Fuel learning control device of vehicle

Abstract

To prevent erroneous learning of fuel learning.SOLUTION: A fuel learning control device of a vehicle 1 comprises: an engine 10 having a crankcase 21; an intake passage 30 having a throttle valve 31 for adjusting an intake amount flowing into a combustion chamber 14 of the engine 10; and a blowby gas passage 50 for making a downstream side of the throttle valve 31 in the intake passage 30 and the crankcase 21 communicate with each other, and returning a blowby gas which leaks out to the crankcase 21 from the combustion chamber 14, to the intake passage 30. The fuel learning control device has: a fuel learning part 62 for performing fuel learning on the basis of a target air-fuel ratio and an actual air-fuel ratio; a determination part 63 for determining whether or not a non-combusted fuel quantity in the blowby gas which is returned to the intake passage 30 at a fuel cut is high in concentration; and a control part 61 for performing control so as to prohibit the fuel learning by the fuel learning part 62 when it is determined that the non-combusted fuel quantity in the blowby gas is high in concentration by the determination part 63.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a fuel learning control device for a vehicle. [Background technology]

[0002] Conventionally, various vehicles perform feedback control by detecting the oxygen concentration in the exhaust gas and injecting fuel at a fuel injection amount that brings the air-fuel ratio, for example, close to the theoretical air-fuel ratio (stoichiometric) based on the detected information (see Patent Document 1). In addition, fuel learning is performed by storing the difference between the target air-fuel ratio and the actual air-fuel ratio as a fuel learning value and correcting the fuel injection amount.

[0003] In recent years, a technology has been developed to prevent unburned gas from leaking into the atmosphere by returning the blow-by gas that has leaked from the combustion chamber into the crankcase to the intake passage, thereby burning the unburned gas contained in the blow-by gas. Normally, the amount of unburned gas contained in the blow-by gas is extremely small compared to the amount of fuel injected, so the effect of the unburned gas contained in the blow-by gas on fuel learning is small and can be ignored. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2002-13428 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, repeated short-term operation in an extremely low-temperature environment may cause oil dilution, in which unburned gas contained in the blow-by gas leaking from the combustion chamber to the crankcase dissolves in the engine oil used to cool the internal combustion engine. The unburned gas dissolved in the engine oil evaporates when the engine is warmed up, so the ratio of unburned gas in the blow-by gas increases rapidly. If fuel learning is performed in a state in which the ratio of unburned gas has increased in this way, it may cause erroneous learning. In Patent Document 1, the occurrence of oil dilution itself is prevented by limiting the fuel injection period, but the impact on fuel learning in the event that oil dilution cannot be prevented and occurs is not taken into consideration.

[0006] The present invention has been made in consideration of the above-mentioned problems, and has an object to prevent erroneous learning of fuel. [Means for solving the problem]

[0007] The present invention is a fuel learning control device for a vehicle equipped with an internal combustion engine having a crankcase, an intake passage having a throttle valve that adjusts the amount of intake air flowing into the combustion chamber of the internal combustion engine, and a blow-by gas passage that connects the downstream side of the throttle valve of the intake passage with the crankcase and returns blow-by gas that has leaked from the combustion chamber to the crankcase to the intake passage, and is characterized in having a fuel learning means that performs fuel learning based on a target air-fuel ratio and an actual air-fuel ratio, a judgment means that judges whether the amount of unburned fuel in the blow-by gas returned to the intake passage during fuel cut is high or not, and a control means that controls the fuel learning by the fuel learning means to be prohibited when the judgment means judges that the amount of unburned fuel in the blow-by gas is high. Effect of the Invention

[0008] According to the present invention, erroneous fuel learning can be prevented. [Brief description of the drawings]

