Fuel injection control device

Abstract

To suppress adhesion of fuel onto a wall surface.SOLUTION: An ECM 30 that controls fuel injection of an engine 10 injecting fuel containing alcohol into a cylinder 12 includes an arithmetic processing circuit 32 that on the basis of fuel injection start timing, performs arithmetic processing for calculating a maximum injection amount that is a maximum value of a fuel injection amount enabling a wall surface adhesion amount of injected fuel to be suppressed within an allowable range when fuel injection is started at the injection start timing. In performing multistage injection, the arithmetic processing circuit 32 sets the fuel injection amount at each stage so that it becomes equal to or smaller than a calculation value of the maximum injection amount in the arithmetic processing at each injection start timing.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a fuel injection control device that is applied to a direct injection engine. [Background technology]

[0002] A known fuel injection control device for a direct injection engine that injects fuel into the cylinder is described in Patent Document 1. In a direct injection engine that uses ethanol blended fuel, this fuel injection control device suppresses fuel dilution of the engine oil by injecting fuel in two separate injections when the ethanol concentration of the fuel is high. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-261231 Summary of the Invention [Problem to be solved by the invention]

[0004] When a direct injection engine is running cold, a large amount of fuel adheres to the cylinder walls and piston top after injection because it is not completely atomized. Because the adhered fuel does not contribute to combustion, the amount of fuel injected must be increased accordingly. Furthermore, there is a risk that emissions will worsen if the adhered fuel is discharged without being completely burned. [Means for solving the problem]

[0005] The fuel injection control device that solves the above problem is a device that controls fuel injection of an engine that injects fuel containing alcohol into cylinders, and is equipped with a calculation processing circuit that performs calculation processing based on the injection start timing to calculate a maximum injection amount, which is the maximum value of the fuel injection amount that can keep the amount of injected fuel adhering to the wall surface within an acceptable range when fuel injection is started at the injection start timing, and the calculation processing circuit is configured to set the fuel injection amount of each stage when performing multi-stage injection so that it is equal to or less than the calculated value of the maximum injection amount in the calculation processing for each injection start timing. [Effects of the Invention]

[0006] The above fuel injection control device has the effect of suppressing adhesion of fuel to the wall surface. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a diagram schematically illustrating a configuration of an embodiment of a fuel injection control device. [Figure 2] 4 is a flowchart of a process performed by the fuel injection control device during multi-stage injection. [Figure 3] 10A is a time chart showing an example of a setting mode of the injection period, and FIG. 10B and FIG. 10C are time charts showing an example and another example of an output mode of the injection command signal during multi-stage injection by the above-mentioned fuel injection control device, respectively. DETAILED DESCRIPTION OF THE INVENTION

[0008] An embodiment of a fuel injection control device will be described in detail below with reference to FIGS. <Engine 10 Configuration> First, the configuration of an engine 10 to be controlled by the fuel injection control device of this embodiment will be described with reference to Figure 1. The engine 10 is configured as an in-vehicle engine that uses alcohol-blended fuel, which is a mixture of gasoline and alcohol, as fuel. In the following description, the alcohol-blended fuel will be simply referred to as fuel.

[0009] The engine 10 includes a cylinder 12 in which a piston 11 is arranged to reciprocate, and an injector 13 that injects fuel into the cylinder 12. An intake passage 15 is connected to the cylinder 12 via an intake valve 14, and an exhaust passage 17 is connected to the cylinder 12 via an exhaust valve 16. A combustion chamber 18 is defined within the cylinder 12 by the piston 11. A mixture of intake air introduced through the intake passage 15 and fuel injected by the injector 13 is burned in the combustion chamber 18. An ignition device 19 that ignites the mixture by spark discharge is installed in the combustion chamber 18. An air flow meter 20 and a throttle valve 21 are installed in the intake passage 15. The air flow meter 20 is a sensor that detects the intake air flow rate GA of the intake passage 15. The throttle valve 21 is a valve for adjusting the intake air flow rate GA. The engine 10 also includes a variable valve mechanism 22 that varies the valve timing of the intake valve 14.

