Control device for internal combustion engines

Abstract

In environments prone to knocking, such as extreme heat, the ignition timing is set appropriately when using alcohol-containing fuels. [Solution] The control device for the internal combustion engine includes a concentration sensor 35 for detecting the alcohol concentration of the fuel, a water temperature sensor 33 and an intake air temperature sensor 34 for detecting the engine coolant temperature and intake air temperature, respectively, and a controller 30 for controlling the spark plug 18 so that the ignition timing becomes the target ignition timing. The controller 30 performs retard control, which retards the ignition timing from the reference ignition timing according to the detected temperature, and advance control, which advances the ignition timing from the ignition timing retarded by the retard control until knocking occurs, up to the limit of the reference ignition timing. The controller 30 sets the target ignition timing based on a knock learning value, which is a parameter corresponding to the amount of ignition timing advance obtained by the advance control, the detected alcohol concentration E, and the detected temperature.

Description

Technical Field

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

Background Art

[0002] In recent years, in order to enable more people to access affordable, reliable, sustainable, and advanced energy, research and development have been conducted on improving fuel efficiency to contribute to energy efficiency. As a technology related to this type of device, conventionally, there is known a device that corrects the ignition timing according to whether knocking has occurred and controls the ignition timing by storing the ignition timing as a learned value (see, for example, Patent Document 1). In the device described in Patent Document 1, the alcohol concentration in the fuel supplied to the internal combustion engine is detected, and when the alcohol concentration is higher than a predetermined value, the update of the learned value is prohibited while continuing the correction of the ignition timing.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, in an environment where knocking is likely to occur, such as in extremely hot weather, it may be necessary to retard the ignition timing. However, the device described in Patent Document 1 does not propose anything regarding the retardation of the ignition timing suitable for such an environment.

Means for Solving the Problems

[0005] One aspect of the present invention is a control device for an internal combustion engine having a fuel injection unit that injects a fuel containing alcohol, and an ignition unit that ignites a mixture of fuel and air injected by the fuel injection unit, comprising: a concentration detection unit that detects the alcohol concentration of the fuel; a temperature detection unit that detects the temperature of at least one of the cooling water of the internal combustion engine and the intake air drawn into the internal combustion engine; and a control unit that controls the ignition unit so that the ignition timing becomes a target ignition timing. When the temperature detected by the temperature detection unit is above a predetermined value, the control unit performs retardation control, which retards the ignition timing from a reference ignition timing according to the temperature, and advancement control, which advances the ignition timing from the ignition timing retarded by the retardation control until knocking occurs, up to the limit of the reference ignition timing, and sets a target ignition timing based on a parameter corresponding to the amount of ignition timing advance obtained by the advancement control, the alcohol concentration detected by the concentration detection unit, and the temperature detected by the temperature detection unit. [Effects of the Invention]

[0006] According to the present invention, the ignition timing can be set appropriately when using alcohol-containing fuel in environments where knocking is likely to occur, such as in extremely hot weather. [Brief explanation of the drawing]

[0007] [Figure 1] A schematic diagram showing the main components 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] A conceptual diagram illustrating retard control and advance ignition timing control by a control device for an internal combustion engine according to an embodiment of the present invention. [Figure 3] A block diagram showing the main components of a control device for an internal combustion engine according to an embodiment of the present invention. [Figure 4] A time chart illustrating the processing in the knock learning section of Figure 3. [Figure 5] A time chart illustrating the processing performed by the ignition timing setting unit in Figure 3. [Figure 6] A flowchart showing an example of the process executed by the controller in Figure 3. [Figure 7] This figure shows the changes in alcohol concentration and knock learning value over time immediately after refueling with fuels of different alcohol concentrations. [Modes for carrying out the invention]

[0008] An embodiment of the present invention will be described below with reference to Figures 1 to 7. The control device for an internal combustion engine according to the embodiment of the present invention can be applied to an internal combustion engine having a fuel injection unit that injects fuel into the combustion chamber in the cylinder and an ignition unit that ignites the fuel-air mixture supplied into the combustion chamber, that is, an engine of various spark-ignition type internal combustion engines.

[0009] This engine is a four-stroke engine, for example, which undergoes four strokes—intake, expansion, compression, and exhaust—during one operating cycle. The engine uses alcohol fuel, such as ethanol. It can also use a fuel mixture of alcohol and gasoline, i.e., a mixed fuel containing a predetermined percentage (e.g., 20% or 85%) of alcohol. Hereafter, both alcohol fuel and a mixed fuel of alcohol and gasoline will be collectively referred to as alcohol-containing fuel.

[0010] Figure 1 is a schematic diagram showing the main components of an engine 1 to which the control device according to this embodiment is applied. As shown in Figure 1, the engine 1 has a cylinder 2 formed in a cylinder block, a piston 3 slidably disposed inside the cylinder 2, and a combustion chamber 4 formed between the piston 3 and the cylinder head. The piston 3 is connected to a crankshaft 6 via a connecting rod 5, and the crankshaft 6 rotates as the piston 3 reciprocates along the inner wall of the cylinder 2.

[0011] The cylinder head is provided with an intake port 11 and an exhaust port 12. The combustion chamber 4 is connected to an intake passage 13 via the intake port 11, and to an exhaust passage 14 via the exhaust port 12. The intake port 11 is opened and closed by an intake valve 15, and the exhaust port 12 is opened and closed by an exhaust valve 16. A throttle valve 17 is provided in the intake passage 13 upstream of the intake valve 15.

