Control device for internal combustion engine

Abstract

To suppress generation of unburned fuel in an internal combustion engine that uses alcohol as fuel.SOLUTION: A control device for an internal combustion engine includes: a request A / F acquisition section that acquires a request A / F in an internal combustion engine on the basis of information on an operating state of the internal combustion engine; a cylinder internal temperature estimation section that estimates a cylinder internal temperature of the internal combustion engine on the basis of information on an operating state of the internal combustion engine; a request vaporization fuel amount acquisition section that acquires a request vaporization fuel amount satisfying the request A / F acquired by the request A / F acquisition section; a request injection amount acquisition section that acquires combinations of injection timing and a request injection amount satisfying the request vaporization fuel amount on the basis of the cylinder internal temperature estimated by the cylinder internal temperature estimation section and the request vaporization fuel amount acquired by the request vaporization fuel amount acquisition section; and a minimum injection amount selection section that selects a minimum injection amount indicating that the request injection amount is minimum among the combinations of the injection timing and the request injection amount and selects injection timing enabling the minimum injection amount.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] Conventionally, there has been a proposal to accurately calculate the in-cylinder charge air amount in consideration of the intake air cooling effect due to the latent heat of vaporization of injected fuel (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Alcohol may be used as fuel for an internal combustion engine. Alcohol has a property of being less likely to vaporize compared to gasoline. Unburned fuel that could not be vaporized and was not used for combustion is considered to be discharged from the cylinder as it is. Therefore, when alcohol is used as fuel, it is desirable to set the fuel injection amount so that unburned fuel is not contained in the exhaust gas as much as possible. The vaporization of fuel is affected by the environment in which the fuel is injected. When the fuel vaporizes, it affects the environment in which the fuel is injected due to the latent heat of vaporization. Patent Document 1 considers the intake air cooling effect due to the latent heat of vaporization, but its purpose is to accurately calculate the in-cylinder charge air amount, not to determine the fuel injection amount.

[0005] The invention disclosed in this specification aims to suppress the generation of unburned fuel in an internal combustion engine using alcohol as fuel.

Means for Solving the Problems

[0006] The above problem is achieved by a control device for an internal combustion engine, including: a required A / F acquisition unit that acquires a required A / F in the internal combustion engine based on information regarding an operating state of the internal combustion engine; a cylinder internal temperature estimation unit that estimates a cylinder internal temperature in the internal combustion engine based on information regarding the operating state of the internal combustion engine; a required vaporized fuel amount acquisition unit that acquires a required vaporized fuel amount that satisfies the required A / F acquired by the required A / F acquisition unit; and a required injection amount acquisition unit that acquires a combination of an injection timing and a required injection amount that satisfies the required vaporized fuel amount, based on the cylinder internal temperature estimated by the cylinder internal temperature estimation unit and the required vaporized fuel amount acquired by the required vaporized fuel amount acquisition unit. The control device further includes a minimum injection amount selection unit that selects a minimum injection amount that is the minimum among the required injection amounts in the combination of the injection timing and the required injection amount, and selects an injection timing at which the minimum injection amount is obtained.

Advantages of the Invention

[0007] The invention disclosed in this specification can suppress the generation of unburned fuel in an internal combustion engine in which alcohol is used as fuel.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0009] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0010] (Embodiment) Referring to FIG. 1, the schematic configuration of the internal combustion engine 100 according to the embodiment will be described. The control for operating the internal combustion engine 100 is executed by an ECU (Electronic Control Unit) 50 which is a control device. The internal combustion engine 100 can use alcohol, which is an alternative fuel to gasoline, as fuel.

[0011] The internal combustion engine 100 includes a plurality of cylinders 2 in a cylinder block (only one cylinder 2 is shown in FIG. 1). A piston 3 is slidably accommodated in each cylinder 2. The piston 3 forms a combustion chamber 2a between itself and a cylinder head disposed above the cylinder block. The piston 3 is connected to a crankshaft 5 via a connecting rod 4. An injector 6 for injecting fuel into the cylinder and a spark plug 7 are provided in the combustion chamber 2a. The fuel injected from the injector 6 is made into an air-fuel mixture in the combustion chamber 2a and is ignited by the spark plug 7. When the ignited air-fuel mixture burns and explodes, the piston 3 is pushed down. The pushed-down piston 3 transmits the explosion force to the crankshaft 5 via the connecting rod 4, rotating the crankshaft 5. A crank angle sensor 28 is provided near the crankshaft 5. The engine speed is acquired based on the detection value of the crank angle sensor 28. A water temperature sensor 14 for detecting the temperature of the cooling water circulating in the internal combustion engine 100 is provided in the cylinder block.

