JP2018184033A - Vehicle control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To secure combustion excellently while restricting torque variation when switching a combustion mode.SOLUTION: When amounts of charge of a battery 27 are comparatively large, when a combustion mode of an internal combustion engine 1 should be switched from a first combustion mode in which compressed self-ignition combustion is performed under a lean air-fuel ratio into a second combustion mode in which spark-ignition combustion is performed under a nearly theoretical air-fuel ratio, an air-fuel ratio, a fresh air amount and a carbon dioxide concentration in intake air are controlled, so as to cause output of the engine to become insufficient for required output of the engine, and then the second combustion mode is started to make power running of a motor generator 21 make up for the insufficiency of the output of the engine. When the amounts of charge of the battery are comparatively small, the air-fuel ratio, the fresh air amount and the carbon dioxide concentration in intake air are controlled so as to make the output of the engine become temporarily excessive for the required output of the engine, and then the second combustion mode is started to absorb the excess of the output of the engine through regenerative operation of the motor generator.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a vehicle control apparatus.

  An internal combustion engine coupled to an axle so as to be able to transmit torque, wherein a combustion mode includes a lean combustion mode in which combustion is performed at a lean air-fuel ratio and a stoichiometric combustion mode in which combustion is performed at substantially a stoichiometric air-fuel ratio. When the combustion mode of the internal combustion engine is to be switched from the lean combustion mode to the stoichiometric combustion mode in a so-called hybrid vehicle having an internal combustion engine that can be switched between and an electric motor that is coupled to the axle so as to transmit torque, While maintaining the total output of the engine and the output of the electric motor to be constant, the output of the internal combustion engine is temporarily reduced and the output of the electric motor is temporarily increased, so that the air-fuel ratio is substantially reduced from the lean air-fuel ratio. A hybrid vehicle that switches to a theoretical air-fuel ratio stepwise is known (see, for example, Patent Document 1). According to Japanese Patent Application Laid-Open No. 2004-260688, when this is done, the torque fluctuation of the internal combustion engine that occurs when switching the combustion mode is reduced.

  Further, the combustion mode of the internal combustion engine is changed to the first combustion mode in which compression auto-ignition combustion is performed under a relatively large amount of EGR gas and a lean air-fuel ratio, and under a relatively small amount of EGR gas and substantially the theoretical air-fuel ratio. There is also known a vehicle that can be switched between a second combustion mode in which spark ignition combustion is performed (see, for example, Patent Document 2). In the first combustion mode, a reduction in fuel consumption, a reduction in NOx generation, and the like can be expected.

JP 2008-068802 A JP 2014-173532 A

  In Patent Document 1, if the above-described first combustion mode is performed as the lean combustion mode and the above-described second combustion mode is performed as the stoichiometric combustion mode, it occurs at the time of switching from the first combustion mode to the second combustion mode. It may be possible to enjoy the benefits of the first combustion mode while reducing torque fluctuations. However, when switching from the first combustion mode to the second combustion mode, it is necessary to significantly reduce the amount of fresh air and the amount of EGR gas. However, even if the throttle opening and the EGR control valve opening are reduced stepwise, the fresh air amount may not immediately decrease stepwise. Further, even if the opening degree of the EGR control valve is decreased in a stepped manner, the EGR gas amount or the intake carbon dioxide concentration may not immediately decrease in a stepped manner. For this reason, there is a possibility that combustion is performed in a state where the fresh air amount and the intake carbon dioxide concentration deviate from the target amounts. As a result, good combustion may not be obtained.

  According to the present invention, an internal combustion engine connected to an axle so as to be able to transmit torque, an EGR passage that connects an engine intake passage and an engine exhaust passage downstream of a throttle valve, and an EGR gas disposed in the EGR passage. An EGR control valve configured to change the intake carbon dioxide concentration by changing the amount, and a combustion mode is a first combustion mode for performing compression auto-ignition combustion under a lean air-fuel ratio; An internal combustion engine configured to be switchable between a second combustion mode in which spark ignition combustion is performed under a substantially stoichiometric air-fuel ratio, and a motor generator coupled to the axle so as to transmit torque, A motor generator configured to execute a power running operation that increases torque of an axle and a regenerative operation that regenerates electric energy from the torque of the axle; and the motor generator A battery configured to supply electric energy to the motor generator when the motor performs the power running operation, and store electric energy regenerated by the motor generator when the motor generator performs the regenerative operation; An electronic control unit configured to switch the combustion mode of the internal combustion engine between the first combustion mode and the second combustion mode in accordance with an engine operating state, the combustion mode being In the engine operating state where the first combustion mode should be switched to the second combustion mode, the target value for the fresh air amount in the second combustion mode is greater than the target value for the new amount in the first combustion mode. And the target value of the intake carbon dioxide concentration in the second combustion mode is the intake carbon dioxide in the first combustion mode. The electronic control unit further changes the combustion mode from the first combustion mode to the second combustion mode when the charge amount of the battery is greater than a predetermined set amount. When switching to the combustion mode, the air-fuel ratio is maintained, the amount of fresh air is reduced, the intake carbon dioxide concentration is lowered, so that the output of the internal combustion engine is temporarily insufficient with respect to the engine required output, and thereafter The second combustion mode is started by changing the air-fuel ratio to a substantially stoichiometric air-fuel ratio stepwise and starting spark ignition combustion. At this time, a temporary shortage of the output of the internal combustion engine is taken into the motor When the battery charge amount is less than the set amount, the combustion mode is changed from the first combustion mode to the second combustion mode. When switching to the engine mode, the air-fuel ratio is reduced within the range of the lean air-fuel ratio, the amount of fresh air is reduced, and the intake carbon dioxide concentration is substantially maintained, so that the output of the internal combustion engine temporarily exceeds the engine required output. Then, the second combustion mode is started by changing the air-fuel ratio to a substantially stoichiometric air-fuel ratio stepwise and starting spark ignition combustion, and the output of the internal combustion engine at this time There is provided a control device for a vehicle configured to absorb the temporary excess of the motor generator by regenerative operation of the motor generator.