[0012] The throttle valve 17 is configured, for example, as a butterfly valve, and the amount of intake air flowing into the combustion chamber 4 is adjusted by the throttle valve 17. The throttle valve 17 is driven by a throttle actuator, such as an electric motor. The intake valve 15 and exhaust valve 16 are driven to open and close at predetermined timings synchronized with the rotation of the crankshaft 6 by a valve train mechanism (not shown). The opening and closing timing of valves 15 and 16 can be changed as appropriate.

[0013] A spark plug 18 and a direct-injection injector 19 are mounted on either the cylinder head or the cylinder block (for example, the cylinder head), facing the combustion chamber 4 of cylinder 2. The spark plug 18 is positioned between the intake port 11 and the exhaust port 12, and generates a spark using electrical energy to ignite the fuel-air mixture in the combustion chamber 4. The injector 19 is positioned near the intake valve 15, and is driven by electrical energy to inject fuel diagonally downward into the combustion chamber 4. The injector 19 is not limited to this position and can also be positioned near the spark plug 18.

[0014] Fuel is supplied to the injector 19 from the fuel supply unit 20. The fuel supply unit 20 has a low-pressure pump 22 that draws in alcohol-containing fuel stored in the fuel tank 21, and a high-pressure pump 23 that pressurizes the fuel drawn in by the low-pressure pump 22. The fuel, pressurized to a target pressure by the high-pressure pump 23, is supplied to the injector 19. The alcohol concentration of the fuel stored in the fuel tank 21 is the percentage of alcohol to the total volume of fuel, and is determined by the fuel supplier. The amount of fuel injected from the injector 19 is controlled according to the intake air amount of the engine 1 so that the actual air-fuel ratio becomes the stoichiometric air-fuel ratio corresponding to the alcohol concentration.

[0015] When such an engine 1 is used in a high-temperature environment such as extreme heat, the temperature of the engine coolant flowing around the engine 1 (coolant temperature) and the temperature of the air drawn into the engine 1 (intake temperature) rise, making knocking more likely. Therefore, in this embodiment, when the engine ambient temperature T (coolant temperature Tw, intake air temperature Tin) exceeds a predetermined temperature (retard start temperature T0), retard control (retard timing control) is performed to retard the ignition timing in order to suppress the occurrence of knocking. Furthermore, advance timing control is performed to advance the ignition timing after the retard control. That is, advance timing control is performed by the knock control system to advance the ignition timing after the retard control. Note that the engine ambient temperature T is a general term for temperatures that affect the occurrence of knocking, and both the coolant temperature and the intake air temperature are included in the engine ambient temperature T.

[0016] FIG. 2 is a conceptual diagram for explaining retard control and advance control. In FIG. 2, the crank angles in the intervals from the start (bottom dead center BDC) to the end (top dead center TDC) of the compression stroke and from the start (top dead center TDC) to the end (bottom dead center BDC) of the expansion stroke are shown by the angles of a circle in the clockwise direction starting from the bottom dead center BDC at the start of the compression stroke. Assuming that the crank angle at the start of the intake stroke is 0°, the compression stroke is in the range where the crank angle is 180° or more and 360° or less, and the expansion stroke is in the range where the crank angle is 360° or more and 540° or less. Note that the range AR1 where the crank angle is 180° or more and 270° or less is sometimes called the first half of the compression stroke, the range AR2 where the crank angle is 270° or more and 360° or less is called the second half of the compression stroke, the range AR3 where the crank angle is 360° or more and 450° or less is called the first half of the expansion stroke, and the range AR4 where the crank angle is 450° or more and 540° or less is called the second half of the expansion stroke.

[0017] The line segment L1 in FIG. 2 indicates the reference ignition timing θa according to the operating state of the engine 1. The reference ignition timing θa is the ignition timing set when the engine ambient temperature T is below the retard start temperature T0. The reference ignition timing θa is set, for example, to the optimum ignition timing MBT at which the torque is maximum. There may be a case where a limited ignition timing that restricts the advance of the ignition timing is set on the retarded side from the optimum ignition timing MBT for reasons such as suppressing the output torque or suppressing noise and abnormal noise. In that case, the reference ignition timing θa becomes the limited ignition timing. In the example of FIG. 2, it is near the top dead center TDC, and the reference ignition timing θa is set on the advanced side by a predetermined crank angle from the top dead center.

[0018] When the engine ambient temperature T becomes equal to or higher than the retard start temperature T0 from the state where the ignition timing is controlled to the reference ignition timing θa, the retard control is started. The line segment L2 in FIG. 2 is the ignition timing after the retard control (referred to as the retarded ignition timing) θr. The retard amount Δθa from the reference ignition timing θa to the retarded ignition timing θr is determined according to the engine ambient temperature T. That is, the retard amount Δθa is set so as to be larger as the engine ambient temperature T (cooling water temperature, intake air temperature) is higher. Thereby, the retarded ignition timing θr is set, and the ignition timing is controlled to the retarded ignition timing θr.

[0019] The retard ignition timing θr is set on the retard side with respect to the ignition timing at which knocking occurs (referred to as the knock ignition timing θb). If the ignition timing remains at the retard ignition timing θr, although the occurrence of knocking can be suppressed, the torque is suppressed more than necessary, which is not preferable. Therefore, following the retard control, an advance control is performed to advance the ignition timing from the retard ignition timing θr to the knock ignition timing θb. That is, after the retard control, an advance control is performed to advance the ignition timing by the knock control system. In the advance control, the ignition timing is gradually advanced, and when knocking is detected, the advance is stopped with the ignition timing being set as the knock ignition timing θb. In the example of FIG. 2, it is on the retard side with respect to the reference ignition timing θa, and the ignition timing advanced by a predetermined ignition timing Δθb (<Δθa) from the retard ignition timing θr is the knock ignition timing θb.

