Fuel injection control device for internal combustion engine

Abstract

To suppress the occurrence of abnormality in an ignition plug in an internal combustion engine performing cylinder inner injection.SOLUTION: A fuel injection control device for an internal combustion engine controls fuel injection of the internal combustion engine having a cylinder inner injection valve and an ignition plug. The fuel injection control device sets fuel injection start timing of the cylinder inner injection valve to be on a timing delay side of a predetermined crank angle when load of the internal combustion engine is a preset specified value or larger. This configuration avoids adhesion of fuel injected from the cylinder inner injection valve to the ignition plug, and suppresses the occurrence of abnormality in the ignition plug (generation of pitting-corrosion).SELECTED DRAWING: Figure 3

Description

Technical Field

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

Background Art

[0002] Conventionally, in an internal combustion engine that performs in-cylinder injection, a proposal has been made to control the fuel injection start timing (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] By the way, the spark plug provided in the internal combustion engine is installed in a state where the tip side thereof is exposed to the combustion chamber that becomes high temperature due to the fueling of the air-fuel mixture of fuel and intake air. In an internal combustion engine that performs in-cylinder injection, depending on the timing of fuel injection, the fuel injected toward the inside of the cylinder may adhere to the spark plug before atomizing. The fuel adhering to the spark plug cools the spark plug due to its latent heat of vaporization. Therefore, when fuel adheres to the spark plug, the spark plug repeatedly receives cooling due to the latent heat of vaporization and heating due to the combustion of the air-fuel mixture. The spark plug may experience abnormalities, for example, pitting corrosion in which its surface is eroded in a porous shape, due to repeated cooling and heating. In order to suppress such abnormalities, it is conceivable to adopt a material that is resistant to corrosion for the spark plug. However, the adoption of such a material increases the cost of the spark plug, which is not desirable.

[0005] Although Patent Document 1 controls the fuel injection start timing, it does not consider avoiding the adhesion of fuel to the spark plug and the abnormalities that may occur in the spark plug due to this fuel adhesion.

[0006] Therefore, an object of the invention disclosed in this specification is to suppress the occurrence of abnormalities in an ignition plug in an internal combustion engine that performs in-cylinder injection.

Means for Solving the Problem

[0007] The fuel injection control device for an internal combustion engine disclosed in this specification is a fuel injection control device for an internal combustion engine that controls fuel injection in an internal combustion engine equipped with an in-cylinder injection valve and an ignition plug. When the load of the internal combustion engine is equal to or greater than a predetermined value, the fuel injection start timing of the in-cylinder injection valve is set on the retarded angle side with respect to a predetermined crank angle.

Effect of the Invention

[0008] The invention disclosed in this specification can suppress the occurrence of abnormalities in an ignition plug in an internal combustion engine that performs in-cylinder injection.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Mode for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, in the drawings, the dimensions, ratios, etc. of each part may not be illustrated so as to exactly match the actual ones. Also, depending on the drawings, details may be omitted.

[0011] (Embodiment)

[0012] Hereinafter, with reference to the drawings, an internal combustion engine 10 equipped with an ECU (Electronic Control Unit) that functions as a fuel injection control device of the present embodiment and fuel injection control in the internal combustion engine 10 will be described.

[0013] [Internal Combustion Engine] The internal combustion engine 10 is a four-cycle engine that ignites a mixture of fuel and air. The internal combustion engine 10 has a cylinder block 20 and a cylinder head 21. As shown in Fig. 1(A), in the internal combustion engine 10, the cylinder head 21 is attached above the cylinder block 20, and a crankcase (not shown) is attached below the cylinder block 20. The piston 22 is housed in a cylinder 20a provided in the cylinder block 20. The piston 22 is connected to the crankshaft via a connecting rod. The piston 22 is slidable in the vertical direction of Fig. 1(A). The combustion chamber 24 is partitioned by the cylinder block 20, the cylinder head 21, and the piston 22. The inner wall of the cylinder head 21 forms the ceiling portion 24a of the combustion chamber 24.

