Control method and control device for internal combustion engine

Abstract

To enable prompt restart in a premixed compression ignition combustion (HCCI) mode when an internal combustion engine is suspended during driving in the HCCI 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 an HCCI mode, when target output becomes 0 and stop of the internal combustion engine is requested (time t1), fuel supply is stopped while a target compression ratio is maintained at an HCCI target compression ratio. Since calculation of the HCCI target compression ratio and control of the variable compression ratio mechanism are continued even during the stop, the target compression ratio and an actual compression ratio are gradually raised along with lowering of a cooling water temperature and an intake air temperature. If restart is requested (time t2), when the actual compression ratio corresponds to the target compression ratio (time t3), motoring is started to reach target speed. When the target speed is reached (time t4), fuel injection is resumed.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 that use gasoline or the like as fuel and burn a premixed air-fuel mixture formed in a combustion chamber by compression ignition have been proposed. Patent Document 1 discloses a control method for an internal combustion engine that executes a spark ignition combustion mode when starting the internal combustion engine and then switches to homogeneous charge compression ignition combustion mode. In Patent Document 1, when switching from the spark ignition combustion mode to the homogeneous charge compression ignition combustion mode, the fuel supply is stopped, and during this fuel cut, the effective compression ratio of the internal combustion engine is increased by changing the valve timing and the rotation speed of the internal combustion engine is reduced, and then the fuel supply is resumed to switch to homogeneous charge compression ignition combustion mode.

[0003] Patent Document 2 discloses an internal combustion engine equipped with a variable compression ratio mechanism that is capable of mechanically changing the compression ratio. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2015-140728 A [Patent Document 2] JP 2014-159770 A Summary of the Invention [Problem to be solved by the invention]

[0005] During operation in the homogeneous charge compression ignition combustion mode, the combustion operation of the internal combustion engine may be temporarily stopped due to a decrease in the required output, etc., and the combustion operation may be resumed after a relatively short time. Patent Document 1 does not disclose any control for such a case. If the mode is switched to the homogeneous charge compression ignition combustion mode via the spark ignition combustion mode every time the engine is restarted, the start of the homogeneous charge compression ignition combustion mode will be delayed. [Means for solving the problem]

[0006] The present invention provides a method for controlling an internal combustion engine, comprising the steps of: When a request is made to stop the internal combustion engine during operation in homogeneous charge compression ignition combustion mode, The supply of fuel is stopped while maintaining the target compression ratio of the variable compression ratio mechanism at the target compression ratio for homogeneous charge compression ignition combustion. Effect of the Invention

[0007] Although the conditions under which homogeneous charge compression ignition combustion is possible are limited, if the engine is stopped for a short period of time, there is a high probability that the conditions will not change significantly and homogeneous charge compression ignition combustion will be possible upon restart. By stopping the fuel supply while maintaining the target compression ratio at the target compression ratio for homogeneous charge compression ignition combustion, it is possible to quickly resume operation in the homogeneous charge compression 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 the flow of processes for stopping and restarting the internal combustion engine while the vehicle is in operation. [Diagram 5] 4 is a time chart showing the behavior of each part when restarting in homogeneous charge compression ignition combustion mode after stopping. [Figure 6] 5 is a time chart showing the behavior of each part when restarting in spark ignition combustion mode due to an increase in the target output. [Figure 7] 4 is a time chart showing the behavior of each part when restarting in spark ignition combustion mode due to a drop in water temperature while the engine is stopped. 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] Therefore, the internal combustion engine 2 repeatedly stops and restarts temporarily while the main switch (so-called ignition switch) of the vehicle is ON.

[0012] 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).

[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 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.

[0014] 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.

[0015] 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).

[0016] 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.

[0017] 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.

[0018] The variable compression ratio mechanism 12 utilizes a known multi-link piston crank mechanism described in Patent Document 2, JP 2005-127200 A, etc., 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.

[0019] 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.

[0020] 4 is a flowchart showing the flow of the process of stopping and restarting the internal combustion engine 2 executed by the engine controller 8 while the vehicle is in operation. The process shown in this flowchart is repeatedly executed while the vehicle is in operation.

[0021] 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) of the internal combustion engine 2 is calculated based mainly 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.

