Control device for internal combustion engine

Abstract

To suppress generation of a backfire during supercharging.SOLUTION: In an internal combustion engine 10 including a cylinder 11 in which a mixture of a gaseous fuel and intake air are burned; an intake passage 12 connected to the cylinder 11; and a supercharger 20 for supercharging intake air, when a backfire is generated during a setting period before supercharging by the supercharger 20, a control device for an internal combustion engine performs supercharging with a smaller boost pressure than that when a backfire is not generated during the setting period.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a control device for an internal combustion engine. [Background technology]

[0002] Patent Document 1 discloses an internal combustion engine and its control device. The internal combustion engine has cylinders, an intake passage connected to the cylinders, and a water injection valve provided in the intake passage. In an internal combustion engine, a backfire can occur, where the air-fuel mixture ignites before ignition while the intake valve is open, causing a flame to flow back from the cylinder to the intake passage. The control device of Patent Document 1 injects water from the water injection valve when a backfire occurs. This reduces the temperature of the intake passage, thereby suppressing the occurrence of a backfire. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-118109 Summary of the Invention [Problem to be solved by the invention]

[0004] An internal combustion engine such as that described in Patent Document 1 may have a supercharger. During supercharging of intake air by the supercharger, the temperature inside the cylinder tends to rise as the engine load increases. This makes pre-ignition ignition more likely. Furthermore, during supercharging, the pressure inside the intake passage and cylinder increases, making it easier for flames to propagate. Therefore, backfires are more likely to occur during operation of the internal combustion engine, particularly during supercharging. Suppose the technology described in Patent Document 1 is adopted in an internal combustion engine with a supercharger, and water is injected into the intake passage during supercharging. Even in this case, the situation in which the pressure inside the intake passage and cylinder is high during supercharging remains unchanged. Therefore, backfires may not be adequately suppressed. [Means for solving the problem]

[0005] The control device for an internal combustion engine for solving the above problem includes a cylinder in which a mixture of gaseous fuel and intake air is burned, an intake passage connected to the cylinder, and , suck A turbocharger that supercharges the incoming air , and crankshaft The control object is an internal combustion engine having The vehicle is a vehicle equipped with the internal combustion engine, the vehicle having a trip meter for measuring the distance traveled by the vehicle, and a stepped automatic transmission, and when the period during which the crankshaft rotates 720 degrees is defined as one combustion cycle, the number of combustion cycles required for the equipped vehicle to travel 1 km is stored in advance for each gear of the automatic transmission, and while the equipped vehicle is traveling, a history of target gears that are target values ​​for the gears is stored, and while the internal combustion engine is operating, a determination is made based on the operating state of the internal combustion engine as to whether or not a condition indicating the occurrence of a backfire is established, and only when the condition is established, the value of the trip meter at the time when the condition is established is stored as specific information; When the value of the trip meter is a requested meter value, a value that is 1 km smaller than the requested meter value is a back-calculated value, and a travel period of the equipped vehicle from when the value of the trip meter reaches the requested meter value from the back-calculated value to when the value of the trip meter reaches the requested meter value is a set period, if the target gear stage is constant during the set period before the supercharging request is generated, the number of backfires that have occurred between the back-calculated value and the requested meter value is calculated based on the specific information stored in the first process, and the calculated number of occurrences is divided by the number of combustion cycles that correspond to the gear stage during the set period ascertained from the history of the target gear stage to calculate a backfire occurrence rate, and the higher the occurrence rate, the more likely it is that a backfire will occur during the set period before the supercharging request is generated. A second process is executed in which supercharging is performed at a lower supercharging pressure than when backfire does not occur.

[0006] With the above configuration, when the engine is in a state where backfire is likely to occur, supercharging is performed at a low supercharging pressure. This makes it possible to make the engine state during supercharging an engine state where backfire is least likely to occur. Therefore, the occurrence of backfire during supercharging can be suppressed. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram of a vehicle. [Figure 2] FIG. 2 is a schematic diagram of an internal combustion engine. [Figure 3] FIG. 3 is a diagram showing an example of the characteristic map. [Figure 4] FIG. 4 is a flowchart showing the procedure of the supercharging routine of the first embodiment. [Figure 5] FIG. 5 is a flowchart showing the processing procedure of the supercharging routine of the second embodiment. [Figure 6] FIG. 6 is a diagram showing an example of the characteristic map. DETAILED DESCRIPTION OF THE INVENTION

[0010] [First embodiment] A first embodiment of a control device for an internal combustion engine will be described below with reference to the drawings. <Overall vehicle configuration> 1, the vehicle 90 includes the internal combustion engine 10, a drive clutch 81, a motor generator 82, a transmission unit 80, a hydraulic mechanism 86, a differential 71, a plurality of drive wheels 72, an inverter 78, and a battery 79. The vehicle 90 is a vehicle on which the internal combustion engine 10 is to be installed.

[0011] The internal combustion engine 10 is a drive source for the vehicle 90. Details of the internal combustion engine 10 will be described later. The internal combustion engine 10 has a crankshaft 17. The motor generator 82 is a drive source for the vehicle 90. The motor generator 82 functions as both an electric motor and a generator. The motor generator 82 has a stator 82C, a rotor 82B, and a rotating shaft 82A. The rotor 82B is rotatable relative to the stator 82C. The rotating shaft 82A rotates integrally with the rotor 82B. The motor generator 82 is electrically connected to a battery 79 via an inverter 78. The battery 79 exchanges power with the motor generator 82. The inverter 78 converts DC to AC.

[0012] The drive clutch 81 is interposed between the internal combustion engine 10 and the motor generator 82. The drive clutch 81 switches between an engaged state and a disengaged state in response to hydraulic pressure from a hydraulic mechanism 86. When hydraulic pressure is supplied to the drive clutch 81, the drive clutch 81 enters a connected state in which the crankshaft 17 and the rotating shaft 82A of the motor generator 82 are connected. When the supply of hydraulic pressure is stopped, the drive clutch 81 enters a disengaged state in which the crankshaft 17 and the rotating shaft 82A are separated.

[0013] The transmission unit 80 has a torque converter 83 and an automatic transmission 85. The torque converter 83 has a pump impeller 83A, a turbine liner 83B, and a lock-up clutch 84. The torque converter 83 is a fluid coupling with a torque amplification function. The pump impeller 83A rotates integrally with a rotating shaft 82A of the motor generator 82. The turbine liner 83B rotates integrally with an input shaft of the automatic transmission 85. The lock-up clutch 84 receives hydraulic pressure from a hydraulic mechanism 86 and directly connects the pump impeller 83A and the turbine liner 83B.

[0014] The automatic transmission 85 is a stepped transmission capable of changing the gear ratio in multiple stages. The automatic transmission 85 has a plurality of clutches and brakes as engagement elements, and a plurality of planetary gear mechanisms. Each engagement element switches between an engaged and disengaged state according to hydraulic pressure from a hydraulic mechanism 86. Depending on the engaged and disengaged state of each engagement element, the automatic transmission 85 can establish one of a plurality of preset gears. Specifically, the automatic transmission 85 can establish a gear for forward driving, a gear for reverse driving, and a gear for non-driving. Furthermore, the automatic transmission 85 can establish one of a plurality of gears for forward driving, such as "1st gear" to "5th gear." The output shaft of the automatic transmission 85 is connected to left and right drive wheels 72 via a differential 71. The differential 71 allows a difference in rotational speed between the left and right drive wheels 72. The drive clutch 81, the motor generator 82, and the transmission unit 80 are housed in a single continuous case. In other words, the drive clutch 81, the motor generator 82, and the transmission unit 80 are configured as an integrated hybrid transaxle.

