Control device for internal combustion engine

Abstract

To suppress misfire during increase correction of a fuel injection amount.SOLUTION: A control device 100 for an internal combustion engine includes an injection mode switching unit 25 that switches an injection mode when fuel is injected into a combustion chamber of the internal combustion engine to any one of a plurality of injection modes according to an operation state of the internal combustion engine, a correction coefficient calculation unit 28 that calculates a correction coefficient for increasing a reference injection amount of fuel calculated according to the operation state of the internal combustion engine over a predetermined period from a starting start time point of the internal combustion engine, and a limit value calculation unit 29 that calculates a limit value of an intake air amount of the internal combustion engine over the predetermined period. A correction coefficient calculation part 28 calculates a correction coefficient so as to be gradually reduced with the lapse of a combustion cycle of the internal combustion engine based on a characteristic predetermined to each of the plurality of injection modes. The limit value calculation unit 29 calculates the limit value so that the limit value gradually increases as the correction coefficient decreases.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] In recent years, research and development has been conducted on direct-injection internal combustion engines that contribute to energy efficiency, ensuring access to affordable, reliable, sustainable, and advanced energy for more people. A known example of this type of technology is a device that controls fuel injection immediately after starting a direct-injection internal combustion engine (see, for example, Patent Document 1). In the device described in Patent Document 1, for a predetermined period after starting, when fuel is injected in divided injections, the boost correction coefficient for boosting the fuel injection amount is set to a larger value than when fuel is injected in batch injections to compensate for insufficient fuel vaporization during cold engine operation. After the predetermined period has elapsed, the boost correction coefficient is set to a larger value when fuel is injected in batch injections than when fuel is injected in divided injections. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-183537 Summary of the Invention [Problem to be solved by the invention]

[0004] However, if the fuel injection amount is increased as in the device described in Patent Document 1, the end of fuel injection (EOI (End Of Injection)) may be delayed, and some of the injected fuel may not be sufficiently vaporized by the time of ignition, which may lead to misfire. [Means for solving the problem]

[0005] According to one aspect of the present invention, there is provided a control device for an internal combustion engine, the control device including: an injection mode switching unit that switches an injection mode for injecting fuel into a combustion chamber of the internal combustion engine to one of a plurality of injection modes depending on an operating state of the internal combustion engine; a correction coefficient calculation unit that calculates a correction coefficient for increasing a reference injection amount of fuel calculated depending on the operating state of the internal combustion engine over a predetermined period from the start of startup of the internal combustion engine; and a limit value calculation unit that calculates a limit value for an intake amount of the internal combustion engine over the predetermined period. The correction coefficient calculation unit calculates the correction coefficient based on predetermined characteristics for each of the plurality of injection modes so that the correction coefficient gradually decreases as the combustion cycle of the internal combustion engine progresses. The limit value calculation unit calculates the limit value so that the limit value gradually increases as the correction coefficient decreases. [Effects of the Invention]

[0006] According to the present invention, misfires can be suppressed during the increase correction of the fuel injection amount. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a diagram showing an example of a configuration of a main part of an engine to which a control device for an internal combustion engine according to an embodiment of the present invention is applied; [Figure 2] 1 is a block diagram that schematically shows an example of the overall configuration of a control device for an internal combustion engine according to an embodiment of the present invention; [Figure 3] 3 is a diagram for explaining a first mode, a second mode, and a third injection mode switched by an injection mode switching unit in FIG. 2; FIG. [Figure 4] 3 is a diagram for explaining an example of a limit value calculated by the limit value calculation unit in FIG. 2; [Figure 5A] 10 is a diagram for explaining another example of the limit value calculated by the limit value calculation unit in FIG. 2 when the injection mode is switched from one in which the correction coefficient of the fuel injection amount is relatively small to one in which the correction coefficient is relatively large. [Figure 5B] 10 is a diagram for explaining another example of the limit value calculated by the limit value calculation unit in FIG. 2 when the injection mode is switched from one in which the correction coefficient of the fuel injection amount is relatively large to one in which the correction coefficient is relatively small. [Figure 6] 10 is a diagram for explaining yet another example of limit value calculation by the limit value calculation unit of FIG. 2. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, an embodiment of the present invention will be described with reference to Figures 1 to 6. A control device for an internal combustion engine according to an embodiment of the present invention can be applied to a direct injection spark ignition internal combustion engine. In particular, an example in which the control device is applied to a direct injection spark ignition internal combustion engine mounted on a vehicle supplied with an alcohol-containing fuel containing alcohol such as bioethanol will be described below.

[0009] FIG. 1 is a diagram that schematically shows an example of the configuration of the main parts of an engine 1 to which an internal combustion engine control device according to an embodiment of the present invention is applied. The engine 1 is a direct-injection, spark-ignition internal combustion engine mounted on a vehicle (not shown), and is a four-stroke engine that undergoes four strokes during one combustion cycle: an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke. The engine 1 has multiple cylinders, such as four cylinders, but FIG. 1 shows the configuration of a single cylinder. Note that the configuration of each cylinder is identical to one another.

