Control device for internal combustion engines

Abstract

To appropriately suppress the torque of the internal combustion engine. [Solution] The control device 100 comprises a spark-ignition type internal combustion engine 1 having a throttle valve 14 and a spark plug 16, to which alcohol fuel containing alcohol is supplied, and a control unit 20 that controls the intake volume and ignition timing of the internal combustion engine 1 by controlling the operation of the throttle valve 14 and the spark plug 16. The control unit 20 controls the operation of the throttle valve 14 to limit the intake volume by restricting the opening of the throttle valve 14 to a predetermined opening or less when the alcohol concentration of the alcohol fuel is less than a predetermined concentration, and controls the operation of the throttle valve 14 to limit the intake volume when the alcohol concentration is above the predetermined concentration, and controls the operation of the spark plug 16 to limit the ignition timing to a predetermined ignition timing or retarded beyond the predetermined ignition timing.

Description

Technical Field

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

Background Art

[0002] Conventionally, efforts for mitigating or reducing the impact of climate change have been continued, and research and development on emission improvement have been conducted towards this realization. In this regard, conventionally, a device has been known that restricts the torque of an internal combustion engine mounted on a FFV (Flexible Fuel Vehicle) that can use a renewable fuel such as bioethanol with a low carbon dioxide emission (see, for example, Patent Documents 1 and 2). In the device described in Patent Document 1, the opening degree of the throttle valve is restricted to be below a guard value set to be smaller as the alcohol concentration of the fuel is higher. On the other hand, in the device described in Patent Document 2, when the alcohol concentration of the fuel becomes equal to or higher than the threshold concentration, the ignition timing is restricted to the retard side from the ignition timing at which the output becomes maximum when the fuel does not contain alcohol.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, when the alcohol concentration of the fuel becomes high, there is a risk that the torque of the internal combustion engine becomes excessive, and thus it is necessary to suppress this. However, it is difficult to appropriately suppress the torque of the internal combustion engine only by restricting the opening degree of the throttle valve as in the device of Patent Document 1 above, or only by restricting the ignition timing as in the device of Patent Document 2 above.

Means for Solving the Problems

[0005] A control device for an internal combustion engine according to one aspect of the present invention comprises a spark-ignition type internal combustion engine having a throttle valve and a spark plug, to which alcohol fuel containing alcohol is supplied, and a control unit that controls the intake volume and ignition timing of the internal combustion engine by controlling the operation of the throttle valve and the spark plug. The control unit controls the operation of the throttle valve to limit the intake volume by restricting the opening of the throttle valve to a predetermined opening or less when the alcohol concentration of the alcohol fuel is at or above a first predetermined concentration, and controls the operation of the spark plug to limit the ignition timing to a predetermined ignition timing or retarded beyond the predetermined ignition timing. When the alcohol concentration is at or above a second predetermined concentration less than the first predetermined concentration and less than the first predetermined concentration, the control unit controls the operation of the throttle valve to limit the intake volume and controls the operation of the spark plug so that the ignition timing becomes a target ignition timing according to the operating conditions of the internal combustion engine. When the alcohol concentration is less than the second predetermined concentration, the control unit controls the operation of the throttle valve to open to a degree corresponding to the accelerator opening and controls the operation of the spark plug so that the ignition timing becomes a target ignition timing. 。 [Effects of the Invention]

[0006] According to the present invention, the torque of an internal combustion engine can be appropriately suppressed. [Brief explanation of the drawing]

[0007] [Figure 1] A schematic diagram showing an example of 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 schematic block diagram showing 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] This diagram illustrates the target ignition timing for the engine shown in Figure 1. [Figure 4] This diagram illustrates the in-cylinder pressure during high-load operation of the engine shown in Figure 1. [Figure 5]Figure 2 illustrates the intake volume limit and ignition timing limit by the ECU. [Figure 6] A flowchart showing an example of the process performed by the ECU in Figure 2. [Modes for carrying out the invention]

[0008] Embodiments of the present invention will be described below with reference to Figures 1 to 6. The control device for an internal combustion engine according to the embodiment of the present invention can be applied to a spark-ignition type internal combustion engine mounted on an FFV (Flexible-Fuel Vehicle) that can use alcohol fuel containing alcohol such as bioethanol and gasoline, alcohol fuel without gasoline (E100), and gasoline fuel without alcohol (E0).

