Fuel injection control device for internal combustion engines

Abstract

This suppresses the sudden decrease in the required injection volume when switching injection modes. [Solution] The internal combustion engine 10 includes a port injection valve 25 that injects fuel into an intake port 17 and an in-cylinder injection valve 26 that injects fuel into a combustion chamber 16. The control device 30 switches between a plurality of injection modes, each with a different ratio of the injection amount of the port injection valve 25 and the injection amount of the in-cylinder injection valve 26 to the requested injection amount, according to the operating conditions of the internal combustion engine 10. When the increase value used to increase the requested injection amount during a cold start decreases with the switching of the injection mode, the control device 30 performs a correction process that increases the requested injection amount more than the correction by the increase value until a predetermined period has elapsed since the injection mode was switched.

Description

Technical Field

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

Background Art

[0002] During cold operation of an internal combustion engine, part of the injected fuel does not contribute to combustion due to fuel adhesion to the wall surface or the like. Therefore, the required injection amount is increased. On the other hand, as seen in Patent Document 1, there is known an internal combustion engine provided with two types of fuel injection valves, a port injection valve that injects fuel into the intake port and an in-cylinder injection valve that injects fuel into the combustion chamber, and that switches injection modes with different injection ratios between in-cylinder injection and port injection.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When the increment value for incrementally correcting the required injection amount decreases with the switching of the injection mode, the required injection amount decreases after the switching of the injection mode. It is desirable to suppress such a rapid decrease in the required injection amount at the time of switching the injection mode.

Means for Solving the Problems

[0005] The fuel injection control device for an internal combustion engine that solves the above problems is applied to an internal combustion engine equipped with a port injection valve that injects fuel into an intake port and an in-cylinder injection valve that injects fuel into a combustion chamber, and switches between a plurality of injection modes, each having a different ratio of the injection amount of the port injection valve and the injection amount of the in-cylinder injection valve to the required injection amount, according to the operating conditions of the internal combustion engine. If the increase value used to increase the required injection amount during a cold start decreases with the switching of the injection mode, this fuel injection control device performs a correction process that increases the required injection amount more than the correction by the increase value until a predetermined period has elapsed since the injection mode was switched. [Effects of the Invention]

[0006] This fuel injection control device for internal combustion engines can suppress the abrupt decrease in the required injection amount when switching injection modes. [Brief explanation of the drawing]

[0007] [Figure 1] Figure 1 is a schematic diagram showing the configuration of an internal combustion engine to which one embodiment of a fuel injection control device is applied. [Figure 2] Figure 2 is a timing chart showing the changes in correction values ​​when switching injection modes. [Figure 3] Figure 3 is a flowchart showing the procedure of processing performed by the control device of the same embodiment. [Modes for carrying out the invention]

[0008] An embodiment of a fuel injection control device will be described below with reference to Figures 1 to 3. <Configuration of an internal combustion engine> First, with reference to Figure 1, the configuration of the internal combustion engine 10 to which the control device 30, which is the fuel injection control device of this embodiment, is applied will be described.

[0009] The internal combustion engine 10 includes a cylinder 12 in which a piston 11 is housed so as to be reciprocable. The piston 11 is connected to a crankshaft 14 via a connecting rod 13, and this connecting structure functions as a crank mechanism that converts the reciprocating motion of the piston 11 into the rotational motion of the crankshaft 14. In addition, a crank angle sensor 15 is installed near the crankshaft 14 in the internal combustion engine 10, which outputs a pulsed signal, a crank angle signal CR, in accordance with the rotation of the crankshaft 14.

[0010] Inside the cylinder 12, a combustion chamber 16 is partitioned by a piston 11. An intake pipe 18 is connected to the combustion chamber 16 via an intake port 17. An exhaust pipe 20 is also connected to the combustion chamber 16 via an exhaust port 19. An intake valve 21, which opens and closes in conjunction with the rotation of the crankshaft 14, is installed at the connection point between the intake port 17 and the combustion chamber 16. An exhaust valve 22, which opens and closes in conjunction with the rotation of the crankshaft 14, is installed at the connection point between the exhaust port 19 and the combustion chamber 16.

[0011] The intake manifold 18 is equipped with an airflow meter 23 for detecting the intake air volume GA, which is the flow rate of intake air sent to the combustion chamber 16 through the intake manifold 18, and a throttle valve 24, which is a valve for adjusting the intake air volume. The intake port 17 is equipped with a port injection valve 25 for injecting fuel into the intake air passing through the intake port 17. Furthermore, the combustion chamber 16 is equipped with an in-cylinder injection valve 26 for injecting fuel into the combustion chamber 16 and a spark plug 27 for igniting the fuel by spark discharge.