[0014] An intake port 26 and an exhaust port 28 are connected to the cylinder head 21. An intake passage 12 is connected upstream of the intake port 26. An exhaust passage 14 is connected downstream of the exhaust port 28.

[0015] An air cleaner 15, an air flow meter 16, a throttle valve 18, and a port injection valve 32a are provided in the intake passage 12 in order from the upstream side. The air cleaner 15 removes dust and the like from the air in the intake passage 12 and purifies the air. The air flow meter 16 detects the flow rate of the air in the intake passage 12. The throttle valve 18 adjusts the flow rate of the air. The larger the opening degree of the throttle valve 18, the greater the flow rate of the air. The smaller the opening degree of the throttle valve 18, the smaller the flow rate of the air. A catalyst 29 is provided in the exhaust passage 14.

[0016] The cylinder head 21 is provided with an intake valve 17, an exhaust valve 19, a spark plug 30, and an in-cylinder injection valve 32b. The intake valve 17 and the exhaust valve 19 are opened and closed by a valve operating mechanism (not shown). When the intake valve 17 opens, the intake port 26 and the combustion chamber 24 communicate with each other. When the exhaust valve 19 opens, the exhaust port 28 and the combustion chamber 24 communicate with each other. The spark plug 30 generates a spark between the electrodes provided at the tip and ignites the air-fuel mixture in the combustion chamber 24. The in-cylinder injection valve 32b injects fuel toward the combustion chamber 24.

[0017] The spark plug 30 and the in-cylinder injection valve 32b are provided at the center of the ceiling portion 24a of the combustion chamber 24. The center portion is a position sandwiched between the intake port 26 and the exhaust port 28. The spark plug 30 and the in-cylinder injection valve 32b are inclined with respect to the extending direction of the cylinder of the internal combustion engine 10 (the vertical direction in Fig. 1(A)). The spark plug 30 is inclined toward the exhaust valve 19 side. The in-cylinder injection valve 32b is inclined toward the intake valve 17 side. The tip of the spark plug 30 and the tip of the in-cylinder injection valve 32b are exposed inside the combustion chamber 24. Thus, the internal combustion engine 10 of the present embodiment employs a center injection structure. By adopting the center injection structure, spraying can be performed near the spark plug 30 by the in-cylinder injection valve 32b, and the flame can be directed in the direction of the spray. As a result, stable combustion in the combustion chamber 24 is realized, and the emission can be effectively reduced.

[0018] The spark plug 30 is located between the exhaust valve 19 and the in-cylinder injection valve 32b. The in-cylinder injection valve 32b is located between the spark plug 30 and the intake valve 17. That is, as shown in Fig. 1(A), the exhaust valve 19, the spark plug 30, the in-cylinder injection valve 32b, and the intake valve 17 are arranged in this order from one inner wall to the opposite inner wall of the internal combustion engine 10.

[0019] The ECU 11 includes a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), a backup RAM, and other storage devices. The ECU 11 performs fuel injection control in the internal combustion engine 10. That is, the ECU 11 functions as a fuel injection control device. The ECU 11 executes arithmetic processing and various controls based on programs and maps stored in the CPU, ROM, and other storage devices. The RAM is a memory that temporarily stores the arithmetic results by the CPU, data input from various sensors, etc., and the backup RAM is a non-volatile memory that stores data etc. to be saved when the internal combustion engine 10 stops. The ECU 11 acquires the air flow rate detected by the air flow meter 16. The ECU 11 controls the injection amount and injection timing of fuel from the port injection valve 32a and the in-cylinder injection valve 32b. The ECU 11 controls the opening degree of the throttle valve 18. Further, the ECU 11 is electrically connected to the rotation speed sensor 33 and acquires the engine rotation speed of the internal combustion engine 10.

[0020] The port injection valve 32a performs fuel injection toward the intake port 26 (port injection). The in-cylinder injection valve 32b injects fuel into the combustion chamber 24 (in-cylinder injection). The ECU 11 selects an injection pattern according to the operating condition of the internal combustion engine 10. That is, the ECU 11 selects either an injection mode that performs only in-cylinder injection, an injection mode that performs only port injection, or an injection mode that performs both in-cylinder injection and port injection. The selection of the injection pattern will be described in detail later.