[0012] An intake port 8 and an exhaust port 9 are provided in the internal combustion engine 100 so as to face the combustion chamber 2a. An intake pipe 10 forming an intake passage is connected to the intake port 8. An exhaust pipe 11 forming an exhaust passage is connected to the exhaust port 9. Note that the injector 6 may be provided in the intake port 8 near the combustion chamber 2a. Further, the internal combustion engine 100 may be configured to include an injector 6 for in-cylinder injection and be equipped with an injector 6 provided in the intake port 8.

[0013] The intake pipe 10 is provided with an air cleaner 12, an air flow meter 13, a throttle valve 17, and an intake manifold 18 in order from the upstream side of the intake air flow. The air flow meter 13 detects the amount of air flowing in the intake pipe 10. The throttle valve 17 adjusts the amount of air sent into the combustion chamber 2a. The intake pipe 10 branches at the intake manifold 18 and is connected to the intake ports 8 of the respective cylinders. The intake pipe 10 is provided with an intake air temperature sensor 27.

[0014] The exhaust pipe 11 is provided with an exhaust manifold 20 and a catalyst 21 in order from the upstream side of the exhaust flow. The catalyst 21 purifies the exhaust gas.

[0015] The internal combustion engine 100 includes an intake valve 23 that opens and closes the intake port 8 and an exhaust valve 24 that opens and closes the exhaust port 9. The intake valve 23 and the exhaust valve 24 open and close in accordance with the rotation of an intake camshaft and an exhaust camshaft (not shown) that are drivingly connected to the crankshaft 5. Thereby, the intake valve 23 and the exhaust valve 24 are synchronized with the rotation of the crankshaft 5 and are driven to open and close at a predetermined timing corresponding to the reciprocating movement of each piston 3. The internal combustion engine 100 includes an intake VVT mechanism 25, which is a variable valve mechanism that variably sets the valve timing, which is the opening and closing timing of the intake valve 23, and an exhaust VVT mechanism 26, which is a variable valve mechanism that variably sets the valve timing, which is the opening and closing timing of the exhaust valve 24.

[0016] The internal combustion engine 100 includes a fuel flow path 30 connected to the injector 6. A fuel pump 31, a fuel pressure sensor 32, and a fuel pressure regulator 33 are arranged in the fuel flow path 30.

[0017] The ECU 50 includes a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), a storage device, etc. The ECU 50 controls the internal combustion engine 100 by executing programs stored in the ROM or the storage device. The ECU 50 is electrically connected to the air flow meter 13, the water temperature sensor 14, the intake air temperature sensor 27, and the crank angle sensor 28, and receives signals from these sensors. The ECU 50 includes a VVT control unit 51 for controlling the intake VVT mechanism 25 and the exhaust VVT mechanism 26 according to the operating state of the internal combustion engine 100. Maps used for control are stored in the storage device.

[0018] By executing a program, the ECU 50 functions as a required A / F (air-fuel ratio) acquisition unit 52, a cylinder internal temperature estimation unit 53, a required vaporized fuel amount acquisition unit 54, a required injection amount acquisition unit 55, and a minimum injection amount selection unit 56.

[0019] The required A / F acquisition unit 52 acquires the required A / F based on information regarding the operating state of the internal combustion engine 100. Here, the information regarding the operating state of the internal combustion engine 100 includes the intake air amount acquired by the air flow meter 13, the water temperature acquired by the water temperature sensor 14, and the engine speed acquired by the crank angle sensor 28. The required A / F is acquired by a map of the engine speed and the intake air amount set for each water temperature. Since such a map is conventionally well-known, detailed description thereof is omitted here.