[0022] 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 cooling water temperature is within the permitted range for homogeneous charge compression ignition combustion. If this condition is met, in step 6, the HCCI permitted flag is set to 1.

[0023] 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 permitted range for homogeneous charge compression ignition combustion in step 5, the process also proceeds to step 8 and the HCCI permission flag is set to 0.

[0024] In the next step 9, it is determined whether the target output is equal to or lower than a predetermined value (set close to 0) at which the internal combustion engine 2 should be stopped, and whether the cooling water temperature is within a predetermined range in which temporary suspension of the internal combustion engine 2 is permitted. In a situation in which the cooling water temperature is excessively low, stopping of the internal combustion engine 2 is prohibited. If the determination in step 9 is YES, in step 10, the engine stop flag is set to 1, and if the determination is NO, in step 11, the engine stop flag is set to 0. The engine stop flag indicates that the internal combustion engine 2 should be stopped.

[0025] Next, the process proceeds to step 12, where it is determined whether or not the HCCI permission flag is 1. If the determination in step 12 is YES, then in step 13, the target compression ratio of the variable compression ratio mechanism 12 is set to an HCCI target compression ratio suitable for homogenous charge compression ignition combustion, and if the determination is NO, then in step 14, the target compression ratio of the variable compression ratio mechanism 12 is set to an SI target compression ratio suitable for spark ignition combustion.

[0026] For example, the target compression ratio for SI is a compression ratio of about 10 to 12, which is variably set according to the load or the target output. The target compression ratio for HCCI is higher than the target compression ratio for SI, for example, about 16 to 20. This is set based on the cooling water temperature, the intake air temperature, and the fuel ignition quality so that combustion occurs at an appropriate timing. The fuel ignition quality is obtained by searching for the knock limit using the knock sensor 39 while spark ignition combustion is being performed. The target compression ratio for HCCI may be feedback-controlled based on detection parameters (combustion center of gravity MB50, maximum cylinder pressure crank angle θPmax, etc.) indicating the combustion state of homogenous charge compression ignition combustion.

[0027] The SI target compression ratio and the HCCI target compression ratio are repeatedly calculated by another control routine (not shown), including while the internal combustion engine 2 is stopped. In addition, the variable compression ratio mechanism 12 is constantly feedback-controlled by another routine (not shown) in accordance with these target compression ratios, including while the internal combustion engine 2 is stopped.

[0028] In the next step 15, it is determined whether or not the engine stop flag is 1. If the engine stop flag is 1, the process proceeds to step 16, where the target rotation speed is set to 0 and fuel injection is stopped (OFF). This causes the internal combustion engine 2 to stop. If the internal combustion engine 2 comes to a stop while operating in the homogenous charge compression ignition combustion mode, the target compression ratio of the variable compression ratio mechanism 12 remains the HCCI target compression ratio that was selected in step 13 during operation. Note that calculation of the HCCI target compression ratio and control of the variable compression ratio mechanism 12 continue even while the internal combustion engine 2 is stopped. Therefore, the actual compression ratio conforms to the HCCI target compression ratio.

[0029] If the engine stop flag is 0 in step 15, the process proceeds to step 17, where it is determined whether the target output large flag is 1 or not. If NO here, the process proceeds to step 18, where it is determined whether the actual compression ratio is equal to the target compression ratio (either the SI target compression ratio or the HCCI target compression ratio). If the actual compression ratio is equal to the target compression ratio, the process proceeds to step 19, where the target rotation speed is calculated and fuel injection is performed (ON). When fuel injection is resumed from a rotation stop state of the internal combustion engine 2, the internal combustion engine 2 is motored along the target rotation speed by the powering of the motor generator 1 mechanically connected to the internal combustion engine 2, and fuel injection is resumed at the stage when the actual rotation speed reaches the target rotation speed. After the fuel injection is resumed, the motor generator 1 transitions from powering to regeneration, and the target rotation speed is maintained. The target compression ratio in step 19 is the HCCI target compression ratio if the cooling water temperature is within the allowable range for homogeneous charge compression ignition combustion (step 5), and is the SI target compression ratio if it is outside the allowable range.