[0015] The vehicle 90 has a vehicle speed sensor 58, an accelerator sensor 59, a battery sensor 60, and a trip meter 35. The vehicle speed sensor 58 detects the traveling speed of the vehicle 90 as a vehicle speed SP. The accelerator sensor 59 detects the depression amount of the accelerator pedal of the vehicle 90 as an accelerator operation amount ACC. The battery sensor 60 detects battery information B such as the current, voltage, and temperature of the battery 79. The trip meter 35 measures the traveling distance M of the vehicle 90 in meters.

[0016] <General configuration of an internal combustion engine> As shown in Fig. 2, the internal combustion engine 10 has a plurality of cylinders 11, a plurality of pistons 51, and the crankshaft 17. Note that Fig. 2 shows only one of the plurality of cylinders 11. The same applies to the pistons 51. Although not shown, the internal combustion engine 10 also has a plurality of connecting rods. A piston 51 and a connecting rod are provided for each cylinder 11. There are four cylinders 11 in total.

[0017] Cylinder 11 is a space for burning a mixture of fuel and intake air. Piston 51 is located inside cylinder 11. Piston 51 reciprocates inside cylinder 11. Piston 51 is connected to crankshaft 17 via a connecting rod. Crankshaft 17 rotates in response to the reciprocating movement of piston 51.

[0018] The internal combustion engine 10 has a plurality of spark plugs 15. Note that FIG. 2 shows only one of the plurality of spark plugs 15. A spark plug 15 is provided for each cylinder 11. The tip of the spark plug 15 is located inside the cylinder 11. The spark plug 15 ignites the air-fuel mixture inside the cylinder 11.

[0019] The internal combustion engine 10 has an intake passage 12, an intercooler 52, a throttle valve 16, multiple fuel injection valves 14, and an exhaust passage 13. The intake passage 12 is a passage for introducing intake air into the cylinders 11. The intake passage 12 is connected to each cylinder 11. The intercooler 52 is located midway through the intake passage 12. The intercooler 52 cools the intake air. The throttle valve 16 is located downstream of the intercooler 52 in the intake passage 12. The opening of the throttle valve 16 is adjustable. The intake air amount GA changes depending on the opening of the throttle valve 16. A fuel injection valve 14 is provided for each cylinder 11. The fuel injection valve 14 is located downstream of the throttle valve 16 in the intake passage 12. The fuel injection valve 14 supplies fuel into the cylinders 11 via the intake passage 12. The fuel injection valve 14 injects hydrogen as fuel. The exhaust passage 13 is a passage for discharging exhaust gas from each cylinder 11. The exhaust passage 13 is connected to each cylinder 11.

[0020] The internal combustion engine 10 has a plurality of intake valves 18 and a plurality of exhaust valves 19. Note that FIG. 2 shows only one of the plurality of intake valves 18. The same applies to the exhaust valves 19. An intake valve 18 is provided for each cylinder 11. The intake valve 18 is located at a connection port of the intake passage 12 with the cylinder 11. The intake valve 18 opens and closes the connection port of the intake passage 12. An exhaust valve 19 is provided for each cylinder 11. The exhaust valve 19 is located at a connection port of the exhaust passage 13 with the cylinder 11. The exhaust valve 19 opens and closes the connection port of the exhaust passage 13.

[0021] The internal combustion engine 10 has a turbocharger 20. The turbocharger 20 is provided across the intake passage 12 and the exhaust passage 13. The turbocharger 20 has a compressor wheel 21, a turbine wheel 22, a bypass passage 24, and a wastegate valve (hereinafter referred to as WGV) 25. The compressor wheel 21 is located upstream of the intercooler 52 in the intake passage 12. The turbine wheel 22 is located midway through the exhaust passage 13. The turbine wheel 22 rotates in accordance with the flow of exhaust gas. The compressor wheel 21 rotates integrally with the turbine wheel 22. At this time, the compressor wheel 21 compresses the intake air and sends it out. That is, the compressor wheel 21 supercharges the intake air.

[0022] The bypass passage 24 connects the upstream and downstream portions of the exhaust passage 13 with respect to the turbine wheel 22. In other words, the bypass passage 24 is a passage that bypasses the turbine wheel 22. The WGV 25 is located at the downstream end of the bypass passage 24. The opening degree of the WGV 25 can be adjusted by an actuator. The larger the opening degree of the WGV 25, the greater the amount of exhaust gas that bypasses the turbine wheel 22 and flows through the bypass passage 24. At the same time, the rotation speeds of the turbine wheel 22 and the compressor wheel 21 decrease. At the same time, the boost pressure QP, which is the pressure of the intake air between the compressor wheel 21 and the throttle valve 16 in the intake passage 12, decreases.

[0023] The internal combustion engine 10 has an air flow meter 33, a boost pressure sensor 37, and an intake air temperature sensor 34. The air flow meter 33 is located upstream of the compressor wheel 21 in the intake passage 12. The air flow meter 33 detects the intake air amount GA. The boost pressure sensor 37 is located between the intercooler 52 and the throttle valve 16 in the intake passage 12. The boost pressure sensor 37 detects the boost pressure QP. The intake air temperature sensor 34 is located downstream of the throttle valve 16 in the intake passage 12. The intake air temperature sensor 34 detects the temperature T of the intake air downstream of the throttle valve 16 in the intake passage 12 (hereinafter referred to as downstream intake air temperature).

[0024] The internal combustion engine 10 includes a sensor plate 53 and a crank position sensor 36. The sensor plate 53 has a disk-shaped body and multiple teeth protruding from the outer periphery of the body. The body rotates integrally with the crankshaft 17. The multiple teeth are generally evenly spaced, except for one missing tooth portion where the spacing between adjacent teeth is larger than the other portions. The crank position sensor 36 is located opposite the outer periphery of the sensor plate 53. As the sensor plate 53 rotates in conjunction with the rotation of the crankshaft 17, the crank position sensor 36 alternates between the teeth of the sensor plate 53 and the gaps between adjacent teeth. The crank position sensor 36 outputs an L signal when facing the teeth of the sensor plate 53 and an H signal when facing the gaps. Corresponding to the tooth arrangement described above, the crank position sensor 36 essentially alternates between the L signal and the H signal at regular, regular intervals. The crank position sensor 36 outputs a missing tooth signal, which is an H signal with a longer interval than normal, only when the missing tooth portion passes in front of the crank position sensor 36. Hereinafter, the signals output by the crank position sensor 36 will be collectively referred to as the crank signal CR. In this embodiment, the position of the missing tooth portion is determined so that when the piston 51 of a specific cylinder (one of the four cylinders 11) is at top dead center, the tooth next to the missing tooth portion faces the crank position sensor 36. This tooth faces the crank position sensor 36 after passing the missing tooth portion during the rotation of the sensor plate 53. Due to this setting, the crank signal CR switches from the missing tooth signal to an L signal around the time when the piston 51 of the specific cylinder reaches top dead center.

