JP3337271B2 - Evaporative fuel processor for internal combustion engines - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the evaporation of an internal combustion engine capable of diagnosing an abnormality of a fuel vapor processing system for discharging (purging) fuel vapor generated in a fuel tank of the internal combustion engine to an intake system. The present invention relates to a fuel processor.

[0002]

2. Description of the Related Art Conventionally, an evaporative fuel processing system including a fuel tank and a canister has been widely used.
There was one disclosed in Japanese Patent Publication No. 362264.

In the apparatus disclosed in this publication, after the evaporative fuel processing system is reduced to a negative pressure state by the negative pressure of the intake system of the internal combustion engine, the evaporative fuel processing system is closed and the evaporative fuel processing system is closed for a predetermined time. A change in the pressure of the fuel processing system is detected, and when this is greater than a predetermined value, it is determined that the fuel vapor processing system is abnormal.

[0004]

However, in the above-described conventional abnormality diagnosis method, when detecting a change in the pressure of the evaporated fuel processing system under a negative pressure state, the fuel in the fuel tank is highly volatile. In this case, the pressure in the fuel tank rises due to the evaporation of the fuel, and as a result, the change in the pressure of the evaporated fuel processing system becomes larger than a predetermined value. There was a risk of judgment.

SUMMARY OF THE INVENTION In view of the above-mentioned conventional problems, an object of the present invention is to provide an evaporative fuel processing apparatus for an internal combustion engine capable of performing accurate abnormality diagnosis irrespective of the properties of fuel in a fuel tank.

[0006]

According to a first aspect of the present invention, there is provided a fuel tank, a canister for adsorbing fuel vapor generated in the fuel tank, and a fuel tank for adsorbing the fuel adsorbed on the canister. An evaporative fuel processing apparatus for an internal combustion engine, comprising: an evaporative fuel processing system having a purge control valve provided in a passage for supplying to an intake system of the engine and an air release valve provided in an air release passage of the canister. ,
Pressure detecting means for detecting the pressure in the evaporative fuel processing system, fuel property detecting means for detecting the property of the fuel in the fuel tank, and opening the purge control valve and closing the atmosphere release valve. A pressure reducing means for setting the vaporized fuel processing system to a predetermined negative pressure state by the negative pressure of the intake system; and
The purge control valve is closed for a predetermined time to detect a pressure fluctuation amount in the evaporative fuel processing system, and a pressure fluctuation amount detecting means, and a determination is made based on the fuel property detected by the fuel property detecting means. Reference value setting means for setting a reference value, and judging means for judging that the evaporative fuel processing system is abnormal when the amount of pressure change during the predetermined time is larger than a judgment reference value set by the reference value setting means. It is provided with.

[0007] A second invention is the above-mentioned first invention, wherein:
Fuel temperature detection means for detecting the temperature of the fuel in the fuel tank, temperature detection means for detecting the temperature around the engine,
Atmospheric pressure detecting means for detecting the atmospheric pressure around the engine, and correcting means for correcting the determination reference value based on at least one of the detected fuel temperature, air temperature, and atmospheric pressure are provided.

[0008]

According to the first aspect of the present invention, the fuel property in the fuel tank is detected by the fuel property detecting means, and the evaporative fuel processing system is brought into a predetermined negative pressure state by the pressure reducing means. The amount of pressure fluctuation in the fuel vapor treatment system during a predetermined time is detected by the amount detecting means. Then, a determination reference value is set based on the fuel property detected earlier,
The determination means compares the detected fluctuation amount of the pressure with the determination reference value to determine the abnormality of the fuel vapor processing system. Accordingly, it is possible to determine the abnormality of the evaporated fuel processing system in consideration of the properties of the fuel in the fuel tank.

According to the second aspect, attention is paid to the fact that fuel properties are different due to changes in fuel temperature, air temperature and atmospheric pressure, and the determination reference value is corrected based on at least one of the fuel temperature, air temperature and atmospheric pressure. Therefore, it is possible to make an abnormality determination in consideration of changes in fuel temperature, air temperature, and atmospheric pressure.

[0010]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is an overall configuration diagram of an evaporative fuel processing apparatus for an internal combustion engine according to one embodiment of the present invention.

