Control device for multi-cylinder internal combustion engines

Abstract

This further reduces variations in the air-fuel ratio between cylinders during the purging process. [Solution] The multi-cylinder internal combustion engine 10 is equipped with a fuel vapor treatment mechanism 90 for performing a purging process that introduces fuel vapor adsorbed by the canister 92 into the intake passage 13. The control device 200 performs the following processes: calculates a cylinder-specific correction coefficient based on a cylinder-specific air-fuel ratio correction coefficient that compensates for variations in fuel vapor distribution between cylinders and a reflection coefficient corresponding to the vapor concentration of the purge gas introduced into the intake passage 13; and calculates the fuel injection amount for each cylinder by correcting the basic injection amount for each cylinder with the cylinder-specific correction coefficient.

Description

Technical Field

[0001] The present invention relates to a control device for a multi-cylinder internal combustion engine.

Background Art

[0002] An internal combustion engine including a fuel vapor processing mechanism that adsorbs fuel vapor generated in a fuel tank to a canister and performs a purge process of introducing the adsorbed fuel vapor into an intake passage is known (for example, Patent Document 1 etc.).

[0003] Here, in a multi-cylinder internal combustion engine having a plurality of cylinders, uneven distribution of fuel vapor occurs between the cylinders, resulting in uneven air-fuel ratio between the cylinders. Therefore, the control device for the internal combustion engine described in Patent Document 1 calculates a correction coefficient for compensating for the uneven distribution of fuel vapor between the cylinders. Then, the control device suppresses such uneven air-fuel ratio between the cylinders by correcting the basic injection amount of each cylinder with the calculated correction coefficient.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] It is desirable to suppress as much as possible the uneven air-fuel ratio between the cylinders during the execution of such a purge process.

Means for Solving the Problems

[0006] The control device for a multi-cylinder internal combustion engine that solves the above problems is applied to a multi-cylinder internal combustion engine equipped with a fuel vapor treatment mechanism for performing a purging process that introduces fuel vapor adsorbed in a canister into the intake passage. This control device performs the following processes: calculating a cylinder-specific correction coefficient based on a cylinder-specific air-fuel ratio correction coefficient that compensates for variations in fuel vapor distribution between cylinders and a reflection coefficient corresponding to the vapor concentration of the purge gas introduced into the intake passage; and calculating the fuel injection amount for each cylinder by correcting the basic injection amount for each cylinder with the cylinder-specific correction coefficient. [Effects of the Invention]

[0007] This control system for multi-cylinder internal combustion engines can further reduce variations in the air-fuel ratio between cylinders during purging. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a schematic diagram showing an internal combustion engine and control device in one embodiment. [Figure 2] Figure 2 is a flowchart showing the processing procedure executed by the control device of the same embodiment. [Modes for carrying out the invention]

[0009] Below, one embodiment of a control device for a multi-cylinder internal combustion engine will be described with reference to Figures 1 and 2. <Configuration of internal combustion engine and control system> As shown in Figure 1, the internal combustion engine 10 has multiple cylinders 10a, and an intake passage 13 is connected to the intake port of each cylinder 10a. A throttle valve 14 is provided in the intake passage 13 to adjust the amount of intake air.

[0010] Each cylinder 10a has a combustion chamber equipped with a fuel injection valve 11. In the combustion chamber of each cylinder 10a, a mixture of air drawn in through the intake passage 13 and fuel injected from the fuel injection valve 11 is ignited by a spark discharge and combusted. The exhaust gas produced by the combustion of the mixture in the combustion chamber is discharged into an exhaust passage 15 connected to the exhaust port of the internal combustion engine 10.

[0011] A three-way catalyst 17 is provided in the exhaust passage 15. This three-way catalyst 17 oxidizes hydrocarbons (HC) and carbon monoxide (CO) contained in the exhaust to produce water and carbon dioxide. In addition, the three-way catalyst 17 reduces nitrogen oxides (NOx) contained in the exhaust to produce nitrogen.