  It is possible to ensure good combustion while restricting torque fluctuation when switching the combustion mode.

1 is an overall view of a vehicle control device. It is a fragmentary sectional view of an internal combustion engine. FIG. 6 is a diagram showing a first region R1, a second region R2, and a third region R3. It is a diagram which shows an example of the setting rate dOPETX. It is a diagram which shows an example of lower limit SOCL. It is a time chart explaining 1st switching control. It is a diagram which shows the relationship between the operating point determined by the ignition timing θ and the intake carbon dioxide concentration CCO2 and various limits in the second combustion mode. It is a time chart explaining 2nd switching control. It is a diagram which shows the relationship between the operating point determined by the ignition timing θ and the intake carbon dioxide concentration CCO2 and various limits in the second combustion mode. It is a flowchart for performing switching control of the combustion mode of the Example by this invention. It is a flowchart for performing 1st switching control. It is a flowchart for performing 2nd switching control.

  FIG. 1 shows an overall view of a vehicle control apparatus according to an embodiment of the present invention. Referring to FIG. 1, the vehicle control apparatus includes an internal combustion engine 1. The internal combustion engine 1 includes an engine body 2 having a plurality of cylinders 2a. The cylinder 2 a is connected to a surge tank 4 through an intake branch pipe 3, and the surge tank 4 is connected to an outlet of a compressor 6 c of an exhaust supercharger 6 through an intake duct 5. The inlet of the compressor 6 c is connected to the air cleaner 8 through the intake air introduction pipe 7. An air flow meter 9 configured to detect the amount of intake air is disposed in the intake introduction pipe 7. In the intake duct 5, a cooler 10 configured to cool intake air and a throttle valve 11 are sequentially arranged. The throttle valve 11 is configured to be able to change the amount of fresh air. On the other hand, a carbon dioxide sensor 12 configured to detect the carbon dioxide concentration in the intake air is disposed downstream of the throttle valve 11, for example, the surge tank 4.

  The cylinder 2 a is connected to the inlet of the turbine 6 t of the exhaust supercharger 6 through the exhaust manifold 13. The outlet of the turbine 6 t is connected to the catalyst 15 through the exhaust pipe 14. An air-fuel ratio sensor 16 configured to detect the air-fuel ratio is disposed in the exhaust pipe 14. The surge tank 4 and the exhaust manifold 13 are connected to each other by an exhaust gas recirculation (hereinafter referred to as EGR) passage 17. In the EGR passage 17, an EGR control valve 18 configured to change the carbon dioxide concentration in the intake air by controlling the amount of EGR gas, and a cooler 19 configured to cool the EGR gas, Is placed.

  The crankshaft 20 and the motor generator 21 of the internal combustion engine 1 are connected to the axle 22 so that torque can be transmitted. Specifically, in the embodiment according to the present invention, the crankshaft 20 is connected to the axle 22 via the power split mechanism 23 and the speed reducer 24. On the other hand, the motor generator 21 of the embodiment according to the present invention includes a first motor generator 21a and a second motor generator 21b. The first motor generator 21 a is connected to the axle 22 via the speed reducer 24. Second motor generator 21 b is connected to power split mechanism 23. Therefore, the torque of the internal combustion engine 1 can be transmitted to at least one of the axle 22 and the second motor generator 21b. In another embodiment (not shown), the motor generator 21 comprises a single motor generator.

  The first motor generator 21 a and the second motor generator 21 b are electrically connected to the battery 27 via the inverter 26. A charge amount sensor 28 configured to detect the charge amount of the battery 27 is attached to the battery 27. In FIG. 1, reference numeral 29 denotes a wheel.

  In the embodiment according to the present invention, the motor generator 21 performs a power running operation that functions as an electric motor and increases the torque of the axle 22, and a regenerative operation that functions as a generator and regenerates electric energy from the torque of the axle 22. Configured to be executable. On the other hand, the battery 27 supplies electric energy to the motor generator 21 when the motor generator 21 performs the power running operation, and stores the electric energy regenerated by the motor generator 21 when the motor generator 21 performs the regenerative operation. It is configured. In the embodiment according to the present invention, the first motor generator 21a mainly performs power running operation, and the second motor generator 21b mainly performs regenerative operation.

