JPH0921359A - Failure diagnostic method of evaporative emission purge system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize an accurate failure diagnosis, by detecting the pressure in a purge passage plurally, in an engine operating condition to satisfy the diagnostic condition, finding the difference between the maximum value and the minimum value of its pulsation pressure, and deciding that an evaporative emission purge system is abnormal when the difference is smaller than a specific deciding value. SOLUTION: The pressure in a purge passage 12 which generates a pulsation by opening and closing a duty control valve 13 to control the purge flow rate of the purge passage 12, is detected by a pressure sensor 17. The maximum value and the minimum value of the pulsation pressure are found from the plural detected pressures, the difference of them is calculated, and when the difference is smaller than a preset deciding value, it is decided that an evaporative emission purge system is abnormal. Consequently, an accurate failure diagnosis can be carried out without monitoring the opening and closing condition of the duty control valve 13, and without receiving the influence of the pressure in the transient condition.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for diagnosing a failure in an evaporative purge system in which vaporized fuel in a fuel tank is stored in a canister and the vaporized fuel stored in the canister is sucked into an engine via a duty control valve. .

[0002]

2. Description of the Related Art Generally, in vehicles such as automobiles, in order to prevent the vaporized gas of fuel generated in a fuel tank from being discharged to the atmosphere, the vaporized fuel gas is temporarily adsorbed on activated carbon in a canister or the like. A so-called evaporative purge system is provided for storing and sucking the evaporated fuel gas in the canister from the intake passage into the combustion chamber of the engine under set operating conditions.

In this case, if an abnormality occurs in the evaporative purge system, it not only causes air pollution but also causes deterioration of exhaust emission and fuel consumption. Therefore, many of them also have a function of diagnosing a failure of the evaporative purge system. For example, in Japanese Unexamined Patent Publication No. 2-130255, the open / closed state of a purge control valve provided in a purge passage communicating with a canister and an intake pipe is monitored, and the purge passage when the purge control valve is switched is monitored. A technique for determining that an abnormality has occurred when the differential pressure is smaller than a set value is disclosed.

[0004]

However, in the above-mentioned prior art, there is a problem that the control becomes complicated because it is necessary to monitor the open / closed state of the purge control valve.

Further, there is a delay until the pressure in the purge passage reaches a constant value after switching the purge control valve.
Simply by detecting the pressure difference in the purge passage before and after switching the purge control valve, the transient pressure is detected,
There is a possibility that the calculated pressure difference becomes small and a false diagnosis is made. In particular, when the purge control valve is a duty control valve and the purge control valve is constantly opened and closed within a short time, the time from the switching of the purge control valve to the detection of the pressure in the purge passage changes every time the pressure is detected. Then, the pressure in the transient state is detected, and even if the engine operating conditions are the same, a constant pressure cannot be detected, and there is a possibility of erroneous diagnosis.

The present invention has been made in view of the above circumstances, and does not monitor the open / closed state of the purge control valve, and even when the purge control valve is a duty control valve, the influence of the pressure in the transient state is affected. It is an object of the present invention to provide a failure diagnosis method for an evaporative purge system that can perform accurate failure diagnosis with simple control without receiving the trouble.

[0007]

In order to achieve the above object, a method for diagnosing a failure of an evaporative purge system according to claim 1 of the present invention provides a purge flow rate to a purge passage communicating a canister for storing evaporated fuel and an intake system. A duty control valve for controlling is installed, and a pressure sensor is connected to the purge passage, and when the engine is in an operating state that satisfies the diagnostic condition, the pressure in the purge passage that pulsates by opening and closing the duty control valve is A plurality of pressure sensors are used to detect the maximum and minimum values of the pulsating pressure from these multiple detected pressures, and the difference is calculated.If the difference is smaller than a preset judgment value, the evaporative purge The system determines that something is wrong.

Further, according to a second aspect of the present invention, there is provided a method for diagnosing a failure of an evaporative purge system, wherein a duty control valve for controlling a purge flow rate is provided in a purge passage communicating a canister for storing evaporated fuel and an intake system. , A pressure sensor that can also be used for other failure diagnosis or control is connected to the purge passage through a switching valve, and the purge passage that pulsates by opening and closing the duty control valve when the engine is in an operating condition that satisfies the diagnosis condition. The pressure inside is switched to the side where the pressure sensor and the purge passage communicate with each other, and a plurality of pressure sensors detect a plurality of pressures, and the maximum and minimum values of the pulsating pressure are calculated from the plurality of detected pressures. Then, the difference is calculated, and when this difference is smaller than the preset judgment value, the evaporative purge system judges that it is abnormal.