[0009] [Figure 1]1 is a diagram showing a schematic configuration of a vehicle equipped with a fuel learning control device; [Diagram 2] FIG. 2 is a diagram illustrating an example of a functional configuration of a fuel learning control device. [Diagram 3] 4 is a flowchart showing an example of a process performed by a fuel learning control device. [Figure 4] 4 is a timing chart showing an example of processing by a fuel learning control device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The embodiment according to the present invention is a fuel learning control device for a vehicle 1 including an engine 10 having a crankcase 21, an intake passage 30 having a throttle valve 31 for adjusting the amount of intake air flowing into a combustion chamber 14 of the engine 10, and a blow-by gas passage 50 for connecting the downstream side of the throttle valve 31 in the intake passage 30 with the crankcase 21 and for recirculating blow-by gas leaking from the combustion chamber 14 to the crankcase 21 to the intake passage 30, the fuel learning control device having a fuel learning unit 62 for performing fuel learning based on a target air-fuel ratio and an actual air-fuel ratio, a determination unit 63 for determining whether the amount of unburned fuel in the blow-by gas recirculated to the intake passage 30 during fuel cut is high or not, and a control unit 61 for controlling the fuel learning unit 62 to prohibit fuel learning when the determination unit 63 determines that the amount of unburned fuel in the blow-by gas is high. Therefore, by prohibiting fuel learning when it is determined that the amount of unburned fuel in the blow-by gas is high, erroneous learning of fuel learning can be prevented. EXAMPLES

[0011] Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. Fig. 1 is a diagram showing a schematic configuration of a vehicle 1 equipped with a fuel learning control device (hereinafter, referred to as a control device) according to this embodiment. Note that Fig. 1 is simplified for the sake of convenience in explaining this embodiment, and components that are normally equipped in a vehicle are assumed to be equipped even if they are not shown in the figure. A vehicle 1 according to this embodiment includes an engine 10 as a drive source, an intake passage 30, an exhaust passage 40, a blow-by gas passage 50, a control device 60, and the like.

[0012] The engine 10 is an internal combustion engine that performs a series of strokes including an intake stroke, a compression stroke, a combustion stroke, and an exhaust stroke. The engine 10 includes a piston 12 accommodated in a cylinder 11 so as to be capable of reciprocating motion, a spark plug 13 disposed in a combustion chamber 14, an intake valve 16 located between the combustion chamber 14 and an intake port 15, an exhaust valve 18 located between the combustion chamber 14 and an exhaust port 17, a crankshaft 20 to which the piston 12 is rotatably connected via a connecting rod 19, and a crankcase 21 that rotatably supports the crankshaft 20.

[0013] During the intake stroke, the piston 12 descends from top dead center to bottom dead center, the intake valve 16 opens, and the exhaust valve 18 closes. As the piston 12 descends, the intake air and fuel mixture flows from the intake passage 30 into the combustion chamber 14. In the compression stroke, the piston 12 moves upward from the bottom dead center to the top dead center, and the intake valve 16 and the exhaust valve 18 close. As the piston 12 moves upward, the air-fuel mixture is compressed. During the combustion stroke, the compressed air-fuel mixture is ignited by the spark plug 13 and combusted, pushing the piston 12 downward, causing it to move from top dead center to bottom dead center. During the exhaust stroke, the piston 12 rises from the bottom dead center to the top dead center, the intake valve 16 closes, and the exhaust valve 18 opens. As the piston 12 rises, exhaust gas generated during the combustion stroke is discharged into the exhaust passage 40.

[0014] As the engine 10 repeats a series of processes, driving force is transmitted from the engine 10 via the crankshaft 20 to the drive wheels, causing the vehicle 1 to run. Note that the configuration of the engine 10 is not particularly limited, and various known engines can be applied.

[0015] The engine 10 also has a crank angle sensor 22 and an engine speed sensor 23. The crank angle sensor 22 detects the crank angle (the rotation angle of the crankshaft 20) and transmits information about the detected crank angle to the control device 60. The control device 60 controls the ignition timing of the spark plug 13 based on the information about the crank angle detected by the crank angle sensor 22.

[0016] The engine speed sensor 23 detects the engine speed, specifically, the number of revolutions per unit time of the crankshaft 20, and transmits the detected engine speed information to the control device 60. The control device 60 uses the engine speed information detected by the engine speed sensor 23 when calculating the reference fuel injection amount.

[0017] The intake passage 30 is a passage that guides intake air taken in from outside the vehicle 1 to the combustion chamber 14 via the intake port 15. The intake passage 30 is formed, for example, by an intake pipe. In the intake passage 30, a throttle valve 31 and a fuel injector 32 are arranged in this order from the upstream side.

[0018] The throttle valve 31 opens and closes to adjust the amount of intake air flowing into the combustion chamber 14 of the engine 10. The throttle valve 31 adjusts the amount of intake air based on the control of the control device 60. Fuel injector 32 injects fuel pumped from a fuel tank into intake passage 30. Fuel injector 32 adjusts the fuel injection amount under the control of control device 60. Note that fuel injector 32 is not limited to injecting fuel into intake passage 30, and may be configured to inject fuel into intake port 15 or combustion chamber 14.

