JP2020029788A - Control device of internal combustion engine and control method of internal combustion engine - Google Patents

Abstract

To provide a control device of an internal combustion engine capable of satisfactorily shifting a SI (Spark Ignition) combustion control mode to a HCCI (Homogeneous Charge Compression Ignition) combustion control mode while keeping high environmental temperature in a combustion chamber, in switching from the SI combustion control mode to the HCCI combustion control mode.SOLUTION: In switching from a SI combustion control mode to a HCCI combustion control mode, at least fuel injection and ignition, and temperature rise control by an opening/closing phase of an intake/exhaust valves are executed for shifting to the HCCI combustion control mode by increasing a compression end temperature of an air-fuel mixture in the combustion chamber in a process for shifting to the HCCI combustion. In a process of switching from the SI combustion control mode to the HCCI combustion control mode, the fuel injection and ignition, and the opening/closing phase of the intake/exhaust valves are properly controlled, so that a compression end temperature of the air-fuel mixture in the cylinder can be set to a temperature suitable for the HCCI combustion, and a shift from the SI combustion control mode to the HCCI combustion control mode can be satisfactorily performed.SELECTED DRAWING: Figure 9

Description

  The present invention relates to a control device and a control method for an internal combustion engine, and more particularly to a control device and a control method for an internal combustion engine that switches between a premixed spark ignition combustion system and a premixed compression ignition combustion system.

  An internal combustion engine that employs a premixed spark ignition combustion method using a spark plug generates abnormal combustion called knocking or preignition if the compression ratio is too high for the purpose of improving thermal efficiency. There is a limit to the improvement of Therefore, development of an internal combustion engine employing a premixed compression ignition combustion system in which a lean combustible mixture diluted with fresh air or exhaust gas is compressed by a piston to perform self-ignition combustion has been promoted.

  In the following description, the premixed spark ignition combustion is referred to as "SI combustion" (Spark Ignition) and the premixed compression ignition combustion is referred to as "HCCI combustion" (Homogeneous Charge Compression Ignition), including the drawings.

  The internal combustion engine of the HCCI combustion type can set a higher compression ratio than the conventional internal combustion engine of the SI combustion type, and furthermore, has a cooling loss (cylinder wall surface) due to the effect of lowering the combustion temperature due to the combustion of the lean mixture. Temperature rise) and reduction of NOx. However, in HCCI combustion, the ignition timing of the air-fuel mixture depends on the chemical reaction process in the compression stroke. Therefore, it is necessary to accurately control the temperature in the cylinder, the dilution ratio with fresh air and exhaust gas, the fuel injection timing, and the like. is there.

  The HCCI combustion type internal combustion engine has a narrower operable range in which normal combustion can be achieved than the conventional SI combustion type internal combustion engine, and cannot cover the entire practical operation range. Therefore, it is necessary to switch between the SI combustion control mode and the HCCI combustion control mode. Since the environmental conditions such as the concentration of the combustible air-fuel mixture and the temperature of the combustion chamber are greatly different between the SI combustion control mode and the HCCI combustion control mode, when switching the combustion mode, the control command values such as the fuel injection time and the ignition timing are changed. There is a problem that the mere changeover causes an increase in harmful exhaust components and a deterioration in drivability due to misfire and abnormal combustion.

  As means for solving such a problem, for example, Japanese Patent Application Laid-Open No. 2015-140728 (Patent Document 1) discloses that, when switching from the SI combustion control mode to the HCCI combustion control mode, a fuel cut is performed as an intermediate state. However, it has been proposed to perform control for increasing the effective compression ratio. According to the control device of Patent Document 1, it is described that it is possible to efficiently switch from one combustion mode to another combustion mode.

JP 2015-140728 A

  By the way, in Patent Document 1, as an intermediate state when switching from the SI combustion control mode to the HCCI combustion control mode, control is performed to reduce the rotation speed while performing fuel cut. Therefore, when shifting from the SI combustion control mode to the HCCI combustion control mode, since combustion is not performed by the fuel cut, there is a possibility that the environmental temperature for performing the HCCI combustion may not be satisfied due to a rapid decrease in the environmental temperature in the combustion chamber. There is a problem that the transition from the SI combustion control mode to the HCCI combustion control mode cannot be performed satisfactorily.

  SUMMARY OF THE INVENTION It is an object of the present invention to provide a novel internal combustion engine control that can form an environmental condition that enables a good transition from the SI combustion control mode to the HCCI combustion control mode when switching from the SI combustion control mode to the HCCI combustion control mode. An object is to provide an apparatus and a control method.

  The main feature of the present invention is that when switching from the SI combustion control mode to the HCCI combustion control mode, at least the fuel injection amount, the ignition timing, and the temperature increase control based on the opening / closing phase of the intake / exhaust valve are executed to shift to HCCI combustion. To increase the compression end temperature of the air-fuel mixture in the combustion chamber and shift to the HCCI combustion control mode.

  According to the present invention, in the process of switching from the SI combustion control mode to the HCCI combustion control mode, the fuel injection amount, the ignition timing, and the opening / closing phase of the intake / exhaust valves are appropriately controlled, and the compression end temperature of the air-fuel mixture in the combustion chamber is controlled. Can be set to a temperature suitable for HCCI combustion, and the transition from the SI combustion control mode to the HCCI combustion control mode can be performed satisfactorily.

1 is a system configuration diagram showing a configuration of an internal combustion engine system to which the present invention is applied. FIG. 3 is an explanatory diagram illustrating a combustion region based on a cylinder gas fuel ratio (G / F) of a combustible mixture and a compression end temperature of the combustible mixture. FIG. 5 is an explanatory diagram for explaining respective valve characteristics when controlling the phase and lift of an intake valve and an exhaust valve. FIG. 4 is an explanatory diagram illustrating changes in phases of an intake valve and an exhaust valve, and changes in an internal EGR and an environmental temperature of a combustion chamber. FIG. 4 is a characteristic diagram illustrating characteristics of an injection flow rate with respect to an injection pulse width. FIG. 4 is an explanatory diagram illustrating a combustion mode of an air-fuel mixture based on a compression end temperature and an injection pulse width. It is a flowchart explaining the control flow at the time of switching from SI combustion control mode to HCCI combustion control mode in the control flow explaining the typical embodiment of the present invention. FIG. 4 is an explanatory diagram illustrating an operation of a typical control target value when switching from the SI combustion control mode to the HCCI combustion control mode in the first embodiment of the present invention. FIG. 8 is an explanatory diagram illustrating a change in a representative state quantity at the time of switching from the SI combustion control mode shown in FIG. 7 to the HCCI combustion control mode. FIG. 8 is an explanatory diagram illustrating a transition of a combustion state based on the in-cylinder gas fuel ratio (G / F) and the compression end temperature of the combustible mixture when switching from the SI combustion control mode to the HCCI combustion control mode shown in FIG. 7. . FIG. 11 is an explanatory diagram illustrating an operation of a representative control target value when switching from the SI combustion control mode to the HCCI combustion control mode in the second embodiment of the present invention. FIG. 11 is an explanatory diagram illustrating a change in a representative state quantity when switching from the SI combustion control mode shown in FIG. 10 to the HCCI combustion control mode. FIG. 11 is a system configuration diagram showing a configuration of another internal combustion engine system to which the present invention is applied. FIG. 13 is an explanatory diagram illustrating an operation of a representative control target value at the time of switching from the SI combustion control mode to the HCCI combustion control mode in the third embodiment of the present invention for the internal combustion engine system shown in FIG. 12. is there. FIG. 14 is an explanatory diagram illustrating a change in a representative state quantity when switching from the SI combustion control mode shown in FIG. 13 to the HCCI combustion control mode. FIG. 15 is an explanatory diagram illustrating a transition of a combustion state based on the in-cylinder gas fuel ratio (G / F) and the compression end temperature of the combustible mixture when switching from the SI combustion control mode to the HCCI combustion control mode shown in FIG. 14. .