[0009] Figure 1 is a schematic diagram showing an example of the main components of an engine 1 to which a control device for an internal combustion engine according to an embodiment of the present invention is applied. Engine 1 is a spark-ignition type internal combustion engine mounted on a vehicle and has multiple cylinders, such as four cylinders, but Figure 1 shows the configuration of a single cylinder. Note that the configuration of each cylinder is identical to that of the others.

[0010] As shown in Figure 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 and the cylinder head 4. The piston 3 is connected to the 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. The combustion chamber 5 is connected to an intake passage 10 via the intake port 8, and to an exhaust passage 11 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 configured, for example, as a butterfly valve, and the amount of intake air into the combustion chamber 5 is adjusted by the throttle valve 14. The intake valve 12 and the exhaust valve 13 are opened and closed by a valve train 15.

[0012] The cylinder head 4 is fitted with a spark plug 16 and a direct-injection injector 17, each facing the combustion chamber 5. The spark 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 positioned near the intake valve 12 and is driven by electrical energy to inject fuel. More specifically, the injector 17 is supplied with high-pressure fuel from the fuel tank via a fuel pump. The injector 17 atomizes the fuel into fine particles and injects the fuel into the combustion chamber 5 at a predetermined timing, diagonally downward. Note that the position of the injector 17 is not limited to this, and it can also be positioned, for example, near the spark plug 16.

[0014] The valve train 15 includes an intake camshaft 18 and an exhaust camshaft 19. The intake camshaft 18 has an intake cam 18a that corresponds to each cylinder (cylinder 2a), and the exhaust camshaft 19 has an exhaust cam 19a that corresponds 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 the intake cam 18a via an intake rocker arm (not shown) by the rotation of the intake camshaft 18. The exhaust valve 13 opens and closes at a predetermined timing according to the profile of the exhaust cam 19a via an exhaust rocker arm (not shown) by the rotation of the exhaust camshaft 19.

[0016] FIG. 2 is a block diagram schematically showing an example of the overall configuration of a control device (hereinafter referred to as the device) 100 for an internal combustion engine 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 of FIG. 1.

[0017] The ECU 20 is configured to include a computer having a processor such as a CPU, memories such as RAM and ROM, and other peripheral circuits. Connected to the ECU 20 are an alcohol concentration sensor 21, a crank angle sensor 22, an accelerator opening sensor 23, an intake air amount sensor 24, a knock sensor 25, the throttle valve 14 of FIG. 1, a spark plug 16, and an injector 17. The ECU 20 controls the intake air amount of the engine 1 by controlling the operation of the throttle valve 14, controls the ignition timing of the engine 1 by controlling the operation of the spark plug 16, and controls the fuel injection amount of the engine 1 by controlling the operation of the injector 17.

[0018] <{ The alcohol concentration sensor 21 is provided in the fuel supply path between the fuel tank of the vehicle and the injector 17 of FIG. 1, and detects the alcohol concentration E of the fuel supplied to the engine 1 (combustion chamber 5) via the injector 17. More specifically, it is provided between a low-pressure fuel pump that pumps up the fuel stored in the fuel tank and a high-pressure fuel pump that pumps the fuel to the injector 17.

[0019] The crank angle sensor 22 is provided on the crankshaft 7 in FIG. 1 and is configured to output a pulse signal as the crankshaft 7 rotates. The ECU 20 identifies the rotational angle (crank angle) of the crankshaft 7 based on the piston 3's top dead center TDC position at the start of the intake stroke as a reference, and calculates the engine speed (engine rotational speed) of the engine 1, based on the pulse signal from the crank angle sensor 22.

[0020] The accelerator opening sensor 23 is provided on the accelerator pedal of the vehicle and detects the accelerator opening, which is the amount of operation of the accelerator pedal. The ECU 20 calculates the target torque of the engine 1 based on the accelerator opening detected by the accelerator opening sensor 23, and calculates the target intake air amount and the target opening degree (target throttle opening) TH0 of the throttle valve 14 to generate the target torque.

