Control device for internal combustion engine

Abstract

To provide a control device for an internal combustion engine capable of suppressing a dilution amount generated during an operation in the spark ignition type internal combustion engine that directly injects fuel containing alcohol into a cylinder.SOLUTION: A control device for a spark ignition type internal combustion engine that directly injects fuel containing alcohol into a cylinder includes: control means for controlling injection timing of injecting the fuel from a fuel injection device into the cylinder; alcohol concentration detection means for detecting an alcohol content included in the fuel; and crank angle detection means for detecting rotation of a crank shaft and outputting a crank angle signal and a top dead center signal. In the control device for the internal combustion engine, the control means executes division injection for dividing and injecting the fuel from the fuel injection device into the cylinder in an intake stroke and a compression stroke when the alcohol concentration in the fuel is a predetermined value or larger.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Traditionally, efforts have been made to mitigate or reduce the impact of climate change, and research and development into reducing carbon dioxide emissions has been carried out to achieve this. In recent years, attempts have been made to use fuels containing alcohol as an alternative to gasoline in spark ignition internal combustion engines (SI engines), which inject fuel directly into the cylinders.

[0003] Patent Document 1 describes an internal combustion engine of a direct injection type in which fuel is injected directly into a combustion chamber. The internal combustion engine described in Patent Document 1 includes a combustion chamber, an intake port and an exhaust port communicating with the combustion chamber, an intake valve and an exhaust valve that can freely open and close the intake port and the exhaust port, a fuel injection means that can inject fuel into the combustion chamber from the intake valve side in multiple divided injections, and an injection period setting means that, when the engine is cold, sets the divided injection period of the fuel by the fuel injection means to the first half of the intake valve opening period during which the intake valve opens toward the combustion chamber. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-121416 Summary of the Invention [Problem to be solved by the invention]

[0005] Alcohols such as methanol and ethanol have a lower calorific value per unit volume than gasoline. Therefore, in a spark-ignition internal combustion engine using fuel containing alcohol, to obtain the same output as when using gasoline, the amount of fuel injected into the cylinder must be increased compared to when using gasoline. Furthermore, alcohol is less likely to vaporize under low-temperature conditions than gasoline. Therefore, when using fuel containing alcohol and operating an internal combustion engine in a low-temperature environment, the amount of fuel injected into the cylinder is increased.

[0006] However, if the amount of alcohol-containing fuel injected into the cylinder is increased, the fuel adhering to the inner wall of the cylinder will flow down along the inner wall of the cylinder, increasing the amount of dilution (oil dilution) mixed into the engine oil. If the amount of dilution is large, the engine oil will be diluted, reducing the lubricating effect of the engine oil. For this reason, in a spark-ignition internal combustion engine in which fuel containing alcohol is directly injected into the cylinder, it is required to suppress the amount of dilution that occurs during operation.

[0007] The present application has been made in view of the above-mentioned problems, and aims to provide a control device for an internal combustion engine that can suppress the amount of dilution generated during operation in a spark-ignition internal combustion engine that directly injects fuel containing alcohol into the cylinders. [Means for solving the problem]

[0008] In order to solve the above problems, the following means are provided.

[0009] A first aspect of the present invention provides a control device for an internal combustion engine for a spark ignition internal combustion engine (3) that directly injects fuel containing alcohol into a cylinder (3 a), and the control device includes: a control means (2) that controls the injection timing of injecting the fuel from a fuel injection device (4) into the cylinder (3 a); an alcohol concentration detection means (24) that detects the alcohol content of the fuel; and a crank angle detection means (21) that detects the rotation of the crankshaft and outputs a crank angle signal and a top dead center signal. When the alcohol concentration in the fuel is equal to or higher than a predetermined value, the control means (2) executes split injection, injecting the fuel from the fuel injection device (4) into the cylinder (3 a) in separate injections during the intake stroke and the compression stroke.

[0010] In the control device for an internal combustion engine of the first aspect, when the alcohol concentration in the fuel is equal to or higher than a predetermined value, the control means executes split injection, injecting fuel into the cylinder from the fuel injector separately during the intake stroke and the compression stroke, thereby ensuring sufficient power output and suppressing the amount of dilution that occurs when operating a spark-ignition internal combustion engine in which fuel containing alcohol is directly injected into the cylinder.

[0011] The control device for an internal combustion engine of a second aspect of the present invention is the control device of the first aspect, wherein the control means (2) executes the split injection when the alcohol concentration in the fuel is 90% by volume or more.