[0019] Additionally, an airflow sensor 33 and a throttle opening sensor 34 are disposed in the intake passage 30 (including the periphery of the intake passage 30). The airflow sensor 33 detects information on the intake amount, and transmits the detected information on the intake amount to the control device 60. The throttle opening sensor 34 detects the opening of the throttle valve 31, and transmits the detected information on the throttle valve opening to the control device 60.

[0020] The exhaust passage 40 is a passage through which exhaust gas combusted in the combustion chamber 14 is exhausted to the outside of the vehicle 1 via the exhaust port 17. The exhaust passage 40 is formed of, for example, an exhaust pipe. A catalytic converter 41 is disposed in the exhaust passage 40.

[0021] The catalytic converter 41 purifies the exhaust gas by oxidizing and reducing harmful components contained in the exhaust gas. The catalytic converter 41 may be a three-way catalyst. In addition, an air-fuel ratio sensor 42 is disposed in the exhaust passage 40 (including the periphery of the exhaust passage 40). The air-fuel ratio sensor 42 is an example of an air-fuel ratio detection means, and detects the air-fuel ratio of the exhaust gas (actual air-fuel ratio) and transmits information on the detected actual air-fuel ratio to the control device 60.

[0022] The blow-by gas passage 50 is a passage for returning the blow-by gas leaking from the combustion chamber 14 to the crankcase 21 to the intake passage 30. The blow-by gas passage 50 is connected between the downstream side of the throttle valve 31 and the crankcase 21 to communicate between the intake passage 30 and the crankcase 21. By returning the blow-by gas to the intake passage 30, the unburned gas contained in the blow-by gas can be caused to flow into the combustion chamber 14 together with the air-fuel mixture.

[0023] The vehicle 1 also includes an accelerator opening sensor 51. The accelerator opening sensor 51 detects the amount of accelerator pedal operation by the driver, and transmits information on the detected amount of operation to the control device 60.

[0024] The control device 60 controls the entire vehicle 1. For example, an ECU (Electronic Control Unit) can be used as the control device 60. The control device 60 has a CPU, a ROM, a RAM, etc. as a hardware configuration. The ROM stores programs and predetermined information for controlling the vehicle 1, the engine 10, etc. The RAM is a work memory that temporarily stores programs and data. The CPU reads out the programs stored in the ROM, expands them in the RAM, and executes them to control the vehicle 1, the engine 10, etc.

[0025] FIG. 2 is a diagram illustrating an example of a functional configuration of the control device 60. As shown in FIG. The control device 60 includes a control unit 61 , a fuel learning unit 62 , and a determination unit 63 . The control unit 61 controls the entire vehicle 1. The control unit 61 controls the throttle valve 31 so that the throttle valve 31 has a target opening calculated based on the accelerator opening detected by the accelerator opening sensor 51. The control unit 61 also controls the fuel injector 32 to inject fuel at a fuel injection amount corrected based on information from various sensors and a fuel learning value (to be described later) based on the reference fuel injection amount calculated based on the engine speed detected by the engine speed sensor 23 and the intake air amount detected by the air flow sensor 33. At this time, the control unit 61 sets a target air-fuel ratio according to the driving situation, and performs feedback control based on the actual air-fuel ratio detected by the air-fuel ratio sensor 42 so as to achieve the set target air-fuel ratio. The control unit 61 is not limited to setting the target air-fuel ratio to the theoretical air-fuel ratio (stoichiometric), but sets the target air-fuel ratio to lean or rich depending on the driving situation. The control unit 61 transmits information on the set target air-fuel ratio to the fuel learning unit 62.

[0026] Furthermore, when a predetermined condition is satisfied, control unit 61 controls fuel injector 32 not to inject fuel, i.e., to cut fuel injection (fuel cut). Here, the predetermined condition is, for example, a case where the accelerator opening degree transitions to 0 from a state where the engine speed is equal to or higher than a predetermined engine speed and a predetermined vehicle speed is equal to or higher than a predetermined vehicle speed. However, the predetermined condition is not limited to this case, and other requirements may be added, or some requirements may be omitted. Furthermore, control unit 61 controls fuel injector 32 to inject fuel again when the accelerator opening degree becomes larger than 0. When fuel is cut off, the piston 12 continues to reciprocate until the vehicle 1 comes to a stop, even though no combustion occurs during the combustion stroke. As a result, the intake valve 16 and exhaust valve 18 open and close, and the blow-by gas that has been recirculated to the intake passage 30 together with the intake air is discharged directly from the intake passage 30 through the combustion chamber 14 to the exhaust passage 40.

