Control device and control method for an internal combustion engine

Abstract

Control device (500) for an internal combustion engine (10), comprising: a power acquisition unit (503) configured to achieve a required torque and operating state of the internal combustion engine; and a control unit (501, P1) configured to control the operation of the internal combustion engine using a required amount of air, a required amount of fuel and a required ignition timing, wherein the control unit is configured such that it: a target air-fuel ratio of an air system is determined according to the achieved required torque and the achieved operating condition; The required amount of air is obtained using the target air-fuel ratio of the air system; performs a torque fluctuation correction on the target air-fuel ratio of the air system to determine a target air-fuel ratio of an injection system in order to reduce a difference between the required torque and an actual torque when a combustion state of the internal combustion engine is in a transition phase between stoichiometric combustion and lean combustion; the target air-fuel ratio of the injection system is determined using the target air-fuel ratio of the air system when the combustion state is not in the transition phase; and The required amount of fuel and the required ignition timing are obtained using the specified target air-fuel ratio of the air system and the specified target air-fuel ratio of the injection system.

Description

Technical area

[0001] The present disclosure relates to a control technology for an internal combustion engine. General state of the art

[0002] A technology is known that continuously changes a target air-fuel ratio to suppress torque fluctuations that occur when an operating state of an internal combustion engine is switched between stoichiometric combustion and lean combustion (for example, JP 2016-138497 A).

[0003] It should be noted that even in a case where the target air-fuel ratio is continuously changed, a response delay occurs in the change in the actual air quantity. Therefore, in a transient phase where the combustion state is switched, the change in the target air-fuel ratio becomes relatively large, so that the change in the actual air quantity may not follow the target air-fuel ratio, and torque fluctuations may occur. Furthermore, in a case where the air-fuel ratio is continuously changed, there is a problem that the configuration must use an air-fuel ratio range where the catalyst performance cannot be maintained.

[0004] Therefore, it is desirable to reduce or eliminate the influence of the delay in response to the change in the actual air quantity and to suppress or limit the torque fluctuation in the transition phase between stoichiometric combustion and lean combustion.

[0005] Furthermore, DE 10 2006 015 264 A1 discloses a method for controlling an internal combustion engine of a vehicle, in particular a direct-injection gasoline engine, with a mixture control system in which an air-fuel mixture can be adjusted to a predetermined target lambda value by changing the fuel quantity and / or the air quantity, with a measuring device for measuring the air-fuel ratio, with a fuel metering device, and with an air-flow measuring device. The disclosed method comprises determining an actual lambda and a deviation of the actual lambda from the target lambda, as well as regulating the mixture control until the deviation of the actual lambda is compensated. The deviation is compensated by proportionally correcting the air quantity and the fuel quantity. Summary of the invention

[0006] The present disclosure may be implemented as the following aspects.

[0007] A first aspect provides a control device for an internal combustion engine. A control device for an internal combustion engine according to the first aspect includes an acquisition unit configured to acquire a required torque and an operating state of the internal combustion engine; and a control unit configured to control an operation of the internal combustion engine using a required air quantity, a required fuel quantity, and a required ignition timing. The control unit is configured to: determine a target air-fuel ratio of an air system according to the acquired required torque and the acquired operating state; acquire the required air quantity using the target air-fuel ratio of the air system;performs torque fluctuation correction on the target air-fuel ratio of the air system to determine a target air-fuel ratio of an injection system to reduce a difference between the required torque and an actual torque when a combustion state of the internal combustion engine is in a transition phase between stoichiometric combustion and lean combustion; determines the target air-fuel ratio of the injection system using the target air-fuel ratio of the air system when the combustion state is not in the transition phase; and obtains the required fuel quantity and the required ignition timing using the determined air-fuel ratio of the air system and the determined target air-fuel ratio of the injection system.

[0008] The control unit for an internal combustion engine according to the first aspect makes it possible to reduce or eliminate an influence of a delay in response to a change in the actual air amount and to suppress or restrict a torque fluctuation in a transition phase between stoichiometric combustion and lean combustion.

[0009] A second aspect provides a method for controlling an internal combustion engine. The method for controlling the internal combustion engine according to the second aspect includes: obtaining a required torque and an operating state of the internal combustion engine; determining a target air-fuel ratio of an air system according to the obtained required torque and the obtained operating state; obtaining the required air quantity using the target air-fuel ratio of the air system; performing torque fluctuation correction on the target air-fuel ratio of the air system to determine a target air-fuel ratio of an injection system to reduce a difference between the required torque and an actual torque when a combustion state of the internal combustion engine is in a transition phase between stoichiometric combustion and lean combustion;Determining the target air-fuel ratio of the injection system using the target air-fuel ratio of the air system when the combustion state is not in the transition phase; and obtaining the required fuel quantity and the required ignition timing using the determined air-fuel ratio of the air system and the determined target air-fuel ratio of the injection system.

[0010] The method for controlling the internal combustion engine according to the second aspect makes it possible to reduce or eliminate the influence of a delay in response to a change in the actual air quantity and to suppress or restrict torque fluctuation in a transition phase between stoichiometric combustion and lean combustion. The present disclosure may also be implemented as a control program for the internal combustion engine or a computer-readable storage medium storing the program.

[0011] Advantageous further developments of the invention are the subject of the subclaims. Short description of the figures