[0010] <Configuration of fuel injection control device> Next, the configuration of the fuel injection control device of this embodiment will be described with reference to Fig. 1. The engine 10 is controlled by an ECM (engine control module) 30. The ECM 30 controls the fuel injection of the engine 10 as part of the engine control. In this embodiment, the ECM 30 corresponds to the fuel injection control device.

[0011] The ECM 30 includes a memory 31 that stores engine control programs and data, and an arithmetic processing circuit 32 that reads and executes the programs from the memory 31. The ECM 30 receives detection results from various sensors that detect information related to the operating conditions of the engine 10 and the vehicle's running conditions. These sensors include the air flow meter 20 described above, as well as a crank angle sensor 33 and a water temperature sensor 34. The crank angle sensor 33 detects the rotation angle of a crankshaft 35, which is the output shaft of the engine 10. The water temperature sensor 34 detects the engine water temperature THW, which is the temperature of the coolant for the engine 10. The arithmetic processing circuit 32 calculates the engine speed NE, which is the rotation speed of the crankshaft 35, based on the detection result of the crank angle sensor 33. The arithmetic processing circuit 32 also calculates the intake air filling rate η of the combustion chamber 18 based on the detection result of the air flow meter 20, the calculation result of the engine speed NE, and the like.

[0012] The arithmetic processing circuit 32 calculates the operation amounts of the engine 10 according to the operating conditions of the engine 10 ascertained from the detection results of each sensor. The operation amounts include the throttle opening, which is the opening rate of the throttle valve 21, the ignition timing of the ignition device 19, the valve timing IVT of the intake valve 14, and the injection start and end timings of the injector 13. The ECM 30 controls the engine by operating the throttle valve 21, the ignition device 19, the variable valve mechanism 22, the injector 13, etc. based on the calculation results of the operation amounts by the arithmetic processing circuit 32.

[0013] <Multi-stage injection control> During cold operation of the engine 10, when the wall temperature of the cylinder 12 is low, some of the fuel injected from the injector 13 does not completely vaporize and remains liquid, adhering to the walls of the cylinder 12 and piston 11. Because alcohol is less likely to vaporize than gasoline, the engine 10 using alcohol-blended fuel experiences greater amounts of fuel adhering to the walls during cold operation than a gasoline engine. Much of the fuel that remains liquid and adheres to the walls does not contribute to the generation of engine output. Therefore, during cold operation of the engine 10, a fuel injection amount equal to the amount required to generate the required engine output plus the amount of fuel adhering to the walls is required. However, such an increase in the fuel injection amount worsens the fuel economy and emissions of the engine 10. The ECM 30 reduces fuel adhesion to the walls by performing multi-stage injection, in which fuel is injected multiple times during cold operation of the engine 10.

[0014] When performing multi-stage injection during cold operation, the ECM 30 first sets a plurality of divided injection periods as periods during which fuel can be injected, and then outputs an injection command signal to the injector 13 so that the required injection amount of fuel set according to the operating conditions of the engine 10 is injected within the set injection period.

[0015] 2 shows the processing procedure of the arithmetic processing circuit 32 for setting the injection possible period. The arithmetic processing circuit 32 repeatedly executes the processing of FIG. 2 at each predetermined control cycle while the engine 10 is running. 2, the calculation processing circuit 32 first reads in the parameters to be used in this process in step S100. The parameters to be read include the engine speed NE, the intake air flow rate GA, the target air-fuel ratio AF*, the valve timing IVT of the intake valve 14, and the engine water temperature THW.

[0016] Next, in step S110, the calculation processing circuit 32 determines whether the engine water temperature THW is equal to or lower than a predetermined cold state determination value. The cold state determination value is a set lower limit value of the engine water temperature THW that keeps the amount of fuel adhering to the wall surface within an allowable range without performing multi-stage injection. If the engine water temperature THW is equal to or lower than the cold state determination value (YES), the calculation processing circuit 32 proceeds to step S120, and if the engine water temperature THW exceeds the cold state determination value (NO), the calculation processing circuit 32 ends the processing of FIG. 2 for the current control cycle.

[0017] When the process proceeds to step S120, the arithmetic processing circuit 32 sets the value of the variable N to an initial value of "1" in step S120. Then, in the following step S130, the arithmetic processing circuit 32 sets the closing timing EVC of the exhaust valve 16 to the first-stage injection start timing SOI[1], and then proceeds to step S140.