[0025] The internal combustion engine 10 is a four-stroke, one-cycle engine in which the intake stroke, compression stroke, expansion stroke, and exhaust stroke of each cylinder 11 are completed by rotating the crankshaft 17 720 degrees. Hereinafter, a series of periods in which one cylinder 11 undergoes one intake stroke, one compression stroke, one expansion stroke, and one exhaust stroke will be referred to as one combustion cycle.

[0026] <Outline of the control device> As shown in FIG. 1, the vehicle 90 includes a control device 100. The control device 100 may be configured as one or more processors that execute various processes according to a computer program (software). The control device 100 may also be configured as a circuit including one or more dedicated hardware circuits, such as an application-specific integrated circuit (ASIC), that execute at least some of the various processes, or a combination thereof. The processor includes a CPU 111 and memories such as RAM and ROM 112. The memory stores program code or instructions configured to cause the CPU 111 to execute processes. The memory, i.e., computer-readable medium, includes any available medium accessible by a general-purpose or dedicated computer. The control device 100 includes a real-time clock, which is a circuit that generates date and time information. The control device 100 includes a storage device 113, which is an electrically rewritable non-volatile memory.

[0027] The control device 100 repeatedly receives information detected or measured by various information acquisition devices attached to the vehicle 90. Specifically, the control device 100 receives the following information.

[0028] The intake air volume GA detected by the air flow meter 33 Boost pressure QP detected by boost pressure sensor 37 The downstream intake air temperature T detected by the intake air temperature sensor 34 Vehicle speed SP detected by vehicle speed sensor 58 Acceleration amount ACC detected by accelerator sensor 59 Battery information B detected by the battery sensor 60 Trip meter 35 measures the vehicle's mileage M In addition to the above information, the control device 100 repeatedly receives a crank signal CR output by the crank position sensor 36. The control device 100 calculates the rotational position (hereinafter referred to as crank position) CRA of the crankshaft 17 as needed based on the transition of the crank signal CR. Specifically, the control device 100 determines the crank position CRA to be zero degrees when the crank signal CR switches from a missing tooth signal to an L signal. The control device 100 then calculates the crank position CRA within a range from zero degrees to 360 degrees based on the transition of the crank signal CR. Note that, taking into account the position of the missing tooth portion described above, the control device 100 determines the crank position CRA to be zero degrees when the piston 51 of a specific cylinder is at top dead center.

[0029] In addition to the crank position CRA, the control device 100 also calculates the following parameters as needed. The control device 100 calculates the engine speed NE, which is the rotational speed of the crankshaft 17, based on the transition of the crank signal CR received from the crank position sensor 36. Furthermore, the control device 100 calculates the engine load factor KL based on the engine speed NE and the intake air amount GA. The engine load factor KL is a parameter that determines the amount of air charged into the cylinders 11. Specifically, the engine load factor KL is the ratio of the amount of air that flows into one cylinder 11 per combustion cycle to a reference air amount. The reference air amount varies depending on the engine speed NE. Furthermore, the control device 100 calculates the charge rate SOC of the battery 79 based on the battery information B. The charge rate SOC of the battery 79 is the ratio of the remaining charge to the full charge capacity of the battery 79.

[0030] The control device 100 controls various components of the vehicle 90. For example, the control device 100 controls the internal combustion engine 10 and the motor generator 82. To control the internal combustion engine 10 and the motor generator 82, the control device 100 calculates a required driving force, which is a required value of driving force required for traveling of the vehicle 90, based on the accelerator operation amount ACC and the vehicle speed SP. The control device 100 then determines the torque distribution between the internal combustion engine 10 and the motor generator 82 based on the required driving force and the state of charge SOC of the battery 79. The control device 100 then calculates an engine required torque, which is a torque that the internal combustion engine 10 needs to output, and a motor required torque, which is a torque that the motor generator 82 needs to output in order to achieve the required driving force. The control device 100 then controls the internal combustion engine 10 and the motor generator 82 based on these required torques. While the vehicle 90 is traveling, the control device 100 repeatedly calculates each required torque and controls the internal combustion engine 10 and the motor generator 82 based on the required torque.

[0031] When controlling the internal combustion engine 10, the control device 100 controls various control variables of the internal combustion engine 10 by operating various control target devices such as the throttle valve 16, the fuel injection valve 14, the spark plug 15, and the WGV 25. The various control variables include, for example, the intake air amount GA, the injected fuel amount, and the boost pressure QP. The control device 100 controls these various control variables so that the actual torque of the internal combustion engine 10 matches the engine required torque. Note that when a second process described below is executed, the actual torque of the internal combustion engine 10 becomes smaller than the engine required torque. In this case, the control device 100 compensates for this torque decrease with the motor generator 82.

[0032] Depending on the situation, the control device 100 stops the internal combustion engine 10 and drives only the motor generator 82, or drives the motor generator 82 while operating the internal combustion engine 10. In the former case, the control device 100 disengages the drive clutch 81, and in the latter case, the control device 100 engages the drive clutch 81. For example, when the state of charge (SOC) of the battery 79 has a margin, the control device 100 stops operation of the internal combustion engine 10 when the required drive force is relatively small, and operates the internal combustion engine 10 when the required drive force is relatively large. Examples of when the required drive force is small include when the vehicle 90 starts moving and when the vehicle is running under a light load with low forward acceleration. Note that operating the internal combustion engine 10 means combusting the air-fuel mixture in each cylinder 11 through fuel injection and ignition. This causes the engine speed NE to be greater than zero.

[0033] The control device 100 also controls the automatic transmission 85. The control device 100 calculates a target gear position, which is a target value for the gear position of the automatic transmission 85, based on the accelerator operation amount ACC and the vehicle speed SP. The control device 100 then controls the automatic transmission 85 so that the actual gear position matches the target gear position. The control device 100 repeats the calculation of the target gear position and the control of the automatic transmission 85 while the vehicle 90 is traveling.

[0034] <Details of processing related to internal combustion engines> The control device 100 is capable of executing a first process as a process for grasping the engine state while the internal combustion engine 10 is operating. The first process is a process for determining whether or not a backfire has occurred. A backfire is a phenomenon in which an air-fuel mixture ignites before ignition while the intake valve 18 is open, causing a flame to flow backward from the cylinder 11 to the intake passage 12. In other words, a backfire occurs during the intake stroke of each cylinder 11. The internal combustion engine 10 uses hydrogen as fuel. Hydrogen is more ignitable than, for example, gasoline, and therefore is more likely to ignite when the fuel injection valve 14 injects the hydrogen into the cylinder 11 during the intake stroke. Under this assumption, during supercharging of intake air by the supercharger 20, the temperature inside the cylinder 11 tends to increase as the engine load factor KL increases. When the temperature inside the cylinder 11 increases, pre-ignition ignition is more likely to occur. Furthermore, during supercharging, the flame is likely to propagate due to the increased pressure of gas in the intake passage 12 and the cylinder 11. Due to these combined factors, backfires are likely to occur during operation of the internal combustion engine 10, particularly during supercharging.

