as the NVO period becomes longer. That is, the MBT tends to advance as the air-fuel ratio increases and the NVO period increases.

  As shown in FIG. 4B, the indicated mean effective pressure is improved over PVO2 when the NVO period is 26 ° CA and 43 ° CA. That is, the lean limit is improved. However, when the NVO period is increased to 60 ° CA, the indicated mean effective pressure is almost the same as in the case of PVO, and is worsened when the NVO period is further increased to 77 ° CA. That is, the indicated mean effective pressure increases if the NVO period is smaller than around 43 ° CA, but worsens if the NVO period is larger than that.

  Also, the fluctuation rate of the indicated mean effective pressure (hereinafter referred to as “the indicated mean effective pressure fluctuation rate” as appropriate) is 3% or less regardless of the air-fuel ratio when the NVO period is 26 ° CA and 43 ° CA, and is stable. doing. That is, the engine operating state is stabilized. However, when the NVO period is 60 ° CA, the indicated mean effective pressure fluctuation rate greatly exceeds 3% when the air-fuel ratio exceeds 18, and when the NVO period is 77 ° CA, the average effective pressure fluctuation rate is 3 when the air-fuel ratio exceeds 16. % Greatly exceeds. That is, the engine operating state tends to become unstable.

  As shown in FIG. 4C, when the engine speed is 1000 rpm and the throttle opening is 10%, the indicated thermal efficiency is lower than in the case of PVO in all four NVO periods.

2-4. Analysis of Lean Limit Improvement Factor As described above, the lean limit is improved in NVO 26 and NVO 43. In the following, the results of studying the improvement factor of the lean limit will be described with reference to the drawings.

2-4-1. Heat Release Rate FIG. 5A is a graph showing the heat release rate characteristics with respect to the crank angle. The heat generation rate (J / ° CA) is a heat generation amount (J) per unit crank angle (° CA). FIG. 5B is a diagram showing characteristics of the MBF 2-50% period with respect to the air-fuel ratio. MBF is a mass burn fraction (Mass Burn Fraction). The heat generation rate in FIG. 5A is the heat generation rate when the air-fuel ratio at which combustion is relatively stable is 16. The arrow indicates the ignition timing in each NVO period. The ignition timing corresponds to the MBT shown in FIG. 4A described above. When each NVO and PVO are compared, the following can be said.
(1) MBT is retarded more than PVO2 in each NVO.
(2) The flame propagation speed is substantially the same as PVO2 in NVO26, NVO43, and NVO60, but is slower than PVO2 in NVO77. Here, the flame propagation speed is a crank angle (° CA) required for MBF to reach 2% to 50% (hereinafter referred to as “MBF 2-50% period” as appropriate). As can be seen from this, it is considered that the factor for improving the lean limit in the NVO 26 and NVO 43 is that the flame propagation speed is maintained.

2-4-2. FIG. 6 is a diagram showing the characteristics of the internal EGR rate with respect to the length of the NVO period and the characteristics of the in-cylinder temperature immediately before ignition (340 ° CA) with respect to the length of the NVO period. is there. The in-cylinder temperature is the temperature (K) of the gas in the combustion chamber 17 (including both the air-fuel mixture and the combustion gas). As shown in FIG. 6A, the longer the NV0 period, the higher the internal EGR rate. Further, as shown in FIG. 6B, the longer the NV0 period, the higher the in-cylinder temperature immediately before ignition. In NVO43, NVO60, and NVO77, the in-cylinder temperature exceeds the gasoline self-ignition temperature (about 700 degrees Celsius). Therefore, it is estimated that self-ignition has occurred in NVO43, NVO60, and NVO77.

2-5. Analysis of Decreasing Factor of Illustrated Thermal Efficiency As described with reference to FIG. 4C, the illustrated thermal efficiency is lower than that of PVO2 in the above four types of NVO periods. This factor will be described with reference to FIG. FIG. 7 is a diagram (Log-PV diagram) showing the pressure of the gas with respect to the volume of the combustion chamber 17 in the cylinder. As can be seen from FIG. 7, each NVO has a higher isovolume than PVO2. On the other hand, in each NVO, the pumping loss increases and the polytropic index decreases compared to PVO2. Thus, with negative overlap (NVO), the isovolume improves, but the pumping loss increases and the polytropic index decreases. Therefore, it is considered that the thermal efficiency shown in each NVO has decreased.

2-6. Summary of Applying NVO in SI Combustion When NVO is applied in SI combustion by the spark ignition engine, the lean limit is improved, but the illustrated thermal efficiency is lowered.
(1) The cause of the lean limit improvement is that the in-cylinder temperature is increased by internal EGR, and self-ignition combustion at an appropriate flame propagation speed is obtained.
(2) The cause of the decrease in the illustrated thermal efficiency is that the deterioration margin due to the increase in the pumping loss and the decrease in the polytropic index is larger than the improvement margin due to the improvement in the equal volume.

2-7. Characteristics of the illustrated thermal efficiency, the net thermal efficiency, and the fuel consumption rate with respect to the torque The inventor of the present application has further studied the characteristics with respect to the torque with respect to the illustrated thermal efficiency, the net thermal efficiency, and the fuel consumption rate in response to the above-described examination results. FIG. 8 is a diagram showing the characteristics of the indicated thermal efficiency, net thermal efficiency, and fuel consumption rate with respect to torque (engine load). As shown in FIGS. 8A and 8B, the illustrated thermal efficiency and net thermal efficiency of the NVO 26 and NVO 43 are in the region where the torque is 10 N · m or less, particularly in the region where the torque is 8 N · m or less ( In the region indicated by the arrow C), it is greatly improved over those in PVO2. In addition, the illustrated thermal efficiency and net thermal efficiency of NVO 26 and NVO 43 are slightly improved in the region where the torque is 15 N · m (the region indicated by arrow D), although slightly less than those in PVO 2.