[0030] On the other hand, if the target output large flag is 1 in step 17, the process proceeds to step 20, where it is determined whether the actual compression ratio is higher than the SI permitted compression ratio. The target compression ratio at this time is the SI target compression ratio in steps 12 and 14. When the target compression ratio changes from the HCCI target compression ratio to the SI target compression ratio, the actual compression ratio gradually decreases toward the SI target compression ratio. The SI permitted compression ratio is set between the HCCI target compression ratio and the SI target compression ratio. That is, it is set relatively higher than the SI target compression ratio. The SI permitted compression ratio is set to a value of, for example, about 12 to 14, which is relatively higher than the SI target compression ratio. In a preferred example, the compression ratio is set based on the cooling water temperature, the intake air temperature, and the fuel ignition property so that the compression ratio is such that 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.

[0031] If the answer is YES in step 20, the current routine is terminated. If the actual compression ratio gradually decreases while the routine is repeated and becomes equal to or less than the SI permitted compression ratio in step 20, the process proceeds from step 20 to step 21, where a target rotation speed suitable for the spark ignition combustion mode is calculated and fuel injection is performed (ON). When fuel injection is resumed from a rotation stop state of the internal combustion engine 2, the internal combustion engine 2 is motored along the target rotation speed by the powering of the motor generator 1 mechanically connected to the internal combustion engine 2, and fuel injection is resumed when the actual rotation speed reaches the target rotation speed. After fuel injection is resumed, the motor generator 1 transitions from powering to regeneration, and the target rotation speed is maintained. Note that even after fuel injection is resumed, the actual compression ratio decreases until it reaches the target compression ratio for SI.

[0032] In most cases, the internal combustion engine 2 is stopped while the vehicle is in operation when the target output becomes substantially 0 (step 9). If the target output and the cooling water temperature immediately before that satisfy the conditions for homogeneous charge compression ignition combustion (steps 3 and 5), the internal combustion engine 2 is stopped in the homogeneous charge compression ignition combustion mode. In this case, in the above embodiment, the internal combustion engine 2 is stopped while the target compression ratio is set to the HCCI target compression ratio. Therefore, when a restart is requested while the conditions for homogeneous charge compression ignition combustion are satisfied, the operation is promptly resumed in the homogeneous charge compression ignition combustion mode. In addition, since the control of the variable compression ratio mechanism 12 continues even while the internal combustion engine 2 is stopped, the HCCI target compression ratio is maintained in accordance with the decrease in the cooling water temperature and the intake air temperature while the internal combustion engine 2 is stopped, and stable homogeneous charge compression ignition combustion is possible from the beginning of the restart.

[0033] 3 is a functional block diagram showing the control of the internal combustion engine 2 including the above-mentioned stopping and restarting of the internal combustion engine 2. As shown in the figure, the engine controller 8 functionally includes a target output power calculation unit 61, a target rotation speed calculation unit 62, a fuel injection amount calculation unit 63, a target compression ratio calculation unit 64, an engine stop determination unit 65, and an HCCI determination unit 66.

[0034] A 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. An HCCI determination unit 66 determines whether to operate in a spark ignition combustion mode or a homogenous charge compression ignition combustion mode based on the target output and the coolant temperature. Then, a target rotation speed by a target rotation speed calculation unit 62, a fuel injection amount by a fuel injection amount calculation unit 63, a target compression ratio by a target compression ratio calculation unit 64, and the like are calculated according to the target output and the combustion mode. An engine stop determination unit 65 controls the stop / restart of the internal combustion engine 2 based on the target output, the coolant temperature, and the actual compression ratio.

[0035] Next, an example of the behavior of each part when the internal combustion engine 2 is stopped and restarted will be described with reference to the time charts of FIGS.

[0036] 5 is a time chart showing an example of a case where the internal combustion engine 2 is stopped in the homogeneous charge compression ignition combustion mode and then restarted in the homogeneous charge compression ignition combustion mode. 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) cooling water temperature, (e) HCCI permission flag, (f) engine stop flag, and (g) fuel injection are shown.

[0037] 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.

[0038] In the illustrated example, at time t1, the target output becomes substantially 0, so the engine stop flag becomes 1 and fuel injection is stopped (OFF). At the same time, the target rotation speed becomes 0, motoring by the motor generator 1 is not performed, and the rotation of the crankshaft stops.

