JPH0586995A - Self-diagnosing device for fuel vaporized gas diffusion preventing device - Google Patents

Abstract

PURPOSE:To provide a self-diagnosing device for a fuel vaporized gas diffusion preventing device which more reliably decides feed ability by taking unevenness in fuel gas density into consideration when feed abnormality owing to which fuel vaporized gas is not introduced to an intake air passage is detected. CONSTITUTION:A flow rate of gas fed from a fuel tank 7 to a canister 37 is detected by means of a diaphragm, a permanent magnet, a magnetic flux detector 20, and a control circuit 44, and gas density is detected by means of an oxygen concentration sensor 46 and a control circuit 44. Through control of a purge valve 40 by means of a control circuit 44, from a gas flow rate and a fuel vaporized gas density, the weight of fuel vaporized gas fed from the fuel tank 7 to the canister 37 is determined in a state to close a discharge passage 39. When the determined value exceeds a set value, through control of the purge valve 40, the discharge passage 39 is brought into an opening or a closed state. From a change in an air-fuel ratio detected by an o, sensor 6, it is decided whether abnormality occurs. When abnormality occurs, an alarm lamp 45 is lighted ON to announce an alarm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a self-diagnosis device in a fuel evaporative gas diffusion prevention device.

[0002]

2. Description of the Related Art Conventionally, as a self-diagnosis device for a fuel evaporative gas diffusion prevention device, there is one disclosed in Japanese Patent Laid-Open No. 2-136558. In this device, when the pressure in the tank is equal to or higher than a predetermined pressure, the opening / closing means provided in the discharge passage communicating between the canister and the intake passage of the internal combustion engine is opened / closed, and the abnormality is determined from the change in the air-fuel ratio at that time.

However, in this device, the density of the fuel evaporative gas from the fuel tank varies depending on the amount of fuel in the tank and the properties of the fuel. For example, when the gasoline component density is low, the opening / closing means is opened and closed. However, there is little change in the air-fuel ratio, and there is a risk of erroneous determination.

Therefore, the applicant of the present application filed Japanese Patent Application No. 3-754.
No. 05 proposes a self-diagnosis device that takes into account variations in fuel gas density due to residual air in the fuel tank.
This device determines the flow rate of gas supplied from the fuel tank to the canister, opens and closes the purge valve when the gas flow rate exceeds a set value, and determines the presence or absence of abnormality based on the change in the air-fuel ratio at that time. In some cases, the gas flow rate setting value is set to a value larger than the values set so far, and the abnormality determination is performed again. That is, the retry operation is performed by increasing the set value (judgment value) of the gas flow rate.

[0005]

[Patent Document 1] Japanese Patent Application No. 3-
Even if the device of No. 75405 is adopted, if only the gas with a low concentration of the fuel evaporative gas is supplied to the canister, the fuel evaporative gas is adsorbed only slightly in the canister.
Re-determine by increasing the set value of gas flow rate (retry operation)
Even if the above is performed, it may be determined that there is an abnormality and an erroneous determination may be made.

An object of the present invention is to provide a fuel evaporative gas diffusion preventive apparatus which can more reliably make a determination in consideration of a variation in fuel gas density when detecting a supply abnormality in which fuel evaporative gas is not guided to an intake passage. It is to provide a self-diagnosis device.

[0007]

The present invention, as shown in FIG. 11, communicates with a fuel tank M1 and
1, a canister M2 containing an adsorbent that adsorbs the fuel evaporative emission gas, the canister M2, and an intake passage M3 of the internal combustion engine.
A discharge passage M4 communicating with the discharge passage M4, and an opening / closing means M5 provided in the discharge passage M4 for opening and closing the discharge passage M4,
The air-fuel ratio detecting means M6 for detecting the air-fuel ratio of the air-fuel mixture to the internal combustion engine, the gas flow rate detecting means M7 for detecting the flow rate of the gas supplied from the fuel tank M1 to the canister M2, and the fuel tank M1 for the canister M2. The gas density detecting means M8 for detecting the density of the fuel evaporating gas supplied, and the fuel tank M1 by the gas flow rate detecting means M7 with the opening / closing means M5 controlled to close the discharge passage M4.
The fuel evaporative gas weight sent from the fuel tank M1 to the canister M2 is determined by the flow rate of gas sent from the fuel tank M1 to the canister M2 and the fuel evaporative gas density by the gas density detecting means M8, and the fuel evaporative gas weight is greater than or equal to a set value. Then, the opening / closing means M5 is controlled to open and close the discharge passage M4, and the air-fuel ratio detecting means M6 at that time is opened.
In the fuel evaporative gas diffusion prevention apparatus, which includes a determination unit M9 that determines whether or not there is an abnormality based on a change in the air-fuel ratio due to the above, and a warning unit M10 that warns when an abnormality is determined by the determination unit M9. The diagnostic device is the gist.