[0012] The above and other objects, features, and advantages of the present disclosure will become more apparent from the following detailed description made with reference to the accompanying drawings. In the drawings: Fig. 1 is an explanatory diagram showing a control device for an internal combustion engine according to a first embodiment and showing an outline of the internal combustion engine to which the control device is applied; Fig. 2 is a block diagram showing a functional configuration of the control device for the internal combustion engine according to the first embodiment; Fig. 3 is a flowchart showing a processing routine of a control process executed by the control device of the internal combustion engine according to the first embodiment to determine a required air amount, a required fuel amount, and a required ignition timing; Fig. 4 is a flowchart showing a processing routine of an internal combustion engine control process executed by the internal combustion engine control device according to the first embodiment; Fig. 5 is a time chart showing temporal changes of various parameters when a combustion state of the internal combustion engine changes from lean combustion to stoichiometric combustion; Fig. 6 is an example of a map showing a relationship between a torque ratio and a target air-fuel ratio of the injection system in a transition phase; Fig. 7 is an example of a map showing a relationship between required torque and a target air-fuel ratio of an air system; Fig. 8 is an example of a map showing a relationship between the required torque and a required air quantity; Fig. 9 is an example of a map showing a relationship between the target air-fuel ratio of the air system and a torque efficiency; Fig. 10 is a time chart showing temporal changes of various parameters when the combustion state of the internal combustion engine changes from stoichiometric combustion to lean combustion; Fig. 11 is an example of a map showing a relationship between the torque ratio and the target air-fuel ratio of the injection system in a transient phase; Fig. 12 is a timing chart showing injection control, torque control, and ignition control in each cylinder of the internal combustion engine; and Fig. 13 is an explanatory diagram showing a relationship between an EGR rate and an air-fuel ratio. Description of embodiments

[0013] A control apparatus for an internal combustion engine and a control method for the internal combustion engine according to the present disclosure will be described below according to embodiments. First embodiment:

[0014] As in the Fig. 1 and Fig. 2, an internal combustion engine 10 to which an internal combustion engine control device 500 according to a first embodiment is applied includes a cylinder block 11, a cylinder head 12, a piston 13, and a crankcase 14. The internal combustion engine 10 is a so-called gasoline engine that uses gasoline as fuel and burns an air-fuel mixture with spark ignition. The cylinder block 11 has a plurality of tubular cylinders 111 and pistons 13 respectively inserted into the cylinders 111. A combustion chamber 15 is defined by the cylinder 111, the cylinder head 12, and an upper surface of the piston 13. The cylinder head 12 is mounted on an upper surface of the cylinder block 11. A crankcase 14 is arranged on the lower surface of the cylinder block 11. A crankcase 14A is provided with a crankshaft 141 and a crank angle sensor 21, which are shown by a hidden line.The underside of the cylinder block 11 is located on the side where the crankshaft 141 is located in the internal combustion engine 10. The top side of the cylinder block 11 is located on the side where the crankshaft 141 is not located and where a camshaft (not shown) is arranged to drive cams 172 and 182.

[0015] The cylinder head 12 has an intake port 17, which corresponds to an intake passage for introducing intake air into the cylinder 111, and an exhaust port 18, which corresponds to an exhaust passage for discharging exhaust gas from the cylinder 111. An intake valve 171, which is opened and closed with the cam 172, is provided at the intake port. An exhaust valve 181, which is opened and closed with the cam 182, is provided at the exhaust port 18. At least one of the intake valve 171 and the exhaust valve 181 may be provided with a variable valve mechanism that changes the valve opening timing and a valve closing timing, as well as the valve lift amount.

[0016] An injector 31 and a spark plug 32 are provided between the intake port 17 and the exhaust port 18 in the cylinder head 12. The injector 31, i.e., the fuel injection device, causes an actuator, such as a solenoid or a piezo element, to drive a piston in response to a control signal input from the control device 500 to inject fuel, such as gasoline, from one or more injection holes. The injector 31 is a direct injection type injector that injects fuel directly into the combustion chamber 15 from the injection hole exposed in the combustion chamber 15. The injector 31 is configured to supply fuel into the combustion chamber 15 regardless of the valve opening timing of the intake valve 171. The injector 31 may be a port injection type injector which is arranged in an intake manifold 40 and injects fuel toward the intake port 17.The spark plug 32 has a ground electrode and a center electrode, which correspond to spark-ignition portions exposed in the combustion chamber 15. The spark plug 32 is energized with a high voltage from a direct ignition coil in response to an ignition control signal input from the control device 500. Consequently, the spark plug 32 generates a spark between the ground electrode and the center electrode, causing spark ignition of the fuel.

[0017] Intake air is supplied to the intake passage 17 via the intake manifold 40, and exhaust gas is discharged from the exhaust passage 18 via an exhaust manifold 41. One end of the intake manifold 40 is connected to the intake passage 17, and the other end of the intake manifold 40 is connected to the compressor side of a turbocharger 19. A throttle valve 33 is provided at one end of the intake manifold 40, and an air flow meter 22 is provided at the other end of the intake manifold 40. The throttle valve 33 is provided with, for example, an electric motor as an actuator for adjusting a valve opening degree. One end of an exhaust manifold 41 is connected to the exhaust passage 18, and the other end of the exhaust manifold 41 is connected to a turbine side of the turbocharger 19. The compressor side of the turbocharger 19 is connected to the atmosphere via an air filter (not shown). The turbine side of the turbocharger 19 is connected to the atmosphere via an exhaust pipe 411.An air-fuel ratio sensor 23 and an exhaust catalyst (not shown) are provided at the exhaust pipe 411. A wastegate line 412 and a wastegate valve 34 are provided on the turbine side of the turbocharger 19. The wastegate line 412 is designed to redirect exhaust gas drawn into the turbocharger 19 to the exhaust pipe 411. The wastegate valve 34 serves to control the amount of exhaust gas flowing through the wastegate line 412. The throttle valve 33 is provided with, for example, an electric motor as an actuator for adjusting a valve opening degree.

[0018] The intake manifold 40 and the exhaust manifold 41 are connected to each other via an exhaust gas recirculation (EGR) line 42. An EGR valve 35 is provided in the EGR line 42 to control the amount of exhaust gas flowing through the EGR line 42.

[0019] As in Fig. As shown in Fig. 2, the internal combustion engine control device 500 according to the first embodiment includes a central processing unit (CPU) 501, a memory 502, an input and output interface 503, and an internal bus 504. The CPU 501, the memory 502, and the input and output interface 503 are connected to each other via the internal bus 504 to enable bidirectional communication with each other. The memory 502 includes a memory such as a ROM that stores an internal combustion engine control program P1 for controlling the operating state of the internal combustion engine 10 and various maps Ma in a non-volatile and write-protected manner. The memory 502 includes a memory such as a RAM that is configured to be read and written by the CPU 501.