In the method for diagnosing a failure of the evaporative purge system according to the first aspect, when the engine is in an operating condition satisfying the diagnostic conditions, the inside of the purge passage pulsating by opening and closing the duty control valve for controlling the purge flow rate of the purge passage is pulsated. A plurality of pressures are detected by the pressure sensor. Then, the maximum value and the minimum value of the pulsation pressure are obtained from the plurality of detected pressures and the difference is calculated, and when the difference is smaller than a preset determination value, the evaporative purge system determines that it is abnormal. .

In the method for diagnosing a failure of the evaporative purge system according to the second aspect, the purge passage pulsating by opening and closing a duty control valve for controlling the purge flow rate of the purge passage when the engine is in an operating condition satisfying the diagnostic condition. A plurality of internal pressures are detected by a pressure sensor which is also used for other failure diagnosis or control by switching the switching valve. Then, the maximum value and the minimum value of the pulsation pressure are obtained from the plurality of detected pressures and the difference is calculated, and when the difference is smaller than a preset determination value, the evaporative purge system determines that it is abnormal. .

[0011]

Next, an embodiment of the present invention will be described with reference to the drawings. 1 to 8 show Embodiment 1 of the present invention.
1, FIG. 1 is a flowchart of an evaporative purge system failure diagnosis process, FIG. 2 is a flowchart following FIG. 1, FIG. 3 is a schematic configuration diagram of an engine control system, FIG. 4 is a circuit configuration diagram of a control device, and FIG. FIG. 6 is an explanatory diagram of a diagnostic region based on the negative pressure of the pipe and the engine speed, FIG. 6 is an explanatory diagram of a diagnostic region based on the throttle opening and the engine speed, and FIG. 7 is an explanatory diagram of a diagnostic region based on the basic injection pulse width and the engine speed. 8 is a time chart showing an example of pressure behavior in the evaporation purge passage.

In FIG. 3, reference numeral 1 is an engine,
The intake passage 3 is communicated with each intake port 2a formed in the cylinder head 2 of the engine 1.
Further, a throttle valve 4 is installed. A throttle opening sensor 5 for detecting the opening of the throttle valve 4 is connected to the throttle valve 4, and an intake air amount sensor 6 is provided on the upstream side thereof. An air cleaner 7 is attached on the upstream side of 6.

An unillustrated spark plug whose tip is exposed to the combustion chamber is attached to the cylinder head 2 for each cylinder, and an injector 8 is exposed immediately upstream of each intake port 2a of each cylinder. . This injector 8
The fuel, which is communicated with the fuel tank 9 through a fuel pipe (not shown), regulates the fuel at a specified pressure to the intake port 2
It is designed to jet to a.

An evaporative fuel gas discharge passage (evaporation passage) 10 for discharging the evaporated fuel generated in the fuel tank 9 extends from the upper portion of the fuel tank 9 and is provided with an adsorption portion made of activated carbon or the like. It communicates with the upper part of the canister 11. The canister 11 is provided with a fresh air introduction port communicating with the atmosphere at the bottom, and a purge passage 12 for guiding the vaporized fuel gas stored in the adsorption unit together with the fresh air from the fresh air introduction port extends from the upper part. Has been issued.

The purge passage 12 is located at the downstream side when the throttle valve 4 is fully closed via a purge control valve 13 which is a linear solenoid valve whose valve opening is controlled by a duty signal. And communicates with the intake passage 3.

Further, the purge passage 12 is branched between the canister 11 and the purge control valve 13, and the branch passage 14 is connected to the pressure sensor 17.

A pressure detection passage 15a is provided downstream of the throttle valve 4 in the intake passage 3 and communicates with an intake pipe pressure sensor 15 for detecting the pressure in the intake passage 3.

Further, a water temperature sensor 1 is provided in a cooling water passage 18 formed in the cylinder block 1a of the engine body 1.
9, an O2 sensor 21 faces an exhaust passage 20 communicating with the exhaust port 2b of the cylinder head 2, and a catalytic converter 22 is provided downstream of the O2 sensor 21.

