JPH06235355A - Failure diagnosis device for evaporation fuel evaporation prevention device of internal combustion engine - Google Patents

Abstract

(57) [Abstract] [Purpose] A failure diagnosis of an evaporated fuel supply system for supplying evaporated fuel generated in a fuel tank to an intake system is accurately performed in a short time with a simple configuration. [Structure] The suction limit negative pressure value when the internal space volume of the evaporated fuel supply system constituted by the evaporated fuel pipes 2a and 2b, the canister 3, and the space volume in the fuel tank 1 is sucked by the engine intake negative pressure It is detected by the pressure sensor 6 or the like.
By comparing the suction limit negative pressure value with the leak determination value, leak diagnosis can be performed in a short time with a simple configuration. Furthermore,
The fuel remaining amount gauge 20 and the fuel temperature sensor 21 are provided, and the leak determination value is corrected based on the detection results of these,
It is possible to perform leak diagnosis that eliminates the effects of the remaining fuel amount and fuel vapor pressure. If the purge cut valve 4 is used as the opening control valve, it is possible to arbitrarily set the detection accuracy of the leak state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a failure diagnosing device for an evaporation fuel evaporation prevention device for preventing evaporation fuel accumulated in a fuel tank from evaporating into the atmosphere.

[0002]

2. Description of the Related Art Conventionally, in order to prevent vaporized fuel vaporized in a vehicle fuel tank or the like from being released into the atmosphere and causing environmental damage, the vaporized fuel adsorbed by an adsorption means (canister). Is provided with an evaporated fuel evaporation prevention device that guides the intake air to the intake passage by using the intake negative pressure of the engine, which allows the evaporated fuel to be sucked into the combustion chamber together with the intake air and burned (hereinafter referred to as a purge process). It has been proposed to prevent the evaporated fuel from evaporating into the atmosphere.

However, if a failure, which will be described later, occurs in such an evaporated fuel evaporation prevention device, the failure causes a problem. That is, in the case where a leak hole is formed in the middle of the vaporized fuel pipe or a defective seal portion is formed at the joint portion of the vaporized fuel pipe, the vaporized fuel will be evaporated into the atmosphere, and the vaporized fuel of the apparatus will be sufficiently evacuated. Sometimes it wasn't effective.

Therefore, for example, Environmental Protect
ion Agency (EPA) and California
The Air Resources Board (CARB [California Atmospheric Resources Bureau]), etc. diagnoses whether the leak amount of the evaporated fuel from the evaporated fuel pipe or the like is below an allowable value, and if it exceeds the allowable value, While taking measures to prevent the evaporation fuel from evaporating into the atmosphere, a leak diagnosis device (fault diagnosis device) and a diagnosis method therefor are proposed.

FIG. 1 is a diagram showing such a conventional evaporated fuel leak diagnosis device.
Shown in 25. According to FIG. 25, one end of the evaporated fuel pipe 2a is connected to the fuel tank 1, and the other end is connected to the canister 3 for adsorbing the evaporated fuel. A pressure sensor 6 for detecting the pressure inside the evaporated fuel pipe is provided in the middle of the evaporated fuel pipe 2a. The signal of the pressure sensor 6 is input to the control module 50, and the rate of pressure change in the evaporated fuel pipe is obtained based on the signal.

Further, the control module 50 includes
A judgment value for leak diagnosis of evaporated fuel is stored, and a leak of evaporated fuel can be diagnosed by comparing the judgment value with the above-described pressure change rate. One end of the evaporated fuel pipe 2b is connected to the canister 3, and the other end is connected to the intake passage of the engine.
A purge cut valve 4 is provided on the way.
The canister 3 is opened to communicate with the atmosphere during normal engine operation and when introducing evaporated fuel into the intake passage,
A drain cut valve 5 is provided which can be closed at the time of leak diagnosis to shut off from the atmosphere.

With the conventional vaporized fuel leak diagnosis apparatus having such a configuration, the vaporized fuel leak diagnosis is carried out based on the flow chart shown in FIG. In step 1 (indicated as S1 in the figure, the same applies hereinafter), the purge cut valve 4 is opened in a predetermined engine operating state, and the evaporated negative fuel adsorbed in the canister 3 is caused by the negative intake pressure of the engine. Is sucked into.

In step 2, by closing the drain cut valve 5, an evaporated fuel supply system (hereinafter simply referred to as an evaporated fuel supply system) composed of the evaporated fuel pipes 2a and 2b, the canister 3, and the internal space of the fuel tank 1 is formed. ) Is introduced to the engine suction negative pressure. In step 3, it is judged whether the pressure of the evaporated fuel supply system has reached a predetermined negative pressure or whether suction has been performed for a predetermined time.

In step 4, the purge cut valve 4 is closed. As a result, the internal space that maintains the negative pressure (hereinafter,
Evaporative fuel piping 2a, 2b, canister 3, fuel tank 1
The space formed by closing the evaporative fuel supply system constituted by the internal space of the purge cut valve 4 and the drain cut valve 5 is referred to as an internal space. In step 5, the pressure change in the internal space is monitored to detect the pressure change rate (pressure increase rate) toward the atmospheric pressure (Fig.
27).

In step 6, if the pressure change speed is larger than the previously stored determination value, the process proceeds to step 7 and it is diagnosed that the leak amount of the evaporated fuel exceeds the allowable value, and the pressure change is performed. When the speed is equal to or lower than the judgment value, the process proceeds to step 8 and it is diagnosed that the leak amount of the evaporated fuel is equal to or lower than the allowable value. Then, in step 9, the drain cut valve 5 is opened and this flow is ended.

[0011]

However, in such a conventional leak diagnosis apparatus for evaporated fuel, the drain cut valve 5 is closed after the evaporated fuel is sucked into the engine to make the fuel supply system have a predetermined negative pressure, and then the purge cut valve 4 is used. Is closed to form a closed space, and the leak diagnosis is performed by detecting the speed at which the pressure in the closed space rises toward the atmospheric pressure. Therefore, there is a problem that the leak diagnosis requires a long time. At the same time, there is a problem that the diagnostic device becomes complicated because the control theory (algorithm) is complicated.
Further, since the pressure change speed changes under the influence of the amount of fuel remaining in the fuel tank (that is, the influence of the change in the internal space volume) and the fuel vapor pressure, accurate leak diagnosis can be performed. It was not (see Figure 27).

