JP2024075344A - Control device for internal combustion engine - Google Patents

Abstract

[Problem] To provide a control device for an internal combustion engine that can make the air-fuel ratio leaner while suppressing torque differences that occur between cylinders. [Solution] An engine control module executes knocking control that detects the presence or absence of knocking in each cylinder and changes the ignition timing, and executes air-fuel ratio control that changes the fuel increase rate based on the results of the knocking control. At this time, if the difference in air-fuel ratio between the cylinders is greater than a predetermined value, the engine control module limits the fuel increase rate so that the air-fuel ratio of the cylinder being controlled shifts to the predetermined value. [Selected Figure] Figure 10

Description

The present invention relates to a control device for an internal combustion engine that performs knocking control and air-fuel ratio control.

As described in JP 64-63638 A (Patent Document 1), an internal combustion engine control device performs knocking control to retard the ignition timing when knocking occurs, while also performing air-fuel ratio control to make the air-fuel ratio leaner based on the results of the knocking control to improve fuel efficiency.

Japanese Patent Application Laid-Open No. 64-63638

However, in the technology described in Patent Document 1, the ignition timing and air-fuel ratio were changed independently for each cylinder, which could lead to, for example, large variations in the air-fuel ratio in each cylinder, which could cause large differences in torque between the cylinders. If a large difference in torque between the cylinders occurs, for example, the engine rotation could pulsate, which could cause large engine surges (vibrations).

The present invention aims to provide a control device for an internal combustion engine that can make the air-fuel ratio leaner while suppressing torque differences that occur between cylinders.

The control device of the internal combustion engine detects the presence or absence of knocking in each cylinder and executes knocking control to change the ignition timing, and executes air-fuel ratio control to change the fuel increase rate based on the results of the knocking control. At this time, if the difference in air-fuel ratio between the cylinders is greater than a predetermined value, the control device of the internal combustion engine limits the fuel increase rate so that the air-fuel ratio of the cylinder being controlled shifts to the predetermined value.

According to the present invention, in an internal combustion engine control device, it is possible to make the air-fuel ratio leaner while suppressing torque differences that occur between cylinders.

FIG. 1 is a schematic diagram showing an example of a control system for a four-stroke engine. FIG. 4 is a plan view showing an example of a crank signal plate. FIG. 4 is a plan view showing an example of a cam signal plate. 5 is a flowchart showing an example of a fuel injection amount setting process. 4 is a flowchart showing an example of a fuel injection execution process. 5 is a flowchart showing an example of an ignition timing setting process. 4 is a flowchart showing an example of a fuel ignition execution process. 5 is a flowchart showing an example of a fuel increase rate setting process. 5 is a flowchart showing a first embodiment of a subroutine for limiting a fuel increase rate. 6 is an explanatory diagram of the action of a fuel increase rate setting process including a subroutine according to the first embodiment; FIG. 10 is a flowchart showing a second embodiment of a subroutine for limiting a fuel increase rate; 13 is an explanatory diagram of the action of a fuel increase rate setting process including a subroutine according to the second embodiment; FIG. 10 is a flowchart showing a third embodiment of a subroutine for limiting a fuel increase rate; FIG. 13 is an explanatory diagram of the action of a fuel increase rate setting process including a subroutine according to the third embodiment. 13 is a flowchart showing a fourth embodiment of a subroutine for limiting a fuel increase rate. FIG. 13 is an explanatory diagram of the action of a fuel increase rate setting process including a subroutine according to the fourth embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 shows an example of a control system for a four-stroke engine mounted on a vehicle such as an automobile.

The engine (internal combustion engine) 100 has a cylinder block 110, a piston 120, a crankshaft 130, a connecting rod 140, and a cylinder head 150. The cylinder block 110 is formed with a cylinder bore 110A into which the piston 120 is fitted so as to be able to reciprocate. The crankshaft 130 is disposed below the cylinder block 110 via a bearing (not shown) so as to be able to rotate relative to the cylinder block 110. The piston 120 is connected to the crankshaft 130 via the connecting rod 140.

The cylinder head 150 is formed with an intake port 150A for introducing intake air and an exhaust port 150B for discharging exhaust air. The cylinder head 150 is fastened to the upper surface of the cylinder block 110, so that the area defined by the cylinder bore 110A of the cylinder block 110, the crown surface of the piston 120, and the lower surface of the cylinder head 150 functions as a combustion chamber 160. An intake valve 180 that is opened and closed by an intake camshaft 170 is disposed at the open end of the intake port 150A facing the combustion chamber 160. An exhaust valve 200 that is opened and closed by an exhaust camshaft 190 is disposed at the open end of the exhaust port 150B facing the combustion chamber 160.

