Control method and control unit for internal-combustion engine

Abstract

To stably obtain combustion timing of each cylinder in premixed compression ignition combustion using spark ignition in a multi-cylinder internal-combustion engine.SOLUTION: When there is difference between cylinders in θPmax showing combustion timing, the difference between cylinders is reduced by correcting an ignition timing (time t1-t2). When the difference between cylinders is reduced, the ignition timings of all cylinders are uniformly corrected so that the cylinder average θPmax approaches a target θPmax (time t2-t3). When an ignition timing correction amount reaches an upper limit / a lower limit, the cylinder average θPmax is made to approach the target θPmax by compression ratio correction by a variable compression ratio mechanism (time t3-t4). When the cylinder average θPmax reaches the target θPmax, compression ration is corrected so that the cylinder average ignition timing returns to a reference ignition timing (time t4-t5).SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The present invention relates to a control method and a control device for an internal combustion engine that performs premixed compression ignition combustion in which, in at least a part of an operating range, a part of a premixed air-fuel mixture is spark-ignited to promote compression self-ignition of the remaining premixed air-fuel mixture.

Background Art

[0002] For example, a premixed compression ignition internal combustion engine that burns a premixed air-fuel mixture formed in a combustion chamber by compression ignition using gasoline or the like as fuel has been proposed. Patent Document 1 discloses a premixed compression ignition internal combustion engine in which, in order to achieve stable compression ignition, a part of the premixed air-fuel mixture is ignited by spark ignition using a spark plug to promote self-ignition of the remaining premixed air-fuel mixture.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a multi-cylinder internal combustion engine having a plurality of cylinders, variations in the combustion state of each cylinder due to compression ignition are likely to occur, which may cause, for example, deterioration of the exhaust composition discharged from the internal combustion engine. Patent Document 1 does not describe at all how to deal with variations in the combustion state of each cylinder in such a multi-cylinder internal combustion engine.

Means for Solving the Problems

[0005] The control method for an internal combustion engine according to the present invention is as follows. An internal combustion engine having a variable compression ratio mechanism capable of changing the mechanical compression ratio of all cylinders or an intake air temperature variable mechanism capable of changing the intake air temperature, and performing premixed compression ignition combustion in which a part of the premixed air is spark-ignited and the compression self-ignition of the remaining premixed air is promoted in at least a part of the operating region, The reference ignition timing for performing spark ignition is preset for each required output and rotational speed of the internal combustion engine, The combustion timing in the actual combustion is detected for each cylinder, The target compression ratio or intake air temperature of the variable compression ratio mechanism is controlled so as to correct the deviation between the target combustion timing and the cylinder average of the actual combustion timing, In order to reduce the difference between cylinders in the actual combustion timing, a correction amount is added to the reference ignition timing for each cylinder to perform ignition timing control for each cylinder.

[0006] The target compression ratio or intake air temperature is controlled so that the cylinder average of the combustion timing follows the target combustion timing. The change in the combustion timing accompanying the control of the compression ratio and intake air temperature occurs relatively slowly. At the same time, the ignition timing of each cylinder is controlled for each cylinder so as to reduce the difference between cylinders in the combustion timing. The change in the combustion timing accompanying this ignition timing control can be obtained relatively quickly. By these two controls, the combustion timing converges to the target combustion timing while becoming equal in each cylinder.

Advantages of the Invention

[0007] According to this invention, the combustion timing of each cylinder becomes almost equal and has a characteristic close to the target combustion timing as a whole, and the exhaust composition becomes good.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0009] Hereinafter, an embodiment in which the present invention is applied to an internal combustion engine for power generation in a series hybrid vehicle will be described. FIG. 1 schematically shows the configuration of a series hybrid vehicle. The series hybrid vehicle mainly includes a power generation motor generator 1 that operates as a generator, an internal combustion engine 2 used as a power generation internal combustion engine that drives the power generation motor generator 1 according to power demand, a traveling motor generator 4 that mainly operates as a motor and drives drive wheels 3, and a battery 5 that temporarily stores the generated power. The power obtained by driving the power generation motor generator 1 by the internal combustion engine 2 is stored in the battery 5 via an inverter device (not shown). The traveling motor generator 4 is driven and controlled using the power of the battery 5. The power during regeneration of the traveling motor generator 4 is also stored in the battery 5 via an inverter device (not shown). In the illustrated example, the motor generator 1 and the internal combustion engine 2 are interlocked via a gear train, but they may be directly connected to each other.

