Control method and control device for internal combustion engine

Abstract

To securely prevent transitional occurrence of knocking during switching from a premixed compression ignition combustion mode to a spark ignition combustion mode.SOLUTION: An internal combustion engine for power generation of a series hybrid vehicle includes a variable compression ratio mechanism that changes a mechanical compression ratio. During driving in a premixed compression ignition combustion mode, when target output exceeds HCCI allowable output and switching to a spark ignition combustion mode is requested (time t1), fuel injection is stopped and a target compression ratio is set to an SI target compression ratio. Speed is maintained without change through motoring. When an actual compression ratio is lowered to an SI allowable compression ratio set higher than the SI target compression ratio (time t2), motoring is performed to reach SI target speed. When actual speed reaches the SI target speed (time t3), the fuel injection is resumed and driving is performed in a spark ignition combustion mode.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a method and device for controlling an internal combustion engine that has a variable compression ratio mechanism that can mechanically change the compression ratio and can switch between a spark ignition combustion mode and a homogeneous charge compression ignition combustion mode. [Background technology]

[0002] For example, homogeneous charge compression ignition internal combustion engines have been proposed that use gasoline or the like as fuel and burn a premixed air-fuel mixture formed in a combustion chamber by compression ignition. In general, such internal combustion engines switch between a spark ignition combustion mode using an ignition plug and a homogeneous charge compression ignition combustion mode in which the premixed air-fuel mixture is compressed and ignited, depending on various conditions such as the load and the cooling water temperature.

[0003] Patent Document 1 describes how, when switching from homogeneous charge compression ignition combustion mode to spark ignition combustion mode as the load or rotation speed increases, the in-cylinder temperature is quickly reduced by throttling the intake air or reducing the compression ratio, thereby achieving a smooth switch in combustion mode. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2003-184606 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, it is difficult to change the in-cylinder temperature in a stepwise manner, and there is a risk of knocking occurring in a transitional cycle in an intermediate temperature state. [Means for solving the problem]

[0006] The present invention provides a method for controlling an internal combustion engine, comprising the steps of: When a switch from homogeneous charge compression ignition combustion mode to spark ignition combustion mode is required, The supply of fuel is stopped, and the target compression ratio of the variable compression ratio mechanism is changed from the compression ratio for homogeneous charge compression ignition combustion to the compression ratio for spark ignition combustion, After the actual compression ratio has decreased to a spark ignition combustion permission compression ratio that is equal to or greater than the compression ratio for spark ignition combustion, the combustion mode is set to spark ignition combustion mode and fuel supply is resumed. Effect of the Invention

[0007] According to this invention, the mechanical compression ratio is changed via a variable compression ratio mechanism while fuel supply is stopped, and combustion operation is resumed in a state where the actual compression ratio has been reduced to at least the compression ratio permitted for spark ignition combustion, thereby suppressing the occurrence of transient knocking when switching from homogeneous charge compression ignition combustion mode to spark ignition combustion mode. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram illustrating the configuration of a series hybrid vehicle. [Diagram 2] 1 is a diagram illustrating the configuration of an internal combustion engine according to an embodiment; [Diagram 3] FIG. 2 is a functional block diagram showing a main part of a control device. [Figure 4] 4 is a flowchart showing a process flow of control for switching from the homogeneous charge compression ignition combustion mode to the spark ignition combustion mode. [Diagram 5] 5 is a time chart showing the behavior of each part when switching from the homogeneous charge compression ignition combustion mode to the spark ignition combustion mode due to an increase in the target output. [Figure 6] 5 is a time chart showing the behavior of each part when switching from the homogeneous charge compression ignition combustion mode to the spark ignition combustion mode due to a decrease in the cooling water temperature. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an embodiment in which the present invention is applied to an internal combustion engine for generating electricity in a series hybrid vehicle will be described. FIG. 1 shows a schematic configuration of a series hybrid vehicle. The series hybrid vehicle is configured to include a power generating motor generator 1 that mainly operates as a generator, an internal combustion engine 2 used as a power generating internal combustion engine that drives the power generating motor generator 1 in response to an electric power request, a traveling motor generator 4 that mainly operates as a motor to drive driving wheels 3, and a battery 5 that temporarily stores the generated electric power. The electric power obtained by the internal combustion engine 2 driving the power generating motor generator 1 is stored in the battery 5 via an inverter device (not shown). The traveling motor generator 4 is driven and controlled using the electric power of the battery 5. The electric power generated by the traveling motor generator 4 during regeneration is 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 linked via a gear train, but they may be directly connected to each other.