An electromagnetic fuel injection valve 210 that injects fuel directly into the combustion chamber 160 and an ignition plug 220 that ignites the mixture of fuel and intake air are attached to predetermined locations of the cylinder head 150 facing the combustion chamber 160. Note that the fuel injection valve 210 is not limited to a configuration that directly injects fuel into the combustion chamber 160, but may also be a configuration that injects fuel toward the intake port 150A, or a configuration that has both.

The crank signal plate 230 is attached to the end of the crankshaft 130. As shown in FIG. 2, the crank signal plate 230 is a detectable member that is an integrated member of a disk-shaped plate portion 230A and a plurality of teeth 230B that extend radially outward from the outer circumferential end of the plate portion 230A at any predetermined angle. In addition, the crank signal plate 230 has a tooth-missing portion 230C that defines the angle reference at a crank angle of 360° formed by missing a part of the tooth portion 230B. Here, in the example of the crank signal plate 230 shown in FIG. 2, two teeth 230B are missing to form the tooth-missing portion 230C, but any number of teeth 230B may be missing to form the tooth-missing portion 230C.

A crank angle sensor 240 is attached to the lower part of the cylinder block 110 at a predetermined location facing the outer circumferential edge of the crank signal plate 230. The crank angle sensor 240 detects the teeth 230B of the crank signal plate 230 and outputs a pulse-like crank signal CRS.

A cam signal plate 250 is attached to the end of the intake camshaft 170. As shown in FIG. 3, the cam signal plate 250 is a detectable member that is an integrated member of a disk-shaped plate portion 250A and an arc-shaped extension portion 250B that extends radially outward from a portion of the outer periphery of the plate portion 250A.

In addition, a cam angle sensor 260 is attached to a predetermined location on the upper part of the cylinder head 150 facing the outer circumferential end of the cam signal plate 250, which detects the extension portion 250B of the cam signal plate 250 and outputs a rectangular cam signal CMS. The extension portion 250B of the cam signal plate 250 is provided so that, for example, at the two tooth missing positions where the crank angle sensor 240 detects the tooth missing portion 230C of the crank signal plate 230 during two rotations of the crankshaft 130, a LOW signal is output at the tooth missing position of the first rotation and a HIGH signal is output at the tooth missing position of the second rotation. Therefore, the cam angle sensor 260 outputs different levels of cam signal CMS depending on whether or not it detects the extension portion 250B of the cam signal plate 250.

Therefore, by monitoring this cam signal CMS, it is possible to distinguish whether the crankshaft 130, which rotates at twice the rotational speed of the intake camshaft 170, is rotating in its first rotation (0°-360°), which corresponds to the 0°-180° of the intake camshaft 170, or in its second rotation (360°-720°), which corresponds to the 180°-360° of the intake camshaft 170. In other words, while the intake camshaft 170 makes one rotation, it is possible to distinguish whether the crankshaft 130 is rotating in its first rotation or in its second rotation.

The cam signal plate 250 and the cam angle sensor 260 are not limited to being provided on the intake camshaft 170, but may also be provided on the exhaust camshaft 190. The cam signal plate 250 is not limited to the shape shown in FIG. 3, and may have any shape as long as it can output signals of different levels at the tooth-missing position on the first rotation and the tooth-missing position on the second rotation.

The crank signal CRS of the crank angle sensor 240 and the cam signal CMS of the cam angle sensor 260 are input to an engine control module (ECM) 270 incorporating a microcomputer 270A. In addition to the output signals of the crank angle sensor 240 and the cam angle sensor 260, the engine control module 270 also receives the output signals of a rotation speed sensor 280 for detecting the rotation speed Ne of the engine 100, a load sensor 290 for detecting the load Q of the engine 100, a water temperature sensor 300 for detecting the water temperature Tw of the engine 100, an air-fuel ratio sensor 310 for detecting the air-fuel ratio ABF in the exhaust gas, a voltage sensor 320 for detecting the terminal voltage VB of a battery (not shown), and a knock sensor 330 for outputting a knock signal KNS that indicates the magnitude of vibration caused by knocking. Here, as the load Q of the engine 100, for example, a state quantity closely related to the required torque, such as an intake flow rate, an intake negative pressure, a supercharging pressure, an accelerator opening, or a throttle opening, can be used. The engine control module 270 is an example of a control device for an internal combustion engine.

The engine control module 270 executes application programs stored in the non-volatile memory (not shown) of the microcomputer 270A to electronically control the fuel injection valve 210 and the spark plug 220 in response to the output signals of the crank angle sensor 240, the cam angle sensor 260, the rotational speed sensor 280, the load sensor 290, the water temperature sensor 300, the air-fuel ratio sensor 310, the voltage sensor 320, and the knock sensor 330, as described in detail below.