[0008]

The determining means M9 controls the opening / closing means M5 and closes the discharge passage M4, and the gas flow rate sent from the fuel tank M1 to the canister M2 by the gas flow rate detection means M7 and the fuel vaporized gas by the gas density detection means M8. The weight of the fuel evaporative gas sent from the fuel tank M1 to the canister M2 is determined by the density, and when the weight of the fuel evaporative gas exceeds a set value, the opening / closing means M5 is controlled to open and close the discharge passage M4. Whether or not there is an abnormality is determined by the change in the air-fuel ratio by the air-fuel ratio detecting means M6. Then, the determination means M9
When it is determined that there is an abnormality by the abnormality determination by, the warning means M10 warns.

That is, the gas flow rate and the fuel evaporative gas density are detected in the passage from the fuel tank to the canister, and the weight of the fuel evaporative gas adsorbed to the canister is estimated to prevent erroneous determination due to variations in the fuel gas density. ..

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described below with reference to the drawings. A multi-cylinder engine 1 as an internal combustion engine shown in FIG. 1 is mounted on a vehicle, and an intake pipe 2 (intake passage) and an exhaust pipe 3 are connected to the engine 1. An electromagnetic fuel injection valve 4 is provided in each cylinder intake portion of the intake pipe 2, and a throttle valve 5 is provided in the intake pipe 2. Further, the exhaust pipe 3 is provided with O as an air-fuel ratio detecting means.
_Two sensors 6 are provided, and the sensor 6 outputs a voltage signal according to the oxygen concentration in the exhaust gas.

In the fuel supply system for supplying the fuel to the fuel injection valve 4, the fuel (gasoline) in the fuel tank 7 is pressure-fed to each injection valve 4 by the fuel pump 8 through the fuel filter 9 and is adjusted. The fuel supplied to each injection valve 4 is adjusted to a predetermined pressure by the pressure valve 10.

As shown in FIG. 2, a gas flow rate detecting sensor housing 12 is fixed to the upper surface of the fuel tank 7, and a diaphragm chamber 13 is formed in the sensor housing 12. This diaphragm chamber 13 is the diaphragm 1
4 is divided into upper and lower chambers 15 and 16, and the lower chamber 16 communicates with the inside of the fuel tank 7 through a communication hole 17. A spring 18 is arranged in the upper chamber 15, and the spring 18
The diaphragm 14 is urged downward by the urging force of. A permanent magnet 19 is fixed to the diaphragm 14, and a magnetic flux detector 20 is arranged on the ceiling surface of the upper chamber 15, and generates a signal according to the distance L from the permanent magnet 19 due to the deformation of the diaphragm 14. An MR element or a Hall element is used as the magnetic flux detector 20.

When the fuel evaporative gas is generated in the fuel tank 7, a force corresponding to the pressure acts on the diaphragm 14 and moves upward. With the deformation of the diaphragm 14, the permanent magnet 19 also moves upward, and the magnetic flux detector 20 extracts an electric signal corresponding to the amount of movement (distance L).

Further, a communication passage 21 is formed in the lower chamber 16, and an electromagnetic opening / closing valve 22 is arranged in the communication passage 21. That is, the valve body 23 is connected to the communication passage 2 by the spring 24.
1 is closed, and the coil 25 is excited to move the valve body 23 against the biasing force of the spring 24 to open the communication passage 21. A communication passage 26 is formed in the upper chamber 15, and the communication passage 26 and the communication passage 21 are gathered on the tip side. Further, a pair of relief valves 27 and 28 (a positive pressure relief valve 27 and a negative pressure relief valve 28) for relieving gases in opposite directions are provided between the communication passages 26 and 21. That is, the communication passage 29 between the communication passages 26 and 21,
The valve bodies 31 and 32 are urged by 30 in the direction of closing the communication passages 29 and 30 by the springs 33 and 34, and are opened when a pressure greater than the set load of the springs 33 and 34 is applied. In this embodiment, the spring 3
Set load of 3,34 is + 18mmHg (relative pressure) and-
It is 22 mmHg (relative pressure).