[0012] The control device 30 in this embodiment is configured as a fuel injection control device that controls the port injection valve 25 and the in-cylinder injection valve 26 in the internal combustion engine 10. The control device 30 has a processing circuit that includes a CPU that executes processing according to a program and a ROM in which the program is stored. The control device 30 performs various controls by having the CPU execute the program stored in the ROM of the processing circuit.

[0013] The control device 30 receives the detection signal of the intake air volume GA and the crank angle signal CR, among other inputs. The control device 30 also receives the detection signal of the water temperature sensor 29, which detects the coolant temperature THW of the internal combustion engine 10. The control device 30 calculates the engine speed NE of the internal combustion engine 10 based on the crank angle signal CR. Furthermore, the control device 30 calculates the engine load ratio KL based on the engine speed NE and the intake air volume GA. The engine load ratio KL is expressed as the ratio of the cylinder inflow air volume, which is the amount of air flowing into the combustion chamber 16, to the value of the internal combustion engine 10 under full load.

[0014] <Regarding fuel injection control performed during startup> The following describes the fuel injection control performed by the control device 30 during the cold start of the internal combustion engine 10. Hereinafter, "cold start" refers to the period from when the internal combustion engine 10 is started while the coolant temperature THW is below a specified temperature until the coolant temperature THW reaches the same specified temperature.

[0015] The control device 30 switches between multiple injection modes, each with a different ratio of the injection amount from the port injection valve 25 and the injection amount from the in-cylinder injection valve 26 to the required injection amount QINJ, according to the operating conditions of the internal combustion engine 10.

[0016] Hereinafter, the type of injection mode in the control device 30 is represented by an array (n, m) having two elements. The first element n of this array representing the type of injection mode represents the number of injections (port injections) performed by the port injection valve 25 in that injection mode, and the second element m represents the number of fuel injections (in-cylinder injections) performed by the in-cylinder injection valve 26 in that injection mode. For example, if the number of port injections is 1 and the number of in-cylinder injections is 2, the array (n, m) will be (1, 2).

[0017] During a cold start of the internal combustion engine 10, the following injection modes are used: port injection mode, selective injection mode, single cylinder injection mode, and multi-injection mode. These injection modes are switched in a predetermined order as the internal combustion engine 10 warms up.

[0018] In the port injection mode, fuel corresponding to the required injection quantity QINJ is injected by one-time port injection. Further, in the split injection mode, the fuel corresponding to the required injection quantity QINJ is divided and injected, for example, into one-time port injection and one to three times of in-cylinder injection. In the single in-cylinder injection mode, the fuel corresponding to the required injection quantity QINJ is injected by one-time in-cylinder injection. In the multi in-cylinder injection mode, it is divided and injected into a plurality of times of in-cylinder injection of the required injection quantity QINJ. Note that in the multi in-cylinder injection mode, for example, there are cases where in-cylinder injection is performed twice and three times. In the following, the former is described as the in-cylinder twice injection mode and the latter as the in-cylinder three times injection mode for distinction.

[0019] Further, in the following, the ratio of the port injection quantity, which is the injection quantity of port injection with respect to the required injection quantity QINJ, is described as the port injection rate KPI. The value of the port injection rate KPI becomes 1 in the port injection mode, and becomes 0 in the single in-cylinder injection mode, the in-cylinder twice injection mode, and the in-cylinder three times injection mode. Also, in the split injection mode, the value of the port injection rate KPI is a value that changes between 0 and 1 according to the ratio of the distribution of the fuel injection quantities of port injection and in-cylinder injection.

[0020] The control device 30 selects an injection mode to be implemented in the internal combustion engine 10 based on the engine rotational speed NE, the engine load ratio KL, the coolant water temperature THW, and the like. Further, the control device 30 also calculates the port injection rate KPI based on the engine rotational speed NE, the engine load ratio KL, the coolant water temperature THW, and the like.

[0021] The control device 30 calculates a basic injection quantity QBSE based on the engine rotational speed NE and the engine load ratio KL and the like. The value of the basic injection quantity QBSE calculated here represents the amount of fuel to be burned in the combustion chamber 16.