Figure 4 shows an example of a fuel injection amount setting process that is repeatedly executed at predetermined time intervals by the microcomputer 270A of the engine control module 270 (hereinafter abbreviated as "engine control module 270") when the engine 100 is started.

In step 10 (abbreviated as "S10" in FIG. 4, and the same applies below), the engine control module 270 reads the rotation speed Ne of the engine 100 from the rotation speed sensor 280. Note that instead of reading the rotation speed Ne from the rotation speed sensor 280, the engine control module 270 may calculate the rotation speed Ne based on the crank signal CRS of the crank angle sensor 240.

In step 11 , the engine control module 270 reads the load Q of the engine 100 from the load sensor 290 .
In step 12, the engine control module 270 refers to a map in which fuel injection timing suited to the rotation speed and load of the engine 100 is preset, and sets the fuel injection timing according to the rotation speed Ne and load Q of the engine 100. Here, the fuel injection timing can be, for example, a rotation angle of the crankshaft 130 from a reference angle.

In step 13, the engine control module 270 calculates a basic fuel injection amount Tp corresponding to the rotation speed Ne and load Q of the engine 100, for example, by referring to a map in which a basic fuel injection amount suitable for the rotation speed and load of the engine 100 is preset.
In step 14 , the engine control module 270 reads the water temperature Tw of the engine 100 from the water temperature sensor 300 .

In step 15, the engine control module 270 refers to a map in which correction coefficients suited to the rotation speed and water temperature of the engine 100 are preset, and sets a correction coefficient Co according to the rotation speed Ne and water temperature Tw of the engine 100. Note that the engine control module 270 may set the correction coefficient Co taking into account, for example, the time of starting, acceleration, etc., in addition to the rotation speed Ne and water temperature Tw of the engine 100.

In step 16, the engine control module 270 reads the battery terminal voltage VB from the voltage sensor 320.
In step 17, the engine control module 270 refers to a map in which a voltage correction amount suited to the terminal voltage of the battery is preset, and calculates a voltage correction amount Ts according to the terminal voltage VB of the battery. That is, taking into consideration that the fuel injection valve 210 has an operation delay time from receiving a drive signal to actually injecting fuel, the engine control module 270 calculates a voltage correction amount Ts for correcting the operation delay caused by the terminal voltage VB of the battery.

In step 18, the engine control module 270 calculates the fuel injection amount Ti by substituting the basic fuel injection amount Tp, the correction coefficient Co, and the voltage correction amount Ts into the formula "fuel injection amount Ti = 2 x basic fuel injection amount Tp x air-fuel ratio feedback coefficient α x air-fuel ratio learning control coefficient K x correction coefficient Co x fuel increase rate TFBA + voltage correction amount Ts". Here, the air-fuel ratio feedback coefficient α and the air-fuel ratio learning control coefficient K are well known to those skilled in the art, so detailed explanations are omitted. The fuel increase rate TFBA is a parameter that indicates the rate at which the air-fuel ratio is enriched due to the occurrence of knocking, and is set by the fuel increase rate setting process described later. After that, the engine control module 270 ends the fuel injection amount setting process for the current control cycle.

According to this fuel injection amount setting process, the engine control module 270 sets the fuel injection timing and calculates the basic fuel injection amount Tp according to the rotation speed Ne and load Q of the engine 100. Furthermore, the engine control module 270 calculates the fuel injection amount Ti by appropriately correcting the basic fuel injection amount Tp using the engine 100 water temperature Tw and the battery terminal voltage VB as parameters in addition to the engine 100 rotation speed Ne and load Q. Therefore, the fuel injection timing and fuel injection amount Ti obtained in this manner are suitable for the operating state of the engine 100.

Figure 5 shows an example of a fuel injection execution process that is executed each time the crankshaft 130 rotates a predetermined angle. Here, the predetermined angle can be, for example, 1 degree, taking into account the fuel injection accuracy. Furthermore, as a premise for the fuel injection execution process, the engine control module 270 sequentially reads the crank signal CRS and the cam signal CMS from the crank angle sensor 240 and the cam angle sensor 260, and calculates the rotation angle of the crankshaft 130 based on the crank signal CRS and the cam signal CMS.

In step 20, the engine control module 270 determines whether or not it is time for fuel injection, in other words, whether or not the rotation angle of the crankshaft 130 has reached the rotation angle that represents the fuel injection timing. If the engine control module 270 determines that it is time for fuel injection (Yes), it advances the process to step 21. On the other hand, if the engine control module 270 determines that it is not time for fuel injection (No), it ends the fuel injection execution process for the current control cycle.

In step 21, the engine control module 270 outputs a drive signal corresponding to the fuel injection amount Ti to the fuel injection valve 210 to inject fuel from the nozzle hole of the fuel injection valve 210 into the combustion chamber 160. After that, the engine control module 270 ends the fuel injection execution process for the current control cycle.