[0035] The control device 100 continuously performs a first process while the internal combustion engine 10 is operating. When a backfire occurs in a cylinder 11, the downstream intake air temperature T momentarily rises during the intake stroke of that cylinder 11. Therefore, in the first process, the control device 100 constantly monitors the downstream intake air temperature T detected by the intake air temperature sensor 34. The control device 100 then determines whether a specific condition is met at intervals of 180 degrees around the crank position CRA, with zero degrees being the reference point. The specific condition is that the downstream intake air temperature T exceeds a threshold temperature for a sustained period of time. If the specific condition is met, the control device 100 determines that a backfire has occurred. If the specific condition is not met, the control device 100 determines that a backfire has not occurred. After determining whether a backfire has occurred, the control device 100 stores an index value indicating the determination result in the storage device 113. For example, the control device 100 stores "1" in the storage device 113 if it determines that a backfire has occurred, and stores "2" if it determines that a backfire has not occurred. The control device 100 repeats this determination and recording of the determination result at intervals of 180 degrees of the crank position CRA. In other words, the control device 100 determines whether or not a backfire has occurred for each intake stroke of each cylinder 11. The control device 100 obtains four determination results per combustion cycle. The control device 100 stores a predetermined number of data in the storage device 113 over time, overwriting old data with new data. The control device 100 treats this group of data over time as a backfire occurrence data group. The predetermined number is twice the set number of times described below. This predetermined number corresponds to the number of intake strokes performed when the crankshaft 17 rotates the set number of times.

[0036] The control device 100 stores the above-mentioned determination temperature and determination period in advance. The determination temperature is determined in advance, for example, through experiments or simulations, as a significantly high temperature that can be detected when a backfire occurs. The determination period is determined in advance, for example, through experiments or simulations, as a minimum length of time during which the downstream intake air temperature T remains equal to or higher than the determination temperature when a backfire occurs.

[0037] <About supercharging> The control device 100 supercharges intake air in the internal combustion engine 10 when the engine required torque exceeds a specified torque. The control device 100 is capable of executing basic processing as a prerequisite process for supercharging. The basic processing is processing for calculating a basic supercharging pressure QPn, which is a basic value of the target supercharging pressure QPt. The target supercharging pressure QPt is a target value of the supercharging pressure QP. The control device 100 continues to perform the basic processing while the internal combustion engine 10 is operating. In the basic processing, the control device 100 repeatedly calculates the basic supercharging pressure QPn. The basic supercharging pressure QPn is the supercharging pressure QP required to achieve the current engine required torque under the current engine speed NE and engine load factor KL. The control device 100 calculates the basic supercharging pressure QPn based on the latest engine required torque, the latest engine speed NE, and the latest engine load factor KL. When this basic supercharging pressure QPn becomes greater than zero, a supercharging request occurs.

[0038] The control device 100 is capable of executing a supercharging process as a process for actually performing supercharging when a supercharging request is made. The supercharging process is a process that repeatedly calculates a target supercharging pressure QPt and controls the WGV 25 based on the target supercharging pressure QPt. Controlling the WGV 25 based on the target supercharging pressure QPt means feedback-controlling the opening of the WGV 25 so that the actual supercharging pressure QP detected by the supercharging pressure sensor 37 matches the target supercharging pressure QPt. When feedback-controlling the opening of the WGV 25, the control device 100 outputs a command signal to an actuator to operate the WGV 25.

[0039] The supercharging process includes a normal process and a second process. The normal process and the second process differ in the way the target supercharging pressure QPt is set. The control device 100 performs the normal process if no backfire has occurred during a set period before supercharging is performed by the supercharger 20. In this normal process, the control device 100 sets the above-mentioned basic supercharging pressure QPn as the target supercharging pressure QPt.

[0040] On the other hand, the control device 100 performs a second process if backfire has occurred during a set period before supercharging. In the second process, the control device 100 performs supercharging at a lower supercharging pressure QP compared to when backfire has not occurred during the set period before supercharging. As a specific process for this purpose, in the second process, the control device 100 calculates an adjusted supercharging pressure ΔQP as an adjustment value for reducing the supercharging pressure QP. Then, as shown in the following (Equation 1), the control device 100 sets a value obtained by subtracting the adjusted supercharging pressure ΔQP from the basic supercharging pressure QPn as the target supercharging pressure QPt. This target supercharging pressure QPt is smaller by the adjusted supercharging pressure ΔQP than the target supercharging pressure QPt when normal processing is performed under conditions where the engine required torque, engine speed NE, and engine load factor KL are the same. (Formula 1) QPt=QPn-ΔQP When the adjusted supercharging pressure ΔQP exceeds the basic supercharging pressure QPn, the control device 100 sets the target supercharging pressure QPt to zero.

[0041] The control device 100 stores a specific map in advance as information for calculating the adjusted boost pressure ΔQP. As shown in FIG. 3, the specific map represents the relationship between the backfire occurrence frequency K during a set period and the adjusted boost pressure ΔQP. In this embodiment, the backfire occurrence frequency K is the number of times backfires occur during the set period. The specific map is created based on experiments or simulations, assuming that backfire occurrence is detected using the first processing method.

[0042] In this specific map, the backfire occurrence frequency K and the adjusted boost pressure ΔQP have the following relationship. When the backfire occurrence frequency K is less than the execution threshold K1, the adjusted boost pressure ΔQP is zero. On the other hand, when the backfire occurrence frequency K is equal to or greater than the execution threshold K1, the higher the backfire occurrence frequency K, the larger the adjusted boost pressure ΔQP. The adjusted boost pressure ΔQP corresponds to the reduction from the basic boost pressure QPn when setting the target boost pressure QPt. In other words, a larger adjusted boost pressure ΔQP means that the target boost pressure QPt is reduced by a larger amount compared to when no backfire occurs. And, if the basic boost pressure QPn is the same, the higher the backfire occurrence frequency K, the smaller the target boost pressure QPt.

[0043] The execution threshold K1 will be explained. Here, the backfire occurrence frequency K is an index showing the engine state regarding the likelihood of backfire occurrence. It can be said that the higher the backfire occurrence frequency K, the more likely the engine state is to cause backfire. The execution threshold K1 is determined as the minimum value of the boost pressure QP at which it is certain that the internal combustion engine 10 is in an engine state in which backfire is likely to occur and measures to suppress the occurrence of backfire are required.

[0044] The set period will now be described. The set period is predetermined as a period suitable for determining whether the internal combustion engine 10 is currently in a condition where backfire is likely to occur. In this embodiment, the set period is predetermined as a period during which the crankshaft 17 has rotated a predetermined number of times, such as 2000 times. In other words, the set period is determined as a period during which the internal combustion engine 10 performs a predetermined number of combustion cycles. As such, the set period in this embodiment is not constant on a time scale but is variable depending on the engine rotation speed NE.

[0045] <Specific processing routine for supercharging> As shown in Fig. 4, when a supercharging request occurs, the control device 100 starts a processing routine for supercharging the intake air (hereinafter referred to as the supercharging routine). That is, the control device 100 starts the supercharging routine when the basic supercharging pressure QPn calculated in the basic processing is switched from a state where the basic supercharging pressure QPn is zero to a value greater than zero. When the control device 100 starts the supercharging routine, it first executes the processing of step S10.

[0046] In step S10, the control device 100 determines whether a backfire occurred between the current time and a set period of time ago. Specifically, the control device 100 references the occurrence data group created in the first process. In relation to the above-described method for creating the occurrence data group, the occurrence data group represents the occurrence or non-occurrence of backfire over time from a set timing to the current time. The set timing is a time point preceding the current time by a period of time required for the crankshaft 17 to rotate a set number of times, i.e., a time point preceding the current time by the set period of time. The control device 100 determines whether at least one identification value indicating the occurrence of backfire exists in the occurrence data group. If no identification value indicating the occurrence of backfire exists (step S10: NO), the control device 100 proceeds to step S80.