  Further, as shown in FIG. 8C, the fuel consumption rates in the NVO 26 and NVO 43 are greatly improved in the region where the torque is 8 N · m or less (the region indicated by the arrow E), compared to those in the PVO 2. Yes. In particular, the fuel consumption rate in NVO 43 is improved by 29.2%.

  In this way, in the region where the torque is 8 N · m or less, by setting the NVO period to 26 ° CA or 43 ° CA, the illustrated thermal efficiency, net thermal efficiency, and fuel consumption rate are greatly improved with respect to PVO 2. Can do.

2-8. Direction of engine control when NVO is applied to SI combustion in a spark ignition engine As has been clarified in the above study, NVO control is performed in a low load region to generate self-ignition in a spark ignition engine. Further, it is effective to perform spark ignition. In particular, in NVO43, as shown in FIG. 5A, the maximum value of the heat generation rate is lower than that in the case of PVO2. This leads to a decrease in combustion pressure and a pumping loss. As a result, as shown in FIG. 8C, the fuel consumption rate is improved by 29.2%. Therefore, the illustrated thermal efficiency, net thermal efficiency, and fuel consumption rate can be improved by adjusting the opening timing of the exhaust valve 16 around the NVO 43. Specifically, referring to the characteristics of the heat generation rate of NVO 43 shown in FIG. 5A, the heat generation rate starts to increase generally in the range of 340 ° CA to 345 ° CA before compression TDC, and becomes large after 345 ° CA. It is starting to rise. It reaches a peak at about 5 ° CA after compression TDC. Therefore, the NVO period and ignition are set such that the heat generation rate reaches a predetermined value in the range of 345 ° CA to 350 ° CA of the compression TDC and reaches the maximum value at about 5 ° CA after the compression TDC. It is effective to adjust the timing.

3. Control operation 3-1. Overview of Control FIG. 9 is a diagram showing an appropriate range of heat generation rate when performing NVO operation in a spark ignition engine. In the present embodiment, the valve operating mechanism 70 is configured so that the crank angle converges to the first predetermined range when the heat generation rate rises to a predetermined value indicating that combustion by self-ignition has reached a predetermined state. While controlling the negative overlap period, the ignition plug 31 is ignited on the retard side with respect to the first predetermined range in each combustion cycle.

  In the present embodiment, the ECU 100 sets the engine operation mode according to the engine load (torque). Specifically, the ECU 100 controls the operation of the engine in the SI + NVO mode when the engine load (torque) is equal to or less than a predetermined load (torque) (when it is in a predetermined low load region (hereinafter referred to as “SI + NVO region” as appropriate)). When the engine load is not in the SI + NVO region, the engine operation is controlled in the SI mode. As a parameter relating to the engine load, for example, the throttle opening degree of the throttle valve 43 controlled according to the user's stepping operation on the accelerator pedal module 80 can be used. The ECU 100 may set the operation mode of the engine 1 according to the current engine load and engine speed.

  FIG. 10 is a diagram illustrating an example of valve opening timing control in each operation mode. The SI mode is a mode in which the air-fuel mixture is ignited by the spark plug. In the SI mode, as shown in FIG. 10A, the exhaust valve 16 is opened for a period of about 180 ° CA in the exhaust stroke, and the intake valve 15 is opened for a period of about 180 ° CA in the intake stroke. The valve opening periods of both valves partially overlap in the range of a small crank angle (approximately 2 ° CA) sandwiching the valve. Ignition by the spark plug 31 is performed, for example, at the timing of MBT.

  The SI + NVO mode is a mode in which the air-fuel mixture is self-ignited (CI) by NVO and then spark ignition (SI) is further performed by the spark plug 31. In the SI + NVO mode, as shown in FIG. 10B, a period from when the exhaust valve 16 is closed to when the intake valve 15 is opened, that is, a negative overlap (NVO) period in which both the intake valve 15 and the exhaust valve 16 are closed. Is provided to leave a large amount of internal EGR gas, which is compressed in the compression stroke to increase the temperature of the air-fuel mixture in the combustion chamber 17, thereby promoting the self-ignition of the air-fuel mixture. In the example of FIG. 10B, the exhaust valve 16 is opened for a period of about 90 ° CA in the exhaust stroke, and the intake valve 15 is opened for a period of about 180 ° CA in the intake stroke. The NVO period is changed according to the operating state of the engine. As the NVO period is lengthened, the ratio of the internal EGR gas in the mixture can be increased to increase the temperature of the mixture.

The ignition timing by the spark plug 31 is based on the MBT, but is advanced or retarded around the MBT so that the maximum heat generation rate timing becomes a predetermined timing.

  CI combustion in which the air-fuel mixture self-ignites can be realized even with an ultra-lean air-fuel mixture that is difficult to realize SI combustion or with an air-fuel mixture diluted with a large amount of internal EGR gas. In other words, when the air-fuel mixture is not so lean or the air-fuel ratio is low, the self-ignition timing is too early, and so-called knocking occurs.

  In other words, the CI combustion is realized by a fairly lean air-fuel mixture or an air-fuel mixture diluted with a large amount of EGR, so that a high output cannot be obtained. Therefore, in the present embodiment, as shown in the above-described control map, the SI mode is set in the operation region on the relatively high load side, and the SI + NVO mode is set in the low load region.