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following embodiments, and various modifications and application examples are included in the technical concept of the present invention. Is included in the range.

  Hereinafter, a first embodiment of the present invention will be described in detail with reference to FIGS. In the first embodiment, the HCCI combustion control mode is switched from the SI combustion control mode to the HCCI combustion control mode in a state where an environmental condition that can perform HCCI combustion is satisfied under a non-supercharging condition in which supercharging by a turbocharger is not performed. The operation when switching to is described.

  FIG. 1 shows a configuration of an internal combustion engine system to which the present invention is applied. The internal combustion engine 1 is connected to an intake passage (intake pipe) and an exhaust passage (exhaust pipe). The internal combustion engine 1 includes a turbocharger 4 that rotates a turbine 2 by the speed and pressure energy of exhaust gas and supercharges intake air by a compressor 3. Downstream of the compressor 3, an intercooler 5 is provided, and further downstream of the intercooler 5, a throttle valve 6 for controlling an amount of intake air flowing into a cylinder 7 through an intake passage is assembled. The throttle valve 6 is an electronically controlled throttle valve that can control a valve opening degree by an electric motor in accordance with the amount of depression of an accelerator pedal.

  An intake manifold 8 is connected downstream of the throttle valve 6, and an intake temperature / pressure sensor 9 for detecting intake temperature and intake pressure is assembled to the intake manifold 8. Downstream of the intake manifold 8, a flow enhancement valve 10 that generates a deviated flow of the intake air to enhance turbulence of the airflow in the cylinder 7 </ b> C is disposed.

  A piston 7P is disposed in the cylinder 7C, and a direct injection fuel injection valve 11 for directly injecting fuel into a combustion chamber formed by the cylinder 7C and the piston 7P is disposed in the cylinder 7C. The internal combustion engine 1 is provided with a variable valve mechanism for continuously changing the opening / closing phase and lift of the intake / exhaust valve in the intake valve 12 and the exhaust valve 13, respectively. Further, in the variable valve mechanism, valve position sensors 14 and 15 for detecting an opening / closing phase and a lift of the intake / exhaust valve, respectively, are assembled to the intake valve 12 and the exhaust valve 13, respectively. Further, an ignition plug 16 that exposes the electrode portion in the cylinder 7 and ignites the combustible air-fuel mixture by a spark is attached to the cylinder head.

  A crank angle sensor 17 is mounted on the crankshaft, and the rotation speed of the internal combustion engine 1 can be detected based on a signal output from the crank angle sensor 17. Further, an alternator 21 with a motor function is connected to suppress the fluctuation of the engine torque. In the present embodiment, when the engine torque fluctuates, the alternator 21 having a motor function can be driven to suppress the engine torque fluctuation.

  An exhaust temperature / pressure sensor 18 for detecting the exhaust gas temperature and the exhaust gas pressure is attached to the exhaust passage. Downstream of the exhaust gas temperature / pressure sensor 18 in the exhaust passage, the turbine 2 of the turbocharger 4 is arranged. An air-fuel ratio sensor 19 is installed downstream of the turbine 2. Based on a detection signal from the air-fuel ratio sensor 19, feedback control is performed so that the fuel injection amount supplied from the fuel injection valve 11 becomes the target air-fuel ratio. Is being done.

  Further, in the present embodiment, as shown in FIG. 1, an ECU (Engine Control Unit) 20 which is an electronic control means is provided. The various sensors and various actuators described above are connected to the ECU 20. Actuators such as the throttle valve 6, the fuel injection valve 11, and the intake / exhaust valves 12 and 13 with a variable valve mechanism are controlled by outputting control signals from the ECU 20. Further, the operation state of the internal combustion engine 1 is detected based on the sensor signals input from the various sensors described above, and various control signals are calculated by the ECU 20 according to the operation state. In the following description, a signal sent from the ECU 20 to the fuel injection valve 11 is referred to as an injection signal, and a signal sent to the spark plug 16 is referred to as an ignition signal.

  FIG. 2 shows an operable range based on the in-cylinder gas fuel ratio (G / F) of the combustible mixture in the cylinder 7 and the compression end temperature. The compression end temperature refers to the environmental temperature in the combustion chamber immediately before ignition of the combustible mixture during SI combustion (= in-cylinder ambient temperature), and in HCCI combustion, the environmental temperature of the combustion chamber immediately before self-ignition of the combustible mixture. Is represented. Therefore, in the following description, the compression end temperature may also be referred to as the ambient temperature of the combustion chamber.

  In FIG. 2, the “SI stoichiometric combustion region” is a region where the compression end temperature is low, the mixture is homogeneous, and the in-cylinder gas fuel ratio (G / F) is operated near the stoichiometric mixture ratio, The "SI lean combustion region" is a region where the compression end temperature is low, the mixture is homogeneous, and the air-fuel ratio and the in-cylinder gas fuel ratio (G / F) are operated at a lean mixture ratio. The vicinity of the stoichiometric mixture ratio includes a range in which HC, CO, NOx, and the like in exhaust gas can be purified by the three-way catalyst. The "SI combustion knock region" is a region in which knocking occurs when the temperature exceeds the knock limit temperature Tknock due to an increase in the compression end temperature, and it is necessary to perform operation while avoiding combustion in the "SI combustion knock region". .

  Next, the "HCCI lean combustion region" indicates a region in which spark ignition by the spark plug 16 is stopped and combustion is performed by compression self-ignition of the combustible mixture. The "HCCI lean combustion region" is a region in which the compression end temperature is high, the air-fuel mixture is homogeneous, and the air-fuel ratio is operated at a lean mixture ratio. The "HCCI lean combustion region" has a leaner air-fuel ratio than the "SI lean combustion region".

  Further, the "HCCI combustion knock region" has a larger calorific value on the rich side when the in-cylinder gas fuel ratio (G / F) of the air-fuel mixture is richer than the "HCCI lean combustion region". This is a region where knocking occurs due to an increase in the end temperature. Further, the “misfire region” is a region in which misfire occurs due to a decrease in the compression end temperature and a shift of the in-cylinder gas fuel ratio (G / F) of the mixture to the lean side. If a misfire occurs in a state where the fuel is injected, a large problem occurs in that a large amount of HC is discharged. Therefore, it is necessary to operate the fuel cell while avoiding combustion in this region.

  As described above, it is necessary to operate while avoiding combustion in the “HCCI combustion knock region” and the “misfire region”. Therefore, when switching from the SI combustion control mode of the “SI stoichiometric combustion region” to the HCCI combustion control mode of the “HCCI lean combustion region”, the in-cylinder gas fuel ratio (G / F) of the air-fuel mixture is significantly different. It is effective to perform switching control such as fuel cut or increase of the effective compression ratio as in Patent Document 1.

