Control device for direct injection internal combustion engines

Abstract

To provide a control device of a direct injection type internal combustion engine capable of reducing a portion of injected fuel not contributing to combustion in injected fuel, and suppressing extinguishing of spark from an ignition plug.SOLUTION: A control device for a direct injection internal combustion engine in which fuel containing alcohol is directly injected into a cylinder by an injector and ignited by a spark plug, is configured to, when a rising edge of an ignition signal to the spark plug is detected while fuel is being injected from the injector, stop the injection of fuel from the injector.SELECTED DRAWING: Figure 5

Description

Technical Field

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

Background Art

[0002] Conventionally, in order to reliably supply a necessary amount of fuel into a cylinder according to the operating state of a vehicle, a direct injection type internal combustion engine that directly injects fuel into the cylinder is known. Further, against the backdrop of the recent soaring crude oil prices and the increasing concern about global warming, etc., as a fuel alternative to fossil fuels, an alcohol blended fuel obtained by mixing gasoline with an alcohol such as ethanol or methanol may be used in an internal combustion engine. However, alcohol has a higher boiling point and lower volatility compared to gasoline, and the higher the alcohol concentration, the more difficult it is for the fuel to atomize or vaporize. Therefore, the higher the alcohol concentration of the alcohol blended fuel, or the lower the temperature, the more difficult it is to burn. As a result, good combustion of the air-fuel mixture cannot be obtained, which may cause a start delay or poor start of the internal combustion engine, or an increase in the emission amount of harmful substances.

[0003] In order to address such problems, as an injection method for promoting the vaporization of fuel with a high alcohol concentration during cold start, control is disclosed in which fuel is injected in a high temperature state near top dead center of compression and the fuel injection pressure is increased to perform fuel injection (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, if fuel injection occurs near the top dead center of the compression stroke, the injection timing and ignition timing may overlap during the compression stroke due to factors such as the extension or contraction of the control interval caused by structural variations in each internal combustion engine, or discrepancies in control calculations. When the injection timing and ignition timing overlap in this way, there is fuel injected even after ignition, which does not contribute to combustion and may also extinguish the spark plug's spark during ignition.

[0006] The present invention has been made in view of the above-mentioned problems, and aims to provide a control device for a direct injection internal combustion engine that can reduce fuel that does not contribute to combustion in the injected fuel and suppress the extinguishing of the spark plug. [Means for solving the problem]

[0007] To solve the above-mentioned problems and achieve the objective, the control device for a direct injection internal combustion engine according to the present invention is a control device for a direct injection internal combustion engine in which alcohol-containing fuel is directly injected into the cylinder by an injector and ignited by a spark plug, characterized in that when the rising of the ignition signal to the spark plug is detected while fuel is being injected from the injector, the injection of fuel from the injector is stopped. [Effects of the Invention]

[0008] According to the present invention, it is possible to reduce the amount of fuel that does not contribute to combustion in the injected fuel, and to suppress the extinguishing of the spark plug. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 shows an example of a schematic configuration of a direct-injection internal combustion engine according to the first embodiment. [Figure 2] Figure 2 illustrates the operation of compression top dead center injection and multi-injection. [Figure 3]Figure 3 illustrates the switching of the injection method based on the alcohol concentration and temperature of the fuel. [Figure 4] Figure 4 illustrates the injection timing and ignition timing of a conventional direct-injection internal combustion engine. [Figure 5] Figure 5 is a diagram showing an example of a timing chart illustrating the injection timing and ignition timing of an internal combustion engine according to the first embodiment. [Figure 6] Figure 6 is a diagram showing an example of a timing chart illustrating the injection timing, ignition timing, and ignition retardation control operation of an internal combustion engine according to the second embodiment. [Figure 7] Figure 7 shows an example of an ignition retardation table used in the operation of an internal combustion engine according to the second embodiment. [Modes for carrying out the invention]

[0010] The following describes in detail embodiments of the control device for a direct injection internal combustion engine according to the present invention with reference to Figures 1 to 7. Furthermore, the present invention is not limited by the following embodiments, and the components in the following embodiments include those easily conceivable by those skilled in the art, those substantially identical, and those within the so-called equivalent range. Moreover, various omissions, substitutions, modifications, and combinations of components can be made without departing from the spirit of the following embodiments.