[0021] When the intake valve 17 opens, air is introduced from the intake port 26 into the combustion chamber 24 as shown in FIG. 1(B). When port injection is performed, air in a state mixed with fuel is introduced into the combustion chamber 24. When in-cylinder injection is performed, an air-fuel mixture is generated in the combustion chamber 24. When the ignition plug 30 ignites the air-fuel mixture, the air-fuel mixture burns. Due to the combustion of the air-fuel mixture, the piston 22 reciprocates up and down. Power is transmitted from the piston 22 to the crankshaft, and the crankshaft rotates. When the exhaust valve 19 opens, the exhaust after combustion is discharged to the exhaust port 28. The catalyst 29 purifies the exhaust.

[0022] [Fuel injection control] Next, the fuel injection control in the internal combustion engine 10 will be described with reference to FIGS. 2(A) to 9(C).

[0023] [Outline of fuel injection control] First, an overview of fuel injection control in the internal combustion engine 10 will be described. In the internal combustion engine 10 of the present embodiment, the fuel injection timing is controlled so that the fuel injected from the in-cylinder injection valve 32b does not adhere to the spark plug 30 before atomization. If the fuel injected from the in-cylinder injection valve 32b adheres to the spark plug 30, an abnormality may occur in the spark plug 30. Examples of the possible abnormalities in the spark plug 30 include pitting corrosion occurring on the surface of the electrode portion located at the tip of the spark plug 30. Pitting corrosion occurs when the electrode portion of the spark plug 30 exposed in the combustion chamber 24 repeatedly undergoes cooling due to the latent heat of vaporization of the adhered fuel and heating by the fuel in the air-fuel mixture, causing the loss of the surface protective layer, followed by the progression of oxidation and corrosion. Here, the adhesion of fuel to the spark plug 30 is more likely to occur as the piston 22 (see FIGS. 1(A) and 1(B)) approaches TDC (Top Dead Centre). This is because when the piston 22 is close to TDC, the fuel injected from the in-cylinder injection valve 32b (see FIGS. 1(A) and 1(B)) is likely to spread in the radial direction of the cylinder 20a (see FIGS. 1(A) and 1(B)). Since the internal combustion engine 10 of the present embodiment adopts a center injection structure in which the spark plug 30 and the in-cylinder injection valve 32b are installed in parallel on the ceiling portion 24a of the combustion chamber 24, the adhesion of fuel to the spark plug 30 is likely to occur. However, when the piston 22 moves away from TDC and the distance between the in-cylinder injection valve 32b and the piston 22 increases, the injected fuel diffuses downward in the cylinder 20a, thus avoiding adhesion to the spark plug 30.

[0024] Therefore, in the internal combustion engine 10 of the present embodiment, when fuel is injected into the cylinder, the fuel injection start timing by the in-cylinder injection valve 32b is controlled so that the fuel injected from the in-cylinder injection valve 32b does not adhere to the spark plug 30. Pitting corrosion occurring on the surface of the spark plug 30 is likely to occur when the inside of the combustion chamber 24 is at a high temperature. For this reason, in the present embodiment, when the load of the internal combustion engine 10 is equal to or greater than a predetermined threshold value, the fuel injection start timing is retarded.

[0025] ≪Details of Fuel Injection Control≫ The following details the fuel injection control. The fuel injection control includes the control of the fuel injection start timing and the fuel injection end timing. The fuel injection start timing and the fuel injection end timing are represented by the position of the piston 22. Therefore, prior to the detailed description of the fuel injection control, the notation of the piston position will be described with reference to FIGS. 2(A) to 2(B-2).