On the other hand, reference numeral 30 is an electronic control unit (ECU).
The ECU 30 is provided with the throttle opening sensor 5, the intake air amount sensor 6, the intake pipe pressure sensor 15, the pressure sensor 17, the water temperature sensor 19, the O2 sensor 21, the crank angle sensor 23 for detecting the crank angle, and the vehicle speed. Sensors such as a vehicle speed sensor 24 for detecting are connected, and actuators such as the injector 8 and the purge control valve 13 are connected.

The ECU 30, as shown in FIG.
PU31, ROM32, RAM33, input port 34,
The output port 35 is mainly composed of a microcomputer connected to each other via a bus line 36 and its peripheral circuits.

The O 2 sensor 21, the crank angle sensor 23, and the vehicle speed sensor 24 are connected to the input port 34 via waveform shaping circuits 37, 38, 39, respectively.
The throttle opening sensor 5, intake air amount sensor 6, intake pipe pressure sensor 15, pressure sensor 17, water temperature sensor 19
Are A / D converters 40, 41, 42, 43, 4 respectively.
4 are connected. In addition, the output port 35
In addition, the injector 8, the purge control valve 13, and an alarm indicator 25 described later are respectively provided in the drive circuit 4
They are connected via 5, 46 and 48.

A control program and fixed data for various controls are stored in the ROM 32, and output signals of the sensors and switches after data processing are performed in the RAM 33 and calculations by the CPU 31. Stores processed data. In the CPU 31, according to the control program stored in the ROM 32,
In addition to performing air-fuel ratio control, ignition timing control, purge control, etc., failure diagnosis of the evaporative purge system is performed, and when it is determined that there is a failure, an abnormality is displayed on the alarm indicator 25 and a driver is warned.

The failure diagnosis processing of the evaporative purge system by the ECU 30 will be described below with reference to the flowcharts of FIGS. 1 and 2.

The programs shown in FIGS. 1 and 2 are executed at regular intervals (for example, 10 ms), for example, by interruption when they are in the purgeable operation region described below.

The purgeable operating region is the suction pipe pressure Pb,
Any of parameters representing engine load such as throttle opening θ and basic injection pulse width Tp, parameters representing traveling environment conditions (high altitude / low altitude traveling) such as atmospheric pressure Pa, and parameters representing engine speed conditions such as engine speed Ne. Alternatively, it is indicated as a setting range determined by the combination thereof, and whether the engine operating state is within this setting range determines whether or not the purgeable operating range is satisfied.

Specifically, for example, as shown in FIG.
Suction pipe pressure Pb is approximately -200 mmHg to -400 mmH
It is in the range of g and the engine speed Ne is approximately 2000 rp.
As shown in FIG. 6, the engine speed Ne is approximately 2000 rpm to 350 rpm when the throttle opening θ is approximately 5 to 20 degrees, as shown in FIG.
As shown in FIG. 7, the basic injection pulse width Tp is approximately 1.3 ms to 3.6 m, as shown in FIG.
s range, engine speed Ne is approximately 2000 rp
The medium-load region of the diagonal line in the range of m to 3500 rpm is set as the purgeable operating region, and when the engine operating state is in this region, the failure diagnosis of the evaporative purge is started, so that the amount of the evaporative purge is extremely small. It is possible to avoid a diagnosis under a stable situation and perform a diagnosis in a stable operation region, and obtain an accurate failure diagnosis result.

When the program starts in the purgeable operating range, first, in step (hereinafter abbreviated as "S") 101, it is judged whether or not the operating condition is such that diagnosis is possible. This diagnosable operating condition is the suction pipe pressure P.
If the difference between b and atmospheric pressure Pa is more than a set value, and the control duty value to the purge control valve 13 is within the set range, it can be diagnosed if the operating condition satisfies this condition. If the condition is not satisfied, it is determined that the reliable diagnosis cannot be performed, the routine is exited, and the failure diagnosis is not executed. That is, when the difference between the suction pipe pressure Pb and the atmospheric pressure Pa is smaller than the set value, the evaporative purge amount is small and the pressure in the purge passage is small between the purging and the purging stop, so that a reliable diagnosis can be made. Do not run diagnostics as they cannot be done. Further, when the control duty value to the purge control valve 13 is larger than the set range, the purge control valve 13 is always opened when the control duty value approaches 100%, and fluctuation (pulsation) does not appear in the pressure in the purge passage, which is reliable. The diagnosis is not executed because it cannot be performed. Similarly,
When the control duty value to the purge control valve 13 is smaller than the set range, when the control duty value approaches 0%, the purge control valve 13 is always closed, and fluctuations (pulsation) in the pressure in the purge passage do not appear, so a reliable diagnosis is made. Do not run diagnostics because you cannot.