[0012] The internal combustion engine 10 is equipped with a fuel vapor treatment mechanism 90 for introducing fuel vapor generated in the fuel tank 91 into the intake passage 13 and treating it in the cylinder 10a. The fuel vapor treatment mechanism 90 includes a canister 92 for adsorbing fuel vapor generated in the fuel tank 91, and a purge passage 94 for introducing the fuel vapor adsorbed by the canister 92 to a part of the intake passage 13 downstream of the throttle valve 14. The fuel vapor treatment mechanism 90 also includes a purge valve 93 provided in the middle of the purge passage 94 to adjust the flow rate of the purge gas flowing through the purge passage 94. The purge gas is a mixture of fresh air and evaporated fuel introduced from the canister 92 into the intake passage 13.

[0013] The control device 200 is equipped with a CPU and memory, and performs various controls on the internal combustion engine 10 by executing a program stored in the memory using the CPU. The control device 200 receives detection signals from various sensors. For example, the control device 200 receives the detection signal from a first air-fuel ratio sensor 51, which is located upstream of the three-way catalytic converter 17 in the exhaust passage 15 and detects the upstream air-fuel ratio AFf. The control device 200 also receives the detection signal from a second air-fuel ratio sensor 52, which is located downstream of the three-way catalytic converter 17 in the exhaust passage 15 and detects the downstream air-fuel ratio AFr. The control device 200 also receives the detection signal from a crank angle sensor 53, which detects the rotation angle of the crankshaft of the internal combustion engine 10. Based on the detection signal from the crank angle sensor 53, the control device 200 calculates the engine speed NE of the internal combustion engine 10. The control device 200 also receives the detection signal from an air flow meter 54, which detects the intake air volume GA. Based on the engine speed NE and intake air volume GA, the control device 200 calculates the engine load ratio KL. The engine load ratio KL represents the ratio of the current cylinder inflow air volume to the cylinder inflow air volume when the internal combustion engine 10 is operating steadily under full load. The cylinder inflow air volume is the amount of air flowing into each cylinder during the intake stroke.

[0014] The control device 200 controls the fuel injection of the fuel injector 11 and the opening degree of the throttle valve 14. Furthermore, the control device 200 implements well-known air-fuel ratio feedback control to correct the fuel injection amount of the fuel injector 11. In this air-fuel ratio feedback control, for example, an upstream air-fuel ratio correction value FAFf is calculated to correct the fuel injection amount based on the deviation between the target air-fuel ratio AFt and the upstream air-fuel ratio AFf. Also, a downstream air-fuel ratio correction value FAFr is calculated to correct the target air-fuel ratio AFt based on the deviation between the stoichiometric air-fuel ratio and the downstream air-fuel ratio AFr. By performing these corrections using each correction value, the exhaust gas purification by the three-way catalytic converter 17 is effectively carried out.

[0015] Furthermore, the control device 200 performs a purging process by introducing fuel vapor adsorbed by the canister 92 into the intake passage 13 through opening control of the purge valve 93. In this purging process, the target purge rate Rp is calculated based on the vapor concentration Lp, which represents the mass ratio of fuel in the purge gas flowing from the canister 92 into the intake passage 13 and indicates the concentration of fuel vapor in the purge gas supplied to cylinder 10a, as well as the intake charging efficiency. Here, the purge rate is the value obtained by dividing the mass flow rate FV of the purge gas flowing from the canister 92 into the intake passage 13 by the intake air volume GA (FV / GA). Also, the vapor concentration Lp increases as the amount of fuel vapor adsorbed in the canister 92 increases. Here, the vapor concentration Lp is reflected in the upstream air-fuel ratio correction value FAFf calculated during the execution of the purging process. Therefore, the control device 200 calculates the vapor concentration Lp based on the upstream air-fuel ratio correction value FAFf calculated during the execution of the purging process.