  FIG. 2 shows in detail an internal combustion engine 1 according to an embodiment of the present invention. Referring to FIG. 2, 30 is a cylinder block, 31 is a cylinder head, 32 is a piston, 33 is a combustion chamber, 34 is an intake port, 35 is an intake valve, 36 is a valve operating mechanism of the intake valve 35, 37 is an exhaust port, Reference numeral 38 denotes an exhaust valve, 39 denotes a valve operating mechanism of the exhaust valve 38, 40 denotes a fuel injection valve arranged almost at the center of the combustion chamber 33, and 41 denotes an ignition plug arranged adjacent to the fuel injection valve 40. The fuel injection valve 40 is configured to be able to change the fuel amount. The spark plug 41 is configured to be able to change the ignition timing.

  Referring again to FIG. 1, the electronic control unit 50 comprises a digital computer and is connected to each other by a bidirectional bus 51, a ROM (Read Only Memory) 52, a RAM (Random Access Memory) 53, a CPU (Microprocessor) 54, An input port 55 and an output port 56 are provided. Output voltages of the air flow meter 9, the carbon dioxide sensor 12, the air-fuel ratio sensor 16, and the charge amount sensor 28 are input to the input port 55 via the corresponding A / D converters 57. Further, a load sensor 60 that generates an output voltage proportional to the amount of depression of the accelerator pedal 59 is connected to the accelerator pedal 59, and the output voltage of the load sensor 60 is input to the input port 55 via the corresponding AD converter 57. The Further, a crank angle sensor 61 that generates an output pulse every time the crankshaft 20 rotates, for example, 30 degrees is connected to the input port 55. The CPU 54 calculates the engine speed based on the output pulse from the crank angle sensor 61. On the other hand, the output port 56 is connected to the fuel injection valve 40 and the spark plug 41 (FIG. 2), the actuator of the throttle valve 11, the EGR control valve 18, the motor generator 21, the power split mechanism 23, Each is connected to an inverter 26.

  The internal combustion engine 1 according to the embodiment of the present invention has two combustion modes: a first combustion mode that performs compression auto-ignition combustion under a lean air-fuel ratio, and a second that performs spark ignition combustion under a substantially stoichiometric air-fuel ratio. It is possible to switch between the combustion modes. In the first combustion mode, for example, fuel injection is performed at the end of the compression stroke, whereby a premixed gas is formed in a part of the combustion chamber 33. This premixed gas is then burned by compression ignition. The air-fuel ratio in this case is a lean air-fuel ratio AFL (for example, 30 to 40) that is leaner than the stoichiometric air-fuel ratio. On the other hand, in the second combustion mode, fuel injection is performed during the intake stroke, whereby a substantially homogeneous premixed gas is formed in the combustion chamber 33. The premixed gas is then ignited by a spark plug 41 and burned by flame propagation. The air-fuel ratio in this case is almost the stoichiometric air-fuel ratio.

  When the first combustion mode is performed, the air-fuel ratio can be made significantly lean, so that the fuel consumption can be reduced. Moreover, since the compression ratio can be increased, the thermal efficiency can be increased. Furthermore, since the combustion temperature is lower than that in the second combustion mode, the generation of NOx can be reduced. Furthermore, since sufficient oxygen is present around the fuel, the generation of unburned HC can be reduced.

  In compression self-ignition combustion, there is a higher possibility of knocking than in spark ignition combustion. Therefore, in the embodiment according to the present invention, the first combustion mode is performed under a relatively large amount of EGR gas, and the second combustion mode is performed under a relatively small amount of EGR gas.

  In the embodiment according to the present invention, as shown in FIG. 3, the first region R1, the second region R2, and the third region R3 are respectively in the engine operating state region determined by the engine torque TQE and the engine speed NE. Partitioned. The first region R1 includes a predetermined lower limit threshold rotational speed NEL, a predetermined upper limit threshold rotational speed NEU, a predetermined lower limit threshold torque TQEL, and a predetermined upper limit threshold torque. Defined by TQEU. The third region R3 is defined by a lower limit threshold rotational speed NEL, an upper limit threshold rotational speed NEU, a second lower limit threshold torque TQEL2, and a lower limit threshold torque TQEL. On the other hand, the second region R2 is a region other than the first region R1 and the third region R3. In the example shown in FIG. 3, the second region R2 is partitioned on the higher torque side and the higher rotation speed side than the first region R1. In FIG. 3, curve TQEF represents the full load.