[0026] The internal combustion engine 10 is a four-cycle engine, and as shown in FIG. 2(A), it repeatedly performs four strokes: an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke. In a four-cycle engine, while these four strokes are being performed, the crankshaft rotates twice, that is, 720°. And the piston 22 reciprocates twice within the cylinder 20a. In such a four-cycle engine, based on the TDC (top dead center) position when the compression stroke is completed and the engine transitions to the expansion stroke, the side advanced from this TDC is denoted as BTDC (Before Top Dead Centre), and the side retarded from the TDC is denoted as ATDC (After Top Dead Centre). When representing a position on the advanced side from the TDC when the compression stroke is completed, for example, a position 180° on the advanced side is denoted as BTDC180, and a position 360° on the advanced side is denoted as BTDC360. Similarly, a position 180° on the retarded side is denoted as ATDC180, and a position 360° on the retarded side is denoted as ATDC360.

[0027] According to this notation, the intake stroke is from BTDC360 to BTDC180, and the compression stroke is from BTDC180 to TDC (=TDC0). Similarly, the expansion stroke is from TDC (=TDC0) to ATDC180, and the exhaust stroke is from ATDC180 to ATDC360.

[0028] Note that the period of the stroke in which the internal combustion engine 10 actually intakes or exhausts depends on the valve opening period of the intake valve 17 and the exhaust valve 19. Here, for the sake of convenience, the periods of the four strokes of the intake stroke, the compression stroke, the expansion stroke, and the exhaust stroke are each assumed to be 180° periods.

[0029] Referring to FIG. 3, in step S1, the ECU 11 acquires the engine speed and the engine load. The engine speed is acquired by the detection value detected by the rotational speed sensor 33 being transmitted to the ECU 11. The engine load is acquired based on the intake air amount detected by the air flow meter 16.

[0030] In step S2, the ECU 11 determines the injection pattern. The injection pattern is determined by fitting the engine speed and the engine load acquired in step S1 to the injection pattern determination map shown in FIG. 4. The injection pattern includes two patterns: a port injection pattern using only the port injection valve 32a and an in-cylinder injection pattern using only the in-cylinder injection valve 32b.

[0031] In step S3, the ECU 11 determines whether to use the in-cylinder injection valve 32b. If the injection pattern determined in step S2 is the port injection pattern, the ECU 11 makes a negative determination (No determination) and proceeds to step S4. On the other hand, if the injection pattern determined in step S2 is the in-cylinder injection pattern, the ECU 11 makes an affirmative determination (Yes determination) and proceeds to step S5.

[0032] In step S4, the ECU 11 performs fuel injection using the port injection valve 32a. Since the port injection in step S4 injects the total amount of fuel injection amount for one intake stroke of the internal combustion engine 10 by the port injection valve 32a, fuel does not adhere to the spark plug 30. Therefore, in the port injection in step S4 of this embodiment, control of the fuel injection start timing for avoiding fuel adhesion to the spark plug 30 is not performed.

[0033] In step S5, the ECU 11 determines the injection start timing for the fuel injection by the in-cylinder injection valve 32b. The injection start timing is determined by fitting the engine speed and engine load acquired in step S1 to the injection start timing determination map shown in FIG. 5. Referring to the injection start timing determination map shown in FIG. 5, a load threshold value Lth is set for the engine load. Here, refer to FIG. 8(A). FIG. 8(A) shows a state where the piston 22 is in a position close to the TDC, and a part of the fuel Fu injected from the in-cylinder injection valve 32b adheres to the spark plug 30. When the load of the internal combustion engine 10 is high and the combustion temperature in the combustion chamber 24 is high, if fuel adheres to the spark plug 30, an abnormality may occur in the spark plug 30. The load threshold value Lth is set to a value that is assumed to be able to avoid the occurrence of an abnormality in the spark plug 30 based on the result of a simulation for verifying whether an abnormality occurs in the spark plug 30 when fuel adheres to the spark plug 30.