[0010] As shown in Fig. 1, the engine 1 has a cylinder 2a formed in a cylinder block 2, a piston 3 slidably disposed inside the cylinder 2a, and a combustion chamber 5 formed between the crown surface of the piston 3 (piston crown surface) and a cylinder head 4. The piston 3 is connected to a crankshaft 7 via a connecting rod 6, and the crankshaft 7 rotates as the piston 3 reciprocates along the inner wall of the cylinder 2a.

[0011] The cylinder head 4 is provided with an intake port 8 and an exhaust port 9. An intake passage 10 communicates with the combustion chamber 5 via the intake port 8, and an exhaust passage 11 communicates with the combustion chamber 5 via the exhaust port 9. The intake port 8 is opened and closed by an intake valve 12, and the exhaust port 9 is opened and closed by an exhaust valve 13. A throttle valve 14 is provided in the intake passage 10 upstream of the intake valve 12. The throttle valve 14 is formed, for example, by a butterfly valve, and adjusts the amount of air intake into the combustion chamber 5. The intake valve 12 and the exhaust valve 13 are driven to open and close by a valve mechanism 15.

[0012] An ignition plug 16 and a direct injection injector 17 are attached to the cylinder head 4 so that they each face the combustion chamber 5. The ignition plug 16 is positioned between the intake port 8 and the exhaust port 9, and generates a spark using electrical energy to ignite the fuel-air mixture in the combustion chamber 5.

[0013] The injector 17 is disposed near the intake valve 12 and is driven by electrical energy to inject fuel. More specifically, the injector 17 receives high-pressure fuel from a fuel tank via a fuel pump. The injector 17 atomizes the fuel and injects the fuel diagonally downward into the combustion chamber 5 at a predetermined timing. The location of the injector 17 is not limited to this, and it may also be disposed near the spark plug 16, for example.

[0014] The valve train 15 has an intake camshaft 18 and an exhaust camshaft 19. The intake camshaft 18 has integrally therewith intake cams 18a corresponding to each cylinder (cylinder 2a), and the exhaust camshaft 19 has integrally therewith exhaust cams 19a corresponding to each cylinder. The intake camshaft 18 and the exhaust camshaft 19 are connected to the crankshaft 7 via a timing belt (not shown), and each rotates once for every two rotations of the crankshaft 7.

[0015] The intake valve 12 opens and closes at a predetermined timing according to the profile of an intake cam 18a via an intake rocker arm (not shown) as a result of the rotation of the intake camshaft 18. The exhaust valve 13 opens and closes at a predetermined timing according to the profile of an exhaust cam 19a via an exhaust rocker arm (not shown) as a result of the rotation of the exhaust camshaft 19.

[0016] Fig. 2 is a block diagram showing an example of the overall configuration of an internal combustion engine control device (hereinafter referred to as device) 100 according to an embodiment of the present invention. As shown in Fig. 2, the device 100 mainly includes an electronic control unit (ECU (Electronic Control Unit)) 20 that controls the engine 1 shown in Fig. 1. Connected to the ECU 20 are a crank angle sensor 21, an accelerator opening sensor 22, a water temperature sensor 23, an intake amount sensor 24, the throttle valve 14 shown in Fig. 1, the spark plug 16, and the injector 17.

[0017] The ECU 20 includes a computer having a processor such as a CPU, memories such as RAM and ROM, and other peripheral circuits. The ECU 20 has, as functional components, an injection mode switching unit 25, an ignition control unit 26, an injection control unit 27, a correction coefficient calculation unit 28, and a limit value calculation unit 29, and functions as the injection mode switching unit 25, the ignition control unit 26, the injection control unit 27, the correction coefficient calculation unit 28, and the limit value calculation unit 29.

[0018] 1, and is configured to output a pulse signal in accordance with the rotation of the crankshaft 7. Based on the pulse signal from the crank angle sensor 21, the ECU 20 determines the rotation angle (crank angle) of the crankshaft 7 relative to the position of top dead center TDC when the piston 3 starts the intake stroke, and calculates the engine speed Ne.

[0019] The accelerator position sensor 22 is provided on an accelerator pedal (not shown) of the vehicle and detects the amount of accelerator pedal operation (accelerator position). The ECU 20 calculates a target torque for the engine 1 based on the detected value of the accelerator position sensor 22, calculates a target intake amount and a target opening of the throttle valve 14 (target throttle opening) for generating the target torque, and controls the throttle valve 14 according to the target opening.

[0020] The water temperature sensor 23 is provided in a path through which coolant for cooling the engine 1 flows, and detects the temperature of the coolant (engine water temperature).