[0010] The operations of the motor generators 1 and 4, the charge and discharge of the battery 5, and the operation of the internal combustion engine 2 are controlled by the controller 6. The controller 6 is composed of a plurality of controllers such as a motor controller 7 that controls the motor generators 1 and 4, an engine controller 8 that controls the internal combustion engine 2, and a battery controller 9 that manages the battery 5, which are connected so as to be able to communicate with each other. Information such as the opening degree of an accelerator pedal (not shown) and the vehicle speed is input to the controller 6. Further, the battery controller 9 obtains the SOC of the battery 5 based on the voltage and current of the battery 5. When the SOC drops to a predetermined lower limit level, the internal combustion engine 2 is started via the engine controller 8 and power generation is performed. As operation modes of such a series hybrid vehicle, there are an EV mode in which the vehicle travels using the power of the battery 5 without the combustion operation of the internal combustion engine 2, and an HEV mode in which the vehicle travels while performing power generation by the combustion operation of the internal combustion engine 2. Even when the SOC is above the lower limit level, when the required driving force of the vehicle is relatively large, the internal combustion engine 2 is driven and the vehicle travels in the HEV mode.

[0011] Figure 2 shows the system configuration of the internal combustion engine 2. This internal combustion engine 2 is, for example, a four-stroke cycle internal combustion engine with a turbocharger equipped with a variable compression ratio mechanism 12 using a multi-link type piston crank mechanism, and performs combustion by the compression self-ignition of a premixed air-fuel mixture in a predetermined operation region on the relatively low output side as a premixed compression ignition combustion mode (HCCI mode). Further, at the time of starting and in a predetermined operation region on the relatively high output side, combustion is performed by spark ignition as a spark ignition combustion mode (SI mode).

[0012] Here, the premixed compression ignition combustion in the present invention is in a form that, in order to accurately control the combustion timing, part of the premixed charge is spark-ignited to promote the compression self-ignition of the remaining premixed charge. Such a form of compression ignition combustion is sometimes called spark-ignition controlled compression ignition (SPCCI). Note that in the operating region operated in the premixed compression ignition combustion mode, there may be a region where spark ignition is used and a region where spark ignition is not used. Hereinafter, the premixed compression ignition combustion that controls the combustion timing using spark ignition will be described.

[0013] A pair of intake valves 14 and a pair of exhaust valves 15 are arranged on the ceiling wall surface of the combustion chamber 13, and a spark plug 16 for performing spark ignition in a specific operating region is arranged at the central portion surrounded by these intake valves 14 and exhaust valves 15. A cylinder pressure sensor 25 for detecting the in-cylinder pressure is provided in the combustion chamber 13.

[0014] Fuel injection valves 18 for injecting fuel toward the intake valve 14 are arranged for each cylinder in the intake port 17 opened and closed by the intake valve 14. The fuel injection valve 18 is an electromagnetic or piezoelectric injection valve that opens when a drive pulse signal is applied, and injects an amount of fuel substantially proportional to the pulse width of the drive pulse signal.

[0015] Upstream of the collector portion 19a of the intake passage 19 connected to the intake port 17, an electronically controlled throttle valve 21 whose opening degree is controlled by a control signal from the engine controller 8 is provided. Further upstream thereof, a compressor 22A of the turbocharger 22 is disposed. An air flow meter 23 for detecting the intake air amount and an air cleaner 24 are disposed upstream of this compressor 22A. The collector portion 19a incorporates a heat exchanger, that is, a water-cooled intercooler 26, which cools the supercharged intake air by heat exchange with the cooling water. In order to detect the temperature of the cooling water flowing through the intercooler 26, a water temperature sensor 36 for the intercooler is provided in the intercooler 26. An intake air temperature sensor 37 is provided on the outlet side of the intake air of the intercooler 26 so as to detect the temperature of the intake air that has passed through the intercooler 26. Separately from the water temperature sensor 36 for the intercooler, a cooling water temperature sensor 38 for detecting the temperature of the cooling water flowing through the water jacket of the internal combustion engine 2 is provided at an appropriate position such as the water jacket. Note that the circuit of the cooling water flowing through the intercooler 26 may be a part of the cooling water circuit flowing through the water jacket, or may have an independent configuration from each other. The degree of heat exchange in the intercooler 26 can be variably adjusted via a cooling water valve (not shown), an intercooler cooling water pump, a cooling water bypass valve, or the like. By these mechanisms, an intake air temperature variable mechanism capable of changing the intake air temperature is configured.