[0039] When the internal combustion engine 2 is stopped, the target compression ratio is maintained at the HCCI target compression ratio. The actual compression ratio is also maintained at the compression ratio immediately before the engine is stopped, and there is no change in the compression ratio at time t1.

[0040] On the other hand, the coolant temperature gradually decreases as the internal combustion engine 2 stops. Although not shown in the figure, the intake air temperature also decreases slightly. Therefore, the HCCI target compression ratio calculated based on the coolant temperature, intake air temperature, and fuel ignition quality gradually increases after time t1, and the actual compression ratio changes accordingly.

[0041] At time t2, the target output increases, requesting a restart of the internal combustion engine 2. In other words, the engine stop flag becomes 0 at time t2. Therefore, thereafter, at time t3 when the actual compression ratio substantially matches the target compression ratio, the target rotation speed is calculated as a rotation speed suitable for homogenous charge compression ignition combustion, and motoring by the motor generator 1 is started. At time t4, the actual rotation speed reaches the target rotation speed, and fuel injection is started (ON).

[0042] The difference between the target compression ratio and the actual compression ratio between time t1 and time t2 is exaggerated in the figure, and is actually very small. Therefore, the delay from time t2 to time t3 and time t4 is relatively small.

[0043] 6 is a time chart showing an example of a case where the internal combustion engine 2 is stopped in the homogeneous charge compression ignition combustion mode and then restarted in the spark ignition combustion mode due to a relatively large increase in the target output. At the beginning of this time chart, the internal combustion engine 2 is operating in the homogeneous charge compression ignition combustion mode.

[0044] 5, at time t1, the target output becomes substantially 0, so the engine stop flag becomes 1 and fuel injection is stopped (OFF). At the same time, the target rotation speed becomes 0, motoring by the motor generator 1 is not performed, and the rotation of the crankshaft stops.

[0045] When the internal combustion engine 2 is stopped, the target compression ratio is maintained at the HCCI target compression ratio. The actual compression ratio is also maintained at the compression ratio immediately before the engine is stopped, and there is no change in the compression ratio at time t1.

[0046] On the other hand, the coolant temperature gradually decreases as the internal combustion engine 2 stops. Although not shown in the figure, the intake air temperature also decreases slightly. Therefore, the HCCI target compression ratio calculated based on the coolant temperature, intake air temperature, and fuel ignition quality gradually increases after time t1, and the actual compression ratio changes accordingly.

[0047] At time t2, the target output increases, so that a restart of the internal combustion engine 2 is requested, and the engine stop flag becomes 0. At this time, in the example of FIG. 6, unlike the example of FIG. 5, the requested target output exceeds the HCCI permitted output. Therefore, the HCCI permission flag becomes 0, and substantially at the same time, the target compression ratio changes to 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. After that, at time t11, the actual compression ratio reaches the SI permitted compression ratio, which is relatively higher than the SI target compression ratio. Accordingly, the target rotation speed is calculated to a target rotation speed suitable for spark ignition combustion, and motoring by the motor generator 1 is started. At time t12, the actual rotation speed reaches the target rotation speed, so that fuel injection is started (ON). As a result, the internal combustion engine 2 is operated in the spark ignition combustion mode.

[0048] In this way, when restarting in the spark ignition combustion mode, 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. In addition, since the SI permitted compression ratio is set higher than the SI target compression ratio, the delay time until operation is resumed is relatively short.

[0049] 7 shows a time chart in the case where the internal combustion engine 2 is stopped in the homogeneous charge compression ignition combustion mode, the homogeneous charge compression ignition combustion is not permitted due to a drop in water temperature during the stop, and the internal combustion engine 2 is restarted in the spark ignition combustion mode. At the beginning of this time chart, the internal combustion engine 2 is operating in the homogeneous charge compression ignition combustion mode.

[0050] 5, at time t1, the target output becomes substantially 0, so the engine stop flag becomes 1 and fuel injection is stopped (OFF). At the same time, the target rotation speed becomes 0, motoring by the motor generator 1 is not performed, and the rotation of the crankshaft stops.

[0051] When the internal combustion engine 2 is stopped, the target compression ratio is maintained at the HCCI target compression ratio. The actual compression ratio is also maintained at the compression ratio immediately before the engine is stopped, and there is no change in the compression ratio at time t1.

