Control device for internal combustion engine

Abstract

To avoid an excess of a fuel injection amount at start time in an internal combustion engine that uses alcohol fuel.SOLUTION: A control device for an internal combustion engine includes: a previous operation time integrated air amount acquisition section that acquires an integrated air amount during a previous operation of the internal combustion engine; a previous start time cylinder internal temperature estimation section that estimates a cylinder internal temperature at previous start time of the internal combustion engine; a previous stop time cylinder internal temperature estimation section that estimates a cylinder internal temperature at previous stop time on the basis of the integrated air amount during the previous operation and the cylinder internal temperature at the previous start time; a cylinder internal temperature lowering amount acquisition section that acquires a lowering amount of the cylinder internal temperature for a soak time from the previous stop time to this start time of the internal combustion engine; a this start time cylinder internal temperature estimation section that estimates a cylinder internal temperature at this start time on the basis of the cylinder internal temperature at the previous stop time and the lowering amount of the cylinder internal temperature; and an injection control section that sets injection timing and fuel injection amount at start time on the basis of the cylinder internal temperature at this start time.SELECTED DRAWING: Figure 2

Description

Technical Field

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

Background Art

[0002] Recently, alcohol fuel may be used as fuel for an internal combustion engine, and fuel injection control considering the characteristics of alcohol fuel has been proposed (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] The water temperature in an internal combustion engine generally has a correlation with the temperatures of each part of the internal combustion engine. For this reason, control of the internal combustion engine may be carried out based on the water temperature. In an internal combustion engine, start-up increment control for increasing the fuel injection amount at start-up may be carried out, and such fuel injection control at start-up may also be controlled based on the water temperature. However, a deviation may occur between the water temperature and the in-cylinder temperature. For example, when an internal combustion engine started from a cold state stops shortly thereafter and then restarts after a short soak time, a deviation may occur between the water temperature and the in-cylinder temperature. This is because even in a short time, when the internal combustion engine operates, the in-cylinder temperature around the combustion chamber rises due to combustion, while the cylinder block and the like are not yet warmed up and the water temperature has not risen.

[0005] By the way, unlike gasoline, alcohol fuel has the property that it is difficult to vaporize unless it reaches a predetermined temperature. The vaporization property of the alcohol fuel injected into the cylinder is affected by the cylinder temperature. When the cylinder temperature is low, the fuel injection amount may be increased in consideration of the property of the alcohol fuel that is difficult to vaporize. However, when there is a deviation between the water temperature and the cylinder temperature as described above, if the fuel injection control at startup is carried out based on the water temperature in the same way as the conventional general control, it is assumed that the fuel injection amount will become excessive. From the perspective of emissions, it is desirable to avoid an excessive fuel injection amount.

[0006] In Patent Document 1, although fuel injection control considering the characteristics of alcohol fuel has been proposed, no special consideration has been given to fuel injection at startup.

[0007] Therefore, the invention disclosed in this specification aims to avoid an excessive fuel injection amount at startup in an internal combustion engine using alcohol fuel.

Means for Solving the Problems

[0008] The above problems are achieved by a control device for an internal combustion engine including: an integrated air amount acquisition unit at the previous operation for acquiring the integrated air amount at the previous operation of the internal combustion engine; a cylinder temperature estimation unit at the previous startup for estimating the cylinder temperature at the previous startup of the internal combustion engine; an integrated air amount at the previous operation; a cylinder temperature estimation unit at the previous stop for estimating the cylinder temperature at the previous stop based on the integrated air amount at the previous operation and the cylinder temperature at the previous startup; a cylinder temperature decrease amount acquisition unit for acquiring the decrease amount of the cylinder temperature during the soak time from the previous stop to the current startup of the internal combustion engine; a cylinder temperature estimation unit at the current startup for estimating the cylinder temperature at the current startup based on the cylinder temperature at the previous stop and the decrease amount of the cylinder temperature; and an injection control unit for setting the injection timing and the fuel injection amount at startup based on the cylinder temperature at the current startup.

Effects of the Invention

[0009] The invention disclosed in this specification can avoid excessive fuel injection amount at startup in an internal combustion engine using alcohol fuel.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0012] (Embodiment) Referring to FIG. 1, the schematic configuration of the internal combustion engine 100 according to the embodiment will be described. Control for the operation of 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 a gasoline alternative fuel. In the present embodiment, ethanol is adopted as the fuel. The internal combustion engine 100 is provided with an alcohol concentration sensor 39. The alcohol concentration sensor 39 detects the concentration of ethanol used as the fuel.