[0016] Also, a knock sensor 39 for detecting knocking vibration is provided at an appropriate position on the cylinder block of the internal combustion engine 2.

[0017] The turbine 22B of the turbocharger 22 disposed in the exhaust passage 31 is provided with a wastegate valve 32 whose opening degree is controlled by a control signal from the engine controller 8. Catalytic devices 33, 34 are disposed downstream of the turbine 22B in the exhaust passage 31, and a muffler 35 is further disposed downstream.

[0018] The variable compression ratio mechanism 12 uses a known multi-link type piston crank mechanism described in, for example, Japanese Patent Application Laid-Open No. 2014-159770 and Japanese Patent Application Laid-Open No. 2005-127200. It includes a lower link 42 rotatably attached to a crank pin 41 of a crankshaft, an upper link 43 connecting an upper pin 48 at one end of the lower link 42 and a piston pin 49 of a piston 40, a control shaft 44 rotatably supported on the engine body side, a control link 45 connecting a control pin 50 at the other end of the lower link 42 and the control shaft 44, and an electric actuator 46 for controlling the rotational position of the control shaft 44. The control shaft 44 has an eccentric shaft portion, and the proximal end of the control link 45 is supported on this eccentric shaft portion so as to be relatively rotatable, that is, swingable. In this variable compression ratio mechanism 12, the posture of each link changes according to the rotational position of the control shaft 44, and the top dead center position of the piston 40 changes up and down, thereby changing the mechanical compression ratio. The mechanical compression ratio is determined by the rotational position of the control shaft 44 moved by the electric actuator 46, and this rotational position is detected as indicating the actual value of the mechanical compression ratio, that is, the actual compression ratio. That is, the electric actuator 46 itself has a configuration that also serves as an actual compression ratio sensor. In such a variable compression ratio mechanism 12, it is possible to detect the actual compression ratio even when the crankshaft is in a stationary state, that is, a non-rotating state.

[0019] In the engine controller 8, in addition to the above-mentioned in-cylinder pressure sensor 25, air flow meter 23, intercooler water temperature sensor 36, coolant temperature sensor 38, knock sensor 39, intake air temperature sensor 37, actual compression ratio sensor (electric actuator 46), there are also a crank angle sensor 52 for detecting the engine speed, an accelerator pedal opening sensor 53 for detecting the depression amount of the accelerator pedal operated by the driver as a sensor for detecting the torque demand by the driver, a supercharging pressure sensor 54 for detecting the supercharging pressure, an air-fuel ratio sensor 55 provided in the exhaust passage 31, and detection signals of these sensors are input. Based on these detection signals, the engine controller 8 optimally controls the fuel injection amount by the fuel injection valve 18, the mechanical compression ratio by the variable compression ratio mechanism 12, the opening degree of the throttle valve 21, the opening degree of the wastegate valve 32, etc., and realizes premixed compression ignition combustion by premixed charge compression self-ignition (compression self-ignition with the combustion timing controlled using spark ignition by the spark plug 16) in a predetermined operation region. Also, in a predetermined operation region including starting when premixed charge compression self-ignition is likely to become unstable, spark ignition combustion by flame propagation using the spark plug 16 is performed.

[0020] For example, in one embodiment, as an index indicating the combustion timing by compression self-ignition, the maximum in-cylinder pressure crank angle (hereinafter abbreviated as θPmax), which is the crank angle at which the in-cylinder pressure becomes the maximum pressure with combustion, is used. As other indexes indicating the combustion timing, so-called MB50, which is the crank angle at which 50% of the fuel has burned, etc. can be used, but θPmax can be most easily obtained by the in-cylinder pressure sensor 25.