[0012] The difference in power output between using fuel containing alcohol and using gasoline becomes more pronounced as the alcohol content in the fuel increases. Therefore, the higher the alcohol content in the fuel, the greater the amount of fuel injected into the cylinders compared to when gasoline is used. Therefore, the higher the alcohol content in the fuel, the greater the amount of dilution that is likely to occur during operation.

[0013] In the control device for an internal combustion engine of the second aspect, the control means executes the split injection when the alcohol concentration in the fuel is 90% by volume or more. Therefore, by executing split injection, the effect of suppressing the amount of dilution becomes more pronounced. Furthermore, fuel containing alcohol is preferable as an alternative fuel to gasoline when the alcohol concentration in the fuel is 90% by volume or more.

[0014] The control device for an internal combustion engine of a third aspect of the present invention is the same as that of the first aspect, and further includes an environmental temperature detection means (20) for detecting an environmental temperature, and the control means (2) executes the split injection when the environmental temperature is equal to or lower than a predetermined value.

[0015] Compared to gasoline, alcohol is less likely to vaporize at low temperatures. Therefore, when an internal combustion engine is operated in a low-temperature environment using a fuel containing alcohol, the amount of fuel injected into the cylinder is increased. Therefore, when an internal combustion engine is operated in a low-temperature environment, the amount of dilution generated during operation tends to be large. In the control device for an internal combustion engine of the third aspect, the control means executes split injection when the ambient temperature is equal to or lower than a predetermined value, thereby suppressing the amount of dilution that occurs when the internal combustion engine is operated in a low-temperature environment, and the effect of suppressing the amount of dilution becomes more pronounced.

[0016] A fourth aspect of the present invention is a control device for an internal combustion engine, wherein in the third aspect, the environmental temperature detection means (20) has an outside air temperature detection means (22) for detecting the temperature of outside air taken into the cylinder (3 a) and an engine water temperature detection means (23) for detecting the temperature of engine water, and the control means (2) executes the split injection when the temperature of the outside air and / or the engine water is equal to or lower than a predetermined value.

[0017] In the control device for an internal combustion engine according to the fourth aspect, the control means executes the split injection when the temperature of the outside air and / or the engine water is equal to or lower than a predetermined value, which makes it easier to more reliably obtain the effect of suppressing the amount of dilution that occurs when the internal combustion engine is operated in a low-temperature environment.

[0018] The control device for an internal combustion engine of a fifth aspect of the present invention is the above-mentioned fourth aspect, wherein the control means (2) executes the split injection when the temperature of the outside air and / or the engine water is within a range of 5°C to -40°C.

[0019] When an internal combustion engine is operated in a low-temperature environment where the temperature of the outside air and / or engine water is 5°C or lower, fuel containing alcohol is less likely to vaporize. For this reason, the amount of fuel containing alcohol injected into the cylinder may be increased. Therefore, when an internal combustion engine is operated in a low-temperature environment where the temperature of the outside air and / or engine water is 5°C or lower, the amount of dilution generated during operation is likely to be greater. In the control device for an internal combustion engine of the fifth aspect, the control means executes split injection when the temperature of the outside air and / or engine water is within the range of 5° C. to −40° C. This makes it possible to more significantly suppress the amount of dilution that occurs when the internal combustion engine is operated in a low-temperature environment.

[0020] A sixth aspect of the present invention is an internal combustion engine control device according to the first aspect, wherein the end of fuel injection during the intake stroke is within a crank angle range of -300 deg. ATDC to -270 deg. ATDC, and the end of fuel injection during the compression stroke is within a crank angle range of -90 deg. ATDC to -30 deg. ATDC. When the intake stroke and compression stroke are within the above ranges, by performing split injection, the amount of dilution can be further suppressed, the injected fuel is more likely to be completely combusted, and sufficient output can be ensured.

[0021] A seventh aspect of the present invention is a control device for an internal combustion engine, which, in the first aspect described above, has an engine water temperature detection means for detecting the temperature of engine water, and the control means performs the split injection again if the temperature of the engine water after performing the split injection is below a predetermined value.

[0022] By executing split injection by the control means, when the alcohol concentration in the fuel is equal to or higher than a predetermined value, the amount of dilution that occurs during operation can be suppressed. However, when the temperature of the engine water of the internal combustion engine is sufficiently high, in order to ensure better operating performance, it may be preferable for the control means to inject fuel at a timing other than split injection.