[0020] The in-cylinder temperature estimation unit 53 estimates the in-cylinder temperature, that is, the temperature in the cylinder 2 where fuel is injected, based on information regarding the operating state of the internal combustion engine 100. The in-cylinder temperature estimated by the in-cylinder temperature estimation unit 53 is a predicted value of the in-cylinder temperature at the time of the next fuel injection. Here, the information regarding the operating state of the internal combustion engine 100 includes the intake air amount acquired by the air flow meter 13, the coolant temperature acquired by the coolant temperature sensor 14, and the engine speed acquired by the crank angle sensor 28. Further, the information includes the integrated air amount obtained by integrating the intake air amount since engine startup, and information for the VVT control unit 51 to control the intake VVT mechanism 25 and the exhaust VVT mechanism 26. The information may include the intake air temperature acquired by the intake air temperature sensor 27 and the fuel pressure acquired by the fuel pressure sensor 32. The in-cylinder temperature may be estimated based on a map prepared in advance, or may be estimated by an operation executed by the ECU 50. The in-cylinder temperature is acquired as a value for each crank angle (CA). The crank angle is acquired by the crank angle sensor 28. FIG. 3(A) is an example of a map showing the relationship between the crank angle (CA) and the in-cylinder temperature.

[0021] The required vaporized fuel amount acquisition unit 54 acquires the required vaporized fuel amount that satisfies the required A / F. The fuel of the internal combustion engine 100 is mixed with the intake air and burned. What is mixed with the intake air is the vaporized fuel. Therefore, the A / F is the ratio of the intake air amount to the vaporized fuel. Thus, the required vaporized fuel amount acquisition unit 54 acquires the amount of vaporized fuel for satisfying the required A / F. This fuel amount is calculated based on the required A / F.

[0022] The required injection amount acquisition unit 55 acquires a combination of an injection timing and a required injection amount that satisfies the required vaporized fuel amount based on the estimated in-cylinder temperature and the acquired required vaporized fuel amount. The required vaporized fuel amount varies depending on the injection timing at which fuel is injected into the cylinder. Different injection timings result in different in-cylinder environments. Different in-cylinder environments lead to different fuel vaporization tendencies. For example, when in-cylinder injection is performed during the compression stroke when the in-cylinder temperature rises, the fuel is more likely to vaporize. That is, for example, even if the same amount of fuel is injected, the amount of fuel vaporized due to the in-cylinder environment is different. In other words, there are multiple conditions under which the same amount of vaporized fuel can be obtained.

[0023] Fig. 3(B) shows a map in which an equal vaporization amount line obtained by combining an injection timing (injection start timing) and an injection amount that can obtain the same amount of vaporized fuel is drawn. The injection timing in Fig. 3(B) is the injection start timing. Here, since the vaporization amount of the fuel being injected is evaluated, the injection start timing is adopted to reflect the temperature of the environment before the fuel is injected and the temperature drops due to the latent heat of vaporization. This map is prepared for each fuel pressure. The equal vaporization amount lines are set for each in-cylinder temperature and ignition timing. The in-cylinder temperature used is the in-cylinder temperature at IVC (Intake Valve Close Timing) shown in Fig. 3(A). Also, the ignition timing is indicated by degBTDC (Before Top Dead Center). When the injector 6 is also installed in the intake port 8, the map is prepared for each injection method. An equal vaporization amount line corresponding to the state of the internal combustion engine 100 at that time is selected from among the plurality of equal vaporization amount lines as a combination indicating the required vaporized fuel amount. This combination indicating the required vaporized fuel amount can efficiently vaporize the fuel. When the fuel vaporizes, the in-cylinder temperature drops due to the latent heat of vaporization. Therefore, the combinations on the equal vaporization amount line result in the same in-cylinder temperature drop generation. The combination indicating the required vaporized fuel amount is selected from among the plurality of equal vaporization amount lines based on the condition that the in-cylinder temperature drop generation is maximized. In this way, the required injection amount acquisition unit 55 acquires a combination of a required injection amount that satisfies the required vaporized fuel amount and an injection timing based on the in-cylinder temperature and the required vaporized fuel amount.