In FIG. 1, reference numeral 1 denotes an internal combustion engine having, for example, four cylinders (hereinafter simply referred to as "engine"), and a throttle valve 3 is disposed in the intake pipe 2 of the engine 1. A throttle valve opening (θTH) sensor 4 is connected to the throttle valve 3, and outputs an electric signal corresponding to the opening of the throttle valve 3 to an electronic control unit (hereinafter referred to as “ECU”) 5. Supply.

The fuel injection valve 6 is provided for each cylinder in the intake pipe 2 and slightly upstream of an intake valve (not shown) between the engine 1 and the throttle valve 3. Each fuel injection valve 6 is connected to a fuel tank 9 via a fuel supply pipe 7, and a fuel pump 8 is provided in the fuel supply pipe 7. The fuel injection valve 6 is electrically connected to the ECU 5, and a signal from the ECU 5 controls the valve opening timing of the fuel injection.

On the downstream side of the throttle valve 3 of the intake pipe 2, an intake pipe absolute pressure (P
BA) sensor 13 and intake air temperature (T
A) The sensors 14 are mounted, and the detection signals of these sensors are supplied to the ECU 5.

An engine water temperature (TW) sensor 15 composed of a thermistor or the like is inserted into the cylinder wall of the cylinder block of the engine 1 which is filled with cooling water, and the engine cooling water temperature TW detected by the TW sensor 15 is converted into an electric signal. The converted data is supplied to the ECU 5.

An engine speed (NE) sensor 16 is provided around a camshaft or a crankshaft (not shown) of the engine 1.
Is attached.

The NE sensor 16 outputs a signal pulse (hereinafter referred to as a “TDC signal pulse”) at a predetermined crank angle position every time the crankshaft of the engine 1 rotates by 180 degrees, and the TDC signal pulse is supplied to the ECU 5. .

An O ₂ sensor 32 as an exhaust gas concentration sensor is mounted in the exhaust pipe 12, detects the oxygen concentration in the exhaust gas, outputs a signal corresponding to the detected value VO 2, and supplies the signal to the ECU 5. I do. O ₂ sensor 32 of exhaust pipe 12
A three-way catalyst 33, which is an exhaust gas purification device, is provided downstream of.

The ECU 5 is connected to a vehicle speed sensor 17 for detecting a running speed VP of a vehicle on which the engine 1 is mounted, a battery voltage sensor 18 for detecting a battery voltage VB, and an atmospheric pressure sensor 19 for detecting an atmospheric pressure PA. The detection signals of these sensors are supplied to the ECU 5.

Next, a description will be given of an evaporative fuel processing system (hereinafter referred to as an "emission suppression system") 31 comprising a fuel tank 53, a fuel vapor flow passage (charge passage) 20, a canister 25, a purge passage 27, and the like.

The fuel tank 53 includes a first tank 53A to which the fuel supply pipe 7 in which the fuel pump 8 is interposed and the fuel vapor flow passage 20 are connected, and a second tank 53B for measuring fuel properties.
The first and second tanks 53A and 53B are communicated via a communication passage 62 in which a solenoid valve 61 is interposed. On the other hand, the second tank 53B is connected to the downstream of the fuel vapor flow passage 20, that is, to the input side of the canister 25 via the atmosphere communication passage 63, and can be opened to the atmosphere through the canister 25. A valve 64 is interposed. The electromagnetic valves 61 and 64 control opening and closing of the communication path 62 and the atmosphere communication path 63 based on each control signal from the ECU 5.

A heater 65 is provided around the second tank 53B, and the heater 65 heats the fuel in the second tank 53B based on a signal from the ECU 5. The second tank 53B is provided with a tank internal pressure sensor 66 and a fuel temperature sensor 67. Emission control system 3
The pressure PT in the first or second tank 53B is detected by a tank internal pressure (PT) sensor 66, and the fuel temperature TF is detected by a fuel temperature (TF) sensor 67,
These detected values are converted into electric signals and supplied to the ECU 5. The outside air temperature T is located around the engine of the vehicle.
An outside air temperature (TO) sensor 68 for detecting O is provided,
The detected value is converted into an electric signal and supplied to the ECU 5.

The first tank 53A is connected to the canister 25 via the charge passage 20, and the charge passage 20 has first to third branch portions 20a to 20c. The first branch portion 20a includes a one-way valve 21 and a puff loss valve 2
2 are provided. The one-way valve 21 has a tank pressure PT
Is opened only when the pressure becomes higher than atmospheric pressure by about 12 to 13 mmHg. Puff loss valve 22
Is an electromagnetic valve that is opened during execution of a purge described later and closed when the engine is stopped, and its operation is controlled by the ECU 5.