[0013] 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 mixed in the combustion chamber 2a and ignited by the spark plug 7. When the ignited air-fuel mixture burns and explodes, the piston 3 is pushed downward. The pushed-down piston 3 transmits the explosion force to the crankshaft 5 via the connecting rod 4, rotating the crankshaft 5. 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.

[0014] The internal combustion engine 100 is provided with an intake port 8 and an exhaust port 9 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.

[0015] An air cleaner 12, an air flow meter 13, a throttle valve 17, and an intake manifold 18 are provided in the intake pipe 10 in order from the upstream side of the intake 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 port 8 of each cylinder.

[0016] An exhaust manifold 20 and a catalyst 21 are provided in the exhaust pipe 11 in order from the upstream side of the exhaust flow. The catalyst 21 purifies the exhaust.

[0017] 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. As a result, 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.

[0018] The ECU 50 includes a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), a storage device, and the like. 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 and the water temperature sensor 14 and receives signals from these sensors. Maps used for control are stored in the storage device. The ECU 50 functions as an operation time measurement unit 51 that measures the time during which the internal combustion engine 100 is in an operating state. The ECU 50 functions as a soak time measurement unit 52 that measures the soak time, which is the time from the previous stop of the internal combustion engine 100 to the current start. Here, the stop of the internal combustion engine 100 is the point in time when the ignition (not shown) is turned off. The start of the internal combustion engine 100 is the point in time when the ignition is turned on.

[0019] By executing programs, the ECU 50 functions as a previous operation integrated air amount acquisition unit 53, a cylinder internal temperature estimation unit 54 at the previous start, and a cylinder internal temperature estimation unit 55 at the previous stop. By executing programs, the ECU 50 functions as a cylinder internal temperature decrease amount acquisition unit 56, a cylinder internal temperature estimation unit 57 at the current start, and an injection control unit 58. The injection control unit 58 includes an injection timing setting unit 58a and an injection amount setting unit 58b.

[0020] The previous operation integrated air quantity acquisition unit 53 acquires the integrated air quantity during the previous operation period of the internal combustion engine 100. The integrated air quantity is calculated based on the measured value of the air flow meter 13 and the time measured by the operation time measurement unit 51. Specifically, the integrated air quantity can be calculated by integrating the change in the measured value of the air flow meter 13 during the previous operation period.

[0021] The previous start cylinder internal temperature estimation unit 54 estimates the cylinder internal temperature at the previous start of the internal combustion engine 100. Specifically, the value estimated by the current start cylinder internal temperature estimation unit 57, which will be described later, as the cylinder internal temperature at the previous start is estimated as the cylinder internal temperature at the previous start.

[0022] The previous stop cylinder internal temperature estimation unit 55 estimates the cylinder internal temperature at the previous stop based on the air quantity during the previous operation period acquired by the previous operation integrated air quantity acquisition unit 53 and the cylinder internal temperature at the previous start estimated by the previous start cylinder internal temperature estimation unit 54. The cylinder internal temperature at the previous stop is estimated, for example, by referring to the map illustrated in FIG. 3(A). In the map illustrated in FIG. 3(A), the horizontal axis represents the integrated air quantity during the previous operation and the vertical axis represents the cylinder internal temperature at the previous stop. And the cylinder internal temperature at the previous start is shown as a line segment indicating an isotherm. The line segment indicating the isotherm is hotter as it goes upward. The value obtained when the integrated air quantity during the previous operation is fitted to the line segment corresponding to the cylinder internal temperature at the previous start is estimated as the cylinder internal temperature at the previous stop.

[0023] Note that the cylinder internal temperature at the previous stop may also be estimated by calculation. By referring to the air quantity during the previous operation period, the amount of heat obtained during the previous operation period is estimated. Based on the estimated amount of heat, the rise in the cylinder internal temperature during the previous operation period is predicted. Starting from the cylinder internal temperature at the previous start, the cylinder internal temperature at the previous stop is estimated by adding this rise.

