JP2001294052A - Abnormality diagnostic method and abnormality diagnostic device for fuel tank - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an abnormality diagnostic device capable of accurately diagnosing the presence or absence of abnormality in a fuel tank at an early period just after staring an engine. SOLUTION: The fuel tank 20 in a fuel vapor purge system can gas-phase communicate with an intake passage 12 of an engine through a vapor passage 33, a canister 40, and a purge passage 34. A forced opening/closing valve (a oil feeding valve) 60 heteronomously controlled by an ECU exists in the middle of the vapor passage 33. At cold starting of an engine, the ECU measures tank internal pressure in a fuel tank sealing state by a pressure sensor 31, and compares an absolute value of a difference between the tank internal pressure and atmospheric pressure with a specified determining value. When the absolute value of the difference is not less than the specified determining value, the fuel tank 20 is determined as having no abnormality such as leakage. Otherwise, after that, a leakage diagnosis of the tank and the whole of the purge system is conducted by means of negative pressure and the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an abnormality diagnosis of a fuel tank, and more particularly to an abnormality diagnosis method and an abnormality diagnosis apparatus for diagnosing and detecting an abnormality of a fuel tank used in a fuel vapor purge system.

[0002]

2. Description of the Related Art Generally, a vehicle provided with a tank for volatile liquid fuel employs a so-called fuel vapor purge system. According to a typical purge system, fuel vapor generated in a fuel tank is once collected in a canister, and the collected fuel vapor is appropriately purged (discharged) into an intake passage of an engine. To ensure the reliability of such fuel vapor purge systems, many purge systems include:
An abnormality diagnosis device for detecting a leak due to a hole or a tear is incorporated. A fuel vapor purge system with a general abnormality diagnosis device includes at least an air introduction valve that controls the air introduction from the upstream side of the engine intake passage to the canister and a fuel vapor purge system that discharges fuel vapor from the canister to the downstream side of the engine intake passage at least. A purge control valve that controls the pressure, a tank pressure control valve that is a pressure difference valve that operates autonomously to release fuel vapor in the tank to the canister when a pressure difference between the fuel tank pressure and the canister pressure exceeds a predetermined set pressure, and A forced open / close valve (also referred to as a negative pressure introduction valve) of a different operation type is provided for forcibly communicating the canister and the fuel tank when necessary. However, in the communication path between the fuel tank and the canister, a path passing through the tank internal pressure control valve and a path passing through the forced open / close valve exist in parallel.

In this system, a prerequisite for entering the leak diagnosis process is that the engine coolant temperature reaches a purge start temperature (for example, 80 ° C.) and a purge operation (releases fuel vapor while introducing air into the canister). Has been started (first precondition), and that the tank internal pressure has been continuously stabilized for a predetermined period of time before opening the forced on-off valve (second precondition).
It is. After these two preconditions are satisfied, a leak diagnosis is performed. In the leak diagnosis process, the air introduction valve is closed and the forcible on-off valve is opened to reduce the pressure in the entire evaporation path including the canister and the fuel tank via the purge control valve. When the evaporative path reaches a predetermined low pressure level, the purge control valve is closed to make the evaporative path an isolated system. Then, based on what the internal pressure of the isolated system shows from the predetermined low pressure level as time elapses, the presence or absence of leakage due to perforation, tear, or the like is rationally determined.

[0004]

However, the above-mentioned leak diagnosis method has the following disadvantages. Even after the two prerequisites for entering the leak diagnosis are satisfied, if the air introduction valve is closed and the forced on-off valve is opened to reduce the pressure in the evaporative path, Residual pressure in the tank flows into the canister, and it takes a certain time until the entire evaporative path including the fuel tank and the canister reaches a predetermined low pressure level. In other words, it is not possible to immediately bring the entire evaporation path to the predetermined low pressure level immediately, and it is not possible to complete the first leak diagnosis early.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object thereof is to diagnose with high accuracy whether or not there is an abnormality in a fuel tank alone before or immediately after the engine is started. It is an object of the present invention to provide a fuel tank abnormality diagnosis method and abnormality diagnosis device that can be used.