The two-way valve 23 is provided in the second branch portion 20b. The two-way valve 23 is activated when the tank internal pressure PT becomes higher than the atmospheric pressure by about 20 mmHg and when the tank internal pressure P
The valve opening operation is performed when T becomes lower than the pressure on the canister 25 side of the two-way valve 23 by a predetermined pressure.

The third branch 20c has a bypass valve 24
Is provided. The bypass valve 24 is a solenoid valve which is normally closed and opened and closed during execution of an abnormality determination which will be described later, and its operation is controlled by the ECU 5.

The canister 25 contains activated carbon for adsorbing fuel vapor, and has an intake port (not shown) communicating with the atmosphere through a passage 26a. A drain shut valve 26 is provided in the middle of the passage 26a. The drain shut valve 26 is an electromagnetic valve which is normally kept in an open state and is temporarily closed during execution of an abnormality determination to be described later, and its operation is controlled by the ECU 5.

The canister 25 is connected to the intake pipe 2 on the downstream side of the throttle valve 3 via a purge passage 27. The purge passage 27 is connected to first and second branch portions 27a and 27a.
7b. The first branch 27a is provided with a jet orifice 28 and a jet purge control valve 29, and the second branch 27b is provided with a purge control valve 30. The jet purge control valve 29 is an electromagnetic valve for controlling a small flow rate of a purge fuel mixture that cannot be accurately controlled by the purge control valve 30.
The solenoid valve is configured so that the flow rate can be continuously controlled by changing the on-off duty ratio of the control signal. The operation of these solenoid valves 29 and 30 is controlled by the ECU 5.

The ECU 5 corrects the voltage level to a predetermined level by shaping the input signal waveforms from the various sensors described above.
An input circuit having a function of converting an analog signal value to a digital signal value, and a central processing circuit (hereinafter, “CPU”)
Storage means for storing a calculation program executed by the CPU, a calculation result, and the like, the fuel injection valve 6, the papulos valve 22, the bypass valve 24, and the jet purge control 29.
And an output circuit for supplying a drive signal to the purge control valve 30.

Further, the ECU 5 (CPU) includes a pressure reducing means, a pressure fluctuation detecting means, a reference value setting means, a determining means and a part of the fuel property detecting means.

Hereinafter, a description will be given of a method for determining an abnormality of the evaporated fuel processing apparatus according to the present embodiment configured as described above.

First, the fuel property detecting process for detecting the property of the fuel in the fuel tank 53 will be described. This is performed in an abnormality diagnosis routine (FIG. 3) described later. This fuel property detection method is disclosed in
According to this method, when the engine 1 is in an idle state, the engine 1 is determined to be stable at a constant low speed and suitable for detecting the fuel property, and the following method is performed. Such detection processing is performed.

First, the solenoid valve 61 is closed and the second tank 5 is closed.
3B is shut off from the first tank 53A, and the electromagnetic valve 64 is opened to open the second tank 53B to the atmosphere.

Then, it is determined whether or not a predetermined time t seconds has elapsed from the opening to the atmosphere. This is performed to determine whether or not the internal pressure of the second tank 53B has completely become equal to the atmosphere. When the predetermined time t seconds has elapsed, the electromagnetic valve 64 is closed to keep the second tank 53B in a closed state.

Subsequently, the heater 65 is energized while the second tank 53B is closed to start heating the second tank 53B, and the second tank 5B detected by the fuel temperature sensor 67.
When the fuel temperature in 3B reaches 38.7 ° C., it is determined that the fuel property detection state has been established, and the tank internal pressure sensor 66
Then, the tank internal pressure value at that time is determined and stored as an RVP (lead vapor pressure) value.

That is, this RVP value indicates that the fuel temperature is 3
It indicates the vapor pressure of the fuel (gasoline) at 8.7 ° C. and indicates the ease with which the fuel evaporates, whereby the properties of the fuel in the fuel tank 53 can be detected. Normally, the RVP value of gasoline ranges from 0.6 to around a saturated vapor pressure of 37.8 ° C.
It is about 1.1 kg / cm2.

After the RVP value is determined, the heater 65 is turned off, the solenoid valve 61 is opened, and the first tank 5
3A is communicated with the second tank 53B to return to the normal state.