[0021] Then, the mechanical compression ratio by the variable compression ratio mechanism 12, the ignition timing of each cylinder, and the fuel injection amount are feedback-controlled so that this θPmax approaches the target θPmax.

[0022] Figure 3 is a characteristic diagram showing the basic relationship between the ignition timing and θPmax in premixed compression ignition combustion. When spark ignition is not performed, θPmax is as indicated by the dashed line θPmax0. By performing spark ignition, as shown by the solid line, θPmax can be advanced to the advanced angle side. And at a certain ignition timing (which will be referred to as the peak ignition timing), θPmax advances to the maximum, and when the ignition timing is on the retarded angle side from this, the amount of advance of θPmax from θPmax0 becomes smaller. In this embodiment, the reference ignition timing ADV0 is set on the retarded angle side from the peak ignition timing, and this reference ignition timing ADV0 corresponds to the target θPmax (shown as tθPmax in the figure). In other words, the ignition timings corresponding to the target θPmax exist on both the advanced angle side and the retarded angle side of the peak ignition timing, but from the perspective of fail-safe, the reference ignition timing ADV0 is set on the retarded angle side from the peak ignition timing.

[0023] Also, an upper limit and a lower limit of the ignition timing correction amount described later are set around the reference ignition timing ADV0, and the control range L of the ignition timing between this upper limit and lower limit is provided on the retarded angle side from the peak ignition timing. This range L is symmetric around the reference ignition timing ADV0, that is, the absolute values of the ignition timing correction amounts from the reference ignition timing ADV0 to the upper limit and the lower limit are equal to each other.

[0024] Figure 4 is a flowchart showing the flow of the combustion timing control process executed by the engine controller 8 during operation in the premixed compression ignition combustion mode. The process shown in this flowchart is repeatedly executed while in the premixed compression ignition combustion mode.

[0025] Read the detection values of various sensors required in step 1, and obtain the values of various parameters in step 2. Specifically, mainly based on the SOC of the battery 5 and the accelerator pedal opening (vehicle required output), calculate the target output of the internal combustion engine 2. Then, based on this target output and the engine rotation speed, calculate the reference target compression ratio, reference ignition timing ADV0, reference fuel injection amount, and target θPmax of the variable compression ratio mechanism 12, respectively. The target output corresponds to the power generation amount required for the motor generator 1. The reference target compression ratio, reference ignition timing ADV0, reference fuel injection amount, and target θPmax are obtained based on, for example, a map with the output and rotation speed of the internal combustion engine 2 as parameters.

[0026] Next, in step 3, determine whether the cylinder-to-cylinder difference (absolute value) of θPmax obtained for each cylinder is greater than or equal to a predetermined value. If YES here, proceed to step 4 and determine whether the ignition timing correction amount from the reference ignition timing of any cylinder has reached the above-mentioned upper limit or lower limit.

[0027] If the determination in step 4 is NO, that is, the ignition timing correction amount has not reached the upper and lower limits, proceed to step 5 to perform ignition timing correction. For the cylinders where θPmax is relatively on the advanced side, correct the ignition timing to the retarded side, and for the cylinders where θPmax is relatively on the retarded side, correct the ignition timing to the advanced side. Within the control range L shown in Figure 3, if the ignition timing is corrected to the retarded side, θPmax will be retarded, and conversely, if the ignition timing is corrected to the advanced side, θPmax will be advanced. For example, obtain the difference between the actual θPmax of each cylinder and the average of the actual θPmax of all cylinders (referred to as the cylinder average θPmax), and multiply this difference by a predetermined gain to obtain the operation amount of the feedback control. Note that, as described above, upper and lower limits are provided for the correction amounts of the ignition timing of each cylinder to the advanced side and the retarded side from the reference ignition timing (see Figure 3).

[0028] If the determination in step 4 is YES, that is, if the ignition timing correction amount has reached the upper or lower limit, proceed to step 6. In order to reduce the difference in θPmax between cylinders, further correction of the fuel injection amount for each cylinder is performed. For the cylinders on the relatively advanced angle side, the fuel injection amount is corrected downward, and for the cylinders where θPmax is on the relatively retarded angle side, the fuel injection amount is corrected upward. For example, the difference between the actual θPmax of each cylinder and the average cylinder θPmax is obtained, and the operation amount of feedback control is obtained by multiplying this difference by a predetermined gain. Upper and lower limits are also provided for the correction amount of the fuel injection amount of each cylinder from the reference fuel injection amount.