[0020] Thereby, the knock ignition timing θb can be set, and the ignition timing can be controlled to the knock ignition timing θb. Incidentally, after the advance control, the ignition timing may be controlled within a predetermined range based on the knock ignition timing θb (for example, the ignition timing on the retard side or the advance side by a predetermined amount from the knock ignition timing θb). By performing the retard control and the advance control in this way to control the ignition timing to the knock ignition timing θb, it is possible to prevent the occurrence of knocking while minimizing the decrease in torque in a high-temperature environment such as in sweltering heat.

[0021] FIG. 2 shows an example of a high load where the load acting on the engine 1, for example, is a predetermined value or more. Although not shown, in the case of a low load where the torque acting on the engine 1 is less than a predetermined value, the knock ignition timing θb may exist on the advance side of the reference ignition timing (for example, the optimum ignition timing MBT). When the knock ignition timing θb is on the advance side with respect to the reference ignition timing θa, the target ignition timing is controlled to the reference ignition timing θa so as to obtain the maximum torque. When the knock ignition timing is on the retard side with respect to the reference ignition timing, the target ignition timing is controlled to the knock ignition timing θb so as to suppress the occurrence of knocking.

[0022] In this embodiment, an alcohol-containing fuel is used in the engine 1. Alcohol-containing fuel has a high octane rating and is less prone to knocking. Therefore, the reference ignition timing θa and the knock ignition timing θb obtained by advance control may be equal, in which case retard control will be performed unnecessarily. Furthermore, even if the knock ignition timing θb is retarded compared to the reference ignition timing θa, if the difference between the knock ignition timing θb and the retard ignition timing θr is large, it takes time to advance from the retard ignition timing θr to determine the knock ignition timing θb during advance control, resulting in a prolonged state of reduced torque, which is undesirable. Therefore, in this embodiment, a control device suitable for an engine 1 using alcohol fuel is configured as follows.

[0023] Figure 3 is a block diagram showing the main components of the control device 100 for an internal combustion engine according to this embodiment, and shows the configuration related to the control of the spark plug 18. As shown in Figure 3, the control device 100 is configured around an engine control controller 30, and includes a crank angle sensor 31, a load sensor 32, a water temperature sensor 33, an intake air temperature sensor 34, a concentration sensor 35, a knock sensor 36, and a spark plug 18, all connected to the controller 30.

[0024] The crank angle sensor 31 is mounted on the crankshaft 6 and is configured to output a pulse signal in accordance with the rotation of the crankshaft 6. Based on the pulse signal output from the crank angle sensor 31, the controller 30 determines the rotation angle (crank angle) of the crankshaft 6 with respect to the position of top dead center (TDC) at the start of the intake stroke of the piston 3, and calculates the engine speed. Therefore, the crank angle sensor 31 also functions as a rotation speed sensor for detecting the engine speed.

[0025] The load sensor 32 detects the load of the engine 1. The load sensor 32 is a sensor that detects a physical quantity correlated with the load of the engine 1, and can be, for example, a pressure sensor that detects the intake pressure downstream of the throttle valve 17, an airflow meter that detects the intake air volume, or a throttle opening sensor that detects the throttle opening. The detected values ​​of the crank angle sensor 31 and the load sensor 32 are used to determine the reference ignition timing θa (Figure 2) according to the operating conditions.

[0026] The water temperature sensor 33 is installed in the path through which engine coolant flows to cool the engine 1, and detects the temperature of the engine coolant (engine coolant temperature). There is a correlation between the engine coolant temperature and the temperature of the engine 1, and the temperature of the engine 1 can be detected (estimated) by the value detected by the water temperature sensor 33. Alternatively, a temperature sensor may be attached to the engine body, and the temperature of the engine 1 may be detected by the temperature sensor.

[0027] The intake air temperature sensor 34 is installed, for example, in the intake passage 13 and detects the intake air temperature. The values ​​detected by the water temperature sensor 33 and the intake air temperature sensor 34 are used to determine whether or not the retard control described above is necessary, and to determine the retard ignition timing θr.

[0028] The concentration sensor 35 is installed in the fuel tank 21, and the alcohol concentration of the alcohol fuel is detected by the signal output from the concentration sensor 35. It is also possible to detect the alcohol concentration without using the concentration sensor 35. For example, the alcohol concentration may be estimated using an oxygen concentration sensor (LAF sensor). That is, since alcohol fuel has a smaller stoichiometric air-fuel ratio than gasoline fuel, the alcohol concentration can be estimated by detecting the oxygen concentration after refueling. For convenience, fuels with alcohol concentrations of 100%, 85%, and 20% will be represented as E100, E85, and E20, respectively. Immediately after refueling with alcohol fuel of different concentrations (for example, immediately after refueling with E100 fuel while E20 fuel is stored in the fuel tank 21), the detected value of the concentration sensor 35 changes rapidly.

[0029] The knock sensor 36 is mounted on the cylinder block and configured to output a signal indicating vibration of the engine 1. The controller 30 determines whether knocking has occurred based on the signal from the knock sensor 36.

[0030] The controller 30 is comprised of an electronic control unit (ECU) and includes a computer with a CPU, ROM, RAM, and other peripheral circuits such as an I / O interface. Based on signals from the crank angle sensor 31, load sensor 32, water temperature sensor 33, intake air temperature sensor 34, concentration sensor 35, and knock sensor 36, the controller 30 outputs control signals to the spark plug 18.

[0031] The controller 30 has a functional configuration consisting of an ignition control unit 40 and a memory unit 45. The memory unit 45 stores various maps, thresholds, control programs, etc. in advance. The ignition control unit 40 has a knock learning unit 41 that learns the knock ignition timing θb (Figure 2) by determining the knock ignition timing θb, an ignition timing setting unit 42 that sets a target ignition timing using the learning result from the knock learning unit 41, and an output unit 43 that outputs a control signal to the spark plug 18 so that the ignition timing becomes the target ignition timing.