[0027] Furthermore, control unit 61 receives the result of determination by determination unit 63 of the concentration of the amount of unburned fuel (amount of unburned gas) in the blow-by gas, and controls fuel learning unit 62 to prohibit fuel learning or release the prohibition of fuel learning according to the result of the determination. The process related to the prohibition and release of fuel learning by control unit 61 will be described later with reference to the flowchart of FIG.

[0028] The fuel learning unit 62 performs fuel learning based on the target air-fuel ratio and the actual air-fuel ratio. Specifically, the fuel learning unit 62 acquires information on the target air-fuel ratio from the control unit 61 and information on the actual air-fuel ratio from the air-fuel ratio sensor 42, and performs fuel learning by calculating the difference between the target air-fuel ratio and the actual air-fuel ratio as a fuel learning value for each combustion cycle. The fuel learning unit 62 transmits information on the calculated fuel learning value to the control unit 61. As described above, the control unit 61 corrects the reference fuel injection amount based on the information on the fuel learning value. Note that the fuel learning unit 62 performs fuel learning only when fuel is being injected from the fuel injector 32, and does not perform fuel learning when fuel is not being injected (when fuel is cut off) because it is not necessary to calculate the fuel injection amount.

[0029] The determination unit 63 determines whether the amount of unburned fuel in the blow-by gas recirculated to the intake passage 30 during fuel cut is high or not. Usually, the amount of unburned gas contained in the blow-by gas is extremely small compared to the amount of fuel injected, but the amount of unburned fuel in the blow-by gas may increase rapidly due to oil dilution and volatilization during warm-up. The determination unit 63 determines the concentration of the amount of unburned fuel in the blow-by gas and transmits the determination result to the control unit 61. As described above, the control unit 61 controls the fuel learning unit 62 to prohibit fuel learning or to cancel the prohibition of fuel learning depending on the determination result.

[0030] Next, an example of processing by the control device 60 will be described with reference to the flowchart of Fig. 3. The flowchart of Fig. 3 is realized, for example, by the ECU, which is the control device 60, executing a program. The flowchart of Fig. 3 is started when the engine 10 is started.

[0031] In S1, the determination unit 63 determines whether or not fuel is being cut. If fuel is being cut, the process proceeds to S2, and if fuel is not being cut, the process of the flowchart in FIG. 3 ends. As described above, when fuel is cut, the blow-by gas that is recirculated to the intake passage 30 together with the intake air is discharged directly from the intake passage 30 to the exhaust passage 40 via the combustion chamber 14. Therefore, the air-fuel ratio sensor 42 arranged in the exhaust passage 40 can detect the air-fuel ratio of the combined gas of the intake air and the blow-by gas after eliminating the influence of the fuel injected from the fuel injector 32.

[0032] In S2, the determination unit 63 determines whether a predetermined time has passed since the fuel cut. If the predetermined time has passed, the process proceeds to S3, and if the predetermined time has not passed, the process waits until the predetermined time has passed. The reason for waiting until the predetermined time has passed is that the air-fuel ratio detected by the air-fuel ratio sensor 42 differs depending on the concentration of the unburned fuel amount in the blow-by gas that flows together with the intake air as the predetermined time passes. The specified time is recorded in advance in the control device 60, and can be set by verifying the time when a difference occurs in the air-fuel ratio detected by the air-fuel ratio sensor 42 depending on the concentration of the unburned fuel amount, or by verifying through simulation.

[0033] In S3, the determination unit 63 determines whether or not the amount of unburned fuel in the blow-by gas recirculated to the intake passage 30 is high. Specifically, the determination unit 63 acquires information on the actual air-fuel ratio detected (output) by the air-fuel ratio sensor 42, and determines whether or not the actual air-fuel ratio is less than a threshold value. Here, when the amount of unburned fuel in the blow-by gas is not highly concentrated (including when the amount of unburned fuel is 0), the amount of unburned fuel is small after fuel cut, and therefore the proportion of oxygen in the combined intake air and blow-by gas is high, so the actual air-fuel ratio after fuel cut increases rapidly (becomes suddenly lean). On the other hand, if the amount of unburned fuel in the blow-by gas is high, the amount of unburned fuel is large after fuel cut, so the proportion of oxygen in the combined intake air and blow-by gas is low, and the actual air-fuel ratio after fuel cut only increases gradually (becomes gradually leaner).