[0023] In the seventh aspect of the control device for an internal combustion engine, the control means executes the split injection again when the temperature of the engine water after the split injection is equal to or lower than a predetermined value. This sufficiently suppresses the amount of dilution that occurs when the engine is operated in a low-temperature environment where the temperature of the engine water is equal to or lower than the predetermined value, and when the temperature of the engine water is sufficiently high, it becomes easier to operate the engine under operating conditions that provide better performance. [Effects of the Invention]

[0024] In the control device of the present invention, when the alcohol concentration in the fuel is equal to or higher than a predetermined value, the control means executes split injection, injecting fuel into the cylinder from the fuel injection device in separate injections during the intake stroke and the compression stroke. Therefore, the control device of the present invention can suppress the amount of dilution that occurs during operation of a spark-ignition internal combustion engine that directly injects fuel containing alcohol into the cylinder, and can ensure sufficient output. [Brief explanation of the drawings]

[0025] [Figure 1] FIG. 1 is a schematic diagram for explaining an internal combustion engine control device according to this embodiment and an internal combustion engine to which the control device is applied. [Figure 2]FIG. 2 is a flowchart illustrating the control process of the engine 3 executed by the control device of this embodiment. [Figure 3] Figure 3 is a graph showing the relationship between the end timing of fuel injection (crank angle) and the amount of dilution for methanol (only one period), gasoline (only one period), and methanol (intake stroke and compression stroke). [Figure 4] Figure 4 is a graph showing the relationship between the fuel injection end timing (crank angle) and power output for methanol (only one period), gasoline (only one period), and methanol (intake stroke and compression stroke). [Figure 5] Figure 5 is a graph showing the relationship between the end timing of fuel injection (crank angle) and the amount of carbon monoxide for methanol (only one period), gasoline (only one period), and methanol (intake stroke and compression stroke). DETAILED DESCRIPTION OF THE INVENTION

[0026] In order to solve the above problems and to suppress the amount of dilution generated by operating a spark-ignition internal combustion engine that directly injects fuel containing alcohol into the cylinders, the inventors conducted extensive research, focusing on the relationship between the amount of dilution and output, and the timing of injecting fuel into the cylinders, as shown below.

[0027] Generally, in spark-ignition internal combustion engines that directly inject gasoline into cylinders, fuel is injected at a timing that minimizes the amount of soot emitted during operation. In contrast, alcohol produces significantly less soot during combustion than gasoline, and the timing of alcohol injection into cylinders also minimizes the change in soot amount. Due to these unique characteristics of alcohol, spark-ignition internal combustion engines that directly inject alcohol-containing fuel into cylinders can determine the timing of fuel injection by prioritizing the reduction of dilution over the reduction of soot emitted during operation.

[0028] Therefore, the present inventors conducted extensive research to investigate the relationship between the timing of injection of alcohol-containing fuel into a cylinder and the amount of dilution. As a result, it was found that when the timing of injection of alcohol-containing fuel is within the crank angle range of -270 deg. ATDC to -90 deg. ATDC, the amount of dilution tends to be large, when the timing is within the range of -240 deg. ATDC to -120 deg. ATDC, the amount of dilution tends to be even larger, and especially when the timing is around -180 deg. ATDC.

[0029] Therefore, in order to suppress the amount of dilution emitted during operation, fuel should be injected at a crank angle that avoids the crank angle at which the amount of dilution is likely to be large. However, when using a fuel containing alcohol, in order to obtain the same output as when using gasoline, it is necessary to inject a larger amount of fuel into the cylinder than when using gasoline. Therefore, when using a fuel containing alcohol, the fuel injection period tends to be longer than when using gasoline, and it is difficult to inject the fuel while sufficiently avoiding crank angles at which the amount of dilution is likely to be large. Furthermore, if the fuel containing alcohol is injected while avoiding crank angles at which the amount of dilution is likely to be large, the output will be lower than when the fuel containing alcohol is injected at crank angles at which the amount of dilution is likely to be large.

[0030] Therefore, the inventors of the present invention have focused on the fuel injection period and conducted extensive research. As a result, they have found that when there are multiple fuel injection periods between the start of the intake stroke and the end of the compression stroke, the amount of dilution that occurs during operation can be reduced compared to when there is only one continuous fuel injection period, regardless of the timing of fuel injection. This is presumably because when there are multiple fuel injection periods, the amount of fuel that reaches the inner wall of the cylinder is reduced compared to when there is only one continuous fuel injection period.