[0032] Figure 4 is a time chart illustrating the processing in the knock learning unit 41. Specifically, Figure 4 shows characteristic f1 indicating the change in ignition timing θ over time, characteristic f2 indicating the change in environmental retard α, characteristics f3 and f4 indicating the change in engine ambient temperature T (coolant temperature Tw, intake air temperature Tin), and characteristic f5 indicating the change in knock learning value β. In addition, Figure 4 also shows the characteristic (dotted line) f6 of the reference ignition timing θa and the characteristic f7 of the alcohol concentration E detected by the concentration sensor 35. The alcohol concentration is, for example, 100% (E100).

[0033] The environmental retard α is a parameter (second parameter) that indicates the amount of retardation Δθa from the reference ignition timing θa (Figure 2). There is a relationship between the engine ambient temperature T and the environmental retard α such that, when the engine ambient temperature T is equal to or greater than the retardation start temperature T0, the higher the engine ambient temperature T, the greater the environmental retard α. This relationship is stored in the memory unit 45 beforehand.

[0034] The knock learning value β is a parameter (first parameter) that indicates the amount of ignition timing advance (Δθb) due to the advance timing control described above. The knock learning unit 41 performs processing to determine the knock learning value β, and the knock learning value β is stored in the memory unit 45 in association with the alcohol concentration E. For convenience, in the following, the environmental retard α and the knock learning value β will be treated as having the same dimensions as the ignition timing θ. In other words, for convenience, they will be treated as representing the ignition timing.

[0035] As shown in Figure 4, up to time t1, the engine ambient temperature T is below the retardation start temperature T0 (for example, T=T0), and the ignition timing is set to the reference ignition timing θa. That is, the controller 30 (knock learning unit 41) calculates the reference ignition timing θa according to the engine speed and load based on signals from the crank angle sensor 31 and the load sensor 32, and controls the ignition timing θ (solid line) to the reference ignition timing θa (dotted line). As an example of the retardation start temperature T0, the retardation start temperature Tin0 corresponding to the intake air temperature Tin is about 35-40°C, and the retardation start temperature Tw0 corresponding to the coolant temperature Tw is about 80°C. However, the retardation start temperature T0 changes depending on the engine speed and intake air volume.

[0036] Between time points t1 and t2, when the intake air temperature Tin detected by the intake air temperature sensor 34 rises to temperature Tin1 (>T0in), the controller 30 performs retard control and sets an environmental retard α1 (increment Δα1 of the retard amount) corresponding to the intake air temperature Tin. As a result, the ignition timing θ is retarded by an amount corresponding to the environmental retard α1 from the reference ignition timing θa, as shown by the arrow. Strictly speaking, advance control is also performed simultaneously with retard control, but since the rate of advance of the ignition timing is significantly slower than the rate of retardation, the retard operation is dominant during retard control.

[0037] Between time points t2 and t3, the engine ambient temperature T remains constant, and the ambient retard α also remains constant. At this time, the ignition timing is advanced by the advance control of the controller 30. As a result, the ignition timing gradually advances as shown by the arrow until knocking is detected by the knock sensor 36, and at time point t3, the ignition timing returns to the initial reference ignition timing θa. At this time, the controller 30 adds an amount corresponding to the advance amount (Δβ1) to the knock learning value β (initial value β0) to set the knock learning value to β1, and stores it in the memory unit 45. If knocking is detected before the ignition timing θ reaches the reference ignition timing θa, the controller 30 terminates the advance control at that point. In this case, the ignition timing is the knock ignition timing θb (Figure 2), and a value smaller than β1 becomes the knock learning value β.

[0038] Between time points t3 and t4, the engine ambient temperature T is constant. Therefore, the ambient retard α is constant (=α1), and the ignition timing is not advanced, so the knock learning value β is also constant (=β1). In this case, the controller 30 temporarily stops the ignition timing advance control.

[0039] Between time points t4 and t5, when the coolant temperature Tw detected by the water temperature sensor 33 rises to temperature Tw1 (>T0w), the controller 30 again performs retard control to set an environmental retard α2 corresponding to the coolant temperature Tw. That is, it adds the environmental retard (Δα2) corresponding to the coolant temperature Tw to the environmental retard α1 corresponding to the intake air temperature Tin, setting an environmental retard α2 (=Δα1+Δα2) corresponding to the increase in intake air temperature Tin and coolant temperature Tw. As a result, the ignition timing θ is retarded by an amount equivalent to the change in environmental retard α Δα2 from the reference ignition timing θa, and the total retard amount from time point t1 onward becomes equal to the environmental retard α2.

[0040] Between time points t5 and t6, the engine ambient temperature T remains constant, and the ambient retard α also remains constant. At this time, the ignition timing is advanced by the advance control of the controller 30. As a result, the ignition timing gradually advances until knocking is detected by the knock sensor 36, and at time point t6, the ignition timing returns to the initial reference ignition timing θa. At this time, the controller 30 adds the knock learning value β to β1 by the amount corresponding to the current advance (Δβ2), updates the knock learning value β to β2, and stores it in the memory unit 45.

[0041] Between time points t6 and t7, the engine ambient temperature T is constant. Therefore, the ambient retard α is constant (=α2), and the ignition timing is not advanced, so the knock learning value β is also constant (=β2). In this case, the controller 30 stops the ignition timing advance control again.