[0020] The CPU 501 serves as a control unit. The CPU 501 develops and executes the internal combustion engine control program P1, which is stored in the memory 502 in a readable and writable memory. The CPU 501 can correspond to a single CPU, multiple CPUs executing corresponding programs, or a multitasking CPU configured to execute multiple programs simultaneously.

[0021] The input and output interface 503 serves as an acquisition unit. The input and output interface 503 is connected to the crank angle sensor 21, the air flow meter 22, the air-fuel ratio sensor 23, and an accelerator opening sensor 24 via detection signal lines, respectively. The input and output interface 503 is connected to the injector 31, the spark plug 32, the throttle valve 33, and the wastegate valve 34 via control signal lines, respectively. The input and output interface 503 receives detection signals from the crank angle sensor 21, the air flow meter 22, the air-fuel ratio sensor 23, and the accelerator opening sensor 24. The input and output interface 503 outputs control signals, such as an injection signal, an ignition signal, and an opening signal, to the injector 31, the spark plug 32, the throttle valve 33, and the wastegate valve 34.

[0022] The crank angle sensor 21 corresponds to, for example, a magnetic-electric conversion device using a Hall IC, and corresponds to a sensor for detecting the rotational speed of the crankshaft 141, that is, the engine speed, and the rotation angle of the crankshaft 141. The rotation angle of the crankshaft 141 is used to detect the position of the piston 13 in the cylinder 111 to control the injection timing of the injector 31 and control the ignition timing of the spark plug 32.

[0023] The air flow meter 22 corresponds to a sensor, such as a hot-wire sensor or a Karman vortex sensor, for detecting the intake air quantity. Note that, instead of the air flow meter 22, an intake air pressure sensor for detecting a pressure of the intake air drawn into the intake manifold 40 may be used to detect the intake air quantity.

[0024] The air-fuel ratio sensor 23 corresponds to a sensor which detects an oxygen concentration contained in the exhaust gas and outputs a current value corresponding to the air-fuel ratio of an air-fuel mixture fed into the internal combustion engine 10.

[0025] The accelerator opening sensor 24 corresponds to a sensor that detects the degree of depression of an accelerator pedal, i.e., the accelerator opening degree. A driver's required torque for the internal combustion engine 10 can be obtained using the detected accelerator opening degree and a predetermined correspondence between the accelerator opening degree and the required torque. Each of the aforementioned sensors is a sensor for detecting the operating state of the internal combustion engine 10. The operating state of the internal combustion engine 10 is determined using the detection signal.

[0026] A control system 50 of the internal combustion engine includes the internal combustion engine control device 500 according to the first embodiment, the actuators including the injector 31 for controlling the operating state of the internal combustion engine 10, and sensors including the crank angle sensor 21 for detecting the operating state of the internal combustion engine.

[0027] The control of the internal combustion engine using the internal combustion engine control device 500 according to the first embodiment will be described. Fig. 3 and Fig. The processing routines shown in Fig. 4 are executed by causing the CPU 501 to repeatedly execute the engine control program P1 at a predetermined timing after the start of the internal combustion engine 10 until the internal combustion engine 10 is stopped. The CPU 501 acquires the operating state and the required torque of the internal combustion engine 10 (step S100). The operating state is acquired via the aforementioned sensors 21 to 24 and includes the operating state and the operating condition of the internal combustion engine 10. Parameters indicative of the operating state include, for example, the engine speed, the intake air amount, the accelerator opening degree, and the air-fuel ratio.The required torque is obtained using the accelerator opening degree detected by the accelerator opening sensor 24 and a predetermined correspondence relationship between the accelerator opening degree and the required torque.

[0028] The CPU 501 determines the target air-fuel ratio of the air system using the required torque and the engine speed. The CPU 501 determines whether the combustion state of the internal combustion engine 10, which is determined using the required torque and the engine speed, corresponds to stoichiometric combustion or not (step S102). Specifically, as shown in Fig. 7, the target air-fuel ratio λa of the air system is determined with reference to a map prepared in advance, which links the required torque [Nm] to the air system target air-fuel ratio λa. Fig. The map CL1 shown in Figure 7 corresponds to an example of a map corresponding to the acquired engine speed [Ne]. For example, a plurality of maps CL1 are prepared according to the engine speed in increments of 100 rpm. Note that the numerical values ​​indicated in the map are merely examples for ease of understanding. Similarly, in the description of the various maps below, the description "according to the engine speed" represents, for example, the engine speed in increments of 100 rpm, and the numerical values ​​indicated in the maps are examples. The determined target air-fuel ratio λa of the air system corresponds to the stoichiometric air-fuel ratio (theoretical air-fuel ratio) λs = 1.0 or the lean air-fuel ratio λ1 > 1.0.The stoichiometric air-fuel ratio λs may include a rich air-fuel ratio and take a value such as λs = 0.9 to 0.8. If it is determined that the combustion state of the internal combustion engine 10 corresponds to stoichiometric combustion (step S102: YES), the CPU 501 determines the stoichiometric air-fuel ratio λs = 1.0, which was previously determined, as the target air-fuel ratio λa of the air system (step S104). The CPU 501 acquires a map, which is prepared in advance and shows the relationship between the torque corresponding to the stoichiometric air-fuel ratio λs and the required air quantity. The CPU 501 acquires the required air quantity using the required torque (step S106). The map showing the relationship between the torque and the required air quantity corresponds, for example, to one shown in FIG. Fig. 8. Several CL2 characteristic curves are prepared according to the engine speed. The required air quantity can be obtained according to the engine speed and torque. To facilitate control, it is desirable to use a dimensionless required charging efficiency instead of the required air quantity.