According to this fuel injection execution process, when the rotation angle of the crankshaft 130 reaches the fuel injection timing, the engine control module 270 outputs a drive signal to the fuel injection valve 210 to inject fuel into the combustion chamber 160. Therefore, fuel is injected into the combustion chamber 160 of the engine 100 at a fuel injection timing that corresponds to the operating state of the engine 100, which can improve, for example, fuel efficiency, exhaust properties, and output.

Figure 6 shows an example of an ignition timing setting process that is repeatedly executed by the engine control module 270 at predetermined time intervals when the engine 100 is started. Here, the predetermined time that specifies the time interval for repeatedly executing the ignition timing setting process may be the same as the predetermined time for the fuel injection amount setting process, or may be different from this. In addition, processes similar to the above fuel injection amount setting process and fuel injection execution process will be explained briefly to avoid duplication. Please refer to the above explanation if necessary. The ignition timing setting process shown in Figure 6 includes knocking control.

In step 30 , the engine control module 270 reads the rotation speed Ne of the engine 100 from the rotation speed sensor 280 .
In step 31 , the engine control module 270 reads the load Q of the engine 100 from the load sensor 290 .

In step 32, the engine control module 270 sets the ignition timing ADA according to the rotation speed Ne and load Q of the engine 100, for example, by referring to a map in which the ignition timing suited to the rotation speed and load of the engine 100 is preset. Here, the ignition timing ADA can be, for example, the rotation angle from the reference angle of the crankshaft 130.

In step 33 , the engine control module 270 reads the water temperature Tw of the engine 100 from the water temperature sensor 300 .
In step 34 , the engine control module 270 corrects the ignition timing ADA based on the water temperature Tw of the engine 100 .

In step 35 , the engine control module 270 reads the knock signal KNS from the knock sensor 330 .
In step 36, the engine control module 270 determines whether or not knocking is occurring in the engine 100, for example, by determining whether or not the absolute value of the magnitude of the knock signal KNS is equal to or greater than a predetermined value. If the engine control module 270 determines that knocking is occurring in the engine 100 (Yes), the process proceeds to step 37. On the other hand, if the engine control module 270 determines that knocking is not occurring in the engine 100 (No), the process proceeds to step 38.

In step 37, the engine control module 270 retards the ignition timing ADA corrected in step 34 by a first predetermined value. The first predetermined value by which the ignition timing ADA is retarded can be determined appropriately, for example, taking into account the performance of the engine 100. After that, the engine control module 270 ends the ignition timing setting process for the current control cycle.

In step 38, the engine control module 270 advances the ignition timing ADA corrected in step 34 by a second predetermined value. The second predetermined value by which the ignition timing ADA is advanced can be determined appropriately, for example, taking into consideration the performance of the engine 100, and may be the same as the first predetermined value or may be different from the first predetermined value. After that, the engine control module 270 ends the ignition timing setting process for the current control cycle.

According to this ignition timing setting process, the engine control module 270 sets the ignition timing ADA according to the rotation speed Ne and load Q of the engine 100, and corrects the ignition timing ADA according to the water temperature Tw of the engine 100. The engine control module 270 then determines whether or not knocking has occurred from the output signal of the knock sensor 330, and if knocking has occurred, retards the ignition timing ADA by a first predetermined value, whereas if knocking has not occurred, advances the ignition timing ADA by a second predetermined value. Therefore, the ignition timing ADA determined in this manner is advanced to the limit at which knocking does not occur in the engine 100, and the output of the engine 100 can be improved.

Figure 7 shows an example of a fuel ignition execution process that is executed each time the crankshaft 130 rotates a predetermined angle.

In step 40, the engine control module 270 determines whether or not it is time to ignite fuel, in other words, whether or not the rotational angle of the crankshaft 130 has reached the ignition timing ADA. If the engine control module 270 determines that it is time to ignite fuel (Yes), it advances the process to step 41. On the other hand, if the engine control module 270 determines that it is not time to ignite fuel (No), it ends the fuel ignition execution process for the current control cycle.

In step 41, the engine control module 270 outputs a drive signal to the spark plug 220 to ignite the fuel-air mixture in the combustion chamber 160. When the mixture is ignited, the volume of the mixture in the combustion chamber 160 increases rapidly, causing the pressure to rise, and the piston 120 moves in the direction of the crankshaft 130, converting the reciprocating motion of the piston 120 into the rotational motion of the crankshaft 130. The engine control module 270 then ends the fuel ignition execution process for this control cycle.