[0024] The in-cylinder temperature decrease amount acquisition unit 56 acquires the amount of decrease in the in-cylinder temperature during the soak time from the previous stop to the current start of the internal combustion engine 100. The amount of decrease in the in-cylinder temperature is acquired by the current water temperature from the water temperature sensor 14 and the soak time measured by the soak time measurement unit 52. The amount of decrease in the in-cylinder temperature is acquired, for example, by referring to the map illustrated in FIG. 3(B). In the map illustrated in FIG. 3(B), the horizontal axis represents the soak time and the vertical axis represents the amount of decrease in the in-cylinder temperature. And the current water temperature is shown as a line segment indicating an isothermal state. The line segment indicating the isothermal state is hotter as it goes upward. The value obtained when the line segment corresponding to the current water temperature is selected and the soak time is fitted is estimated as the amount of decrease in the in-cylinder temperature.

[0025] The current start in-cylinder temperature estimation unit 57 estimates the in-cylinder temperature at the current start based on the in-cylinder temperature at the previous stop estimated by the previous stop in-cylinder temperature estimation unit 55 and the amount of decrease in the in-cylinder temperature acquired by the in-cylinder temperature decrease amount acquisition unit 56. The in-cylinder temperature at the current start is obtained by subtracting the amount of decrease in the in-cylinder temperature from the in-cylinder temperature at the previous stop.

[0026] The injection control unit 58 sets the injection timing and the fuel injection amount at the current start based on the in-cylinder temperature at the current start estimated by the current start in-cylinder temperature estimation unit 57. Then, the injection control unit 58 injects the fuel of the set fuel injection amount at the set injection timing.

[0027] 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 operation history of the internal combustion engine 100 and the operation conditions at start. Specifically, the ECU 50 reads the in-cylinder temperature at the previous start, the integrated air amount during the previous operation, the soak time, and the current water temperature.

[0028] After the ECU 50 finishes the process of step S1, it proceeds to step S2. In step S2, the ECU 50 determines whether the ethanol concentration detected by the alcohol concentration sensor 39 is equal to or higher than a predetermined value. Here, the predetermined value serving as the determination threshold is, for example, a value preset through experiments. This embodiment performs fuel injection at startup considering the vaporization characteristics of the alcohol fuel injected into the cylinder. Even when alcohol is used as the fuel, it is known that good starting performance of the internal combustion engine 100 can be obtained by including gasoline in the fuel. Therefore, the predetermined value in step S2 is set to a value that can determine whether the alcohol concentration is so high that such good starting performance cannot be obtained. When the ECU 50 makes an affirmative determination (Yes determination) in step S2, it proceeds to step S3. When the ECU 50 makes a negative determination (No determination) in step S2, it proceeds to step S10. Steps S10 and the subsequent step S11 will be described later.

[0029] In step S3, the ECU 50 determines whether the current water temperature is equal to or lower than a predetermined value. The predetermined value in step S3 is a threshold for determining whether the warm-up of the internal combustion engine 100 is complete. The determination in step S3 is made because when it is determined based on the water temperature that the warm-up of the internal combustion engine 100 is complete, there is no need to perform special control considering the use of alcohol fuel at startup. When the ECU 50 makes an affirmative determination in step S3, it proceeds to step S4. When the ECU 50 makes a negative determination in step S3, it proceeds to step S10.

[0030] In step S4, the ECU 50 determines whether the soak time is equal to or less than a predetermined value. The predetermined value in step S4 is a threshold value for determining whether the in-cylinder temperature can be evaluated by the water temperature. The internal combustion engine 100 may, for example, start from a cold state, then stop in a short time, and restart after a short soak time has elapsed. In such a case, a divergence may occur between the water temperature and the in-cylinder temperature. This is because when the internal combustion engine 100 starts even for a short time, the in-cylinder temperature around the combustion chamber 2a rises due to combustion, while the cylinder block and the like have not yet warmed up and the water temperature has not risen either. Even if the internal combustion engine 100 is in such a state where the water temperature and the in-cylinder temperature diverge, if the subsequent soak time becomes longer, the in-cylinder temperature gradually decreases and approaches the water temperature. Step S4 is a step for determining whether such a divergence between the water temperature and the in-cylinder temperature has occurred in the internal combustion engine 100. When the ECU 50 makes an affirmative determination in step S4, it proceeds to step S5. When the ECU 50 makes a negative determination in step S4, it proceeds to step S10.