[0011] [First Embodiment] (Outline configuration of a direct injection internal combustion engine) Figure 1 is a diagram showing an example of the schematic configuration of a direct-injection internal combustion engine according to the first embodiment. The schematic configuration of the direct-injection internal combustion engine 1 according to this embodiment will be described with reference to Figure 1.

[0012] The internal combustion engine 1 shown in Fig. 1 is a direct injection reciprocating engine in which fuel is directly injected from an injector into the combustion chamber in the cylinder. As shown in Fig. 1, the internal combustion engine 1 includes a cylinder 10, a combustion chamber 11, an intake valve 12, an exhaust valve 13, an injector 14, a spark plug 15, an intake passage 21, an exhaust passage 22, and a throttle valve 23.

[0013] The cylinder 10 is a cylinder in which a piston (piston 31 described later) reciprocates by the force of fuel combustion in the combustion chamber 11. A plurality of cylinders 10 are provided in the internal combustion engine 1.

[0014] The combustion chamber 11 is formed by the inner wall inside the cylinder 10 and the upper surface of the piston, and is a space where fuel burns.

[0015] The intake valve 12 is a valve mechanism for controlling the air supplied into the combustion chamber 11 via the intake passage 21. The exhaust valve 13 is a valve mechanism for exhausting the combustion gas when fuel is burned in the combustion chamber 11.

[0016] The injector 14 is a device that injects an alcohol - mixed fuel (hereinafter sometimes simply referred to as fuel) in which alcohol is mixed with gasoline in a mist form into the combustion chamber 11 according to the control from an ECU (Electronic Control Unit) 50 described later.

[0017] The spark plug 15 is a device that ignites and burns (explodes) the air - fuel mixture of the air supplied into the combustion chamber 11 via the intake passage 21 and the fuel injected by the injector 14. Specifically, the spark plug 15 ignites the air - fuel mixture at a timing just before the piston 31 moving up and down in the cylinder 10 reaches the top dead center.

[0018] The intake passage 21 is connected to the combustion chamber 11 via the intake valve 12 and is a passage for supplying air into the combustion chamber 11 via the intake valve 12. The intake passage 21 branches at a position upstream of the intake valve 12 and is connected to the combustion chamber 11 of each cylinder 10. The exhaust passage 22 is connected to the combustion chamber 11 via the exhaust valve 13 and is a passage for discharging the combustion gas after combustion in the combustion chamber 11 via the exhaust valve 13.

[0019] The throttle valve 23 is installed in the intake passage 21 and is a valve device for adjusting the flow rate of air flowing through the intake passage 21 by controlling the opening degree by the ECU 50.

[0020] In addition, as shown in FIG. 1, the internal combustion engine 1 further includes a piston 31, a connecting rod 32, a crankshaft 33, a flywheel 34, and a crank angle sensor 40.

[0021] The piston 31 is connected to the crankshaft 33 via the connecting rod 32 and is a member that moves up and down in the cylinder 10 by receiving the expansion force due to the combustion (explosion) of the air-fuel mixture in the combustion chamber 11. The connecting rod 32 connects the piston 31 and the crankshaft 33 and is a member that converts the up-and-down movement (reciprocating movement) of the piston 31 due to the force caused by the combustion (explosion) of the air-fuel mixture in the combustion chamber 11 into the rotational movement of the crankshaft 33.

[0022] The crankshaft 33 is a rotating shaft that rotates by the transmission of the connecting rod 32 with respect to the up-and-down movement force of the piston 31.

[0023] The flywheel 34 is fixed to the crankshaft 33 and is a wheel member that rotates in conjunction with the rotation of the crankshaft 33. The flywheel 34 stabilizes the rotation of the crankshaft 33 by the moment of inertia due to its rotation.