[0018] In the following explanation, the Nth stage injection start timing will be referred to as "SOI[N]". The in-cylinder pressure at the Nth stage injection start timing SOI[N] will be referred to as "PC[N]", the maximum injection amount at the Nth stage will be referred to as "QM[N]", and the Nth stage injection period will be referred to as "TAU[N]".

[0019] In step S140, the calculation processing circuit 32 calculates the in-cylinder pressure PC[N] at the Nth stage injection start timing SOI[N]. The calculation of the in-cylinder pressure PC[N] is performed based on the injection start timing SOI[N], the engine rotation speed NE, the intake air flow rate GA, the valve timing IVT, etc.

[0020] Next, in step S150, the calculation processing circuit 32 calculates the maximum injection amount QM[N] for the Nth stage of fuel injection based on the injection start time SOI[N] and the in-cylinder pressure PC[N]. The maximum injection amount QM[N] represents the maximum value of the fuel injection amount that keeps the amount of injected fuel adhering to the wall surface within an acceptable range when fuel injection is started at the injection start time SOI[N]. Furthermore, in step S160, the calculation processing circuit 32 calculates the injection period TAU[N] of the injector 13 required to inject fuel equivalent to the maximum injection amount QM[N]. The lower the in-cylinder pressure PC[N], the more easily the fuel injected from the injector 13 vaporizes. Furthermore, the higher the position of the piston 11 in the cylinder 12 during fuel injection, the more easily the fuel injected from the injector 13 adheres to the top surface of the piston 11. Therefore, the calculation processing circuit 32 calculates the maximum injection amount QM[N] as a value that increases as the in-cylinder pressure PC[N] decreases and decreases as the position of the piston 11 at the injection start timing SOI[N] increases.

[0021] Next, in step S170, the arithmetic processing circuit 32 calculates the sum of the N-th stage injection start timing SOI[N], injection period TAU[N], and injection interval INT. Then, in step S170, the arithmetic processing circuit 32 determines whether the sum is greater than the compression stroke injection start timing SOIP. The arithmetic processing circuit 32 determines the compression stroke injection start timing SOIP based on the valve timing IVT, etc. The injection interval INT represents the minimum time from when the injector 13 completes fuel injection until the injector 13 can start the next fuel injection. The value of the injection interval INT is set as a constant determined by the mechanical characteristics of the injector 13. The sum (SOI[N] + TAU[N] + INT) represents the time when the next fuel injection can be started when the maximum injection amount QM[N] of fuel is injected in the N-th stage fuel injection. Such a positive determination (YES) in step S170 indicates that if fuel equivalent to the maximum injection amount QM[N] is injected in the Nth stage fuel injection, it will be impossible to start compression stroke injection at the start time SOIP. In contrast, a negative determination (NO) in step S170 indicates that compression stroke injection can be started at the start time SOIP even if fuel equivalent to the maximum injection amount QM[N] is injected in the Nth stage fuel injection.

[0022] If the determination in step S170 is negative, the calculation processing circuit 32 proceeds to step S180. In step S180, the calculation processing circuit 32 sets the N-stage injection end timing EOI[N] to a timing (=SOIP-INT) that is earlier than the compression stroke injection start timing SOIP by the injection interval INT. In this case, the longest period within the range in which compression stroke injection can be started at the start timing SOIP is set as the N-stage injection period. Then, the calculation processing circuit 32 ends the processing in FIG. 2 for the current control cycle.