  However, due to the responsiveness of various actuators such as the fuel injection valve 11 and the variable valve mechanism, the HCCI combustion in the "SI stoichiometric combustion region" or the SI combustion control mode in the "SI lean combustion region" is immediately performed. It is difficult to switch to the control mode. For this reason, when shifting from the SI combustion control mode to the HCCI combustion control mode, even if the effective compression ratio is increased, the environmental temperature in the combustion chamber sharply drops due to the effect of the fuel cut (by scavenging) and the HCCI combustion There is a possibility that the environmental condition for executing the control may not be satisfied, which may cause a state in which the transition from the SI combustion control mode to the HCCI combustion control mode cannot be performed well.

  Therefore, when switching from the SI combustion control mode of the "SI stoichiometric combustion region" or the "SI lean combustion region" to the HCCI combustion control mode of the "HCCI lean combustion region", the environmental conditions for executing HCCI combustion, particularly, the compression end temperature Needs to be properly controlled.

  FIG. 3 shows the operation of the variable valve mechanism of the variable phase type and the variable valve mechanism of the variable lift type. FIG. 3A shows an example of a variable valve mechanism of a variable phase type, in which only the open / close phase can be changed while the valve open period (valve operating angle) is constant. FIG. 3B shows an example of a variable valve mechanism of a variable lift type, in which the valve lift and the operating angle can be changed simultaneously. Further, FIG. 3C shows an example in which both the variable phase valve mechanism and the variable lift valve mechanism are used. In the state where either the valve opening timing or the valve closing timing is fixed, the valve closing timing or the valve closing timing is set. The valve opening timing and the lift can be changed simultaneously.

  In the present embodiment, control for increasing the effective compression ratio using these variable valve mechanisms is also used. That is, in the present embodiment, the environmental temperature in the combustion chamber is increased by executing control to increase the effective compression ratio using the variable valve mechanism of the variable phase type and the variable valve mechanism of the variable lift mechanism. I have.

  A simple reason for increasing the environmental temperature will be described with reference to FIG. In FIG. 4, EVO represents the exhaust valve opening timing, EVC represents the exhaust valve closing timing, IVO represents the intake valve opening timing, and IVC represents the intake valve closing timing. By simultaneously operating the phase and the lift by using the variable valve mechanism of the variable phase type and the variable valve mechanism of the variable lift mechanism type, the valve opening / closing characteristics of FIG. The phase and lift of the intake valve and the exhaust valve can be changed so as to achieve the valve opening / closing characteristics described above.

  As shown in FIG. 4 (B), in the present embodiment, when shifting from the SI combustion control mode to the HCCI combustion control mode, the negative valve overflow occurs between the exhaust valve closing timing EVC and the intake valve opening timing IVO. A wrap (hereinafter, referred to as NO / L) section is formed. In FIG. 4A, the closing timing EVC of the exhaust valve and the opening timing IVO of the intake valve overlap each other, and a positive valve overlap (denoted by PO / L) section is formed.

  When this NO / L is formed, the exhaust valve and the intake valve are closed in the process from the exhaust stroke to the intake stroke, so that the exhaust gas is confined in the combustion chamber and internal EGR (residual combustion gas). The amount increases. FIG. 4C shows the internal EGR amount. The state in which NO / L is formed (shown by a solid line) is compared with the state in which NO / L is not formed (shown by a broken line). The internal EGR amount has increased.

  Therefore, as shown in FIG. 4D, the state in which NO / L is formed (indicated by a solid line) is greater than the state in which NO / L is not formed (indicated by a broken line). Of the ambient temperature is reduced. Further, since the residual combustion gas in the combustion chamber is compressed by the piston 7P in the NO / L section, the ambient temperature of the combustion chamber is further increased. This makes it possible to increase the environmental temperature of the combustion chamber when shifting from the SI combustion control mode to the HCCI combustion control mode, and to approach an environment in which the HCCI combustion control mode can be executed. Needless to say, the compression end temperature in SI combustion and HCCI combustion increases when there is an NO / L section.

  FIG. 5A shows the injection amount with respect to the injection pulse width. The injection amount increases as the injection pulse width increases. However, if the injection pulse width does not reach a certain value (TQmin), the injection flow rate with respect to the injection pulse width becomes The error increases and the required injection flow rate cannot be satisfied. In this embodiment, in FIG. 5A, the minimum injection flow rate when satisfying the required injection flow rate is defined as Qmin, and the injection pulse width is defined as the minimum injection pulse width TQmin. In addition, in the present embodiment, it is considered that the injection has stopped even if the injection pulse (the injection pulse in the section T) having a width smaller than the minimum injection pulse width TQmin is generated once or more than once.

  FIG. 5B shows the combustibility of the air-fuel mixture based on the compression end temperature and the in-cylinder gas-fuel ratio (G / F) of the air-fuel mixture. Knocking in the combustion process is partly due to the fact that the unburned portion of the mixture (= unburned mixture) is compressed by the effect of the pressure increase in the burned portion of the mixture (= burned mixture), and self-ignition occurs. . The self-ignition limit shown in FIG. 5B is a limit at which the air-fuel mixture generates self-ignition and burns, and indicates that when the compression end temperature increases, the air-fuel mixture tends to self-ignite. When the injection pulse width becomes large and the air-fuel ratio of the air-fuel mixture shifts to the rich side, the self-ignition limit is lowered even if the compression end temperature is low, and self-ignition becomes easy.

  The flame propagation limit is a limit at which the air-fuel mixture is ignited by the discharge of the spark plug, and indicates that when the fuel is injected with an injection pulse width greater than the flame propagation limit, the air-fuel mixture ignites and propagates the flame. . Further, it is shown that the flame propagation limit increases toward the decreasing side of the injection pulse as the compression end temperature increases. Here, the flame propagation limit and the self-ignition limit in FIG. 5B vary depending on the rotation speed and the required torque.

  A region where self-ignition and flame propagation are impossible (a region surrounded by a solid line in FIG. 5B) is a region where combustion does not occur or a flame is not stably formed even if combustion occurs. In the present embodiment, a region surrounded by a solid line in FIG. 5B is defined as a misfire region. Further, in FIG. 5B, even if the injection pulse width in the section T defined in FIG. 5A is overlapped, even if the injection pulse is generated once or plural times in the section T, the combustion pulse does not enter the misfiring region, so that no combustion occurs. You can see that.

  Next, a control flow when switching from the SI combustion control mode to the HCCI combustion control mode, which is a typical embodiment of the present invention, will be described with reference to FIG. This control flow is executed for each combustion cycle.

{Step S10}
In step S10, the operation state amount of the internal combustion engine is detected from various sensors. For example, the state quantity of the internal combustion engine is detected from the intake temperature / pressure sensor 9, the valve position sensors 14, 15, the air-fuel ratio sensor 19, and other necessary sensors. When the operation state amount of the internal combustion engine is detected, the process proceeds to step S11.

{Step S11}
In step S11, the in-cylinder air amount flowing into the cylinder is estimated from the intake air temperature, the intake pressure, and the opening timing and closing timing of the intake valve. The in-cylinder air amount can be obtained from other sensor information. Further, the required fuel injection amount is determined from the obtained in-cylinder air amount, target in-cylinder gas-fuel ratio (G / F), target torque, and the like. Here, the fuel injection amount is replaced by the injection pulse width.

  Further, in step S11, the compression end temperature Tc in the combustion chamber is estimated from the intake air temperature, the intake pressure, and the closing timing of the exhaust valve. As the compression end temperature Tc, first, the internal EGR gas amount is estimated from the intake air temperature, the intake pressure, and the closing timing of the exhaust valve. This estimation can be obtained by constructing a physical model.