[0024] The crank angle sensor 40 is installed near the flywheel 34 and is a sensor that detects the rotation angle of the crankshaft 33. The crank angle sensor 40 outputs the detected rotation angle information to the ECU 50, and the ECU 50 calculates the rotation speed of the crankshaft 33, i.e., the engine speed, based on the received rotation angle information.

[0025] The ECU 50 is a control device (controller) that calculates the engine speed from the rotation angle of the crankshaft 33 detected by the crank angle sensor 40 and controls the operation of the injector 14, spark plug 15, and throttle valve 23. The ECU 50 is equipped with a memory 51 that stores programs and various parameters.

[0026] (Regarding compression top dead center injection and multi-injection) Figure 2 illustrates the operation of compression top dead center injection and multi-injection. Figure 3 illustrates the switching of the injection method based on the alcohol concentration and temperature of the fuel. Compression top dead center injection and multi-injection in the internal combustion engine 1 according to this embodiment will be described with reference to Figures 2 and 3.

[0027] First, let's explain multi-injection (stratified injection) with reference to Figure 2. Multi-injection is a control method in which, when injecting fuel from the injector 14 into the combustion chamber 11, the fuel used for one combustion cycle is not injected all at once, but is injected into the combustion chamber 11 in several stages. For example, in the example shown in Figure 2, with one reciprocation of the piston 31 being a 360-degree combustion cycle, and with top dead center (TDC) as the reference (0°), the multi-injection consists of a first injection 101 that injects 20% of the fuel used for one combustion cycle at a timing 260° ahead of top dead center, a second injection 102 that injects another 20% of the fuel at a timing 180° ahead of top dead center, and a third injection 103 that injects the remaining 60% of the fuel at a timing 30° ahead of top dead center. In the example shown in Figure 2, fuel is injected in three separate stages: the first injection 101, the second injection 102, and the third injection 103. Ignition then occurs at a timing 5° ahead of top dead center. While Figure 2 shows an example of multi-injection with three separate injections, the number of injections is not limited to three; other numbers of injections may also be used.

[0028] By injecting fuel into the combustion chamber 11 in several stages using this multi-injection control method, it becomes easier to atomize the fuel within the combustion chamber 11, improves the premixing with the air supplied through the intake valve 12, and suppresses the temperature drop of the mixture due to the heat of vaporization, thereby making it easier to burn the mixture.

[0029] Next, we will explain compression top dead center injection. Compression top dead center injection is a control method in which, when the piston 31 reaches near top dead center, the temperature of the compressed air in the combustion chamber 11 near the compression end (top dead center) is used to inject the fuel to be used for one combustion cycle into the combustion chamber 11 all at once.

[0030] This control method using injection at the top dead center of compression allows fuel to be injected into the combustion chamber 11 at once near the compression end temperature. By utilizing the temperature near the compression end temperature, the fuel can be vaporized and burned, thereby increasing thermal efficiency.

[0031] Next, referring to Figure 3, we will explain the relationship between the alcohol concentration of the fuel being used (alcohol-blended fuel) and the temperature.

[0032] Figure 3 shows an example of the relationship between the alcohol concentration of the fuel (alcohol-blended fuel) being used and the temperature. As shown in the example in Figure 3, in the case of high concentration and low temperature, such as when the alcohol concentration of the fuel is 60% or higher and the temperature is 20°C or lower, the internal combustion engine 1 is controlled using top dead center injection, which utilizes the temperature near the compression end temperature to inject and burn the fuel all at once, both during startup and after startup, thereby promoting fuel vaporization and combustion. Furthermore, when the alcohol concentration of the fuel is 650% or higher but less than 60% and the temperature is 20°C or lower, the internal combustion engine 1 is controlled using top dead center injection, which utilizes the temperature near the compression end temperature to inject and burn the fuel all at once, only during startup. In other alcohol concentration and temperature ranges, the internal combustion engine 1 is controlled using multi-injection, both during startup and after startup. Note that the switching of control methods shown in Figure 3 is just one example, and it is possible to appropriately switch the control method depending on the characteristics of the fuel, as well as the characteristics or structure of the vehicle and internal combustion engine 1.