In step S101, it is determined that the operating condition is fault diagnosable. When the process proceeds to step S102, it is determined whether or not the pressure sensor 17 is determined to be normal by another fault diagnostic processing program, and it is determined to be abnormal. In this case, while the routine is exited and the diagnosis is stopped, if the pressure sensor 17 is normal, the process proceeds to S103, where the number of pressure measurement samplings n
Is set to 0.

Next, in S104, the pressure sensor 17
Thus, the pressure P0 in the purge passage 12 is detected.

Then, in S105, the pressure P0 in the purge passage is compared with the maximum pressure value P1, and when the pressure P0 in the purge passage is larger than the maximum pressure value P1 (P1 <P0
In the case of), the process proceeds to S106, the pressure P0 in the purge passage is set as the maximum pressure value P1 (P1 ← P0), and S10
9, the pressure P0 in the purge passage is increased to the maximum pressure value P1.
In the following cases (when P1 ≧ P0), the process proceeds to S107.

In S105, it is determined that P1 ≥ P0 and S
Proceeding to 107, the pressure P0 in the purge passage and the minimum pressure value P
When the pressure P0 in the purge passage is smaller than the minimum pressure value P2 (when P2> P0), the routine proceeds to S108, where the pressure P0 in the purge passage is set as the minimum pressure value P2 (P2 ← P0), while proceeding to S109, when the pressure P0 in the purge passage is the minimum pressure value P2 or more (P2 ≤ P
If 0), the process directly proceeds to S109.

When the processing proceeds to S109, the sampling number n is incremented (n = n + 1), and the processing proceeds to S110. When the sampling number is equal to or more than the set value N (n ≧ N), the processing proceeds to S111 and sampling is performed. If the number has not reached the set value N, the process returns to S104. That is, steps S103 to S110 are procedures for obtaining the maximum pressure value P1 and the minimum pressure value P2 from the N detected purge passage internal pressures P0.

In the above S110, n ≧ N and S111
If it is determined that the operating condition has changed, the difference between the suction pipe pressure Pb and the atmospheric pressure Pa is not more than the set value, and the control duty value to the purge control valve 13 is out of the set range. If the operating conditions for accurately performing the failure diagnosis are not satisfied, it is determined that the reliable diagnosis cannot be performed, and the routine is exited, and the failure diagnosis is not executed.

When it is determined in S111 that there is no change in the operating conditions, the process proceeds to S112, and the differential pressure ΔP between the maximum pressure value P1 and the minimum pressure value P2 is calculated (ΔP ← P1-P2
), The flow proceeds to S113, and the differential pressure ΔP is compared with the determination value PSET that has been set beforehand by experiments or the like.

When the differential pressure ΔP is equal to or larger than the judgment value PSET (when PSET ≦ ΔP), the process proceeds to S114, the evaporative purge system is judged to be normal, and the process proceeds to S118, where the maximum pressure value P1 is set as the atmospheric pressure value. If the differential pressure ΔP is smaller than the judgment value PSET (PSET> ΔP), the fluctuation (pulsation) of the pressure in the purge passage is small and any part of the purge passage (including the purge control valve 13) is exited from the routine. ), The amount of evaporative purge is reduced or the evaporative purge is not performed, or it is considered that the purge control valve 13 is continuously open and the evaporative purge is always performed. Then, the process proceeds to S116, an alarm is displayed on the alarm display 25 to warn the driver, and the process proceeds to S117.

At S117, the atmospheric pressure value is fixed to a predetermined value (a predetermined value at which controllability can be ensured at a minimum), and the routine is exited.