  When the internal EGR amount is estimated, an effective compression ratio defined by a ratio between the combustion chamber volume at the closing timing of the intake valve and the combustion chamber volume at the top dead center is obtained. Further, an estimated value Tc of the compression end temperature is estimated by a calculation assuming adiabatic compression from the in-cylinder temperature and the specific heat ratio when the intake valve is closed. The estimated value Tc of the compression end temperature can also be obtained by constructing a physical model. When the fuel injection amount, the compression end temperature Tc, and the effective compression ratio are obtained, the process proceeds to step S12.

{Step S12}
In step S12, the target in-cylinder gas-fuel ratio (G / F) and the compression end temperature Tc are read, and the current intake air / exhaust valve phase angle and operation are obtained from the intake side position sensor 14 and the exhaust side position sensor 15. Find the corner. When these parameters are determined, the process moves to step S13.

{Step S13}
In step S13, it is determined whether or not the current combustion mode of the internal combustion engine is changed. If the change in the combustion mode has not been requested, the process proceeds to step S14, and if the change in the combustion mode has been requested, the process proceeds to step S15.

{Step S14}
In step S14, since the change of the current combustion mode of the internal combustion engine is not requested, the current combustion mode is continued. In the present embodiment, since it is assumed that the mode shifts from the SI combustion control mode to the HCCI combustion control mode, the SI combustion control mode is continued in step S14. The combustion mode executed in step S14 corresponds to mode 1 described later with reference to FIG. If the SI combustion control mode is continued, the process goes to the end and waits for the start timing of the next combustion cycle.

{Step S15}
Since it is determined in step S13 that a change in the combustion mode has been requested, it is determined in step S15 whether the current combustion mode is the SI combustion control mode. In this determination, it can be determined whether or not the mode is the SI combustion control mode depending on whether or not the following determination conditions are satisfied.

(1) The first determination condition is that the target in-cylinder gas fuel ratio (G / F) read in step S12 is controlled to be close to the stoichiometric mixture ratio. (See Fig. 2)
(2) The second determination condition is that the compression end temperature Tc is lower than a knocking limit temperature Tknock in SI combustion. (See Fig. 2)
(3) The third determination condition is that it is determined that the phase angle and the operating angle of the intake and exhaust valves cannot shift to the target operation value in HCCI combustion in the next combustion cycle.
(4) The fourth determination condition is that the temperature falls below the self-ignition limit shown in FIG. 5B from the relationship between the compression end temperature Tc estimated from the phase angle and the operating angle of the intake / exhaust valve in the next combustion cycle and the injection pulse width. It is.

  Only when all of the above criteria are satisfied, the SI combustion control mode is determined. If it is determined that the mode is the SI combustion control mode, the process proceeds to step S16. If it is not determined that the mode is the SI combustion control mode, the process proceeds to step S19.

{Step S16}
In step S16, it is determined from the target in-cylinder gas fuel ratio (G / F) and the compression end temperature Tc obtained in step S12 whether or not the "temperature-increase SI combustion control mode" is possible. In this determination, it can be determined whether or not the temperature-increase SI combustion control mode is possible, depending on whether or not the following determination conditions are satisfied. The temperature-increased SI combustion control mode refers to control for increasing the environmental temperature of the combustion chamber under SI combustion. This temperature-increase SI combustion control mode will be described later.

(1) The first determination condition is that the compression end temperature Tc exceeds the knocking limit temperature Tknock in SI combustion (Tc> Tknock) in the temperature increase SI control mode of the next combustion cycle.
(2) The second determination condition is that the phase angle and the operating angle of the intake and exhaust valves can reach near the target operation value in HCCI combustion after three combustion cycles. Note that the second determination condition is a case where it is determined that the phase angle and the operating angle of the intake and exhaust valves can reach the vicinity of the target operation value in HCCI combustion after three combustion cycles, but is not necessarily limited to three combustion cycles. Alternatively, the determination may be made in a combustion cycle before or after the three combustion cycles.
(3) The third determination condition is that the self-ignition limit shown in FIG. 5B is exceeded from the relationship between the compression end temperature Tc estimated from the phase angle and the operating angle of the intake and exhaust valves after three combustion cycles and the injection pulse width. It is.

  If all of the above criteria are not satisfied, it is determined that the temperature-increase SI combustion control mode can be executed, and the process proceeds to step S17. If at least one of the above criteria is satisfied, the process proceeds to step S18 on the assumption that the temperature-increase SI combustion control mode cannot be executed.

{Step S17}
Since it is determined that the temperature-increase SI combustion control mode can be executed in step S16, the temperature-increase SI combustion control mode is executed in step S17. In the temperature-rising SI combustion control mode, control for increasing the environmental temperature of the combustion chamber under SI combustion is performed, and a specific method thereof will be described in detail with reference to FIG. The combustion mode executed in step S17 corresponds to mode 2 described later with reference to FIG. When the temperature-increase SI combustion control mode is executed, the process ends and waits for the start timing of the next combustion cycle.

{Step S18}
On the other hand, since it is determined in step S16 that the temperature-increase SI combustion control mode cannot be executed, the "temperature-increase intermediate combustion control mode" is executed in step S18. In the heating intermediate combustion control mode, the fuel injection control and the ignition control, which were performed in the heating SI combustion control, are stopped, and the control for shifting the intake and exhaust valves to the target operating value of HCCI combustion is performed. The specific method will be described in detail with reference to FIG. The temperature-raising intermediate combustion control mode executed in step S18 corresponds to mode 3 described later with reference to FIG. When the temperature-rising intermediate combustion control mode is executed, the process ends and waits for the start timing of the next combustion cycle.

{Step S19}
Since it is determined in step S15 that the temperature is not in the SI combustion region, in step S19, it is determined whether the temperature increase intermediate combustion control mode is being performed. Since the control flow shown in FIG. 6 is started for each combustion cycle as described above, at the start timing before step 19 is executed, the temperature rising intermediate combustion control mode of step S18 is executed. Therefore, in step S19, the combustion state of the previous combustion cycle is determined. The same applies to the following control steps.

Here, in step S19, it is determined whether or not the mode is the temperature rising intermediate combustion control mode, and the determination criteria are as follows.
(1) The first determination condition is that the compression end temperature Tc and the injection pulse in FIG. 5B are controlled to enter the misfire range.
(2) The second determination condition is that the phase angle and the operating angle of the intake and exhaust valves are controlled during the transition to the target operation value in the HCCI combustion control mode.

  If all of the above criteria are satisfied, it is determined that the mode is the temperature-rising intermediate combustion control mode, and the process proceeds to step S20. If at least one of the above criteria is not satisfied, it is determined that the mode is not the temperature-rising intermediate combustion control mode, and the process proceeds to step S22.

{Step S20}
Since it is determined in step S19 that the mode is the temperature increase intermediate combustion control mode, it is determined in step S20 whether HCCI combustion is possible. The criteria are as follows.
(1) The phase angle and the operating angle of the intake and exhaust valves can be shifted to the target operation value of HCCI combustion after two combustion cycles from the current phase angle and the operating angle of the intake and exhaust valves.

  When it is determined that the operation can be shifted to the target operation value for HCCI combustion, it is determined that the operation can be performed in the HCCI combustion control mode, and the process proceeds to step S21. On the other hand, if it is determined that the operation cannot be performed in the HCCI combustion control mode, the process shifts to step S18 to continue the temperature rising intermediate combustion control mode.