[0034] According to the injection start timing determination map shown in FIG. 5, in a region where the engine load is lower than the load threshold value Lth, the injection start timing corresponding to the engine speed is set in the range of BTDC280 to BTDC330. Specifically, in a region where the engine load is lower than the load threshold value Lth, as the engine speed increases, the injection start timing is set on the advanced angle side. On the other hand, in a region where the engine load is equal to or higher than the load threshold value Lth, regardless of the engine speed, the injection start timing is uniformly set to BTDC300. Here, referring to FIG. 8(A) again, the position of the piston 22 is approximately at the position of BTDC330. When the fuel injection is started from the in-cylinder injection valve 32b at such a piston position Fuel injection there is a possibility that fuel adheres to the spark plug 30. In contrast, FIG. 8(B) shows a state where the position of the piston 22 is approximately BTDC300. Thus, when the position of the piston 22 is about BTDC300, the adhesion of fuel to the spark plug 30 is avoided. That is, by starting the fuel injection at the timing when the position of the piston 22 moves to the retarded angle side, the adhesion of fuel to the spark plug 30 is avoided.

[0035] In step S6, the ECU 11 calculates the required fuel injection amount [mg / st]. The required fuel injection amount [mg / st] is calculated using the engine load and the equivalence ratio (or target A / F: target air-fuel ratio) obtained in step S1. The equivalence ratio is a preset value. For example, a numerical value of 1.1 (13.2 in terms of target A / F) is given. Note that the order of steps S5 and S6 does not matter; they may be swapped, or they may be executed simultaneously. Note that the values of the equivalence ratio and target A / F are just examples and are not limited thereto.

[0036] In step S7, the ECU 11 calculates the provisional injection end timing. Here, the reason for using the provisional injection end timing is that when the calculated injection end timing is close to TDC, the fuel injected at a timing close to the injection end timing may adhere to the spark plug 30, so the injection end timing may be changed. The explanation of the change in the injection end timing will be given together with the explanation of step S8. First, the provisional injection end timing is determined by fitting the required fuel injection amount calculated in step S6 and the engine speed obtained in step S1 to the injection period determination map shown in FIG. 6 to determine the injection period required to inject the required fuel injection amount. Here, the injection period is expressed by the crank angle rather than the injection time. Therefore, when the engine speed is high, the injection period becomes longer even if the injection time is the same. The provisional injection end timing is calculated based on the injection period calculated in this way and the injection start timing determined in step S5. That is, the end of the period obtained by adding the injection period to the injection start timing is the provisional injection end timing.

[0037] In step S8, the ECU 11 calculates the limit injection end timing. Here, the limit injection end timing is set such that by approaching the TDC at the injection end timing, it is possible to avoid fuel injected from the in-cylinder injection valve 32b from adhering to the ignition plug 30. That is, the limit injection end timing is set to a timing at which if fuel injection continues to the retard side beyond this timing, there is a possibility of fuel adhering to the ignition plug 30. Referring to FIGS. 9(A) and 9(B), the limit injection end timing is set to BTDC90. The limit injection end timing is determined by fitting the engine speed and engine load acquired in step S1 to the limit injection end timing determination map shown in FIG. 7. Referring to the limit injection end timing determination map shown in FIG. 7, a rotation speed threshold NEth is set. When the engine speed is lower than the rotation speed threshold NEth, the limit injection end timing is set to BTDC60, and when the engine speed is equal to or higher than the rotation speed threshold NEth, the limit injection end timing is set to BTDC90. When the engine speed is high, setting the limit injection end timing on the advance side is because when the engine speed is high, the rising speed of the piston 22 is fast, and fuel is likely to adhere to the ignition plug 30. Note that BTDC60 and BTDC90 as the limit injection end timing are examples and are not limited thereto.

[0038] In step S9, the ECU 11 determines whether the provisional injection end timing is on the advance side of the limit injection end timing. If the ECU 11 makes an affirmative determination in step S9, it proceeds to step S10. In step S10, fuel is injected from the in-cylinder injection valve 32b with the provisional injection end timing as the final injection end timing. On the other hand, if the ECU 11 makes a negative determination in step S9, it proceeds to step S11.

[0039] In step S11, the ECU 11 calculates the excess injection period. The excess injection period is the period during which the provisional injection end timing exceeds the limit injection end timing. Here, the excess injection period is expressed in crank angle [CA].