[0010] The operation of the motor generators 1 and 4, the charging and discharging of the battery 5, and the operation of the internal combustion engine 2 are controlled by a controller 6. The controller 6 is composed of a plurality of controllers connected to each other so as to be able to communicate with each other, such as a motor controller 7 for controlling the motor generators 1 and 4, an engine controller 8 for controlling the internal combustion engine 2, and a battery controller 9 for managing the battery 5. Information such as the accelerator pedal opening degree and the vehicle speed (not shown) is input to the controller 6. The battery controller 9 also calculates 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 to generate electricity. The driving modes of such a series hybrid vehicle include an EV mode in which the vehicle runs on the power of the battery 5 without the combustion operation of the internal combustion engine 2, and an HEV mode in which the vehicle runs while generating electricity through the combustion operation of the internal combustion engine 2. Even if the SOC is equal to or higher than 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 runs in the HEV mode.

[0011] 2 shows the system configuration of the internal combustion engine 2. The internal combustion engine 2 is, for example, a four-stroke cycle turbocharged internal combustion engine equipped with a variable compression ratio mechanism 12 that utilizes a multi-link piston crank mechanism, and performs combustion by compression autoignition of a premixed mixture in a homogeneous charge compression ignition combustion mode (HCCI mode) in a predetermined operating range on the relatively low power side. Also, in the remaining operating range on the high power side or when the cooling water temperature is lower than a predetermined allowable water temperature, combustion by spark ignition is performed in a spark ignition combustion mode (SI mode).

[0012] 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 an ignition plug 16 for spark ignition in a specific operating region is arranged in the center surrounded by these intake valves 14 and exhaust valves 15. The combustion chamber 13 is provided with an in-cylinder pressure sensor 25 for detecting the in-cylinder pressure.

[0013] A fuel injection valve 18 that injects fuel toward the intake valve 14 is disposed for each cylinder in an intake port 17 that is 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 thereto, and injects an amount of fuel that is substantially proportional to the pulse width of the drive pulse signal.

[0014] An electronically controlled throttle valve 21, the opening of which is controlled by a control signal from the engine controller 8, is provided upstream of the collector section 19a of the intake passage 19 connected to the intake port 17, and a compressor 22A of a turbocharger 22 is provided further upstream of the electronically controlled throttle valve 21. An air flow meter 23 for detecting the amount of intake air and an air cleaner 24 are provided upstream of the compressor 22A. A heat exchanger for cooling the supercharged intake air by exchanging heat with cooling water, that is, a water-cooled intercooler 26, is built into the collector section 19a. An intercooler water temperature sensor 36 is provided in the intercooler 26 to detect the temperature of the cooling water flowing through the intercooler 26. An intake air temperature sensor 37 is provided on the intake air outlet side of the intercooler 26 to detect the temperature of the intake air that has passed through the intercooler 26. In addition to the intercooler water temperature sensor 36, 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 on the water jacket, etc. The cooling water circuit flowing through the intercooler 26 may be part of the cooling water circuit flowing through the water jacket, or may be configured independent of each other. The degree of heat exchange in the intercooler 26 can be variably adjusted via a cooling water valve, an intercooler cooling water pump, a cooling water bypass valve, or the like (not shown).

[0015] Furthermore, a knock sensor 39 for detecting knocking vibrations is provided at an appropriate position on the cylinder block of the internal combustion engine 2.

[0016] The turbine 22B of the turbocharger 22 disposed in the exhaust passage 31 is equipped with a wastegate valve 32 whose opening is controlled by a control signal from the engine controller 8. Catalyst devices 33, 34 are disposed downstream of the turbine 22B in the exhaust passage 31, and a silencer 35 is disposed further downstream.