[0029] If the determination in step 3 is NO, that is, if the difference in θPmax between cylinders has converged to less than a predetermined value, proceed from step 3 to step 7, and determine whether the difference (absolute value) between the actual average cylinder θPmax and the target θPmax is greater than or equal to a predetermined value. If YES here, proceed to step 8 and determine whether the ignition timing correction amount from the reference ignition timing of any cylinder has reached the above-mentioned upper or lower limit.

[0030] If the determination in step 8 is NO, that is, if the ignition timing correction amount has not reached the upper or lower limit, proceed to step 9 and perform ignition timing correction for each cylinder. If the average cylinder θPmax is on the advanced angle side of the target θPmax, the ignition timing of all cylinders is uniformly corrected to the retarded angle side. If the average cylinder θPmax is on the retarded angle side of the target θPmax, the ignition timing of all cylinders is uniformly corrected to the advanced angle side. Within the control range L shown in FIG. 3, if the ignition timing is corrected to the retarded angle side, θPmax is retarded, and conversely, if the ignition timing is corrected to the advanced angle side, θPmax is advanced. For example, the difference between the actual average cylinder θPmax and the target θPmax is obtained, and the operation amount of feedback control is obtained by multiplying this difference by a predetermined gain. Upper and lower limits are provided for the correction amount of the ignition timing of each cylinder to the advanced angle side and the retarded angle side from the reference ignition timing (see FIG. 3).

[0031] If the determination in step 8 is YES, that is, when the ignition timing correction amount has reached the upper limit or the lower limit, proceed to step 10, and in order to bring the cylinder average θPmax closer to the target θPmax, correct the target compression ratio. If the cylinder average θPmax is on the advanced angle side of the target θPmax, correct the target compression ratio downward, and if the cylinder average θPmax is on the retarded angle side of the target θPmax, correct the target compression ratio upward. When the compression ratio decreases, θPmax retards, and conversely, when the compression ratio increases, θPmax advances. For example, obtain the difference between the actual cylinder average θPmax and the target θPmax, and multiply this difference by a predetermined gain to obtain the operation amount of the feedback control.

[0032] If in step 7 the determination is NO, that is, when the difference between the cylinder average θPmax and the target θPmax has converged to less than a predetermined value, proceed from step 7 to step 11, and determine whether the difference (absolute value) between the cylinder average ignition timing, which is the average of the ignition timings of all cylinders, and the reference ignition timing is greater than or equal to a predetermined value. If the determination here is NO, it means that the difference in θPmax between cylinders is small and the current ignition timing in the state where the cylinder average θPmax has converged to the target θPmax is not far from the reference ignition timing, so end the routine as it is. On the other hand, if the determination in step 11 is YES, it means that the difference in θPmax between cylinders is small and the current ignition timing in the state where the cylinder average θPmax has converged to the target θPmax is relatively far from the reference ignition timing, so proceed to step 12 and correct the target compression ratio to bring the ignition timing closer to the reference ignition timing. If the cylinder average ignition timing is on the retarded angle side of the reference ignition timing, correct the target compression ratio downward. Due to the decrease in the compression ratio, the ignition timing required to obtain the target θPmax advances, so it approaches the reference ignition timing. Conversely, if the cylinder average ignition timing is on the advanced angle side of the reference ignition timing, correct the target compression ratio upward. Due to the increase in the compression ratio, the ignition timing required to obtain the target θPmax retards, so it approaches the reference ignition timing. For example, obtain the difference between the cylinder average ignition timing and the reference ignition timing, and multiply this difference by a predetermined gain to obtain the operation amount of the feedback control.

[0033] The change in the compression ratio by the variable compression ratio mechanism 12 and thus the change in θPmax are relatively slow. On the other hand, the change in θPmax due to the change in the ignition timing occurs with good responsiveness. By the processes of steps 11 and 12, the ignition timing advanced or retarded for combustion timing control returns to the vicinity of the reference ignition timing. Next, when the combustion timing changes due to some disturbance or the like, it becomes possible to control θPmax with good responsiveness by the processes of steps 5 and 9. In other words, the actual ignition timing always exists near the center of the control range L, and a margin for correction is ensured on both the advanced angle side and the retarded angle side.