According to this fuel ignition execution process, when the rotation angle of the crankshaft 130 reaches the ignition timing ADA, the engine control module 270 outputs a drive signal to the spark plug 220 to ignite the mixture. Therefore, the mixture present in the combustion chamber 160 is ignited at a fuel ignition timing that corresponds to the operating state of the engine 100, which can improve, for example, fuel economy, exhaust properties, and output.

Figure 8 shows an example of a fuel increase rate setting process that is repeatedly executed by the engine control module 270 at predetermined time intervals when the engine 100 is started. Here, the predetermined time that specifies the time interval for repeatedly executing the fuel increase rate setting process may be the same as the predetermined time for the fuel injection amount setting process or the ignition timing setting process, or may be different from these. Note that the fuel increase rate setting process shown in Figure 6 includes air-fuel ratio control.

In step 50 , the engine control module 270 reads the rotation speed Ne of the engine 100 from the rotation speed sensor 280 .
In step 51 , the engine control module 270 reads the load Q of the engine 100 from the load sensor 290 .

In step 52, the engine control module 270, for example, refers to a map in which the fuel increase rate suited to the rotation speed and load of the engine 100 is preset, and sets the fuel increase rate TFBA according to the rotation speed Ne and load Q of the engine 100. Here, the fuel increase rate TFBA is, for example, 1.0 when the fuel injection amount is not increased, and is a parameter that indicates how much the fuel injection amount is increased or decreased based on this.

In step 53 , the engine control module 270 reads the water temperature Tw of the engine 100 from the water temperature sensor 300 .
In step 54 , the engine control module 270 corrects the fuel increase rate TFBA based on the water temperature Tw of the engine 100 .

In step 55, the engine control module 270 corrects the fuel increase rate TFBA based on the result of the ignition timing setting process including knocking control. Specifically, the engine control module 270 determines whether the ignition timing ADA has been advanced or retarded in the ignition timing setting process including knocking control. If the engine control module 270 determines that the ignition timing ADA has been advanced, the engine control module 270 corrects the fuel increase rate TFBA to be reduced by a predetermined value to make the air-fuel ratio leaner. On the other hand, if the engine control module 270 determines that the ignition timing ADA has been retarded, the engine control module 270 returns the fuel increase rate TFBA to the fuel increase rate TFBA set and corrected according to the rotation speed Ne, load Q, and water temperature Tw of the engine 100 in order to stop making the air-fuel ratio leaner. Here, the predetermined value for reducing the fuel increase rate TFBA can be appropriately determined, for example, taking into consideration the characteristics of the engine 100.

In step 56, the engine control module 270 calls a subroutine to limit the fuel increase rate TFBA, which will be described below, and then ends the fuel increase rate setting process for the current control cycle. In the subroutine to limit the fuel increase rate TFBA, if the difference in the air-fuel ratio ABF between the cylinders is greater than a predetermined value, which will be described later, the engine control module 270 limits the fuel increase rate TFBA so that the air-fuel ratio ABF of the cylinder to be controlled shifts to a predetermined value, in other words, reduces the fuel increase rate TFBA. Note that this subroutine may be expanded into the fuel increase rate setting process shown in FIG. 8 (same below).

Figure 9 shows a first embodiment of a subroutine that limits the fuel increase rate TFBA. As a prerequisite for executing the subroutine according to the first embodiment, when the engine 100 has N cylinders, the volatile memory of the engine control module 270 has N-1 variable areas ABF_1 to ABF_N-1 secured therein for temporarily storing the air-fuel ratios of the previous N-1 cylinders that have been processed consecutively in time (same below). Note that the variable areas ABF_1 to ABF_N-1 are each initialized to "0" when the engine control module 270 is started (same below).

In step 60, the engine control module 270 refers to the variable ranges ABF_1 to ABF_N-1 and selects the maximum air-fuel ratio from among these as the reference value.
In step 61, the engine control module 270 reads the air-fuel ratio ABF from the air-fuel ratio sensor 310 as the air-fuel ratio of the cylinder to be controlled for which the fuel increase rate is to be limited.

In step 62, the engine control module 270 determines whether the absolute value of the value obtained by subtracting the reference value from the air-fuel ratio ABF read in step 61 is greater than a predetermined value. Here, the predetermined value is a threshold value for suppressing the variation in the air-fuel ratio in each cylinder, and can be, for example, a tolerable value of a surge caused by a torque step occurring between each cylinder, taking into account the characteristics of the engine 100. If the engine control module 270 determines that the absolute value of the value obtained by subtracting the reference value from the air-fuel ratio ABF is greater than the predetermined value (Yes), the process proceeds to step 63. On the other hand, if the engine control module 270 determines that the absolute value of the value obtained by subtracting the reference value from the air-fuel ratio ABF is equal to or less than the predetermined value (Yes), the process proceeds to step 64.