As shown in FIG. 1, the communication passages 26 and 21 are communicated with a surge tank 35 of an intake system by a purge pipe 36, and a canister containing activated carbon as an adsorbent is provided in the purge pipe 36. 37 is provided. Then, the fuel evaporative gas in the fuel tank 7 is adsorbed by the activated carbon in the canister 37. Further, the canister 37 is provided with an atmosphere opening hole 38 for introducing fresh air. The purge pipe 36 has a discharge passage 39 on the side closer to the surge tank 35 than the canister 37, and a purge solenoid valve (hereinafter referred to as a purge valve) 40 as an opening / closing means is provided in the discharge passage 39.

In the purge valve 40, the valve body 41 is always urged by a spring (not shown) in a direction to open the seat portion 42, but by exciting the coil 43, the valve body 41 moves the seat portion 42. It is supposed to close. Therefore, the degassing of the coil 43 of the purge valve 40 causes the discharge passage 3
9 is opened, and the discharge passage 39 is closed by exciting the coil 43.

An oxygen concentration sensor 46 is provided in the purge pipe 36 extending from the fuel tank 7 to the canister 37, and this sensor 46 detects the oxygen concentration in the gas passing through the purge pipe 36. The oxygen concentration sensor 46 is shown in FIG.
Indicates. The oxygen concentration sensor 46 is of a diaphragm galvanic cell type. That is, the gas passage 48 is formed in the sensor housing 47 to which the purge pipe 36 is connected, and the gas in the purge pipe 36 passes through the gas passage 48. Further, the sensor housing 47 has a noble metal electrode (P
t, Ag, etc.) 49, base metal electrode (Pb) 50, and electrolytic solution 5
1 and the noble metal electrode 49 is in contact with the air in the gas passage 48 through the Teflon film 52. And both poles 4
A load resistor 53 is connected between 9 and 50, and a potential difference at the load resistor 53 is detected by a voltmeter 54.

In the noble metal electrode 49, O ₂
+ 2H ₂ O + 4e ⁻ → 4OH ⁻ , and in the base metal electrode 50, the reaction of 2Pb → 2Pb ²⁺ + 4e ⁻ progresses and an electric current proportional to the oxygen concentration in the air flows. Here, when the gas passing through the gas passage 48 does not contain a gasoline component, the oxygen concentration is 21%, and when the gas is completely filled with the gasoline component, the oxygen concentration is 0% and the gasoline component density at that time is 2%. It becomes 0.32 g / liter. Therefore, as shown in FIG. 4, the relationship between the voltage proportional to the oxygen concentration and the gasoline component density is obtained. That is, the voltage output by the voltmeter 54 of the oxygen concentration sensor 46 has a correspondence relationship with the gasoline component density.

In this embodiment, as described above, the oxygen concentration is 0.
The gasoline density was calculated from the characteristic that the gasoline density when it becomes% is 2.32 g / l. This characteristic shows that the difference in the outside air temperature and the difference in the gasoline component (especially the difference in the volatility of gasoline) ), The value slightly changes from the value in this embodiment.

In FIG. 1, a control opening 44, which constitutes a gas flow rate detecting means, a gas density detecting means, and a judging means having a built-in microcomputer, is a throttle opening from a throttle sensor (not shown) for detecting the opening of the throttle valve 5. Degree signal, an engine speed signal from a speed sensor (not shown) that detects the speed of the engine 1, an intake air amount signal from an intake air amount sensor (not shown) that detects an intake air amount, and an engine cooling A cooling water temperature signal from a water temperature sensor (not shown) that detects the temperature of water and an intake air temperature signal from an intake air temperature sensor (not shown) that detects the intake air temperature are input. Then, the control circuit 44 receives the throttle valve 5 from these signals.
The opening degree, engine speed, intake air amount, engine cooling water temperature, and intake air temperature are detected.