[0021] The intake air amount sensor 24 is a sensor that detects the intake air amount Ga of the engine 1, and is configured, for example, by an air flow meter that is arranged in the intake passage 10 (more specifically, upstream of the throttle valve 14). The ECU 20 calculates a target injection amount (reference injection amount Q0) based on the intake air amount detected by the intake air amount sensor 24 so that the actual air-fuel ratio becomes the target air-fuel ratio.

[0022] The injection mode switching unit 25 switches the injection mode when injecting fuel into the combustion chamber 5 of the engine 1 to one of a plurality of injection modes depending on the operating state of the engine 1. The injection modes include a start mode, a catalyst warm-up mode, and a normal mode, and the normal mode includes a first mode, a second mode, and a third mode.

[0023] The start mode is a mode for starting the engine 1. In the start mode, after cranking of the engine 1, fuel is injected once during the compression stroke (when the crank angle is between 180° and 360°) to generate an air-fuel mixture (first compression stage). Injecting fuel during the compression stroke can improve the startability of the engine 1. The injection mode switching unit 25 determines whether starting of the engine 1 is complete based on a signal from the crank angle sensor 21, depending on whether the number of times the top dead center (TDC) has passed (the number of elapsed TDCs) has reached a predetermined number. Alternatively, the injection mode switching unit 25 determines whether starting of the engine 1 is complete based on whether the engine speed Ne after cranking has increased to a full-combustion speed at which the engine can maintain rotation on its own. The injection mode switching unit 25 determines whether starting of the engine 1 is complete based on whether the engine speed Ne after cranking, calculated based on the signal from the crank angle sensor 21, has increased to a full-combustion speed at which the engine can maintain rotation on its own.

[0024] When the injection mode switching unit 25 determines that the start of the engine 1 is complete, it determines whether the catalyst device is in a warm-up state. For example, it determines whether the catalyst device is in a warm-up state based on whether the engine coolant temperature is equal to or higher than a predetermined coolant temperature for determining whether the catalyst is in a warm-up state. It may also determine whether the catalyst device is in a warm-up state based on whether the catalyst temperature detected by a temperature sensor provided in the catalyst device or the catalyst temperature estimated based on the operating state of the engine 1 reaches a predetermined catalyst temperature for determining whether the catalyst is in a warm-up state. It may also be possible to set a target workload required to warm up the catalyst device according to the engine coolant temperature at the completion of the start, and determine whether the catalyst device is in a warm-up state based on whether the total workload since the completion of the start of the engine 1 reaches the target workload. When it determines that the catalyst device is not in a warm-up state, the injection mode switching unit 25 switches the injection mode from the start mode to the catalyst warm-up mode. When it determines that the catalyst device is in a warm-up state, it switches the injection mode from the start mode to the normal mode.

[0025] The catalyst warm-up mode is a mode for promoting the warm-up of a catalyst device provided in the exhaust passage 11 to purify exhaust gas and realizing early activation of the catalyst. In the catalyst warm-up mode, fuel is injected once during the intake stroke (range where the crank angle is 0° or more and 180° or less) and once during the compression stroke (range where the crank angle is 180° or more and 360° or less), and an air-fuel mixture is generated (intake and compression two-stage). Further, in the catalyst warm-up mode, the target air-fuel ratio is set to an air-fuel ratio suitable for the warm-up of the catalyst device, and the ignition timing by the ignition plug 16 is retarded from the optimum ignition timing MBT at which maximum torque is obtained.

[0026] The injection mode switching unit 25 determines whether or not the catalyst is in a warm-up state even in the catalyst warm-up mode. When the injection mode switching unit 25 determines that the catalyst is in a warm-up state in the catalyst warm-up mode, it switches the injection mode from the catalyst warm-up mode to the normal mode (the first mode, the second mode, and the third mode). Note that the injection mode switching unit 25 also determines whether or not the catalyst is in a warm-up state even in the normal mode. When the injection mode switching unit 25 determines that the catalyst is not in a warm-up state in the normal mode, it switches the injection mode from the normal mode to the catalyst warm-up mode. For example, when fuel cut that stops fuel injection is performed for a long time during deceleration driving of the vehicle or the like, the engine coolant temperature may fall below a predetermined coolant temperature for catalyst warm-up determination even in the normal mode.

[0027] FIG. 3 is a diagram for explaining the first mode, the second mode, and the third mode of the normal mode. As shown in FIG. 3, the injection mode switching unit 25 switches the injection mode to the first mode in the low rotation range where the engine speed Ne is equal to or higher than the threshold value Ne1 corresponding to the idle speed and lower than the threshold value Ne2, switches the injection mode to the second mode in the medium rotation range where the engine speed Ne is equal to or higher than the threshold value Ne2 and lower than the threshold value Ne3, and switches the injection mode to the third mode in the high rotation range when the engine speed Ne is equal to or higher than the threshold value Ne3 (Ne1 < Ne2 < Ne3). In the example of FIG. 3, the threshold values Ne1, Ne2, and Ne3 of the engine speed Ne are shown as constant values regardless of the intake air amount Ga, but each of the threshold values Ne1, Ne2, and Ne3 may be set to change according to the intake air amount Ga.