In step 63, the engine control module 270 limits the fuel increase rate TFBA so that the air-fuel ratio ABF of the cylinder to be controlled for which the fuel increase rate is to be limited shifts to a predetermined value, in other words, so that the difference between the reference value and the air-fuel ratio ABF becomes a predetermined value. Here, the limit value of the fuel increase rate TFBA may be set continuously or stepwise, for example, according to the difference between the air-fuel ratio ABF and the reference value. After that, the engine control module 270 proceeds to step 63. Note that the limit value of the fuel increase rate TFBA may be set continuously or stepwise, for example, according to the combustion torque of each cylinder estimated from the differential of the output signal of the crank angle sensor 240.

In step 64, the engine control module 270 updates the N-1 consecutive air-fuel ratios stored in the variable areas ABF_1 to ABF_N-1. Specifically, the engine control module 270 overwrites the air-fuel ratios stored in the variable areas ABF_2 to ABF_N-1 into ABF_1 to ABF_N-2, respectively, and overwrites the air-fuel ratio ABF read in step 61 into the variable area ABF_N-1. Therefore, the N-1 most recent consecutive air-fuel ratios are stored in the variable areas ABF_1 to ABF_N-1. The engine control module 270 then returns the process to the fuel increase rate setting process.

According to the fuel increase rate setting process including the subroutine of the first embodiment, the engine control module 270 sets the fuel increase rate TFBA according to the rotation speed Ne and load Q of the engine 100, and corrects the fuel increase rate TFBA according to the water temperature Tw of the engine 100. In addition, the engine control module 270 further corrects the fuel increase rate TFBA based on the result of the ignition timing setting process including knocking control, and calls a subroutine that limits the fuel increase rate TFBA.

In the subroutine for limiting the fuel increase rate TFBA, the engine control module 270 selects the maximum air-fuel ratio from among the previous N-1 cylinder air-fuel ratios for which the ignition timing setting process including knocking control and the fuel increase rate setting process including air-fuel ratio control have been executed as a reference value, and determines whether the absolute value of the value obtained by subtracting the reference value from the air-fuel ratio ABF of the cylinder to be controlled is greater than a predetermined value. If the absolute value of the value obtained by subtracting the reference value from the air-fuel ratio ABF is greater than the predetermined value, the engine control module 270 limits the fuel increase rate TFBA so that the air-fuel ratio ABF shifts to the predetermined value.

Therefore, the variation in the air-fuel ratio of each cylinder is reduced during two rotations of the crankshaft 130. This makes it difficult for large differences in torque to occur between the cylinders, and, for example, it is possible to suppress pulsation of engine rotation and large engine surges. In addition, because the fuel increase rate TFBA is changed to the limit at which knocking does not occur in the engine 100, the air-fuel ratio can be made leaner, improving fuel efficiency.

Consider an engine 100 with four cylinders, in which the ignition timing setting process including knocking control and the fuel increase rate setting process including air-fuel ratio control are executed in the order of cylinders #1, #2, #3, and #4 as shown in FIG. 10. When executing the ignition timing setting process and the fuel increase rate setting process for cylinder #4, as shown in the figure, the air-fuel ratio ABF of cylinder #1 to #3 with the largest air-fuel ratio ABF, for example, the air-fuel ratio ABF of cylinder #3 with the richest (largest) air-fuel ratio ABF, is selected as the reference value. Then, since the air-fuel ratio ABF of cylinder #4 is greater than a predetermined value based on the reference value, the fuel increase rate TFBA is limited so that the air-fuel ratio ABF is shifted to a predetermined value. By executing such a process, as described above, the variation in the air-fuel ratio of each cylinder is reduced, and the torque step generated between each cylinder can be reduced.

Figure 11 shows a second embodiment of a subroutine that limits the fuel increase rate TFBA. Here, the same or similar processing as in the first embodiment of the subroutine that limits the fuel increase rate TFBA will be explained briefly in order to avoid duplication (as below). If necessary, please refer to the previous explanation (as below).

In step 70, the engine control module 270 refers to the variable ranges ABF_1 to ABF_N-1 and selects the maximum air-fuel ratio from among these as the reference value.
In step 71, the engine control module 270 reads the air-fuel ratio ABF from the air-fuel ratio sensor 310 as the air-fuel ratio of the cylinder to be controlled for which the fuel increase rate is to be limited.

In step 72, the engine control module 270 determines whether the ignition timing ADA has been retarded by correction in the ignition timing setting process including the knocking control shown in FIG. 6. If the engine control module 270 determines that the ignition timing ADA has been retarded (Yes), the process proceeds to step 73. On the other hand, if the engine control module 270 determines that the ignition timing ADA has not been retarded (No), the process proceeds to step 76.