[0023] On the other hand, if the determination in step S170 is affirmative, the arithmetic processing circuit 32 proceeds to step S190. In step S190, the arithmetic processing circuit 32 sets the time when the injection period TAU[N] has elapsed from the injection start time SOI[N] (=SOI[N]+TAU[N]) as the Nth-stage injection end time EOI[N]. In this case, the longest period (=TAU[N]) within the range that keeps the wall adhesion amount within an allowable range is set as the Nth-stage injection period. Next, in step S200, the arithmetic processing circuit 32 determines whether or not a second fuel injection can be performed before the compression stroke injection start time SOIP. In making this determination, the arithmetic processing circuit 32 first calculates the sum of the injection interval INT multiplied by two, the Nth-stage injection end time EOI[N], and the minimum injection period MIN. The minimum injection period MIN is the minimum value of the injection period of the injector 13. The sum represents the timing at which the next fuel injection can be started if fuel injection for the minimum injection period MIN is performed after the completion of the Nth stage fuel injection. If the sum is equal to or less than the compression stroke injection start time SOIP, the calculation processing circuit 32 determines that another fuel injection can be performed before the start time SOIP. If the calculation processing circuit 32 makes a negative determination (NO) in step S200, it ends the processing of FIG. 2 for the current control cycle.

[0024] On the other hand, if the determination in step S200 is affirmative (YES), the arithmetic processing circuit 32 proceeds to step S210. In step S210, the arithmetic processing circuit 32 sets the injection start timing SOI[N+1] of the (N+1)th stage to the time when the injection interval INT has elapsed since the Nth stage injection end timing EOI[N]. Then, in step S220, the arithmetic processing circuit 32 increments the value of "N" and then returns the process to step S140.

[0025] FIG. 3(a) shows an example of the injection period setting for multi-stage injection using the process of FIG. 2. In this example, k stages of injection periods are set during the intake stroke from the exhaust valve closing timing EVC to the compression stroke injection start timing SOIP. The injection periods of all k stages of fuel injections set before the compression stroke injection start timing SOIP, except for the last one, are set to the injection period TAU[N] calculated based on the injection start timing SOI[N] of each stage. The injection period of the kth stage of fuel injection is set to be equal to or shorter than the injection period TAU[k]. The injection period TAU[N] is set to the injection period of the injector 13 required to inject fuel equivalent to the maximum injection amount QM[N]. As described above, the maximum injection amount QM[N] represents the maximum fuel injection amount that can keep the wall adhesion amount of injected fuel within an acceptable range when fuel injection is started at the injection start timing SOI[N]. Furthermore, the injection periods of the fuel injections up to the kth stage are set at an interval equal to the injection interval INT. Furthermore, the injection end timing EOI[k] of the kth stage fuel injection is set so as to be spaced apart from the compression stroke injection start timing SOIP by an interval equal to or greater than the injection interval INT.

[0026] The arithmetic processing circuit 32 performs multi-stage injection by outputting an injection command signal to the injector 13 so as to inject fuel equivalent to the required injection amount Q* based on the injection period set in this manner. In the present embodiment, the arithmetic processing circuit 32 allocates the period for actually commanding fuel injection in order from the earliest to the latest of the injection periods set in the processing of Fig. 2 until the total amount of injection reaches the required injection amount Q*.

[0027] 3(b) and 3(c) show examples of the waveform of the injection command signal output by the arithmetic processing circuit 32 to the injector 13 for the injection period set as shown in FIG. 3(a). FIG. 3(b) shows the waveform of the injection command signal set when the total amount of fuel injection up to the jth stage exceeds the required injection amount Q*. FIG. 3(c) shows another example of the waveform of the injection command signal. FIG. 3(c) shows the waveform of the injection command signal when the total amount of fuel injection up to the kth stage set before the compression stroke injection start timing SOIP is less than the required injection amount Q*. In the case of FIG. 3(b), the arithmetic processing circuit 32 commands the injector 13 to inject fuel up to the (j-1)th stage by the maximum injection amount QM[N], and for the jth stage, by an amount such that the total amount of fuel injection is equal to the required injection amount Q*. In the case of FIG. 3(c), in addition to the fuel injection up to the kth stage set by the processing of FIG. 2, the arithmetic processing circuit 32 commands the injector 13 to inject fuel during the compression stroke injection period TP from the start timing SOIP. In this case, the arithmetic processing circuit 32 sets the compression stroke injection period TP so that the total amount of fuel injection becomes equal to the required injection amount Q*.