[0017] The variable compression ratio mechanism 12 utilizes a known multi-link piston crank mechanism described in JP 2005-127200 A and 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 to a piston pin 49 of a piston 40, a control shaft 44 rotatably supported on the engine body, a control link 45 connecting a control pin 50 at the other end of the lower link 42 to 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 a base end of the control link 45 is supported on the eccentric shaft portion so as to be relatively rotatable, i.e., swingable. In the variable compression ratio mechanism 12, the attitude 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 simultaneously detected as indicating the actual value of the mechanical compression ratio, i.e., the actual compression ratio. In other words, the electric actuator 46 itself is configured to also function 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 stationary, i.e., not rotating.

[0018] In addition to the above-mentioned in-cylinder pressure sensor 25, air flow meter 23, intercooler water temperature sensor 36, cooling water temperature sensor 38, knock sensor 39, intake air temperature sensor 37, and actual compression ratio sensor (electric actuator 46), detection signals from various sensors such as a crank angle sensor 52 for detecting engine speed, an accelerator pedal opening sensor 53 for detecting the amount of depression of an accelerator pedal operated by a driver as a sensor for detecting a torque request by the driver, a boost pressure sensor 54 for detecting boost pressure, and an air-fuel ratio sensor 55 provided in the exhaust passage 31 are input to the engine controller 8. Based on these detection signals, the engine controller 8 optimally controls the amount of fuel injected 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, and the like, and realizes homogeneous charge compression ignition combustion (HCCI) by compression self-ignition of the premixed mixture in a predetermined operating range. In addition, in a certain operating range including low water temperatures where homogenous charge compression ignition is likely to become unstable, spark ignition (SI) combustion using the spark plug 16 is performed.

[0019] 4 is a flowchart showing the flow of the SI switching control process executed by the engine controller 8 when the combustion mode of the internal combustion engine 2 switches from the homogeneous charge compression ignition combustion mode to the spark ignition combustion mode. The process shown in this flowchart is repeatedly executed during operation in the homogeneous charge compression ignition combustion mode.

[0020] In step 1, the detection values ​​of various necessary sensors are read out, and in step 2, the target output (in other words, the required output) is calculated mainly based on the SOC of the battery 5 and the accelerator pedal opening degree (vehicle required output). The target output corresponds to the amount of power generation required for the motor generator 1.

[0021] In step 3, it is determined whether the target output is equal to or less than a predetermined value (HCCI permitted output) at which homogeneous charge compression ignition combustion is permitted. If this condition is met, the process proceeds to step 4, where a large target output flag indicating that the target output is greater than the HCCI permitted output is set to 0. The process then proceeds to step 5, where it is determined whether the coolant temperature is within a predetermined range. If this condition is met, in step 6, the HCCI permitted flag is set to 1.

[0022] If the target output is greater than the HCCI permitted output in step 3, the large target output flag is set to 1 in step 7, and the HCCI permission flag is set to 0 in step 8. If the coolant temperature is outside the predetermined range in step 5, the process also proceeds to step 8, and the HCCI permission flag is set to 0.

[0023] In step 9, it is determined whether the HCCI permission flag has been inverted from 1 to 0. In other words, it is determined whether the previous HCCI permission flag was 1 and the current HCCI permission flag is 0. If the result is YES, the process proceeds to step 10, the switching flag is set to 1, and fuel injection is stopped. In addition, the target compression ratio of the variable compression ratio mechanism 12 is set to an SI target compression ratio suitable for spark ignition combustion. The SI target compression ratio is generally a lower compression ratio than the HCCI target compression ratio in the homogeneous charge compression ignition combustion mode. Therefore, by setting the SI target compression ratio as the target compression ratio, the variable compression ratio mechanism 12 is controlled in a direction to decrease the compression ratio.

[0024] Proceed from step 10 to step 11 and determine whether the switching flag is 1. If the switching flag is 1, this means that the switching process is not complete. If the answer is NO in step 9, proceed from step 9 to step 11. If the answer is NO in step 11, this means that switching to the spark ignition combustion mode is not necessary, so the current routine is terminated.