In step 73, the engine control module 270 determines whether or not the fuel increase rate TFBA has been corrected and increased in step 55 of the fuel increase rate setting process shown in FIG. 8 as a result of the ignition timing setting process including knocking control shown in FIG. 6 and FIG. 7. If the engine control module 270 determines that the fuel increase rate TFBA has been increased (Yes), the process proceeds to step 74. On the other hand, if the engine control module 270 determines that the fuel increase rate TFBA has not been increased (No), the process proceeds to step 76.

In step 74, the engine control module 270 determines whether the absolute value of the value obtained by subtracting the reference value from the air-fuel ratio ABF read in step 71 is greater than a predetermined value. If the engine control module 270 determines that the absolute value of the value obtained by subtracting the reference value from the air-fuel ratio ABF is greater than the predetermined value (Yes), the process proceeds to step 75. On the other hand, if the engine control module 270 determines that the absolute value of the value obtained by subtracting the reference value from the air-fuel ratio ABF is equal to or less than the predetermined value (No), the process proceeds to step 76.

In step 75, the engine control module 270 limits the fuel boost rate TFBA. The engine control module 270 then advances the process to step 76.
In step 76, the engine control module 270 updates N-1 consecutive air-fuel ratios stored in the variable areas ABF_1 to ABF_N-1, and then returns the process to the fuel increase rate setting process.

According to the fuel increase rate setting process including the subroutine of the second embodiment, as shown in FIG. 12, when the ignition timing ADA is retarded based on the result of knocking control and the fuel increase rate TFBA is increased based on the result of air-fuel ratio control in the control of the #3 cylinder, the engine control module 270 limits the fuel increase rate TFBA of the #4 cylinder as necessary. Therefore, the frequency with which the condition for limiting the fuel increase rate TFBA is satisfied is reduced, and the processing load of the engine control module 270 can be reduced. Note that other actions and effects are the same or similar to those of the fuel increase rate setting process including the subroutine of the first embodiment, so explanations will be omitted in order to avoid duplication (same below). Please refer to the previous explanation if necessary (same below).

FIG. 13 shows a third embodiment of a subroutine for limiting the fuel increase rate TFBA.
In step 80, the engine control module 270 refers to the variable ranges ABF_1 to ABF_N-1 and selects the maximum air-fuel ratio from among these as the reference value.
In step 81, the engine control module 270 reads the air-fuel ratio ABF from the air-fuel ratio sensor 310 as the air-fuel ratio of the cylinder to be controlled for which the fuel increase rate is to be limited.

In step 73, the engine control module 270 determines whether the absolute value of the value obtained by subtracting the reference value from the air-fuel ratio ABF read in step 81 is greater than a predetermined value. If the engine control module 270 determines that the absolute value of the value obtained by subtracting the reference value from the air-fuel ratio ABF is greater than the predetermined value (Yes), the process proceeds to step 83. On the other hand, if the engine control module 270 determines that the absolute value of the value obtained by subtracting the reference value from the air-fuel ratio ABF is equal to or less than the predetermined value (No), the process proceeds to step 85.

In step 83, the engine control module 270 limits the fuel boost rate TFBA.
In step 84, the engine control module 270 limits the advance of the ignition timing ADA. That is, since the step in the air-fuel ratio was not eliminated despite the fuel increase rate TFBA being limited in the previous cylinder control, the engine control module 270 retards the ignition timing ADA to a predetermined limit, for example, in order to further reduce the step in the air-fuel ratio. Here, the predetermined limit can be appropriately determined, for example, taking into consideration the characteristics of the engine 100. After that, the engine control module 270 proceeds to step 85.

In step 85, the engine control module 270 updates the N-1 consecutive air-fuel ratios stored in the variable ranges ABF_1 to ABF_N-1. The engine control module 270 then returns the process to the fuel increase rate setting process.

According to the fuel increase rate setting process including the subroutine of the third embodiment, as shown in FIG. 14, if the absolute value of the value obtained by subtracting the reference value from the air-fuel ratio ABF of the controlled cylinder #4 is greater than a predetermined value despite limiting the fuel increase rate TFBA in the control of cylinder #3, the engine control module 270 shifts and retards the ignition timing ADA of cylinder #4 to a predetermined limit to limit the advance of the ignition timing ADA. Therefore, since the advance of the ignition timing ADA of each cylinder is limited as necessary, the increase in exhaust temperature is suppressed, and it is possible to avoid affecting the three-way catalyst arranged in the exhaust passage, etc.

Figure 15 shows a fourth embodiment of a subroutine that limits the fuel increase rate TFBA. As a prerequisite for executing the subroutine according to the fourth embodiment, an area is secured in the volatile memory of the engine control module 270 for temporarily storing the immediately preceding value, which is the air-fuel ratio ABF of the cylinder that was controlled immediately prior in time, and this is initialized to "0", for example, when the engine control module 270 is started.