3-2. Optimum Combustion in SI + NVO Mode The inventor of the present application generally shows that the optimal combustion in SI + NVO is the combustion that shows the change in the heat generation rate as shown in the NVO 43 in FIG. 5A when the A / F is about 16 (lean state). I believe that. FIG. 9 is a diagram showing the characteristics of optimum combustion defined by the inventor based on the change in the heat generation rate of the NVO 43 in FIG. 5A. Note that a line indicated as PVO2 is a reference line for comparison, and shows characteristics in the SI mode in which A / F is 11 and NVO is not performed. The optimum combustion line in FIG. 9 is a line when the A / F is 16 and the NVO period is 43 ° CA. The shaded area is a range in which appropriate combustion according to optimum combustion is obtained. In the present embodiment, the NVO period and the ignition timing are controlled so that the change in the heat generation rate converges to the range of the netting. The optimum combustion in SI + NVO is combustion that satisfies the following conditions (1) and (2) at an A / F of about 16.
(1) The crank angle when the heat generation rate due to self-ignition rises to a predetermined value (0.5) is in the range of 345 to 350 ° CA before 10 to 15 ° CA with respect to the compression TDC (360 ° CA). It must be within ΔCa (hereinafter referred to as “first predetermined range ΔCa” as appropriate).
(2) The crank angle when the heat generation rate is maximized (hereinafter referred to as “the maximum time of heat generation rate” as appropriate) is 4 to 6 ° CA centered at 5 ° CA after the compression TDC (360 ° CA). Within the range of ΔCb (hereinafter referred to as “second predetermined range ΔCb” as appropriate), and thereafter, combustion is finished immediately.

  As described above, at A / F16, an appropriate flame propagation speed (for example, 0.5 J / CA) that does not cause knocking or the like by controlling the start timing of combustion by self-ignition and the maximum timing of heat generation rate. The optimal combustion by. As a result, compared with the combustion in PVO2 at A / F11, (a) the isovolume, the polytropic index, and the combustion mass ratio (MBF) of the expansion stroke are increased, and the indicated thermal efficiency is improved. Further, (b) the maximum combustion pressure is reduced, the frictional force (friction loss) when the piston slides is reduced, and the net thermal efficiency is improved. Furthermore, (c) ignition energy is reduced and fuel consumption is improved.

  FIG. 11 is a graph showing the characteristics of the heat release rate with respect to the crank angle for explaining the optimum combustion. As shown in FIG. 11A, the crank angle when the heat generation rate due to self-ignition rises to a predetermined value (0.5) is 10 to 15 ° CA before the compression TDC (360 ° CA). If it is in the range ΔCa (indicated by symbol A) of 345 to 350 ° CA, the waveform indicating the heat generation rate when the ignition is performed thereafter with MBT is the maximum heat generation rate as shown in FIG. There is a high possibility that the timing draws a trajectory passing through a range of 4 to 6 ° CA (desired range; range indicated by symbol B) centered on 5 ° CA after compression TDC (360 ° CA).

  FIG. 12 is a diagram illustrating an example of combustion when optimal combustion is not obtained. In combustion example 1 shown in FIG. 12 (a), the maximum heat release rate timing is in the vicinity of 385 (25) ° CA. In this case, during the expansion stroke, when the maximum heat generation rate is from 385 (25) ° CA until the maximum heat generation rate is 385 (25) ° CA, the piston 12 is prevented from descending and the pumping loss increases. In the combustion example 2 shown in FIG. 12B, the rise of the heat generation rate is larger than that of the optimal combustion. That is, the flame propagation speed is high. Therefore, knocking is likely to occur.

  In the present embodiment, based on the above knowledge, the NVO period is adjusted and the ignition timing is adjusted by the spark plug 31 in the SI + NVO region so that the conditions (1) and (2) are satisfied.

3-3. Specific Control The combustion control in the engine 1 of the present embodiment will be described. FIG. 13 is a flowchart showing a flow of control by the engine control apparatus (ECU 100) of the first embodiment. The control according to this flowchart is repeatedly executed for each combustion cycle.

  The ECU 100 reads the latest measurement values measured by various sensors in the previous combustion cycle (S11).

  The ECU 100 determines whether a misfire has occurred (S12). Specifically, the ECU 100 determines whether or not the maximum value of the pressure value detected by the in-cylinder pressure sensor 18 in each combustion cycle is equal to or greater than a first predetermined value, and the maximum value of the pressure value is the first value. If it is equal to or greater than 1 predetermined value, it is determined that no misfire has occurred, and if the pressure value is not less than the first predetermined value, it is determined that misfire has occurred.

  If it is determined that a misfire has occurred (Yes in S12), the ECU 100 controls the exhaust gas recirculation valve 61 so that the exhaust gas recirculation amount from the exhaust passage 50 to the intake passage 40 decreases. Specifically, the ECU 100 controls the exhaust gas recirculation valve 61 so that its opening degree becomes small. Thereby, G / F (ratio of external EGR gas to fuel) is reduced (riched), and misfire is less likely to occur.

  On the other hand, when it is determined that no misfire has occurred (No in S12), the ECU 100 determines whether knock has occurred (S13). Specifically, the ECU 100 determines whether or not the pressure value detected by the pressure sensor 18 is equal to or greater than a second predetermined value. If the pressure value is not equal to or greater than the second predetermined value, knocking has occurred. If the pressure value is equal to or greater than the second predetermined value, it is determined that knocking has occurred. Here, the second predetermined value is a value smaller than the first predetermined value.

  When it is determined that knocking has occurred (Yes in S13), the ECU 100 controls the exhaust gas recirculation valve 61 so that the exhaust gas recirculation amount from the exhaust passage 50 to the intake passage 40 increases. Specifically, the ECU 100 controls the exhaust gas recirculation valve 61 so that its opening degree is increased. Thereby, G / F becomes large (lean), and knocking hardly occurs.