Therefore, the present invention has been made in view of the above-mentioned conventional circumstances, and it is possible to perform a leak diagnosis in a short time, a simple control theory, and an accuracy in consideration of the influence of the residual fuel amount and the fuel vapor pressure. A first object of the present invention is to provide a failure diagnosis device for an evaporated fuel evaporation prevention device for an internal combustion engine, which can perform a good leak diagnosis. By the way, the following problems are caused by the failure of the other evaporated fuel transpiration prevention device.

For example, during the purge process in which the purge cut valve 4 is opened to suck the evaporated fuel adsorbed in the canister 3, the evaporated fuel pipe 2b which is a communication passage between the canister 3 and the engine intake system is clogged. If the purge cut valve 4 is stuck or remains closed despite the instruction to open it, the purge process is performed because the communication between the canister 3 and the engine intake system is cut off. Can not be done. If the defect is left as it is, the canister 3 exceeds the adsorption limit of the evaporated fuel, and the evaporated fuel is not adsorbed by the canister 3 and evaporates into the atmosphere.

If the purge cut valve 4 is stuck and remains open despite the valve closing instruction, the evaporated fuel is always inadvertently sucked into the engine and the air-fuel ratio fluctuates greatly. In addition to the deterioration of drivability, there arises a problem that the exhaust purification performance of the three-way catalyst installed in the exhaust passage for maximizing purification of exhaust harmful components near the stoichiometric air-fuel ratio is lowered.

Therefore, for example, in the failure diagnosing device disclosed in Japanese Patent Laid-Open No. 2-136558, it is determined that the pressure detected by the pressure sensor 6 is equal to or higher than a predetermined value and that the evaporated fuel is sufficiently generated. At this time, the purge cut valve 4 is opened / closed, and an air-fuel ratio change associated with the opening / closing operation is detected by an air-fuel ratio sensor provided in the exhaust passage, and the above-mentioned failure is detected based on the detected air-fuel ratio change. I try to diagnose the presence or absence of.

However, even with such a conventional failure diagnosis device, the evaporated fuel pipe 2 during the purging process is performed.
Since the air-fuel ratio of the evaporated fuel gas (purge mixture) passing through b cannot be specified, it is difficult to set the criterion for judging the change in the engine air-fuel ratio for the failure diagnosis, and the diagnostic accuracy is low. Further, if the diagnosis is executed only when the pressure in the fuel tank 1 is equal to or higher than the predetermined value, there are few diagnosis opportunities.
There is a problem that quick failure detection cannot be performed.

Therefore, a second object of the present invention is to perform a failure diagnosis of an evaporated fuel evaporation preventing apparatus for an internal combustion engine capable of accurately detecting an abnormality in the communication state between the adsorption means (canister) and the engine intake system. To provide a device.

[0018]

Therefore, as shown in FIG. 1, a failure diagnostic device for an evaporated fuel evaporation prevention apparatus for an internal combustion engine according to a first aspect of the invention adsorbs evaporated fuel accumulated inside a fuel tank. Is temporarily adsorbed, and the adsorbing means is communicated with the intake system of the engine in a predetermined engine operating state, and the evaporated fuel is desorbed from the adsorbing means by the negative pressure of the intake of the engine and is sucked and guided to the intake system. In an internal combustion engine equipped with an evaporated fuel transpiration prevention device, pressure detection means A for detecting the pressure in the evaporated fuel supply system from the fuel tank to an intake system via an adsorption means under predetermined conditions, and the evaporated fuel supply system Is communicated only with the intake system of the engine, the converging negative pressure in the evaporated fuel supply system is detected by the pressure detecting means A, and the negative pressure and the leak determination value set in advance are used to detect the negative pressure. evaporation A fuel vapor leakage diagnosis means B for diagnosing a leakage state of charge supply system configured to include a.

Further, as indicated by a broken line in FIG.
Internal volume detection means C for detecting the internal volume of the evaporated fuel supply system, and leak determination value correction means D for correcting the leakage determination value according to the internal volume of the evaporated fuel supply system detected by the internal volume detection means C. And may be added for configuration. Further, as indicated by a broken line in FIG. 3, a fuel vapor generation amount detecting means E for predictively detecting the fuel vapor generation amount in the fuel tank, and a fuel vapor generation amount predicted and detected by the fuel vapor generation amount detecting means E. A leak determination value correcting means F for correcting the leak determination value in accordance with the above may be additionally configured.

As shown by the broken line in FIG. 4, the vaporized fuel evaporation prevention apparatus is provided with an opening control valve G whose opening can be adjusted as means for communicating or blocking the adsorption means with the intake system of the engine, Further, it may be configured to include a leak judgment value setting changing unit H that changes the setting of the leak judgment value according to the opening degree of the opening control valve G. Also, the second
As shown in FIG. 5, the failure diagnosis apparatus for the evaporated fuel evaporation prevention apparatus for an internal combustion engine according to the invention described above temporarily adsorbs the evaporated fuel accumulated in the fuel tank by the adsorbing means, and in a predetermined engine operating state, The adsorption means is in communication with the intake system of the engine, and is equipped with a vaporized fuel evaporation prevention device adapted to separate and suck the evaporated fuel from the adsorption means by the negative pressure of the intake air of the engine to guide it to the intake system, and In an internal combustion engine equipped with an air-fuel ratio feedback control device I for detecting an air-fuel ratio and correcting the basic control value of the air-fuel ratio via the air-fuel ratio feedback correction value so that the detected air-fuel ratio becomes the target air-fuel ratio, Two communication / interruption means J, K are provided in a communication path for communicating the adsorption means with the intake system of the engine, and the empty space is generated when both the communication / interruption means J, K are instructed to communicate with each other. Fuel ratio The feedback correction value and the air-fuel ratios of the two communication / interruption means J, K when the communication instructions are selectively issued to the two communication / interruption means J, K in order. And a communication state abnormality diagnosing means L for diagnosing an abnormality in the communication state between the suction means and the intake system based on the feedback correction value.

[0021]

In the configuration of the failure diagnosis device for the evaporated fuel transpiration prevention device according to the first aspect of the present invention, when the evaporated fuel supply system is communicated with the engine intake system and the evaporated fuel supply system is sucked by the engine intake negative pressure, The negative pressure that converges in the evaporated fuel supply system is detected by the pressure detection means. As shown in FIG. 10, since the negative pressure (suction limit negative pressure) differs depending on the leak state,
By utilizing this, it is possible to easily perform the leak diagnosis of the evaporated fuel in a short time and with a simple configuration.