FIG. 2 shows a puff loss valve 22 in this embodiment.
It is a figure which shows the operation | movement pattern of the bypass valve 24, the drain shut valve 26, the purge control valve 30, and the jet purge control valve 29, and the transition of the tank internal pressure PTNK at that time, and the abnormality determination method in this embodiment with reference to the figure. Will be described. The tank pressure PTNK is equal to the atmospheric pressure (PAT).
It is indicated by the differential pressure with respect to M).

First, in the purge mode during normal operation (FIG. 2), the puff loss valve 22, the drain shut valve 2
6. Purge control valve 30 and jet purge control valve 29
Is opened, and the bypass valve 24 is closed. At this time, the fuel vapor generated in the fuel tank 53 flows into the canister 25 through the charge passage 20, and is temporarily stored in the canister 25. Then, air is introduced from the passage 26 and the fuel vapor flowing into the canister 25 is
The air is supplied to the intake pipe 2 through the purge passage 27 together with the air.

Next, a precondition (abnormality judgment permission condition) described later.
Is established, the respective solenoid valves are actuated as shown in FIG.

First, an open-to-atmosphere process (FIG. 2) is performed.
That is, the puff loss valve 22, the drain shut valve 26 and the jet purge control valve 29 continue to be opened, the bypass valve 24 is opened, the purge control valve 30 is closed, and the inside of the fuel tank 53 is opened to the atmosphere. I do.

Next, pressure reduction processing (FIG. 2) is performed. That is, the purge control valve 30 is opened and the puff loss valve 2 is opened.
2 and the drain shut valve 26 are closed, and the other valves maintain the previous state. In this state, the negative pressure of the intake pipe 2 causes
The discharge suppression system 31 is depressurized. In this pressure reduction process, the tank internal pressure PTNK is reduced to a predetermined pressure PTLVL (for example, -15 mmH
g).

Next, a leak down check is performed (shown in FIG. 2).

That is, the jet purge control valve 29 and the purge control valve 30 are closed from the decompression state, and P
The change state of the tank internal pressure PT is checked by the T sensor 66. That is, when there is no leak from the discharge suppression system 31, there is almost no change in the tank internal pressure PT as shown by a two-dot chain line, but when evaporative fuel is leaking from the discharge suppression system 31, as shown by a solid line. The degree of change in the tank internal pressure PT is large, and it is determined that an abnormality has occurred in the discharge suppression system 31.

Hereinafter, a method of diagnosing abnormality of the emission suppression system 11 will be described in detail.

FIG. 3 is a flowchart showing an abnormality diagnosis method according to the present invention. This program is executed during background processing.

First, in step S41, the above-described fuel property detection processing is performed to determine the RVP value. In the following step S42, as the monitor permission condition (pre-condition), for example, whether the engine 1 is warming up and the operating state is stable is determined by the cooling water temperature TA, the intake air temperature TW, the engine speed NE, and the like. Judge by When the precondition is satisfied, the flag FMON is set to “1”, and when the precondition is not satisfied, the flag FMON is set to “0”. In a succeeding step S43, the flag FMON is determined by the monitor permission judgment.
Is set to “1”. And
Immediately after the start of the engine, the engine 1 does not satisfy the monitoring condition, and the answer to step S43 is negative (NO), and the step S43
Proceeding to 44, the first timer tmPTO is set to a predetermined time T1.
Set to. The predetermined time T1 is set to a time sufficient for the tank pressure PT to stabilize when the tank pressure PT is released to the atmosphere, for example, 30 seconds. And this first
After starting the timer tmPTO of step S45
To set the discharge suppression system 11 to the normal purge mode,
Exit this program. That is, as shown in FIG. 2 described above, the open / close state of each valve is controlled, and this program ends.

On the other hand, when a predetermined monitoring condition is satisfied in a subsequent loop, the flag FMON becomes "1", and it is determined whether or not the first timer tmPTO has become "0" after a lapse of a predetermined time T1 (step S1). S46). Since the answer is initially negative (NO), the process proceeds to step S47, and the discharge suppression system 11 is set to the tank internal pressure atmosphere release mode. That is, the open / close state of each valve is controlled as shown in FIG. Next, the second timer tmPTD is set to “0” (step S48). This second timer tmPTD is a timer for measuring a time required for a pressure reduction process of the tank internal pressure PT described later, and tmPTD =
Initially set to 0. And the tank pressure PT at the time of opening to the atmosphere
O is set to the current tank pressure PT detected by the PT sensor 66 (step S49), and when the pressure reduction process is completed, the flag FRDC set to "1" is set to "0" (step S50), and this program ends. I do. That is, the tank internal pressure PTO at the time of opening to the atmosphere is updated to the current value, the flag FRDC is reset, and the program ends.