  On the other hand, when it is determined that knocking has not occurred (No in S13), ECU 100 determines whether or not the operating region of engine 1 is in the SI + NVO region (S14). Specifically, ECU 100 applies the engine speed and the engine load to the operation region determination map of FIG. 9 and determines whether or not the operation region is in the SI + NVO region. At this time, the ECU 100 determines whether or not the engine load (torque) is equal to or lower than a predetermined low load (low torque).

  When it is determined that the operation region of the engine 1 is not in the SI + NVO region (No in S14), the ECU 100 sets the intake valve 15 and the exhaust valve 16 to the PVO state and performs combustion control in the SI mode (S21).

  On the other hand, when it is determined that the operation region of the engine 1 is in the SI + NVO region (Yes in S14), the ECU 100 sets the intake valve 15 and the exhaust valve 16 to the NVO state and starts combustion control in the SI + NVO mode. More specifically, the ECU 100 controls the exhaust-side valve mechanism 72 so that the NVO period becomes a predetermined period when the control in the SI + NVO mode is started. The predetermined period is an initial value of the NVO period when the combustion control in the SI + NVO mode is started. For example, as described above, the NVO 26 or NVO 43 that obtains relatively high thermal efficiency, or the middle thereof, or the vicinity thereof. Is the period of the value of. Note that after the start of combustion control in the SI + NVO mode, the NVO period is adjusted by the control described later so that the above-described optimum combustion can be obtained.

  During control in the SI + NVO mode, the ECU 100 determines whether or not self-ignition has occurred (S15). Specifically, when the pressure value detected by the pressure sensor 18 becomes equal to or greater than a third predetermined value before ignition by the spark plug 31, the ECU 100 determines that self-ignition has occurred and is less than the third predetermined value. Judge that it has not ignited. The third predetermined value is a value smaller than the first predetermined value and the second predetermined value.

  When it is determined that the self-ignition is performed (Yes in S15), the ECU 100 determines whether or not the self-ignition timing is appropriate (S16). Specifically, the ECU 100 obtains the heat generation rate by calculation based on the pressure value detected by the pressure sensor 18. The calculation of the heat generation rate based on the pressure value may be performed by a known method. The ECU 100 determines that the crank angle when the obtained heat generation rate rises to a predetermined value (for example, 0.5 J / ° CA. predetermined heat generation rate) is 10 to 15 ° CA (compressed TDC (360 ° CA)). It is determined whether or not the first predetermined crank angle) is within a range of 345 to 350 ° CA (first predetermined range ΔCa) on the advance side, and when it is within the first predetermined range ΔCa, the self-ignition timing is appropriate. If it is not within the first predetermined range ΔCa, it is determined that the self-ignition timing is not appropriate. Here, the first predetermined crank angle is a crank angle at which the crank angle when the heat generation rate is maximum is more likely to be in a second predetermined range ΔCb described later than the other crank angles. The “first predetermined range” in the present invention may be one crank angle included in the range ΔCa. For example, whether the self-ignition timing is appropriate by determining whether or not the crank angle when the heat generation rate has increased to a predetermined value matches the first predetermined crank angle (for example, 348 ° CA). Judge whether or not. Then, it is determined that the crank angle when the heat generation rate is increased to a predetermined value matches the first predetermined crank angle, and is not appropriate when the crank angle does not match the first predetermined crank angle. Judge.

  When it is determined that the self-ignition timing is appropriate (Yes in S16), the ECU 100 determines the crank angle when the heat generation rate obtained based on the pressure value detected by the pressure sensor 18 is maximized ( Hereinafter, the range “Cb (second predetermined range ΔCb) on the retarded side of 4 to 6 ° CA centered at 5 ° CA in the vicinity thereof with respect to the compression TDC (360 ° CA)” is appropriately referred to as “maximum heat generation rate”. ), And when it is within the second predetermined range ΔCb, it is determined that the maximum heat generation rate is appropriate, and when it is not within the second predetermined range ΔCb, the maximum heat generation rate is determined. Judge that the time is not appropriate. The “second predetermined range” in the present invention may be one crank angle included in the range on the 4 to 6 ° CA retard side. For example, it is determined whether or not the maximum heat generation rate coincides with a predetermined time (for example, 5 ° CA). When the maximum heat generation rate coincides with the predetermined time, it is determined that the maximum heat generation rate is appropriate. When the maximum heat generation rate does not coincide with the predetermined time, the maximum heat generation rate is not appropriate. to decide.

  When it is determined that the maximum heat generation rate is appropriate (Yes in S17), the ECU 100 maintains the current combustion control in the SI + NVO region (S18).

  On the other hand, if it is determined in step S15 that self-ignition has not occurred (No in S15), the ECU 100 controls the exhaust-side valve mechanism 72 so that the NVO period becomes longer (S22). Specifically, the ECU 100 controls the exhaust side valve mechanism 72 so that the opening timing of the exhaust valve 16 is advanced. Thereby, the internal EGR gas remaining in the cylinder is increased and the temperature gas of the air-fuel mixture in the combustion chamber 17 becomes higher than in the previous combustion cycle, and the air-fuel mixture is easily ignited.

  If it is determined in step S16 that the self-ignition timing is not appropriate (No in S16), the ECU 100 determines whether the self-ignition timing is earlier than the proper timing (S23).

  When the self-ignition timing is earlier than the appropriate timing (Yes in S23), the ECU 100 controls the exhaust-side valve mechanism 72 so that the NVO period becomes small (S24). Specifically, the ECU 100 controls the exhaust side valve mechanism 72 so that the opening timing of the exhaust valve 16 is retarded. As a result, the internal EGR gas remaining in the combustion chamber 17 is reduced and the temperature of the air-fuel mixture in the combustion chamber 17 becomes lower than in the previous combustion cycle, and the air-fuel mixture is less likely to self-ignite.