In the case where the internal volume detecting means is provided, the internal volume of the evaporated fuel supply system is detected by this, and the leak judgment value is corrected in accordance with the detected internal volume. Since the fluctuation of the suction limit negative pressure value due to such a change of the internal volume (change of the remaining fuel amount) can be taken into consideration, the leak diagnosis can be performed with high accuracy.

Further, in the case where the fuel vapor generation amount detecting means is provided, the fuel vapor generation amount is predicted and detected by this, and the leak judgment value is corrected based on the predicted detection amount. Since the fluctuation of the suction limit negative pressure value due to the change of the fuel vapor pressure as shown can be taken into consideration, the leak diagnosis can be performed with high accuracy. Further, when the evaporated fuel evaporation prevention device is provided with an opening control valve capable of adjusting the opening so that the adsorption means communicates with the intake system of the engine, the opening control valve is opened as shown in FIG. Since the negative pressure (suction limit negative pressure value) at which the evaporated fuel supply system converges can be variably set according to the degree, the leak amount detection accuracy can be set arbitrarily. Therefore, if the evaporative fuel leak diagnosis device is provided with a leak judgment value setting changing means, and by changing the leak judgment value according to the opening of the opening control valve, the leak amount to be detected can be arbitrarily set. It becomes possible to change, that is, the allowable value of the leak amount can be arbitrarily changed.

Further, in the configuration of the failure diagnosing device for the evaporated fuel evaporation preventing device according to the second aspect of the invention, the air-fuel ratio when the communication state abnormality diagnosing means issues a communication instruction to both of the two communication / cutting means. Based on the feedback correction value and the respective air-fuel ratio feedback correction values when the disconnection instructions are sequentially and selectively issued to the two communication / interruption means from the state of issuing the communication instruction to the two communication / interruption means. ,
An abnormality in the state of communication between the adsorption means and the engine intake system is diagnosed. As a result, it is possible to easily and highly accurately detect an abnormality in the communication state between the suction means and the engine intake system, that is, the clogging of the communication passage connecting the suction means and the engine intake system, or the failure of the two communication / cutoff means. In addition, the diagnosis can be performed more quickly.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to the accompanying drawings. However, the same parts as those of the conventional example shown in FIG. 25 are designated by the same reference numerals. In FIG. 6, an upper wall of the fuel tank 1 is connected to one end of an evaporated fuel pipe 2a, and the other end of the evaporated fuel pipe 2a is connected to a canister 3 for temporarily adsorbing the evaporated fuel. A pressure sensor 6 for detecting the pressure inside the evaporated fuel supply system is provided in the middle of the evaporated fuel pipe 2a. Here, the pressure sensor 6 constitutes a pressure detecting means.

Then, one end of the evaporated fuel pipe 2b is connected to the canister 3, the other end is connected to the intake passage of the engine, and a purge cut valve 4 is provided in the middle thereof. Further, the canister 3 is provided with a drain cut valve 5 as in the conventional example. still,
The check valve 7 may be omitted as in the conventional example, but if provided, the check valve 7 is opened at a predetermined pressure between the fuel tank 1 and the canister 3 to send the evaporated fuel to the canister 3.
Since it is possible to prevent the evaporative fuel from flowing back into the fuel tank 1 at a pressure lower than the predetermined pressure, the evaporative fuel can be reliably transferred to the canister 3.
Can be adsorbed on. Furthermore, as shown in FIG. 7, a bypass passage 30 that bypasses the check valve 7 is provided.
And a bypass valve 31 is added in the middle of the bypass passage 30 so that the bypass valve 31 can be used for leak diagnosis of evaporated fuel.
If the valve 31 is opened and the check valve 7 is bypassed, it is possible to eliminate an error in leak diagnosis caused by the opening pressure of the check valve 7.
After the leak diagnosis, the bypass valve 31 is closed to change the flow direction of the evaporated fuel to the check valve 7.
Can be regulated by

By the way, the signal of the pressure sensor 6 is input to the control module 50 so that the control module 50 can detect the negative pressure value (suction limit negative pressure value) at which the pressure change based on the signal is monitored and converged. It has become. The pressure sensor 6 constitutes pressure detecting means. Further, the internal memory of the control module 50 stores a leak determination value for leak diagnosis of evaporated fuel, and compares the detected suction limit negative pressure value with the leak determination value to determine the leak state of the evaporated fuel. Can be diagnosed.

With the evaporative fuel leak diagnosing device having such a configuration, the control module 50 carries out a leak diagnosis of the evaporative fuel supply system based on the flow chart shown in FIG. In step 10, the purge cut valve 4 is opened in a predetermined engine operating state, so that the vaporized fuel adsorbed in the canister 3 is sucked into the engine by the negative pressure of the intake air of the engine.

In step 11, by closing the drain cut valve 5, the engine suction negative pressure is introduced into the evaporated fuel supply system constituted by the evaporated fuel pipes 2a and 2b, the canister 3, and the internal space of the fuel tank 1. In step 12, it is determined whether the negative pressure in the evaporated fuel supply system has converged. If it has not converged, the process returns to step 11, and if it has converged, the process proceeds to step 13.

In step 13, the converged negative pressure value (suction limit negative pressure value) is read. In step 14, the read suction limit negative pressure value is compared with a preset stored leak determination value, and if the suction limit negative pressure value is smaller than the leak determination value, proceed to step 15. , It is diagnosed that the leak amount of the evaporated fuel exceeds the allowable value, and when the suction limit negative pressure value is the leak determination value or more, the process proceeds to step 16, and the leak amount of the evaporated fuel is the allowable value or less. (See Figure 10). The step 14,
Reference numerals 15 and 16 constitute evaporative fuel leak diagnosis means.

In step 17, the drain cut valve 5 is opened and this flow is finished. As described above, in the first embodiment, the negative pressure value (suction limit negative pressure value) at which the inside of the evaporated fuel supply system converges when the inside of the evaporated fuel supply system is sucked by the engine intake negative pressure is detected and the suction is performed. Since the leak diagnosis is performed by comparing the limit negative pressure value and the leak determination value, the leak diagnosis can be performed in a shorter time and more easily than the conventional one.