  In the example shown in FIG. 3, the lower limit threshold rotational speed NEL is set as a constant value that does not depend on the engine torque TQE from the second lower limit threshold torque TQEL2 to the upper limit threshold torque TQEU. Upper limit threshold rotation speed NEU is set as a constant value that does not depend on engine torque TQE from second lower limit threshold torque TQEL2 to upper limit threshold torque TQEU. On the other hand, lower limit threshold torque TQEL is set as a value determined according to engine speed NE from lower limit threshold speed NEL to upper limit threshold speed NEU. Upper limit threshold torque TQEU is set as a value determined according to engine speed NE from lower limit threshold speed NEL to upper limit threshold speed NEU. Further, the second lower limit threshold torque TQEL2 is set as a constant value that does not depend on the engine speed NE from the lower limit threshold speed NEL to the upper limit threshold speed NEU, for example, zero. Lower limit threshold rotation speed NEL, upper limit threshold rotation speed NEU, lower limit threshold torque TQEL, upper limit threshold torque TQEU, and second lower limit threshold torque TQEL2 are stored in advance in ROM 52, respectively.

  In one example, line segments (NEL, NEU, TQEL, TQEU) that divide the first region R1 belong to the first region R1. In another example, the line segment (NEL, NEU, TQEL, TQEU) that divides the first region R1 belongs to the second region R2 or the third region R3 adjacent to the first region R1. In one example, line segments (NEL, NEU, TQEL2, TQEU) that divide the third region R3 belong to the third region R3. In another example, the line segment (NEL, NEU, TQEL2, TQEU) that divides the third region R3 belongs to the first region R1 or the second region R2 adjacent to the third region R3.

  In the embodiment according to the present invention, when the engine operating state in the steady state belongs to the first region R1, the combustion mode of the internal combustion engine 1 is set to the first combustion mode, and the engine operating state belongs to the second region R2. Sometimes the combustion mode of the internal combustion engine 1 is set to the second combustion mode. Further, in the embodiment according to the present invention, when the engine operating state in the steady state belongs to the third region R3, the combustion mode of the internal combustion engine 1 is different from the first combustion mode and the second combustion mode. The combustion mode is In the third combustion mode, for example, compression auto-ignition combustion is performed under a relatively small amount of EGR gas and lean air-fuel ratio. Since the third region R3 has a lower engine torque TQE than the first region R1, knocking is less likely to occur. For this reason, the third combustion mode is executed under a relatively small amount of EGR gas. In another example, spark ignition combustion is performed under a lean air-fuel ratio.

  Therefore, in general terms, the electronic control unit 50 switches the combustion mode of the internal combustion engine 1 between the first combustion mode, the second combustion mode, and the third combustion mode according to the engine operating state. It is said that it is configured. Further, the electronic control unit 50 is configured to switch the combustion mode of the internal combustion engine 1 between the first combustion mode and the second combustion mode in accordance with the engine operating state.

  When the combustion mode is the first combustion mode, for example, if the engine required torque exceeds the upper limit threshold torque TQEU, the combustion mode is switched to the second combustion mode. In the embodiment according to the present invention, as described above, the first combustion mode is performed under the lean air-fuel ratio, and the second combustion mode is performed substantially under the stoichiometric air-fuel ratio. The first combustion mode is performed under a relatively large amount of EGR gas, and the second combustion mode is performed under a relatively small amount of EGR gas. Therefore, in the engine operating state where the combustion mode should be switched from the first combustion mode to the second combustion mode, the target value of the new air amount in the second combustion mode is greater than the target value of the new amount in the first combustion mode. And the target value of the intake carbon dioxide concentration in the second combustion mode is lower than the target value of the intake carbon dioxide concentration in the first combustion mode.

  For this reason, in order to switch the combustion mode from the first combustion mode to the second combustion mode, it is necessary to significantly reduce the amount of fresh air and greatly reduce the intake carbon dioxide concentration. However, even if the opening degree of the throttle valve 11 is reduced stepwise, the fresh air amount may not immediately decrease stepwise. Further, even if the opening degree of the EGR control valve 18 is decreased in a stepped manner, the EGR gas amount or the intake carbon dioxide concentration may not be immediately decreased in a stepped manner. For this reason, there is a possibility that combustion is performed in a state where the fresh air amount and the intake carbon dioxide concentration deviate from the target amounts. As a result, combustion fluctuations and emissions may be deteriorated.

  Therefore, in the embodiment according to the present invention, the combustion mode of the internal combustion engine 1 is switched from the first combustion mode to the second combustion mode as follows. That is, in the embodiment according to the present invention, first, when the combustion mode of the internal combustion engine 1 is the first combustion mode, it is determined whether or not the combustion mode should be switched to the second combustion mode. In the embodiment according to the present invention, it is determined that the combustion mode should be switched to the second combustion mode when the increase rate dOPET of the engine required output OPET is higher than a predetermined set rate dOPETX, and otherwise the combustion mode is changed to the combustion mode. It is determined that the first combustion mode should be maintained. In other words, when the rapid acceleration operation is performed when the combustion mode of the internal combustion engine 1 is the first combustion mode, it is determined that the combustion mode should be switched to the second combustion mode.