[0034] Next, FIGS. 5 and 6 are time charts showing the behavior of each part after switching from the spark ignition combustion mode to the premixed compression ignition combustion mode. In order from the top of the figure, (a) θPmax (the broken line is the target value, the solid line is the actual value), (b) the compression ratio (the actual compression ratio), (c) the ignition timing (the broken line is the reference ignition timing, the solid line is the actual ignition timing), (d) the fuel injection amount (the broken line is the reference fuel injection amount, the solid line is the actual fuel injection amount) are respectively shown. In these time charts, for simplicity of explanation, it is assumed to have two cylinders (cylinder #1 and cylinder #2), and the cylinder-averaged θPmax, θPmax for each cylinder, etc. are shown.

[0035] In any of the time charts, after switching from the spark ignition combustion mode to the premixed compression ignition combustion mode, at time t1, feedback control for controlling the combustion timing (θPmax) has started. Fig. 5 shows an example in which although there is a difference in θPmax between cylinders at the start point (t1) of the feedback control, the average cylinder θPmax is almost the same as the target θPmax. In this example, with the start of the feedback control at time t1, in order to reduce the difference in θPmax between cylinders, the ignition timing is corrected to the advanced side in cylinder #1 where the actual θPmax is on the retarded side, and the ignition timing is corrected to the retarded side in cylinder #2 where the actual θPmax is on the advanced side. As a result, each θPmax approaches each other, and the difference between cylinders is reduced. However, before the difference between cylinders is sufficiently reduced, at time t2, the ignition timing correction amount reaches the upper and lower limits, and no further ignition timing correction is made. Therefore, in order to further reduce the remaining difference between cylinders, correction of the fuel injection amount is performed from time t2. The fuel injection amount is increased in cylinder #1 where the actual θPmax is on the retarded side, and the fuel injection amount is decreased in cylinder #2 where the actual θPmax is on the advanced side. As a result, the θPmax of each cylinder approaches each other and substantially coincides at time t3. Since the average cylinder θPmax coincides with the target θPmax, the compression ratio remains at the reference target compression ratio.

[0036] Fig. 6 shows an example in which there is a difference in θPmax between cylinders at the start point (t1) of the feedback control and the average cylinder θPmax deviates from the target θPmax to the advanced side. In this example, with the start of the feedback control at time t1, in order to reduce the difference in θPmax between cylinders, the ignition timing is corrected to the advanced side in cylinder #1 where the actual θPmax is on the retarded side, and the ignition timing is corrected to the retarded side in cylinder #2 where the actual θPmax is on the advanced side. As a result, each θPmax approaches each other, and the difference between cylinders is reduced. Since the θPmax of both cylinders converges at time t2, uniform ignition timing correction for all cylinders to bring the average cylinder θPmax closer to the target θPmax starts. Since the average cylinder θPmax at time t2 is on the advanced side of the target θPmax, the ignition timing of each cylinder is corrected to the retarded side.

[0037] In this example, before the average cylinder θPmax reaches the target θPmax, at time t3, the ignition timing of cylinder No. 2 reaches the lower limit, that is, the limit on the retarded side. Therefore, at time t3, the correction of the compression ratio is started, specifically, the reduction correction of the compression ratio is started so as to retard θPmax. In the variable compression ratio mechanism 12 of the embodiment, since the compression ratios of all cylinders change simultaneously, the average cylinder θPmax, that is, the average cylinder θPmax, is retarded by the compression ratio reduction correction. At time t4, the average cylinder θPmax substantially coincides with the target θPmax.

[0038] At time t4 when the average cylinder θPmax converges to the target θPmax, in this example, the average cylinder ignition timing is relatively far from the reference ignition timing. Therefore, the compression ratio correction for bringing the average cylinder ignition timing closer to the reference ignition timing is started at time t4. Specifically, the compression ratio is corrected to be reduced. As a result, the ignition timing required to obtain the target θPmax for θPmax advances, and as a result of the feedback control of the ignition timing, the average cylinder ignition timing approaches the reference ignition timing. At time t5, the average cylinder ignition timing reaches the reference ignition timing.