That is, when the evaporative purge is stopped with the purge control valve 13 closed, the pressure detected by the pressure sensor 17 is the pressure in the canister 11 because there is no flow of the evaporated fuel gas in the purge passage 12, but the canister 11 Since the lower part of the adsorption section is open to the atmosphere, as a result, of the pressure detected by the pressure sensor 17 when the evaporation purge is stopped,
The maximum pressure value P1 can be regarded as atmospheric pressure. Therefore, if the process proceeds from S113 to S114 and the evaporative purge system is determined to be normal, the process proceeds to S118 and the maximum pressure value P1 is set as the atmospheric pressure value. This atmospheric pressure value is used as data in other control or failure diagnosis. On the other hand, if it is determined that the evaporative purge system is abnormal by proceeding from S113 to S115, there is a possibility that the maximum pressure value P1 is abnormal (for example, the purge control valve 13 is not closed). The atmospheric pressure value is fixed at a predetermined value.

P1 and P2 set by the above program
, ΔP is shown in the time chart of FIG. In this example, the control duty value to the purge control valve 13 is approximately 50%, and a plurality of purge passage pressures that fluctuate (pulsate) according to the opening and closing of the purge control valve 13 are checked at predetermined sampling times. Then, the maximum pressure value P1 and the minimum pressure value P2 are obtained from the calculated value, and ΔP (= P1 −
P2) is calculated. The maximum pressure value P1 is set as the atmospheric pressure value. Here, when an abnormality occurs in which the purge control valve 13 cannot be completely closed, the maximum pressure value P1 becomes small and PSET> ΔP, and the abnormality is detected. On the contrary, when an abnormality occurs in which the purge control valve 13 cannot be completely opened, the minimum pressure value P2 becomes large and PSET>
It becomes ΔP and an abnormality is detected. Further, when the purge control valve 13 is left open or is left closed, ΔP becomes close to 0 and PSET> ΔP, and an abnormality is detected. Similarly, in the purge passage, if a dropout, crushing, blockage or the like occurs in the passage, PSET> ΔP and an abnormality is detected.

As described above, according to the first embodiment of the present invention, a plurality of pressures in the purge passage that fluctuate (pulsate) due to opening / closing of the duty-controlled purge control valve are detected by the pressure sensor at a predetermined sampling time. Since the maximum and minimum values of the pulsating pressure are calculated from these multiple detected pressures and the pressure difference is calculated, the maximum and minimum values of the pulsating pressure can be reliably detected, and the transient It is possible to prevent erroneous diagnosis due to the influence of the pressure change of the state. Also,
After the engine operating conditions satisfying the diagnostic conditions,
It is only necessary to detect a plurality of pressures in the purge passage at a predetermined sampling time, and in particular, it is not necessary to monitor the open / closed state of the purge control valve, and accurate failure diagnosis can be performed with simple control. Furthermore, the atmospheric pressure value can also be measured by executing the failure diagnosis, and it also has a function as an atmospheric pressure sensor.

Next, FIGS. 9 to 12 show a second embodiment of the invention.
9 is a schematic configuration diagram of an engine control system, FIG. 10 is a circuit configuration diagram of a control device, FIG. 11 is a flowchart of an evaporative purge system failure diagnosis process, and FIG. 12 is a flowchart subsequent to FIG. Incidentally, Embodiment 2 of the present invention
In the first embodiment of the present invention, the pressure sensor for detecting the pressure in the purge passage also serves as the intake pipe pressure sensor.

That is, as shown in FIG. 9, a switching valve 16 which is a two-way switching valve is provided in the middle of the branch passage 14 from the purge passage 12, and this switching valve 16 is provided.
Is connected to the pressure detection passage 15a from the intake passage 3. Further, as shown in FIG. 10, the switching valve 1
6 is an output port 35 of the electronic control unit (ECU) 50.
To a drive circuit 47. In Embodiment 2 of the present invention, the portion related to the intake pipe pressure sensor described in Embodiment 1 of the present invention is not provided, and other configurations are the same as those of Embodiment 1 of the present invention.

The failure diagnosis processing of the evaporative purge system by the ECU 50 will be described below with reference to the flowcharts of FIGS. 11 and 12. The main procedure of this program, such as the diagnosis starting condition and the like, is the same as that of the first embodiment of the invention, and only the procedure different from the first embodiment of the invention will be described in detail.