  On the other hand, when the self-ignition timing is later than the appropriate timing (No in S23), the ECU 100 controls the exhaust-side valve mechanism 72 so that the NVO period becomes longer (S25). Specifically, the ECU 100 controls the exhaust side valve mechanism 72 so that the opening timing of the exhaust valve 16 is advanced. Thereby, the internal EGR gas remaining in the combustion chamber 17 is increased and the temperature of the air-fuel mixture in the combustion chamber 17 becomes higher than that in the previous combustion cycle, and the air-fuel mixture is easily ignited.

  When it is determined in step S17 that the maximum heat generation rate is not appropriate (No in S17), the ECU 100 determines whether the maximum heat generation rate is earlier than a predetermined appropriate time (S26). ).

  When the maximum heat generation rate timing is earlier than the appropriate timing (Yes in S26), the ECU 100 retards the ignition timing in the cycle from the ignition timing in the previous combustion cycle (S27). Thereby, the start of flame propagation is delayed more than the previous combustion cycle, and the maximum heat generation rate is retarded.

  On the other hand, when the maximum heat generation rate timing is later than the appropriate timing (No in S26), the ECU 100 advances the ignition timing in the cycle from the ignition timing in the previous combustion cycle (S28). Thereby, the flame propagation starts earlier than the previous combustion cycle, and the maximum heat generation rate is retarded.

4). Summary 4-1. Summary of Optimal Combustion Control in SI + NVO Mode As described above, the ECU 100 (control device) of the engine 1 (internal combustion engine) of the present embodiment ignites the air-fuel mixture in the combustion chamber 17 by the spark plug 31. This is a control device for an internal combustion engine of the type.
Engine 1
The intake valve 15, the exhaust valve 16, the intake valve 15 and the exhaust valve 16 are opened and closed, and at least the opening timing of the exhaust valve 16 among the intake valve 15 and the exhaust valve 16 can be changed. A valve mechanism 70;
ECU 100 (ignition control means) for controlling the ignition timing of the spark plug 31;
The valve mechanism 70 is caused to generate a negative overlap state in which both the intake valve 15 and the exhaust valve 16 are closed in the exhaust stroke or the intake stroke so that the air-fuel mixture in the combustion chamber 17 is self-ignited in the compression stroke. ECU 100 (valve mechanism control means);
ECU 100 (heat generation rate estimating means) for obtaining a heat generation rate based on a combustion pressure (parameter value) indicating the combustion state of the air-fuel mixture in the combustion chamber 17.
The ECU 100 (valve mechanism control means) is configured so that the crank angle converges to the first predetermined range ΔCa when the heat generation rate rises to a predetermined value indicating that combustion due to self-ignition has reached a predetermined combustion state. The negative overlap period of the valve mechanism 70 is controlled.
The ECU 100 (ignition control means) ignites the spark plug 31 on the retard side with respect to the first predetermined range ΔCa in each combustion cycle.

  According to the ECU 100 of the engine 1 of the present embodiment, in the spark ignition type engine, a negative overlap period in which both the intake valve 15 and the exhaust valve 16 are closed in the exhaust stroke or the intake stroke is generated, and combustion occurs in the compression stroke. Self-ignition occurs in the air-fuel mixture in the chamber 17, and then the spark plug 31 is ignited in each combustion cycle. In that case, the negative overlap period is such that the crank angle converges to the first predetermined range ΔCa when the heat generation rate rises to a predetermined value indicating that combustion by self-ignition has reached a predetermined state. Be controlled. Therefore, even when the air-fuel mixture is in a lean state, the timing of self-ignition can be stabilized, and further stable combustion can be performed by flame propagation by subsequent ignition. Therefore, according to the present invention, even when the air-fuel mixture is in a lean state, it is possible to stabilize combustion and improve thermal efficiency.

In this embodiment,
ECU 100 (valve mechanism control means)
When the crank angle when the heat generation rate rises to a predetermined value is on the advance side with respect to the first predetermined range ΔCa, the negative overlap period is shortened,
When the crank angle when the heat generation rate rises to a predetermined value is on the retard side with respect to the first predetermined range ΔCa, the negative overlap period is lengthened.

  As a result, the crank angle when the heat generation rate rises to a predetermined value can be favorably converged within the first predetermined range.

ECU 100 (valve mechanism control means)
Based on the combustion pressure detected by the pressure sensor 18, the presence or absence of self-ignition is determined,
If it is determined that self-ignition has not occurred, the negative overlap period is lengthened.

  As a result, the internal EGR gas remaining in the cylinder is increased and the temperature of the air-fuel mixture in the combustion chamber 17 becomes higher than in the previous combustion cycle, and the air-fuel mixture is easily ignited.

In this embodiment,
ECU 100 (ignition control means)
The ignition timing of the spark plug 31 is controlled so that the crank angle when the heat generation rate becomes maximum converges to the second predetermined range ΔCb.

  Thereby, the time when the heat generation rate becomes maximum can be converged within a certain time. Therefore, combustion is performed appropriately and thermal efficiency is further improved.

In this embodiment,
ECU 100 (ignition control means)
When the crank angle at the time when the heat generation rate reaches the maximum is on the advance side with respect to the second predetermined range ΔCb, the ignition timing of the spark plug 31 is retarded,
When the crank angle at the time when the heat generation rate reaches the maximum is on the retard side with respect to the second predetermined range ΔCb, the ignition timing of the spark plug 31 is advanced.

  As a result, the crank angle at which the heat generation rate is maximized can be favorably converged to the second predetermined range ΔCb.

In this embodiment,
The first predetermined range ΔCa is provided on the first predetermined crank angle advance side with respect to the compression top dead center.
The second predetermined range ΔCb is provided near the compression top dead center and on the retard side,
The first predetermined crank angle is a crank angle at which the crank angle at which the heat generation rate is maximized is more likely to be in the second predetermined range ΔCb than the other crank angles.