[0029] The CPU 501 determines whether the combustion state of the internal combustion engine is in a transition phase from stoichiometric combustion to lean combustion (step S108). For example, the CPU 501 may determine that it is in the transition phase if the combustion state determination in the previous step S102 corresponds to lean combustion or if a reference time has not elapsed since the lean combustion determination in the previous step S102. If the CPU 501 determines that it is not in the transition phase (step S108: NO), the CPU 501 determines the target air-fuel ratio λf of the injection system (step S110). Specifically, the same air-fuel ratio as the target air-fuel ratio λa of the air system is set to the target air-fuel ratio λf of the injection system, that is, λf = λs.The CPU 501 determines an ignition timing correction value for a base ignition timing (step S112), and the processing routine proceeds to step S114. Specifically, the CPU 501 sets the ignition timing correction value = 0 and does not perform retardation correction and advancement correction of the ignition timing. When stoichiometric combustion continues, the operating state of the internal combustion engine 10, that is, the target air-fuel ratio of the air system and the air-fuel ratio of the injection system, remain constant or fluctuate slightly. Therefore, large torque fluctuations do not occur, and it is not necessary to reduce the torque by retarding or advancing the ignition timing. Generally, the ignition timing control is performed at the MBT, so the torque cannot be expected to increase by further advancing.

[0030] The CPU 501 determines the required injection amount (= actual air amount × λf) using the actual air amount and the target air-fuel ratio λf of the injection system (step S114). The CPU 501 adds a retard correction value to the basic ignition timing to determine the required ignition timing (step S116) and terminates this processing routine. The basic ignition timing may use, for example, a map for determining the ignition timing with the required injection amount and the engine speed as parameters, or a map for determining the ignition timing with the intake air amount and the engine speed as parameters.

[0031] The CPU 501 performs the Fig. 4 shown flowchart separately from the one in Fig. 3. The CPU 501 controls the operation of the internal combustion engine 10 at a time when the required air quantity, the required injection quantity, and the required ignition timing are determined. When the required air quantity is determined, the CPU 501 controls the throttle valve 33 using the required air quantity (step S200). Specifically, the CPU 501 determines the throttle valve opening degree corresponding to the determined required air quantity using a map that defines a characteristic showing a relationship between the required air quantity and the throttle valve opening degree and that is prepared in advance according to the engine speed. The CPU 501 controls the throttle valve 33 according to the determined opening degree. Consequently, in each processing step after step S104 or S124 of Fig. 3 the actual air quantity can be used according to the operation of the throttle valve 33.

[0032] When the required injection amount is determined, the CPU 501 controls the injector 31 using the required injection amount (step S210). Specifically, the CPU 501 controls the injector 31 according to a number of injections and an injection timing predetermined in advance according to the operating state of the internal combustion engine 10, to cause the injector 31 to inject fuel into the combustion chamber 15 at a certain required fuel amount during one cycle. When the required ignition timing is determined, the CPU 501 controls the spark plug 32 according to the required ignition timing (step S220) and terminates this processing routine. Specifically, the CPU 501 applies a voltage to the spark plug 32 one or more times according to the determined required ignition timing and causes a spark in the combustion chamber 15 to ignite the air-fuel mixture.Consequently, a drive torque is output from the crankshaft 141 of the internal combustion engine 10, and the drive torque is transmitted to the drive wheels via drive units such as a transmission and a drive shaft.

[0033] The description is made with reference to Fig. 3. If the CPU 501 determines in step S108 that it is in the transition phase (step S108: YES), the CPU 501 determines the target air-fuel ratio λft of the injection system in the transition phase (step S118). As in Fig. 5, the transition phase determined in step S108 corresponds to the transition phase from lean combustion to stoichiometric combustion. The target air-fuel ratio λft of the injection system in the transition phase is determined by performing torque fluctuation correction on the target air-fuel ratio λa of the air system to reduce the difference between the required torque and the actual torque. Specifically, the CPU 501 calculates a ratio of the required torque to the actual torque as a correction torque ratio (required torque / actual torque). The CPU 501 determines the target air-fuel ratio λft of the injection system in the transition phase using the Fig. 6 as an example. The map shows a relationship between the torque ratio and the target air-fuel ratio λft of the injection system in the transient phase. In the relationship between the torque ratio and the target air-fuel ratio λft of the injection system in the transient phase, the engine speed can be neglected as a factor. The actual torque corresponds to an actual torque output from the internal combustion engine 10 according to an actual air quantity obtained using the air flow meter 22. The required torque corresponds to a target torque to be output from the internal combustion engine 10, which is obtained in step S100. The relationship between the actual torque and the actual air quantity is stored in advance as a map.The actual torque can be obtained using the map and the actual air quantity. The actual torque in the map corresponds to a torque output by the internal combustion engine 10 under the condition that the air-fuel ratio λs is stoichiometric and the ignition timing is MBT (Minimum Advance For Best Torque), at which the torque is maximum. The correction torque ratio can be easily calculated using the required air quantity instead of the required torque and using the actual air quantity instead of the actual torque. The required torque and the required air quantity have a high correlation with each other. The actual torque and the actual air quantity have a high correlation with each other.Therefore, the value of required torque / actual torque and the value of required air volume / actual air volume can be considered equal to each other.

[0034] As in Fig. As shown in Figure 5, during the transient phase, even if the target air-fuel ratio λa of the air system is set to a value of 1.6 in a lean region to 0.9 in a stoichiometric region, a response delay in the change of the actual air amount X2 occurs. Therefore, there is a gap between the actual air amount X2 and the required air amount X1, that is, there is a period in which the air amount is too high. Therefore, in a case where the target air-fuel ratio λf of the injection system is immediately set to the target air-fuel ratio λa of the air system, an actual torque greater than the required torque is output, and therefore torque fluctuations occur due to the increase in torque.Therefore, during the transition phase from lean combustion to stoichiometric combustion, the CPU 501 performs torque fluctuation correction to lean the target air-fuel ratio λa of the air system, and determines the target air-fuel ratio λft of the injection system in the transition phase. The CPU 501 suppresses the occurring increase in torque, that is, guides the torque downward. Thus, in the transition phase from lean combustion to stoichiometric combustion, the actual air amount becomes > the required air amount as described above, and therefore the corrected torque ratio becomes less than 1. The target air-fuel ratio λft of the injection system in the transition phase decreases over time to the target air-fuel ratio fa of the air system. In addition, in the flowchart shown in FIG. Fig. 5, in order to avoid a state in which the target air-fuel ratio λf of the injection system becomes a value at which the NOx storage reduction catalyst cannot capture NOx, for example, 1.0 < λf < 1.3, in step S118, when the target air-fuel ratio λft of the injection system in the transition phase falls below 1.3, an air-fuel ratio limitation is performed to set the target air-fuel ratio λft of the injection system in the transition phase to 1.0. It should be noted that when the air-fuel ratio limitation is performed, the injection amount increases, as shown in Fig. 5. Therefore, the torque increase due to the gap between the actual air quantity and the required air quantity caused by leaning the target air-fuel ratio λf of the injection system cannot be suppressed. Therefore, as described below, the ignition timing is retarded to perform torque reduction.