[0025] If the answer is YES in step 11, the process proceeds to step 12, where it is determined whether the actual compression ratio is higher than the SI permitted compression ratio at which spark ignition combustion can be permitted. The SI permitted compression ratio is set between the target compression ratio for HCCI and the target compression ratio for SI. In other words, it is set relatively higher than the target compression ratio for SI. In one preferred example, it is set to a compression ratio at which knocking does not occur when the intake pressure is atmospheric pressure. As described above, the variable compression ratio mechanism 12 of the embodiment is capable of detecting the actual compression ratio even when the rotation is stopped.

[0026] If the actual compression ratio is higher than the SI permitted compression ratio in step 12, the process proceeds to step 13, where it is determined whether the target output large flag is 1. This means whether the switch to the spark ignition combustion mode is due to an increase in the target output. If it is YES, the process proceeds to step 14, where the target rotation speed of the internal combustion engine 2 is set to the current rotation speed. As a result, while the combustion operation of the internal combustion engine 2 is stopped, the internal combustion engine 2 is motored by the powering of the motor generator 1 mechanically connected to the internal combustion engine 2, and the rotation speed is maintained at the rotation speed immediately before the switch. If it is NO, the process proceeds to step 15, where the target rotation speed of the internal combustion engine 2 is set to 0. As a result, the rotation of the internal combustion engine 2 and the motor generator 1 is stopped. If the determination in step 13 is NO, it means that the switch request is due to the non-satisfaction of an HCCI permission condition other than the target output, for example, a decrease in the cooling water temperature.

[0027] While the routine is repeated, the actual compression ratio gradually decreases, and when the actual compression ratio becomes equal to or less than the SI permitted compression ratio in step 12, the process proceeds from step 12 to step 16, where the target rotation speed is set to an SI target rotation speed suitable for switching to the spark ignition combustion mode. In a preferred embodiment, the SI target rotation speed is given with characteristics according to the target output. Note that the homogeneous charge compression ignition combustion mode is limited to a region where the target output is small, and if the target output is larger than the HCCI permitted output, the spark ignition combustion mode is selected. Therefore, the SI target rotation speed is generally relatively higher than the rotation speed under the homogeneous charge compression ignition combustion mode. However, depending on the target output and settings, the SI target rotation speed may be approximately the same as the rotation speed under the homogeneous charge compression ignition combustion mode. As described above, the internal combustion engine 2 is motored by the motor generator 1 along this SI target rotation speed.

[0028] In the next step 17, it is determined whether the actual rotation speed of the internal combustion engine 2 has substantially reached the SI target rotation speed, specifically, whether the difference between the SI target rotation speed, which is the target rotation speed, and the actual rotation speed is equal to or smaller than a relatively small predetermined value. If the answer is NO in step 17, the current routine is terminated. After repeating the routine, if the actual rotation speed has substantially reached the SI target rotation speed, the routine proceeds from step 17 to step 18, where fuel injection is resumed and the switching in progress flag is set to 0. This resumption of fuel injection starts combustion operation in the spark ignition combustion mode in accordance with the target output. Incidentally, as the operation of the internal combustion engine 2 is resumed, the operation of the motor generator 1 shifts from power running to regeneration (power generation).

[0029] FIG. 3 is a functional block diagram showing the control of the internal combustion engine 2 including the switching control from the homogeneous charge compression ignition combustion mode to the spark ignition combustion mode. As shown in the figure, the engine controller 8 functionally includes a target output calculation unit 61, a target rotation speed calculation unit 62, a fuel injection amount calculation unit 63, a target compression ratio calculation unit 64, a target boost pressure calculation unit 65, and an HCCI switching calculation unit 66. The target output calculation unit 61 calculates a target output based on a power generation request based on the battery SOC output by the battery controller 9 and a vehicle driving force request output by the accelerator pedal opening sensor 53. Except during the switching of the combustion mode, the engine is operated in the spark ignition combustion mode or the homogeneous charge compression ignition combustion mode according to this target output. That is, the target rotation speed calculated by the target rotation speed calculation unit 62, the fuel injection amount calculated by the fuel injection amount calculation unit 63, the target compression ratio calculated by the target compression ratio calculation unit 64, the target boost pressure calculated by the target boost pressure calculation unit 65, and the like are calculated according to the target output.