[0028] In the normal mode, fuel is injected in a region other than a predetermined injection prohibition region near the intake top dead center TDC at the start of the intake stroke and the compression top dead center TDC at the end of the compression stroke, that is, in a region where the piston crown surface moves away from the injector 17 (injectable region). The injection prohibition region is set, for example, in a part or almost the entire first half of the intake stroke and a part or almost the entire second half of the compression stroke.

[0029] More specifically, the injection prohibition region is set according to the engine speed Ne. The higher the engine speed Ne, the faster the speed at which the piston crown surface retreats from the injector 17 in the intake stroke and the speed at which the piston crown surface approaches the injector 17 in the compression stroke. Therefore, the higher the engine speed Ne, the narrower the injection prohibition region in the intake stroke (the end of the injection prohibition region moves to the advanced angle side), and the wider the injection prohibition region in the compression stroke (the start of the injection prohibition region moves to the advanced angle side).

[0030] In the first mode in the low rotation range (Ne1 ≦ Ne < Ne2), fuel is injected twice in the compression stroke to generate an air-fuel mixture (compression two-stage). By injecting fuel in the compression two-stage, the air-fuel mixture is homogenized and the combustion efficiency is increased. Note that the minimum injection amount per injection of the injector 17 is defined by the specifications of the injector 17, and the injector 17 cannot inject an amount less than the minimum injection amount. Therefore, in a region where the target injection amount per combustion cycle is small, the injection mode is set according to the operating state of the engine 1, such as setting the number of injections to one (compression one-stage) and advancing the injection timing to the intake stroke (intake one-stage). When using an alcohol-containing fuel containing alcohol with a lower calorific value than gasoline, the reference injection amount Q0 increases, so there is a high possibility that the injection end (EOI (End Of Injection)) enters the injection prohibition region during the increment correction.

[0031] In the second mode of the medium rotation range (Ne2 ≦ Ne < Ne3), fuel is injected once during the intake stroke and once during the compression stroke, and an air-fuel mixture is generated (intake-compression two-stage). That is, in the medium rotation range, the injection prohibited region in the compression stroke becomes wider than in the low rotation range, so the injection time in the compression stroke cannot be ensured, and the first injection is performed during the intake stroke. Note that even in the medium rotation range, in a region where the target injection amount is small, the number of injections is one (compression single-stage). When using an alcohol-containing fuel containing alcohol with a lower calorific value than gasoline, the reference injection amount Q0 increases, so there is a high possibility that the injection end EOI enters the injection prohibited region during the increment correction.

[0032] In the third mode of the high rotation range (Ne3 ≦ Ne), fuel is injected once during the intake stroke, and an air-fuel mixture is generated (intake single-stage). That is, to increase the number of injections, it is necessary to drive the injector 17 at high speed. For example, since it is necessary to repeatedly charge and discharge the capacitor in the injector drive circuit of the ECU20 in a short time, the electrical load of the ECU20 increases and the calorific value of the ECU20 increases. Due to such thermal constraints of the ECU20, in the third mode of the high rotation range, the number of injections is limited to one.

[0033] Also, from the start of the first injection (SOI (Start Of Injection)) to the start of the second injection SOI, it is necessary to ensure the charging time of the capacitor in the injector drive circuit of the ECU20, and from the end of the first injection EOI to the start of the second injection SOI, it is necessary to ensure the rest time of the injector 17. From this perspective as well, in the third mode of the high rotation range, the number of injections is limited to one. Furthermore, in the high rotation range, the injection prohibited region in the compression stroke becomes even wider than in the low to medium rotation ranges, so the injection time in the compression stroke can no longer be ensured, and the injection is performed during the intake stroke. When using an alcohol-containing fuel containing alcohol with a lower calorific value than gasoline, the reference injection amount Q0 increases, so there is a high possibility that the injection end EOI enters the injection prohibited region during the increment correction.

[0034] The ignition control unit 26 outputs a control signal to the spark plug 16 so that the ignition timing becomes a target ignition timing according to characteristics predetermined for each injection mode depending on the operating state of the engine 1. For example, in the catalyst warm-up mode, the ignition control unit 26 outputs a control signal to the spark plug 16 so that the ignition timing is retarded from the optimal ignition timing MBT.

[0035] The injection control unit 27 calculates a target injection amount (reference injection amount Q0), more specifically, a target injection amount per combustion cycle, based on the intake air amount Ga detected by the intake air amount sensor 24. Then, the injection control unit 27 calculates a target injection amount per injection (unit target injection amount) according to the injection mode, and outputs a control signal to the injector 17 so as to inject this unit target injection amount.