[0006]

According to the first aspect of the present invention, there is provided a method for diagnosing the presence or absence of an abnormality in a fuel tank configured to be able to communicate with an engine intake passage in a gas phase through a path having a forced open / close valve. Measuring the tank internal pressure in a fuel tank closed state in which the forcible on-off valve is closed, comparing the absolute value of the difference between the tank internal pressure and the atmospheric pressure with a predetermined determination value, and based on the comparison result, This is a method for diagnosing abnormality of a fuel tank, which comprises determining whether or not there is an abnormality in the fuel tank.

If the difference between the tank internal pressure and the atmospheric pressure is large in the closed state of the fuel tank, there is no unintended communication between the inside of the tank and the atmosphere (outside the tank). It can be determined that there is no tear or the like. The diagnostic method of the present invention is based on such a concept. However, simply determining that the tank is normal simply because there is a slight difference between the tank internal pressure and the atmospheric pressure means that the fuel itself has a vapor pressure (partial pressure).
Considering that there is a problem, it may cause an erroneous determination. Therefore, in order to avoid such erroneous determination and ensure the reliability of the diagnostic determination,
A predetermined determination value is set, and it is determined whether or not there is an abnormality such as leakage in the fuel tank based on a comparison result between the absolute value of the difference between the tank internal pressure and the atmospheric pressure and the determination value. According to this method, the abnormality diagnosis of the fuel tank can be completed at an early stage with high accuracy in the closed state of the tank before the forced on-off valve is opened.

According to a second aspect of the present invention, in the fuel tank abnormality diagnosis method according to the first aspect, when the absolute value of the difference between the tank internal pressure and the atmospheric pressure is equal to or greater than the predetermined determination value, It is characterized that it is determined that there is no abnormality such as leakage in the tank.

This specifies the conditions for determining that there is no abnormality such as leakage in the fuel tank. However, the opposite is not necessarily true, and it is too early to immediately determine that there is an abnormality such as leakage when the absolute value of the difference between the tank internal pressure and the atmospheric pressure is less than a predetermined determination value. That is, when the absolute value of the difference is less than the predetermined determination value, it cannot be determined that there is no abnormality. Therefore, it is preferable to perform a careful leak diagnosis by another diagnosis method (for example, a conventional negative pressure method) thereafter.
A significant point of the present invention is that it is possible to quickly conclude that there is clearly no abnormality in the fuel tank by a simple determination method without using a complicated and time-consuming conventional diagnosis method.

According to a third aspect of the present invention, in the fuel tank abnormality diagnosis method according to the first or second aspect, the measurement of the tank internal pressure in the fuel tank closed state is performed at the time of a cold start or before the start of the engine. It is characterized by being performed.

After the engine is warmed up, the residual heat of the engine is also transmitted to the fuel tank, which tends to increase the fuel vapor pressure and the tank internal pressure. Under such circumstances, even if there is a small hole in the tank, the tank internal pressure rises beyond the pressure released by the steam leak from the hole, and the absolute value of the difference from the atmospheric pressure becomes the determination value. It can exceed. In such a case, if an abnormality diagnosis is performed based on the diagnosis method of the present invention, an erroneous determination may be made. Therefore,
In using this method, in order to ensure the reliability of diagnosis, it is preferable to measure the tank internal pressure in a fuel tank closed state before the engine is warmed up, that is, at the time of cold start or before the engine is started. Even if another diagnosis method (for example, a conventional negative pressure method) is subsequently performed, it is still more preferable to execute the present method before the purge to the path is started.