[0022] The control device 30 calculates an increment value FWLB, a switching-time increment value FWLBTRN, and other various correction values as correction values for increasing the fuel injection quantity performed at the cold start of the internal combustion engine 10.

[0023] The fuel injection increase value FWLB and the fuel injection increase value FWLBTRN at the time of switching are as follows. Specifically, a portion of the fuel injected from the port injection valve 25 adheres to the walls of the intake port 17 and intake valve 21, and a portion of the fuel injected from the in-cylinder injection valve 26 adheres to the walls of the cylinder 12 and piston 11. During cold starts, the temperature of these walls is low, and more fuel adheres to the walls. The fuel injection increase value FWLB is a correction value used to increase the fuel injection amount to account for the fuel that does not contribute to combustion due to this wall adhesion. The fuel injection increase value FWLB is set in advance for each injection mode, and when the injection mode is switched, the fuel injection increase value FWLB is also switched to the value corresponding to the injection mode.

[0024] Furthermore, the switching-time increase value FWLBTRN is a correction value that compensates for the transient change in the amount of material adhering to the wall immediately after switching the spray mode. The calculation of the switching-time increase value FWLBTRN will be described later.

[0025] The control device 30 calculates the required injection amount QINJ based on the following equation (1). QINJ=QBASE×(1+FWLB+FWLBTRN+Kn)…(1) QINJ:Required injection amount QBASE: Basic injection amount FWLB: Weight gain FWLBTRN: Increased value at switchover Kn: Other various correction values The correction performed using the above-mentioned increase value FWLBTRN during switching corresponds to a correction process that increases the required injection amount QINJ compared to the correction performed using the increase value FWLB.

[0026] The control device 30 sets the port injection amount and the in-cylinder injection amount based on the injection mode, port injection rate KPI, and requested injection amount QINJ. The control device 30 then controls the port injection valve 25 and the in-cylinder injection valve 26 to inject the set amount of fuel.

[0027] Figure 2 shows an example of the changes in the increased fuel amount FWLB and the increased fuel amount FWLBTRN during injection mode switching while cold starting is being performed. At time t1, when the injection mode is switched from double injection mode to single injection mode, the control device 30 increases the increased amount FWLB by switching the increased amount FWLB(0,2) to FWLB(0,1). The control device 30 also assigns an initial value to the increased amount FWLBTRN at the time of switching. The calculation of this initial value will be described later.

[0028] The fuel enrichment value FWLBTRN at the time of switching is maintained at its initial value until one combustion cycle is performed in all cylinders of the internal combustion engine 10 (i.e., until the crankshaft 14 has rotated twice). When one combustion cycle occurs in all cylinders of the internal combustion engine 10 (time t2), the transition enrichment value FWLBTRN decreases as the number of combustion cycles in the internal combustion engine 10 increases. Specifically, for each predetermined crank angle relative to the intake top dead center, the transition enrichment value FWLBTRN is multiplied by the damping coefficient DEC, causing the transition enrichment value FWLBTRN to gradually decrease. When the transition enrichment value FWLBTRN decreases to below a predetermined value, its value is set to 0 (time t3).

[0029] At time t4, when the injection mode is switched from single-cylinder injection mode to double-cylinder injection mode, the control device 30 decreases the increased amount value FWLB by switching from increased amount value FWLB(0,1) to increased amount value FWLB(0,2). The control device 30 also assigns an initial value to the increased amount value FWLBTRN at the time of switching. The calculation of this initial value will be described later.

[0030] The switching-increase value FWLBTRN is maintained at its initial value until one combustion cycle is performed in all cylinders of the internal combustion engine 10 (i.e., until the crankshaft 14 has rotated twice).

[0031] When combustion occurs once in all cylinders of the internal combustion engine 10 (time t5), the transition enrichment value FWLBTRN decreases as the number of combustion cycles in the internal combustion engine 10 increases. That is, each time combustion occurs in a cylinder of the internal combustion engine 10, the transition enrichment value FWLBTRN is multiplied by the damping coefficient DEC, causing the transition enrichment value FWLBTRN to gradually decrease. When the transition enrichment value FWLBTRN decreases to below a default value, the value of the transition enrichment value FWLBTRN is set to 0 (time t6).

[0032] Figure 3 shows the procedure performed by the control device 30 to calculate the initial value of the injection mode increase value FWLBTRN and the damping coefficient DEC. The procedure shown in Figure 3 is performed prior to the injection mode switch when a switch mode switch request is made. In the following, the step number of each procedure is represented by a number preceded by "S".