Further, the control circuit 44 inputs a signal (voltage signal) from the O ₂ sensor 6 and compares it with a threshold value Vref to judge rich / lean of the air-fuel mixture as shown in FIG. .. Then, the control circuit 44 changes (skips) the feedback correction coefficient FAF stepwise in order to increase / decrease the fuel injection amount when reversing from rich to lean and when reversing from lean to rich, and when rich or lean. The feedback correction coefficient FAF is gradually increased or decreased. It should be noted that this feedback control is not performed when the engine cooling water temperature is low and when the vehicle is running under high load and high rotation. Further, the control circuit 44 obtains the basic injection time from the engine speed and the intake air amount, corrects the basic injection time with the feedback correction coefficient FAF, etc. to obtain the final injection time, and at the predetermined injection timing by the fuel injection valve 4. Fuel injection.

The control circuit 44 also receives a signal from the magnetic flux detector 20. Further, the control circuit 44 inputs a signal (voltage value) from the voltmeter 54 of the oxygen concentration sensor 46, and calculates the gasoline component density using the map of FIG. Further, the control circuit 44 is connected to the electromagnetic opening / closing valve 22 and the purge valve 40, and controls the opening / closing of the opening / closing valve 22 and the purge valve 40. A warning lamp 45 as a warning means is provided on the instrument panel of the vehicle, and the control circuit 44
Connected with.

In this embodiment, the diaphragm 14, the permanent magnet 19, the magnetic flux detector 20 and the control circuit 44 shown in FIG. 2 constitute a gas flow rate detecting means, and the oxygen concentration sensor 46 and the control circuit 44 detect the gas density. Constitutes a means.

Next, the operation of the self-diagnosis device in the fuel evaporative gas diffusion prevention device thus constructed will be described. First, the operation of detecting the gas flow rate from the fuel tank 7 to the canister 37 will be described.

Normally, the electromagnetic on-off valve 22 of FIG. 2 is closed, and when the fuel in the fuel tank 7 begins to evaporate, the pressure in the fuel tank 7 rises because the fuel tank 7 is sealed. The pressure in the tank is applied to the diaphragm 14, and the permanent magnet 19 attached to the diaphragm 14 moves upward. An electric signal associated with the upward movement is output from the magnetic flux detector 20 to the control circuit 44. In the control circuit 44, this tank pressure is 15 mmHg and 8 mmHg in FIG.
It is determined whether or not.

When the control circuit 44 reaches 15 mmHg (timing t1 in FIG. 6), it opens the electromagnetic on-off valve 22 and starts the counting operation of the valve opening time. In this way, by opening the electromagnetic opening / closing valve 22, the pressure in the fuel tank 7 drops, and the diaphragm 14 moves downward in an attempt to return to its original position. Then, when the tank internal pressure reaches 8 mmHg, the control circuit 44 (see FIG. 6).
At timing t2), the electromagnetic opening / closing valve 22 is closed and the counting operation for measuring the valve opening time is stopped.

Further, while the temperature of the fuel in the fuel tank 7 rises and the fuel continues to evaporate, such an operation is repeated and the opening time of the electromagnetic opening / closing valve 22 is integrated. This integrated time corresponds to the integrated gas flow rate Q flowing from the tank 7 to the canister 37, as shown in FIG.

Further, the control circuit 44 controls the integrated gas flow rate (unit: liter) thus determined and the oxygen concentration sensor 4
6 Fuel Evaporation Gas Density (Unit: Gram / L)
Multiply by and the fuel evaporative emission gas weight G (unit: gram),
That is, the canister adsorbed gasoline weight is calculated.

However, when the electromagnetic on-off valve 22 fails in the fully closed state or when the magnetic flux detector 20 fails, the fuel gas pressure in the fuel tank 7 rises. Then, as shown in FIG. 8, the tank internal pressure is 18 mm.
When the pressure reaches Hg, the positive pressure relief valve 27 opens and the vaporized gas in the fuel tank 7 escapes to the canister 37 side to reach 18 mmHg.
The deformation (expansion) of the tank 7 is avoided by holding it below.
On the other hand, as when the engine is stopped, the fuel temperature in the tank 7 decreases and the fuel evaporative gas is not generated. The temperature inside the tank 7 decreases and the tank internal pressure becomes a negative pressure. try to. However, −
At 22 mmHg, the negative pressure relief valve 28 opens and air is introduced into the fuel tank 7 from the canister 37 side.
The deformation (contraction) of the tank 7 is avoided by maintaining the pressure at -22 mmHg or more.

Next, self-diagnosis by the control circuit 44 will be described. 9 and 10 show a control routine of the purge valve 40 which is performed every predetermined time. When the ignition switch is turned on, the control circuit 44 sets the cumulative gas flow rate Q, the fuel evaporative gas weight G, and the flag F described later to "0". Then, the control circuit 44 determines in step 100 whether or not the diagnostic condition is satisfied. The establishment of this diagnostic condition means that the engine cooling water temperature is 80 ° C. or higher.