  Thereby, after the start of combustion by self-ignition, the time when the heat generation rate by the combustion becomes maximum can be converged to the vicinity of the compression top dead center and to the retard side with respect to the compression top dead center.

In this embodiment,
The parameter value indicating the combustion state of the air-fuel mixture in the combustion chamber 17 is the gas pressure in the combustion chamber 17.

  As a result, the heat generation rate can be accurately obtained based on the pressure of the gas in the combustion chamber 17 reflecting the combustion state of the air-fuel mixture in the combustion chamber 17.

In this embodiment,
Engine 1
An accelerator pedal module 80 (load detection means) for detecting the load of the engine 1 is further provided.
The ECU 100 controls the valve mechanism 70 so that a negative overlap period is generated when the engine load is in the SI + NVO region (predetermined low load region).

  Thereby, the driving | running state (combustion state) of the engine 1 can be controlled according to engine load.

4-2. Summary of switching between SI mode and SI + NVO mode based on engine load (torque) The ECU 100 (control device) of the engine 1 (internal combustion engine) of the present embodiment ignites the air-fuel mixture in the combustion chamber 17 by the spark plug 31. A control device for a spark ignition internal combustion engine.
Engine 1
The intake valve 15, the exhaust valve 16, the intake valve 15 and the exhaust valve 16 are opened and closed, and at least the opening timing of the exhaust valve 16 among the intake valve 15 and the exhaust valve 16 can be changed. And a valve mechanism 70.
The ECU 100
A valve mechanism control means for controlling the operation of the valve mechanism 70;
Ignition control means for controlling the ignition timing of the spark plug 31.
The ECU 100 (valve mechanism control means) controls the valve mechanism 70 so that the air-fuel mixture in the combustion chamber 17 is self-ignited during the compression stroke when the load is in a predetermined low load region. In the stroke, a negative overlap period is generated in which both the intake valve 15 and the exhaust valve 16 are closed.
ECU 100 (ignition control means) ignites spark plug 31 at a predetermined timing after the timing at which self-ignition occurs.

  Thus, in the spark ignition engine, when the load is in a predetermined low load region, in the spark ignition engine, both the intake valve 15 and the exhaust valve 16 are closed in the exhaust stroke or the intake stroke. A lap period is generated, self-ignition occurs in the air-fuel mixture in the combustion chamber 17 during the compression stroke, and then the spark plug 31 is ignited in each combustion cycle. According to the knowledge of the present inventor, as explained based on the above-mentioned experiment and simulation results, when the load is in a predetermined low load region, self-ignition occurs as a negative overlap state, and then the ignition plug By igniting, the combustion can be stabilized and the thermal efficiency can be improved even when the air-fuel mixture is in a lean state.

In this embodiment,
Engine 1
ECU 100 (heat generation rate estimation means) is further provided for determining a heat generation rate based on a combustion pressure (parameter value) indicating the combustion state of the air-fuel mixture in the combustion chamber 17.
The ECU 100 (valve mechanism control means) is configured so that the crank angle converges to the first predetermined range ΔCa when the heat generation rate rises to a predetermined value indicating that combustion due to self-ignition has reached a predetermined combustion state. The negative overlap period of the valve mechanism 70 is controlled.

  As a result, even when the air-fuel mixture is in a lean state, combustion can be further stabilized and thermal efficiency can be improved.

Engine Control Method, Control Program, and Engine System Corresponding to 4-3.4-1, 4-2 As described above, the present embodiment is an engine 1 (internal combustion engine) as a control method for an internal combustion engine of the present invention. The control method of the engine) is disclosed. In that case, each operation (step) performed by the valve mechanism control means, the heat generation rate estimation means, and the ignition control means of the control device for the internal combustion engine of the present invention is the valve operation of the control method for the internal combustion engine of the present invention. This corresponds to a mechanism control process, a heat release rate estimation process, and an ignition control process. In addition, the present embodiment discloses a control program for causing the ECU 100 (computer) to function as a control device for the engine 1 (internal combustion engine) as a program of the present invention. Further, in the present embodiment, as an internal combustion engine system of the present invention, a spark ignition type engine 1 (internal combustion engine) that ignites an air-fuel mixture in a combustion chamber 17 by a spark plug 31 and an ECU 100 (control) that controls the engine 1 And an internal combustion engine system.

(Embodiment 2)
The engine of Embodiment 2 further has an ion current sensor. ECU 100 inputs a signal indicating the current value of the ion current detected by the ion current sensor, and whether or not the self-ignition timing in step S16 of FIG. 13 is appropriate based on the input current value of the ion current. Make a decision. First, the configuration of the ion current sensor will be described with reference to FIG.

  FIG. 14 is a diagram showing a configuration of an ion current sensor. The ion current sensor includes the above-described ignition plug 31, ignition coil 32, igniter 33, and ion current detection unit 102.

  The spark plug 31 has a pair of electrodes and discharges between the pair of electrodes when a predetermined voltage is applied by the ignition coil 32.

  The ignition coil 32 includes a primary coil L1, a secondary coil L2, an iron core, and the like. When the current flowing through the primary coil L1 varies, the ignition coil 32 generates an induced voltage from the secondary coil L2 according to the variation in the current. The ignition coil 32 is packaged with an insulating resin, and is connected to the terminal portion of the ignition plug 31 and attached. The voltage VB of the in-vehicle battery 34 is applied to the primary coil L1. The secondary coil L2 is electrically connected to the spark plug 31, and outputs an induced voltage to the spark plug 31 in accordance with fluctuations in the passing current of the primary coil L1.