According to a fourth aspect of the present invention, there is provided an apparatus for diagnosing the presence or absence of an abnormality in a fuel tank configured to be able to communicate with an engine intake passage in a gas phase via a path having a forced open / close valve. Internal pressure measuring means for measuring the internal pressure,
Diagnostic control means for controlling the opening and closing of the forcible on-off valve and for obtaining information about the internal pressure of the fuel tank from the internal pressure measuring means, wherein the diagnostic control means is in a fuel tank hermetically closed state in which the forcible on-off valve is closed. The tank internal pressure is obtained from the internal pressure measuring means, the absolute value of the difference between the tank internal pressure and the atmospheric pressure is compared with a predetermined determination value, and based on the comparison result, it is determined whether or not the fuel tank is abnormal. An abnormality diagnosis device for a fuel tank characterized by making a determination. This expresses the abnormality diagnosis method (claim 1) as an apparatus invention, and has the same technical significance as the abnormality diagnosis method.

According to a fifth aspect of the present invention, in the fuel tank abnormality diagnosing apparatus according to the fourth aspect, the diagnosis control means includes:
When the absolute value of the difference between the tank internal pressure and the atmospheric pressure is equal to or greater than a predetermined determination value, it is determined that there is no abnormality such as leakage in the fuel tank. This expresses the abnormality diagnosis method (claim 2) as a device invention, and has the same technical significance as the abnormality diagnosis method.

According to a sixth aspect of the present invention, in the fuel tank abnormality diagnostic apparatus according to the fourth or fifth aspect, the diagnostic control means measures the tank internal pressure in the fuel tank closed state when the engine is cold started. Alternatively, it is performed before starting. This expresses the abnormality diagnosis method (claim 3) as an apparatus invention, and has the same technical significance as the abnormality diagnosis method.

According to a seventh aspect of the present invention, in the abnormality diagnosis apparatus for a fuel tank according to any one of the fourth to sixth aspects, the path for allowing the fuel tank and the engine intake passage to communicate with each other in a gas phase includes a canister. A purge passage connecting the canister and the engine intake passage, and a vapor passage connecting the canister and the fuel tank, and the forcible on-off valve is a refueling valve provided in the middle of the vapor passage. Is what you do. This specifies the best mode of the abnormality diagnosis device, and its technical significance will be clear in the following description of the “embodiment of the invention”.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A specific example of a purge system abnormality diagnosis apparatus including a vehicle fuel vapor purge system and a fuel tank abnormality diagnosis apparatus will be described below with reference to the drawings.

As shown in FIG. 1, the engine 10 includes a combustion chamber 11, an intake passage 12, and an exhaust passage 13. When the engine 10 is operated, the fuel (for example, gasoline) stored in the fuel tank 20 is pumped out by the fuel pump 21 and delivered through the fuel supply passage.
After that, the fuel is injected into the intake passage 12 by the fuel injection valve 15. The intake passage 12 includes a surge tank 16 in the middle thereof, and an accelerator pedal (not shown) upstream thereof.
A throttle valve 17 that varies the flow passage area of the intake passage 12 based on the depression operation of the throttle valve 17 is provided. Further upstream, an air cleaner 18 for purifying intake air and an air flow meter 19 for detecting the amount of intake air to the engine are provided.

The fuel tank 20 is a highly airtight tank, and an FKM gasket 22 is provided at a connection portion with various pipes.
Etc. are used. An inlet pipe 23 is connected to the fuel tank 20 as a fuel introduction passage from the outside into the tank. At the outer end of the inlet pipe 23, a flapper valve 24 is provided as an oil supply port.
Is provided with a check valve 25 at its inner end to prevent backflow. A pressure sensor 31 is provided on the ceiling of the fuel tank 20 as internal pressure measuring means. Pressure sensor 3
1 measures or detects the pressure in the fuel tank 20 and the area communicating with the fuel tank. This detected pressure is a relative pressure based on the atmospheric pressure. A fuel pump 21 is provided in the fuel tank 20. The fuel pump 21 and the pressure sensor 31 are electrically connected to an ECU (electronic control unit) described later. Although the fuel tank main body is made of metal, its outer surface is covered with a heat insulating material (for example, urethane foam) and a protective material (for example, polypropylene) (not shown).