[0047] In step S80, the control device 100 selects normal supercharging processing. The control device 100 then starts supercharging the intake air using normal processing. That is, from this point onward, the control device 100 controls the WGV 25 using the most recent basic supercharging pressure QPn calculated in the basic processing as the target supercharging pressure QPt. The control device 100 repeatedly calculates the target supercharging pressure QPt and controls the WGV 25 based on the target supercharging pressure QPt. Here, the basic supercharging pressure QPn calculated by the control device 100 in the basic processing changes as needed depending on the transition of the engine required torque, etc. Until the normal processing ends in step S50, which will be described later, the control device 100 feedback-controls the opening degree of the WGV 25 in accordance with the basic supercharging pressure QPn so as to realize the constantly changing basic supercharging pressure QPn. After starting normal processing, the control device 100 proceeds to step S40.

[0048] On the other hand, in step S10, if the occurrence data group contains at least one identification value that indicates the occurrence of a backfire (step S10: YES), the control device 100 proceeds to step S20.

[0049] In step S20, the control device 100 selects the second process as the supercharging process. Then, the control device 100 calculates the adjusted supercharging pressure ΔQP as a preparatory process of the second process. Specifically, the control device 100 refers to the occurrence data group. Then, the control device 100 counts the number of backfire occurrences. Then, the control device 100 treats the counted number of backfire occurrences as the pre-supercharging frequency, which is the backfire occurrence frequency K from the current time until a set period ago. Next, the control device 100 refers to a specific map. Then, the control device 100 calculates the adjusted supercharging pressure ΔQP corresponding to the pre-supercharging frequency based on the specific map. After this, the control device 100 proceeds to step S30.

[0050] In step S30, the control device 100 starts the main processing of the second set of steps. That is, from this point on, the control device 100 repeatedly calculates the target boost pressure QPt using (Equation 1) and controls the WGV 25 based on the target boost pressure QPt. When calculating the target boost pressure QPt, the control device 100 applies the latest basic boost pressure QPn, which is calculated as needed in the basic processing, and the adjusted boost pressure ΔQP calculated in step S20 to (Equation 1). As described in step S80, the basic boost pressure QPn calculated by the control device 100 in the basic processing changes as needed. Accordingly, the target boost pressure QPt calculated at each timing by the control device 100 using (Equation 1) also changes as needed. The control device 100 continues to feedback-control the opening degree of the WGV 25 so as to achieve this constantly changing target boost pressure QPt until the second processing ends in step S50, which will be described later. When the control device 100 starts the main processing of the second process, the control device 100 proceeds to step S40. During execution of the second process, the control device 100 makes the torque of the motor generator 82 greater than the motor required torque determined from the required driving force. Specifically, the control device 100 calculates an estimate of the current torque of the internal combustion engine 10 based on the latest engine speed NE, the latest engine load factor KL, the latest target boost pressure QPt, etc. Then, the control device 100 makes the torque of the motor generator 82 greater than the motor required torque by the absolute value of the difference between this estimate and the engine required torque.

[0051] In step S40, the control device 100 determines whether or not the supercharging request has disappeared. Specifically, the control device 100 determines whether or not the basic supercharging pressure QPn calculated in the basic processing has switched from a value greater than zero to zero. If the basic supercharging pressure QPn remains greater than zero (step S40: NO), the control device 100 executes the processing of step S40 again. The control device 100 repeats the processing of step S40 until the basic supercharging pressure QPn switches to zero. If the basic supercharging pressure QPn switches to zero (step S40: YES), the control device 100 proceeds to the processing of step S50.

[0052] In step S50, the control device 100 ends the supercharging process currently being executed, and then ends the series of processes in the supercharging routine. <Operation of the First Embodiment> Assume now that backfires are occurring frequently. Assume that a supercharging request is made under these circumstances. Then, the control device 100 calculates an adjusted supercharging pressure ΔQP corresponding to the backfire occurrence frequency K from the present time until a set period ago (step S20). Then, the control device 100 sets a value obtained by subtracting the adjusted supercharging pressure ΔQP from the basic supercharging pressure QPn as the target supercharging pressure QPt, and controls the WGV 25 (step S30).

[0053] <Effects of the first embodiment> (1-1) If backfire has occurred during a set period before a supercharging request is made, the engine state at the time the supercharging request is made is often one in which backfire is likely to occur. In this case, supercharging may be performed under engine conditions in which backfire is likely to occur. Therefore, in this embodiment, if backfire has occurred before a supercharging request is made, supercharging is performed at a lower supercharging pressure QP than when backfire has not occurred. This makes it possible to make the engine state during supercharging an engine state in which backfire is least likely to occur. Therefore, it is possible to suppress the occurrence of backfire during supercharging.

[0054] (1-2) As described above, the backfire occurrence frequency K during the set period serves as an index showing the engine state regarding the likelihood of backfire. The higher the backfire occurrence frequency K, the more likely the engine state is to cause backfire. Therefore, in this embodiment, the higher the backfire occurrence frequency K, that is, the more likely the situation is to cause backfire, the larger the adjusted boost pressure ΔQP, which is the amount by which the target boost pressure QPt is reduced. In this way, by determining the amount by which the target boost pressure QPt is reduced depending on the likelihood of backfire, backfire can be more appropriately suppressed.

[0055] (1-3) The greater the number of combustion cycles, i.e., the greater the number of intake strokes, the greater the backfire occurrence frequency K. In this embodiment, the setting period is determined based on the number of combustion cycles. Therefore, when determining the adjusted boost pressure ΔQP, which is the amount of reduction in the target boost pressure QPt, the backfire occurrence frequency K that occurs under the same number of combustion cycles can be used as a reference. Therefore, a target boost pressure QPt that is more appropriate for suppressing backfire can be set.

[0056] [Second embodiment] A second embodiment of the control device for an internal combustion engine will be described. In the second embodiment, only the content of the supercharging process differs from the first embodiment. In the following, the differences from the first embodiment will be mainly described, and the description of the content that overlaps with the first embodiment will be simplified or omitted.

[0057] As in the first embodiment, the control device 100 repeatedly calculates the target boost pressure QPt and controls the WGV 25 based on the target boost pressure QPt during the supercharging process. However, in this embodiment, the control device 100 calculates the target boost pressure QPt using a method different from that of the first embodiment. Specifically, the control device 100 takes into account the upper limit of the boost pressure QP of the supercharger 20 when calculating the target boost pressure QPt. As prerequisite information for this calculation, the control device 100 pre-stores a basic upper limit value Vs. The basic upper limit value Vs is an upper limit value of the boost pressure QP that is allowed when backfire suppression does not need to be considered, and is determined in advance, for example, through experiments or simulations. The basic upper limit value Vs is a value determined in consideration of limits determined from various specifications of the internal combustion engine 10, such as the volume of the cylinder 11 and the supercharging capacity of the supercharger 20. Prior to calculating the target boost pressure QPt, the control device 100 calculates an upper limit boost pressure Vm, which is the upper limit value of the boost pressure QP that should be set at the current time, based on the basic upper limit value Vs. Then, the control device 100 calculates the target boost pressure QPt using this upper limit boost pressure Vm as the upper limit.