[0036] The correction coefficient calculation unit 28 calculates a correction coefficient K for increasing the reference fuel injection amount Q0 calculated according to the operating state of the engine 1, based on characteristics predetermined for each injection mode, over a predetermined period (amount increase correction period) from the start of starting the engine 1. That is, when the engine 1 is started, the temperatures (in-cylinder temperatures) of the piston crown surface and the cylinder head wall surface facing the combustion chamber 5 in FIG. 1 are low, so some of the fuel injected from the injector 17 adheres to the piston crown surface and the cylinder wall surface without vaporizing. The fuel that adheres to the piston crown surface and the cylinder wall surface without vaporizing does not contribute to combustion. When using an alcohol-containing fuel that contains alcohol, which has a greater latent heat of vaporization than gasoline, the fuel is less likely to vaporize.

[0037] The correction coefficient K is a value equal to or greater than "1" that is multiplied by the reference injection amount Q0 to perform an increase correction to compensate for the fuel that does not contribute to combustion, and is determined in advance for each injection mode depending on the operating state (e.g., engine water temperature) at the time of starting the engine 1. More specifically, the lower the engine water temperature, the higher the proportion of fuel that does not contribute to combustion, so the correction coefficient K is calculated to increase, and the higher the engine water temperature, the lower the proportion of fuel that does not contribute to combustion, so the correction coefficient K is calculated to decrease.

[0038] Since the engine water temperature gradually increases as the combustion cycle of the engine 1 progresses, the correction coefficient K is calculated to gradually decrease as the combustion cycle of the engine 1 progresses. When the increase correction period has elapsed, the in-cylinder temperature rises to a warm-up state, the engine water temperature reaches a predetermined water temperature during in-cylinder warm-up, the correction coefficient K becomes "1", and the increase correction ends. The increase correction period is the period from the start of engine 1 startup to the time the in-cylinder warm-up state is reached, and the length of the increase correction period varies depending on the engine water temperature (in-cylinder temperature) at the start of startup and the operating state of the engine 1 after startup (load and total workload since startup).

[0039] Of the first, second, and third modes, the correction coefficient K is calculated to be smallest in the first mode in which fuel is injected in the second compression stage, and largest in the third mode in which fuel is injected in the first intake stage. That is, when the same fuel is injected into the combustion chamber 5 at the same in-cylinder temperature, vaporization of the fuel injected from the injector 17 is not promoted as much in the intake stroke as in the compression stroke, and the proportion of fuel that does not contribute to combustion increases. For this reason, the correction coefficient K is calculated to be largest in the third mode in which fuel is injected in the intake stroke.

[0040] However, such an increase in the fuel injection amount may cause the fuel injection end EOI to be delayed and fall into the injection prohibition region. In this case, a portion of the injected fuel may not be sufficiently vaporized by the ignition timing, making it impossible to form a mixture with an appropriate air-fuel ratio, which may lead to misfire. In particular, in the high load range where the reference injection amount Q0 is large and the injection time (the injector 17 opening time) from the injection start SOI (the injector 17 valve opening time) to the injection end EOI (the injector 17 valve closing time) is long, the injection end EOI is more likely to fall into the injection prohibition region during the increase in the fuel injection amount. Furthermore, in the high load range, the combustion state is more likely to deteriorate, so the injection prohibition region is wider (the injection region is narrower) than in the low to medium load range, further increasing the possibility that the injection end EOI will fall into the injection prohibition region during the increase in the fuel injection amount. Furthermore, when using an alcohol-containing fuel containing alcohol, which has a lower calorific value than gasoline, the reference injection amount Q0 becomes even larger, further increasing the possibility that the injection end EOI will fall into the injection prohibition region during the increase in the fuel injection amount.

[0041] Therefore, in this embodiment, the device 100 is configured as follows so that misfires can be suppressed by limiting the intake air amount Ga of the engine 1 (that is, limiting the output) during the increasing correction.

[0042] The limit value calculation unit 29 calculates a limit value GaL of the intake air amount of the engine 1. The limit value GaL can be calculated, for example, in the third mode among the first mode, the second mode, and the third mode, in which the fuel injection amount correction coefficient K is calculated to be the largest, based on the correction coefficient K calculated in accordance with the operating state of the engine 1 (engine water temperature) at the start of starting. In this case, the intake air amount Ga of the engine 1 is limited to a certain limit value GaL or less over the increase correction period, and the output of the engine 1 is limited, so that misfires can be reliably suppressed during the increase correction period.

[0043] However, if the intake air amount Ga during the increasing correction period is limited to a certain limit value GaL or less, excessive output restriction will be performed when the injection mode is the first mode or the second mode, or when the engine water temperature rises and the fuel injection amount correction coefficient K becomes small. If such excessive output restriction is performed, there is a risk that the vehicle user's request, such as running at high speed immediately after starting the engine 1, will not be satisfied, and the marketability of the vehicle may be impaired. Therefore, the limit value calculation unit 29 calculates the limit value GaL in accordance with the actual correction coefficient K calculated corresponding to the injection mode and the operating state of the engine 1 (engine water temperature), so that the limit value GaL gradually increases as the correction coefficient K decreases.

