Controller of internal combustion engine

Abstract

To stabilize combustion of an air fuel mixture in an internal combustion engine at a low temperature.SOLUTION: An internal combustion engine 1 comprises: a fuel injection valve 4 that injects a mixed fuel, in which alcohol fuel and gasoline fuel are mixed in an arbitrary ratio, into a cylinder during a compression stroke; and an intake-side variable valve mechanism 13 that changes a closing timing of the intake valve 9. When the internal combustion engine 1 is in a low-temperature state, a controller 100 executes a process to advance an injection start timing at which fuel is injected from the fuel injection valve 4 in accordance with an increase in an actual compression ratio due to a change in the closing timing of the intake valve 9.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] For example, Patent Document 1 describes an internal combustion engine that injects a mixed fuel in which an alcohol fuel and a gasoline fuel are mixed at an arbitrary ratio during a compression stroke.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Alcohol fuel has poor vaporization characteristics compared to gasoline fuel. Therefore, in an internal combustion engine in a low-temperature state, such as during cold start or in a cold state from start-up until it reaches a warm state, the combustion of the air-fuel mixture tends to become unstable. Therefore, it is desirable to stabilize the combustion of the air-fuel mixture.

Means for Solving the Problems

[0005] The control device for an internal combustion engine that solves the above problems is applied to an internal combustion engine including a fuel injection valve that injects a mixed fuel in which an alcohol fuel and a gasoline fuel are mixed at an arbitrary ratio into a cylinder during a compression stroke, and a variable valve mechanism that changes the valve closing timing of an intake valve. When the internal combustion engine is in a low-temperature state, this control device executes a process of advancing the injection start timing at which fuel is injected from the fuel injection valve in accordance with an increase in the actual compression ratio accompanying the change in the valve closing timing.

Effects of the Invention

[0006] According to this invention, the combustion of the air-fuel mixture becomes stable in an internal combustion engine in a low-temperature state.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0008] Hereinafter, an embodiment will be described in which a control device for an internal combustion engine using a mixed fuel in which an alcohol fuel and a gasoline fuel are mixed at an arbitrary ratio as the fuel of the engine is embodied. <Regarding the internal combustion engine and the control device> As shown in FIG. 1, air is inhaled into the combustion chamber 2 of the internal combustion engine 1 through the intake passage 3 and the intake port 3a. Further, the fuel injected from the fuel injection valve 4 that injects fuel into the cylinder of the internal combustion engine 1 is supplied to the combustion chamber 2. When the air-fuel mixture composed of air and fuel is ignited by the spark plug 5, the air-fuel mixture burns and the piston 6 reciprocates, and the crankshaft 7 which is the output shaft of the internal combustion engine 1 rotates. The air-fuel mixture after combustion is discharged from the combustion chamber 2 to the exhaust passage 8 as exhaust. A catalyst 50 for purifying the exhaust is provided in the exhaust passage 8.

[0009] A throttle valve 29 for measuring the amount of inhaled air is provided in the intake passage 3 of the internal combustion engine 1. The opening degree of this throttle valve 29 is adjusted by an electric motor. An intake valve 9 is provided in the intake port 3a connected to the intake passage 3. An exhaust valve 10 is provided in the exhaust port 8a connected to the exhaust passage 8. These intake valve 9 and exhaust valve 10 open and close respectively with the rotation of the intake side camshaft 11 and the exhaust side camshaft 12 to which the rotation of the crankshaft 7 is transmitted.

[0010] An intake-side variable valve mechanism 13 is provided on the intake-side camshaft 11 to change the valve timing, which is the opening and closing timing of the intake valve 9, by changing the relative phase of the intake-side camshaft 11 with respect to the crankshaft 7.

[0011] The control device 100 performs various controls of the internal combustion engine 1 by controlling the throttle valve 29, the fuel injection valve 4, the ignition plug 5, the intake-side variable valve mechanism 13, etc. This control device 100 includes a CPU 110 and a memory 120 composed of a ROM and a RAM, etc. The CPU 110 executes a program stored in the memory 120 to perform various controls.