[0042] As the coolant temperature Tw and intake air temperature Tin rise further from time t7 to t8 (Tw2, Tin2), the controller 30 again performs retard control, adding the change in environmental retardation Δα3 corresponding to the coolant temperature Tw and intake air temperature Tin to the environmental retardation α2, thereby setting the environmental retardation α3. As a result, the ignition timing θ is retarded by an amount equivalent to the change in environmental retardation α Δα3 from the reference ignition timing θa, and the total retardation amount becomes equal to the environmental retardation α3. From time t7 to t8, the increase in engine ambient temperature T is greater than from time t1 to t2 and from time t4 to t5, so the change in environmental retardation α Δα3 is larger. Therefore, the amount of ignition timing retardation is also larger.

[0043] Between time points t8 and t9, the engine ambient temperature T remains constant, and the ambient retard α also remains constant. At this time, the ignition timing is advanced by the advance control of the controller 30. As a result, the ignition timing gradually advances until knocking is detected by the knock sensor 36, and at time point t9, the ignition timing returns to the initial reference ignition timing θa. At this time, the controller 30 adds the knock learning value β to β2 by an amount (Δβ3) corresponding to the current advance amount. Then, the knock learning value β is updated to β3 and stored in the memory unit 45 in association with the alcohol concentration E.

[0044] On the other hand, when using fuels with different alcohol concentrations E (for example, fuel with an alcohol concentration of E85), if knocking is detected between time points t8 and t9 while advancing the ignition timing, the advance is stopped as shown by the dashed-dotted characteristic f8. The ignition timing at this time is the knock ignition timing θb (Figure 2), and the controller 30 stores the knock learning value β4 (dashed-dotted characteristic f9) corresponding to the knock ignition timing θb, associating it with the alcohol concentration E.

[0045] The knock learning unit 41 stores knock learning values ​​β3 and β4 corresponding to the alcohol concentration E in the storage unit 45 by performing the retard control and advance angle control described above. Specifically, it stores the knock learning value β3 corresponding to the alcohol concentration E100 and the knock learning value β4 corresponding to the alcohol concentration E85. Here, the knock learning value θ4 is a value obtained when knocking is detected, while the knock learning value β3 is a value obtained without knocking being detected. Therefore, when using fuel with an alcohol concentration of E100, if the environmental retardation becomes greater than α3, knocking may be detected, and in that case, the knock learning value corresponding to the alcohol concentration E100 is updated to a value greater than θ3.

[0046] The ignition timing setting unit 42 sets the target ignition timing based on the knock learning value β. Figure 5 is a time chart to explain the processing by the ignition timing setting unit 42. This time chart is the time chart after the knock learning value β3 corresponding to the alcohol concentration E100 in Figure 4 has been stored, and time points t11 to t19 correspond to time points t1 to t9 in Figure 4. Therefore, as shown in Figure 5, at time points t11 to t12, the intake air temperature Tin rises and the environmental retardation becomes α1, at time points t14 to t15, the coolant temperature Tw rises and the environmental retardation becomes α2, and at time points t17 to t18, the intake air temperature Tin and coolant temperature Tw rise and the environmental retardation becomes α3.

[0047] On the other hand, the knock learning value β is constant (=β3) regardless of changes in the engine ambient temperature T, because it uses the value β3 stored in the memory unit 45. At this time, the controller 30 determines the magnitude of the environmental retard α3 and the knock learning value β3, or more specifically, the magnitude of the retard amount determined by the environmental retard α3 and the advance amount determined by the knock learning value β. The retard amount determined by the environmental retard α3 means the retard amount required when the engine ambient temperature T rises. On the other hand, the knock learning value β3 means the retard amount that becomes unnecessary because fuel with an alcohol concentration of E100 is used.

[0048] The controller 30 determines that retard control is unnecessary when the environmental retard α3 is less than or equal to the knock learning value β3. Therefore, the ignition timing remains constant at the reference ignition timing θa, and the controller 30 (ignition timing setting unit 42) sets the reference ignition timing θ1 to the target ignition timing. However, if, for example, after time t19 in Figure 5, the engine ambient temperature T rises (Tin3) as shown by the dotted line, and the environmental retard becomes greater than α3 (α4), the environmental retard α4 exceeds the knock learning value β3. At this time, the controller 30 determines that retard control is necessary and retards the ignition timing by an amount corresponding to the difference between α3 and α4 (Δα4), as shown by the dotted line. Furthermore, the ignition timing is advanced up to the limit of the reference ignition timing θa until knocking occurs, and the knock learning value β is updated (β5).

[0049] Figure 6 is a flowchart showing an example of a process performed by the controller 30. The process shown in this flowchart is started, for example, when the engine key switch is turned on, and is executed repeatedly at predetermined intervals. This results in the time charts shown in Figures 4 and 5.

[0050] As shown in Figure 6, first, in step S1, the controller 30 reads the signals from sensors 31 to 36. Next, in step S2, the controller 30 determines whether the engine ambient temperature T (coolant temperature Tw, intake air temperature Tin) detected by the water temperature sensor 33 and the intake air temperature sensor 34 is higher than a predetermined retard start temperature T0. If the result in step S2 is positive, the process proceeds to step S3; otherwise, it proceeds to step S11.

[0051] In step S11, the controller 30 calculates a reference ignition timing θa according to the engine operating state based on signals from the crank angle sensor 31 and the load sensor 32, and sets the reference ignition timing θa as the target ignition timing. For example, the optimal ignition timing MBT is calculated as the reference ignition timing θa. Alternatively, if the characteristics of the knock ignition timing θb corresponding to the alcohol concentration (for example, characteristics showing the relationship between volumetric efficiency and knock ignition timing θb) are stored in advance, the knock ignition timing θb according to the engine operating state is calculated based on these characteristics and set as the reference ignition timing θa. In some cases, the ignition timing may be restricted to the retarded side compared to the optimal ignition timing MBT or knock ignition timing θb for reasons such as suppressing torque or noise and abnormal sounds, in which case the restricted ignition timing is set as the target ignition timing as the reference ignition timing θa. Then, a control signal is output to the spark plug 18 to control the ignition timing to the target ignition timing, and the process ends.