[0021] The intake air amount sensor 24 is constituted by, for example, an air flow meter disposed in the intake passage 10 in FIG. 1 (more specifically, upstream of the throttle valve 14), and detects the intake air amount of the engine 1. The ECU 20 calculates the target injection amount 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, and controls the operation (valve opening time) of the injector 17 according to the calculated target injection amount.

[0022] The knock sensor 25 is provided on the cylinder block 2 in FIG. 1 and detects knocking by detecting the vibration of the cylinder block 2.

[0023] FIG. 3 is a diagram for explaining the target ignition timing θ0 of the injector 17, and shows an example of the characteristics of the target ignition timing θ0 with respect to the engine load at a specific engine speed, which is stored in advance in the memory of the ECU 20. The engine load can be expressed, for example, as the torque or the filling efficiency of the engine 1. The filling efficiency is the ratio (percentage) of the intake air amount (volume in the standard state) per cycle to the cylinder volume (displacement) of the engine 1, and can be calculated based on the intake air amount from the intake air amount sensor 24. The torque of the engine 1 is proportional to the filling efficiency.

[0024] The characteristics of the optimal ignition timing θm, which maximizes the torque of engine 1, are predetermined by combustion tests based on engine speed and engine load. Similarly, the characteristics of the knock ignition timing θk, which is the most advanced ignition timing without knocking, are also predetermined by combustion tests based on engine speed and engine load. As shown in Figure 3, the more retarded ignition timing among the optimal ignition timing θm and the knock ignition timing θk is set as the target ignition timing θ0, which maximizes torque within the range where knocking does not occur.

[0025] The characteristics of the optimal ignition timing θm and knock ignition timing θk are determined by conducting combustion tests for each fuel octane rating. In the case of alcohol fuel, the higher the alcohol concentration E, the higher the octane rating and the more difficult it tends to burn. Therefore, the optimal ignition timing θm shifts toward the advanced side as the alcohol concentration E and octane rating of the fuel supplied to engine 1 increase, and toward the retarded side as the alcohol concentration E and octane rating decrease. On the other hand, knocking is less likely to occur as the fuel octane rating increases and more likely to occur as the fuel octane rating decreases. Therefore, the knock ignition timing θk shifts toward the advanced side as the alcohol concentration E and octane rating of the fuel increase, and toward the retarded side as the alcohol concentration E and octane rating decrease.

[0026] The octane rating of the fuel supplied to engine 1 can be estimated, for example, by gradually advancing the ignition timing when changes in engine speed and engine load are small, and determining the octane rating corresponding to the ignition timing at which knocking is detected by the knock sensor 25. The ECU 20 calculates the target ignition timing θ0 according to the estimated octane rating (estimated octane rating) and the operating conditions of engine 1 (engine speed and engine load) by referring to the characteristics of the target ignition timing θ0 stored in memory. When fuel with a different octane rating than the fuel stored in the vehicle's fuel tank, or fuel with a different octane rating due to a different alcohol concentration, is supplied, the octane rating of the fuel supplied to engine 1 changes. Even in such cases, by estimating the octane rating of the fuel supplied to engine 1 and calculating an appropriate target ignition timing θ0 according to the estimated octane rating, the ignition timing can be controlled to the optimal level within a range that can suppress knocking.

[0027] Figure 4 is a diagram illustrating the in-cylinder pressure of engine 1 during high-load operation. Alcohol burns more slowly than gasoline and burns relatively gradually. As shown in Figure 4, the higher the alcohol concentration E of the fuel, the lower the combustion pressure and the less likely knocking is to occur. Therefore, the higher the alcohol concentration E and the higher the estimated octane number, the more the knock ignition timing θk, which corresponds to the target ignition timing θ0 during high-load operation, is advanced (Figure 3), and the torque (maximum torque) of engine 1 increases.

[0028] However, depending on the alcohol concentration E of the fuel, such a maximum torque may become excessive and exceed the allowable torque that the vehicle's powertrain, including the engine 1 and transmission, can transmit. Therefore, in this embodiment, the device 100 is configured as follows to appropriately suppress the torque of the engine 1 by limiting the intake volume and limiting the ignition timing of the engine 1.