The control circuit 44 has an engine cooling water temperature of 80 ° C.
If it is less than 0, it is determined in step 101 whether or not the flag F is "1". Initially, since F = 0, the process proceeds to step 102. Then, in step 102, the control circuit 44 sets the flag F.
= 0, and the engine cooling water temperature is 40 ° C. in step 103.
It is determined whether or not the above. The control circuit 44 is step 1
If the engine cooling water temperature is not less than 40 ° C. in 03, it is determined in step 104 whether the opening degree of the throttle valve 5 is not less than the predetermined opening α, and if it is not less than the predetermined opening α, step 105
Then, the purge valve 40 is opened. If the engine cooling water temperature is less than 40 ° C. in step 103 or the opening of the throttle valve 5 is less than the predetermined opening α in step 104, the control circuit 44 closes the purge valve 40 in step 106.

On the other hand, when the engine cooling water temperature becomes 80 ° C. or more and the diagnosis condition is satisfied for the first time after the ignition switch is turned on in step 100, the control circuit 44 determines in step 107 of FIG. 10 whether the flag F is “0”. Since F = 0 at the beginning, the process proceeds to step 108.

When the diagnosis condition is satisfied, the control circuit 44 performs preliminary diagnosis by detecting the fuel evaporative gas density in steps 108 to 112. That is, in step 108, it is determined whether or not the density of the fuel evaporative gas supplied from the fuel tank 7 to the canister 37 is a predetermined value (ρ 1) or more, and if it is the predetermined value or more, the purge valve 40 is closed in step 109, In step 110, it is determined whether the feedback correction coefficient FAF has become lean.

That is, if the device is functioning normally, the fuel evaporation gas density is not less than a predetermined value (ρ1; for example, 0.08 g / liter), and the purge valve 40 is opened to evaporate the fuel adsorbed on the activated carbon. When the purge valve 40 is closed in the state where the gas is discharged to the intake system, the fuel evaporative gas becomes the intake pipe 2
It is no longer supplied inside, and the air-fuel ratio becomes lean. Therefore, the FAF difference can be made by closing the purge valve 40. However, the fact that the FAF does not become large may cause an abnormality such as clogging of the purge pipe 36.

If there is no difference in the feedback correction coefficient FAF before and after closing the purge valve 40, the purge valve 40 is closed in step 111, and step 11
In step 2, the flag F is set to "1".

In the routine processing after the next time, since F = 1 in step 107, step 113
Move to. Then, the control circuit 44 determines in step 113 whether the fuel evaporation gas weight G (multiplied value of the integrated gas flow rate and the gas density) sent from the fuel tank 7 to the canister 37 is a predetermined value (G1; for example, 10 grams) or more. If it is equal to or more than the predetermined value, the purge valve 40 is opened for a short time in step 114 to release the fuel evaporative gas adsorbed by the activated carbon of the canister 37, and in step 115, the feedback correction coefficient FAF is rich (for example, 10%). Rich) is determined. That is, if the device is functioning normally, when the purge valve 40 is opened after adsorbing a predetermined amount of fuel evaporative gas on the activated carbon with the purge valve 40 closed, the fuel evaporative gas adsorbed on the activated carbon of the canister 37 is opened. Are supplied into the intake pipe 2, the air-fuel ratio becomes rich, and the purge valve 40 is opened, so that the FAF can be made different. However, the fact that there is no difference in FAF may indicate that the purge pipe 36 has an abnormality such as clogging.

Therefore, if it is determined in step 115 that it is not rich, it is determined that there is an abnormality. Step 115
If it does not become rich, the warning lamp 45 is turned on in step 116.

As described above, in this embodiment, the diaphragm 1
4, the permanent magnet 19, the magnetic flux detector 20, and the control circuit 44 constitute a gas flow rate detecting means, and the oxygen concentration sensor 46 and the control circuit 44 constitute a gas density detecting means. The weight of the fuel evaporative gas sent from the fuel tank 7 to the canister 37 is obtained from the flow rate of the gas sent from the fuel tank 7 to the canister 37 and the fuel evaporative gas density while controlling the (opening / closing means) to close the discharge passage 39, When the weight of the fuel evaporative gas exceeds the set value, the purge valve 40 is controlled to open and close the discharge passage 39, and the air-fuel ratio (feedback correction coefficient FAF) by the O ₂ sensor 6 (air-fuel ratio detecting means) at that time is set. The presence or absence of abnormality is determined by the change of. When the control circuit 44 determines that there is an abnormality by this determination, the warning lamp 45
A warning is given by lighting (warning means).