  FIG. 4 shows an example of the set rate dOPETX. In the example shown in FIG. 4, the set rate dOPETX decreases as the engine request output OPET increases from the engine request output OPETL corresponding to the lower limit threshold torque TQEL to the engine request output OPETU corresponding to the upper limit threshold torque TQEU. Become. In FIG. 4, dOPEM indicates the maximum required engine output increase rate dOPET that the internal combustion engine 1 can take. Therefore, in other words, the operating point determined by the engine required output OPET and the engine required output increase rate dOPET belongs to the region RX defined by the set rate dOPETX, the engine required output increase rate maximum value dOPETM, and the engine required outputs OPETL, OPETU. When it is determined that the combustion mode should be switched from the first combustion mode to the second combustion mode, and the operating point does not belong to the region RX, the combustion mode is changed from the first combustion mode to the second combustion mode. It is determined that switching should not be performed. Note that the set rate dOPETX and the engine request outputs OPETL and OPETU are stored in the ROM 52 in advance.

  Combustion mode When it is determined that the first combustion mode should be switched to the second combustion mode, it is then determined whether or not the charge amount of the battery 27 is larger than a predetermined set amount. In the embodiment according to the present invention, when the SOC of the battery 27 (for example, the remaining charge of the battery with respect to the full charge capacity of the battery) is larger than a predetermined lower limit SOCL, the charge amount of the battery 27 is the power running of the motor generator 21. It is determined that the battery 27 is sufficient for operation. When the SOC is equal to or lower than the lower limit SOCL, it is determined that the charge amount of the battery 27 is insufficient for the power running operation of the motor generator 21. FIG. 5 shows an example of the lower limit value SOCL. Lower limit value SOCL increases as engine request output OPET increases from engine request output OPETL corresponding to lower limit threshold torque TQEL to engine request output OPETU corresponding to upper limit threshold torque TQEU. The lower limit SOCL is stored in the ROM 52 in advance.

  When it is determined that the charge amount of the battery 27 is sufficient for the power running operation of the motor generator 21, the first switching is performed to switch the combustion mode of the internal combustion engine 1 from the first combustion mode to the second combustion mode. Control is performed. Next, the first switching control will be described with reference to FIG.

  In FIG. 6, the engine output OPE, the air-fuel ratio AF, the fresh air amount QAE, the intake carbon dioxide concentration CCO2, and the ignition timing θ in the first switching control are indicated by solid lines. In FIG. 6, the broken lines indicate the air-fuel ratio AF, the fresh air amount QAE, the intake carbon dioxide concentration CCO2 when the second combustion mode is started at the time ta1 and the engine operation is in a steady state, and Each target value of the ignition timing θ is shown. The dotted line indicates the ignition timing θTS necessary for eliminating the torque step when it is assumed that the second combustion mode is started at time ta1.

  Referring to FIG. 6, time ta1 indicates the time when the first switching control should be started. In the first switching control, even if it is determined that the combustion mode should be switched, the second combustion mode is not immediately started and the first combustion mode is continued. In this case, the air-fuel ratio AF is maintained at a relatively large lean air-fuel ratio AFL. On the other hand, at time ta1, the throttle opening is reduced. As a result, the fresh air amount QAE gradually decreases. Further, at the time ta1, the opening degree of the EGR control valve 18 is reduced. As a result, the intake carbon dioxide concentration CCO2 decreases with a delay. In addition, since the first combustion mode, that is, the compression ignition combustion is continued, the ignition action of the spark plug 41 is not performed.

  Next, when the intake carbon dioxide concentration CCO2 becomes lower than a predetermined set value CCO2X at time ta2, the combustion mode is switched to the second combustion mode. That is, the air-fuel ratio AF is reduced to the stoichiometric air-fuel ratio AFS in steps. Further, the ignition action of the spark plug 41 is started. In this case, the ignition timing θ is set on the retard side with respect to the target value (broken line).

  Thereafter, transient control is performed to bring the fresh air amount QAE, the intake carbon dioxide concentration CCO2, and the ignition timing θ closer to their respective targets (broken lines). Next, at time ta3, when the fresh air amount QAE, the intake carbon dioxide concentration CCO2, and the ignition timing θ coincide with the respective target values, the transient control is terminated, that is, the first switching control is terminated. Thereafter, the normal second combustion mode is performed.

  On the other hand, as shown in FIG. 6, when the air-fuel ratio AF, the fresh air amount QAE, and the intake carbon dioxide concentration CCO2 are controlled as described above, the output OPE of the internal combustion engine 1 temporarily changes with respect to the engine required output OPET. Shortage. The shortage at this time is indicated by SH in FIG. In the first switching control, the shortage SH is compensated by the power running operation of the motor generator 21. Therefore, the engine required output OPET is maintained, and good drivability is ensured. In addition, the above-mentioned lower limit SOCL is set so that the power running operation at this time is possible.

  FIG. 7 shows the relationship between the operating point determined by the ignition timing θ and the intake carbon dioxide concentration CCO2 and various limits in the second combustion mode. In FIG. 7, KN indicates a knocking limit. That is, knocking occurs when the ignition timing θ is more advanced than the knocking limit KN or when the intake carbon dioxide concentration CCO2 is lower than the knocking limit KN. In FIG. 7, CF indicates a combustion fluctuation limit. That is, if the ignition timing θ is on the retard side with respect to the combustion fluctuation limit CF, or if the intake carbon dioxide concentration CCO2 is higher than the combustion fluctuation limit CF, the combustion fluctuation deteriorates beyond an allowable level. Further, in FIG. 7, MF indicates a misfire limit. That is, misfiring occurs when the ignition timing θ is retarded from the misfire limit MF or when the intake carbon dioxide concentration CCO2 is higher than the misfire limit MF. Accordingly, in FIG. 7, a region RD <b> 2 with dots represents a region where good combustion is obtained when the second combustion mode is performed.