[0029] Figure 5 is a diagram illustrating the intake volume limit and ignition timing limit by the ECU 20 in Figure 2, and shows an example of the characteristics of the throttle opening limit value THlmt and the ignition timing limit value θlmt at a predetermined engine speed, which are stored in the memory of the ECU 20 in advance. With intake volume limiting, the throttle opening is limited to less than or equal to the limit value THlmt. With ignition timing limiting, the ignition timing is limited to the limit value θlmt or retarded beyond the limit value θlmt.

[0030] <Very Low Alcohol Concentration Range> As shown in Figure 5, when the alcohol concentration E of the fuel is at an extremely low concentration, below the threshold Eα (for example, around 22% (E22)) (including cases where the fuel does not contain alcohol), the throttle opening limit value THlmt is set to the maximum opening, and the ignition timing limit value θlmt is set to the maximum advance timing. In other words, by setting the throttle opening limit value THlmt to the maximum opening and the ignition timing limit value θlmt to the maximum advance timing, the intake volume limit and ignition timing limit by the ECU20 are effectively prohibited, and normal intake volume control and ignition timing control are performed. The maximum opening is, for example, the throttle opening when fully open (for example, around 80 degrees), and the maximum advance timing is, for example, the optimal ignition timing θm.

[0031] In normal intake volume control, the ECU 20 controls the operation of the throttle valve 14 so that the throttle opening becomes a target throttle opening TH0 corresponding to the accelerator opening. In normal ignition timing control, the ECU 20 controls the operation of the spark plug 16 so that the ignition timing becomes a target ignition timing θ0 corresponding to the operating conditions of the engine 1. In the extremely low alcohol concentration region where the alcohol concentration E of the fuel is extremely low, the gasoline component content in the fuel is high, so the maximum torque will not exceed the allowable torque in normal intake volume control and normal ignition timing control.

[0032] <Low alcohol concentration range> When the fuel alcohol concentration E is above the threshold Eα and below the threshold Eβ, the limit value θlmt is set to the maximum advance timing, prohibiting ignition timing restriction and enabling normal ignition timing control. At the same time, the limit value THlmt is set to a value smaller than the maximum opening, limiting the intake volume. In other words, the ECU 20 controls the operation of the throttle valve 14 to perform normal ignition timing control while simultaneously limiting the intake volume by restricting the throttle opening to a value less than or equal to the limit value THlmt.

[0033] In intake volume restriction, the target throttle opening TH0, which exceeds the limit value THlmt, is reduced to the limit value THlmt. Consequently, the intake volume of engine 1 decreases, and the target injection amount calculated based on the intake volume decreases, resulting in a decrease in engine 1 torque. Therefore, by reducing the throttle opening limit value THlmt in intake volume restriction, the torque of engine 1 can be significantly suppressed without worsening the combustion state. In relatively low-load regions where the target torque of engine 1 corresponding to the accelerator opening is relatively small and the target throttle opening TH0 is below the limit value THlmt, intake volume restriction is not performed, and normal intake volume control is carried out.

[0034] In the low alcohol concentration range where the fuel alcohol concentration E is relatively low, the throttle opening limit THlmt for intake volume restriction is set to be smaller as the alcohol concentration E increases, so that the maximum torque of engine 1 remains below the allowable torque. By setting the throttle opening limit THlmt to the minimum necessary value (i.e., the largest allowable value) according to the fuel alcohol concentration E, excessive torque suppression due to excessive intake volume restriction can be prevented.

[0035] <High alcohol concentration range> When the fuel alcohol concentration E is equal to or greater than the threshold Eβ, intake volume is restricted, and the ignition timing limit value θlmt is set to retard the ignition timing beyond the maximum advance timing, thereby restricting the ignition timing. In other words, the ECU 20 controls the operation of the throttle valve 14 to restrict intake volume, and controls the operation of the spark plug 16 to restrict the ignition timing to the limit value θlmt or retard it beyond the limit value θlmt. In relatively low-load regions where the target torque of the engine 1 corresponding to the accelerator opening is relatively small and the target throttle opening TH0 is less than or equal to the limit value THlmt, intake volume restriction is not performed, and normal intake volume control is performed. Also, in relatively low-load regions where the target ignition timing θ0 corresponding to the operating conditions of the engine 1 is retarded beyond the limit value θlmt or the limit value θlmt, ignition timing restriction is not performed, and normal ignition timing control is performed.