[0031] Furthermore, the inventors have studied the timing of fuel injection when there are multiple periods during which alcohol-containing fuel is injected, and have found that by performing split injection, in which fuel is injected into a cylinder from a fuel injection device in separate injections during the intake stroke and the compression stroke, it is possible to suppress the amount of dilution while maintaining an output similar to that obtained when fuel is injected at a crank angle at which the amount of dilution is likely to be large, and have arrived at the present invention.

[0032] The control device for an internal combustion engine according to this embodiment will be described in detail below with reference to the accompanying drawings. The drawings used in the following description may show characteristic portions enlarged for the sake of clarity. Therefore, the dimensional ratios of the components may differ from the actual ones. The materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not limited thereto. Appropriate modifications may be made within the scope of the present invention.

[0033] 1 is a schematic diagram for explaining an internal combustion engine controlled by an internal combustion engine control device according to this embodiment, and the control device. In this embodiment, the internal combustion engine control device according to this embodiment is described as an example in which the internal combustion engine control device is applied as a control device for controlling an engine 3 shown in FIG. 1, which is an example of an internal combustion engine. 1 is a spark-ignition internal combustion engine that directly injects fuel containing alcohol into cylinders 3a. The engine 3 may be mounted on a vehicle (not shown), for example.

[0034] Examples of the alcohol contained in the alcohol-containing fuel include one or more alcohols selected from methanol, ethanol, propanol, butanol, etc. Among the above, the alcohol contained in the alcohol-containing fuel is preferably methanol and / or ethanol.

[0035] Methanol and ethanol have a lower calorific value per unit volume than gasoline, so the amount of fuel must be increased to obtain the same output as when gasoline is used. On the other hand, methanol and ethanol produce less soot when burned than gasoline. By utilizing this characteristic, when the alcohol contained in the alcohol-containing fuel is methanol and / or ethanol, the control device of this embodiment can be used to control the engine 3, thereby significantly reducing the amount of dilution generated during operation.

[0036] The alcohol-containing fuel may contain only alcohol, or may contain alcohol and compounds other than alcohol. Examples of compounds other than alcohol that may be contained in the alcohol-containing fuel include fuels other than alcohol, such as gasoline, impurities such as water, and additives. When the alcohol-containing fuel contains alcohol and compounds other than alcohol, the alcohol concentration in the fuel is preferably 90% by volume or more, and more preferably 95% by volume or more.

[0037] The engine 3 is, for example, a four-cylinder engine having four cylinders 3a (only one is shown in FIG. 1). A combustion chamber 3d is provided between the piston 3b of each cylinder 3a and a cylinder head 3c. A fuel injector 4 and an ignition plug 5 are provided in the cylinder head 3c for each cylinder 3a. In the engine 3 shown in FIG. 1, fuel is injected directly from the fuel injector 4 into the cylinder 3a.

[0038] 1, the fuel injector 4 and the spark plug 5 are electrically connected to the control means 2 of the control device of this embodiment. The injection timing and injection amount at which fuel is injected from the fuel injector 4 into the cylinder 3a, and the ignition timing at which the fuel in the cylinder 3a is spark-ignited are controlled by control signals from the control means 2.

[0039] As shown in FIG. 1, an intake passage 6 is connected to the cylinder head 3c of each cylinder 3a. A throttle valve 7 is provided in the intake passage 6. The throttle valve 7 has a butterfly-type valve element 7a and an actuator 7b that drives the valve element 7a. The actuator 7b is electrically connected to the control means 2 and is driven by a control signal from the control means 2. This controls the opening of the valve element 7a, and thereby the amount of air taken into the cylinder 3a.

[0040] The control device of this embodiment is provided with crank angle detection means 21, ambient temperature detection means 20 for detecting ambient temperature, alcohol concentration detection means 24, and in-cylinder pressure detection means (not shown). As shown in Fig. 1, these detection means (sensors) are each electrically connected to control means 2. Output signals output by these detection means are each input to control means 2.

[0041] In this embodiment, the environmental temperature detecting means 20 includes an outside air temperature detecting means 22 and an engine water temperature detecting means 23. The control device of this embodiment may include both the outside air temperature detecting means 22 and the engine water temperature detecting means 23 as the environmental temperature detecting means 20, or may include only one of them. Furthermore, in this embodiment, an example is described in which the environmental temperature detection means 20 is provided, but the environmental temperature detection means 20 (outside air temperature detection means 22 and engine water temperature detection means 23) may not be provided.