[0034] Therefore, if the actual air-fuel ratio when a predetermined time has elapsed since the fuel cut is less than the threshold, it can be determined that the amount of unburned fuel in the blow-by gas is high, and if the actual air-fuel ratio when a predetermined time has elapsed since the fuel cut is greater than the threshold, it can be determined that the amount of unburned fuel in the blow-by gas is not high. The determination unit 63 transmits information on the determination result to the control unit 61. If the air-fuel ratio is not less than the threshold, the process proceeds to S4, and if the air-fuel ratio is less than the threshold, the process proceeds to S5. The threshold value is recorded in advance in the control device 60, and may be the value of the air-fuel ratio at the flammable limit in the engine 10. The threshold value differs depending on the amount of intake air of the vehicle, and is therefore set for each vehicle model.

[0035] In S4, the control unit 61 instructs the fuel learning unit 62 to cancel the prohibition of fuel learning. For example, the control unit 61 turns off the fuel learning prohibition flag when the fuel learning prohibition flag is on, and keeps the fuel learning prohibition flag off when the fuel learning prohibition flag is off. When the fuel learning prohibition flag is off, the amount of unburned fuel in the blow-by gas is not high, so that the fuel learning unit 62 can appropriately perform fuel learning.

[0036] In S5, the control unit 61 instructs the fuel learning unit 62 to prohibit fuel learning. For example, when the fuel learning prohibition flag is off, the control unit 61 turns on the fuel learning prohibition flag, and when the fuel learning prohibition flag is on, the control unit 61 keeps the fuel learning prohibition flag on. When the fuel learning prohibition flag is on, the amount of unburned fuel in the blow-by gas is highly concentrated, and therefore, there is a possibility of erroneous learning if fuel learning is performed, and therefore the fuel learning unit 62 prohibits fuel learning. In other words, even when fuel that would normally require fuel learning is being injected, the fuel learning unit 62 can prevent erroneous learning by prohibiting fuel learning.

[0037] 3 is executed repeatedly from the start of engine 10 until the ignition is turned off. Therefore, when the fuel learning prohibition flag is on and fuel learning is prohibited, and then the prohibition of fuel learning is lifted in S4 via S1, S2, and S3, fuel learning unit 62 can perform fuel learning as usual while fuel is being injected.

[0038] FIG. 4 is a timing chart of each item when the flowchart of FIG. 3 is executed. FIG. 4(a) shows the fuel cut state, FIG. 4(b) shows the actual air-fuel ratio detected by the air-fuel ratio sensor, FIG. 4(c) shows the judgment timer, and FIG. 4(d) shows the fuel learning prohibition state. Here, as shown in Fig. 4(a), fuel cut is started at time T0. As a result of the fuel cut being started, the actual air-fuel ratio detected by the air-fuel ratio sensor changes from stoichiometric to lean as shown in Fig. 4(b), and the determination timer starts counting as shown in Fig. 4(c).

[0039] Here, the dashed line in FIG. 4(b) shows the output change of the actual air-fuel ratio when the amount of unburned fuel in the blow-by gas is not high. As shown by the dashed line in FIG. 4(b), the actual air-fuel ratio after the fuel cut increases rapidly because the ratio of oxygen to the combined gas of the intake air and the blow-by gas is high after the fuel cut. Therefore, at time T1, which is a predetermined time after time T0, the actual air-fuel ratio is larger than the threshold value. Here, as shown by the dashed line in FIG. 4(b), the actual air-fuel ratio reaches the detection limit of the air-fuel ratio sensor before time T1.

[0040] On the other hand, the solid line shown in FIG. 4(b) shows the output change of the actual air-fuel ratio when the amount of unburned fuel in the blow-by gas is high. As shown by the solid line in FIG. 4(b), the ratio of oxygen to the combined gas of the intake air and the blow-by gas is low after the fuel cut, so the actual air-fuel ratio after the fuel cut only increases gradually. Therefore, even at time T1, which is a predetermined time after time T0, the actual air-fuel ratio is smaller than the threshold value. Here, as shown by the solid line in FIG. 4(b), the actual air-fuel ratio reaches the detection limit of the air-fuel ratio sensor at time T2, which is later than time T1.