{Step S21}
Since it is determined in step S20 that the HCCI combustion control mode can be executed, in step S21, the "temperature-increase switching combustion control mode" is executed. In the heating-up switching combustion control mode, fuel injection control and ignition control are restarted while maintaining the target operating value of the heating-up intermediate combustion control mode, and the in-cylinder gas fuel ratio (G / F) of the air-fuel mixture is stoichiometrically determined. The SI combustion is performed while the mixture ratio is kept in the vicinity of the mixing ratio.

  The temperature change switching combustion control mode executed in step S21 corresponds to mode 4 described later with reference to FIG. When the temperature increase switching combustion control mode is executed, the process ends and waits for the start timing of the next combustion cycle.

{Step S22}
It is determined based on the determination criterion in step S19 whether or not the mode is the temperature-rising intermediate combustion control mode. If it is determined that the mode is not the temperature-rising intermediate combustion control mode, the HCCI combustion control mode in step S22 is executed.

  The HCCI combustion control mode executed in step S22 corresponds to a mode 5 described later with reference to FIG. When the HCCI combustion control mode is executed, the process exits to the end and waits for the start timing of the next combustion cycle.

  As described above, since the control flow shown in FIG. 6 is started every combustion cycle, basically, in the process of switching from the SI combustion control mode to the HCCI combustion control mode, the SI combustion control mode (mode 1) ⇒ Heating SI combustion control mode (Mode 2) ⇒ Heating intermediate combustion control mode (Mode 3) ⇒ Heating switching combustion control mode (Mode 4) ⇒ HCCI combustion control mode (Mode 5) . However, it is also possible to provide a combustion cycle counter and execute the above-described control flow by interrupting a plurality of combustion cycles, for example, every two combustion cycles. In this case, successive combustion cycles execute the same combustion control mode.

  Next, specific combustion control in each combustion control mode will be described with reference to FIGS. FIG. 7 shows a change in the control target value of each actuator in the process of switching from the SI combustion control mode to the HCCI combustion control mode. The abscissa indicates the passage of time, and the ordinate indicates the control target values of the intake pipe pressure, fuel injection amount, ignition timing, intake / exhaust valve timing, and alternator assist.

  Similarly, FIG. 8 shows a change in each state quantity in the process of switching from the SI combustion control mode to the HCCI combustion control mode, in which the abscissa indicates the passage of time, the ordinate indicates the intake air amount, and the cylinder gas. The figure shows each control state quantity such as fuel ratio (G / F), compression end temperature, fuel injection quantity, ignition timing, and engine torque.

  7 and 8, the SI combustion control mode is “mode 1”, the temperature-increased SI combustion control mode is “mode 2”, the temperature-increased intermediate combustion control mode is “mode 3”, and the temperature-increase switching combustion control mode is “mode 1”. “Mode 4” and the HCCI combustion control mode are described as “mode 5”.

{SI combustion control mode (mode 1)}
The SI combustion control mode executes premixed spark ignition combustion using a normal spark plug, and is operated with a fuel injection amount, ignition timing, and intake / exhaust valve timing in accordance with the operation state of the internal combustion engine. The intake and exhaust valve timing is set to a positive valve overlap (PO / L) having a valve overlap.

温 SI heating control mode (mode 2) ≫
Next, when shifting from the SI combustion control mode to the temperature-increase switching combustion control mode for HCCI combustion, the temperature-rising SI combustion control mode is executed as shown in FIG. 7 as a preparation stage.

  First, as shown in FIGS. 4A to 4B, the opening timing (IVO) of the intake valve in the SI combustion control mode is retarded, and the closing timing (EVC) of the exhaust valve is advanced. That is, when the temperature is lower than the knocking limit temperature Tknock of SI combustion while estimating the compression end temperature Tc, the above-described intake / exhaust valve is operated, and the operation is ended at a predetermined position not exceeding the knocking limit temperature Tknock.

  When the variable valve mechanism is driven to increase the amount of NO / L, the internal temperature of the combustion chamber increases due to an increase in the amount of internal EGR, so that the compression end temperature Tc increases. Furthermore, by increasing the operating angle of the intake valve and bringing the closing timing of the intake valve closer to the vicinity of the bottom dead center, the NO / L amount further increases, the actual compression ratio increases, and the compression end temperature Tc decreases. Get higher.

  When the operating angle of the intake valve is increased, the amount of intake air is increased, but the amount of fuel injection is also increased to suppress the air-fuel ratio fluctuation of the air-fuel mixture. Further, the ignition timing is retarded from that in the SI combustion control mode so that the torque fluctuation based on the increase of the air-fuel mixture does not increase. As a result, as shown in FIG. 8, the amount of air-fuel mixture (intake amount) is increased, the in-cylinder gas fuel ratio (G / F) is maintained near stoichiometry to increase the amount of heat generated, and the ignition timing is retarded to retard Deterioration of drivability due to fluctuations is suppressed.

  By the above-described control, as shown in FIG. 8, before the transition to the HCCI combustion control mode, the mixing amount is increased in advance, and the compression end temperature Tc can be increased by increasing the effective compression ratio. The period to the intermediate combustion control mode can be shortened. As a result, the switching period from the SI combustion control mode to the HCCI combustion control mode can be shortened. When the heating SI combustion control mode is completed, the heating intermediate combustion control mode is executed. If the temperature-increase SI combustion cannot be performed, the temperature-increase SI combustion control mode is not executed, and the temperature-increase intermediate combustion control mode is executed.

<< Heating intermediate combustion control mode (mode 3) >>
When shifting from the SI combustion control mode to the HCCI combustion control mode, if the operation cannot be performed in the temperature-increased SI combustion control mode or the HCCI combustion control mode, the temperature-rising intermediate combustion control mode is executed. In this case, the fuel injection control and the ignition control are stopped without using the target operation value in the temperature-rising SI combustion control mode, and the intake / exhaust valve is shifted to the target operation value in the HCCI combustion control mode. In this case, the target operation value of the intake / exhaust valve is set to be the same as that in the temperature rise SI combustion control mode, but may be a different target operation value.

  As a result, the compression end temperature Tc increases as the effective compression ratio increases when shifting from the SI combustion control mode to the HCCI combustion control mode. However, since the fuel injection control and the ignition control have been stopped, the vehicle enters the misfire region of FIG. 5B. It should be noted that even if a misfire occurs, there is no fuel in the first place, and therefore no increase in exhaust harmful components is caused. Thus, even if the compression end temperature Tc rises, the combustion of the air-fuel mixture is not performed, so that the high-temperature internal EGR maintained in the temperature-rising SI combustion control mode can be scavenged, and the inside of the combustion chamber can be scavenged. The environmental temperature can be lowered to the knock limit temperature Tknock or lower. As a result, the compression end temperature Tc in the HCCI combustion temperature-increase switching combustion control mode in the next combustion cycle is reduced, and the combustion control mode in the SI stoichiometric combustion region can be executed.

  In other words, if SI stoichiometric combustion is performed with the compression end temperature Tc being high, there is a danger that knocking will occur due to a shift to the SI combustion knock region (see FIG. 2), so that fuel injection control and ignition control are stopped. By not performing the combustion of the air-fuel mixture, the compression end temperature Tc is lowered to the knock limit temperature Tnock or lower.

  At this time, since the combustion of the air-fuel mixture is not performed, a phenomenon occurs in which the engine torque decreases. However, the alternator with a motor function performs the torque assist for the engine torque reduction to suppress the torque fluctuation. I have. When the temperature increase intermediate combustion control mode is completed, a temperature increase switching combustion control mode for HCCI combustion is executed.