If the bypass passage 30 that bypasses the check valve 7 and the bypass valve 31 are added in the middle of the bypass passage 30, in step 11,
By opening the bypass valve 31, it is possible not to be affected by the opening pressure of the check valve 7 at the time of leak diagnosis, so whether the leak position is closer to the fuel tank 1 than the check valve 7, or It is possible to reduce the error caused by the presence of the engine, and it is possible to perform more accurate vapor fuel leak diagnosis.

As a means for detecting the suction limit negative pressure value, it is of course possible to use a pressure switch which outputs an ON signal to the control unit 50 when the pressure value exceeds a predetermined pressure value. In such a case, leak diagnosis is performed according to the flowchart shown in FIG. That is, steps 20 and 21 are the same as steps 10 and 11 described above, and it is determined in step 22 whether or not a predetermined time has elapsed. If not, return to step 21,
If it has elapsed, go to step 23.

At step 23, it is judged if the ON signal of the pressure switch is inputted to the control module 50. If the ON signal is input, the routine proceeds to step 24, where it is diagnosed that the leak amount of evaporated fuel exceeds the allowable value. If the ON signal is not input, the routine proceeds to step 25, where the leak amount of evaporated fuel is Is below the allowable value. Here, steps 23, 24 and 25 constitute evaporative fuel leak diagnosis means.

At step 26, the drain cut valve 5 is opened and the present flow ends. As described above, when the pressure switch is used instead of the pressure sensor 6, the leak diagnosis can be more simplified. Subsequently, a second embodiment of the present invention will be described with reference to the accompanying drawings. Second
As shown in FIG. 11, the configuration of this embodiment is different from the configuration of the first embodiment in that a fuel gauge 20 for detecting the amount of fuel remaining in the fuel tank 1 is newly provided. The output signal is input to the control module 50. The fuel gauge 20 constitutes an internal volume detecting means of the evaporated fuel supply system.

The signal from the pressure sensor 6 is input to the control module 50 as in the conventional example, and the suction limit negative pressure value of the internal volume of the evaporated fuel supply system is obtained based on the signal. The internal memory of the control module 50 in the second embodiment stores a leak judgment value for leak diagnosis of the evaporated fuel, and by comparing the judgment value with the detected suction limit negative pressure value. , The leak of evaporated fuel can be diagnosed, but such a leak determination value is changed by the negative pressure as shown in the leak determination value correction table in the space volume (change in the remaining fuel amount). The leak determination value is corrected to take into consideration the fluctuation of the suction limit negative pressure value (see FIG. 13). The leak determination value correction table constitutes a leak determination value correction means.

Next, based on the flow chart shown in FIG. 12, the leak diagnosis of the evaporated fuel performed by the control module 50 will be described. In step 30, the purge cut valve 4 is opened in a predetermined engine operating state, so that the vaporized fuel adsorbed in the canister 3 is sucked into the engine due to the intake negative pressure of the engine.

In step 31, the signal of the fuel gauge 20 is read to detect the remaining fuel amount in the fuel tank. In step 32, a leak judgment value is searched from the above-mentioned leak judgment value correction table based on the detected remaining fuel amount. In step 33, the suction negative pressure negative pressure of the engine is introduced into the evaporated fuel supply system by closing the drain cut valve 5.

In step 34, based on the signal from the pressure sensor 6, it is judged whether or not the pressure in the fuel vapor piping has converged. If it has not converged, the process returns to step 33, and if it has converged, the process proceeds to step 35. In step 35, the converged negative pressure value (suction limit negative pressure value) is read. In step 36, the read suction limit negative pressure value is compared with the retrieved leak determination value, and if the suction limit negative pressure value is smaller than the leak determination value, the process proceeds to step 37 to evaporate. It is diagnosed that the fuel leak amount exceeds an allowable value, and if the suction limit negative pressure value is equal to or more than the leak determination value, the process proceeds to step 38, and the evaporated fuel leak amount is diagnosed as being less than the allowable value. To do. Where steps 36, 37, 38
Constitutes an evaporated fuel leak diagnosis means.

In step 39, the drain cut valve 5
To open this flow and end this flow. According to the second embodiment of the present invention having such a configuration, the fuel gauge 20 detects the amount of fuel remaining in the fuel tank, or the internal volume of the evaporated fuel supply system is determined based on the detected amount of fuel. Seeking,
Since the leak determination value is corrected accordingly, it is possible to perform accurate leak diagnosis without being affected by changes in the internal volume of the evaporated fuel supply system. In the second embodiment as well, it goes without saying that the pressure sensor 6 can be substituted for the pressure switch as in the first embodiment.

Next, the third embodiment will be described. The third embodiment is different from the second embodiment in that the leakage due to the fluctuation of the suction limit negative pressure accompanying the change of the fuel vapor generation amount. It is configured to prevent a decrease in diagnostic accuracy. Therefore, as shown in FIG. 15, with respect to the configuration of the second embodiment,
Fuel temperature sensor 21 for detecting the temperature of fuel in the fuel tank 1
Is provided, and the output signal from the fuel temperature sensor 21 is input to the control module 50. The control module 50 can predictively detect the fuel vapor generation amount (in other words, fuel vapor pressure) based on the detected fuel temperature (see FIG. 18). Where the fuel temperature sensor
21 and the control unit 50 constitute the evaporated fuel generation amount detecting means.

The signals of the pressure sensor 6 and the fuel gauge 20 are
As in the second embodiment, the suction limit negative pressure value of the internal volume of the evaporated fuel supply system and the residual fuel amount in the fuel tank (internal volume) are input to the control module 50 so as to be obtained based on the signals of these sensors. It has become. Here, the pressure sensor 6 constitutes a pressure detecting means, and the fuel gauge
20 constitutes an internal space detecting means.

By the way, the internal memory of the control module 50 in the third embodiment stores a leak judgment value for leak diagnosis of evaporated fuel, and the leak judgment value and the detected suction limit negative pressure value. By comparing
Although it is possible to diagnose the leak state of the evaporated fuel, the leak determination value is based on the leak determination value correction tables shown in FIGS. 14 and 19, and changes in the remaining fuel amount and the fuel vapor pressure (FIG. 13). , FIG. 17), the leak determination value correction table shown in FIG. 20 is set in consideration of the variation in the suction limit negative pressure value, and the leak determination value is corrected based on the leak determination value correction table. It has become. The leak determination value correction table constitutes a leak determination value correction means.