[0052] In step S3, the controller 30 uses the relationship between the engine ambient temperature T and the ambient retardation α, which is stored in the memory unit 45 beforehand, that is, the relationship that the higher the engine ambient temperature T, the larger the ambient retardation α, to calculate the ambient retardation α corresponding to the engine ambient temperature T.

[0053] Next, in step S4, the controller 30 reads the knock learning value β, which corresponds to the alcohol concentration E detected by the concentration sensor 35 and has been previously stored in the memory unit 45. If learning corresponding to the alcohol concentration E has not been performed (for example, at time t1 in Figure 4), the initial value β0 (for example, 0) is used as the knock learning value β. Furthermore, the controller 30 determines whether the knock learning value β is greater than the environmental retardation α calculated in step S2. If the result in step S4 is positive, the process proceeds to step S11.

[0054] In the example shown in Figure 5 (for example, time t12 in Figure 5), β3 > α1, so it is affirmed in step S4. Therefore, retard control is unnecessary in this case. On the other hand, in the example shown in Figure 4 (for example, time t2 in Figure 4), β0 < α1, so it is denied in step S4, and the process proceeds to step S5. In step S4, instead of determining the magnitude of the knock learning value β and the environmental retard α, it may be possible to calculate a value by adding the knock line estimated by feedforward control, the knock learning value β, and the environmental retard α, and then determine whether this value is greater than the reference ignition timing θa (for example, the optimal ignition timing MBT). In this case, if it is affirmed in step S4, the reference ignition timing θa is retarded compared to the knock ignition timing, so ignition can be performed at the optimal ignition timing.

[0055] In step S5, the controller 30 outputs a control signal to the spark plug 18, gradually retarding the ignition timing by an amount equivalent to the environmental retard α calculated in step S2. In other words, retard control is performed (for example, at times t1-t2, t4-t5, and t7-t8 in Figure 4). Next, in step S6, the controller 30 outputs a control signal to the spark plug 18, gradually advancing the ignition timing. In other words, advance control is performed (for example, at times t2-t3, t5-t6, and t8-t9 in Figure 4). During advance control, the knock learning value β increases each time the ignition timing advances.

[0056] Next, in step S7, the controller 30 determines whether knocking has occurred based on the signal from the knock sensor 36. If the result in step S7 is negative, the process proceeds to step S8. In step S8, the controller 30 determines whether the ignition timing has advanced to the reference ignition timing θa. If the result in step S8 is positive, the process proceeds to step S9; otherwise, the process returns to step S6.

[0057] In step S9, the controller 30 outputs a control signal to the spark plug 18 to stop the advance of the ignition timing (for example, at times t3, t6, and t9 in Figure 4). Next, in step S10, the controller 30 stores the knock learning value β in the memory unit 45, corresponding to the alcohol concentration E detected by the concentration sensor 35. If the knock learning value β is already stored (for example, at times t6 and t9 in Figure 4), the knock learning value β is updated. Next, in step S11, the controller 30 sets the reference ignition timing θa to the target ignition timing, outputs a control signal to the spark plug 18 to control the ignition timing to the target ignition timing, and ends the process.

[0058] On the other hand, if the result in step S7 is positive, the process proceeds to step S12, where the controller outputs a control signal to the spark plug 18 and stops the advance of the ignition timing (for example, characteristic f8 after time t8 in Figure 4). Next, in step S13, the controller 30 stores the knock learning value β (for example, β4 in Figure 4) corresponding to the knock ignition timing θb (Figure 2) in the storage unit 45.

[0059] Next, in step S14, the controller 30 sets the knock ignition timing θb to the target ignition timing. Then, it outputs a control signal to the spark plug 18 to control the ignition timing to the target ignition timing, and the process ends.

[0060] In step S11 of the above process, the controller 30 sets the reference ignition timing θa to the optimal ignition timing MBT or knock ignition timing θb corresponding to the engine operating state. Then, when performing advance timing limit control to restrict the advance of the ignition timing for reasons such as suppressing output torque or suppressing noise or abnormal noise, the controller sets the reference ignition timing θa to a limiting ignition timing that is retarded more than the optimal ignition timing MBT or knock ignition timing θb. Although not shown in the diagram, the limiting ignition timing is set, for example, between the retarded ignition timing θr and the knock ignition timing θb in Figure 2. When the ignition timing reaches the limiting ignition timing during advance timing limit control, the controller 30 stops the advance timing control.

[0061] From this state, when the advance timing restriction is released due to a change in engine operating conditions (engine speed or load) (when the advance timing restriction control ends), the reference ignition timing θa changes to, for example, the knock ignition timing θb (when the optimal ignition timing MBT is advanced beyond the knock ignition timing θb) or the optimal ignition timing MBT (when the optimal ignition timing MBT is retarded beyond the knock ignition timing θb). In this embodiment, a knock learning value β corresponding to the alcohol concentration E is stored in the memory unit 45, so it is possible to determine how far the ignition timing can be advanced. Therefore, when the advance timing restriction is released, the reference ignition timing θa (knock ignition timing θb or optimal ignition timing MBT) can be immediately set using the knock learning value β. For this reason, when the advance timing restriction is released, there is no need to perform advance timing control to gradually advance the ignition timing to determine the reference ignition timing θa, and the decrease in torque can be minimized.