[0039] As described above, in the above embodiment, the difference in θPmax between cylinders is reduced by correcting the ignition timing and the fuel injection amount, and the compression ratio is corrected so that the average cylinder θPmax approaches the target θPmax. Therefore, θPmax in all cylinders becomes along the target θPmax. Therefore, it is possible to realize stable premixed compression ignition combustion having a good exhaust composition.

[0040] As described above, one embodiment of the present invention has been described in detail. However, the present invention is not limited to the above embodiment, and various modifications are possible. For example, in the above example, it has been described that the ignition timing feedback control for reducing the difference in θPmax between cylinders is first performed, and the compression ratio feedback control is started when the difference between cylinders disappears. However, it is also possible to perform both in parallel. Alternatively, conversely, the compression ratio feedback control may be started first.

[0041] Further, instead of θPmax, the combustion center of gravity (MB50) or other detection parameters may be used as parameters indicating the combustion timing.

[0042] Furthermore, in the present invention, as a means for changing the combustion timing of each cylinder all at once, instead of (or in addition to) the variable compression ratio mechanism 12 of the above-described embodiment, an intake air temperature variable mechanism for changing the intake air temperature can be used. Since the control using the intake air temperature variable mechanism overlaps with the description of the above-described embodiment using the variable compression ratio mechanism 12, the description thereof will be omitted. However, for example, by performing intake air temperature correction instead of the compression ratio correction in step 10 or step 12 of FIG. 4, combustion timing control similar to that of the above-described embodiment can be realized. For example, in the process of step 10, if the cylinder-average θPmax is on the advanced angle side with respect to the target θPmax, the target intake air temperature is corrected in a direction in which the intake air temperature decreases, and if the cylinder-average θPmax is on the retarded angle side with respect to the target θPmax, the target intake air temperature is corrected in a direction in which the intake air temperature increases. Then, the heat exchange amount of the water-cooled intercooler 26 is adjusted along the corrected target intake air temperature. For example, the heat exchange amount can be increased or decreased via a cooling water valve (not shown), an intercooler cooling water pump, or a cooling water bypass valve, etc., to change the intake air temperature. The intake air temperature may be controlled via variable control of the water temperature of the cooling water flowing through the water jacket of the internal combustion engine 2. It is also possible to increase the intake air temperature by appropriate heating means.

[0043] Since the change in θPmax due to the control of the intake air temperature is slow, it is still desirable to return the ignition timing to the vicinity of the reference ignition timing by the same process as step 12 of FIG. 3.

[0044] In the above-described embodiment, an example applied to a series hybrid vehicle has been described. However, the present invention is not limited to the internal combustion engine for power generation of a series hybrid vehicle, and can also be applied to a general internal combustion engine used as a driving source of a vehicle.

[0045] Further, as the variable compression ratio mechanism, other known variable compression ratio mechanisms such as a type that changes the mechanical compression ratio by changing the positional relationship between the cylinder and the crankshaft may be used.

Description of Symbols

[0046] 1…Motor generator 2…Internal combustion engine 8…Engine controller 12…Variable compression ratio mechanism 16…Spark plug 18…Fuel injection valve 21…Throttle valve 22…Turbocharger 23…Air flow meter 25…In-cylinder pressure sensor 38…Coolant temperature sensor 39…Knock sensor 46…Electric actuator 52…Crank angle sensor 53…Accelerator pedal opening sensor

Claims

1. An internal combustion engine having a variable compression ratio mechanism capable of changing the mechanical compression ratio of all cylinders, and performing premixed compression ignition combustion in which a part of the premixed air-fuel mixture is spark-ignited and the compression self-ignition of the remaining premixed air-fuel mixture is promoted in at least a part of the operating region, The reference ignition timing for performing spark ignition is set in advance for each required output and rotational speed of the internal combustion engine, The combustion timing in the actual combustion is detected for each cylinder, The target compression ratio of the variable compression ratio mechanism is controlled so as to correct the deviation between the target combustion timing and the cylinder average of the actual combustion timing, Cylinder-by-cylinder ignition timing control is performed by adding a correction amount to the reference ignition timing for each cylinder so as to reduce the difference in the actual combustion timing between cylinders, A control method for an internal combustion engine.