[0033] When this process is started, the control device 30 determines whether the difference ΔFWLB is "0" or greater (S100). The difference ΔFWLB is the value obtained by subtracting the increase value FWLB before switching the injection mode from the increase value FWLB after switching the injection mode. If the difference ΔFWLB is "0" or greater, it means that the increase value FWLB increases with the switching of the injection mode. On the other hand, if the difference ΔFWLB is not "0" or greater, it means that the increase value FWLB decreases with the switching of the injection mode.

[0034] Then, if it is determined that the difference ΔFWLB is "0" or greater (S100: YES), the control device 30 calculates the fuel injection switching coefficient KFWLBTRN based on the current coolant temperature THW and the previous fuel injection value (S110). The previous fuel injection value is the fuel injection value FWLB before the injection mode switching. The control device 30 calculates the fuel injection switching coefficient KFWLBTRN by referring to a two-dimensional map that shows the correspondence between the coolant temperature THW, the previous fuel injection value and the fuel injection switching coefficient KFWLBTRN, for example.

[0035] When the process in S110 is executed, the control device 30 then calculates the initial value of the switching-time increase value FWLBTRN (S120). In the process in S120, the control device 30 calculates a value obtained by multiplying the difference ΔFWLB by the increase-time switching coefficient KFWLBTRN. Then, it substitutes this calculated value into the initial value of the switching-time increase value FWLBTRN. In the example shown in Figure 2, the initial value of the switching-time increase value FWLBTRN set at time t1 is "{FWLB(0,1) - FWLB(0,2)} × increase-time switching coefficient KFWLBTRN".

[0036] When the process in S120 is executed, the control device 30 then sets the damping coefficient DEC as described above (S130). In the process of S130, the control device 30 substitutes the damping coefficient KDEC for the damping coefficient DEC. The damping coefficient KDEC for damping is a value within the range greater than "0" and less than "1". This damping coefficient KDEC for damping is a suitable value for damping the switching-time damping value FWLBTRN, which is set when the damping value FWLB increases due to the switching of the injection mode, and is set in advance.

[0037] In the process of S100 described above, if it is determined that the difference ΔFWLB is not "0" or greater (S100: NO), the control device 30 calculates the reduction switching coefficient KFWLBTRNM based on the current coolant temperature THW (S140). The control device 30 calculates the reduction switching coefficient KFWLBTRNM by referring to a two-dimensional map that shows the correspondence between the coolant temperature THW and the reduction switching coefficient KFWLBTRNM, for example.

[0038] When the process in S140 is executed, the control device 30 then calculates the initial value of the switching-time increase value FWLBTRN (S150). In the process in S150, the control device 30 calculates the absolute value of the difference ΔFWLB multiplied by the reduction-time switching coefficient KFWLBTRNM. Then, it substitutes this calculated value into the initial value of the switching-time increase value FWLBTRN. In the example shown in Figure 2, the initial value of the switching-time increase value FWLBTRN set at time t4 is "|{FWLB(0,2) - FWLB(0,1)} × reduction-time switching coefficient KFWLBTRNM|".

[0039] When the process in S150 is executed, the control device 30 then sets the damping coefficient DEC as described above (S160). In the process in S160, the control device 30 substitutes the damping coefficient KDECM during weight reduction into the damping coefficient DEC. The damping coefficient KDECM during weight reduction is a value within the range greater than "0" and less than "1". This damping coefficient KDECM during weight reduction is a suitable value for dampening the switching-time increase value FWLBTRN, which is set when the increase value FWLB decreases due to the switching of the injection mode, and is set in advance. In this embodiment, the damping coefficient KDECM during weight reduction and the damping coefficient KDEC during weight increase are different values, but they may be set to the same value.

[0040] When the process in S130 or S160 is completed, the control device 30 terminates this process. <Operation and Effects of This Embodiment> (1) When the increase value FWLB, which corrects the required injection amount QINJ by increasing it during a cold start, decreases with the switching of the injection mode, the required injection amount QINJ decreases after the switching of the injection mode. Here, when the injection mode is switched, the fuel injection timing changes, so the part of the wall to which the fuel adheres changes. Therefore, immediately after the switching of the injection mode, the amount of fuel adhering to the wall increases. Consequently, from the time the injection mode is switched until the amount of fuel adhering to the wall stabilizes, the amount of fuel that does not contribute to combustion increases. Therefore, there is a risk that the amount of fuel contributing to combustion will be insufficient and the air-fuel ratio will become lean. For these reasons, when the increase value FWLB, which corrects the required injection amount QINJ by increasing it, decreases with the switching of the injection mode, it is desirable to suppress a sharp decrease in the required injection amount QINJ.