[0044] Fig. 4 is a diagram for explaining an example of the limit value GaL calculated by the limit value calculation unit 29. As shown in Fig. 4, when the engine 1 starts at time t1 and the injection mode is switched from the start mode to the first mode, a correction coefficient K for the fuel injection amount is calculated in accordance with the operating state of the engine 1 (engine water temperature) based on characteristics predetermined for the first mode. Furthermore, a limit value GaL for the intake air amount is calculated in accordance with the calculated correction coefficient K. Thereafter, as the number of elapsed TDCs increases and the combustion cycle of the engine 1 progresses, the engine water temperature gradually rises, the correction coefficient K gradually decreases, and the limit value GaL gradually increases.

[0045] Similarly, when the injection mode is switched from the first mode to the second mode at time t2, a correction coefficient K for the fuel injection amount is calculated in accordance with the operating state (engine water temperature) of the engine 1 based on characteristics predetermined for the second mode. Also, a restriction value GaL for the intake air amount is calculated in accordance with the calculated correction coefficient K. Then, as the number of elapsed TDCs increases and the combustion cycle of the engine 1 progresses, the engine water temperature gradually rises, the correction coefficient K gradually decreases, and the restriction value GaL gradually increases.

[0046] In this way, by calculating the limit value GaL according to the actual correction coefficient K calculated in accordance with the operating conditions of the engine 1, such as the engine water temperature, misfires can be reliably suppressed during the increase correction period without excessive output restriction. That is, as the engine 1 combustion cycle progresses and the engine water temperature increases and the correction coefficient K decreases, a margin of time is created between the end of fuel injection (EOI) and the start of the injection prohibition region, so the limit value GaL is increased by that amount. This makes it possible to relax the output restriction while reliably suppressing misfires during the increase correction period.

[0047] 5A and 5B are diagrams illustrating another example of the limit value GaL calculated by the limit value calculation unit 29. Fig. 5A shows a case where the injection mode is switched from an injection mode in which the fuel injection amount correction coefficient K is relatively small to an injection mode in which the correction coefficient K is relatively large, and Fig. 5B shows a case where the injection mode is switched from the injection mode in which the correction coefficient K is relatively large to an injection mode in which the correction coefficient K is relatively small.

[0048] When the intake air amount limit value GaL is calculated based on the correction coefficient K for each injection mode, as shown in FIG. 5A, when the injection mode is switched from the second mode to the third mode at time t3, the correction coefficient K increases sharply as indicated by the solid line, and the limit value GaL decreases sharply as indicated by the dashed line. When the target torque of the engine 1 calculated based on the detection value of the accelerator opening sensor 22 is large and the target intake air amount corresponding to the target torque exceeds the limit value GaL, the target intake air amount coincides with the limit value GaL. If the limit value GaL decreases sharply under such conditions, the target intake air amount also decreases sharply, and the target throttle opening corresponding to the target intake air amount also decreases sharply. However, as indicated by the dashed line, there is a delay before the actual intake air amount Ga follows the target intake air amount (limit value GaL). During this time, however, the reference injection amount Q0 calculated based on the actual intake air amount Ga also increases, and the corrected injection amount (reference injection amount Q0 × correction coefficient K) also increases. In this case, the injection end EOI may be delayed and enter the injection prohibition region, potentially resulting in a misfire.

[0049] Therefore, the restriction value calculation unit 29 calculates the restriction value GaL of the intake air amount according to the correction coefficient K of the third mode, which has the largest correction coefficient K among the first mode, second mode, and third mode. That is, as shown by the solid line, during the increase correction period, regardless of the actual injection mode, the restriction value GaL is calculated according to the correction coefficient K of the third mode, which has the largest correction coefficient K, so that it gradually increases as the correction coefficient K of the third mode decreases. In this case, as shown by the solid line, even if the injection mode is switched at time t3, the restriction value GaL of the intake air amount does not change suddenly, and misfires do not occur due to a delay in the response of the intake air amount Ga.

[0050] Furthermore, when the limit value GaL is calculated in accordance with the correction coefficient K for each injection mode, as shown in Figure 5B, when the injection mode is switched from the third mode to the second mode at time t4, the correction coefficient K decreases sharply as shown by the solid line. In this case, as shown by the dashed line, the limit value GaL and the actual intake air amount Ga increase sharply, which may cause the output torque of the engine 1 to increase sharply and cause the vehicle's traveling speed to accelerate regardless of the driver's accelerator operation. When the intake air amount limit value GaL is calculated in accordance with the correction coefficient K for the third mode, which has the largest correction coefficient K, the intake air amount limit value GaL does not change suddenly as shown by the solid line even when the injection mode is switched at time t4, and the intake air amount Ga and output torque do not increase sharply.