[0042] The crank angle detection means 21 detects the rotation of the crankshaft 3e of the engine 3 and outputs a crank angle (CRK) signal and a top dead center (TDC) signal. The outside air temperature detection means 22 detects the temperature of the air flowing through the intake passage 6 as the temperature of the outside air taken into the cylinder 3a. The engine water temperature detection means 23 detects the temperature of the engine water, which is the temperature of the cooling water circulating inside the cylinder block of the engine 3.

[0043] The alcohol concentration detection means 24 detects the alcohol content in the fuel by a known method. The alcohol concentration detection means 24 is installed, for example, in a pipe connecting the fuel injection device 4 and a fuel tank (not shown). An in-cylinder pressure detecting means (not shown) is installed in the cylinder 3a and detects the pressure in the cylinder 3a by a known method.

[0044] An ECU (electronic control unit), for example, can be used as the control means 2. The control means 2 is configured with a microcomputer including a CPU, RAM, ROM, EEPROM, an I / O interface, etc. The control means 2 executes various engine control processes in accordance with a control program stored in the ROM based on signals input from the above-mentioned detection means (sensors), etc. The control means 2 calculates the output obtained by burning fuel based on the change in pressure inside the cylinder 3a detected by an internal cylinder pressure detection means (not shown).

[0045] The control means 2 of the control device of this embodiment controls the injection timing of fuel injection into the cylinder 3a from the fuel injection device 4. When the alcohol concentration in the fuel is equal to or higher than a predetermined value, the control means 2 executes split injection, injecting fuel into the cylinder 3a from the fuel injection device 4 separately during the intake stroke and the compression stroke. In the split injection performed by the control means 2, the period during which fuel is injected during the intake stroke may be one period or multiple periods, and the period during which fuel is injected during the compression stroke may be one period or multiple periods.

[0046] The split injection performed by the control means 2 preferably ends when the fuel injection during the intake stroke is within a crank angle range of -300 deg. ATDC to -270 deg. ATDC, and when the fuel injection during the compression stroke is within a crank angle range of -90 deg. ATDC to -30 deg. ATDC.

[0047] If fuel injection during the intake stroke ends before the crank angle is -270 deg. ATDC, the amount of dilution can be suppressed. If fuel injection during the compression stroke ends at a crank angle of -90 degrees ATDC or later, the amount of dilution can be suppressed.

[0048] The predetermined value of the alcohol concentration in the fuel in this embodiment can be determined as appropriate depending on the application of the engine 3. The predetermined value of the alcohol concentration in the fuel in this embodiment is preferably 90% by volume or more, and more preferably 95% by volume or more, at which point it is likely that the injection amount of alcohol-containing fuel to be injected into the cylinder 3a will need to be increased and the amount of dilution will tend to increase, and the higher the alcohol concentration, the better.

[0049] The control means 2 preferably performs split injection when the alcohol concentration in the fuel is equal to or higher than a predetermined value and the ambient temperature is equal to or lower than a predetermined value, because this effectively reduces the amount of dilution that occurs when the engine 3 is operated in a low-temperature environment. In this embodiment, the environmental temperature may be either the temperature of the outside air or the temperature of the engine water, or may be both the temperature of the outside air and the temperature of the engine water. In this embodiment, when the environmental temperature is both the temperature of the outside air and the temperature of the engine water, the predetermined value of the temperature of the outside air and the predetermined value of the temperature of the engine water may be the same or different.

[0050] The predetermined value of the environmental temperature in this embodiment can be determined appropriately depending on the application of the engine 3. The predetermined value of the environmental temperature in this embodiment is preferably 5°C or less, which is a temperature at which it is likely necessary to increase the injection amount of alcohol-containing fuel injected into the cylinder 3a and at which the amount of dilution is likely to increase, and may be 0°C or less. The predetermined value of the environmental temperature can have a lower limit of, for example, -40°C or more.

[0051] It is preferable that the control means 2 executes split injection again if the temperature of the engine water after executing split injection is equal to or lower than a predetermined value. In this case, the effect of suppressing the amount of dilution is sufficiently obtained, and if the temperature of the engine water is sufficiently high, it becomes easier to operate under operating conditions that provide better performance.