[0030] The HCCI switching calculation unit 66 determines whether or not switching between the homogeneous charge compression ignition combustion mode and the spark ignition combustion mode is necessary based on the HCCI permission conditions including the cooling water temperature and the target output, and executes the switching control example described in FIG. 4 when switching from the homogeneous charge compression ignition combustion mode to the spark ignition combustion mode.

[0031] Figure 5 is a time chart showing the behavior of each part when switching from homogeneous charge compression ignition combustion mode to spark ignition combustion mode. In particular, Figure 5 shows an example of switching from homogeneous charge compression ignition combustion mode to spark ignition combustion mode as the target output increases. From the top of the figure, (a) target output, (b) rotation speed (dashed line indicates target rotation speed, solid line indicates actual rotation speed), (c) compression ratio (dashed line indicates target compression ratio, solid line indicates actual compression ratio), (d) coolant temperature, (e) fuel injection, (f) HCCI permission flag, and (g) switching flag are shown.

[0032] At the initial point in time in this time chart, the internal combustion engine 2 is operated in the homogeneous charge compression ignition combustion mode.

[0033] In the illustrated example, at time t1, the target output exceeds the HCCI permissible output, so that the HCCI permission flag becomes 0, and furthermore, the switching in progress flag, which indicates that the switching process is in progress, becomes 1. Then, substantially at the same time, fuel injection is stopped (OFF), and furthermore, the actual rotation speed at that time point is set as the target rotation speed. As a result, motoring by the motor generator 1 is started, and the actual rotation speed is maintained as it is. Furthermore, substantially at the same time, the target compression ratio of the variable compression ratio mechanism 12 becomes the SI target compression ratio. The actual compression ratio (i.e., the rotational position of the control shaft 44) changes relatively slowly toward this target compression ratio.

[0034] After that, at time t2, the actual compression ratio reaches the SI allowable compression ratio, which is relatively higher than the SI target compression ratio. Accordingly, the target rotation speed is set to the SI target rotation speed. The actual rotation speed becomes the SI target rotation speed with some delay.

[0035] At the point in time (time t3) when the actual rotation speed reaches the SI target rotation speed, fuel injection is resumed (ON) as the spark ignition combustion mode. At the same time, the switching in progress flag becomes 0. After that, at time t4, the actual compression ratio reaches the SI target compression ratio. In one preferred example, during the period from time t3 when the combustion operation is resumed to time t4 when the actual compression ratio reaches the SI target compression ratio, the output of the internal combustion engine is limited according to the actual compression ratio. The output limit is realized by an appropriate means, for example, a reduction in the boost pressure or a reduction in the throttle valve opening. Incidentally, as the torque of the internal combustion engine 2 rises at time t3, the motor generator 1 transitions from power running to regeneration.

[0036] In this manner, in the above embodiment, when a switch from the homogeneous charge compression ignition combustion mode to the spark ignition combustion mode is requested, fuel injection is stopped and combustion operation is not performed until the actual compression ratio by the variable compression ratio mechanism 12 falls to at least the SI permitted compression ratio, so transient knocking is reliably prevented. Also, since spark ignition combustion is started with the actual compression ratio set to the SI permitted compression ratio or lower and the rotational speed set to the SI target rotational speed by motoring, stable spark ignition combustion can be started from the beginning, and misfire and knocking during the switch can be prevented.

[0037] Here, the SI permitted compression ratio is set relatively higher than the SI target compression ratio, which is the final target compression ratio, and therefore combustion is resumed without waiting for the actual compression ratio to drop to the SI target compression ratio. In other words, the combustion stop period is minimized. Then, by applying output restrictions according to the actual compression ratio until the actual compression ratio drops to the SI target compression ratio, knocking is reliably suppressed.