As a result, in the apparatus of Japanese Patent Application No. 3-75405, when only the gas having a low concentration of fuel evaporative gas is supplied to the canister, the fuel evaporative gas is adsorbed only slightly in the canister. Even if the set value of is increased and re-determination is performed, it may be determined that there is an abnormality, resulting in an erroneous determination. However, in the present embodiment, the gas flow rate and the fuel evaporative gas density in the passage extending from the fuel tank 7 to the canister 37 can be detected to estimate the weight of the fuel evaporative gas adsorbed to the canister 37, and the fuel evaporative gas is taken into the intake pipe. It is possible to more reliably determine the supply abnormality that is not led to 2.

The present invention is not limited to the above embodiment, and for example, in the above embodiment, the oxygen concentration sensor 4 is used.
6, the oxygen concentration of the gas sent from the fuel tank 7 to the canister 37 was obtained, and the fuel evaporative gas density was calculated from this oxygen concentration. In addition, the fuel evaporative gas concentration (gasoline component concentration) was obtained by the HC concentration meter. , To this gas concentration,
The fuel evaporative gas density may be calculated by multiplying the density when the gas is completely filled with the gasoline component (2.32 g / liter).

[0041]

As described in detail above, according to the present invention,
When detecting a supply abnormality in which the fuel evaporative gas is not guided to the intake passage, it is possible to more reliably make a determination in consideration of variations in the fuel gas density.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration around an engine of an embodiment.

FIG. 2 is a sectional view of a fuel tank portion.

FIG. 3 is a diagram showing an oxygen concentration sensor.

FIG. 4 is a sensor characteristic diagram for obtaining a gasoline component concentration.

FIG. 5 is a diagram for explaining sensor signal processing.

FIG. 6 is a diagram for explaining sensor signal processing.

FIG. 7 is a diagram showing a relationship between a passage opening cumulative time and an integrated gas flow rate.

FIG. 8 is a diagram showing changes in fuel tank internal pressure.

FIG. 9 is a flowchart for explaining the operation.

FIG. 10 is a flowchart for explaining the operation.

FIG. 11 is a claim correspondence diagram.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 engine (internal combustion engine) 2 intake pipe as an intake passage 6 O ₂ sensor as air-fuel ratio detecting means 7 fuel tank 14 diaphragm constituting gas flow rate detecting means 19 permanent magnet constituting gas flow rate detecting means 20 gas flow rate detecting means Magnetic flux detector 37 canister 39 discharge passage 40 purge valve as opening / closing means 44 control circuit constituting gas flow rate detecting means, gas density detecting means, judging means 45 warning lamp as warning means 46 gas density detecting means Oxygen concentration sensor

Claims (1)

[Claims] 1. A canister, which is in communication with a fuel tank and stores an adsorbent that adsorbs fuel evaporative gas in the fuel tank, a discharge passage that connects the canister and an intake passage of an internal combustion engine, and the discharge passage. An opening / closing means for opening / closing the discharge passage, an air-fuel ratio detecting means for detecting an air-fuel ratio of the air-fuel mixture to the internal combustion engine, and a gas flow rate detecting means for detecting a gas flow rate supplied from the fuel tank to the canister. A gas density detecting means for detecting a density of fuel evaporative gas supplied from the fuel tank to the canister; and a gas density detecting means for controlling the opening / closing means to close the discharge passage from the fuel tank by the gas flow rate detecting means. Of the fuel evaporative gas sent from the fuel tank to the canister according to the flow rate of the gas sent to the canister and the density of the fuel evaporative gas detected by the gas density detecting means. When the weight of the fuel evaporative gas exceeds the set value, the opening / closing means is controlled to open and close the discharge passage, and the presence or absence of abnormality is detected by the change of the air-fuel ratio by the air-fuel ratio detecting means at that time. A self-diagnosis device in a fuel-evaporated-gas-diffusion prevention apparatus, comprising: determination means for determining; and warning means for issuing a warning when it is determined that there is an abnormality by the abnormality determination by the determination means.