Then, in the subsequent loop, the first timer t
If the answer of step S46 is affirmative (YES) after mPTO has passed the predetermined time T1, the second timer tmP
It is determined whether or not TD is greater than a predetermined time T4 (step S50). Since the answer is initially negative (NO),
Proceeding to step S52, it is determined whether or not the flag FRDC is "1". Initially, this answer is negative (NO), and it is determined whether or not the tank internal pressure PT has become equal to or less than a predetermined reference value PTLVL (step S53). Initially tank pressure PT
Is in the atmosphere open state, the answer is negative (NO), and a pressure reduction process is performed (step S54). That is, as shown in FIG. 2 described above, the open / close state of each valve is controlled to bring the discharge suppression system 31 into a negative pressure state.

Next, the value of the second timer tmPTD is set to the time required for the decompression process, that is, tmPTD in step S48.
It is set as the elapsed time T2 since TD = 0 was set (step S55). Then, the process proceeds to a step S56, wherein a third timer tmPTD for leak down check is performed.
C is set to a predetermined time T3, and the program ends.
The predetermined time T3 is set to a time required for a leak down check, for example, 30 seconds.

On the other hand, pressure reduction processing is performed, and step S53 is performed.
If the answer is affirmative (YES), the flag FRDC is set to "1" (step S57), and then it is determined whether or not the third timer tmPTDC has become "0".
It is determined whether the time required for the leak down check has elapsed (step S58). If step S51 is affirmative (YES), step S5 is performed as it is.
Proceed to 8.

In the first loop, since the answer is negative (NO), the process proceeds to step S59, in which the emission suppression system 31 is set to the leak-down check mode, and as shown in FIG. To measure the tank internal pressure PT. The PT measured at this time is stored as PEND. On the other hand, the answer to step S58 is affirmative (YE
In S), the process proceeds to step S60, executes an abnormality determination routine, returns to the normal purge mode (step S45), and ends the program.

FIG. 4 is a flowchart showing an abnormality determination routine executed in step S60 (FIG. 3).

PEN measured at leak down check
Based on D, the fluctuation amount PVARIB of the tank internal pressure PT per unit time during the leak down check by the following equation
Is calculated (step S70).

PVARIB = (PEND-PTLVL) / T3 In the next step S71, a reference value PRPV corresponding to the RVP value determined in the fuel property detection processing in step S30 is searched using the reference value table shown in FIG. . This reference value table takes into account that the higher the RVP value, the easier the fuel evaporates, and the higher the RVP value, the higher the PVP value.
The setting is such that the change in the RPV value is large.

In consideration of the fact that the degree of evaporation of the fuel varies depending on the fuel temperature and the outside air temperature, the fuel temperature sensor 6
7 and the current fuel temperature (TF) and the outside air temperature (TO) detected by the outside air temperature sensor 68 are applied to a reference value correction map to search for a correction coefficient KPT (step S7).
2). The reference value correction map stores correction coefficient values KPT corresponding to the respective outside air temperatures TO and the atmospheric pressure PA.

Further, since the amount of fuel vapor generated varies depending on the atmospheric pressure, the current atmospheric pressure (PA) detected by the atmospheric pressure sensor 69 is applied to the reference value correction table to search for the correction coefficient KPA. (Step S73). The reference value correction table is set so that the value of the correction coefficient KPA gradually decreases as the atmospheric pressure (PA) increases.

In this manner, the reference value PRPV and the correction coefficients KPT and KPA for correcting the reference value PRPV are determined.

Then, in a step S74, it is determined whether or not the following expression is satisfied.

PVARIB- (PRPV × KPT × KPA) ≧
Predetermined value PTJDG When the answer is affirmative (YES), it is determined that the leak amount is large and the device is abnormal (step S75), and the process returns to the main routine (FIG. 3). If the answer to step S74 is negative (NO), it is determined that the leak amount is small and the device is normal (step S76), and the process returns to the main routine (FIG. 3).

As described above, in this embodiment, the fuel tank 5
Since the properties of the fuel in the fuel tank 3 are detected and the abnormality of the emission suppression system 31 is determined based on the detected properties, accurate abnormality determination can be performed even if the fuel in the fuel tank 53 is highly volatile. Becomes possible.