  A1 shown in FIG. 6 indicates an operating point determined by the ignition timing θ and the intake carbon dioxide concentration CCO2 when it is assumed that the second combustion mode is started at the time ta1. This operating point A1 is outside the region RD2 in FIG. Therefore, in the first switching control, the second combustion mode is not performed at the operating point A1. On the other hand, A2 shown in FIG. 6 indicates an operating point in the first switching control at time ta2. The operating point A2 belongs to the region RD2 in FIG. Further, A3 shown in FIG. 6 indicates an operating point in the first switching control at time ta3. The operating point A3 also belongs to the region RD2 in FIG. Therefore, good combustion is obtained at the operating points A2 and A3.

  As described above, in the first switching control, the second combustion mode is started in a state where the fresh air amount QAE is reduced, and at this time, the ignition timing θ is retarded, so that the torque fluctuation at the time of switching the combustion mode Is reduced. At the same time, knocking is avoided, combustion fluctuations are suppressed, and misfires are avoided. Moreover, since the air-fuel ratio AF is not changed between the lean air-fuel ratio AFL and the stoichiometric air-fuel ratio AFS, the generation of NOx is limited. Therefore, the first switching control can ensure good combustion while limiting the torque fluctuation when switching the combustion mode.

  On the other hand, when it is determined that the charge amount of the battery 27 is insufficient for the power running operation of the motor generator 21, the first combustion mode is switched from the first combustion mode to the second combustion mode. 2 switching control is performed. Next, the second switching control will be described with reference to FIG.

  In FIG. 8, the engine output OPE, the air-fuel ratio AF, the fresh air amount QAE, the intake carbon dioxide concentration CCO2, and the ignition timing θ in the second switching control are shown by solid lines. In FIG. 8, broken lines indicate the air-fuel ratio AF, the fresh air amount QAE, the intake carbon dioxide concentration CCO2, and the intake air carbon dioxide concentration CCO2 when the second combustion mode is started at the time tb1 and the engine operation is in a steady state. Each target value of the ignition timing θ is shown.

  Referring to FIG. 8, time tb1 indicates the time when the second switching control should be started. In the second switching control, even if it is determined that the combustion mode should be switched, the second combustion mode is not immediately started and the first combustion mode is continued. In this case, at time tb1, the air-fuel ratio AF is gradually decreased from the lean air-fuel ratio AFL within the range of the lean air-fuel ratio, that is, within the range smaller than the lean air-fuel ratio AFL and larger than the theoretical air-fuel ratio. Further, at time tb1, the throttle opening is reduced. As a result, the fresh air amount QAE gradually decreases. At time tb1, the opening degree of the EGR control valve 18 is reduced. As a result, the intake carbon dioxide concentration CCO2 decreases with a delay. That is, after the time tb1, the intake carbon dioxide concentration CCO2 is substantially maintained for a while. In addition, since the first combustion mode, that is, the compression ignition combustion is continued, the ignition action of the spark plug 41 is not performed.

  Next, when the intake carbon dioxide concentration CCO2 starts to decrease at time tb2, the combustion mode is switched to the second combustion mode. That is, the air-fuel ratio AF is reduced to the stoichiometric air-fuel ratio AFS in steps. Further, the ignition action of the spark plug 41 is started. In this case, the ignition timing θ is set to the advance side with respect to the target value (broken line).

  Thereafter, transient control is performed to bring the fresh air amount QAE, the intake carbon dioxide concentration CCO2, and the ignition timing θ closer to their respective targets (broken lines). Next, at time tb3, when the fresh air amount QAE, the intake carbon dioxide concentration CCO2, and the ignition timing θ coincide with the respective target values, the transient control is terminated, that is, the second switching control is terminated. Thereafter, the normal second combustion mode is performed.

  On the other hand, as shown in FIG. 8, when the air-fuel ratio AF, the fresh air amount QAE, and the intake carbon dioxide concentration CCO2 are controlled as described above, the output OPE of the internal combustion engine 1 temporarily changes with respect to the engine required output OPET. Become excessive. The excess at this time is indicated by EX in FIG. In the second switching control, this excess EX is absorbed by the regenerative operation of the motor generator 21. Therefore, the engine required output OPET is maintained, and good drivability is ensured. The lower limit SOCL described above is set so that the battery 27 can store the electric energy regenerated by the regenerative operation at this time.

  FIG. 9 is a view similar to FIG. 7 showing the relationship between the operating point determined by the ignition timing θ and the intake carbon dioxide concentration CCO2 and various limits in the second combustion mode. In FIG. 9, KN is a knocking limit, CF is a combustion fluctuation limit, MF is a misfire limit, and a region RD2 with dots is a region where good combustion is obtained when the second combustion mode is performed. , Respectively.