  The igniter 33 includes a switching element Tr and a controller CNT (control IC). The switching element Tr is provided between the output terminal of the primary coil L1 of the ignition coil 32 and the ground, and is configured by a power transistor such as an IGBT or a MOSFET. The controller CNT controls ON / OFF of the switching element Tr based on the ignition signal from the ECU 100. Thus, the energization state of the primary coil L1 of the ignition coil 32 can be controlled in accordance with the ignition signal from the ECU 100.

  The ion current detector 102 detects an ion current generated in the combustion chamber 17 during combustion. The ion current detection unit 102 is built in the ECU 100. The ion current detection unit 102 may be built in the igniter 33 or the like. The ion current detection unit 102 further includes a Zener diode ZD, diodes D1 and D2, a capacitor C1, resistors R1, R2, and R3, and an operational amplifier AMP. The operational amplifier AMP amplifies the ion current I2 flowing between the spark plug 31 gaps. Then, it is converted into a voltage value proportional to the current value of the ion current I2 and output (hereinafter referred to as a detection signal Sion). The detection signal Sion is input to an AD conversion input terminal of the ECU 100.

  When the ignition signal SG is output from the ECU 100, a discharge is generated in the gap of the spark plug 31, and a discharge current I1 flows through the path of the spark plug 31, the secondary coil L2, the capacitor C1, and the diode D1. At this time, the capacitor C1 is charged with power for ion current detection. Thereafter, when a chemical reaction due to combustion proceeds, an ionic current I2 flows in the circuit through a path of resistance R2, resistance R1, capacitor C1, secondary coil L2, and spark plug 31. This ion current I2 changes depending on the combustion state of the air-fuel mixture. Therefore, the combustion state of the air-fuel mixture can be estimated (detected) by detecting the ionic current I2.

  In the present embodiment, the ECU 100 detects that combustion by self-ignition has reached a predetermined state based on the ion current value detected by the ion current detection unit 102 as described above in step S15 of each combustion cycle. In step S15, it is determined whether or not the crank angle at that time is appropriate. ECU 100 obtains integrated value ratio Rs of ion current I2 based on ion current I2 detected by ion current detection unit 102. The ECU 100 has a crank angle when the integrated value ratio Rs exceeds 10% of the ratio value RATEth within a range of 345 to 350 ° CA, which is 10 to 15 ° CA before the compression TDC (360 ° CA). If it is within the range of 345 to 350 ° CA, it is determined that the self-ignition timing is appropriate. If it is not within the range of 345 to 350 ° CA, the self-ignition timing is Judge that it is not appropriate. The crank angle when the integrated value ratio Rs exceeds 10% of the ratio value RATEth is obtained as follows, for example. That is, the total integrated value Sw obtained by integrating the value indicated by the standard ion current waveform with time is stored in advance, and the ion current detected in each combustion cycle is integrated with time. When the allocation to the total integrated value Sw becomes 10%, the crank angle at that time is acquired. A specific calculation method of RATEth (10%) is disclosed in Japanese Patent Application Laid-Open No. 2012-132344 related to the application of the present applicant.

As described above, in this embodiment,
The combustion state detection means is an ion current sensor that detects the current value of the ion current I2 in the combustion chamber 17.

  As a result, the heat generation rate can be accurately obtained based on the current value of the ion current I2 in the combustion chamber 17 reflecting the combustion state of the air-fuel mixture in the combustion chamber 17.

(Embodiment 3)
In the first and second embodiments, when the self-ignition is not performed (No in S15) and when the self-ignition timing is later than the appropriate time (No in S23), the ECU 100 has a long NVO period. Thus, the exhaust side valve mechanism 72 is controlled (S25). However, when the temperature of the fresh air sucked into the intake passage is low, even when the NVO period is maximized, there is a possibility that self-ignition does not occur or the self-ignition timing is not appropriate. In order to cope with this, the present embodiment adopts the following configuration.

  FIG. 15 is a diagram illustrating a configuration of an engine system according to the third embodiment. FIG. 16 is a flowchart showing a flow of control by the engine control apparatus (ECU 100) of the third embodiment. In the present embodiment, in addition to the configuration of the first embodiment, a heater 81 that warms fresh air flowing through the intake passage 40 is provided. The heater 81 is a ceramic heater, for example, and is disposed in the vicinity of the intake passage 40. In the present invention, the heater may be any heater instead of a ceramic heater as long as it can warm fresh air flowing through the passage.

When the ECU 100 (heater control means) does not self-ignite (when No in S15), or when the self-ignition timing is later than the appropriate time (No in S23), the current NVO period is set. It is determined whether it is equal to the longest possible period (S31). When the current NVO period is equal to the maximum settable period (Yes in S31), ECU 100 energizes heater 81. Thereby, the fresh air drawn into the intake passage 40 is warmed by the heater 81. Therefore, when the self-ignition is not performed, the self-ignition becomes easy. When the self-ignition timing is late, the self-ignition timing is advanced. As described above, according to the present embodiment, it is possible to perform self-ignition or to control the self-ignition timing to an appropriate time.
(Embodiment 4)
In the first and second embodiments, when the heat generation rate maximum timing is later than the appropriate timing (No in S26), the ECU 100 advances the ignition timing in the cycle from the ignition timing in the previous combustion cycle ( S28). However, even when the ignition timing is advanced to the maximum, the maximum heat generation rate may not be an appropriate time. In other words, the flame propagation speed may not increase to an appropriate speed. In order to cope with this, the present embodiment adopts the following configuration.

  FIG. 17 is a diagram illustrating a configuration of an ignition system of an engine according to the fourth embodiment. FIG. 18 is a flowchart showing a flow of control by the engine control apparatus (ECU 100) of the fourth embodiment. In the present embodiment, a DC / DC converter 91 (step-up means) is provided between the in-vehicle battery 34 and the ignition coil 32, and the output voltage of the in-vehicle battery 34 is boosted based on a control signal SD from the ECU 100 for ignition. The coil 32 can be supplied.