As shown in FIG. 1, the fuel vapor purge system includes a canister 40 for collecting fuel vapor generated from the fuel tank 20, a passage connecting the canister and the fuel tank, a canister and an engine intake system. And an electric control system including various sensors and valves. Canister 40
Is provided with an adsorbent (for example, activated carbon) inside, adsorbs fuel vapor on the adsorbent, temporarily stores the fuel vapor, and then adsorbs the fuel vapor on the adsorbent by being placed under a pressure lower than the atmospheric pressure. It is possible to re-dissipate the fuel vapor. Hereinafter, in this specification, a pressure lower than the atmospheric pressure is referred to as “negative pressure”, and a pressure higher than the atmospheric pressure is referred to as “positive pressure”.

The canister 40 is capable of communicating with the fuel tank 20 via the vapor passage 33 in the gas phase, and is also capable of communicating with the intake passage 12 via the purge passage 34 in the gas phase. Further, the canister 40 can communicate with the air cleaner 18 of the intake passage 12 via the air introduction passage 35 and can also communicate with the atmosphere (outside air) via the atmosphere valve (also referred to as a drain valve) 36 and the atmosphere discharge passage 37. Has become. One end of the vapor passage 33 is connected to the fuel tank 2.
0, and a float valve (also referred to as a rollover valve) 26 for detecting a full tank and responding to a rollover is attached to the front end.

The purge passage 34 is a passage for purging (discharging) the fuel vapor collected in the canister 40 into the intake passage 12 of the engine. In the middle of the purge passage 34, a solenoid valve or a VSV (vacuum switching valve) is used. The purge control valve 34a is provided. The air introduction passage 35 is a passage for guiding refresh air to the canister 40, and an air introduction valve (also referred to as a closing valve) 35a including a solenoid valve or a VSV is provided in the middle of the passage. The atmospheric valve 36 includes a diaphragm valve that receives both the internal pressure of the canister and the atmospheric pressure. The diaphragm valve opens when the internal pressure of the canister reaches a positive pressure equal to or higher than a predetermined pressure. Excess air is discharged to the discharge passage 37.

The interior of the canister 40 is divided by a partition plate 41 into a first adsorbent chamber 42 and a second adsorbent chamber 43. Although both the adsorbent chambers 42 and 43 are filled with an adsorbent (activated carbon), both chambers communicate with each other via a gas permeable filter 44 at the bottom of the canister. The first adsorbent chamber 42 is
It can communicate with the fuel tank 20 via the vapor passage 33. The atmosphere introduction passage 35 and the atmosphere valve 36 communicate with the second adsorbent chamber 43. Further, the purge passage 34 connects the first adsorbent chamber 42 and a position downstream of the throttle valve of the intake passage 12, and the first adsorbent chamber 42 and the intake passage 12 are opened and closed according to the opening / closing operation of the purge control valve 34 a. Are selectively communicated. That is, the fuel vapor introduced through the vapor passage 33 is temporarily adsorbed by the first adsorbent chamber 42 and then discharged through the purge passage 34. In addition,
Even when the air valve 36 is opened and excess air in the canister 40 is discharged outside from the air discharge passage 37, the fuel vapor remaining in the canister 40 is discharged from both the adsorbent chambers 42 and 4.
When passing through 3, the adsorbent almost completely adsorbs and does not leak outside.

In addition, a pressure sensor 32 is provided in the canister 40. The pressure sensor 32 is exposed in the gas phase region of the second adsorbent chamber 43 where the adsorbent is not filled, and detects the pressure in the canister 40. This detected pressure is a relative pressure based on the atmospheric pressure. This pressure sensor 32 is also ECU
Is electrically connected to

As shown in FIGS. 1 and 2, a vapor passage 3 connecting the fuel tank 20 and the canister 40 is formed.
3 is configured to branch into three systems on the way. A different purpose valve mechanism is provided for each branch system, and these three branch systems are parallel to each other.