[0012] When performing various controls, the control device 100 refers to the intake air amount GA detected by the air flow meter 31 and the throttle opening TA, which is the opening of the throttle valve 29 detected by the throttle sensor 30. Further, the control device 100 refers to the cooling water temperature THW detected by the water temperature sensor 33 and the engine rotational speed NE calculated from the output signal Scr of the crank angle sensor 34. Further, the control device 100 refers to the output signal Scai of the intake-side cam angle sensor 35 that detects the rotational angle of the intake-side camshaft 11. Further, the control device 100 refers to the air-fuel ratio AF of the air-fuel mixture detected by the air-fuel ratio sensor 37 provided in the exhaust passage 8. Further, the control device 100 refers to the output signal of the accelerator position sensor 28 that detects the operation amount (accelerator operation amount ACCP) of the accelerator pedal 27 operated by the driver of the vehicle equipped with the internal combustion engine 1.

[0013] <Processing executed by the control device> The control device 100 calculates the intake-side timing VTinr, which is the actual valve timing of the intake valve 9, based on the output signal Scr of the crank angle sensor 34 and the output signal Scai of the intake-side cam angle sensor 35. Incidentally, in the present embodiment, the state where the intake valve timing is at the most retarded timing is set as the initial value "0", and the valve timing of the intake valve 9 is grasped by the amount of valve timing advance from this initial value. Note that the valve closing timing of the intake valve 9 when the intake valve timing is at the initial value is at a retarded timing compared to the intake bottom dead center.

[0014] Further, the control device 100 calculates the engine load ratio KL. The engine load ratio KL is a parameter that determines the amount of air filled in the combustion chamber 2, and is the ratio of the amount of intake air per combustion cycle of one cylinder to the reference intake air amount. Note that the reference intake air amount may be variably set according to the engine rotational speed NE.

[0015] The control device 100 performs valve timing control of the intake valve 9. That is, the control device 100 calculates the intake-side target value VTint, which is the target value of the valve timing of the intake valve 9, based on the engine rotational speed NE, the engine load ratio KL, and the like. The intake-side target value VTint is the amount of valve timing advance from the above-described initial value. When this intake-side target value VTint is calculated, the control device 100 controls the drive of the intake-side variable valve mechanism 13 so that the intake-side timing VTinr matches the intake-side target value VTint.

[0016] Note that the intake valve closing timing IVC of the intake valve 9 at the start of the engine is set to the timing of the above-described initial value, that is, the timing on the retarded side from the intake bottom dead center. When the engine start is initiated, the control device 100 gradually changes the intake side target value VTint to a value on the advanced side with the passage of time, so that the intake valve closing timing IVC of the intake valve 9 also changes to a value on the advanced side. When the intake valve closing timing IVC of the intake valve 9, which was set to a timing on the retarded side from the intake bottom dead center, changes to the advanced side, the amount of air blown back from the cylinder into the intake passage 3 in the first half of the compression stroke decreases. Therefore, the actual compression ratio increases until the closing timing IVC reaches the intake bottom dead center. When the actual compression ratio increases in this way, the in-cylinder gas temperature, which is the temperature of the gas in the cylinder, rises during the compression stroke. In the present embodiment, until the internal combustion engine 1 reaches a warm state, the intake side target value VTint is restricted so that the closing timing IVC does not become a timing on the advanced side from the intake bottom dead center.

[0017] The control device 100 executes well-known air-fuel ratio feedback control. In this air-fuel ratio feedback control, a correction value for correcting the fuel injection amount of the fuel injection valve 4 is calculated based on the detection value of the air-fuel ratio sensor 37 or the like so that the air-fuel ratio of the air-fuel mixture becomes a predetermined air-fuel ratio. Then, the fuel injection amount is corrected using the correction value.

[0018] In addition, in the internal combustion engine 1, not only gasoline fuel but also alcohol fuel is used. In such an internal combustion engine 1, the fuel injection amount corresponding to a predetermined air-fuel ratio changes according to the alcohol concentration AD in the fuel. Basically, the higher the alcohol concentration AD, the more necessary it is to increase and correct the fuel injection amount. Such an alcohol concentration AD is correlated with the correction value of the fuel injection amount calculated by the air-fuel ratio feedback control. Therefore, the control device 100 executes a concentration learning process for estimating the alcohol concentration AD based on the correction value of the fuel injection amount calculated by the air-fuel ratio feedback control. Note that the alcohol concentration AD may be estimated by other methods or directly detected by a sensor or the like.