[0041] Therefore, when the amount of unburned fuel in the blow-by gas is high, the actual air-fuel ratio does not exceed the threshold value within a specified time, so that the fuel learning prohibition flag changes from off to on at time T1 as shown in Figure 4(d), and fuel learning is prohibited until the fuel prohibition flag changes from off to on at the time of the next fuel cut.

[0042] As described above, in this embodiment, the control device 60 has the fuel learning section 62 that performs fuel learning based on the target air-fuel ratio and the actual air-fuel ratio, the judgment section 63 that judges whether the amount of unburned fuel in the blow-by gas recirculated to the intake passage 30 is high or not during fuel cut, and the control section 61 that controls the fuel learning section 62 to prohibit fuel learning when the judgment section 63 judges that the amount of unburned fuel in the blow-by gas is high. In this way, when it is judged that the amount of unburned fuel in the blow-by gas is high, fuel learning is prohibited, thereby preventing erroneous learning of fuel learning. Also, in this embodiment, whether the amount of unburned fuel in the blow-by gas is high or not can be judged using existing parts that the vehicle 1 normally has, and there is no need to add new parts, so that costs can be reduced.

[0043] In this embodiment, the determination unit 63 determines whether the amount of unburned fuel in the blow-by gas is high in concentration based on the output change of the actual air-fuel ratio detected by the air-fuel ratio sensor 42 after the fuel cut. After the fuel cut, the output of the air-fuel ratio sensor 42 transitions from stoichiometric to lean, but the higher the concentration of the unburned fuel in the blow-by gas, the slower the rate of change becomes. Therefore, based on the output change of the actual air-fuel ratio detected by the air-fuel ratio sensor 42, it is possible to determine whether the amount of unburned fuel in the blow-by gas is high in concentration.

[0044] In addition, in this embodiment, the determination unit 63 determines that the amount of unburned fuel in the blow-by gas is high when the actual air-fuel ratio detected by the air-fuel ratio sensor 42 does not exceed the threshold within a predetermined time after the fuel cut. After the fuel cut, the output of the air-fuel ratio sensor 42 transitions from stoichiometric to lean, but the higher the concentration of the unburned fuel in the blow-by gas, the slower the rate of change becomes. Therefore, when the actual air-fuel ratio detected by the air-fuel ratio sensor 42 does not exceed the threshold within a predetermined time, it can be determined that the amount of unburned fuel in the blow-by gas is high.

[0045] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and modifications and the like are possible within the scope of the present invention. [Explanation of symbols]

[0046] 1: vehicle 10: engine 12: piston 13: spark plug 14: combustion chamber 16: intake valve 18: exhaust valve 21: crankcase 30: intake passage 31: throttle valve 32: fuel injector 33: air flow sensor 34: throttle opening sensor 40: exhaust passage 42: air-fuel ratio sensor 50: blow-by gas passage 60: control device (fuel learning control device) 61: control unit 62: fuel learning unit 63: determination unit

Claims

1. an internal combustion engine having a crankcase; an intake passage having a throttle valve for adjusting the amount of intake air flowing into a combustion chamber of the internal combustion engine; a blow-by gas passage that connects the intake passage downstream of the throttle valve with the crankcase and returns blow-by gas leaking from the combustion chamber to the crankcase to the intake passage, A fuel learning means for performing fuel learning based on a target air-fuel ratio and an actual air-fuel ratio; a determination means for determining whether or not the amount of unburned fuel in the blow-by gas recirculated to the intake passage during a fuel cut is high; and a control means for controlling the fuel learning means to prohibit fuel learning when the determination means determines that the amount of unburned fuel in the blow-by gas is at a high concentration.

2. The vehicle has an air-fuel ratio detection means for detecting an actual air-fuel ratio, The determination means is 2. A fuel learning control device for a vehicle according to claim 1, wherein whether or not the amount of unburned fuel in the blow-by gas is high is determined based on an output change of an actual air-fuel ratio detected by said air-fuel ratio detection means after a fuel cut.

3. The determination means is 3. A fuel learning control device for a vehicle as described in claim 2, characterized in that if the actual air-fuel ratio detected by the air-fuel ratio detection means does not exceed a threshold value within a predetermined time after fuel cut, it is determined that the amount of unburned fuel in the blow-by gas is high.

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