Here, the leakage diagnosis of the evaporated fuel which is carried out by the control module 5 will be described with reference to the flow chart shown in FIG. In step 40, the purge cut valve 4 is opened in a predetermined engine operating state, so that the vaporized fuel adsorbed in the canister 3 is sucked into the engine by the negative pressure of the intake air of the engine.

In step 41, the residual fuel amount and the fuel temperature are detected based on the signals from the fuel gauge 20 and the fuel temperature sensor 21. In step 42, the leak determination value correction table (FIG. 20) is searched for a leak determination value based on the detected remaining fuel amount and fuel temperature. In step 43, the suction negative pressure negative pressure of the engine is introduced into the evaporated fuel supply system by closing the drain cut valve 5.

In step 44, it is judged based on the signal from the pressure sensor 6 whether or not the pressure in the evaporated fuel pipe has converged. If it has not converged, the process returns to step 43, and if it has converged, the process proceeds to step 45. In step 45, the converged negative pressure value (suction limit negative pressure value) is read. In step 46, the read suction limit negative pressure value is compared with the retrieved leak determination value. If the suction limit negative pressure value is smaller than the leak determination value, the process proceeds to step 47 to evaporate. It is diagnosed that the leak amount of fuel exceeds the allowable value, and if the suction limit negative pressure value is equal to or more than the leak determination value, the process proceeds to step 48, and the leak amount of evaporated fuel is diagnosed to be less than the allowable value. To do. Here, steps 46, 47, and 48 constitute evaporative fuel leak diagnosis means.

Then, in step 49, the drain cut valve 5 is opened and the present flow chart is terminated.
According to the third embodiment of the present invention having such a configuration, the fuel gauge 20 detects the amount of fuel remaining in the fuel tank, and the leak determination value is corrected accordingly.
Moreover, the fuel temperature sensor 21 detects the temperature of the fuel remaining in the fuel tank, the fuel vapor generation amount is predicted and detected accordingly, and the leak determination value is corrected based on the prediction result. It is possible to perform accurate leak diagnosis in consideration of the variation in the suction limit negative pressure value due to the change in the remaining amount and the change in the fuel vapor pressure.

In the third embodiment, the fuel gauge
20 and the fuel temperature sensor 21 are provided, and the leak determination value is corrected based on these signals. However, of course, only the fuel temperature sensor 21 is provided and the fuel vapor is corrected by the leak determination value correction table shown in FIG. It goes without saying that the leak determination value may be corrected in consideration of only the pressure.
Further, the fuel vapor generation amount detection means has been described using the fuel temperature sensor 21, but the amount of high temperature return fuel returned to the fuel tank without being supplied to the engine is detected by a flow meter or the like, or from the engine operating condition. It is also possible to estimate the fuel temperature in the fuel tank based on the magnitude of the return amount and detect the fuel vapor generation amount.

The pressure sensor 6 in the third embodiment can of course be replaced with a pressure switch capable of detecting a predetermined pressure value or more, as in the first and second embodiments. By the way, it is more advantageous when the opening control valve whose opening can be adjusted is used as the purge cut valve 4 in the first to third embodiments. That is, when the opening degree of the opening control valve is large, the suction limit negative pressure value of the evaporated fuel supply system is close to the intake negative pressure of the engine, but the opening degree of the opening control valve is small. With the use of the characteristic that the suction limit negative pressure of the evaporated fuel supply system approaches zero, the suction limit negative pressure value can be arbitrarily changed by appropriately setting the opening of the opening control valve. Because. This makes it possible to set the leak amount detection accuracy (in other words, the leak amount allowable value) to a desired value (see FIG. 21). That is,
When a large suction limit negative pressure is generated by increasing the opening of the opening control valve, even a very small leak amount can be detected, and the suction limit negative pressure can be reduced by decreasing the opening of the opening control valve. By doing so, it is possible to eliminate the detection of the extremely small leak amount.

Therefore, as shown in FIG. 22, if the leak judgment value is changed according to the opening of the opening control valve, the allowable value of the leak amount can be set to a desired value. Further, if the leak amount detection accuracy is set low, the influence of the detection error of the pressure sensor 6 or the like on the leak diagnosis can be reduced, so that the leak diagnosis can be prevented from being erroneously diagnosed. Here, the leak determination value setting change table shown in FIG. 22 constitutes a leak determination value setting changing means.

In each of the above embodiments, when the accuracy of the leak diagnosis is lowered due to the amount of the fuel remaining in the fuel tank (for example, the suction itself of the engine causes the fuel itself to be sucked up from the fuel tank). In cases such as when it happens), it is natural not to make a diagnosis. Next, a failure diagnosis apparatus for an evaporated fuel evaporation preventing apparatus for an internal combustion engine, which is capable of accurately detecting an abnormality in the communication state between the canister 3 and the engine intake system, which is the second invention, is based on the fourth embodiment. Explain.

As shown in FIG. 23, the overall construction of the fourth embodiment is different from the overall construction of the first embodiment (FIG. 6 or FIG. 7) in that the canister 3 communicates with the engine intake system. A purge cut valve 4A is provided between the purge cut valve 4 of the fuel pipe 2b and the canister 3. Drain cut valve 5, pressure sensor 6, bypass passage 30,
The bypass valve 31 may not be provided in this embodiment.

The purge cut valve 4A incorporates a valve connected to a diaphragm. When the solenoid valve 4B interposed in the negative pressure introducing passage 2c is closed, the valve connected to the diaphragm is closed by a spring or the like. The valve is energized to shut off the evaporated fuel pipe 2b. on the other hand,
The solenoid valve 4B interposed in the negative pressure introducing passage 2c is opened by the opening instruction of the control unit 50,
When the engine intake negative pressure introduced through the negative pressure introduction passage 2c acts on the diaphragm, the urging force of the spring is overcome, the diaphragm and the valve connected thereto move in the valve opening direction, and the evaporated fuel pipe 2b is closed. It is designed to communicate.

When the purge cut valves 4 and 4A are arranged in series in the vaporized fuel pipe 2b as described above,
A valve whose opening can be adjusted by a stepping motor or the like is usually used as the purge cut valve 4, and the flow rate of the purge mixture is adjusted during the purge process to optimize the purge process and the air-fuel ratio of the mixture drawn into the engine. Is controlled so as to prevent large fluctuations in In other words, such a valve is somewhat unreliable due to its complicated structure, and its failure frequency is higher than that of the ON / OFF valve. Therefore, the purge cut valve 4A, which is a highly reliable ON / OFF valve, is provided near the canister 3 in consideration of the case where the valve cannot be fully closed.