[0019] <Setting of Injection Start Timing in a Low-Temperature State Internal Combustion Engine> When the internal combustion engine 1 is in a low-temperature state, the control device 100 calculates the injection start timing IST of the fuel injection valve 4 by executing the processes shown in FIG. 2 and the process shown in FIG. 3. The internal combustion engine 1 in a low-temperature state is, for example, the internal combustion engine 1 in a state where the coolant water temperature THW is less than a warm-region determination value THWref indicating that the internal combustion engine 1 is in a warm region. Further, the injection start timing IST calculated by the processes shown in FIG. 2 and the process shown in FIG. 3 is a timing during the compression stroke.

[0020] The process shown in FIG. 2 is a process executed by the control device 100 during the period from when the engine start is started until it is determined that the internal combustion engine 1 has completed combustion. The process shown in FIG. 3 is a process executed by the control device 100 during the period from when it is determined that the internal combustion engine 1 has completed combustion until it becomes a warm region state.

[0021] Note that the control device 100 determines that the internal combustion engine 1 has completed combustion when, for example, a state where the engine rotational speed NE is equal to or higher than a predetermined complete combustion determination value continues for a predetermined time or more. Further, the control device 100 determines that the internal combustion engine 1 is in a warm region state when the coolant water temperature THW reaches the predetermined warm-region determination value THWref.

[0022] The processes shown in FIGS. 2 and 3 are implemented by the CPU 110 executing a program stored in the memory 120 of the control device 100 at a predetermined cycle. Hereinafter, the step number is expressed by a number with "S" added at the beginning.

[0023] When starting the process shown in FIG. 2, the control device 100 determines whether or not the alcohol concentration AD calculated by the concentration learning process is equal to or higher than a determination value ADref (S100). The determination value ADref is, for example, set in advance to the minimum value of the alcohol concentration AD at which the combustion stability of the air-fuel mixture deteriorates.

[0024] When it is determined that the alcohol concentration AD is equal to or higher than the determination value ADref (S100: YES), the control device 100 calculates the injection start timing IST based on the coolant water temperature THW, the engine rotational speed NE, the alcohol concentration AD, and the intake-side timing VTinr (S110).

[0025] In the process of S110, the control device 100 sets the injection start timing IST so that the lower the coolant temperature THW, the more retarded the injection start timing IST becomes, that is, the injection start timing IST approaches the top dead center of compression. This is due to the following reasons. That is, as the piston 6 approaches the top dead center of compression, the in-cylinder gas temperature increases, so the fuel is more likely to vaporize. Here, the lower the coolant temperature and the lower the in-cylinder temperature, the less likely the fuel is to vaporize. Therefore, the more difficult it is for the fuel to vaporize, the closer the injection start timing IST is brought to the top dead center of compression where the in-cylinder gas temperature becomes higher, thereby promoting the vaporization of the fuel and stabilizing the combustion of the air-fuel mixture.

[0026] Also, in the process of S110, the control device 100 sets the injection start timing IST so that the higher the engine rotational speed NE, the more advanced the injection start timing IST becomes, that is, the injection start timing IST moves away from the top dead center of compression. This is due to the following reasons. That is, as the engine rotational speed NE increases, the in-cylinder gas temperature rises. Therefore, even if the injection start timing IST is advanced compared to when the engine rotational speed NE is low, the fuel will vaporize. Here, when the injection start timing IST is advanced, the injection end timing also becomes earlier. Therefore, the vaporization period during which the fuel vaporizes after the fuel injection ends and before the air-fuel mixture is ignited becomes longer. When the vaporization period becomes longer, the amount of vaporized fuel contained in the air-fuel mixture at the ignition timing increases. Therefore, in the internal combustion engine 1 in a low-temperature state, the combustion of the air-fuel mixture is stabilized and the output torque of the internal combustion engine 1 is improved. Also, when the above vaporization period becomes longer, the mixing of air and fuel progresses, so the fuel concentration in the air-fuel mixture is made uniform. Therefore, also for this reason, in the internal combustion engine 1 in a low-temperature state, the combustion of the air-fuel mixture is stabilized and the output torque of the internal combustion engine 1 is improved.