<< Temperature changeover combustion control mode (mode 4) >>
When shifting from the temperature increase intermediate combustion control mode to the HCCI combustion control mode, a temperature increase switching combustion control mode for HCCI combustion is executed as a preparation stage as shown in FIG. In this temperature-increase switching combustion control mode, fuel injection control and ignition control are restarted using the target operation value of the temperature-increase SI combustion control mode before switching to the temperature-increase intermediate combustion control mode, and the in-cylinder gas fuel ratio (G / F) is controlled close to the stoichiometric mixture ratio to perform SI combustion.

  As described above, by maintaining the in-cylinder gas fuel ratio (G / F) near the stoichiometric mixture ratio, the calorific value is increased, and the combustion temperature is greatly increased. The internal EGR at a high temperature is maintained. As a result, the environmental temperature of the combustion chamber in the next combustion cycle is increased to increase the compression end temperature Tc, thereby forming an environmental condition for achieving HCCI combustion. When the temperature increase switching combustion control mode of HCCI combustion is completed, the HCCI combustion control mode is executed.

{HCCI combustion control mode (mode 5)}
The HCCI combustion control mode performs premixed self-ignition combustion by compression without using a spark plug.Ignition control is stopped but operation is performed with the fuel injection amount and intake / exhaust valve timing in accordance with the operation state of the internal combustion engine. ing. The in-cylinder gas-fuel ratio (G / F) is controlled to be lean over the misfire region, and the intake / exhaust valve timing is set to N-O / L without valve overlap.

  Further, a change in the state quantity when the switching from the SI combustion control mode to the HCCI combustion control mode is executed will be described with reference to FIG.

  In the heating SI combustion control mode, the in-cylinder gas fuel ratio (G / F) is kept close to the stoichiometric mixture ratio by increasing the fuel injection amount in accordance with the increase in the intake air amount, and further, the ignition timing is retarded. As a result, the exhaust loss is increased, thereby lowering the output and suppressing fluctuations in the engine torque.

  Next, in the temperature rise intermediate combustion control mode, the fuel injection control and the ignition control are stopped to eliminate the occurrence of knocking and self-ignition combustion of the air-fuel mixture, and to suppress the occurrence of abnormal combustion accompanying an increase in the effective compression ratio. Thus, the mode can be switched to the temperature increase switching combustion control mode.

  Next, in the temperature rise switching combustion control mode, the fuel injection control and the ignition control are returned, and the in-cylinder gas fuel ratio (G / F) is brought close to the stoichiometric mixture ratio by increasing the intake air amount and the fuel injection amount. The variation in engine torque is suppressed by increasing the calorific value while maintaining the temperature, and further delaying the ignition timing to increase the exhaust loss and reduce the output.

  Lastly, in the HCCI combustion control mode, the fuel injection amount is reduced to rapidly make the in-cylinder gas fuel ratio (G / F) of the air-fuel mixture lean, and the ignition control by the ignition plug is stopped to thereby reduce knocking. It is possible to perform good HCCI combustion by suppressing the generation.

  By executing such control, the compression end temperature Tc in the combustion chamber is knocked or misfired in the course of passing through the temperature-rising SI combustion control mode, the temperature-rising intermediate combustion control mode, and the temperature-rising switching combustion control mode. Can be controlled so as to become higher sequentially in the process of shifting from the SI combustion control mode to the HCCI combustion control mode while suppressing the occurrence of abnormal combustion including.

  Next, a control mode and a combustion region according to the above-described control flow will be described. FIG. 9 shows the relationship between the in-cylinder gas fuel ratio (G / F), the compression end temperature Tc, and the combustion region when switching from the SI combustion control mode to the HCCI combustion control mode is performed based on FIG. Is shown. In addition, "●" mark exemplarily shows a passing point of the combustion cycle during a transition from the SI combustion control mode to the HCCI combustion control mode.

  When shifting from the SI combustion control mode (mode 1) to the temperature-increase SI combustion control mode (mode 2), the ignition timing is delayed while maintaining the in-cylinder gas fuel ratio (G / F) near the stoichiometric mixture ratio. By setting N / O / L, the compression end temperature Tc increases every time the combustion cycle increases.

  Next, when shifting from the temperature-rising SI combustion control mode (mode 2) to the intermediate combustion control (mode 3), the in-cylinder gas fuel ratio (G / F) is infinite (大 air ), The compression end temperature Tc becomes higher because the specific heat ratio is lower than in the state where the in-cylinder gas fuel ratio (G / F) is close to the stoichiometric mixture ratio. In addition, the compression end temperature Tc is further increased because the effective compression ratio is increased.

  Next, when shifting from the temperature rising intermediate combustion control mode (mode 3) to the temperature rising switching combustion control mode (mode 4), the in-cylinder gas fuel ratio (G / F) becomes close to the stoichiometric mixture ratio. , The fuel injection amount is set. Since the fuel injection control was stopped in the previous combustion cycle, the internal EGR held by the setting of NO / L is scavenged, and the temperature of the air-fuel mixture in the combustion chamber before compression is knocked. The temperature becomes lower than the limit temperature Tnock.

  If the mode is switched to the temperature-increase switching combustion control mode without performing scavenging with fresh air in the temperature-increase intermediate combustion control mode, the temperature-increase switching combustion control mode becomes the compression end temperature Tc indicated by “○”, and the SI The engine enters the combustion knock region, and knocking occurs. On the other hand, since the temperature rise intermediate combustion control mode is executed to reduce the environmental temperature of the combustion chamber in the combustion chamber before the compression, the combustion in the SI combustion knock region is avoided to prevent the combustion in the SI stoichiometric combustion region. Combustion can be continued.

  Next, when shifting from the temperature-increase switching combustion control mode (mode 4) to the HCCI combustion control mode (mode 5), the target operation value has shifted to the target operation value in the HCCI combustion control mode. HCCI combustion is performed at the target in-cylinder gas fuel ratio (G / F). Since the high-temperature exhaust gas in the temperature-increase switching combustion control mode is held by setting NO-O / L in the temperature-increase switching combustion control mode in the previous combustion cycle, the mode is shifted to the HCCI combustion control mode. Can further increase the compression end temperature Tc.

  As described above, according to this embodiment, when switching from the SI combustion control mode to the HCCI combustion control mode, at least the opening / closing phase of the variable valve mechanism, the fuel injection amount, and the ignition timing are appropriately adjusted to perform the temperature increase control. By executing, the process shifts to the HCCI combustion control mode by increasing the compression end temperature of the air-fuel mixture in the combustion chamber in the process of shifting to the HCCI combustion.

  According to this, in the process of switching from the SI combustion control mode to the HCCI combustion control mode, the fuel injection, ignition, and the opening / closing phase of the intake / exhaust valve are appropriately controlled, and the compression end temperature of the air-fuel mixture in the cylinder is reduced. The temperature can be set to a suitable temperature, and the transition from the SI combustion control mode to the HCCI combustion control mode can be performed satisfactorily while avoiding abnormal combustion such as knocking or misfire.

  The target air-fuel ratio is controlled by controlling the intake air amount by the operating angle of the intake valve, controlling the internal EGR amount by the closing timing of the exhaust valve, and controlling the fuel injection amount based on the intake air amount estimated from the operating angle of the intake valve. The in-cylinder gas fuel ratio (G / F) and the compression end temperature can be estimated by the operation of the intake and exhaust valves. Therefore, the operation of calculating the control amount such as the target operation value is reduced, so that high-speed and high-precision control can be realized.