As a method of detecting the fuel property, in addition to the technique described in the above embodiment, a technique of irradiating the fuel with light to detect the refractive index of the light and thereby detecting the fuel property may be used. Good.

[0062]

As described above, according to the first aspect, the pressure detecting means for detecting the pressure in the fuel vapor processing system, the fuel property detecting means for detecting the fuel property in the fuel tank, A pressure reducing means that opens the purge control valve and closes the atmosphere release valve to bring the evaporative fuel processing system into a predetermined negative pressure state by the negative pressure of the intake system. After the negative pressure state, the purge control valve is closed for a predetermined time to detect a pressure fluctuation amount in the evaporative fuel processing system, and a pressure fluctuation amount detection unit detects the pressure fluctuation amount. A reference value setting means for setting a judgment reference value based on the fuel property, and an abnormality in the evaporative fuel processing system when the amount of pressure change during the predetermined time is larger than the judgment reference value set by the reference value setting means. Is determined to be Since a stage, regardless of the property of the fuel in the fuel tank, allows an accurate diagnosis.

According to a second aspect, in the first aspect, a fuel temperature detecting means for detecting a fuel temperature in the fuel tank, an air temperature detecting means for detecting an air temperature around the engine, and a large temperature around the engine. Since atmospheric pressure detecting means for detecting atmospheric pressure and correcting means for correcting the determination reference value based on at least one of the detected fuel temperature, air temperature, and atmospheric pressure are provided, fluctuations in fuel temperature, air temperature, and atmospheric pressure are detected. A more accurate abnormality diagnosis can be performed in consideration of the above.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram showing one embodiment of an evaporative fuel processing apparatus for an internal combustion engine according to the present invention.

FIG. 2 is a diagram showing an operation pattern of each valve and a fluctuation of a tank internal pressure.

FIG. 3 is a flowchart illustrating a control procedure of an abnormality diagnosis method.

FIG. 4 is a flowchart of an abnormality determination routine.

FIG. 5 is a diagram showing a reference value table.

[Explanation of symbols]

 Reference Signs List 1 internal combustion engine 5 ECU 22 puff loss valve 24 bypass valve 25 canister 26 drain shut valve 29 jet purge control valve 30 purge control valve 31 evaporative fuel processing system 53 fuel tank 53A first tank 53B second tank 66 tank internal pressure (PT) sensor 67 Fuel temperature sensor 68 Outside temperature (TO) sensor 69 Atmospheric pressure (PA) sensor

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Kenichi Maeda 1-4-1 Chuo, Wako-shi, Saitama Prefecture Honda Technical Research Institute Co., Ltd. (56) References JP-A-6-235355 (JP, A) (58) Field surveyed (Int.Cl. ⁷ , DB name) F02M 25/08 F02M 25/08 301

Claims (2)

(57) [Claims] 1. A fuel tank, a canister for adsorbing fuel vapor generated in the fuel tank, a purge control valve provided in a passage for supplying the fuel adsorbed by the canister to an intake system of an internal combustion engine, An evaporative fuel processing apparatus for an internal combustion engine including an evaporative fuel processing system having an air release valve provided in an air release passage of the canister, wherein a pressure detecting unit that detects a pressure in the evaporative fuel processing system, A fuel property detecting means for detecting a property of the fuel in the fuel tank; opening the purge control valve and closing the atmosphere release valve, and setting the evaporative fuel processing system to a predetermined pressure by the negative pressure of the intake system. A depressurizing means for bringing the evaporative fuel processing system into a negative pressure state by the depressurizing means; and closing the purge control valve for a predetermined time to change the pressure in the evaporative fuel processing system. Pressure fluctuation amount detecting means for detecting the amount; reference value setting means for setting a judgment reference value based on the fuel property detected by the fuel property detecting means; and the pressure fluctuation amount in the predetermined time is the reference value setting. Determining means for determining that the evaporated fuel processing system is abnormal when the value is greater than a determination reference value set by the means. 2. A fuel temperature detecting means for detecting a fuel temperature in the fuel tank, an air temperature detecting means for detecting an air temperature around an engine, and an atmospheric pressure detecting means for detecting an atmospheric pressure around the engine. 2. The apparatus according to claim 1, further comprising a correction unit configured to correct the determination reference value based on at least one of a fuel temperature, an air temperature, and an atmospheric pressure.