[0062] In this embodiment, a knock learning value β corresponding to the alcohol concentration E is stored in the storage unit 45. Figure 7 is a time chart showing the change over time between the alcohol concentration E detected by the concentration sensor 35 and the knock learning value β when fuels with different alcohol concentrations E are supplied. Figure 7 is a time chart showing the state when fuel with an alcohol concentration of E20 remains in the fuel tank 21, and at time t21, fuel with an alcohol concentration of E100 is supplied.

[0063] As shown in Figure 7, the alcohol concentration E changes rapidly from time t21 to t22, and consequently the knock learning value β also changes rapidly from β10 to β11. If the controller 30 were to set the target ignition timing using the knock learning value β as is, the target ignition timing might change rapidly. To avoid this, in this embodiment, a limit is placed on the rate of change dβ / dt, which indicates the amount of change of the knock learning value β per unit time. Specifically, the controller 30 determines whether the rate of change dβ / dt (magnitude of the rate of change) of the knock learning value β is less than or equal to a predetermined value γ, and if it exceeds the predetermined value γ, it changes the knock learning value β so that the rate of change dβ / dt becomes the predetermined value γ.

[0064] As a result, the knock learning value β changes gradually over time, as shown by the dotted line (characteristic f11) in Figure 7. This change occurs over a constant period of time. Consequently, when the alcohol concentration changes rapidly, it is possible to prevent a sudden change in the target ignition timing and suppress abrupt fluctuations in torque. The reason for limiting the rate of change of the knock learning value β is to keep the rate of change of the target ignition timing below a predetermined value when fuels with different alcohol concentrations E are supplied. Therefore, the target ignition timing may be set so that the magnitude of the rate of change of the target ignition timing is below a predetermined value, without limiting the rate of change of the knock learning value β.

[0065] This embodiment can provide the following effects and advantages. (1) The control device 100 for the internal combustion engine is configured to control an engine 1 having an injector 19 that injects fuel containing alcohol and a spark plug 18 that ignites the mixture of fuel and air injected by the injector 19 (Figure 1). The control device 100 includes a concentration sensor 35 that detects the alcohol concentration E of the fuel, a water temperature sensor 33 and an intake air temperature sensor 34 that detect the coolant temperature Tw of the engine 1 and the temperature of the air drawn into the engine 1 (intake air temperature Tin), respectively, as the engine ambient temperature T, and a controller 30 that controls the spark plug 18 so that the ignition timing becomes the target ignition timing (Figure 3). When the engine ambient temperature T detected by the water temperature sensor 33 and the intake air temperature sensor 34 is T0 or higher, the controller 30 performs retard control, which retards the ignition timing from the reference ignition timing θa according to the engine ambient temperature T, and advance control, which advances the ignition timing from the ignition timing retarded by the retard control until knocking occurs, up to the limit of the reference ignition timing θa. At the same time, it sets a target ignition timing based on the knock learning value β, which is a parameter corresponding to the amount of ignition timing advance obtained by the advance control, the alcohol concentration E detected by the concentration sensor 35, and the engine ambient temperature T detected by the water temperature sensor 33 and the intake air temperature sensor 34 (Figure 6).

[0066] This prevents excessive retardation control when using fuels with a high alcohol concentration E, i.e., fuels with a large knock learning value (magnitude of knock learning value β), in extremely hot environments, even when an environmental retardation α is set as the engine ambient temperature T rises. Therefore, the ignition timing is not unnecessarily retarded, and the ignition timing retardation can be performed effectively. In other words, the ignition timing can be set appropriately when using alcohol-containing fuels. As a result, the reduction in torque (and the duration of the reduction) can be minimized.

[0067] (2) The controller further includes a memory unit 45 that stores the relationship between the alcohol concentration E and the knock learning value β (Figure 3). Based on the relationship stored in the memory unit 45, the controller 30 sets the knock learning value β according to the alcohol concentration E detected by the concentration sensor 35, and sets the target ignition timing based on the knock learning value β and the engine ambient temperature T detected by the water temperature sensor 33 and the intake air temperature sensor 34 (Figure 6). This makes it easy to set the target ignition timing corresponding to the change in engine ambient temperature T using the knock learning value β corresponding to the alcohol concentration E.

[0068] (3) The memory unit 45 further stores the relationship between the environmental retard α, which corresponds to the amount of ignition timing retardation during retard control, and the engine ambient temperature T. The controller 30 compares the knock learning value β, which corresponds to the alcohol concentration E, with the environmental retard α, which corresponds to the engine ambient temperature T, to determine whether retard control is necessary, and sets the target ignition timing based on the determination result (Figure 6). This makes it easy to determine whether retard control is necessary using the knock learning value, which corresponds to the alcohol concentration E, and the environmental retard α, which corresponds to the engine ambient temperature T.

[0069] (4) The controller 30 sets the reference ignition timing θa to a retarder angle than the knock ignition timing θb at which knocking occurs or the optimal ignition timing MBT at which torque is maximized, and further performs ignition timing limit control to restrict the ignition timing to the reference ignition timing θa during advance control (Figure 4). After the advance of the ignition timing is restricted in this way, when the advance restriction is released, the target ignition timing returns to the value before the restriction (optimal ignition timing MBT or knock ignition timing θb). However, in this embodiment, since the knock learning value β is stored, the ignition timing can be immediately changed to the target ignition timing using the knock learning value β after the advance restriction is released. As a result, the decrease in torque can be kept to a minimum in a short time.

[0070] (5) When the alcohol concentration E detected by the concentration sensor 35 changes, the controller 30 sets the target ignition timing so that the magnitude of the rate of change of the ignition timing is less than or equal to a predetermined value (Figure 7). Specifically, by setting a limit on the rate of change of the knock learning value β dβ / dt so that the rate of change of the knock learning value β dβ / dt is less than or equal to a predetermined value γ, the rate of change of the target ignition timing is kept below a predetermined value. This makes it possible to suppress sudden fluctuations in torque.