[0027] Also, in the process of S110, the control device 100 sets the injection start timing IST such that the higher the alcohol concentration AD, the later the injection start timing IST becomes, that is, the injection start timing IST approaches the top dead center of compression. This is for the following reason. That is, the higher the alcohol concentration AD, the more difficult it is for the fuel to vaporize. Therefore, the closer the injection start timing IST is to the top dead center of compression where the in-cylinder gas temperature is higher when the fuel is difficult to vaporize, the more the vaporization of the fuel is promoted, thereby achieving the combustion stabilization of the air-fuel mixture.

[0028] Also, in the process of S110, the control device 100 sets the injection start timing IST such that the more advanced the intake-side timing VTinr, the more advanced the injection start timing IST becomes, that is, the injection start timing IST moves away from the top dead center of compression. This is for the following reason. That is, as described above, the higher the intake-side timing VTinr, the higher the actual compression ratio. When the actual compression ratio increases, the in-cylinder gas temperature rises during the compression stroke. Therefore, even if the injection start time is advanced by advancing the injection start timing IST of the fuel, the fuel will vaporize. Here, when the injection start timing IST of the fuel is advanced, the injection end timing also becomes earlier, so the vaporization period becomes longer. When the vaporization period becomes longer, the amount of vaporized fuel contained in the air-fuel mixture at the ignition timing increases. Therefore, in the internal combustion engine 1 in the low-temperature state, the combustion of the air-fuel mixture is stabilized and the output torque of the internal combustion engine 1 is improved. Also, when the vaporization period becomes longer, the mixing of air and fuel progresses, so the fuel concentration in the air-fuel mixture is made uniform. Therefore, also for this reason, in the internal combustion engine 1 in the low-temperature state, the combustion of the air-fuel mixture is stabilized and the output torque of the internal combustion engine 1 is improved.

[0029] On the other hand, in the process of S100, when it is determined that the alcohol concentration AD is less than the determination value ADref (S100: NO), the control device 100 calculates the injection start timing IST based on the engine rotation speed NE and the injection number IN (S120). In the process of S120, the calculation of the injection start timing IST based on the engine rotation speed NE is the same as the process of S110 above. Further, the injection number IN is the number of fuel injections of one fuel injection valve 4 from the start of engine startup to the present. The higher the injection number IN, the higher the temperature in the cylinder and the easier it is for the fuel to vaporize. Therefore, the control device 100 sets the injection start timing IST so that the injection start timing IST becomes a timing on the advanced angle side as the injection number IN increases, that is, the injection start timing IST is set to be away from top dead center of compression.

[0030] Then, when the process of S110 or the process of S120 is executed, the control device 100 temporarily ends this process. When starting the process shown in FIG. 3, the control device 100 determines whether the alcohol concentration AD is greater than or equal to the determination value ADref (S200). The process of S200 is the same as the process of S100 above.

[0031] When it is determined that the alcohol concentration AD is greater than or equal to the determination value ADref (S200: YES), the control device 100 executes the process of S210. In the process of S210, the control device 100 calculates the injection start timing IST based on the coolant water temperature THW, the engine rotation speed NE, the engine load factor KL, the alcohol concentration AD, and the intake side timing VTinr. In this process of S210, the calculation of the injection start timing IST based on the coolant water temperature THW, the engine rotation speed NE, the alcohol concentration AD, and the intake side timing VTinr is the same as the process of S110 above.

[0032] Also, in the process of S210, the control device 100 sets the injection start timing IST such that the higher the engine load ratio KL, the more advanced the injection start timing IST, that is, the injection start timing IST is away from top dead center of compression. This is due to the following reasons. That is, since the in-cylinder gas temperature rises as the engine load ratio KL increases, the fuel vaporizes even if the injection start timing IST is advanced compared to when the engine rotational speed NE is low. Here, when the injection start timing IST is advanced, the injection end timing also becomes earlier, so the vaporization period during which the fuel vaporizes from the end of fuel injection until the air-fuel mixture is ignited becomes longer. When the vaporization period becomes longer, the amount of vaporized fuel contained in the air-fuel mixture at the ignition timing increases. Therefore, in the internal combustion engine 1 in a low-temperature state, the combustion of the air-fuel mixture is stabilized and the output torque of the internal combustion engine 1 is improved. Also, when the above vaporization period becomes longer, the mixing of air and fuel progresses, so the fuel concentration in the air-fuel mixture is made uniform. Therefore, also for this reason, in the internal combustion engine 1 in a low-temperature state, the combustion of the air-fuel mixture is stabilized and the output torque of the internal combustion engine 1 is improved.