[0052] Next, the control process of the engine 3 performed by the control device of this embodiment will be described. FIG. 2 is a flowchart illustrating the control process of the engine 3 executed by the control device of this embodiment. In this embodiment, first, the control means 2 causes the engine water temperature detection means 23 to detect the temperature of the engine water (step S1). Next, the control means 2 causes the outside air temperature detection means 22 to detect the temperature of the outside air taken into the cylinder 3a (step S2). Next, the control means 2 causes the alcohol concentration detection means 24 to detect the alcohol content contained in the fuel (step S3).

[0053] Next, the control means 2 determines whether the temperature of the outside air, which is the environmental temperature, and the temperature of the engine water are each equal to or lower than a predetermined value, and also determines whether the alcohol concentration in the fuel is equal to or higher than a predetermined value (step S4). Then, if it is determined that both the outside air temperature and the engine water temperature are below a predetermined value and the alcohol concentration in the fuel is above a predetermined value, the process proceeds to step S5, as shown in FIG. 2, and the control means 2 executes split injection, injecting fuel from the fuel injection device 4 into the cylinder 3a in separate injections during the intake stroke and the compression stroke (step S5).

[0054] On the other hand, if one or more of the following conditions are met: the outside air temperature exceeds a predetermined value, the engine water temperature exceeds a predetermined value, or the alcohol concentration in the fuel is less than a predetermined value (in other words, if one or more of the conditions of the outside air temperature, the engine water temperature, and the alcohol concentration in the fuel are outside a predetermined numerical range), the control process by the control device of this embodiment is terminated.

[0055] In step S5, it is preferable that the control means 2 executes split injection when the temperature of the outside air and / or engine water is within the range of 5°C to -40°C. In step S5, the control means 2 preferably performs split injection when the alcohol concentration in the fuel is 90% by volume or more.

[0056] If the control means 2 determines in step S4 that both the outside air temperature and the engine water temperature are below a predetermined value and that the alcohol concentration in the fuel is above a predetermined value, it is preferable to perform split injection in step S5. In addition, in step S5, the control means 2 preferably performs split injection in which the end of fuel injection during the intake stroke is within a crank angle range of -300 deg. ATDC to -270 deg. ATDC, and the end of fuel injection during the compression stroke is within a crank angle range of -90 deg. ATDC to -30 deg. ATDC.

[0057] Here, the relationship between the timing of fuel injection and the amount of dilution generated during operation of a spark ignition internal combustion engine in which fuel containing alcohol is directly injected into the cylinder will be described. Figure 3 is a graph showing the relationship between the end timing of fuel injection (crank angle) and the amount of dilution for methanol (only one period), gasoline (only one period), and methanol (intake stroke and compression stroke).

[0058] Methanol (only one period) and gasoline (only one period) in Figure 3 are examples where fuel is injected for only one period. Methanol (only one period) and gasoline (only one period) in Figure 3 were injected at injection amounts that generated equal amounts of heat in the cylinder.

[0059] Methanol (intake stroke and compression stroke) in Figure 3 is an example in which the fuel injection period is divided into two periods: the intake stroke and the compression stroke. For methanol (intake stroke and compression stroke), the total injection amount in the two periods is the same as the fuel injection amount injected in methanol (only one period). Also, half of the amount to be injected was injected in the first period and the second period (compression stroke). The first period (intake stroke) for methanol (intake stroke and compression stroke) is the period from crank angle -320 deg. ATDC to -290 deg. ATDC (the dilution amount during this period is not shown), and Figure 3 shows only the dilution amount when the fuel injection end timing during the second period (intake stroke) is changed.

[0060] Figure 3 shows the results when the engine was operated under the following conditions: engine speed: 2500 rpm, intake manifold pressure: 80 kPa, engine water temperature: 40°C, and outside air temperature taken into the cylinder: 25°C. Only methanol or only gasoline was used as fuel. The dilution amount in Figure 3 was measured by the following method: the difference between the amount of fuel injected per unit time and the amount of fuel consumed by combustion was calculated and used as the dilution amount.

[0061] As shown in Figure 3, methanol (only one period) produces a larger amount of dilution than gasoline (only one period), and the amount of dilution also varies significantly depending on the timing of fuel injection. Specifically, with methanol (only one period), the amount of dilution is larger when the crank angle end timing is within the range of -270 deg. ATDC to -90 deg. ATDC.