The first branch system of the vapor passage 33 is composed of a main bypass passage 51 and a tank internal pressure control valve 52 provided in the middle thereof. One end of the main bypass passage 51 communicates with the canister 40, and the other end communicates with the float valve 26. The tank pressure control valve 52 is connected to the atmosphere valve 36.
This is an autonomously operated diaphragm type differential pressure valve having substantially the same structure as that described above, and includes a diaphragm valve body 53 and a coil spring 54 for urging the diaphragm valve body 53 in the valve closing direction. Coil spring 5
The internal pressure of the canister acts as a back pressure on the back side of the diaphragm valve element 53 in which the diaphragm valve 4 is disposed, while the tank internal pressure acts on a large part of the front side of the diaphragm valve element 53. The set valve opening pressure of the tank internal pressure control valve 52 is determined using the spring force of the coil spring 54 and the elasticity of the diaphragm itself. For this reason, when the tank internal pressure becomes higher than the canister internal pressure by a predetermined pressure or more, the tank internal pressure control valve 5
The valve 2 opens to release fuel vapor to the canister 40 via the first branch system.

The second branch system of the vapor passage 33 is composed of a sub bypass passage 55 and an oil supply valve 60 disposed in the middle of the sub bypass passage 55. The sub bypass passage 55 has a larger diameter than the main bypass passage 51, but is normally closed by a refueling valve 60, and is forcibly opened only in special cases to allow communication between the fuel tank 20 and the canister 40. It is an emergency passage. As shown in FIGS. 2 and 3, the sub bypass passage 55 is divided on the way, and a communication chamber 56 is provided between two divided ends (one of which functions as the valve seat 61).
Is secured.

The refueling valve 60 mainly includes a valve seat 61 constituted by one of the divided ends, a movable body 62 slidably provided in the sub bypass passage 55, and a movable body 62.
, And an electromagnetic coil 64 that surrounds a sub bypass passage that supports the movable body 62 and is energized and controlled by the ECU. Movable body 62
Is movable between a closed position seated on the valve seat 61 (see FIG. 2) and an open position away from the valve seat 61 (see FIG. 3). The movable body 62 is composed of a disc-shaped valve body 65 that can be moved toward and away from the valve seat 61 as it slides back and forth, and a cylindrical portion 66 that extends rearward from the valve body 65. The outer peripheral surface of the cylindrical portion 66 is substantially in close contact with the inner peripheral surface of the sub bypass passage 55, and the amount of gas leaking from between the two peripheral surfaces is extremely small.
Instead, a plurality of communication holes 67 are formed in the cylindrical portion 66. Each communication hole 67 is formed so that the communication chamber 56 and the inside of the cylindrical portion 66 (the inside of the sub bypass passage 55) are always in communication within the moving range of the movable body 62. The coil spring 63 urges the movable body 62 toward the valve seat 61,
As long as the electromagnetic coil 64 is not energized, the valve body 65 is
1 to close the sub bypass passage 55. Also,
A high valve opening set pressure is determined by the spring force of the coil spring 63, and it is possible to prevent the tank from falling into an excessively negative pressure state.
The movable body 62 is made of a magnetic material,
When an electromagnetic force is generated by energization of the coil spring 63, the coil spring 63 retracts to the open position in FIG. 3 against the urging force of the coil spring 63. As a result, the valve body 65 is separated from the valve seat 61, the sub bypass passage 55 is opened through the inside of the valve seat 61, the communication chamber 56 and the communication hole 67, and the fuel tank 20 is opened via the second branch system. And the canister 40 are communicated. As described above, the refueling valve 60 is a differently-operated forced open / close valve that operates differently based on control of energization of the electromagnetic coil 64.