[0033] On the other hand, in the process of S200, when it is determined that the alcohol concentration AD is less than the determination value ADref (S200: NO), the control device 100 executes the process of S2120. In the process of S220, the control device 100 calculates the injection start timing IST based on the coolant water temperature THW, the engine rotational speed NE, the engine load ratio KL, and the alcohol concentration AD. The calculation of the injection start timing IST based on the coolant water temperature THW, the engine rotational speed NE, the engine load ratio KL, and the alcohol concentration AD in this process of S220 is the same as the process of S210 described above.

[0034] Then, when the process of S210 or the process of S220 is executed, the control device 100 temporarily ends this process. <Actions and Effects of the Present Embodiment> In the processes of S110 and S210 described above, when the internal combustion engine 1 is in a low-temperature state, a process of advancing the injection start timing IST at which fuel is injected from the fuel injection valve 4 in accordance with an increase in the actual compression ratio accompanying the change in the valve closing timing IVC of the intake valve 9 is executed.

[0035] As described above, when the actual compression ratio increases due to the change in the valve closing timing IVC of the intake valve 9, the in-cylinder gas temperature rises during the compression stroke. Therefore, even if the injection start time IST of the fuel is advanced to advance the start time of injection, the fuel will vaporize. Here, when the injection start time IST of the fuel is advanced, the injection end time also becomes earlier, so the vaporization period during which the fuel vaporizes after the fuel injection ends and before the air-fuel mixture is ignited becomes longer. When the vaporization period becomes longer, the amount of vaporized fuel contained in the air-fuel mixture at the ignition time increases. Therefore, in the internal combustion engine 1 in the low-temperature state, the combustion of the air-fuel mixture becomes stable, and the low-temperature startability is also improved.

[0036] Further, when the above-described vaporization period becomes longer, the mixing of air and fuel progresses, so that the fuel concentration in the air-fuel mixture is made uniform. Therefore, also by this, in the internal combustion engine 1 in the low-temperature state, the combustion of the air-fuel mixture becomes stable, and for example, the low-temperature startability is also improved.

[0037] <Modification Example> Note that this embodiment can be implemented with the following modifications. This embodiment and the following modification examples can be implemented in combination with each other within a technically non-conflicting range.

[0038] · In the process shown in FIG. 2, the processes of S100 and S120 may be omitted. In this case, during the period from when the engine start is started until it is determined that the internal combustion engine 1 has completed explosion, the injection start time IST is set by the process of S110.

[0039] · In the process shown in FIG. 3, the processes of S200 and S220 may be omitted. In this case, during the period from when it is determined that the internal combustion engine 1 has completed explosion until it becomes a warm state, the injection start time IST is set by the process of S210.

[0040] · As a parameter referred to for calculating the injection start timing IST in the process of S110 shown in FIG. 2, at least one of the coolant water temperature THW, the engine rotational speed NE, and the alcohol concentration AD may be omitted.

[0041] · As a parameter referred to for calculating the injection start timing IST in the process of S210 shown in FIG. 3, at least one of the coolant water temperature THW, the engine rotational speed NE, the engine load factor KL, and the alcohol concentration AD may be omitted.

[0042] · The internal combustion engine 1 may be provided with an exhaust-side variable valve mechanism that changes the valve timing of the exhaust valve 10.

Description of Reference Numerals

[0043] 1... Internal combustion engine, 2... Combustion chamber, 3... Intake passage, 4... Fuel injection valve, 5... Spark plug, 6... Piston, 7... Crankshaft, 8... Exhaust passage, 9... Intake valve, 10... Exhaust valve, 11... Intake-side camshaft, 12... Exhaust-side camshaft, 13... Intake-side variable valve mechanism, 100... Control device

Claims

Claims 1 A control device applied to an internal combustion engine including a fuel injection valve that injects a mixed fuel in which an alcohol fuel and a gasoline fuel are mixed at an arbitrary ratio into a cylinder during a compression stroke, and a variable valve mechanism that changes a valve closing timing of an intake valve, When the internal combustion engine is in a low temperature state, a process of advancing an injection start timing at which fuel is injected from the fuel injection valve in accordance with an increase in an actual compression ratio accompanying the change in the valve closing timing is executed. A control device for an internal combustion engine.

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