An air flow meter 8 for detecting the engine intake air flow rate Q is provided facing an intake manifold (not shown), and a crank angle sensor 9 is built in a distributor (not shown). Then, the control unit 50 counts the crank unit angle signal output from the crank angle sensor 9 in synchronization with the engine rotation for a certain period of time or measures the cycle of the crank reference angle signal to detect the engine rotation speed N. It is supposed to do.

Further, in the exhaust passage of the engine (not shown),
An oxygen sensor 10 is provided. The oxygen sensor 10 is a sensor having an output characteristic that is inverted to the rich side and the lean side (with the stoichiometric air-fuel ratio as a boundary) according to the oxygen concentration in the exhaust gas. By the way, the CPU of the microcomputer incorporated in the control unit 50 controls the fuel injection to the engine by performing arithmetic processing in the following manner. The control unit 50 has a function as an air-fuel ratio feedback control device.

The control unit 50 uses the intake air flow rate Q obtained from the voltage signal from the air flow meter 8 and the engine rotation speed N obtained from the signal from the crank angle sensor 9 as the basic fuel injection amount Tp = c × Q. /
N (c is a constant) is calculated, and the final effective fuel injection amount Te = Tp × (based on the water temperature correction coefficient Kw, which is forcibly corrected to the rich side when the water temperature is low, the air-fuel ratio feedback correction coefficient α, and the like. 1 + Kw + ...) × α is calculated.

Here, the basic fuel injection amount Tp is set by calculation so that the air-fuel ratio of the air-fuel mixture sucked into the engine becomes the stoichiometric air-fuel ratio, but individual manufacturing variations of the fuel injection valve. Since the actual air-fuel ratio deviates from the theoretical air-fuel ratio due to the air-fuel ratio of the purge air during the purging process or the purging process, feedback control by proportional-plus-integral control based on the rich / lean inversion output of the oxygen sensor 10 is performed. The basic fuel injection amount Tp is corrected via the air-fuel ratio feedback correction coefficient α so that the air-fuel ratio of is the stoichiometric air-fuel ratio.

That is, the air-fuel ratio feedback correction coefficient α
The value obtained by averaging corresponds to the amount of deviation between the actual air-fuel ratio and the theoretical air-fuel ratio, that is, the actual air-fuel ratio. In the present embodiment, similar to the invention disclosed in Japanese Patent Application Laid-Open No. 2-136558, the failure diagnosis is performed by using the air-fuel ratio feedback correction coefficient α which changes according to the air-fuel ratio of the purge air during the purging process. The air-fuel ratio feedback correction coefficient α when the two purge cut valves 4 and 4A are both opened,
The two purge cut valves 4 and 4A are sequentially opened and closed, and the failure diagnosis is performed based on the respective air-fuel ratio feedback correction coefficient α at that time, so that the fuel vapor pipe 2b can be clogged and purged easily and accurately. Cut valve 4,
An abnormality in the communication state between the canister 3 and the engine intake system due to a failure such as sticking of 4A is detected.

The communication state abnormality detection control performed by the control unit 50 having the function as the communication state abnormality detecting means will be described below with reference to the flowchart shown in FIG. In step 50, it is judged whether or not the diagnostic condition is satisfied. The judgment is made based on the fact that the air-fuel ratio control is being executed in the steady operation state during the purge process (when both the purge cut valves 4 and 4A are open). In the case of YES, the routine proceeds to step 51, and in the case of NO, the routine proceeds to step 70, where the diagnosis is not established, and this flow is ended.

At step 51, the value obtained by averaging the current air-fuel ratio feedback correction coefficient α is stored as the air-fuel ratio a, and the routine proceeds to step 52. In step 52, the purge cut valve 4 in the open state is closed, and the process proceeds to step 53. In step 53, an average value of the air-fuel ratio feedback correction coefficient α at this time is stored as the air-fuel ratio A in order to detect a change in the air-fuel ratio accompanying the closing of the purge cut valve 4, and the routine proceeds to step 54.

At step 54, if the air-fuel ratio a≈air-fuel ratio A, the flag F1 = 1 is set. If the air-fuel ratio a ≠ air-fuel ratio A, the flag F1 = 0 is set, and the routine proceeds to step 55. Step 55
Then, the purge cut valve 4 is opened, and the routine proceeds to step 56. In step 56, it is determined whether or not the average value of the air-fuel ratio feedback correction coefficient α in this state has returned to the air-fuel ratio a. If YES, it is considered that the diagnosis condition is continued, and the process proceeds to step 57. If NO, the routine proceeds to step 70, where it is determined that the engine operating state has changed and the diagnosis condition has not been satisfied, and this flow is ended.

At step 57, the purge cut valve 4A in the open state is closed, and the routine proceeds to step 58. In step 58, an average value of the air-fuel ratio feedback correction coefficient α at this time is stored as the air-fuel ratio B in order to detect a change in the air-fuel ratio due to the closing of the purge cut valve 4A, and the routine proceeds to step 59.

In step 59, if the air-fuel ratio a≈air-fuel ratio B, the flag F2 = 1 is set. If the air-fuel ratio a ≠ air-fuel ratio B, the flag F2 = 0 is set, and the routine proceeds to step 60. Step 60
Then, it is determined whether or not the flag F1 = 1 and the flag F2 = 1. If YES, purge cut valve 4,
Since the air-fuel ratio does not change even if 4A is opened / closed, the reason why it does not change is that the communication between the canister 3 and the engine intake system is always interrupted (at least one of the purge cut valves 4 and 4A cannot be opened, or Whether the vaporized fuel pipe 2b is clogged) or is always in communication (both the purge cut valves 4 and 4A cannot be closed), or the air-fuel ratio of the purge mixture is the air-fuel ratio a. Go to step 61 to determine if they are equal.

On the other hand, if NO, the air-fuel ratio changes when one of the purge cut valves 4 and 4A is opened and closed, so that the communication / interruption function between the canister 3 and the engine intake system is maintained to some extent. Purge cut valve 4, 4A
It is possible that any of the above may be out of order with the valve open.
If the purge cut valve 4 fails in the open state, control that prevents a large change in the air-fuel ratio of the air-fuel mixture sucked into the engine becomes impossible while optimizing the purge process, while the purge cut valve 4A does not operate. If a failure occurs in the valve open state, as described above, if the relatively unreliable purge cut valve 4 cannot be closed, the communication between the canister 3 and the engine intake system cannot be cut off. Therefore, go to step 64 to diagnose this.