2. When the deviation between the target combustion timing and the cylinder average of the actual combustion timing is less than a predetermined value, and the deviation between the reference ignition timing and the cylinder average of the corrected ignition timing is greater than or equal to the predetermined value, The target compression ratio of the variable compression ratio mechanism is corrected so that the cylinder average of the ignition timing approaches the reference ignition timing, The control method for an internal combustion engine according to claim 1.

3. The fuel injection amount of each cylinder is corrected so as to reduce the difference in the actual combustion timing between cylinders remaining in a state where the correction amount has reached a predetermined upper limit or lower limit, The control method for an internal combustion engine according to claim 1.

4. When the ignition timing at which the combustion timing advances maximally by performing spark ignition as compared with the combustion timing when no spark ignition is performed is defined as the peak ignition timing, The reference ignition timing is set on the retarded side of the peak ignition timing, The control method for an internal combustion engine according to claim 1.

5. An internal combustion engine having an intake air temperature variable mechanism capable of changing the intake air temperature, and performing premixed compression ignition combustion in which a part of the premixed air-fuel mixture is spark-ignited and the compression self-ignition of the remaining premixed air-fuel mixture is promoted in at least a part of the operating region, The reference ignition timing for performing spark ignition is set in advance for each required output and rotational speed of the internal combustion engine, The combustion timing in the actual combustion is detected for each cylinder, The intake air temperature is controlled so as to correct the deviation between the target combustion timing and the cylinder average of the actual combustion timing, Cylinder-by-cylinder ignition timing control is performed by adding a correction amount to the reference ignition timing for each cylinder so as to reduce the difference in the actual combustion timing between cylinders, A control method for an internal combustion engine.

6. When the deviation between the target combustion timing and the cylinder average of the actual combustion timing is less than a predetermined value, and the deviation between the reference ignition timing and the cylinder average of the corrected ignition timing is greater than or equal to the predetermined value, Correct the intake air temperature so that the cylinder average at the ignition timing approaches the reference ignition timing. The method for controlling an internal combustion engine according to claim 5.

7. Correct the fuel injection amount of each cylinder so as to reduce the difference between cylinders in the actual combustion timing remaining in a state where the correction amount has reached a predetermined upper limit or lower limit. The method for controlling an internal combustion engine according to claim 5.

8. When the ignition timing at which the combustion timing advances maximally by performing spark ignition as compared to the combustion timing when no spark ignition is performed is defined as the peak ignition timing, the reference ignition timing is set on the retarded side of the peak ignition timing. The method for controlling an internal combustion engine according to claim 5.

9. An internal combustion engine that performs premixed compression ignition combustion in which a part of the premixed air-fuel mixture is subjected to spark ignition and the compression self-ignition of the remaining premixed air-fuel mixture is promoted in at least a part of the operating range, a variable compression ratio mechanism capable of changing the mechanical compression ratio, a storage unit that stores the reference ignition timing for performing spark ignition for each required output and rotational speed of the internal combustion engine, a controller, and comprising: the controller detects the combustion timing in actual combustion for each cylinder, controls the target compression ratio of the variable compression ratio mechanism so as to correct the deviation between the target combustion timing and the cylinder average of the actual combustion timing, performs cylinder-by-cylinder ignition timing control by adding a correction amount to the reference ignition timing for each cylinder so as to reduce the difference between cylinders in the actual combustion timing. A control device for an internal combustion engine.

10. An internal combustion engine that performs premixed compression ignition combustion in which a part of the premixed air-fuel mixture is subjected to spark ignition and the compression self-ignition of the remaining premixed air-fuel mixture is promoted in at least a part of the operating range, an intake air temperature variable mechanism capable of changing the intake air temperature, a storage unit that stores the reference ignition timing for performing spark ignition for each required output and rotational speed of the internal combustion engine, a controller, and comprising: the controller detects the combustion timing in actual combustion for each cylinder, controls the intake air temperature so as to correct the deviation between the target combustion timing and the cylinder average of the actual combustion timing, performs cylinder-by-cylinder ignition timing control by adding a correction amount to the reference ignition timing for each cylinder so as to reduce the difference between cylinders in the actual combustion timing. A control device for an internal combustion engine.

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