[0028] <Actions and Effects of the Embodiment> In the present embodiment configured as described above, the ECM 30 performs multi-stage injection when the engine coolant temperature THW is equal to or lower than the cold-state determination value. The calculation processing circuit 32 of the ECM 30 performs calculation processing to calculate the maximum injection amount QM[N] based on the fuel injection start timing SOI[N] during multi-stage injection (FIG. 2: S140, S150). The maximum injection amount QM[N] is calculated as the maximum fuel injection amount that keeps the amount of fuel adhering to the wall surface within an acceptable range when fuel injection is started at the injection start timing SOI[N]. The calculation processing circuit 32 then sets the fuel injection amount for each stage performed before the compression stroke injection start timing SOIP during multi-stage injection to be equal to or lower than the calculated maximum injection amount QM[N] for the respective injection start timing SOI[N]. Therefore, the amount of fuel adhering to the wall surface during each stage of fuel injection performed before the compression stroke injection start timing SOIP is kept within an acceptable range. Therefore, the fuel injection control device of this embodiment effectively suppresses fuel adhering to the wall surface. Furthermore, since the increase in the fuel injection amount required to compensate for the fuel adhering to the wall surface can be reduced, the fuel injection control device of this embodiment also has the effect of reducing fuel consumption of the engine 10. Reducing fuel consumption also reduces the amount of harmful exhaust components such as carbon dioxide emitted. Furthermore, the fuel that adheres to the wall surface will later burn incompletely, which can cause emissions to worsen. Therefore, the fuel injection control device of this embodiment also has the effect of reducing deterioration in the emissions performance of the engine 10.

[0029] (Other embodiments) This embodiment can be modified as follows: This embodiment and the following modifications can be combined and implemented within the scope of technical compatibility.

[0030] In the above embodiment, for intake stroke injection, which is performed before the start timing SOIP of compression stroke injection, the fuel injection amount for each stage is set so that it is equal to or less than the maximum injection amount QM[N] at each injection start timing SOI[N], thereby performing multi-stage injection. For fuel injection during the compression stroke, there is also a maximum injection amount, which is the maximum value of the fuel injection amount that keeps the wall adhesion amount of injected fuel within an acceptable range. This maximum injection amount can be calculated based on the injection start timing, etc. Therefore, for compression stroke injection, as with intake stroke injection, the maximum injection amount may be calculated based on the injection start timing, etc., and the fuel injection amount for each stage may be set so that it is equal to or less than the maximum injection amount, thereby performing multi-stage injection. During the compression stroke, the in-cylinder pressure increases as the piston 11 rises, while the temperature of the intake air in the cylinder 12 increases due to compression. The increased temperature of the intake air in the cylinder 12 makes the injected fuel more likely to vaporize. Therefore, the calculation of the maximum injection amount for compression stroke injection must take into account the effect of the increase in intake air temperature due to compression.

[0031] The amount of fuel adhering to the wall surface also varies depending on the temperature of the intake air before it enters the cylinder 12 and the wall temperature of the cylinder 12. Therefore, the maximum injection amount QM[M] may be calculated based on the intake air temperature, the engine water temperature THW, etc. in addition to the injection start timing SOI[N] and the in-cylinder pressure PC[N].

[0032] The calculation of the in-cylinder pressure PC[N] in step S140 of FIG. 2 may be omitted, and the maximum injection amount QM[N] may be calculated from the injection start timing SOI[N] in step S150.

[0033] In the above embodiment, the closing timing EVC of the exhaust valve 16 is set to the first stage injection start timing SOI[1], but it may be set to another timing. In the above embodiment, multi-stage injection is performed when the engine coolant temperature THW is equal to or lower than the cold determination value, but the conditions for performing multi-stage injection may be changed. [Explanation of symbols]

[0034] 10...engine, 12...cylinder, 13...injector, 30...ECM (fuel injection control device), 32...arithmetic processing circuit.

Claims

[Claim 1] A device for controlling fuel injection of an engine that injects fuel containing alcohol into a cylinder, comprising: a calculation processing circuit that performs calculation processing based on a fuel injection start timing to calculate a maximum injection amount, which is a maximum value of the fuel injection amount that can keep the amount of injected fuel adhering to a wall surface within an allowable range when fuel injection is started at the injection start timing, Furthermore, the calculation processing circuit sets the fuel injection amount for each stage when performing multi-stage injection so that it is equal to or less than the calculated value of the maximum injection amount in the calculation processing for each injection start timing. Fuel injection control device.

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