[0040] In step S12, the ECU 11 calculates the excessive in-cylinder injection amount [mg / st]. To calculate the excessive in-cylinder injection amount [mg / st], the ECU 11 first converts the excessive injection period [CA] expressed in terms of the crank angle calculated in step S11 into the excessive injection time [ms] using the engine speed [rpm]. Then, the ECU 11 calculates the excessive in-cylinder injection amount [mg / st] based on the injection characteristics including the fuel injection pressure [MPa] of the in-cylinder injection valve 32b. Here, referring to FIG. 9(B), the excessive in-cylinder injection amount [mg / st] is the amount of fuel injected on the retarded angle side from the limit injection end time. The excessive in-cylinder injection amount [mg / st] is injected by the port injection valve 32a.

[0041] In step S13, the ECU 11 calculates the final in-cylinder injection amount [mg / st]. The final in-cylinder injection amount [mg / st] is calculated by subtracting the excessive in-cylinder injection amount [mg / st] calculated in step S12 from the required fuel injection amount [mg / st] calculated in step S6.

[0042] In step S14, the ECU 11 instructs the port injection valve 32a to inject an amount corresponding to the excessive in-cylinder injection amount, and instructs the in-cylinder injection valve 32b to inject an amount corresponding to the final in-cylinder injection amount.

[0043] Through the above steps, the injection of the total amount of fuel injection for one intake stroke of the internal combustion engine 10 is executed. The fuel injected by the in-cylinder injection valve 32b is injected within a period during which it is avoided that the fuel adheres to the spark plug 30.

[0044] [Effect] In this embodiment, when the load of the internal combustion engine 10 is equal to or greater than a predetermined load threshold value Lth, the fuel injection start timing of the in-cylinder injection valve 32b is set on the retarded angle side from a predetermined crank angle. As a result, since the fuel injection by the in-cylinder injection valve 32b starts at a position where the position of the piston 22 has dropped, it is avoided that the fuel adheres to the spark plug 30, and the occurrence of abnormalities in the spark plug 30 is suppressed.

[0045] The above embodiments are merely examples for implementing the present invention, and the present invention is not limited thereto. Modifying these examples in various ways is within the scope of the present invention. Further, it is obvious from the above description that various other embodiments are possible within the scope of the present invention.

Explanation of Signs

[0046] 10 Internal combustion engine 11 ECU (fuel injection control device) 12 Intake passage 14 Exhaust passage 15 Air cleaner 16 Airflow meter 17 Intake valve 18 Throttle valve 19 Exhaust valve 20 Cylinder block 20a Cylinder 21 Cylinder head 22 Piston 24 Combustion chamber 24a Ceiling part 26 Intake port 28 Exhaust port 29 Catalyst 30 Spark plug 32a Port injection valve 32b In-cylinder injection valve

Claims

【Claim 1】 A fuel injection control device for an internal combustion engine that controls fuel injection in an internal combustion engine equipped with an in-cylinder injection valve, a port injection valve, and a spark plug, the fuel injection control device determines the use of the in-cylinder injection valve among the in-cylinder injection valve and the port injection valve based on the load of the internal combustion engine and the rotational speed of the internal combustion engine, and then, when the load of the internal combustion engine is equal to or greater than a predetermined value, the fuel injection start timing of the in-cylinder injection valve is set to a region on the advanced angle side with respect to the top dead center at the end of compression in the internal combustion engine as the reference of the crank angle, and is set to a retarded angle side with respect to the crank angle on the retarded angle side among the crank angles at which adhesion of the fuel injected by the in-cylinder injection valve to the spark plug is recognized. The required fuel injection amount of the internal combustion engine is calculated, and when it is determined that the tentative injection end timing set based on the required fuel injection amount is on the retarded angle side with respect to the limit injection end timing set so as to avoid adhesion of the fuel injected by the in-cylinder injection valve to the spark plug, an excessive in-cylinder injection amount that is assumed to be injected during an excessive injection period, which is a period in which the tentative injection end timing exceeds the limit injection end timing, is injected by the port injection valve, and the final in-cylinder injection amount obtained by subtracting the excessive in-cylinder injection amount from the required fuel injection amount is injected by the in-cylinder injection valve. A fuel injection control device for an internal combustion engine.

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