In step 61, whether the air-fuel ratio does not change is because the canister 3 and the engine intake system are always shut off or whether they are in continuous communication.
Alternatively, in order to determine whether the air-fuel ratio of the purge mixture is equal to the air-fuel ratio a, the number of diagnoses is counted (n = n
+1) and proceed to step 62. In step 62, n
= 3 is determined.

If YES, the process proceeds to step 61, and it is diagnosed that the communication state is abnormal. That is, if the above diagnosis is performed three times, and if the canister 3 and the engine intake system are in communication with each other, the purge process proceeds during this period and the air-fuel ratio of the purged mixture gradually decreases, and the air-fuel ratio of the purged mixture is gradually reduced. Is the air-fuel ratio a
Therefore, if the air-fuel ratio does not change even if the purge cut valves 4 and 4A are opened and closed three times in a row, the canister 3 and the engine intake system are always shut off, or It can be diagnosed that they are in communication (the purge cut valves 4 and 4A cannot both be closed).

On the other hand, if NO, return to step 50,
The above flow is repeated. By the way, if it is determined to be NO in step 60, it is possible that one of the purge cut valves 4 and 4A is out of order and is open as described above. , Go to step 64, reset n to 0, and then execute the following steps.

In step 65, it is judged whether or not the air-fuel ratio A≈the air-fuel ratio B. In the case of YES, it is temporarily determined that both the purge cut valves 4 and 4A are normal, and the routine proceeds to step 66. On the other hand, in the case of NO, it is judged that one of the purge cut valves 4 and 4A cannot be closed, and the routine proceeds to step 69, where it is diagnosed that one of the purge cut valves 4 and 4A is abnormal, and the driver After the failure is recognized by turning on a warning lamp or the like, the present flow is ended.

At step 66, the purge cut valve 4A
Is opened again, and it is judged at step 67 whether or not the air-fuel ratio in this state has returned to the original air-fuel ratio a. If YES, it is assumed that the diagnosis condition is continued, the diagnosis result is reliable, and the diagnosis in step 65 is correct.
Then, the routine proceeds to step 68, where it is diagnosed that the communication / cutoff function between the canister 3 and the engine intake system is normal, and this flow is ended.

As described above, according to this embodiment, both the air-fuel ratios A and B when the purge cut valves 4 and 4A are sequentially closed during the purge process are before the valve is closed (during the purge process). If there is no change with respect to the air-fuel ratio a, the operation is performed three times to eliminate erroneous diagnosis when the air-fuel ratio of the purged mixture matches the engine air-fuel ratio. It can be accurately diagnosed that the canister 3 and the engine intake system are always shut off, or that the communication / shutoff function that is always in communication is impaired. Further, by comparing the air-fuel ratio A and the air-fuel ratio B when the purge cut valves 4 and 4A are sequentially closed, it is possible to accurately determine an abnormal state in which one of the purge cut valves 4 and 4A cannot be closed. Can be diagnosed.

In other words, in the present embodiment, the detection values (air-fuel ratios a, A, B) are compared with each other to make a diagnosis, so that it is predetermined as in the prior art (the invention disclosed in Japanese Patent Laid-Open No. 2-136558). It is difficult to set the judgment value because the air-fuel ratio of the purged air-fuel mixture cannot be specified, which is the case when comparing the judgment value with the detection value. Therefore, the canister 3 is easy and highly accurate.
It is possible to diagnose an abnormality in the communication state between the engine and the intake system.

Moreover, according to the present embodiment, it is considered that the evaporated fuel is surely generated with respect to the judgment value and the air-fuel ratio feedback correction coefficient α changes more than the predetermined value as in the conventional example ( Since it is not necessary to limit the diagnosis execution only when the pressure in the fuel tank 1 is equal to or higher than a predetermined value), the chances of diagnosis increase and quick failure diagnosis can be performed. In the present embodiment, the average value of the air-fuel ratio feedback correction coefficient α is compared, but the maximum value or the minimum value of the air-fuel ratio feedback correction coefficient α may be compared.

[0074]

As described above, according to the invention described in claim 1, when the inside of the evaporated fuel supply system is sucked by the engine intake negative pressure, the negative pressure value (suctioned inside the evaporated fuel supply system is converged). The leak diagnosis is performed by detecting the limit negative pressure value) and comparing the suction limit negative pressure value with the leak judgment value. Therefore, the leak diagnosis can be simplified in a shorter time than the conventional one. Can be done.

According to the second aspect of the present invention, in addition to the above effects, the internal volume of the evaporated fuel supply system is detected and the leak judgment value is corrected accordingly. It is possible to perform an accurate leak diagnosis in consideration of the variation of the suction limit negative pressure value due to the change of (the remaining fuel amount in the fuel tank). According to the invention described in claim 3, the fuel vapor generation amount is further predicted and detected, and the leak determination value is corrected based on the prediction result. Therefore, the change in the fuel vapor generation amount (fuel vapor pressure Change), it is possible to perform accurate rake diagnosis in consideration of the variation in the suction limit negative pressure value.

According to the invention described in claim 4, the opening control valve is used as a means for communicating the adsorption means with the intake system of the engine, and the leak judgment value is changed according to the opening degree of the opening control valve. By doing so, it becomes possible to set the allowable value of the leak amount to a desired value, and further, if the leak amount detection accuracy is set low, the influence of the detection error of the pressure detection means on the leak diagnosis will be affected. Since it can be reduced, it is possible to prevent erroneous diagnosis of leak diagnosis.

According to the invention described in claim 5, 2
The air-fuel ratio feedback correction value when both the communication / cutoff means are instructed to be instructed, and the two communication / interruption means are selectively instructed to be interrupted in order from the state in which the two communication / interruption means are both instructed to communicate. Since the abnormality of the communication state between the adsorption means and the engine intake system is diagnosed based on the respective air-fuel ratio feedback correction values when the That is, it is possible to diagnose easily and highly accurately and quickly whether or not the communication passage connecting the adsorption means and the engine intake system is clogged or the two communication / cutoff means have a failure.

[Brief description of drawings]

FIG. 1 is a block diagram of a failure diagnosis device according to a first aspect of the invention.