The third branch system of the vapor passage 33 includes a pressure equalizing passage 71, the communication chamber 56, and the communication hole 6 of the movable body 62.
7 and a pressure release valve 73 for opening and closing a valve hole 72 formed in a partition wall between the pressure equalizing passage 71 and the communication chamber 56. The valve hole 72 is always closed by a valve element 74 constituting a pressure release valve 73. The pressure release valve 73 is electrically connected to the ECU, and is opened and closed by the ECU. When the pressure sensor 31 detects that the tank internal pressure is excessively lower than the atmospheric pressure (excessive negative pressure), the ECU moves the valve body 74 of the pressure release valve to forcibly open the valve hole 72. Then, via the third branch system, the fuel tank 20 communicates with the canister 40 and the area connected to the canister 40, and the pressure in the tank and the canister and other areas are equalized, and the negative pressure state of the tank internal pressure is reduced. Be relaxed. If the atmosphere introduction valve 35a is open at that time, the tank internal pressure is returned to the atmospheric pressure. In other words, the pressure release valve 73 functions as a controlled operation type relief valve for returning steam or air from the canister 40 to the fuel tank 20 to prevent the tank from falling into an excessively negative pressure state. .

In the present embodiment, the fuel vapor purge which communicates with each other is opened by opening the fuel supply valve 60 in a state where the purge control valve 34a is in an open state and a negative pressure is introduced into the canister 40. Shared space in the system,
That is, the fuel tank 20, the vapor passage 33, the canister 40, and the purge passage 34 are called an evaporation route in the same system.

Further, the engine 10 and the fuel vapor purge system are provided with an ECU (Electronic Control Unit) which plays a role as a control system and a diagnostic system of the engine. As shown in FIG. 4, the ECU is mainly configured by a microcomputer 81 that executes various processes related to engine control and a leak diagnosis of an evaporation path of a purge system including a fuel tank. The microcomputer 81 includes a CPU 82 that performs various types of arithmetic processing, a ROM 8 that is a read-only memory that stores various programs related to the above control and diagnosis.
3. RAM, a volatile memory that can be read and written freely
84, a backup RAM 8 which is a non-volatile memory in which reading and writing are free and a battery is backed up, so that the stored contents are retained even after the engine 10 is stopped.
5 and an internal timer 86 for time measurement.

On the output side of the microcomputer 81,
Fuel injection valve 15, fuel pump 21, purge control valve 34
a, atmosphere introduction valve 35a, refueling valve 60, and pressure release valve 73
Are connected via respective drive circuits.

On the input side of the microcomputer 81,
The air flow meter 19 and the two pressure sensors 31, 3
In addition to the above, various sensors for acquiring information necessary for operation control of the engine 10, such as a water temperature sensor of the engine cooling water, a rotation speed sensor and a cylinder discrimination sensor, are connected directly or indirectly. In addition, as shown in FIGS. 1 and 4,
The lid opener detection circuit 27 is connected to the input side of the microcomputer 81. The lid opener detection circuit 27 is connected to a fueling port (ie, the flapper valve 2
When the lid (fuel lid) 28 provided near 4) is opened and gasoline can be supplied to the fuel tank 20, a lid open signal for notifying the ECU is output. When the ECU receives the lid open signal from the lid opener detection circuit 27, the ECU instructs the energization of the electromagnetic coil 64 and forcibly opens the refueling valve 60 to secure an escape route for air or steam in the fuel tank 30 during refueling. I do. On the other hand, lid 2
When 8 is closed, the ECU stops energizing the electromagnetic coil 64 and closes the fueling valve 60. The tank internal pressure control valve 5
The valve opening set pressure of 2 is set so high that it does not easily open when the tank internal pressure increases during refueling.
In this sense, the existence of the refueling valve 60 is recognized.

The ECU executes engine control such as fuel injection control and air-fuel ratio control based on various information provided from various sensors. Meanwhile, the ECU provides the pressure sensor 31,
The purge control valve 34 recognizes the output signal from the
a, atmosphere introduction valve 35a, refueling valve 60, and pressure release valve 73
Is appropriately controlled to open and close to perform abnormality diagnosis and the like of the purge system including the fuel tank 20. In this sense, the ECU is positioned as diagnostic control means.