[0058] As explained in the first embodiment, there are two types of supercharging processing: normal processing and second processing. The normal processing is performed when backfire has not occurred before supercharging. The second processing is performed when backfire has occurred before supercharging. In this embodiment, the normal processing and the second processing differ in the way the upper limit supercharging pressure Vm is set. In the normal processing, the control device 100 sets the above-mentioned basic upper limit value Vs as the upper limit supercharging pressure Vm.

[0059] On the other hand, in the second processing, the control device 100 reduces the upper limit boost pressure Vm compared to when backfire did not occur during the set period before supercharging. As a specific processing for this purpose, in the second processing, the control device 100 calculates an adjusted boost pressure ΔQP as an adjustment value for reducing the upper limit boost pressure Vm. Then, as shown in the following (Equation 2), the control device 100 sets the upper limit boost pressure Vm to a value obtained by subtracting the adjusted boost pressure ΔQP from the basic upper limit value Vs. This upper limit boost pressure Vm is reduced by the adjusted boost pressure ΔQP compared to the upper limit boost pressure Vm when normal processing is performed. (Formula 2) Vm=Vs-ΔQP The control device 100 pre-stores a specific map similar to that of the first embodiment as information for calculating the adjusted boost pressure ΔQP. That is, the specific map represents the relationship between the backfire occurrence frequency K during a set period and the adjusted boost pressure ΔQP. However, the adjusted boost pressure ΔQP defined in the specific map of this embodiment is a value dedicated to adjusting the upper limit boost pressure Vm. The maximum value of the adjusted boost pressure ΔQP defined in the specific map is smaller than the basic upper limit value Vs. As described in the first embodiment, the backfire occurrence frequency K and the adjusted boost pressure ΔQP have the following relationship. When the backfire occurrence frequency K is less than the execution threshold K1, the adjusted boost pressure ΔQP is zero. On the other hand, when the backfire occurrence frequency K is equal to or greater than the execution threshold K1, the adjusted boost pressure ΔQP increases as the backfire occurrence frequency K increases. Note that, as in the first embodiment, the backfire occurrence frequency K is the number of backfire occurrences during the set period itself.

[0060] <Operation of the Second Embodiment> As an operation of this embodiment, a processing step according to the supercharging routine shown in FIG. 5 will be briefly described. The processing contents of steps S10, S40, and S50 are the same as those of the first embodiment, and therefore will not be described here. When the control device 100 determines in step S10 that backfire has not occurred (step S10: NO), the control device 100 proceeds to step S180. In this case, the control device 100 starts supercharging of intake air using normal processing. As described above, in normal processing, the control device 100 sets the basic upper limit value Vs as the upper limit supercharging pressure Vm. Then, the control device 100 calculates the smaller of the upper limit supercharging pressure Vm and the latest basic supercharging pressure QPn as the target supercharging pressure QPt. Then, the control device 100 controls the WGV 25 based on the target supercharging pressure QPt. The control device 100 repeatedly calculates the target supercharging pressure QPt and controls the WGV 25 based on the target supercharging pressure QPt.

[0061] On the other hand, if the control device 100 determines in step S10 that backfire has occurred (step S10: YES), the control device 100 proceeds to step S20. Then, in step S20, the control device 100 calculates the adjusted boost pressure ΔQP in the same manner as in step S20 of the first embodiment. After this, in step S130, the control device 100 starts the main processing of the second processing. As described above, in the second processing, the control device 100 calculates the upper limit boost pressure Vm by applying the basic upper limit value Vs and the adjusted boost pressure ΔQP calculated in step S20 to (Equation 2). Then, the control device 100 calculates the smaller of the upper limit boost pressure Vm or the latest basic boost pressure QPn as the target boost pressure QPt. Then, the control device 100 controls the WGV 25 based on the target boost pressure QPt. The control device 100 repeatedly calculates the target boost pressure QPt and controls the WGV 25 based on the target boost pressure QPt.

[0062] <Effects of the second embodiment> (2-1) As explained in the first embodiment, if backfire occurs during a set period before a supercharging request is made, the engine state at the time the supercharging request is made is often one in which backfire is likely to occur. Therefore, in this embodiment, if backfire occurs before a supercharging request is made, the upper limit supercharging pressure Vm is made smaller than when backfire does not occur. This makes it possible to perform supercharging at the lowest possible supercharging pressure QP. This also makes it possible to make the engine state during supercharging an engine state in which backfire is least likely to occur. Therefore, it is possible to suppress the occurrence of backfire during supercharging.

[0063] (2-2) In this embodiment, the higher the backfire occurrence frequency K, that is, the more likely a backfire is to occur, the larger the adjusted boost pressure ΔQP, which is the amount by which the upper limit boost pressure Vm is reduced. In this way, by determining the amount by which the upper limit boost pressure Vm is reduced depending on the likelihood of backfire occurring, backfire can be more appropriately suppressed.

[0064] (2-3) As in the first embodiment, in this embodiment, the set period is determined based on the number of combustion cycles. Therefore, the frequency K of backfires occurring under the same number of combustion cycles can be used as a reference when determining the adjusted boost pressure ΔQP, which is the amount by which the upper limit boost pressure Vm is reduced. Therefore, the upper limit boost pressure Vm can be set to a value that is more appropriate for suppressing backfires.

[0065] [Example of change] The above-described embodiments can be modified as follows: The embodiments and the following modifications can be combined with each other within the scope of technical compatibility.

[0066] The method for determining whether or not a backfire has occurred in the first process is not limited to the example of the above embodiment. For example, the occurrence of a backfire may be determined using a parameter other than the downstream intake air temperature T. Here, when a backfire occurs, the pressure of the intake air downstream of the throttle valve 16 in the intake passage 12 momentarily increases. Focusing on this point, the occurrence of a backfire may be determined based on the change in the intake air pressure downstream of the throttle valve 16 in the intake passage 12. When adopting such an embodiment, an intake pressure sensor that detects the pressure of the intake air may be attached downstream of the throttle valve 16 in the intake passage 12. Alternatively, the occurrence of a backfire may be determined using the change in the pressure of the gas in the cylinder 11, the change in the engine speed NE, or the like. Any determination method may be used as long as it is based on the operating state of the internal combustion engine 10 and can appropriately detect the occurrence of a backfire.

[0067] The method of recording the determination results in the first process is not limited to the example of the above embodiment. The method of recording the determination results may be any method that allows the occurrence of backfires at a stage prior to the occurrence of a supercharging request to be grasped. As in the modified example below, the set of data required to grasp the backfire occurrence frequency K varies depending on how the set period is defined. Therefore, the method of recording the determination results may be changed according to how the set period is defined.

[0068] In determining whether or not a backfire has occurred before supercharging in step S10, the criteria may not be whether or not a single backfire has occurred, but may be whether or not multiple backfires have occurred. In other words, it may be determined whether or not backfire has occurred a predetermined number of times or more before supercharging. In step S10, it is sufficient to be able to determine whether or not a backfire has occurred before supercharging.

[0069] In step S20, the adjusted boost pressure ΔQP is calculated based on the correspondence with the backfire occurrence frequency K. The definition of the backfire occurrence frequency K used at this time is not limited to the number of backfires. The backfire occurrence frequency K may be anything that can grasp the degree of backfire occurrence. For example, the backfire occurrence frequency K may be a percentage instead of the number of backfire occurrences. If the definition of the backfire occurrence frequency K is changed, the content of the specific map can be changed accordingly.