  In addition, during the transition from SI combustion to HCCI combustion, the combustion control mode can be determined based on the estimated compression end temperature and the in-cylinder gas fuel ratio (G / F). Accordingly, it is possible to appropriately control the opening / closing phase of the variable valve mechanism, the fuel injection amount, and the ignition timing.

  Next, a second embodiment of the present invention will be described with reference to FIGS. 10 and 11, but the configuration, operation, and effects common to the first embodiment will be described unless necessary. Is omitted. The third embodiment aims to increase the ambient temperature in the combustion chamber by increasing the intake pressure to the positive pressure side by using the turbocharger 4.

  The operation time of the turbocharger 4 can be selected by a bypass valve on the compressor side, a waste gate valve on the turbine side, or the like, so that the operation is switched from the SI combustion control mode to the HCCI combustion control mode. Advantageously, it is configured to operate in the area.

  In FIGS. 10 and 11, when the mode shifts from the SI combustion control mode to the temperature-increased SI combustion control mode, the operation of the turbocharger 4 is started, so that the intake pressure and the intake density are increased. Therefore, the environmental temperature in the combustion chamber increases, and the compression end temperature Tc increases. By utilizing the turbocharger 4 in this manner, the compression end temperature Tc required for HCCI combustion can be quickly reached, so that the switching period between the SI combustion control mode and the HCCI combustion control mode can be shortened. .

  That is, in the temperature-increase SI combustion control mode, not only the effect of increasing the intake air amount by the turbocharger 4 and the effect of increasing the compression end temperature Tc due to the increase in the effective compression ratio, but also from the SI combustion control mode to the HCCI combustion control mode. This has the effect of shortening the period of the switching process to the temperature rising intermediate combustion control mode.

  Further, in the temperature increase intermediate combustion control mode, the intake pressure and the intake density by the turbocharger 4 are further increased as compared with the temperature increase SI combustion control mode. At this time, the fuel injection control and the ignition control are stopped, and control is performed so as to enter the misfire region of FIG. 5B. As a result, the compression end temperature Tc can be further increased. However, in this case, since combustion is not performed, high-temperature internal EGR can be scavenged, and the environmental temperature in the combustion chamber can be reduced to the knock limit temperature Tnock or lower.

  Also in the temperature increase switching combustion control mode, since the intake pressure and the intake density increase due to the operation of the turbocharger 4, the environmental temperature rises and the compression end temperature Tc of the next combustion cycle rises. . Such an operation makes it possible to quickly establish an environment in which HCCI combustion is performed.

  Next, a third embodiment of the present invention will be described with reference to FIGS. 12 to 15, but this embodiment is based on the second embodiment. For this reason, descriptions of configurations, operations, and effects that are common to the second embodiment will be omitted unless necessary.

  In the third embodiment, when the turbocharger 4 is used, the ratio of the amount of air passing through the intercooler 5 to the amount of air not passing through the intercooler 5 is changed so that the high-temperature air causes the environment inside the combustion chamber to change. The aim is to increase the temperature. It is another object of the present invention to reduce fuel consumption in the temperature-increase switching combustion control mode, and further reduce exhaust loss to improve fuel efficiency.

  FIG. 12 shows a configuration of an internal combustion engine system according to the third embodiment. The basic configuration is the same as that of the internal combustion engine system described in FIG. However, the configuration downstream of the compressor 3 is different from that of FIG.

  The downstream of the compressor 3 is branched into two flow paths, and the first flow path 22 is provided with the intercooler 5. Downstream of the intercooler 5, a first throttle valve 6 for restricting the intake passage and controlling the amount of intake air flowing into the cylinder 7C is mounted. A second throttle valve 24 for restricting the intake passage and controlling the amount of intake air flowing into the cylinder 7 is attached to the second passage 23.

  The two throttle valves 6 and 24 are electronically controlled throttle valves that can control the valve opening in accordance with the accelerator pedal depression amount. The first flow path 22 and the second flow path 23 join at the downstream of the throttle valves 6 and 24, and the intake manifold 8 is connected to the downstream thereof. Therefore, by changing the ratio between the opening of the first throttle valve 6 and the opening of the second throttle valve 24, the temperature of the intake air supplied to the cylinder 7C can be controlled.

  That is, while the air passing through the first flow path 22 is cooled by the intercooler 5, the air passing through the second flow path 23 is not cooled and maintains a high temperature. Therefore, if the amount of air flowing through the first flow path 22 is reduced by the first throttle 6 and the amount of air flowing through the second flow path 23 is increased by the second throttle 6, the total air supplied to the cylinder 7C is reduced. Temperature rises. On the other hand, when the amount of air flowing through the first flow path 22 is increased by the first throttle 6 and the amount of air flowing through the second flow path 23 is reduced by the second throttle 6, the temperature of the whole air supplied to the cylinder 7C is reduced. Will be lower. Therefore, in the process of shifting from the SI combustion control mode to the HCCI fuel control mode, the amount of air flowing through the first flow path 22 is reduced by the first throttle 6, and the amount of air flowing through the second flow path 23 is reduced by the second throttle 6. When it is increased at 6, the intake air temperature becomes higher, so that the environmental temperature in the combustion chamber can be raised.

  13 and 14, the opening degree of the first throttle valve 6 is gradually reduced in the process of shifting to the temperature-rising SI combustion control mode, the temperature-rising intermediate combustion control mode, and the temperature-rising switching combustion control mode. By reducing the amount of air flowing into the intercooler 5 and gradually increasing the opening of the second throttle valve 24, the temperature of the air taken into the internal combustion engine can be increased. Thus, by increasing the environmental temperature in the combustion chamber, it is possible to further increase the compression end temperature Tc during the compression stroke.

  In the present embodiment, unlike the second embodiment, in the temperature-increasing switching combustion control mode, as shown in the item of the fuel injection amount in FIG. 15, the fuel injection amount is reduced to perform combustion in the SI lean combustion region. I have to. As a result, fuel consumption can be reduced. At this time, as described in the item of the ignition timing, the ignition timing is controlled to be advanced to compensate for a decrease in torque due to lean combustion. Further, the control of the ignition timing to the advanced side also contributes to reducing exhaust loss and improving fuel efficiency.

  Here, by maintaining the in-cylinder gas fuel ratio (G / F) in the SI lean combustion region, there is a possibility that the combustion temperature may be reduced as compared with the case where the stoichiometric mixture ratio is maintained near. However, by gradually bringing the opening of the first throttle valve 6 close to fully closed and gradually approaching the opening of the second throttle valve 24 to fully open, the amount of air flowing into the intercooler 5 is reduced, Since the temperature of the intake air taken into the internal combustion engine has been increased, the environmental temperature of the combustion chamber in the HCCI combustion in the next combustion cycle is increased, and the environmental conditions for executing the HCCI combustion by increasing the compression end temperature Tc are established. ing.

  FIG. 15 shows the relationship between the in-cylinder gas fuel ratio (G / F), the compression end temperature Tc, and the combustion region when switching from the SI combustion control mode to the HCCI combustion control mode is performed based on FIG. Is shown. In addition, "●" mark exemplarily shows a passing point of the combustion cycle during a transition from the SI combustion control mode to the HCCI combustion control mode.

  Basically, the operation is the same as the operation shown in FIG. 9, but in the temperature-increase switching combustion control mode, since the fuel injection amount is reduced and the compression end temperature Tc is reduced, the symbol “で” is used. Since it is possible to shift from the SI combustion knock region to the SI lean combustion region, abnormal combustion such as knocking can be avoided. Furthermore, since the lean injection is performed by reducing the fuel injection amount, the fuel consumption can be reduced. In addition, since the ignition timing is controlled to be advanced, the exhaust loss can be reduced, and the fuel efficiency can be further improved.