FIG. 2 is a block diagram of a failure diagnosis device according to a second aspect of the invention.

FIG. 3 is a block diagram of a failure diagnosis device according to a third aspect of the invention.

FIG. 4 is a block diagram of a failure diagnosis device according to a fourth aspect of the invention.

FIG. 5 is a block diagram of a failure diagnosis device according to a fifth aspect of the invention.

FIG. 6 is an overall configuration diagram according to a first embodiment of the present invention.

FIG. 7 is another overall configuration diagram according to the embodiment.

FIG. 8 is a flowchart according to the embodiment.

FIG. 9 is a flowchart (for a pressure switch) according to the embodiment.

FIG. 10 is a diagram showing a pressure change with time of the internal volume of the evaporated fuel supply system depending on the presence or absence of a leak according to the embodiment.

FIG. 11 is an overall configuration diagram according to a second embodiment of the present invention.

FIG. 12 is a flowchart according to the embodiment.

FIG. 13 is a diagram showing a change in pressure of the internal volume with time due to a change in the internal volume of the evaporated fuel supply system according to the above embodiment.

FIG. 14 is a leak determination value correction table for changes in the internal volume of the evaporated fuel supply system according to the embodiment.

FIG. 15 is an overall configuration diagram according to a third embodiment of the present invention.

FIG. 16 is a flowchart according to the embodiment.

FIG. 17 is a diagram showing a pressure change with time of the internal volume due to a change in a fuel vapor generation amount (fuel vapor pressure) according to the embodiment.

FIG. 18 is a diagram showing a relationship between a fuel temperature and a fuel vapor generation amount according to the embodiment.

FIG. 19 is a leak determination value correction table for changes in the fuel vapor generation amount according to the embodiment.

FIG. 20 is a leak determination value correction table that takes into consideration a change in the fuel vapor generation amount and a change in the internal volume of the evaporated fuel supply system according to the embodiment.

FIG. 21 is a diagram showing a pressure change with time of the internal volume of the evaporated fuel supply system when the opening degree of the opening control valve is changed.

FIG. 22 is a leak determination value setting change table for the opening of the opening control valve.

FIG. 23 is an overall configuration diagram according to a fourth embodiment of the present invention.

FIG. 24 is a flowchart according to the embodiment.

FIG. 25 is an overall configuration diagram according to a conventional example.

FIG. 26 is a flowchart according to a conventional example.

FIG. 27 is a view showing a pressure change with respect to time showing an influence of a residual fuel amount and a fuel vapor pressure on a pressure increase rate of an internal volume of an evaporated fuel supply system.

[Explanation of symbols]

 1 Fuel Tank 2 Evaporative Fuel Pipe 2a Evaporative Fuel Pipe 2b Evaporative Fuel Pipe 3 Canister 4 Purge Cut Valve 4A Purge Cut Valve 5 Drain Cut Valve 6 Pressure Sensor 7 Check Valve 8 Air Flow Meter 10 Oxygen Sensor 20 Fuel Remaining Gauge 21 Fuel Temperature Sensor 50 control module

Claims (5)

[Claims] 1. An evaporative fuel accumulated in a fuel tank is temporarily adsorbed by an adsorbing means, the adsorbing means is made to communicate with an intake system of the engine in a predetermined engine operating state, and the adsorbing means is caused by an intake negative pressure of the engine. In an internal combustion engine equipped with a vaporized fuel evaporation prevention device that separates and sucks vaporized fuel and guides it to the intake system, within the vaporized fuel supply system that reaches the intake system from the fuel tank through adsorption means under predetermined conditions When the vaporized fuel supply system is communicated only with the intake system of the engine, the negative pressure that converges in the vaporized fuel supply system is detected by the pressure detecting means, and the negative pressure An evaporated fuel evaporation prevention apparatus for an internal combustion engine, comprising: an evaporated fuel leak diagnosis means for diagnosing a leaked state of evaporated fuel based on a pressure and a preset leak judgment value. Disabilities diagnostic equipment. 2. An internal volume detecting means for detecting an internal volume of the evaporated fuel supply system, and a leak determination value for correcting a leak determination value according to the internal volume of the evaporated fuel supply system detected by the internal volume detecting means. A failure diagnosis device for an evaporated fuel evaporation prevention device for an internal combustion engine according to claim 1, further comprising: a correction unit. 3. A fuel vapor generation amount detecting means for predictively detecting a fuel vapor generation amount in a fuel tank, and a leak judgment value is corrected according to the fuel vapor generation amount predicted and detected by the fuel vapor generation amount detecting means. 3. A failure diagnosis device for an evaporated fuel evaporation prevention device for an internal combustion engine according to claim 1, further comprising a leak judgment value correction means. 4. An evaporative fuel transpiration prevention device is provided with an opening control valve capable of adjusting the opening as means for communicating or blocking the adsorption means with an intake system of an engine, and the opening control valve has an opening control valve. A leak determination value setting changing means for changing the setting of the leak determination value in response to the leak determination value setting change means, and the evaporated fuel evaporation prevention apparatus for an internal combustion engine according to any one of claims 1 to 3, Fault diagnosis device. 5. Evaporated fuel accumulated in a fuel tank is temporarily adsorbed by an adsorbing means, the adsorbing means is made to communicate with an intake system of the engine in a predetermined engine operating state, and the adsorbing means is caused by an intake negative pressure of the engine. Equipped with a vaporized fuel evaporation prevention device adapted to separate and suck the vaporized fuel and guide it to the intake system, and detect the air-fuel ratio of the engine intake air-fuel mixture so that the detected air-fuel ratio becomes the target air-fuel ratio. In an internal combustion engine equipped with an air-fuel ratio feedback control device that corrects a basic control value of an air-fuel ratio via an air-fuel ratio feedback correction value, 2 is provided in a communication passage that connects the adsorbing means and an intake system of the engine.
From the state in which two communication / interruption means are provided and the air-fuel ratio feedback correction value when both the communication / interruption means are instructed to communicate, and the two communication / interruption means are both instructed to communicate. A communication state abnormality for diagnosing an abnormality in the communication state between the adsorbing means and the intake system based on the respective air-fuel ratio feedback correction values when the shutoff instruction is selectively issued to the two communication / blocking means in order. A failure diagnostic device for an evaporated fuel evaporation prevention device for an internal combustion engine, comprising: a diagnostic means.