[0033] (Regarding the problems with conventional control systems) Figure 4 illustrates the injection timing and ignition timing of a conventional direct-injection internal combustion engine. The problems with conventional direct-injection internal combustion engines will be explained with reference to Figure 4.

[0034] Figure 4 illustrates the operation of a conventional direct-injection internal combustion engine in which fuel is injected and ignited in three stages using a multi-injection control method. Specifically, the example shown in Figure 4 shows a multi-injection system consisting of the first injection 111, the second injection 112, and the third (final) injection 113.

[0035] In the final injection of the multi-injection system (the third injection 113 in Figure 3), the injection timing needs to be retarded as much as possible for reasons such as utilizing the temperature near the compression end to promote vaporization, and because an advanced timing would cool the air-fuel mixture already present in the combustion chamber 11. Furthermore, regarding the ignition timing, it is necessary to advance the ignition timing as much as possible within the range where the piston 31 does not rotate in reverse, because retarding the ignition timing reduces the thermal efficiency of combustion and thus the torque.

[0036] As a result, as shown in Figure 4, an event can occur where the timing of the final injection and the ignition timing overlap. When this event occurs, the fuel after ignition does not contribute to combustion, resulting in the wasteful exhaust of unburned fuel. Furthermore, because the spark plug ignites the fuel while it is being injected from the injector, there is a risk that the turbulence of the fuel in the combustion chamber caused by the injection may extinguish the ignition spark. It should be noted that the above problems can occur not only with multi-injection control systems but also with compression top dead center injection control systems.

[0037] In this embodiment, the control operations for resolving the above-mentioned problems will be described in detail below.

[0038] (Control operations for the internal combustion engine according to this embodiment) Figure 5 is a diagram illustrating an example of a timing chart explaining the injection timing and ignition timing of an internal combustion engine according to the first embodiment. The control operation of the ECU 50 for the internal combustion engine 1 according to this embodiment will be explained with reference to Figure 5.

[0039] The timing chart shown in Figure 5(a) illustrates the operation of a conventional direct-injection internal combustion engine in multi-injection where the final injection timing coincides with the ignition timing. As shown in Figure 5(a), when the injection signal to the injector moves from a low level to an intermediate level (a level between the low and high levels), preparation for injection is initiated, and when it moves from the intermediate level to a high level, fuel is injected into the combustion chamber. The three intervals in Figure 5(a) where the injection signal is at a high level correspond to the first injection 111, the second injection 112, and the third injection 113 shown in Figure 4, respectively. Then, as shown in Figure 5(a), during the third injection, the ignition signal moves from a low level to a high level, and the spark plug ignites. As a result, as mentioned above, since the fuel after ignition does not contribute to combustion, the unburned fuel is exhausted, wasting fuel, and there is a risk that the turbulence of the fuel in the combustion chamber due to injection may extinguish the ignition spark.

[0040] Therefore, the ECU 50 according to this embodiment executes the control shown in the timing chart in Figure 5(b) for the internal combustion engine 1. That is, as shown in Figure 5(b), when the ECU 50 is outputting an injection signal at a high level to the injector 14 for the last injection (in this case, the third injection), that is, while the injector 14 is injecting fuel, if it detects that the ignition signal to the spark plug 15 has changed from a low level to a high level (detection of the rising edge of the ignition signal), it stops outputting the injection signal (sets the injection signal to a low level) and stops the injection of fuel from the injector 14. As a result, fuel is not injected while the spark plug 15 is igniting, so fuel that does not contribute to combustion is eliminated and the spark of ignition at the spark plug 15 that is being injected is prevented from being extinguished. Furthermore, since the extinguishing of the ignition spark is prevented, the robustness of the internal combustion engine 1 during startup can be improved, the deterioration of combustion can be suppressed, and further, output fluctuations between cylinders can be suppressed and vibrations can be suppressed. Furthermore, because fuel that does not contribute to combustion can be eliminated, exhaust emissions are improved compared to conventional control systems, unburned gases and CO can be reduced, and fuel efficiency can also be improved.