[0038] In addition, when the mechanical compression ratio is changed due to the switch, the variable compression ratio mechanism 12 of the above embodiment can detect the actual compression ratio in real time and can reliably detect when the compression ratio has actually decreased to the SI permitted compression ratio, thereby stably controlling the switch from the homogeneous charge compression ignition combustion mode to the spark ignition combustion mode.

[0039] Note that the higher the SI permitted compression ratio is set, the earlier combustion is restarted, but the more likely knocking occurs. As described above, the SI permitted compression ratio is preferably set to a compression ratio that does not cause knocking when the intake pressure is atmospheric pressure. This allows early combustion restart while avoiding knocking.

[0040] Furthermore, in the case of switching caused by an increase in the target output, the rotation speed is maintained by motoring by the motor generator 1 while fuel injection is stopped, so the delay period (between time t2 and time t3) from when the actual compression ratio becomes the SI permitted compression ratio until the actual rotation speed reaches the SI target rotation speed and combustion is actually restarted is shortened. In other words, it is possible to respond to an increase in the target output in a relatively short time.

[0041] As an example of the numerical values ​​of the mechanical compression ratio in the above embodiment, the SI target compression ratio is in the range of about 10 to 12, which is variably set according to the load or the target output. On the other hand, the SI permission compression ratio is set to a value relatively higher than the SI target compression ratio, in the range of about 12 to 14. More specifically, it is set based on the cooling water temperature, the intake air temperature, and the fuel ignition quality so that knocking does not occur when the intake pressure is atmospheric pressure. The fuel ignition quality is obtained by searching for the knock limit using the knock sensor 39 while spark ignition combustion is being performed. Note that, in the early stage when spark ignition combustion is started under the SI permission compression ratio, the supercharging pressure by the turbocharger 22 has not yet risen, and the intake pressure is approximately atmospheric pressure.

[0042] The target compression ratio for HCCI in the homogeneous charge compression ignition combustion mode is, for example, about 16 to 20. This is set based on the cooling water temperature, intake air temperature, and fuel ignition quality so that combustion occurs at an appropriate timing. Feedback control of the target compression ratio for HCCI may be performed based on detection parameters (combustion center of gravity MB50, maximum cylinder pressure crank angle θPmax, etc.) that indicate the combustion state of homogeneous charge compression ignition combustion.

[0043] Next, the operation when switching from the homogeneous charge compression ignition combustion mode to the spark ignition combustion mode due to the non-establishment of the HCCI permission conditions other than the increase in the target power will be described. Figure 6 shows an example in which the switching is caused by the cooling water temperature shown in (d) dropping below the HCCI permission water temperature.

[0044] When the condition is other than an increase in the target output, unlike the example shown in the time chart of Fig. 5, the target rotation speed becomes 0 between time t1 and time t2, as shown in (b), and the rotation of the internal combustion engine 2 stops. In other words, motoring is not performed while fuel injection is stopped. Therefore, power consumption associated with motoring is suppressed.

[0045] When the actual compression ratio reaches the SI permitted compression ratio at time t2, motoring is started with the target rotation speed set to the SI target rotation speed. The rest is the same as the example in Figure 5. In the example in Figure 6, since the target output is constant, the SI target rotation speed is approximately the same as the rotation speed in the homogeneous charge compression ignition combustion mode immediately before the switch.

[0046] Although one embodiment of the present invention has been described above in detail, the present invention is not limited to the above embodiment and various modifications are possible. For example, in the above embodiment, an example applied to a series hybrid vehicle has been described, but the present invention is not limited to the power generating internal combustion engine of a series hybrid vehicle, and can be applied to other types of internal combustion engines in which the output of the internal combustion engine can be used as at least a part of the vehicle's running power source. In addition, the variable compression ratio mechanism may be 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. Furthermore, as another example of setting the SI allowed compression ratio, the SI allowed compression ratio may be a compression ratio value equal to the SI target compression ratio. [Explanation of symbols]

[0047] 1...Motor generator 2. Internal combustion engine 8. Engine controller 12...Variable compression ratio mechanism 16…Spark plug 18...Fuel injector 21...Throttle valve 22...Turbocharger 23...Air flow meter 25...Cylinder pressure sensor 38...Coolant temperature sensor 39...Knock sensor 46...Electric actuator 52...Crank angle sensor 53...Accelerator pedal opening sensor 61...Target output calculation unit 62...Target rotation speed calculation unit 63…Fuel injection amount calculation section 64...Target compression ratio calculation unit 65...Target boost pressure calculation section 66...HCCI switching calculation section