[0035] The CPU 501 performs ignition timing correction using the determined target air-fuel ratio λft of the injection system in the transition phase (step S120), executes steps S114 and S116, and ends the processing routine. When determining the ignition timing correction value, the retardation correction value is determined using the correction torque ratio, as in the case of the target air-fuel ratio λft of the injection system in the transition phase. Specifically, a relationship between the correction torque ratio and the retardation correction value is prepared in advance as a map, and the retardation correction value is determined using the calculated correction torque ratio.The map showing the relationship between the correction torque ratio and the retardation correction value has a plurality of maps corresponding to the target air-fuel ratio λft of the transition-stage injection system. The retardation correction value is determined using the map corresponding to the target air-fuel ratio λft of the transition-stage injection system at the time of determination and the correction torque ratio. In the map showing the relationship between the correction torque ratio and the retardation correction value, the retardation correction value is 0 in the range where the target air-fuel ratio λft of the transition-stage injection system is 1.3 ≤ λft. Alternatively, the retardation correction value may be determined only in the range where the target air-fuel ratio λft of the transition-stage injection system is 1.0 < λft < 1.3. As shown in . Fig. As shown in Figure 5, the ignition timing is retarded until the required air amount X1 and the actual air amount X2 are substantially the same, and the retardation amount becomes smaller over time. It is not necessary to perform air-fuel ratio limitation, that is, to avoid the target air-fuel ratio λf of the injection system at which the NOx storage reduction catalyst cannot adsorb NOx, for example, to avoid 1.0 < λf < 1.3.

[0036] The actual torque used in calculating the correction torque ratio is the torque corresponding to the target air-fuel ratio λft of the transition-stage injection system. The map linking the actual torque to the actual air quantity, as described above, corresponds to the stoichiometric air-fuel ratio λs. Therefore, a torque efficiency of the torque corresponding to the target air-fuel ratio λft of the transition-stage injection system is calculated with respect to the torque corresponding to the stoichiometric air-fuel ratio λs. The actual air quantity is corrected using the calculated torque efficiency, and the actual torque is determined using the corrected actual air quantity.The torque efficiency represents a ratio of the torque value corresponding to the non-stoichiometric air-fuel ratio λ under a condition that the torque value corresponding to the stoichiometric air-fuel ratio λs is 100%. That is, the torque efficiency represents the efficiency. Details of the torque efficiency will be described later.

[0037] In step S102, the CPU 501 determines the target air-fuel ratio λa of the air system using the Fig. 7, as described above. Upon determining that the combustion state of the internal combustion engine does not correspond to stoichiometric combustion (step S102: NO), the CPU 501 determines the determined lean air-fuel ratio λ1 as the target air-fuel ratio λa of the air system (step S122). The CPU 501 determines the torque efficiency of the determined target air-fuel ratio λa with reference to the stoichiometric air-fuel ratio λs (step S124). Specifically, the CPU 501 determines the torque efficiency using a previously prepared and stored Fig. 9, which shows a relationship between the target air-fuel ratio λa of the air system and the torque efficiency [%]. In the present embodiment, in determining the required air quantity, a map is used which shows a relationship between a torque corresponding to the stoichiometric air-fuel ratio λs and the required air quantity, regardless of the combustion state of the internal combustion engine, that is, regardless of the air-fuel ratio λ. When the required intake quantity is determined with respect to the stoichiometric air-fuel ratio λs, that is, the same required intake quantity, the fuel quantity becomes relatively small to produce the lean air-fuel ratio.

[0038] Consequently, the torque output by the internal combustion engine 10 operating at the lean air-fuel ratio becomes smaller than the torque output by the internal combustion engine 10 operating at the stoichiometric air-fuel ratio λs. The relationship between the two torques is linked to a torque efficiency (lean torque / stoichiometric torque), which corresponds to a ratio representing the torque at the lean air-fuel ratio λ1 to the torque at the stoichiometric air-fuel ratio λs. Fig. 9, the torque efficiency corresponding to the stoichiometric air-fuel ratio λs is 100%, and the torque efficiency decreases with increasing air-fuel ratio λ.

[0039] The CPU 501 uses the determined torque efficiency and multiplies the required torque calculated in step S100 by the inverse of the torque efficiency to correct the required torque, thereby calculating the required air quantity using the torque efficiency calculated in Fig. 8 (step S126). For example, in step S122, the target air-fuel ratio of the air system λa = 1.8 is set corresponding to the required torque of 120 Nm, and in step S124, the torque efficiency = 53% corresponding to λa = 1.8 is determined. The required torque of 120 Nm is multiplied by 100 / 53 to obtain the corrected required torque of 226 Nm. The required air quantity is determined using the obtained required torque of 226 Nm. That is, the required air quantity to generate the target air-fuel ratio of the air system λa = 1.8 is determined using the fuel quantity used to generate the required torque set in step S100.

[0040] The CPU 501 determines whether or not the combustion state of the internal combustion engine is in a transition phase from lean combustion to stoichiometric combustion (step S128). For example, the CPU 501 may determine that it is in the transition phase if the combustion state determination in the previous step S102 corresponds to stoichiometric combustion or if a reference time has not elapsed since the stoichiometric combustion determination in the previous step S102. If the CPU 501 determines that it is not in the transition phase (step S128: NO), the CPU 501 determines the target air-fuel ratio λf of the injection system (step S130). Specifically, the same air-fuel ratio as the target air-fuel ratio λa of the air system is set to the target air-fuel ratio λf of the injection system, that is, λf = λ1.The CPU 501 executes the ignition timing correction (step S132), and the processing routine proceeds to step S114. Specifically, for the basic ignition timing, the ignition timing correction value is set to 0, and the retardation correction and the advancement correction of the ignition timing are not executed. When lean combustion continues, the operating state of the internal combustion engine 10, that is, the target air-fuel ratio of the air system and the air-fuel ratio of the injection system, remain constant or fluctuate slightly. Therefore, large torque fluctuations do not occur, and it is not necessary to reduce the torque by retarding or advancing the ignition timing.