[0024] The minimum injection amount selection unit 56 selects the minimum injection amount with the minimum required injection amount among the combinations of the injection timing and the required injection amount acquired by the required injection amount acquisition unit 55. Further, the minimum injection amount selection unit 56 selects the injection timing corresponding to the minimum injection amount in addition to the selection of the minimum injection amount. The combinations of the injection timing and the required injection amount acquired by the required injection amount acquisition unit 55 can obtain the same amount of vaporized fuel. However, as shown by the arrows 15a, 15b, and 15c, the required injection amounts are different even though the same amount of vaporized fuel is obtained. That is, in the case of a combination with a larger required injection amount, the amount of fuel that cannot be vaporized increases accordingly. When the amount of fuel that cannot be vaporized increases, the amount of fuel discharged unburned increases. Therefore, the minimum injection amount selection unit 56 selects the combination with the minimum injection amount among the combinations that can obtain the same amount of vaporized fuel (see arrow 15a). Note that the map shown in FIG. 3(B) is prepared for each fuel pressure. Therefore, by the minimum injection amount selection unit 56 selecting the minimum injection amount, the minimum injection amount, the injection timing, and the fuel pressure can be obtained as the output of the ECU 50. When the map shown in FIG. 3(B) is prepared for each injection method, the injection method is also included in the output.

[0025] Next, an example of the control executed by the ECU 50 will be described with reference to FIGS. 2 to 3(B). In step S1, the ECU 50 reads the current operating conditions of the internal combustion engine 100. The operating conditions include the engine speed, the intake air amount, the current in-cylinder temperature, the required A / F, the fuel temperature, and the fuel pressure. The intake air amount includes the current intake air amount and the integrated air amount. The required A / F is acquired by the required A / F acquisition unit 52. After the ECU 50 finishes the process of step S1, it executes the processes of step S2 and step S3. The processes of step S2 and step S3 may be executed in either order, but in order to improve the control accuracy, it is desirable to execute the two processes in parallel.

[0026] In step S2, the required vaporized fuel amount acquisition unit 54 calculates the vaporized fuel amount that satisfies the required A / F. In step S3, the in-cylinder temperature estimation unit 53 estimates the in-cylinder temperature for each crank angle. After the ECU 50 finishes the processes of step S2 and step S3, it proceeds to step S4.

[0027] In step S4, the required injection amount acquisition unit 55 selects the condition under which the in-cylinder temperature drop generation is maximized. Specifically, the required injection amount acquisition unit 55 acquires the combination of the required injection amount and the injection timing that satisfies the required vaporized fuel amount. After the ECU 50 finishes the process of step S4, it proceeds to step S5.

[0028] In step S5, the minimum injection amount selection unit 56 selects the minimum injection amount indicated by arrow 15a based on the map shown in FIG. 3(B). By selecting the minimum injection amount, the injection timing and the combustion pressure are obtained. After the ECU 50 finishes the process of step S5, it repeats the process from step S1. Also, the ECU 50 executes fuel injection based on the specifications regarding the fuel injection acquired in step S5.

[0029] In this embodiment, since the required injection amount is set so as to obtain the vaporized fuel amount that satisfies the required A / F based on the estimated in-cylinder temperature, the generation of unburned fuel is suppressed.

[0030] The above embodiment is merely an example for implementing the present invention, and the present invention is not limited thereto. It is obvious from the above description that various modifications of these examples are within the scope of the present invention, and various other embodiments are possible within the scope of the present invention.

Explanation of Reference Numerals

[0031] 50... ECU, 52... required A / F acquisition unit, 53... in-cylinder temperature estimation unit, 54... required vaporized fuel amount acquisition unit, 55... required injection amount acquisition unit, 56... minimum injection amount selection unit, 100... internal combustion engine

Claims

【Claim 1】 A required A / F acquisition unit that acquires a required A / F in the internal combustion engine based on information regarding the operating state of the internal combustion engine; A cylinder internal temperature estimation unit that estimates the cylinder internal temperature in the internal combustion engine based on information regarding the operating state of the internal combustion engine; A required vaporized fuel amount acquisition unit that acquires a required vaporized fuel amount that satisfies the required A / F acquired by the required A / F acquisition unit; A required injection amount acquisition unit that acquires a combination of an injection timing and a required injection amount that satisfies the required vaporized fuel amount based on the cylinder internal temperature estimated by the cylinder internal temperature estimation unit and the required vaporized fuel amount acquired by the required vaporized fuel amount acquisition unit; A minimum injection amount selection unit that selects a minimum injection amount that is the minimum among the combinations of the injection timing and the required injection amount, and selects the injection timing that results in the minimum injection amount; A control device for an internal combustion engine, comprising the above.

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