[0062] In contrast, with methanol (intake stroke and compression stroke), when the end of fuel injection during the compression stroke is within the crank angle range of -120 deg. ATDC to -30 deg. ATDC, the amount of dilution is significantly reduced compared to methanol (only one period), as shown in Figure 3. Furthermore, with methanol (intake stroke and compression stroke), when the crank angle is within the range of -90 deg. ATDC to -30 deg. ATDC, the amount of dilution is approximately the same as that of gasoline (only one period).

[0063] Next, the relationship between the fuel injection end timing (crank angle), output, and amount of carbon monoxide when the engine is operated under the same operating conditions as in FIG. 3 except for the fuel injection amount will be described.

[0064] Figure 4 shows the relationship between fuel injection end timing (crank angle) and power output for methanol (one period only), gasoline (one period only), and methanol (intake stroke and compression stroke). As with Figure 3, the results for methanol (intake stroke and compression stroke) in Figure 4 show only the results when the fuel injection end timing in the second period (intake stroke) was varied. For methanol (one period only) and gasoline (one period only) in Figure 4, a constant injection amount was used within the power output range of 700 kPa to 1000 kPa. For methanol (intake stroke and compression stroke), the total injection amount for the two periods was the same as the fuel injection amount for methanol (one period only). Half the amount of fuel was injected during the first and second periods (compression stroke). The power output in Figure 4 was calculated based on changes in cylinder pressure.

[0065] As shown in Figure 4, with gasoline (only one period), there is little change in power output due to the fuel injection period. In contrast, with methanol (only one period), power output decreases as the end of fuel injection approaches a crank angle between -150 deg. ATDC and 0 deg. ATDC. However, with methanol (intake stroke and compression stroke), higher power output is obtained when fuel injection ends within the crank angle range of -120 deg. ATDC to -30 deg. ATDC compared to methanol (only one period).

[0066] Figure 5 is a graph showing the relationship between the fuel injection end timing (crank angle) and the amount of carbon monoxide for methanol (one period only), gasoline (one period only), and methanol (intake stroke and compression stroke). As with Figure 3, the results for methanol (intake stroke and compression stroke) in Figure 5 show only the results when the fuel injection end timing in the second period (intake stroke) was changed. The conditions for the fuel injection amount in Figure 5 were the same as in Figure 4. The amount of carbon monoxide in Figure 5 was calculated by calculating the volumetric ratio of carbon monoxide contained in the total amount of gas emitted from the engine.

[0067] As shown in Figure 5, methanol (only one period) and methanol (intake stroke and compression stroke) produce less carbon monoxide than gasoline (only one period), indicating a tendency for the injected fuel to be more completely combusted. In particular, within the crank angle range of -120° ATDC to -30° ATDC, the amount of carbon monoxide for methanol (only one period) and methanol (intake stroke and compression stroke) is significantly less than for gasoline (only one period). Furthermore, methanol (intake stroke and compression stroke) produces less carbon monoxide than methanol (only one period) within the crank angle range of -120° ATDC to -30° ATDC.

[0068] 3 to 5, when a spark-ignition internal combustion engine that directly injects fuel containing alcohol into a cylinder is operated using the control device of this embodiment, it is estimated that sufficient power output can be ensured and the amount of dilution can be suppressed by performing split injection, in which fuel is injected into the cylinder from the fuel injection device separately during the intake stroke and the compression stroke.

[0069] In contrast, for example, when the second period in methanol (intake stroke and compression stroke) is the intake stroke (in other words, when both periods in which fuel is injected are the intake stroke), or when the first period is the compression stroke (in other words, when both periods in which fuel is injected are the compression stroke), the amount of dilution is also reduced compared to methanol (only one period).

[0070] However, when the second period in the methanol (intake stroke and compression stroke) is the intake stroke, or when the first period is the compression stroke, power output decreases within the crank angle range of -120 deg. ATDC to -30 deg. ATDC, where dilution can be suppressed, as with methanol (only one period) (see Figures 3 and 4). This is presumably because the amount of carbon monoxide is high within this period (see Figure 5), resulting in incomplete combustion of the injected fuel. Therefore, when the second period in the methanol (intake stroke and compression stroke) is the intake stroke, or when the first period is the compression stroke, insufficient power output can be ensured by injecting fuel at a crank angle that avoids the tendency for high dilution.