[0016] Then, based on the intake air volume GA and other factors, a command value for the opening of the purge valve 93 is calculated so that the purge rate reaches the target purge rate Rp, and the opening of the purge valve 93 is adjusted to match that command value. By adjusting the opening of the purge valve 93 in this way, the vapor concentration Lp is controlled to an appropriate value while fuel vapor is introduced into the intake passage 13, and the amount of fuel vapor adsorbed by the canister 92 decreases.

[0017] <Process to suppress variations in air-fuel ratio between cylinders> In an internal combustion engine 10 having multiple cylinders 10a, when the above-mentioned purging process is performed, variations in the distribution of fuel vapor between cylinders occur, resulting in variations in the air-fuel ratio between cylinders. Therefore, the control device 200 suppresses variations in the air-fuel ratio between cylinders by executing the process shown in Figure 2 while the purging process is in progress. The series of processes shown in Figure 2 are realized by the CPU executing a program stored in the memory of the control device 200 while the purging process is in progress. In the following, step numbers are represented by numbers preceded by "S".

[0018] When starting the process shown in FIG. 2, the control device 200 determines whether the current engine speed NE is within a predetermined range (S100). As the predetermined range, for example, a range of the engine speed NE suitable for calculating the cylinder-by-cylinder correction coefficient EKCYLFPG# described later is set in advance.

[0019] In the process of S100, when it is determined that the current engine load factor KL is within a predetermined range (S100: YES), the control device 200 determines whether the current engine speed NE is within a predetermined range (S110). As the predetermined range, for example, a range of the engine load factor KL suitable for calculating the cylinder-by-cylinder correction coefficient EKCYLFPG# described later is set in advance.

[0020] In the process of S110, when it is determined that the current engine load factor KL is within a predetermined range (S110: YES), the control device 200 executes the process of S120. In the process of S120, the control device 200 calculates a reflection coefficient EKFPG according to the vapor concentration Lp of the purge gas introduced into the intake passage 13 based on the purge correction amount (S120). The purge correction amount is a multiplication value of the current vapor concentration Lp and the current purge rate, which is calculated by the control device 200. The purge correction amount is a value indicating the amount of fuel contained in the purge gas. In the present embodiment, the reflection coefficient EKFPG is calculated by referring to a one-dimensional map of the purge correction amount, but the reflection coefficient EKFPG may be calculated using a functional formula with the purge correction amount as a variable.

[0021] Next, the control device 200 calculates the cylinder-by-cylinder air-fuel ratio correction coefficient KCYLFPG# based on the current engine rotational speed NE and the current engine load factor KL (S130). Here, "#" indicates the cylinder number for which the fuel injection amount is to be calculated at the time of executing this process. The cylinder-by-cylinder air-fuel ratio correction coefficient KCYLFPG# is a value preset for each cylinder to compensate for the variation in the distribution of fuel vapor between cylinders, and it is the appropriate value when the purge correction amount is at its assumed maximum value. In the present embodiment, the cylinder-by-cylinder air-fuel ratio correction coefficient KCYLFPG# is calculated by referring to a two-dimensional map of the engine rotational speed NE and the engine load factor KL, but it may also be calculated using a functional formula with the engine rotational speed NE and the engine load factor KL as variables.

[0022] Next, the control device 200 calculates the cylinder-by-cylinder correction coefficient EKCYLFPG# (S140). The cylinder-by-cylinder correction coefficient EKCYLFPG# is a value obtained by multiplying the cylinder-by-cylinder air-fuel ratio correction coefficient KCYLFPG# calculated in the process of S130 by the reflection coefficient EKFPG calculated in the process of S120. This cylinder-by-cylinder correction coefficient EKCYLFPG# is a correction value for correcting the fuel injection amount for each cylinder 10a in consideration of the variation in the distribution of fuel vapor between cylinders and the vapor concentration Lp.