[0071] The above embodiment can be modified in various ways. Modifications are described below. In the above embodiment, the injector 19, which serves as a fuel injection unit for injecting alcohol-containing fuel, is of the direct injection type, but the fuel injection unit may also be of the port injection type. In the above embodiment, the spark plug 18, which serves as an ignition unit for igniting the fuel-air mixture, is placed between the intake port 11 and the exhaust port 12, but the arrangement of the ignition unit is not limited to this. In the above embodiment, the alcohol concentration E is detected by a concentration sensor 35 provided in the fuel tank 21, but the concentration detection unit may be provided in another location. In the above embodiment, the coolant temperature Tw and intake air temperature Tin, which have a correlation with the engine temperature, are detected by a water temperature sensor 33 and an intake air temperature sensor 34, respectively, which serve as temperature detection units, but the temperature detection unit may be configured to detect either the engine temperature or the intake air temperature.

[0072] In the above embodiment, the controller 30, acting as a control unit, controls the spark plug 18 so that the ignition timing becomes the target ignition timing. Specifically, the relationship between the alcohol concentration E and the knock learning value β (parameter, first parameter) corresponding to the amount of ignition timing advance obtained by advance control, and the relationship between the environmental retard α (second parameter) corresponding to the amount of ignition timing retard during retard control and the engine ambient temperature T are stored in the memory unit 45. By comparing the knock learning value β and the environmental retard α, the necessity of retard control (reducing the ignition timing) is determined, and the target ignition timing is set based on the determination result. In this regard, when the engine ambient temperature T is above a predetermined value (retard start temperature T0), the control unit can be configured in any way as long as it performs retardation control, which retards the ignition timing from the reference ignition timing according to the engine ambient temperature, and advancement control, which advances the ignition timing from the ignition timing retarded by the retardation control until knocking occurs, up to the limit of the reference ignition timing, and sets a target ignition timing based on a parameter corresponding to the amount of ignition timing advance obtained by the advancement control, the alcohol concentration E, and the engine ambient temperature T.

[0073] In the above embodiment, the controller 30 performs ignition timing limit control, which restricts the reference ignition timing to a retarded position compared to the optimal ignition timing or knock ignition timing. However, ignition timing limit control is not required. In the above embodiment, the controller 30 restricts the magnitude of the rate of change of the knock learning value β to a predetermined value γ or less when the alcohol concentration E changes, thereby suppressing the magnitude of the rate of change of the ignition timing. However, as long as the target ignition timing is set so that the magnitude of the rate of change of the ignition timing is less than or equal to a predetermined value, the configuration of the control unit when the alcohol concentration changes is not limited to that described above.

[0074] The above description is merely an example, and the present invention is not limited by the embodiments and modifications described above, as long as the features of the present invention are not impaired. It is also possible to arbitrarily combine one or more of the above embodiments and modifications, and to combine modifications with each other. [Explanation of Symbols]

[0075] 1 Engine, 18 Spark plug, 19 Injector, 30 Controller, 33 Water temperature sensor, 34 Intake air temperature sensor, 35 Concentration sensor, 36 Knock sensor, 40 Ignition control unit, 41 Knock learning unit, 42 Ignition timing setting unit, 45 Memory unit, 100 Control device, β Knock learning value

Claims

1. A control device for an internal combustion engine having a fuel injection unit that injects a fuel containing alcohol, and an ignition unit that ignites a mixture of the fuel injected by the fuel injection unit and air, A concentration detection unit for detecting the alcohol concentration of the fuel, A temperature detection unit for detecting the temperature of at least one of the cooling water of the internal combustion engine and the intake air drawn into the internal combustion engine, The system comprises a control unit that controls the ignition unit so that the ignition timing becomes the target ignition timing, The control unit is characterized by performing: retardation control, which retards the ignition timing from a reference ignition timing according to the temperature detected by the temperature detection unit when the temperature is above a predetermined value; advancement control, which advances the ignition timing from the ignition timing retarded by the retardation control until knocking occurs, up to the reference ignition timing limit; and setting the target ignition timing based on a parameter indicating the amount of ignition timing advance obtained by the advancement control, the alcohol concentration detected by the concentration detection unit, and the temperature detected by the temperature detection unit.

2. In the control device for an internal combustion engine according to claim 1, The system further includes a storage unit that stores the relationship between the alcohol concentration and the parameter, The control unit is characterized in that it sets the parameters according to the alcohol concentration detected by the concentration detection unit based on the relationship stored in the storage unit, and sets the target ignition timing based on the parameters and the temperature detected by the temperature detection unit.

3. In the control device for an internal combustion engine according to claim 2, The aforementioned parameter is the first parameter, The memory unit further stores the relationship between the second parameter corresponding to the amount of ignition timing retardation during the retardation control and the temperature. The control unit is characterized in that it determines whether or not the timing retardation control is necessary by comparing the first parameter corresponding to the alcohol concentration with the second parameter corresponding to the temperature, and sets the target ignition timing based on the determination result.

4. In the control device for an internal combustion engine according to claim 2, The control unit is characterized in that it sets the reference ignition timing to a retarded position compared to the knock ignition timing at which knocking occurs, and further performs ignition timing limiting control to restrict the ignition timing to the reference ignition timing when advancing the timing.

5. In the control device for an internal combustion engine according to any one of claims 1 to 4, The control unit is characterized in that, when the alcohol concentration detected by the concentration detection unit changes, it sets the target ignition timing such that the magnitude of the rate of change in the ignition timing is less than or equal to a predetermined value.

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