In step 90, the engine control module 270 reads the air-fuel ratio ABF from the air-fuel ratio sensor 310 as the air-fuel ratio of the cylinder to be controlled for which the fuel increase rate is to be limited.
In step 91, the engine control module 270 determines whether or not the absolute value of the value obtained by subtracting the immediately preceding value from the air-fuel ratio ABF read in step 90 is greater than a predetermined value. If the engine control module 270 determines that the absolute value of the value obtained by subtracting the immediately preceding value from the air-fuel ratio ABF is greater than the predetermined value (Yes), the process proceeds to step 92. On the other hand, if the engine control module 270 determines that the absolute value of the value obtained by subtracting the immediately preceding value from the air-fuel ratio ABF is equal to or less than the predetermined value (No), the process proceeds to step 93.

In step 92, the engine control module 270 limits the fuel boost rate TFBA. The engine control module 270 then advances the process to step 93.
In step 93, the engine control module 270 updates the immediately preceding value, specifically, by overwriting the immediately preceding value in the volatile memory with the air-fuel ratio ABF read in step 90. Thereafter, the engine control module 270 returns the process to the fuel increase rate setting process.

According to the fuel increase rate setting process including the subroutine of the fourth embodiment, as shown in FIG. 16, if the difference in the air-fuel ratio between two consecutive cylinders in time is greater than a predetermined value, the engine control module 270 shifts and limits the air-fuel ratio of the cylinder to be controlled to a predetermined value. Therefore, the variation in the air-fuel ratio between two cylinders that are processed consecutively in time is reduced. This makes it difficult for a large difference in torque to occur between the cylinders, and, for example, it is possible to suppress pulsation of the engine rotation and large engine surges.

A person skilled in the art will easily understand that new embodiments can be created by omitting parts of the technical ideas of the various embodiments described above, combining parts of them as appropriate, or replacing parts of them with well-known technology.

As an example, the subroutine of the fourth embodiment shown in FIG. 15 may incorporate at least one of the additional features of the subroutine of the second embodiment shown in FIG. 11 and the additional features of the subroutine of the third embodiment shown in FIG. 13. In addition, the air-fuel ratio ABF of each cylinder is not limited to being detected by the air-fuel ratio sensor 310, and may be estimated from, for example, the intake flow rate, the intake distribution ratio of each cylinder, the fuel injection amount Ti, and the water temperature Tw.

100...Engine (internal combustion engine) 210...Fuel injector 220...Spark plug 270...Engine control module (control device) 330...Knock sensor

Claims (6)

A control device for an internal combustion engine that performs knocking control to change an ignition timing by detecting the presence or absence of knocking in each cylinder, and performs air-fuel ratio control to change a fuel increase rate based on a result of the knocking control,
if the difference in the air-fuel ratio among the cylinders is greater than a predetermined value, the fuel increase rate is limited so that the air-fuel ratio of the cylinder to be controlled shifts to the predetermined value.
A control device for an internal combustion engine. When the internal combustion engine has N cylinders, the maximum air-fuel ratio among the N-1 cylinders for which the knocking control and the air-fuel ratio control have been performed is selected as a reference value, and if the absolute value of the value obtained by subtracting the reference value from the air-fuel ratio of the cylinder to be controlled is greater than the predetermined value, the fuel increase rate is limited so that the air-fuel ratio shifts to the predetermined value.
The control device for an internal combustion engine according to claim 1. if the absolute value of the difference between the air-fuel ratio of the cylinder to be controlled and the reference value is greater than the predetermined value despite the limiting of the fuel increase rate, the advance of the ignition timing is further limited.
The control device for an internal combustion engine according to claim 2. if an absolute value of a value obtained by subtracting the air-fuel ratio of the cylinder immediately before the knocking control and the air-fuel ratio control are executed from the air-fuel ratio of the cylinder to be controlled is greater than the predetermined value, the fuel increase rate is limited so that the air-fuel ratio shifts to the predetermined value.
The control device for an internal combustion engine according to claim 1. if an absolute value of a value obtained by subtracting the air-fuel ratio of the cylinder immediately before the knocking control and the air-fuel ratio control are executed from the air-fuel ratio of the cylinder to be controlled is greater than the predetermined value despite the restriction of the fuel increase rate, further restricting the advance of the ignition timing.
The control device for an internal combustion engine according to claim 4. the restriction of the fuel increase rate is executed when the ignition timing is retarded based on the result of the knocking control and the fuel increase rate is increased based on the result of the air-fuel ratio control.
The control device for an internal combustion engine according to any one of claims 1 to 5.