  B1 shown in FIG. 8 indicates an operating point in the second switching control at time tb2. The operating point B1 belongs to the region RD2 in FIG. Further, B2 shown in FIG. 8 indicates an operating point in the second switching control at time tb2. The operating point B2 also belongs to the region RD2 in FIG. Therefore, good combustion is obtained at the operating points B1 and B2.

  Thus, in the second switching control, the second combustion mode is started in a state where the fresh air amount QAE is reduced, so that torque fluctuation at the time of switching the combustion mode is reduced. In addition, since the engine output OPE is temporarily increased when the combustion mode is switched, the request for retarding the ignition timing θ is relaxed. Further, since the fresh air amount QAE is reduced, the retarding requirement of the ignition timing θ from knocking and torque fluctuation suppression is relaxed. As a result, knocking is avoided, combustion fluctuation is suppressed, and misfire is avoided. Furthermore, since the compression self-ignition combustion is continued while the intake carbon dioxide concentration CCO2 is maintained, misfire is avoided. Further, by continuing the compression auto-ignition combustion, the increase in generation of NOx due to the change of the air-fuel ratio AF between the lean air-fuel ratio AFL and the stoichiometric air-fuel ratio AFS is limited. Therefore, the second switching control can ensure good combustion while limiting the torque fluctuation when switching the combustion mode.

  If the second switching control is performed when the charge amount of the battery 27 is relatively large, the electric energy regenerated by the regenerative operation in the second switching control may not be stored in the battery 27. In this case, the excess EX of the engine output OPE may not be sufficiently absorbed. In addition, if the first switching control is performed when the charge amount of the battery 27 is relatively small, the battery 27 may not be able to supply electric energy necessary for performing the power running operation in the first switching control. In this case, the shortage SH of the engine output OPE may not be sufficiently compensated. On the other hand, in the embodiment according to the present invention, the first switching control is performed when the charging amount of the battery 27 is relatively large, and the second switching control is performed when the charging amount of the battery 27 is relatively small. . Therefore, the engine output OPE can be reliably maintained at the engine required output OPET regardless of the charge amount of the battery 27.

Therefore, conceptually, the electronic control unit 50 is configured to switch the combustion mode from the first combustion mode to the second combustion mode when the charge amount of the battery 27 is larger than a predetermined set amount. The air-fuel ratio AF is maintained, the fresh air amount QAE is decreased, and the intake carbon dioxide concentration CCO2 is decreased, so that the output OPE of the internal combustion engine 1 is temporarily insufficient with respect to the engine required output OPET. The second combustion mode is started by changing the fuel ratio AF substantially to the stoichiometric air-fuel ratio AFS and starting spark ignition combustion. At this time, the temporary shortage SH of the output OPE of the internal combustion engine 1 is reduced to the motor. It is compensated by the power running operation of the generator 21,
When the combustion mode is to be switched from the first combustion mode to the second combustion mode when the charge amount of the battery 27 is smaller than the set amount, the air-fuel ratio AF is reduced within the range of the lean air-fuel ratio, and the fresh air amount QAE And the intake carbon dioxide concentration CCO2 is substantially maintained, so that the output OPE of the internal combustion engine 1 temporarily exceeds the engine required output OPET, and then the air-fuel ratio AF is substantially equal to the stoichiometric air-fuel ratio AFS. The second combustion mode is started by changing to a step shape and starting spark ignition combustion, and the temporary excess EX of the output OPE of the internal combustion engine 1 at this time is absorbed by the regenerative operation of the motor generator 21. It is configured as follows.

  FIG. 10 shows a routine for executing the combustion mode switching control of the embodiment according to the present invention. Referring to FIG. 10, in step 100 (FIG. 10), the engine required load is acquired. The engine required load is calculated based on the amount of depression of the accelerator pedal 59, for example. In the subsequent step 101, the engine required output OPET is calculated based on the engine required load. In the following step 102, it is determined whether or not the combustion mode of the internal combustion engine 1 should be switched from the first combustion mode to the second combustion mode. That is, it is determined whether or not the operating point determined by the engine required output OPET and the engine required output increase rate dOPET belongs to the region RX shown in FIG. When the combustion mode should not be switched, the processing cycle is terminated. When the combustion mode should be switched, the routine proceeds to step 103 where the SOC of the battery 27 is acquired. In the following step 104, the lower limit SOCL is calculated using the map of FIG. In the following step 105, it is determined whether or not the SOC of the battery 27 is larger than the lower limit value SOCL. When SOC> SOCL, the routine proceeds to step 106 where the first switching control is executed. A routine for executing the first switching control is shown in FIG. On the other hand, when SOC ≦ SOCL, the routine proceeds to step 107 where second switching control is executed. A routine for executing the second switching control is shown in FIG.