[0031] In step S5, the in-cylinder temperature estimation unit 57 at the current start estimates the in-cylinder temperature at the current start. The ECU 50 subsequently performs step S6 following step S5. Note that the in-cylinder temperature at the current start estimated in step S5 is set as the in-cylinder temperature at the previous start at the next start.

[0032] In step S6, the ECU 50 determines whether the in-cylinder temperature at the current start estimated in step S5 is equal to or lower than the boiling point of ethanol. If the in-cylinder temperature is equal to or lower than the boiling point of ethanol, the fuel does not vaporize and cannot contribute to combustion. Step S6 is a step for determining whether the in-cylinder temperature can be brought into a state where it can vaporize the fuel and contribute to combustion. When the ECU 50 makes an affirmative determination in step S6, it proceeds to step S7. When the ECU 50 makes a negative determination in step S6, it proceeds to step S8.

[0033] In step S7, the injection timing setting unit 58a selects compression stroke injection as the injection timing. After the ECU 50 finishes the process of step S7, it proceeds to step S9. On the other hand, in step S8, the injection timing setting unit 58a selects injection other than compression stroke injection, for example, intake stroke injection, as the injection timing. Here, injection modes other than compression stroke injection can be variously set according to the specifications of the internal combustion engine 100. After the ECU 50 finishes the process of step S8, it proceeds to step S9.

[0034] In step S9, the injection amount setting unit 58b determines a correction amount based on which of the steps S7 and S8 the process reaches step S9 through, and sets the injection amount. When passing through step S7, the water temperature is below a predetermined value, and the in-cylinder temperature is also below the boiling point of ethanol. Therefore, the fuel injection amount in the conventionally implemented compression stroke injection is set. In contrast, when passing through step S8, the water temperature is below the predetermined value, but the in-cylinder temperature is higher than the boiling point of ethanol. That is, the fuel injected into the cylinder can be efficiently vaporized and contribute to combustion as an air-fuel mixture. Therefore, the fuel injection amount can be reduced. If the fuel injection amount is set based on the water temperature as in the conventional case, the injection amount may be excessive based on the water temperature below the predetermined value. In this embodiment, since the injection timing and the fuel injection amount are set based on the in-cylinder temperature at the start this time, it is possible to avoid the fuel injection amount from becoming excessive while ensuring the starting performance of the internal combustion engine 100. As a result, the deterioration of emissions can be suppressed. After the process of step S9 is completed, the process returns.

[0035] Note that the ECU 50 regards the estimated in-cylinder temperature as the current water temperature in step S10 and performs normal control in step S11. This is because in the case of reaching step S10, there is no significant deviation between the in-cylinder temperature and the water temperature in any case. Here, the normal control is a control in which the fuel injection timing and the fuel injection amount are set based on the water temperature. After the process of step S11 is completed, the process returns.

[0036] In this embodiment, since the injection timing and the fuel injection amount are set based on the in-cylinder temperature at the current start-up, it is possible to avoid an excessive fuel injection amount.

[0037] The above embodiments are merely examples for carrying out 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

[0038] 50... ECU, 53... Acquisition unit for the integrated intake air amount during the previous operation, 54... Estimation unit for the in-cylinder temperature at the previous start-up, 55... Estimation unit for the in-cylinder temperature at the previous stop, 56... Acquisition unit for the in-cylinder temperature decrease amount, 57... Estimation unit for the in-cylinder temperature at the current start-up, 58... Injection control unit.

Claims

【Claim 1】 A previous operation integrated air amount acquisition unit that acquires the integrated air amount during the previous operation of the internal combustion engine; A cylinder internal temperature estimation unit at the previous start that estimates the cylinder internal temperature at the previous start of the internal combustion engine; A cylinder internal temperature estimation unit at the previous stop that estimates the cylinder internal temperature at the previous stop based on the integrated air amount during the previous operation and the cylinder internal temperature at the previous start; A cylinder internal temperature decrease amount acquisition unit that acquires the decrease amount of the cylinder internal temperature during the soak time from the previous stop to the current start of the internal combustion engine; A current start cylinder internal temperature estimation unit that estimates the cylinder internal temperature at the current start based on the cylinder internal temperature at the previous stop and the decrease amount of the cylinder internal temperature; An injection control unit that sets the injection timing and the fuel injection amount at the start based on the cylinder internal temperature at the current start; A control device for an internal combustion engine, including the above components.

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