[0041] Furthermore, when the control operation shown in Figure 5(b) above is executed, fuel injection is stopped, resulting in some fuel remaining uninjected. In this case, the ECU 50 may, upon detecting that the ignition signal has risen from a low level to a high level (detection of the rising ignition signal), temporarily increase the fuel injection pressure from the injector 14 to completely inject the planned fuel amount and then stop the injection. This allows the fuel to be completely injected on the third injection, suppressing the decrease in torque due to the reduced amount of fuel contributing to combustion.

[0042] Furthermore, the control operation of the ECU 50 to the internal combustion engine 1 according to this embodiment, as shown in Figure 5(b), is not limited to the case of multi-injection, but can also be applied to the case of compression top dead center injection.

[0043] As described above, in the ECU 50 that controls the internal combustion engine 1 according to this embodiment, in a direct injection type internal combustion engine 1 in which alcohol-containing fuel is directly injected into the cylinder 10 (combustion chamber 11) by an injector 14 and ignited by a spark plug 15, when fuel is being injected from the injector 14, if the rising ignition signal to the spark plug 15 is detected, the injection of fuel from the injector 14 is stopped. This reduces the amount of fuel that does not contribute to combustion in the injected fuel and prevents the spark of the spark plug 15 from being extinguished. Furthermore, since the extinguishing of the ignition spark can be prevented, the robustness of the internal combustion engine 1 during startup can be improved, combustion deterioration can be suppressed, and output fluctuations between cylinders can be suppressed and vibrations can be suppressed. In addition, since fuel that does not contribute to combustion can be eliminated, exhaust gases can be improved compared to conventional control, unburned gases and CO can be reduced, and fuel efficiency can also be improved.

[0044] [Second Embodiment] The control operation of the ECU 50 that controls the internal combustion engine 1 according to the second embodiment will be described, focusing on the differences from the first embodiment. In the first embodiment, control focusing on a specific cylinder 10 of the internal combustion engine 1 was described. In this embodiment, the control operation for other cylinders 10 that is executed in conjunction with the above-described control for injection timing and ignition timing in a specific cylinder 10 will be described. Note that the configuration of the internal combustion engine 1 and ECU 50 according to this embodiment is the same as the configuration described in the first embodiment.

[0045] (Control operations for the internal combustion engine according to this embodiment) Figure 6 is a diagram showing an example of a timing chart illustrating the injection timing, ignition timing, and ignition retardation control operation of an internal combustion engine according to the second embodiment. Figure 7 is a diagram showing an example of an ignition retardation table used in the operation of the internal combustion engine according to the second embodiment. The control operation of the ECU 50 for the internal combustion engine 1 according to this embodiment will be described with reference to Figures 6 and 7.

[0046] The timing chart shown in Figure 6(a) illustrates the operation in a conventional direct-injection internal combustion engine where the final injection timing coincides with the ignition timing in multi-injection, and is similar to the timing chart shown in Figure 5(a) above.

[0047] In the timing chart shown in Figure 6(b), the timing charts for the injection signal and ignition signal are the same as those shown in Figure 5(b) above. This prevents fuel from being injected while the spark plug 15 is igniting, thus eliminating fuel that does not contribute to combustion. However, this also means that combustion does not occur with the amount of fuel that should have been injected, which may cause the rotational speed of the internal combustion engine 1 to decrease. In this case, the ignition timing is retarded for cylinders 10 other than the cylinder 10 whose injection timing and ignition timing were controlled as described above. Furthermore, for the cylinder 10 whose injection timing and ignition timing were controlled, the ignition timing is retarded in the next combustion cycle. This control is performed to suppress and recover the decrease in engine speed.