  Referring to FIG. 11 showing a routine for executing the first switching control, in step 110, the fresh air amount QAE is decreased, and the intake carbon dioxide concentration CCO2 is decreased. In the following step 111, it is determined whether or not the intake carbon dioxide concentration CCO2 is lower than the set value CCO2X. When CCO2 ≧ CCO2X, the routine proceeds to step 112 where the motor generator 21 is powered to compensate for the shortage SH of the engine output OPE. In the following step 113, it is determined whether or not the control parameters such as the fresh air amount QAE, the intake carbon dioxide concentration CCO2, and the ignition timing θ match the target values of the second combustion mode. When the control parameter does not match the target value, the process returns to step 111. Next, when CCO2 <CCO2X, the routine proceeds from step 111 to step 114, where the second combustion mode is started. In other words, the air-fuel ratio AF is substantially made the stoichiometric air-fuel ratio, and spark ignition combustion is performed. In the following step 115, the above-described transient control is performed. Next, the routine proceeds to step 112 where the power running operation of the motor generator 21 is performed. Next, the process proceeds to step 113, and when the control parameter does not match the target value, the process returns to step 111, and when it matches, the processing cycle is ended. That is, the first switching control is terminated.

  Referring to FIG. 12 showing a routine for executing the second switching control, in step 120, the air-fuel ratio AF is decreased, the fresh air amount QAE is decreased, and the intake carbon dioxide concentration CCO2 is decreased. In the following step 121, it is determined whether or not the intake carbon dioxide concentration CCO2 has started to decrease. When the intake carbon dioxide concentration CCO2 is substantially maintained, the routine proceeds to step 122, where the motor generator 21 is regenerated to absorb the excess EX of the engine output OPE. In the following step 123, it is determined whether or not the control parameter matches each target value in the second combustion mode. When the control parameter does not match the target value, the process returns to step 121. Next, when the intake carbon dioxide concentration CCO2 starts to decrease, the process proceeds from step 121 to step 124, and the second combustion mode is started. In other words, the air-fuel ratio AF is substantially made the stoichiometric air-fuel ratio, and spark ignition combustion is performed. In the subsequent step 125, the above-described transient control is performed. Next, the routine proceeds to step 122 where the regenerative operation of the motor generator 21 is performed. Next, the process proceeds to step 123. When the control parameter does not match the target value, the process returns to step 121, and when it matches, the processing cycle is ended. That is, the second switching control is terminated.

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 11 Throttle valve 17 EGR passage 18 EGR control valve 21 Motor generator 22 Axle 27 Battery 41 Spark plug 50 Electronic control unit

Claims (1)

An internal combustion engine connected to an axle so as to be able to transmit torque, and an EGR passage that connects an engine intake passage and an engine exhaust passage downstream of a throttle valve, and an EGR gas amount disposed in the EGR passage by changing the amount of EGR gas An EGR control valve configured to be able to change the intake carbon dioxide concentration, and the combustion mode is set to a first combustion mode in which compression auto-ignition combustion is performed under a lean air-fuel ratio, and to a substantially stoichiometric air-fuel ratio. An internal combustion engine configured to be switchable between a second combustion mode in which spark ignition combustion is performed, and
A motor generator coupled to the axle so as to be able to transmit torque, wherein the motor generator is configured to execute a power running operation for increasing the torque of the axle and a regenerative operation for regenerating electric energy from the torque of the axle. When,
The motor generator is configured to supply electric energy to the motor generator when the power running operation is performed, and to store the electric energy regenerated by the motor generator when the motor generator performs the regenerative operation. Battery,
An electronic control unit configured to switch a combustion mode of the internal combustion engine between the first combustion mode and the second combustion mode according to an engine operating state;
With
In the engine operating state where the combustion mode should be switched from the first combustion mode to the second combustion mode, the target value of the new air amount in the second combustion mode is the new amount in the first combustion mode. Less than the target value, and the target value of the intake carbon dioxide concentration in the second combustion mode is lower than the target value of the intake carbon dioxide concentration in the first combustion mode,
The electronic control unit further includes
If the combustion mode should be switched from the first combustion mode to the second combustion mode when the charge amount of the battery is larger than a predetermined set amount, the air-fuel ratio is maintained and the fresh air amount is reduced. Then, the intake carbon dioxide concentration is lowered, so that the output of the internal combustion engine is temporarily insufficient with respect to the engine required output, and then the air-fuel ratio is changed stepwise to the theoretical air-fuel ratio and spark ignition combustion is performed. The second combustion mode is started by starting the operation, and a temporary shortage of the output of the internal combustion engine at this time is compensated by the power running operation of the motor generator,
When the combustion mode is to be switched from the first combustion mode to the second combustion mode when the charge amount of the battery is smaller than the set amount, the air-fuel ratio is reduced within the range of the lean air-fuel ratio, and a new The air volume is reduced and the intake carbon dioxide concentration is substantially maintained, so that the output of the internal combustion engine temporarily exceeds the required engine output, and then the air-fuel ratio is stepped substantially to the stoichiometric air-fuel ratio. The second combustion mode is started by changing and starting spark ignition combustion, and a temporary excess of the output of the internal combustion engine at this time is absorbed by the regenerative operation of the motor generator,
A vehicle control device configured as described above.

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