[0051] Fig. 6 is a diagram for explaining yet another example of calculation of the limit value GaL by the limit value calculation unit 29. As shown in Fig. 6, the limit value calculation unit 29 may calculate the limit value GaL in accordance with the correction coefficient K of the third mode as shown in Figs. 5A and 5B only in a high load range where the intake air amount Ga corresponding to the load of the engine 1 is equal to or greater than the threshold value α. In this case, in a low to medium load range where the intake air amount Ga is less than the threshold value α, the limit value GaL is calculated in accordance with the correction coefficient K of the actual injection mode as shown in Fig. 4.

[0052] In the high load range, the reference injection amount Q0 is large, the injection time from the injection start SOI to the injection end EOI is long, and the injection prohibition region is wider (the injection possible region is narrower) than in the low to medium load range. Therefore, the possibility that the injection end EOI will enter the injection prohibition region during the injection amount increase correction is higher than in the low to medium load range. In such a high load range, when the injection mode is switched from a relatively small injection mode to a relatively large injection mode as shown in Figure 5A and the correction coefficient K increases rapidly, the limit value GaL (target intake air amount) decreases rapidly, but the actual intake air amount Ga decreases with a delay. In this case, the reference injection amount Q0 and the corrected injection amount (reference injection amount Q0 × correction coefficient K) calculated based on the actual intake air amount Ga also increase, further increasing the possibility that the injection end EOI will enter the injection prohibition region, and the possibility of misfire becoming even higher than in the low to medium load range. In the low to medium load range, the reference injection amount Q0 is small and there is a margin between the injection end EOI and the start of the injection prohibition region. Therefore, even if the intake air amount Ga is delayed in following the target value when the injection mode is switched and the injection amount increases, the injection end EOI is unlikely to fall into the injection prohibition region.

[0053] If the limit value GaL is calculated based on the correction coefficient K of the third mode, which has the largest correction coefficient K, excessive output restriction will be performed in the other injection modes (first mode, second mode). In the low to medium load range, where the injection end EOI is unlikely to enter the injection prohibition region even if the intake air amount Ga is delayed in tracking the target value when the injection mode is switched and the injection amount increases, excessive output restriction can be suppressed by calculating the limit value GaL based on the correction coefficient K of each injection mode. Furthermore, by calculating the limit value GaL based on the correction coefficient K of the third mode, which has the largest correction coefficient K, only in the high load range, where the injection end EOI is likely to enter the injection prohibition region, excessive output restriction can be suppressed while reliably suppressing misfires during the increase correction period.

[0054] According to the embodiment of the present invention, the following advantageous effects can be achieved. (1) The device 100 includes an injection mode switching unit 25 that switches the injection mode for injecting fuel into the combustion chamber 5 of the engine 1 to one of multiple injection modes depending on the operating state of the engine 1, a correction coefficient calculation unit 28 that calculates a correction coefficient K for increasing the reference injection amount Q0 of fuel calculated depending on the operating state of the engine 1 over an increase correction period from the start of engine 1 startup, and a limit value calculation unit 29 that calculates a limit value GaL of the intake amount of the engine 1 over the increase correction period (FIGS. 1 and 2). The correction coefficient calculation unit 28 calculates the correction coefficient K so that it gradually decreases as the combustion cycle of the engine 1 progresses based on characteristics predetermined for each of the multiple injection modes (FIG. 4). The limit value calculation unit 29 calculates the limit value GaL so that it gradually increases as the correction coefficient K decreases (FIG. 4). This makes it possible to suppress misfires during the increase correction period without excessively restricting output.

[0055] (2) The multiple injection modes include multiple injection modes (first mode, second mode, and third mode) that are switched according to the operating state of the engine 1 (engine speed Ne) after the engine 1 has been started (FIG. 3). The limit value calculation unit 29 calculates the limit value GaL so that it gradually increases as the correction coefficient K decreases in the third mode, which has the largest correction coefficient K among the first mode, second mode, and third mode (FIGS. 5A and 5B). In this case, the intake air amount limit value GaL does not change suddenly even when the injection mode is switched, so misfires due to a delay in the intake air amount Ga can be suppressed (FIG. 5A), and a sudden increase in the intake air amount Ga and output torque can be suppressed (FIG. 5B).

[0056] (3) The multiple injection modes that are switched depending on the operating state of the engine 1 (engine speed Ne) include a first mode that is switched when the engine speed Ne is equal to or greater than a threshold value Ne1 and less than a threshold value Ne2, a second mode that is switched when the engine speed Ne is equal to or greater than a threshold value Ne2 and less than a threshold value Ne3, and a third mode that is switched when the engine speed Ne is equal to or greater than the threshold value Ne3 (Fig. 3). In the first mode, fuel is injected multiple times during the compression stroke, in the second mode, fuel is injected during both the intake stroke and the compression stroke, and in the third mode, fuel is injected during the intake stroke (Fig. 3). The third mode is the injection mode with the largest correction coefficient K.