  As described above, according to the present invention, at the time of switching from the SI combustion control mode to the HCCI combustion control mode, at least the fuel injection and ignition, and the temperature increase control based on the opening / closing phase of the intake / exhaust valve are executed to shift to HCCI combustion. In the process, the temperature of the compression end of the air-fuel mixture in the combustion chamber is raised to shift to the HCCI combustion control mode.

  According to this, in the process of switching from the SI combustion control mode to the HCCI combustion control mode, the fuel injection, ignition, and the opening / closing phase of the intake / exhaust valve are appropriately controlled, and the compression end temperature of the air-fuel mixture in the cylinder is reduced. Can be set to a temperature suitable for the combustion mode, and the transition from the SI combustion control mode to the HCCI combustion control mode can be performed satisfactorily.

  Note that the present invention is not limited to the above-described embodiment, and includes various modifications. For example, the above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described above. Further, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of one embodiment can be added to the configuration of another embodiment. Also, for a part of the configuration of each embodiment, it is possible to add, delete, or replace another configuration.

  DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine, 2 ... Turbine, 3 ... Compressor, 4 ... Turbocharger, 5 ... Intercooler, 6 ... Throttle valve, 7 ... Cylinder 7C, 8 ... Intake manifold, 9 ... Intake temperature / pressure sensor, 10 ... Flow enhancement valve, 11: fuel injection valve, 12: intake valve, 13: exhaust valve, 14, 15: valve position sensor, 16: spark plug, 17: crank angle sensor, 18: exhaust temperature / pressure sensor, 19: empty Fuel ratio sensor, 20 ... ECU.

Claims (9)

At least fuel control means for supplying a fuel to the combustion chamber to form a combustible mixture, ignition control means for igniting the combustible mixture in the combustion chamber, an intake valve and an exhaust valve provided in the combustion chamber Used in an internal combustion engine having an intake / exhaust variable valve mechanism for changing the opening / closing phase of premixed spark ignition combustion (hereinafter referred to as SI combustion) by the ignition control means, and premixed compression by a compression action of a piston. Ignition combustion (hereinafter, referred to as HCCI combustion) in the control device of the internal combustion engine provided with control means for switching and controlling,
When switching from the SI combustion control mode for performing the SI combustion to the HCCI combustion control mode for performing the HCCI combustion, the control means includes at least a fuel injection amount by the fuel control means, an ignition timing by the ignition control means, and Controlling the opening / closing phase of the variable exhaust valve mechanism to increase the compression end temperature of the air-fuel mixture in the combustion chamber in the process of shifting to the HCCI combustion and executing a temperature increase control for shifting to the HCCI combustion control mode. Control device for an internal combustion engine. The control device for an internal combustion engine according to claim 1,
The temperature raising control includes:
Heated SI combustion in which fuel is supplied by the fuel control means, ignition by the ignition control means, and temperature rise by negative valve overlap (hereinafter referred to as NO / L) by the intake / exhaust variable valve mechanism. Control mode,
Stopping the fuel by the fuel control means, stopping the ignition by the ignition control means, and raising the temperature by N / O / L by the intake / exhaust variable valve mechanism;
A fuel supply switching by the fuel control means, an ignition by the ignition control means, and a temperature switching combustion control mode in which the temperature is raised by NO / L by the intake / exhaust variable valve mechanism;
The control means includes:
When switching from the SI combustion control mode to the HCCI combustion control mode for performing the HCCI combustion, at least a transition is made from the SI combustion control mode to the temperature raising intermediate combustion control mode, and the temperature raising switching combustion is switched from the temperature raising intermediate combustion control mode. A control apparatus for an internal combustion engine, wherein the control mode is shifted to a control mode, and the mode is shifted from the temperature-increase switching combustion control mode to the HCCI combustion control mode. The control device for an internal combustion engine according to claim 2,
The control means includes:
A control device for an internal combustion engine, wherein the temperature-rising SI combustion control mode is executed between the SI combustion control mode and the temperature-rising intermediate combustion control mode. The control device for an internal combustion engine according to claim 2,
The control means includes:
The in-cylinder gas fuel ratio of the combustible mixture in the temperature-increased SI combustion control mode is controlled to an in-cylinder gas-fuel ratio near the stoichiometric mixture ratio, and the ignition timing in the temperature-increased SI combustion control mode is The ignition timing is controlled to be delayed from the ignition timing in the SI combustion control mode,
The in-cylinder gas fuel ratio of the combustible mixture in the temperature-increase switching combustion control mode is controlled to a cylinder gas-fuel ratio near the stoichiometric mixture ratio, and the ignition timing in the temperature-increase switching combustion control mode is A control device for an internal combustion engine, which controls an ignition timing delayed from an ignition timing in an SI combustion control mode. The control device for an internal combustion engine according to claim 4,
The control means includes:
A control device for an internal combustion engine, wherein an ignition timing in the temperature-rising SI combustion control mode and an ignition timing in the temperature-rising switching combustion control mode are set to be the same. The control device for an internal combustion engine according to claim 2,
The control means includes:
The air-fuel ratio of the combustible air-fuel mixture in the temperature-increased SI combustion control mode is controlled to a cylinder gas fuel ratio near the stoichiometric mixture ratio, and the ignition timing in the temperature-increased SI combustion control mode is controlled by the SI combustion control. The ignition timing is controlled to be delayed from the ignition timing in the mode,
The in-cylinder gas fuel ratio of the combustible air-fuel mixture in the temperature rising switching combustion control mode is controlled to a cylinder gas fuel ratio leaner than the stoichiometric mixture ratio, and the ignition timing in the temperature rising switching combustion control mode is A control device for an internal combustion engine, wherein the ignition timing is controlled to be retarded from the ignition timing in the SI combustion control mode and advanced to the ignition timing in the temperature-increased SI combustion control mode. The control device for an internal combustion engine according to claim 4 or claim 6,
The control means includes:
A control device for an internal combustion engine, wherein a supercharger is operated when shifting from the SI combustion control mode to the HCCI combustion control mode. The control device for an internal combustion engine according to claim 4 or claim 6,
The control means includes:
When shifting from the SI combustion control mode to the HCCI combustion control mode, the amount of air passing through an intercooler provided downstream of the supercharger is reduced, and the amount of air not passing through the intercooler is increased. Control device for an internal combustion engine. At least fuel control means for supplying a fuel to the combustion chamber to form a combustible mixture, ignition control means for igniting the combustible mixture in the combustion chamber, an intake valve and an exhaust valve provided in the combustion chamber Intake / exhaust variable valve mechanism for changing the opening / closing phase of the engine; premixed spark ignition combustion (hereinafter, referred to as SI combustion) by the ignition control means; and premixed compression ignition combustion (hereinafter, HCCI combustion) by the compression action of the piston. Notation) and the control method of the internal combustion engine provided with a control means for switching,
The control means includes:
Switching from the SI combustion control mode for performing the SI combustion to the HCCI combustion control mode for performing the HCCI combustion,
In the process of shifting to the HCCI combustion, at least the fuel injection amount by the fuel control means, the ignition timing by the ignition control means, and the opening / closing phase by the intake / exhaust variable valve mechanism are controlled to control the mixture in the combustion chamber. Characterized by sequentially increasing the compression end temperature of the internal combustion engine to shift to an HCCI combustion control mode.

Images