[0070] The backfire that occurs closest to the time when a supercharging request was made is called the final backfire. The backfire occurrence frequency K may be calculated by using the period from the time when the final backfire occurred until the time when a supercharging request was made. The shorter this period, the higher the backfire occurrence frequency K may be considered.

[0071] The method for determining the set period is not limited to the example of the above embodiment. For example, the set period may be a fixed value (hereinafter referred to as a fixed set period). The fixed set period may be, for example, about several minutes. Such a time scale is suitable for determining whether the internal combustion engine 10 is currently in a condition where backfire is likely to occur.

[0072] When a fixed set period is used, the set period is determined as an absolute time, unlike the above embodiment in which the set period was determined based on the number of rotations of the crankshaft 17 and thus the number of combustion cycles. In this case, when calculating the backfire occurrence frequency K within the set period in step S20, it is easier to grasp the backfire occurrence frequency K if there is a backfire history along the time progression rather than a backfire history along the progression of the combustion cycle. In light of this, when a fixed set period is used, the following first aspect may be adopted when recording the backfire occurrence status in the first process. Here, in the above embodiment, the determination results were chronologically recorded, including not only cases in which a backfire occurred but also cases in which a backfire did not occur, to create an occurrence data group. In the first aspect, information when a backfire did not occur is not recorded, and only information when a backfire occurred is stored in the storage device 113. In other words, the first determination information is stored in the storage device 113 only when the above specific condition is met. The first determination information represents the time when the specific condition is met, expressed in units of seconds or less. If the time information is recorded, when a supercharging request is made, by comparing the time when the supercharging request was made with the time when the backfire occurred, it is possible to determine whether the backfire occurred within a set period before the supercharging request was made. In the first mode, a certain number of pieces of such time information are accumulated while overwriting old data with new data to form an occurrence data group. In such an occurrence data group, by omitting information indicating that a backfire did not occur, the number of pieces of data necessary to determine the occurrence status of a backfire can be kept to a minimum. Therefore, the number of pieces of data that make up the occurrence data group can be set to be small. This also reduces the data capacity of the occurrence data group.

[0073] The set period may be determined as a period during which the vehicle 90 has traveled a predetermined distance (hereinafter referred to as the "specified distance"). The specified distance may be, for example, about 1 km, as long as the set period can be determined from the same perspective as in the above embodiment. Hereinafter, the set period determined in correspondence with the travel distance of the vehicle 90 will be referred to as the "set travel period."

[0074] When using the set driving period, the following second mode may be employed to record the occurrence of backfire in the first process. That is, in the second mode, similar to the first mode, the second identification information is stored in the storage device 113 only when the specific condition indicating the occurrence of backfire is met. The second identification information is the value of the trip meter 35 expressed in meters at the time the specific condition is met. That is, the occurrence data group in this case is a certain number of accumulated trip meter 35 values, with new data overwriting old data. In this case, the value of the trip meter 35 is used to determine whether or not a backfire occurred during the set driving period before supercharging, and therefore the number of times a backfire occurred. Specifically, the occurrence of a backfire can be determined as follows. Now, suppose that supercharging is requested. The value of the trip meter 35 at the time this supercharging request is requested is referred to as the requested meter value. A value smaller than this requested meter value by a specified distance is referred to as the back-calculated value. If the value of the trip meter 35 stored in the storage device 113 is between the meter value at the time of request and the back-calculation value, it can be determined that a backfire occurred after the specified timing. The specified timing is a timing that goes back a specified distance from the time when a supercharging request was made, that is, a timing that goes back a set traveling period from the time when a supercharging request was made. In this way, by determining whether the value of the trip meter 35 included in the generated data group is a value that goes back a specified distance from the meter value at the time of request and the back-calculation value, it is possible to determine the occurrence of a backfire during the set traveling period before supercharging was performed.

[0075] When the above-described travel setting period is employed, it is preferable to employ the backfire occurrence rate as the backfire occurrence frequency K used to calculate the adjusted boost pressure ΔQP. The reason is as follows. Consider a situation in which the vehicle 90 travels the specified distance while remaining in a certain gear. Because the gear is constant, the number of rotations of the crankshaft 17, and therefore the number of combustion cycles, required to travel this specified distance is determined to a unique value corresponding to the wheel diameter and the gear ratio. This unique value differs for each gear. In other words, if a certain gear remains in a certain gear during the travel setting period, the number of combustion cycles during that travel setting period is determined to a unique value for each gear. Therefore, by using the travel setting period, it is possible to count the number of backfire occurrences by aligning the number of combustion cycles for each gear, even if the gear remains constant during the travel setting period. In light of this, when using the travel setting period, the following specification is also effective. That is, in the prescribed mode, the number of combustion cycles in the travel setting period is stored in advance in the storage device 113 for each gear position. Supercharging When requested, Supercharging The number of backfire occurrences during the travel setting period before the request is divided by the number of combustion cycles corresponding to the gear during that travel setting period. This calculates the backfire occurrence rate as the backfire occurrence frequency K. The calculated backfire occurrence rate is then applied to a specific map to calculate the adjusted boost pressure ΔQP. The above-described specification mode is also effective when the gear is constant during the travel setting period. In this specification mode, a specific map showing the relationship between the backfire occurrence rate and the adjusted boost pressure ΔQP may be created in advance. This specific map establishes a relationship such that the higher the backfire occurrence rate, the greater the adjusted boost pressure ΔQP. Furthermore, when the specification mode is adopted, the memory device 113 may store a history of the target gear set as needed while the vehicle 90 is traveling. This allows the gear during the travel setting period before the boost pressure is increased to be known.

[0076] The adoption of the above-described defining aspect has the following advantages. First, as described above, by using the set travel time period, it is possible to count the number of backfire occurrences by aligning the number of combustion cycles for each gear. Furthermore, by using the backfire occurrence rate, it is possible to calculate the backfire occurrence frequency K while eliminating the influence of differences in the number of combustion cycles for each gear. By calculating the adjusted boost pressure ΔQP from this occurrence frequency K, it is possible to calculate the adjusted boost pressure ΔQP based on a uniform standard for the likelihood of backfire occurrence. Here, when using the set travel time period, the above-described second aspect can be used to record the backfire occurrence status. In this case, the second aspect can reduce the data volume of the occurrence data group, as in the first aspect. Therefore, by combining the second aspect with the defining aspect, it is possible to set an appropriate adjusted boost pressure ΔQP while reducing the data volume.