[0057] (4) The multiple injection modes include multiple injection modes (first mode, second mode, and third mode) that are switched depending on the operating state of the engine 1 (engine speed Ne) after the engine 1 has been started (FIG. 3). When the load (intake amount Ga) of the engine 1 is equal to or greater than the threshold value α, the limit value calculation unit 29 calculates the limit value GaL so that it gradually increases as the correction coefficient K of the injection mode with the largest correction coefficient K among the first mode, the second mode, and the third mode decreases (FIG. 6). In this way, by calculating the limit value GaL according to the correction coefficient K of the normal mode with the largest correction coefficient K only in the high load range, it is possible to suppress excessive output restriction while reliably suppressing misfires during the increase correction period.

[0058] In the above embodiment, an example was described in which the device 100 is applied to an engine 1 mounted on a vehicle supplied with alcohol-containing fuel, but the internal combustion engine is not limited to this and may be an internal combustion engine mounted on a vehicle (FFV (Flexible-Fuel Vehicle)) supplied with either gasoline fuel or alcohol-containing fuel, or an internal combustion engine mounted on a vehicle (gasoline vehicle) supplied with only gasoline fuel.

[0059] The above description is merely an example, and the present invention is not limited to the above-described embodiment and modifications, as long as the features of the present invention are not impaired. One or more of the above-described embodiment and modifications can be arbitrarily combined, and modifications can also be combined with each other. [Explanation of symbols]

[0060] 1 engine, 2a cylinder, 3 piston, 5 combustion chamber, 14 throttle valve, 16 spark plug, 17 injector, 20 electronic control unit (ECU), 21 crank angle sensor, 22 accelerator opening sensor, 23 water temperature sensor, 24 intake amount sensor, 25 injection mode switching unit, 26 ignition control unit, 27 injection control unit, 28 correction coefficient calculation unit, 29 limit value calculation unit, 100 control device (device) for internal combustion engine

Claims

1. an injection mode switching unit that switches an injection mode when injecting fuel into a combustion chamber of an internal combustion engine to one of a plurality of injection modes in accordance with an operating state of the internal combustion engine; a correction coefficient calculation unit that calculates a correction coefficient for increasing the reference injection amount of fuel calculated in accordance with an operating state of the internal combustion engine over a predetermined period from the start of startup of the internal combustion engine; a limit value calculation unit that calculates a limit value of an intake air amount of the internal combustion engine over the predetermined period, the correction coefficient calculation unit calculates the correction coefficient based on predetermined characteristics for each of the plurality of injection modes so that the correction coefficient gradually decreases as a combustion cycle of the internal combustion engine progresses, The control device for an internal combustion engine, wherein the limit value calculation unit calculates the limit value so that the limit value gradually increases as the correction coefficient decreases.

2. 2. The control device for an internal combustion engine according to claim 1, the plurality of injection modes include a plurality of injection modes that are switched according to an operating state of the internal combustion engine after completion of starting the internal combustion engine, the limit value calculation unit calculates the limit value so that the limit value gradually increases with a decrease in the correction coefficient of an injection mode having the largest correction coefficient among a plurality of injection modes that are switched in accordance with an operating state of the internal combustion engine after the internal combustion engine has been started.

3. 3. The control device for an internal combustion engine according to claim 2, a control device for an internal combustion engine, characterized in that the multiple injection modes that are switched depending on the operating state of the internal combustion engine after completion of starting the internal combustion engine include a first mode that is switched when the rotational speed of the internal combustion engine is equal to or greater than a first threshold value and less than a second threshold value, a second mode that is switched when the rotational speed is equal to or greater than the second threshold value and less than a third threshold value, and a third mode that is switched when the rotational speed is equal to or greater than the third threshold value.

4. 4. The control device for an internal combustion engine according to claim 3, In the first mode, the fuel is injected multiple times during the compression stroke, In the second mode, the fuel is injected during both the intake stroke and the compression stroke, In the third mode, the fuel is injected during the intake stroke, 10. A control device for an internal combustion engine, wherein the third mode is a normal mode in which the correction coefficient is the largest.

5. 2. The control device for an internal combustion engine according to claim 1, the plurality of injection modes include a plurality of injection modes that are switched according to an operating state of the internal combustion engine after completion of starting the internal combustion engine, a control device for an internal combustion engine, characterized in that, when a load on the internal combustion engine is equal to or greater than a threshold value, the limit value calculation unit calculates the limit value so as to gradually increase as the correction coefficient of an injection mode having the largest correction coefficient decreases among a plurality of injection modes that are switched in accordance with an operating state of the internal combustion engine after starting of the internal combustion engine is completed.

6. 2. The control device for an internal combustion engine according to claim 1, 10. A control device for an internal combustion engine, wherein the fuel is an alcohol-containing fuel that contains alcohol.

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