[0041] If the CPU 501 determines in step S128 that it is in the transition phase (step S128: YES), the CPU 501 determines the target air-fuel ratio λft of the injection system in the transition phase (step S134). As in Fig. 10, the transition phase determined in step S128 corresponds to the transition phase from stoichiometric combustion to lean combustion. The target air-fuel ratio λft of the injection system in the transition phase is determined by performing a correction to the target air-fuel ratio λa of the air system in order to reduce the difference between the required torque and the actual torque. Specifically, the CPU 501 calculates the ratio of the required torque to the actual torque as the correction torque ratio. The CPU 501 determines the target air-fuel ratio λft of the injection system in the transition phase using the Fig. 11 as an example and prepared in advance. The map shows the relationship between the torque ratio and the target air-fuel ratio λft of the injection system in the transition phase. In the relationship between the torque ratio and the target air-fuel ratio λft of the injection system in the transition phase, the engine speed can be neglected as a factor. The actual torque and the required torque are as described above. The actual torque can be determined using the map showing the relationship between the actual torque and the actual air quantity.As described above, the actual torque in the map corresponds to the torque output by the internal combustion engine 10 under the condition that the stoichiometric air-fuel ratio λs corresponds to the air-fuel ratio and the MBT corresponds to the ignition timing. Therefore, the actual torque is determined using the actual air quantity corrected using the torque efficiency described above, that is, using the actual air quantity multiplied by the torque efficiency.

[0042] As in Fig. As shown in Figure 10, during the transient phase, even if the target air-fuel ratio λa of the air system is set to a value of 1.0 in the stoichiometric region to 1.6 in the lean region, a response delay in the change of the actual air amount X2 occurs. Therefore, there is a gap between the actual air amount X2 and the required air amount X1, that is, there is a period in which the air amount is insufficient. Therefore, in a case where the target air-fuel ratio λf of the injection system is immediately set to the target air-fuel ratio λa of the air system, an actual torque smaller than the required torque is output, and therefore torque fluctuations occur due to the torque drop.Therefore, during the transition phase from stoichiometric combustion to lean combustion, the CPU 501 performs a correction to enrich the target air-fuel ratio λa of the air system and determines the target air-fuel ratio λft of the injection system in the transition phase. The CPU 501 suppresses the resulting torque drop, i.e., it increases the torque. In the transition phase from stoichiometric combustion to lean combustion, the actual air quantity becomes < the required air quantity, as described above, and thus the corrected torque ratio becomes greater than 1.

[0043] The target air-fuel ratio λft of the injection system in the transition phase increases over time to the target air-fuel ratio fa of the air system. Although in the example in Fig. 10, in order to avoid the condition of the target air-fuel ratio λf of the injection system in which the NOx storage reduction catalyst cannot adsorb NOx, the stoichiometric air-fuel ratio λs may be maintained until the actual air amount becomes sufficiently close to the required air amount, and after the actual air amount becomes sufficiently close to the required air amount, restriction may be performed to set the target air-fuel ratio λft of the injection system in the transition period to 1.3 or more.

[0044] The CPU 501 executes the ignition timing correction (step S136), executes steps S114 and S116, and ends the processing routine. During the transition phase from stoichiometric combustion to lean combustion, a torque shortage occurs. Therefore, an advance angle correction is performed as the ignition timing correction to increase the torque due to the ignition timing. However, ignition is performed at the MBT as the base ignition timing, and no increase in torque can be expected even if the ignition timing is further advanced. Therefore, the ignition timing correction value is set to 0.

[0045] The target air-fuel ratio λf of the injection system, the torque efficiency and the ignition timing as described above are calculated for each cylinder 111 as a unit included in the internal combustion engine 10. Fig. Figure 12 shows an example of a 4-cylinder engine with the first cylinder #1, the second cylinder #2, the third cylinder #3, and the fourth cylinder #4. The first, second, third, and fourth cylinders indicate the firing order. Fig. 12, the symbol fu indicates a time at which an injection condition, such as the injection quantity and the injection timing, including the determination of the target air-fuel ratio λf of the injection system, is determined. The symbol ig indicates a time at which an ignition condition, such as the ignition timing, is determined. Fig. 12, the injection control indicates the target air-fuel ratio λf and the determination timing of the injection conditions in each cylinder #1 to #4. The torque control indicates the timing at which the torque efficiency and the retardation correction value are determined for cylinders #1 to #4. The ignition control indicates the determination timing of the ignition conditions in cylinders #1 to #4. In the example of Fig. 12, fuel injection and spark ignition are repeatedly performed in order from the first cylinder #1 to the fourth cylinder #4. First, the injection condition including the injection system target air-fuel ratio λf for the first cylinder #1 at time fu is determined. Then, the torque efficiency and the retard correction value for the first cylinder #1 are determined using the injection system target air-fuel ratio λf. Furthermore, the ignition condition for the first cylinder #1 is subsequently determined using the basic ignition timing and the retard correction value. This process is sequentially performed in the second cylinder #2, the third cylinder #3, and the fourth cylinder #4.As described above, in the internal combustion engine control device 500 according to the present embodiment, the target air-fuel ratio λf of the injection system is determined as a unit at each time point in each cylinder 111, and then the torque efficiency and the retardation correction value are determined. Next, the ignition timing is determined. In the transition phase, the target air-fuel ratio λft of the transition-phase injection system is used instead of the target air-fuel ratio λf of the injection system.