When the program is started and the process proceeds from S101 to S102 and the pressure sensor 17 is determined to be normal, the process proceeds to S201, the switching valve 16 is operated, and the pressure sensor 17 and the purge passage 12 are connected. By this procedure, the pressure in the purge passage 12 can be detected. After that, in S103 to S110, the maximum pressure value P1 and the minimum pressure value P2 are obtained from the N detected purge passage internal pressures P0, the process proceeds to S111, and it is determined whether or not the operating conditions have changed. If there is a change in the operating conditions, it is determined that a reliable diagnosis cannot be made, and the process jumps to S202. If there is no change in the operating conditions, the process proceeds to S112, ΔP is calculated, and the normality / abnormality of the evaporation purge system is determined in S113 to S116, and S117 or S11 is determined.
The atmospheric pressure value is set at 8 and the process proceeds to S202. This S202
Then, the switching valve 16 is operated in reverse, and the pressure sensor 17
Communicates with the intake passage 3. That is, the above S201
That is, the switching valve 16 operated in step 3 is returned to its original state. After that, the routine is exited to complete the failure diagnosis.

As described above, according to the second embodiment of the present invention, in addition to the effects of the first embodiment of the present invention, cost reduction is achieved without providing a dedicated pressure sensor for failure diagnosis of the evaporative purge system. It becomes possible. still,
In Embodiment 2 of the present invention, the pressure sensor is also used as the intake pipe pressure sensor, but it can also be used as another pressure sensor for failure diagnosis or control.

[0045]

As described above, according to the present invention, the influence of the pressure in the transient state is monitored without monitoring the open / closed state of the purge control valve and even if the purge control valve is a duty control valve. Accurate failure diagnosis can be performed by simple control without receiving the error.

[Brief description of drawings]

FIG. 1 is a flowchart of an evaporation purge system failure diagnosis process according to a first embodiment of the invention.

FIG. 2 is a flowchart continued from FIG. 1;

FIG. 3 is a schematic configuration diagram of an engine control system according to the first embodiment of the invention.

FIG. 4 is a circuit configuration diagram of the control device according to the first embodiment of the invention.

FIG. 5 is an explanatory diagram of a diagnostic region based on suction pipe negative pressure and engine speed according to the first embodiment of the invention.

FIG. 6 is an explanatory diagram of a diagnostic region based on a throttle opening and engine speed according to the first embodiment of the invention.

FIG. 7 is an explanatory diagram of a diagnostic region based on a basic injection pulse width and an engine speed according to the first embodiment of the invention.

FIG. 8 is a time chart showing an example of pressure behavior in the evaporation purge passage according to the first embodiment of the invention.

FIG. 9 is a schematic configuration diagram of an engine control system according to a second embodiment of the invention.

FIG. 10 is a circuit configuration diagram of a control device according to a second embodiment of the invention.

FIG. 11 is a flowchart of an evaporation purge system failure diagnosis process according to the second embodiment of the invention.

FIG. 12 is a flowchart continued from FIG.

[Explanation of symbols]

 11 canister 12 purge passage 13 purge control valve (duty control valve) 17 pressure sensor P0 purge passage internal pressure P1 maximum pressure value P2 minimum pressure value ΔP differential pressure PSET judgment value

Claims (2)

[Claims] 1. A purge passage that connects a canister for storing evaporated fuel and an intake system is provided with a duty control valve for controlling a purge flow rate, and a pressure sensor is connected to the purge passage to satisfy a diagnostic condition. When the engine is operating, the pressure sensor detects a plurality of pressures in the purge passage that pulsate by opening and closing the duty control valve, and obtains the maximum value and the minimum value of the pulsating pressure from the plurality of detected pressures. A method for diagnosing a failure of an evaporative purge system, which comprises: calculating the difference, and determining that the evaporative purge system is abnormal when the difference is smaller than a preset determination value. 2. A duty control valve for controlling a purge flow rate is provided in a purge passage communicating between a canister for storing evaporated fuel and an intake system, and a pressure sensor which can also be used for other failure diagnosis or control is a switching valve. When the engine is in an operating state satisfying the diagnostic condition, the pressure in the purge passage pulsating by opening and closing the duty control valve is used to switch the switching valve to the pressure sensor and the purge passage. , The pressure sensor detects a plurality of the pressure sensors, calculates the maximum value and the minimum value of the pulsating pressure from the plurality of detected pressures and calculates the difference, and this difference is set in advance. A method for diagnosing a failure in an evaporative purge system, which comprises determining that the evaporative purge system is abnormal when the value is smaller than a determination value.