[0041] Therefore, in this embodiment, if the increase value FWLB, which is used to increase the required injection amount QINJ, decreases with the switching of the injection mode, the following process is performed. That is, until a predetermined period has elapsed since the injection mode was switched, a correction process is performed that increases the required injection amount QINJ rather than the correction by the increase value FWLB. More specifically, in addition to the correction by the increase value FWLB, a correction is also performed by the switching-time increase value FWLBTRN described above. This correction by the switching-time increase value FWLBTRN is performed until the switching-time increase value FWLBTRN decays to "0". This correction process suppresses a sharp decrease in the required injection amount QINJ, thereby compensating for the shortage of fuel contributing to combustion immediately after the injection mode is switched, and also suppressing the leaning of the air-fuel ratio described above.

[0042] (2) The switching-time increase value FWLBTRN, which is the amount of correction for the increase in the required injection amount QINJ due to the above correction process, is attenuated as the number of combustion cycles of the internal combustion engine 10 increases. Therefore, it is possible to suppress sudden changes in the required injection amount QINJ due to sudden changes in the switching-time increase value FWLBTRN.

[0043] Furthermore, the value of the transition increment value FWLBTRN is adjusted using the attenuation coefficient DEC. Therefore, compared to the case where the transition increment value FWLBTRN is not attenuated, that is, the transition increment value FWLBTRN is maintained at a predetermined initial value for a specified period and then immediately set to "0", it becomes easier to optimize the transition increment value FWLBTRN.

[0044] (3) In order to calculate the initial value of the increase value FWLBTRN during switching, the increase switching coefficient KFWLBTRN and the decrease switching coefficient KFWLBTRNM are set. Therefore, the initial value of the increase value FWLBTRN during switching when the increase value FWLB increases with the switching of the injection mode, and the initial value of the increase value FWLBTRN during switching when it decreases, can be set to optimal values, respectively.

[0045] (4) The damping coefficient DEC is set to include an increasing damping coefficient KDEC and a decreasing damping coefficient KDECM. Therefore, the increasing damping coefficient KDEC and the decreasing damping coefficient KDECM can be set to optimal values.

[0046] <Example of changes> The above embodiment can be implemented with the following modifications. The above embodiment and the following modifications can be combined with each other to the extent that they do not contradict each other technically.

[0047] • The value of the transition increment value FWLBTRN was reduced using the attenuation coefficient DEC, but this attenuation process can be omitted. In other words, the transition increment value FWLBTRN can be maintained at the default initial value for a specified period and then immediately set to "0".

[0048] Figure 2 illustrates an example where the injector boost value FWLB, which increases the required injection amount QINJ during cold starts, decreases with the switching of injection modes. This example shows the case when the injection mode is switched from single-cylinder injection mode to double-cylinder injection mode. Other examples of this include cases where the number of injections in the in-cylinder injection mode increases due to the switching of injection modes, or when switching from port injection mode to multi-cylinder injection mode. [Explanation of Symbols]

[0049] 10... Internal combustion engine 11… Piston 12... Cylinder 13…Connecting rod 14…Crankshaft 15... Crank angle sensor 16… Combustion chamber 17…Intake port 18…Intake pipe 19... Exhaust port 20... Exhaust pipe 21…Intake valve 22... Exhaust valve 23... Airflow meter 24... Throttle valve 25…Port injection valve 26...In-cylinder injection valve 27... Spark plug 29...Water temperature sensor 30...Control device

Claims

1. A fuel injection control device applied to an internal combustion engine equipped with a port injection valve for injecting fuel into an intake port and an in-cylinder injection valve for injecting fuel into a combustion chamber, which switches between a plurality of injection modes having different ratios of the injection amount of the port injection valve and the injection amount of the in-cylinder injection valve to the required injection amount, according to the operating conditions of the internal combustion engine, If the increase value used to correct the requested injection amount during a cold start decreases with the switching of the injection mode, a correction process that increases the requested injection amount more than the correction using the increase value will be executed until a predetermined period has elapsed since the injection mode was switched. Fuel injection control device for internal combustion engines.

2. The correction amount for the increase in the required injection amount due to the correction process is reduced as the number of combustion cycles of the internal combustion engine increases. A fuel injection control device for an internal combustion engine according to claim 1.

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