[0071] Returning to Fig. 2, after executing step S5, the control means 2 determines whether the temperature of the engine water after executing the split injection is equal to or lower than a predetermined value (step S6). If the temperature of the engine water after executing the split injection is equal to or lower than the predetermined value, the process returns to step S5, and the control means 2 executes the split injection again. On the other hand, if the temperature of the engine water after executing the split injection exceeds the predetermined value, the control process by the control device of this embodiment ends.

[0072] The predetermined value for the engine water temperature in step S6 may be the same as the predetermined value for the engine water temperature in step S4, or may be a temperature higher than the predetermined value for the engine water temperature in step S4. The predetermined value for the engine water temperature in step S6 may be within the range of 5°C to -40°C, for example.

[0073] In the control device of this embodiment, when the alcohol concentration in the fuel is equal to or higher than a predetermined value, the control means 2 executes split injection, injecting fuel into the cylinder 3a from the fuel injector 4 in separate injections during the intake stroke and the compression stroke. Therefore, according to the control device of this embodiment, the amount of dilution that occurs during operation of a spark ignition internal combustion engine in which fuel containing alcohol is directly injected into the cylinder 3a can be suppressed, and sufficient output can be ensured.

[0074] In the above embodiment, as shown in FIG. 2, an example has been described in which steps S1 to S3 are executed in this order, but the order of steps S1 to S3 is not particularly limited. In the above embodiment, the control means 2 determines whether the ambient temperature (outside air temperature) and the engine water temperature are each equal to or lower than a predetermined value, and also determines whether the alcohol concentration in the fuel is equal to or higher than a predetermined value in step S4. However, the control means may be any means that determines whether the alcohol concentration in the fuel is equal to or higher than a predetermined value. Therefore, as shown in Fig. 2, steps S1 to S3 may all be executed, but it is sufficient to execute at least step S3, and step S1 and / or step S2 may not be executed.

[0075] In the above embodiment, the case where step S6 is executed is described as an example, as shown in Fig. 2, but the control process may be ended without executing step S6. When the control process is ended without executing step S6, the control process of the engine 3 shown in Fig. 2 may be executed repeatedly. [Explanation of symbols]

[0076] 2...control means, 3...engine, 3a...cylinder, 3b...piston, 3c...cylinder head, 3d...combustion chamber, 3e...crankshaft, 4...fuel injection device, 5...spark plug, 6...intake passage, 7...throttle valve, 7a...valve body, 7b...actuator, 20...ambient temperature detection means, 21...crank angle detection means, 22...outside air temperature detection means, 23...engine water temperature detection means, 24...alcohol concentration detection means.

Claims

1. A control device for a spark ignition internal combustion engine that directly injects fuel containing alcohol into a cylinder, comprising: a control means for controlling an injection timing at which the fuel is injected into the cylinder from a fuel injection device; an alcohol concentration detection means for detecting the alcohol content contained in the fuel; a crank angle detection means for detecting the rotation of the crankshaft and outputting a crank angle signal and a top dead center signal; The control means performs split injection of the fuel into the cylinder from the fuel injection device, dividing the injection into the intake stroke and the compression stroke, when the alcohol concentration in the fuel is equal to or higher than a predetermined value.

2. 2. The control device for an internal combustion engine according to claim 1, wherein the control means executes the split injection when the alcohol concentration in the fuel is 90% by volume or more.

3. An environmental temperature detection means for detecting an environmental temperature is provided, 2. The control device for an internal combustion engine according to claim 1, wherein the control means executes the split injection when the environmental temperature is equal to or lower than a predetermined value.

4. the environmental temperature detecting means is an outside air temperature detecting means for detecting the temperature of outside air taken into the cylinder; an engine water temperature detecting means for detecting the temperature of engine water; 4. The control device for an internal combustion engine according to claim 3, wherein the control means executes the split injection when the temperature of the outside air and / or the engine water is equal to or lower than a predetermined value.

5. 5. The control device for an internal combustion engine according to claim 4, wherein the control means executes the split injection when the temperature of the outside air and / or the engine water is within a range of 5°C to -40°C.

6. the end of the fuel injection during the intake stroke is within a crank angle range of −300 deg. ATDC to −270 deg. ATDC, 2. The control device for an internal combustion engine according to claim 1, wherein the end of the fuel injection in the compression stroke is within a crank angle range of −90 degrees ATDC to −30 degrees ATDC.

7. an engine water temperature detecting means for detecting the temperature of engine water; 2. The control device for an internal combustion engine according to claim 1, wherein the control means executes the split injection again when the temperature of the engine water after the split injection is equal to or lower than a predetermined value.

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