[0077] The parameter (hereinafter referred to as the "prescribed parameter") that prescribes the magnitude of the adjusted boost pressure ΔQP when calculating the adjusted boost pressure ΔQP in step S20 is not limited to the backfire occurrence frequency K. The prescribed parameter may be any parameter that serves as an index showing the engine state regarding the likelihood of backfire occurrence. The downstream intake air temperature T may be used as the prescribed parameter. In this case, for example, the specific temperature map shown in FIG. 6 may be used to calculate the adjusted boost pressure ΔQP. This specific map represents the relationship between the pre-intake air temperature TB, which is the downstream intake air temperature T before supercharging, and the adjusted boost pressure ΔQP. The pre-intake air temperature TB is, for example, the average value of the downstream intake air temperature T over a certain period of time before a supercharging request is made. The certain period is, for example, one minute, and is predetermined as a length of time that allows the average downstream intake air temperature T at the start of supercharging to be determined. The set period used in step S10 may be used as the certain period. In the specific map, the pre-intake air temperature TB and the adjusted boost pressure ΔQP have the following relationship: When the pre-intake temperature TB is less than the first threshold T1, the adjusted boost pressure ΔQP is zero. On the other hand, when the pre-intake temperature TB is equal to or greater than the first threshold T1, the adjusted boost pressure ΔQP increases as the pre-intake temperature TB increases. Furthermore, even when the pre-intake temperature TB is equal to or greater than the first threshold T1, the rate of increase of the adjusted boost pressure ΔQP relative to the pre-intake temperature TB varies depending on the magnitude of the pre-intake temperature TB. Specifically, when the pre-intake temperature TB is equal to or greater than the second threshold T2, the rate of increase is greater than when the pre-intake temperature TB is equal to or greater than the first threshold T1 and less than the second threshold T2. Based on this setting, when the pre-intake temperature TB is equal to or greater than the second threshold T2, the adjusted boost pressure ΔQP increases significantly. The first threshold T1 will be explained. Here, the higher the pre-intake temperature TB, the more likely the engine is to experience backfire. The first threshold T1 is defined as the minimum pre-intake temperature TB at which it is certain that the internal combustion engine 10 is in an engine state prone to backfire and measures to suppress backfire are necessary. The second threshold value T2 will now be described. The second threshold value T2 is set as the pre-intake air temperature TB at which a significant measure is required to prevent backfire.The specific map including the first threshold value T1 and the second threshold value T2 is created based on experiments or simulations.

[0078] When the specific map shown in FIG. 6 is applied to the configuration of the first embodiment, the following can be said. As described in the first embodiment, the adjusted boost pressure ΔQP corresponds to the amount of reduction from the basic boost pressure QPn when setting the target boost pressure QPt. In other words, a larger adjusted boost pressure ΔQP means that the target boost pressure QPt is reduced by a larger amount compared to when backfire does not occur. Therefore, when the adjusted boost pressure ΔQP is set using the above specific map, the higher the pre-intake air temperature TB, the larger the amount of reduction in the boost pressure QP is compared to when backfire does not occur. For the same basic boost pressure QPn, the higher the pre-intake air temperature TB, the smaller the target boost pressure QPt. In this way, by determining the amount of reduction in the target boost pressure QPt depending on the likelihood of backfire occurring, backfire can be more appropriately suppressed.

[0079] Similarly, when the specific map shown in FIG. 6 is applied to the configuration of the second embodiment, the following can be said. As explained in the second embodiment, the adjusted boost pressure ΔQP corresponds to the amount of reduction from the basic upper limit value Vs when setting the upper limit boost pressure Vm. In other words, a large adjusted boost pressure ΔQP means that the amount of reduction in the upper limit boost pressure Vm is increased compared to when backfire does not occur. Therefore, when the adjusted boost pressure ΔQP is set using the above specific map, the higher the pre-intake air temperature TB, the greater the amount of reduction in the upper limit boost pressure Vm is increased compared to when backfire does not occur. In this way, by determining the amount of reduction in the upper limit boost pressure Vm depending on the likelihood of backfire occurring, backfire can be more appropriately suppressed.

[0080] 6, the adjustment supercharging pressure ΔQP can be calculated by storing the history of the downstream intake air temperature T in the storage device 113. In this way, when a supercharging request is made, the pre-intake air temperature TB can be calculated for a certain period of time from that point in time.

[0081] As described in the various modified examples above, the content of the specific map is not limited to the example of the above embodiment. The content of the specific map may be changed as appropriate depending on how the set period is determined, the specified parameters, etc. The specific map only needs to have content that allows the adjusted boost pressure ΔQP to be calculated appropriately. The specific map is not limited to a table or graph, and may also be a mathematical formula.

[0082] It is not essential to increase or decrease the adjusted boost pressure ΔQP depending on the backfire occurrence frequency K, etc. In other words, the adjusted boost pressure ΔQP may be set to a predetermined fixed value. The overall configuration of the internal combustion engine 10 is not limited to the example of the above embodiment. For example, the number of cylinders 11 may be changed. The fuel injection valve 14 may be changed to a type that injects fuel directly into the cylinder 11. The fuel injected from the fuel injection valve 14 is not limited to hydrogen, and any gaseous fuel may be used. If the downstream intake air temperature T is not used in both the first process and the second process, the intake air temperature sensor 34 may be eliminated. The internal combustion engine 10 only needs to have the cylinders 11, the intake passage 12, and the turbocharger 20.

[0083] The configuration of the turbocharger 20 may be changed. For example, a variable displacement turbocharger equipped with a nozzle vane may be used. In this case, the opening of the nozzle vane may be changed to make the actual supercharging pressure QP coincide with the target supercharging pressure QPt during the supercharging process. Also, an electric supercharger in which a compressor wheel is rotated by an electric motor may be used. In this case, the rotation speed of the electric motor may be changed to make the actual supercharging pressure QP coincide with the target supercharging pressure QPt during the supercharging process.

[0084] The overall configuration of the vehicle 90 is not limited to the example of the above embodiment. For example, a continuously variable transmission may be used as the automatic transmission 85. The vehicle may have only the internal combustion engine 10 as a drive source. In this case, it is possible to compensate to some extent for the decrease in torque of the internal combustion engine 10 that occurs when the second process is performed by adjusting, for example, the ignition timing or the air-fuel ratio. [Explanation of symbols]

[0085] 10...Internal combustion engine 11...cylinder 12...Intake passage 17...Crankshaft 20...Turbocharger 34...Intake air temperature sensor 90...Vehicle 100...Control device

Claims

[Claim 1] The control target is an internal combustion engine having a cylinder in which a mixture of gaseous fuel and intake air is burned, an intake passage connected to the cylinder, a supercharger that supercharges the intake air, and a crankshaft, The vehicle is a vehicle equipped with the internal combustion engine, the vehicle having a trip meter that measures the mileage of the vehicle and a stepped automatic transmission, When the period during which the crankshaft rotates 720 degrees is defined as one combustion cycle, the number of combustion cycles required for the vehicle to travel 1 km is stored in advance for each gear position of the automatic transmission; While the vehicle is running, a history of a target gear position, which is a target value of the gear position, is stored; During operation of the internal combustion engine, a first process for determining whether a condition indicating the occurrence of a backfire is satisfied based on an operating state of the internal combustion engine, and storing the value of the trip meter at the time when the condition is satisfied as specific information only when the condition is satisfied; When the value of the trip meter at the time when a supercharging request is made is defined as a requested meter value, a value that is 1 km smaller than the requested meter value is defined as a back-calculated value, and a travel period of the equipped vehicle during which the value of the trip meter reaches the requested meter value from the back-calculated value is defined as a set period, When the target gear position is constant during the set period before the supercharging request occurs, a second process for calculating the number of backfire occurrences between the back-calculated value and the requested meter value based on the specific information stored in the first process, calculating a backfire occurrence rate by dividing the calculated number of occurrences by the number of combustion cycles corresponding to the gear position during the set period ascertained from the history of the target gear position, and performing supercharging at a lower supercharging pressure as the occurrence rate increases compared to when no backfire occurred during the set period before the supercharging request is made; Run Control device for internal combustion engines.

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