[0048] Specifically, as shown in Figure 6(b), the ECU 50 detects that the ignition signal to the spark plug 15 has changed from a low level to a high level (detects the rising edge of the ignition signal) and stops the output of the injection signal (sets the injection signal to a low level), and turns on the cut flag. After turning on the cut flag, the ECU 50 determines whether the engine speed calculated by the output of the crank angle sensor 40 has decreased. For example, if the difference between the previous engine speed (for example, the engine speed a predetermined unit time ago) and the current engine speed is ΔNE [rpm], and the absolute value of ΔNE exceeds a predetermined threshold, the ECU 50 performs control to retard the ignition timing in accordance with the amount of decrease in engine speed for a cylinder 10 different from the cylinder 10 for which injection timing and ignition timing control was performed, as shown in Figure 6(b) (hereinafter sometimes referred to as ignition timing retard control). In this case, the ECU 50 pre-stores an ignition timing retardation table in memory 51 that associates ΔNE (absolute value) as shown in Figure 7 with the amount of ignition timing retardation, and refers to this ignition timing retardation table to perform ignition timing retardation control by the amount of retardation corresponding to the calculated absolute value of ΔNE (a negative value if the engine speed is decreasing). Furthermore, for the cylinder 10 for which injection timing and ignition timing control has been performed, the ECU 50 similarly performs ignition timing retardation control in the next combustion cycle. As a result, the fuel injection time before ignition is extended in each cylinder 10, improving combustion stability, increasing torque, and allowing the engine speed to increase. On the other hand, if the absolute value of ΔNE is less than a predetermined threshold, the ECU 50 should continue the current control for that different cylinder 10. Then, in response to the recovery (increase) of engine speed, the ECU 50 gradually advances the ignition timing for each cylinder 10 for which ignition timing retardation control has been performed, returning it to the original ignition timing.

[0049] As described above, in the ECU 50 that controls the internal combustion engine 1 according to this embodiment, if the engine speed of the internal combustion engine 1 decreases after fuel injection from the injector 14 is stopped, the ignition timing of the cylinders 10 other than the cylinder 10 from which fuel injection from the injector 14 was stopped is retarded according to the amount of decrease in engine speed, and the ignition timing of the cylinder 10 from which fuel injection was stopped is retarded in the next combustion cycle. As a result, the fuel injection time before ignition is extended in all cylinders 10, improving combustion stability, increasing torque, and allowing the engine speed to increase. Furthermore, since ignition timing retardation control is performed only when the engine speed decreases, the effect of cutting the fuel injection amount can be maximized if the engine speed does not decrease. Even when the engine speed decreases, by setting the retardation amount according to ΔNE, the effect of cutting the injection amount can be obtained while compensating for the decrease in engine speed when the injection amount is cut. In addition, the combustion becomes more stable because the amount of fuel injected and atomized in the cylinder 10 targeted by the ignition timing retardation control increases. [Explanation of Symbols]

[0050] 1. Internal combustion engine 10 cylinders 11 Combustion chamber 12 Intake valve 13 Exhaust valve 14 Injectors 15 Spark plugs 21 Intake passage 22 Exhaust passage 23 Throttle valve 31 pistons 32 Connecting Rods 33 Crankshaft 34 Flywheel 40 Crank angle sensor 50 ECU 51 memory 101 1st injection 102 2nd injection 103 Third injection 111 1st injection 112 Second Spray 113 Third Spray

Claims

1. A control device for a direct injection internal combustion engine in which an alcohol-containing fuel is injected directly into a cylinder where a piston reciprocates by an injector and ignited by a spark plug, A control device for a direct injection internal combustion engine that, when the piston reaches near top dead center and fuel is being injected from the injector, detects the rising of the ignition signal to the spark plug and stops the injection of fuel from the injector.

2. When the piston has reached near top dead center and fuel is being injected from the injector, if the rising of the ignition signal to the spark plug is detected, the control device for a direct injection internal combustion engine according to Claim 1, the device temporarily increases the fuel pressure of the fuel injection from the injector to stop the injection by blowing out the amount of fuel that was to be injected.

3. A control device for a direct injection internal combustion engine according to claim 1, wherein, if the rotational speed of the direct injection internal combustion engine decreases after the injection of fuel from the injector is stopped, the ignition timing of the cylinders other than the cylinder from which the injection of fuel from the injector was stopped is retarded in proportion to the amount of the decrease in rotational speed, and the ignition timing of the cylinder from which the injection was stopped is retarded in the next combustion cycle.

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