(Outline of Fuel Purge by Fuel Vapor Purge System) When the fuel in the fuel tank 20 vaporizes and its vapor pressure reaches a predetermined pressure or more, the tank internal pressure control valve 52 is opened and the fuel tank 20 canister 40 The fuel vapor is allowed to flow into the inside. The fuel vapor flowing into the canister 40 is temporarily adsorbed by the adsorbent in the canister 40.
If the cooling water temperature of the engine 10 has reached a predetermined purge start water temperature (for example, 80 ° C.), a command from the ECU causes
The purge control valve 34a and the atmosphere introduction valve 35a are appropriately opened. Then, the suction negative pressure is guided from the intake passage 12 into the canister 40 through the purge passage 34, and fresh air is introduced from the air cleaner 18 into the canister 40 through the air introduction passage 35. The fuel vapor is released from the adsorbent by the introduction of the negative pressure and the fresh air, and is purged to the intake passage 12 through the purge passage 34.

(Diagnosis of Leakage in Evaporation Path of Fuel Vapor Purging System) In this embodiment, the fuel tank 20 is a highly airtight tank, and the fueling valve 60 is closed except during refueling. Diagnosis, and a vapor passage 33, a canister 40, and a purge passage 3 outside the fuel tank, which are components of an evaporative path excluding the fuel tank 20.
4 (hereinafter, the vapor path 33, the canister 40, and the purge path 34 are referred to as a group of canister paths).

FIGS. 5 and 6 are flowcharts showing the outline of an abnormality diagnosis routine for diagnosing the presence or absence of an abnormality in the evaporation path of the fuel vapor purge system. This routine is executed by the ECU as a periodic interruption process every predetermined time (for example, several tens to several hundreds of milliseconds).

When there is an interrupt processing request, the ECU first determines in step 101 whether or not the engine 10 is in a cold start. Specifically, under the condition that the ignition switch is turned on, it is determined whether or not the cooling water temperature of the engine is lower than a predetermined temperature (for example, 35 ° C.). If the cooling water temperature is lower than the predetermined temperature (YES in step 101), it is determined that the engine is in the cold start mode, and step 1
In 02, the ECU reads the tank internal pressure Pt based on the atmospheric pressure from the pressure sensor 31. On the other hand, if the determination in step 101 is NO, it is determined that the engine has been warmed up or during a warm start, and step 102 is skipped and the process proceeds to step 111.

Subsequently, at step 103, the ECU
Determines whether the absolute value of the tank internal pressure Pt is equal to or greater than a predetermined determination value α. That is, the tank internal pressure Pt
Is positive pressure, it is determined whether or not it is equal to or more than a value α (α> 0). If the tank internal pressure Pt is negative pressure, it is determined whether or not it is equal to or less than a value −α. Step 103 is YE
In the case of S, the difference between the tank internal pressure Pt and the atmospheric pressure is equal to or more than α, indicating that the airtightness of the fuel tank 20 is sufficiently maintained. Therefore, if the determination in step 103 is YES, the ECU sets the fuel tank 2
It is determined that there is no abnormality such as a hole or a tear in 0 (step 104). It should be noted that by setting the judgment value α to a certain large value, the steps 103 → 104
The reliability of the determination of no abnormality in the flow of the flow can be improved. On the other hand,
If the determination in step 103 is NO, it cannot be immediately determined that there is a hole or the like in the tank 20 by itself. Therefore, the ECU executes the processing of step 111 and subsequent steps in order to perform more strict abnormality diagnosis.

The processing of steps 111 to 123 shows an outline of the procedure for diagnosing the abnormality of the evaporative path by the negative pressure method. In particular, the processing of steps 111 to 119 shows the procedure of diagnosing the abnormality of the fuel tank, and the processing of steps 120 to 123 shows the procedure of the canister path. 1 shows a group abnormality diagnosis procedure. The timing chart of FIG. 7 corresponds to the procedure for diagnosing the abnormality of the evaporative path by the negative pressure method.