[0036] In the high-alcohol concentration region where the alcohol concentration E of the fuel is relatively high, the throttle opening limit value THlmt for limiting the intake volume is set to a fixed value independent of the alcohol concentration E. The fixed value is, for example, the throttle opening (nozzle limit opening) that allows for stable adjustment of the intake volume of engine 1. The fixed value may also be the nozzle limit opening plus a predetermined value that takes into account variations in the throttle valve 14. In normal intake volume control, a throttle opening TH greater than the nozzle limit opening is not commanded except when commanding the throttle valve 14 to be fully open, and the target throttle opening TH0 corresponding to the accelerator opening is set within a range below the nozzle limit opening.

[0037] At throttle openings near full open, from the nozzle limit to full open, the pressure difference between the upstream and downstream sides of the throttle valve 14 in the intake passage 10 shown in Figure 1 is relatively small. Therefore, a certain degree of throttle opening change is necessary to alter the intake volume and torque of the engine 1. On the other hand, at throttle openings below the nozzle limit, this pressure difference becomes large, causing significant changes in the intake volume and torque of the engine 1 in response to small fluctuations in throttle opening. For this reason, when limiting intake volume by setting a limit value THlmt below the nozzle limit, it becomes necessary to set a limit value Tlmt that is sufficiently smaller than the opening corresponding to the allowable torque, so that the torque of the engine 1 does not exceed the allowable torque even when the throttle opening fluctuates. In other words, excessive torque suppression becomes necessary.

[0038] The nozzle limit opening is larger as the engine speed increases and the intake airflow velocity of the engine increases. For example, it is about 15 degrees at 1000 rpm, about 30 degrees at 3000 rpm, and about 45 degrees at 6000 rpm. By setting the limit value THlmt to the nozzle limit opening according to the engine speed, excessive torque suppression can be prevented and appropriate intake air volume limiting can be achieved.

[0039] The threshold Eβ for the fuel alcohol concentration E is the alcohol concentration E at which the throttle opening limit THlmt, which makes the maximum torque of engine 1 match the allowable torque when torque suppression is performed solely by limiting the intake volume, coincides with the nozzle limit opening. Therefore, when the fuel alcohol concentration E is greater than or equal to the threshold Eβ, limiting the intake volume alone, with the limit THlmt set to the nozzle limit opening, is insufficient to suppress the maximum torque of engine 1 to below the allowable torque.

[0040] The ignition timing limit value θlmt is set to retard the ignition timing as the alcohol concentration E increases, so that the maximum torque of engine 1 remains below the allowable torque when the throttle opening is limited to the nozzle limit opening due to intake volume restriction. By setting the ignition timing limit value θlmt to the minimum necessary value (i.e., the allowable advanced value) according to the fuel's alcohol concentration E, excessive torque suppression due to excessive ignition timing restriction can be prevented. In ignition timing restriction, the torque of engine 1 is reduced by retarding the target ignition timing θ0, which is advanced beyond the limit value θlmt, to the limit value θlmt.

[0041] When using the throttle valve 14, the torque of the engine 1 changes according to the intake air volume, which changes according to the throttle opening, and then according to the fuel injection volume, which changes according to the intake air volume. However, when using the spark plug 16, the torque of the engine 1 changes immediately according to the ignition timing. For this reason, ignition timing limitation by the spark plug 16 can suppress torque with higher precision and responsiveness than intake air volume limitation by the throttle valve 14.

[0042] While ignition timing limitation allows for torque suppression with high precision and responsiveness, excessive retardation can lead to poor fuel efficiency due to deteriorating combustion, misfires, and damage to the catalytic converter in the exhaust passage 11 shown in Figure 1 due to increased exhaust temperature. In high-alcohol concentration regions where the fuel alcohol concentration E is high and the maximum torque significantly exceeds the allowable torque with normal intake volume control and normal ignition timing control, significant torque suppression is necessary. In such high-alcohol concentration regions, appropriate power limiting without excess or deficiency can be achieved by limiting the intake volume by setting the throttle opening limit value THlmt to the nozzle limit opening, and by using ignition timing limitation in conjunction.