[0023] Next, the control device 200 calculates the fuel injection amount Q# for the cylinder # that is the target of fuel injection amount calculation (S150). In the process of S150, the control device 200 calculates a value obtained by multiplying the basic injection amount QB# by the cylinder-by-cylinder correction coefficient EKCYLFPG#. Then, by substituting the calculated value into the fuel injection amount Q#, the fuel injection amount Q# for the cylinder # is calculated. The basic injection amount QB# is the basic value of the fuel injection amount calculated for the cylinder # and is a value calculated based on the engine operating state such as the engine rotational speed NE and the engine load factor KL. Then, the control device 200 controls the drive of the fuel injection valve 11 so that the amount of fuel injected from the fuel injection valve 11 of the cylinder # becomes the fuel injection amount Q#.

[0024] If the process in S150 is completed, or if a negative result is obtained in the process in S100, or if a negative result is obtained in the process in S110, the control device 200 terminates the process for the current calculation cycle.

[0025] <Operation and Effects of This Embodiment> When the vapor concentration Lp is high, compared to when it is low, a larger amount of fuel is contained in the purge gas among the fuel supplied to the cylinder, and therefore its proportion to the air-fuel ratio increases. As a result, when the vapor concentration Lp is high, the air-fuel ratio of cylinders with a high distribution of fuel vapor becomes richer, and the air-fuel ratio of cylinders with a low distribution of fuel vapor becomes leaner compared to cylinders with a high distribution, leading to greater variation in the air-fuel ratio between cylinders.

[0026] Thus, variations in the air-fuel ratio between cylinders due to purging are not only due to variations in the distribution of fuel vapor between cylinders, but also to differences in the vapor concentration Lp of the purge gas. Therefore, in this embodiment, a cylinder-specific air-fuel ratio correction coefficient KCYLFPG# is calculated to compensate for variations in fuel vapor distribution between cylinders, and a reflection coefficient EKFPG is calculated according to the vapor concentration Lp of the purge gas introduced into the intake passage 13. Then, a cylinder-specific correction coefficient EKCYLFPG# is calculated based on the cylinder-specific air-fuel ratio correction coefficient KCYLFPG# and the reflection coefficient EKFPG. Finally, the fuel injection amount Q# for each cylinder 10a is calculated by correcting the basic injection amount QB# for each cylinder 10a with the cylinder-specific correction coefficient EKCYLFPG#.

[0027] In this way, the fuel injection amount Q# for each cylinder 10a is calculated by considering not only the variation in fuel vapor distribution between cylinders but also the vapor concentration Lp of the purge gas. Therefore, variations in the air-fuel ratio between cylinders during the purging process can be further suppressed.

[0028] <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.

[0029] The cylinder-specific air-fuel ratio correction coefficient KCYLFPG# was calculated based on engine rotational speed NE and engine load ratio KL, but it may also be calculated based on other values.

[0030] The reflection coefficient EKFPG was calculated based on the purge correction amount, but it may be calculated in other ways. For example, the reflection coefficient EKFPG may be calculated based on the vapor concentration Lp, and the calculated reflection coefficient EKFPG may be corrected according to the purge rate. [Explanation of Symbols]

[0031] 10... Internal combustion engine 10a... Cylinder 11…Fuel injector 13…Intake passage 14…Throttle valve 15… Exhaust passage 17...Three-way catalyst 51...First air-fuel ratio sensor 52...Second air-fuel ratio sensor 53... Crank angle sensor 54…Air flow meter 90…Fuel vapor processing mechanism 91…Fuel tank 92... Canister 93... Purge valve 94... Purge Passage 200... Control device

Claims

[Claim 1] A control device applicable to a multi-cylinder internal combustion engine equipped with a fuel vapor treatment mechanism for performing a purging process that introduces fuel vapor adsorbed in a canister into the intake passage, A process for calculating a cylinder-specific correction coefficient based on a cylinder-specific air-fuel ratio correction coefficient that compensates for variations in fuel vapor distribution between cylinders, and a reflection coefficient corresponding to the vapor concentration of the purge gas introduced into the intake passage, The process of calculating the fuel injection amount for each cylinder by correcting the basic injection amount for each cylinder using the aforementioned cylinder-specific correction coefficient is executed. A control device for multi-cylinder internal combustion engines.

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