[0046] In the control device 500 of the internal combustion engine according to the first embodiment described above, after determining the target air-fuel ratio λa of the air system, the target air-fuel ratio λf of the injection system is determined, and the target ignition timing is further determined. Therefore, in the transition phase between stoichiometric combustion and lean combustion, in order to reduce the difference between the required torque and the actual torque, torque fluctuation correction can be performed on the target air-fuel ratio λa of the air system to determine the target air-fuel ratio λft of the injection system in the transition phase. Consequently, the influence of the response delay of the change in the actual air amount can be reduced or eliminated, and the torque fluctuation in the transition phase can be suppressed or eliminated.That is, in the internal combustion engine control device 500 according to the first embodiment, torque fluctuation correction is performed on the target air-fuel ratio λa of the air system to reduce the difference between the required torque and the actual torque, and the target air-fuel ratio λft of the injection system is determined. Therefore, torque control of the internal combustion engine 10 can be performed using the target air-fuel ratio λf of the injection system, which reflects the delay in the change of the actual air quantity. Consequently, the configuration enables suppressing or eliminating the torque increase or torque decrease due to the difference between the change in the actual air quantity and the change in the required air quantity.The operating conditions of the internal combustion engine in the first embodiment can correspond to homogeneous combustion, weakly stratified combustion, or stratified combustion. In the case of homogeneous combustion or weakly stratified combustion, it is possible to benefit more from the suppression of torque fluctuation.

[0047] In the control device 500 of the internal combustion engine according to the first embodiment, the required air quantity during stoichiometric combustion and the required air quantity during lean combustion are calculated using the map showing the correspondence between the torque and the required air quantity at the stoichiometric air-fuel ratio λs and the map showing the correspondence between the torque and the actual air quantity. Therefore, it is not necessary to prepare maps for stoichiometric combustion and lean combustion individually, and it is not necessary to store the maps in the memory 502. The number of maps can therefore be reduced.

[0048] In the control device 500 of the internal combustion engine according to the first embodiment, during the transition phase, for example, during the transition phase from lean combustion to stoichiometric combustion, the target air-fuel ratio λf of the transition-phase injection system is determined so as to avoid the target air-fuel ratio λf of the injection system at which the NOx storage reduction catalyst cannot store NOx. Therefore, the configuration makes it possible to suppress or prevent a decrease in catalyst efficiency and to suppress or prevent NOx leakage even during the transition phase. As a result, the configuration makes it possible to suppress or prevent a decrease in exhaust performance during the transition phase and to maintain excellent exhaust performance in each combustion region. Second embodiment:

[0049] In the first embodiment, the example in which the target air-fuel ratio λf of the injection system in which the NOx storage reduction catalyst is incapable of NOx storage is avoided was described as the air-fuel ratio limitation in determining the target air-fuel ratio λft of the transition-phase injection system. In the second embodiment, the air-fuel ratio limitation is performed taking a misfire limit into account as the air-fuel ratio limitation.For example, in a case where the target air-fuel ratio λft of the transient injection system, obtained by lean correction as the torque fluctuation correction, is corrected to an air-fuel ratio that exceeds the misfire limit, an air-fuel ratio that does not exceed the misfire limit is set to the target air-fuel ratio λft of the transient injection system. In the second embodiment, the configuration enables preventing or suppressing misfire in the internal combustion engine 10 and outputting the required torque. Third embodiment:

[0050] The internal combustion engine control device according to the third embodiment is configured to coordinate EGR control and air-fuel ratio control. The configuration of the internal combustion engine control device according to the third embodiment is the same as that of the internal combustion engine control device 500 according to the first embodiment, so the same reference numerals are given, and the description of each configuration is omitted. In EGR control, the opening degree of the EGR valve 35 provided at the EGR passage 42 is controlled to change the EGR rate. The conditions for the cooperative control are as follows. - A plurality of target air-fuel ratio maps and a plurality of target EGR rate maps are provided according to the operating state of the internal combustion engine 10. - The air-fuel ratio and EGR rate are changed to change the required torque or to clean the catalyst. - There is an area in which several combustion states are set for the same operating states of the internal combustion engine 10. - The air-fuel ratio and EGR rate are gradually changed with reference to the target. - The target air-fuel ratio, ignition timing and injection mode can be set individually. - The target air-fuel ratio and EGR rate are adjusted so that combustion continuously passes through a stable range.

[0051] For example, the EGR rate and the air-fuel ratio can change, as in Fig. 13 is shown. In Fig. 13, the first point Ps indicates a stoichiometric combustion point, and the second point Pl indicates a lean combustion point. When the combustion point is changed between the stoichiometric combustion point Ps and the lean combustion point Pl, it is desirable that the EGR ratio and the air-fuel ratio change so that the combustion point does not pass through the misfire region indicated by the characteristic curve EL1. On the other hand, changes in the EGR rate and the air-fuel ratio that pass through the misfire region indicated by the characteristic curve EL2 should be avoided. However, the response of the EGR valve 35 is low, and the response of the exhaust gas with respect to the change in flow rate is also low.Therefore, in the transition phase of the combustion state, even if a closing signal is output to the EGR valve 35, the EGR rate does not immediately decrease, and even if an opening signal is output to the EGR valve 35, the EGR rate does not immediately increase. Therefore, in a case where the EGR rate and the air-fuel ratio are independently controlled based on the signal output, the EGR rate and the air-fuel ratio may consequently change, as shown by the characteristic curve EL2.

[0052] In the third embodiment, when the combustion state of the internal combustion engine 10 is switched from stoichiometric combustion to lean combustion, the EGR valve 35 is first closed to reduce the EGR rate, and then the air-fuel ratio is changed. Furthermore, when the combustion state of the internal combustion engine 10 is switched from lean combustion to stoichiometric combustion, the air-fuel ratio is first changed, and then the EGR valve 35 is opened to increase the EGR rate. The actual EGR rate and the air-fuel ratio change as shown in Fig.13, by executing coordinated control of the EGR rate and the air-fuel ratio. In contrast, with existing independent control, when the combustion state of the internal combustion engine 10 changes from stoichiometric combustion to lean combustion, the EGR valve 35 is closed and the air-fuel ratio is changed. When the combustion state of the internal combustion engine 10 changes from lean combustion to stoichiometric combustion, the EGR valve 35 is opened with a change in the air-fuel ratio. Consequently, the combustion point passes through the misfire region.