[0043] Figure 6 is a flowchart showing an example of the process performed by the ECU 20 in Figure 2. The process shown in this flowchart starts, for example, when the vehicle is started and the ECU 20 is activated, and is repeated at predetermined intervals. It may also be performed after refueling the vehicle, within a predetermined period during which the alcohol concentration E of the fuel supplied to the engine 1 changes.

[0044] As shown in Figure 6, first in step S1, it is determined whether the alcohol concentration E of the fuel detected by the alcohol concentration sensor 21 is equal to or greater than the threshold Eβ. If the result in step S1 is positive, the process proceeds to step S2, where the operation of the throttle valve 14 is controlled to limit the intake volume using the throttle opening limit value THlmt as the nozzle limit opening, and the operation of the spark plug 16 is controlled to limit the ignition timing. If the result in step S1 is negative, the process proceeds to step S3, where it is determined whether the alcohol concentration E of the fuel detected by the alcohol concentration sensor 21 is equal to or greater than the threshold Eα. If the result in step S3 is positive, the process proceeds to step S4, where the operation of the throttle valve 14 is controlled to limit the intake volume, and the operation of the spark plug 16 is controlled to perform normal ignition timing control by prohibiting ignition timing restriction. If the process is rejected in step S3, the process proceeds to step S5, where intake volume restriction and ignition timing restriction are prohibited, and the operation of the throttle valve 14 and spark plug 16 is controlled to perform normal intake volume control and ignition timing control.

[0045] According to embodiments of the present invention, the following effects can be achieved. (1) The device 100 includes a spark-ignition engine 1 having a throttle valve 14 and a spark plug 16, to which alcohol fuel containing alcohol is supplied, and an ECU 20 that controls the intake volume and ignition timing of the engine 1 by controlling the operation of the throttle valve 14 and the spark plug 16 (Figures 1 and 2).

[0046] The ECU 20 controls the operation of the throttle valve 14 to limit the intake volume by restricting the throttle opening to a limit value THlmt or less when the alcohol concentration E of the fuel is less than the threshold Eβ, and controls the operation of the spark plug 16 to limit the intake volume when the alcohol concentration E is greater than or equal to the threshold Eβ, and to limit the ignition timing by restricting the ignition timing to a limit value θlmt or retarding it beyond the limit value θlmt (steps S1, S2, S4 in Figures 5 and 6).

[0047] In other words, in low alcohol concentration regions where the maximum torque of engine 1 can be kept below the allowable torque by limiting the intake volume alone, only intake volume limitation is performed. In high alcohol concentration regions where intake volume limitation alone is insufficient to keep the torque below the allowable torque, intake volume limitation and ignition timing limitation are used in combination. This allows the torque of engine 1 to be appropriately controlled so as not to exceed the allowable torque, regardless of the alcohol concentration E of the fuel.

[0048] (2) The throttle opening limit value THlmt is set to be smaller as the alcohol concentration E increases, and the ignition timing limit value θlmt is set to be retarded as the alcohol concentration E increases (Figure 5). By setting the throttle opening limit value THlmt for limiting intake volume and the ignition timing limit value θlmt for limiting ignition timing to the minimum necessary values ​​according to the fuel alcohol concentration E, excessive torque suppression can be prevented.

[0049] (3) The limit value THlmt is set to a fixed value independent of the alcohol concentration E when the alcohol concentration E is equal to or greater than the threshold Eβ (Figure 5). In the high alcohol concentration region where significant torque suppression is required, appropriate power limiting can be achieved by setting the throttle opening limit value THlmt to a fixed value to restrict the intake volume and by using ignition timing restriction in conjunction with this.

[0050] (4) The fixed value is the throttle opening (nozzle limit opening) that allows for stable adjustment of the intake volume of engine 1, and is set according to the engine speed. By setting the intake volume limit value THlmt to the nozzle limit opening and avoiding the use of an opening range in which the intake volume and torque of engine 1 change significantly in response to minute opening fluctuations, excessive torque suppression due to excessive intake volume restriction can be prevented. Furthermore, by performing intake volume restriction with the limit value THlmt set to the nozzle limit opening and using ignition timing restriction in conjunction, torque can be sufficiently suppressed to reliably prevent exceeding the allowable torque, thereby enabling appropriate power limiting without excess or deficiency.