[0052] On the other hand, the coolant temperature gradually decreases as the internal combustion engine 2 stops. Although not shown in the figure, the intake air temperature also decreases slightly. Therefore, the HCCI target compression ratio calculated based on the coolant temperature, intake air temperature, and fuel ignition quality gradually increases after time t1, and the actual compression ratio changes accordingly.

[0053] In the example of FIG. 7, while the internal combustion engine 2 is stopped, the cooling water temperature decreases, and at time t21, the water temperature becomes lower than the HCCI permission water temperature. Therefore, homogeneous charge compression ignition combustion is not permitted, and the HCCI permission flag becomes 0. At substantially the same time, the target compression ratio changes to 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. In other words, the actual compression ratio decreases under the control of the variable compression ratio mechanism 12 while the internal combustion engine 2 is stopped.

[0054] In the illustrated example, at time t22 after the actual compression ratio reaches the SI target compression ratio, the target output is increased and a restart of the internal combustion engine 2 is requested. Accordingly, the target rotation speed is calculated to a target rotation speed suitable for spark ignition combustion, and motoring by the motor generator 1 is started. At time t22, the actual rotation speed reaches the target rotation speed, and fuel injection is started (ON). As a result, the internal combustion engine 2 is operated in the spark ignition combustion mode. Note that since the target output at time t22 is smaller than the HCCI permissible output, when the cooling water temperature becomes equal to or higher than the HCCI permissible water temperature, the combustion mode will shift from the spark ignition combustion mode to the homogeneous charge compression ignition combustion mode as long as other permissible conditions are satisfied.

[0055] In this way, if the HCCI permission conditions such as the cooling water temperature are not satisfied while the internal combustion engine 2 is stopped, the target compression ratio is switched to the SI target compression ratio while the engine is stopped, and the variable compression ratio mechanism 12 is controlled to the SI target compression ratio while the engine is stopped. Therefore, in many cases, when a restart is requested, the actual compression ratio is close to the SI target compression ratio or the SI permission compression ratio, making it possible to restart the engine quickly in the spark ignition combustion mode. Also, the occurrence of transient knocking can be avoided.

[0056] 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 a 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 temporary stop of the internal combustion engine may include a temporary stop accompanying the stopping of the vehicle at an intersection or the like, so-called idling stop. Furthermore, 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. [Explanation of symbols]

[0057] 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…Engine stop determination unit 66…HCCI judgment unit

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 request is made to stop the internal combustion engine during operation in homogeneous charge compression ignition combustion mode, stopping the fuel supply while maintaining the target compression ratio of the variable compression ratio mechanism at the target compression ratio for homogeneous charge compression ignition combustion; A method for controlling an internal combustion engine.

2. The compression ratio for homogeneous charge compression ignition combustion is set based on at least one parameter among a cooling water temperature, an intake air temperature, and a fuel ignition property, while the internal combustion engine is stopped, the variable compression ratio mechanism is controlled while the internal combustion engine is stopped, with the target compression ratio for homogeneous charge compression ignition combustion, which changes over time, as a target compression ratio.

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

3. When a restart in homogeneous charge compression ignition combustion mode is requested, fuel injection is inhibited until the actual compression ratio reaches the target compression ratio.

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

4. When the condition for permitting the homogeneous charge compression ignition combustion mode is not satisfied without a restart request while the internal combustion engine is stopped, the target compression ratio is changed to a target compression ratio for spark ignition combustion while the internal combustion engine is stopped, and the variable compression ratio mechanism is controlled.

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

5. When the internal combustion engine is stopped and a restart request is made and the homogeneous charge compression ignition combustion mode permission condition is not satisfied, changing the target compression ratio from the target compression ratio for homogeneous charge compression ignition combustion to the target compression ratio for spark ignition combustion to control the variable compression ratio mechanism; After the actual compression ratio is reduced to a spark ignition combustion permitted compression ratio that is relatively higher than the target compression ratio for spark ignition combustion, fuel supply is resumed in a spark ignition combustion mode.

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

6. 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.

7. 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.

8. 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 stop of the internal combustion engine is requested during operation in a homogeneous charge compression ignition combustion mode, the fuel supply is stopped while the target compression ratio of the variable compression ratio mechanism is maintained at the target compression ratio for homogeneous charge compression ignition combustion; A control device for an internal combustion engine.

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