[0053] As described above, the control device 500 for the internal combustion engine according to the third embodiment cooperatively controls the EGR rate and the air-fuel ratio. Therefore, misfire in the internal combustion engine 10 is prevented or suppressed, and the required torque is output. Further embodiments:

[0054] (1) In the above embodiment, the actual air quantity is controlled by adjusting the opening degree of the throttle valve 33 and the opening degree of the EGR valve 35. Note that the actual air quantity can be controlled by further adjusting the opening degree of the wastegate valve 34.

[0055] (2) In the above embodiment, various maps are used. Note that the calculation may be dynamically performed using the acquired control parameters using a pre-prepared function instead of the map. Further, the target air-fuel ratio λft of the injection system in the transition phase is determined using the map showing the correction torque ratio and the relationship between the torque ratio and the target air-fuel ratio λft of the injection system in the transition phase. On the other hand, a map for linking the correction torque ratio to the target air-fuel ratio correction value of the injection system in the transition phase may be prepared in advance.The target air-fuel ratio λft of the injection system in the transition phase can be determined by correcting the torque fluctuation of the target air-fuel ratio of the air system by adding the target air-fuel ratio correction value of the injection system obtained using the map and the correction torque ratio to the target air-fuel ratio λa of the air system. Also in this case, the target air-fuel ratio λf of the injection system, which is different from the target air-fuel ratio λa of the air system, is used in the transition phase, and the advantages produced in the first embodiment can be achieved.

[0056] (3) In the above embodiment, the required air quantity during stoichiometric combustion and the required air quantity during lean combustion are calculated using the map showing the correspondence between the torque and the required air quantity and the torque and the actual air quantity at the stoichiometric air-fuel ratio λs. Alternatively, a map showing the correspondence between the torque and the required air quantity and the correspondence between the torque and the actual air quantity according to stoichiometric combustion and lean combustion may be used. In this case, torque fluctuation in the transient phase can be suppressed or prevented.

[0057] (4) In the above embodiment, the CPU 501 executes the internal combustion engine control program P1 to realize the control unit that stores the detection signal in software. Note that the control unit may be realized in hardware using a preprogrammed integrated circuit or a discrete circuit.

Claims

[1] Control device (500) for an internal combustion engine (10), comprising: an acquisition unit (503) configured to acquire a required torque and an operating state of the internal combustion engine; and a control unit (501, P1) configured to control an operation of the internal combustion engine using a required air quantity, a required fuel quantity and a required ignition timing, wherein the control unit is configured in such a way that it: determines a target air-fuel ratio of an air system according to the obtained required torque and the obtained operating condition; the required amount of air is obtained using the target air-fuel ratio of the air system; performs torque fluctuation correction on the target air-fuel ratio of the air system to determine a target air-fuel ratio of an injection system to reduce a difference between required torque and actual torque when a combustion state of the internal combustion engine is in a transition phase between stoichiometric combustion and lean combustion; determines the target air-fuel ratio of the injection system using the target air-fuel ratio of the air system when the combustion state is not in the transition phase; and the required fuel quantity and the required ignition timing are obtained using the determined target air-fuel ratio of the air system and the determined target air-fuel ratio of the injection system. [2] A control device for an internal combustion engine according to claim 1, wherein the control unit is configured to perform the torque fluctuation correction using a ratio of the required torque to the actual torque in the transient phase and determine the target air-fuel ratio of the injection system. [3] A control device for an internal combustion engine according to claim 2, wherein the control unit is configured to perform the torque fluctuation correction to cause the target air-fuel ratio of the injection system to be lean when the transition phase corresponds to a transition phase from the lean combustion to the stoichiometric combustion. [4] The control device for an internal combustion engine according to claim 3, wherein the control unit is configured to obtain a retardation correction value of the ignition timing using the ratio of the required torque and the actual torque, and to control the operation of the internal combustion engine using the required ignition timing and the retardation correction value when the transition phase corresponds to a transition phase from lean combustion to stoichiometric combustion. [5] A control device for an internal combustion engine according to any one of claims 2 to 4, wherein the control unit is configured to perform the torque fluctuation correction to cause the target air-fuel ratio of the injection system to be rich when the transition phase corresponds to a transition phase from the stoichiometric combustion to the lean combustion. [6] A control device for an internal combustion engine according to any one of claims 1 to 5, wherein the control unit is configured to: the required air quantity is obtained using a relationship between a torque and the required air quantity corresponding to the air-fuel ratio for stoichiometric combustion, which is determined in advance, and a torque corresponding to the target air-fuel ratio of the air system; obtains a torque efficiency of the torque corresponding to the target air-fuel ratio of the air system based on the torque corresponding to the air-fuel ratio for stoichiometric combustion when the combustion state is in lean combustion; and the required air quantity is obtained using the obtained torque efficiency and the relationship. [7] A control device for an internal combustion engine according to claim 1, wherein the control unit is configured to perform the torque fluctuation correction using a ratio of the required air amount to the actual air amount in the transient phase and determine the target air-fuel ratio of the injection system. [8] A control device for an internal combustion engine according to any one of claims 1 to 7, wherein the control unit is further configured to change the target air-fuel ratio of the injection system to which the torque fluctuation correction has been performed, in order to restrict or prevent at least one of a reduction in an efficiency of an exhaust catalyst, a misfire, and a deterioration in a property of the exhaust gas. [9] Control method for an internal combustion engine (10), comprising: Obtaining a required torque and an operating state of the internal combustion engine (S100); Determining a target air-fuel ratio of an air system according to the obtained required torque and the obtained operating state (S102, S104, S122); Obtaining a required amount of air using the target air-fuel ratio of the air system (S106, S126); Performing a torque fluctuation correction on the target air-fuel ratio of the air system to determine a target air-fuel ratio of an injection system to reduce a difference between the required torque and an actual torque when a combustion state of the internal combustion engine is in a transition phase between stoichiometric combustion and lean combustion (S118, S134); Determining the target air-fuel ratio of the injection system using the target air-fuel ratio of the air system when the combustion state is not in the transition phase (S110, S130); Obtaining a required fuel quantity and a required ignition timing using the determined target air-fuel ratio of the air system and the determined target air-fuel ratio of the injection system (S114, S113); and Controlling an operation of the internal combustion engine using the obtained required air quantity, the obtained required fuel quantity and the obtained required ignition timing.

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