[0051] (5) The ECU20 prohibits intake volume restriction when the alcohol concentration E is less than the threshold Eα, which is smaller than the threshold Eβ (steps S3 and S5 in Figures 5 and 6). In the extremely low alcohol concentration region, where the gasoline component content is high and the maximum torque does not exceed the allowable torque, neither intake volume restriction nor ignition timing restriction is performed. Instead, normal intake volume control and ignition timing control are performed, which allows for simple and reliable prevention of unnecessary torque suppression.

[0052] In the above embodiment, an engine 1 having a direct injection injector 17 was used as an example in Figure 1, etc., but the spark-ignition internal combustion engine is not limited to direct injection; it may also be a port injection type.

[0053] In the above embodiment, an example of a device 100 having an alcohol concentration sensor 21 was illustrated in Figure 2, etc., and an example of limiting intake air volume and ignition timing according to the alcohol concentration E detected by the alcohol concentration sensor 21 was described. However, the control device for an internal combustion engine is not limited to this. The control device for an internal combustion engine may not have a sensor to detect alcohol concentration. For example, it may estimate the alcohol concentration based on the estimated octane number and limit intake air volume and ignition timing according to the estimated alcohol concentration.

[0054] In the above embodiment, the characteristics of the predetermined optimal ignition timing θm and knock ignition timing θk are illustrated in Figure 3, etc., and an example is described in which the ignition timing on the retarder side of these ignition timings is set as the target ignition timing θ0. However, the characteristics of the ignition timing before ignition timing limitation are not limited to those illustrated, and can be anything. For example, it may be a single characteristic that determines a single ignition timing according to the engine speed and engine load, or it may be multiple characteristics that can be switched according to the operating conditions.

[0055] 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]

[0056] 1 Engine, 14 Throttle valve, 16 Spark plug, 17 Injector, 20 Electronic control unit (ECU), 21 Alcohol concentration sensor, 22 Crank angle sensor, 23 Accelerator position sensor, 24 Intake volume sensor, 25 Knock sensor, 100 Control device for internal combustion engine

Claims

1. A spark-ignition internal combustion engine having a throttle valve and a spark plug, and supplied with alcohol fuel containing alcohol, The engine comprises a control unit that controls the intake air volume and ignition timing of the internal combustion engine by controlling the operation of the throttle valve and the spark plug, The control unit, When the alcohol concentration of the alcohol fuel is equal to or greater than a first predetermined concentration, the operation of the throttle valve is controlled to limit the intake volume by restricting the opening of the throttle valve to a predetermined opening or less, and the operation of the spark plug is controlled to limit the ignition timing to a predetermined ignition timing or to a retarded ignition timing beyond the predetermined ignition timing. When the alcohol concentration is greater than or equal to a second predetermined concentration that is less than the first predetermined concentration, and less than the first predetermined concentration, the operation of the throttle valve is controlled to limit the intake volume, and the operation of the spark plug is controlled so that the ignition timing becomes a target ignition timing according to the operating conditions of the internal combustion engine. A control device for an internal combustion engine, characterized in that, when the alcohol concentration is less than the second predetermined concentration, it controls the operation of the throttle valve so that the throttle opening corresponds to the accelerator opening, and controls the operation of the spark plug so that the ignition timing becomes the target ignition timing.

2. In the control device for an internal combustion engine according to claim 1, The predetermined opening is set to be smaller as the alcohol concentration increases. A control device for an internal combustion engine, characterized in that the predetermined ignition timing is set to the retarded side as the alcohol concentration increases.

3. In the control device for an internal combustion engine according to claim 2, A control device for an internal combustion engine, characterized in that the predetermined opening degree is set to a fixed value independent of the alcohol concentration when the alcohol concentration is equal to or greater than the first predetermined concentration.

4. In the control device for an internal combustion engine according to claim 3, The control device for an internal combustion engine is characterized in that the fixed value is set according to the rotational speed of the internal combustion engine.

5. In the control device for an internal combustion engine according to claim 3, The control device for an internal combustion engine is characterized in that the fixed value is the opening degree that allows the intake air volume to be stably adjusted.

6. In the control device for an internal combustion engine according to claim 1, A control device for an internal combustion engine, characterized in that the second predetermined concentration is greater than 0%.

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