Claims

1. An internal combustion engine having a variable compression ratio mechanism capable of mechanically changing the compression ratio and capable of switching between a spark ignition combustion mode and a homogeneous charge compression ignition combustion mode, When a switch from homogeneous charge compression ignition combustion mode to spark ignition combustion mode is required, The supply of fuel is stopped, and the target compression ratio of the variable compression ratio mechanism is changed from the compression ratio for homogeneous charge compression ignition combustion to the compression ratio for spark ignition combustion, After the actual compression ratio is reduced to a spark ignition combustion permitted compression ratio that is equal to or greater than the spark ignition combustion compression ratio, fuel supply is resumed in a spark ignition combustion mode. A method for controlling an internal combustion engine.

2. The spark ignition combustion permission compression ratio is set to a compression ratio higher than the spark ignition combustion compression ratio.

2. A method for controlling an internal combustion engine according to claim 1.

3. When the actual compression ratio is reduced to the spark ignition combustion permitted compression ratio, a target rotation speed of the internal combustion engine controlled via the electric motor is set to a spark ignition combustion switching rotation speed, When the actual rotation speed of the internal combustion engine reaches the rotation speed for switching to the spark ignition combustion mode, the fuel supply is resumed as the spark ignition combustion mode.

2. A method for controlling an internal combustion engine according to claim 1.

4. when a switch from the homogeneous charge compression ignition combustion mode to the spark ignition combustion mode is requested based on an increase in the required output, the rotation speed before the switch is maintained by the electric motor until the actual compression ratio is reduced to the spark ignition combustion permitted compression ratio.

4. A method for controlling an internal combustion engine according to claim 3.

5. When a switch from the homogeneous charge compression ignition combustion mode to the spark ignition combustion mode is requested due to a condition other than an increase in the required output, the electric motor is not rotated until the actual compression ratio is reduced to the spark ignition combustion permitted compression ratio.

4. A method for controlling an internal combustion engine according to claim 3.

6. After the fuel supply is resumed, the output of the internal combustion engine is limited according to the actual compression ratio until the actual compression ratio decreases to the compression ratio for spark ignition combustion.

3. A method for controlling an internal combustion engine according to claim 2.

7. The spark ignition combustion permitting compression ratio is set to a compression ratio at which knocking does not occur when the intake pressure is atmospheric pressure.

3. A method for controlling an internal combustion engine according to claim 2.

8. The internal combustion engine is an internal combustion engine for a series hybrid vehicle that drives a generator.

2. A method for controlling an internal combustion engine according to claim 1.

9. The variable compression ratio mechanism is a multi-link piston crank mechanism including: a lower link rotatably supported on a crank pin of a crankshaft; an upper link connecting an upper pin at one end of the lower link and a piston pin of a piston; a control link having one end connected to a control pin at the other end of the lower link; and a control shaft having an eccentric shaft portion swingably supporting the other end of the control link; an actuator for controlling a rotational position of the control shaft; Equipped with an actual compression ratio is detected based on a rotational position of the control shaft; 2. A method for controlling an internal combustion engine according to claim 1.

10. An internal combustion engine capable of switching between a spark ignition combustion mode and a homogeneous charge compression ignition combustion mode; A variable compression ratio mechanism capable of mechanically changing the compression ratio; A controller; Equipped with The above controller is when a switch from the homogeneous charge compression ignition combustion mode to the spark ignition combustion mode is requested, the fuel supply is stopped, and the target compression ratio of the variable compression ratio mechanism is changed from the homogeneous charge compression ignition combustion compression ratio to the spark ignition combustion compression ratio, and after the actual compression ratio is reduced to a spark ignition combustion permitted compression ratio that is equal to or higher than the spark ignition combustion compression ratio, the fuel supply is resumed as the spark ignition combustion mode. A control device for an internal combustion engine.

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