  ECU 100 determines whether or not the current ignition timing is the most advanced timing when the maximum heat generation rate timing is later than the appropriate timing (No in S26). When the current ignition timing is the maximum advanced timing, ECU 100 outputs a control signal SD for increasing the output voltage to DC / DC converter 91. Thereby, the spark voltage (energy) output from the spark plug 31 is increased. Thereby, the combustion energy given to the air-fuel mixture in the combustion chamber 17 increases, and the propagation of the flame becomes faster. That is, the flame propagation speed can be increased to an appropriate speed, and the maximum heat generation rate can be set to an appropriate time.

(Other embodiments)
In each of the embodiments described above, the valve operating mechanism 70 changes the negative overlap period by changing the opening timing of the exhaust valve 16 of the intake valve 15 and the exhaust valve 16. However, the valve operating mechanism 70 may change the negative overlap state by changing the valve opening timings of both the intake valve 15 and the exhaust valve 16.

  The present invention can be widely used in a spark ignition type internal combustion engine controller, a control method, a control program, and an internal combustion engine system for igniting an air-fuel mixture in a combustion chamber with an ignition plug.

1 engine (internal combustion engine)
DESCRIPTION OF SYMBOLS 10 Engine body 12 Piston 13 Piston rod 14 Crankshaft 15 Intake valve 16 Exhaust valve 17 Combustion chamber 18 Pressure sensor 19 Crank position sensor 20 Fuel supply system 21 Injector 22 Fuel pump 23 Fuel tank 30 Ignition system 31 Spark plug 32 Ignition coil 33 Igniter 34 In-vehicle battery 40 Intake passage 41 Air cleaner 42 Intake flow rate sensor 43 Throttle valve 50 Exhaust passage 60 Exhaust recirculation passage 61 Exhaust recirculation valve 70 Valve mechanism 71 Intake side valve mechanism 72 Exhaust side valve mechanism 80 Accelerator pedal module 81 Heater 91 DC / DC converter 100 ECU (control device)
102 Ion current detector ZD Zener diode D1, D2 Diode C1 Capacitor R1, R2, R3 Resistor AMP Operational amplifier L1 Primary coil L2 Secondary coil CNT Controller Tr Switching element I1 Discharge current I2 Ion current

Claims (5)

A control device for a spark ignition type internal combustion engine that ignites an air-fuel mixture in a combustion chamber with a spark plug,
The internal combustion engine
An intake valve, an exhaust valve, and a valve operating mechanism configured to open and close the intake valve and the exhaust valve, and to change a valve opening timing of at least the exhaust valve of the intake valve and the exhaust valve And
The controller is
A valve mechanism control means for controlling the operation of the valve mechanism;
Ignition control means for controlling the ignition timing of the spark plug,
The valve mechanism control means controls the valve mechanism so that an auto-ignition occurs in the air-fuel mixture in the combustion chamber during the compression stroke when the load of the internal combustion engine is in a predetermined low load region. Generating a negative overlap condition in which both the intake valve and the exhaust valve are closed in a stroke;
The ignition control means ignites the spark plug at a predetermined time after the time when the self-ignition occurs;
Control device for internal combustion engine. A heat generation rate estimating means for obtaining a heat generation rate based on a parameter value indicating a combustion state of the air-fuel mixture in the combustion chamber;
The valve mechanism control means is configured so that the crank angle converges to a first predetermined range when the heat generation rate rises to a predetermined value indicating that combustion due to self-ignition has reached a predetermined state. Controlling the length of the negative overlap period of the valve mechanism;
The control device for an internal combustion engine according to claim 1. A spark ignition type internal combustion engine control method for igniting an air-fuel mixture in a combustion chamber with a spark plug,
The internal combustion engine
An intake valve, an exhaust valve, and a valve operating mechanism configured to open and close the intake valve and the exhaust valve, and to change a valve opening timing of at least the exhaust valve of the intake valve and the exhaust valve And
The control method is:
A valve mechanism control step for controlling the operation of the valve mechanism;
An ignition control step for controlling the ignition timing of the spark plug,
In the valve mechanism control step, when the load of the internal combustion engine is in a predetermined low load region, the valve mechanism is provided with an exhaust stroke or an intake stroke so that self-ignition occurs in the air-fuel mixture in the combustion chamber during the compression stroke. Generating a negative overlap condition in which both the intake valve and the exhaust valve are closed in a stroke;
In the ignition control step, the ignition plug is ignited at a predetermined timing after the timing at which the self-ignition occurs.
A method for controlling an internal combustion engine.   A control program for an internal combustion engine that causes a computer to function as the control device for the internal combustion engine according to claim 1. An internal combustion engine system having a spark ignition type internal combustion engine that ignites an air-fuel mixture in a combustion chamber with an ignition plug, and a control device that controls the internal combustion engine,
The internal combustion engine
An intake valve, an exhaust valve, and a valve operating mechanism configured to open and close the intake valve and the exhaust valve, and to change a valve opening timing of at least the exhaust valve of the intake valve and the exhaust valve And
The controller is
A valve mechanism control means for controlling the operation of the valve mechanism;
Ignition control means for controlling the ignition timing of the spark plug,
The valve mechanism control means controls the valve mechanism so that an auto-ignition occurs in the air-fuel mixture in the combustion chamber during the compression stroke when the load of the internal combustion engine is in a predetermined low load region. Generating a negative overlap condition in which both the intake valve and the exhaust valve are closed in a stroke;
The ignition control means ignites the spark plug at a predetermined time after the time when the self-ignition occurs;
Internal combustion engine system.

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