First, in step 111, the ECU
Initiate fuel vapor purge by the system. Specifically, the purge control valve 34a is opened while the air introduction valve 35a is open (time t1 in FIG. 7). At this time,
Both the refueling valve 60 and the pressure release valve 73 are closed. Thereafter, in step 112, the fuel tank 20
Of the internal pressure Pt is confirmed. For example, as shown in FIG. 7, the pressure sensor 31 measures a pressure change amount ΔP1 of the tank internal pressure Pt in a predetermined time (for example, 15 seconds),
When it is confirmed three consecutive times that the pressure change amount ΔP1 is equal to or less than the predetermined value, it is determined that the tank internal pressure Pt is stable.

When the stability of the tank internal pressure Pt is confirmed, in step 113, a negative pressure is introduced to the entire evaporative path including the fuel tank 20 and the canister 40. Specifically, the ECU closes the air introduction valve 35a and forcibly opens the refueling valve 60 while keeping the purge control valve 34a open (time t2 in FIG. 7). As a result, the canister 40 is shut off from the atmosphere, and a negative pressure is led to the canister 40 from the intake passage 12 through the purge passage 34. In addition, the fuel tank 2 is opened by opening the refueling valve 60.
0, vapor passage 33, canister 40 and purge passage 3
4 (that is, the entire evaporation path) becomes a negative pressure state, and the tank internal pressure Pt decreases. The internal pressure of the entire evaporative path is
Pressure sensor 31 attached to fuel tank 20 (and / or pressure sensor 3 attached to canister 40)
2) is detected.

During this time, the ECU determines that the tank internal pressure Pt has reached a predetermined target low pressure level (for example, -2.67 kPa = -20).
mmHg) is monitored (step 1).
14). Then, when the tank internal pressure Pt has decreased to the predetermined target low pressure level (YES in step 114, time t3 in FIG. 7), the ECU closes both the refueling valve 60 and the purge control valve 34a in step 115. The fuel tank 20 is closed in a negative pressure state by closing the refueling valve 60, and the canister path group is closed in a negative pressure state by closing the purge control valve 34a.

At this time, if there is no abnormality such as a hole in the fuel tank 20, the fuel in the tank evaporates, and the tank internal pressure Pt gradually approaches the equilibrium pressure of the remaining air and fuel vapor. (Ie, slowly rise). On the other hand, if there is a leak in the fuel tank 20, the tank internal pressure Pt rapidly approaches the outside pressure (atmospheric pressure). In any case, after the time t3, the tank internal pressure P
Although t increases, the degree of increase in the internal pressure differs depending on the presence or absence of leakage. In the present embodiment based on this concept, the tank internal pressure Pt is again reduced to the predetermined pressure p1 (for example,-
2.00 kPa = −15 mmHg), the pressure change rate ΔP as the pressure change degree with reference to time t4.
t (−15) (kPa / sec or mmHg / sec) is measured (step 116). Specifically, the pressure p2 after a predetermined time T (for example, 5 seconds) from the time t4 is measured, and the pressure change rate ΔPt (−15) = (p2−p1) /
T is calculated.

Based on the pressure change rate ΔPt (−15), it is determined whether the fuel tank 20 has an abnormality such as a hole. Specifically, in step 117, the ECU
It is determined whether ΔPt (−15) is equal to or higher than a predetermined threshold speed β (β> 0). If the determination in step 117 is NO, in step 118 the fuel tank 2
It is determined that there is no abnormality such as a hole in 0. On the other hand, if the determination in step 117 is YES, it is determined in step 119 that the fuel tank 20 has an abnormality such as a hole.

If there is no abnormality such as a hole in the canister path group, the volume of the canister 40 is small and the amount of generated steam is small, so that the pressure change of the canister internal pressure Pc should be small (ie, increase slowly). is there. On the other hand, if there is a leak in the canister path group, the canister internal pressure Pc rapidly approaches the external pressure (atmospheric pressure). Based on such a concept, in the present embodiment, the canister internal pressure P
c is a predetermined pressure p3 (for example, −2.53 kPa = −19)
mmHg), the pressure change rate ΔPc (−19) (kPa
/ S or mmHg / s) (step 12).
0). Specifically, the pressure p3 after a predetermined time T (for example, 5 seconds) from the time t31 is measured, and the pressure change rate Δ during that time is measured.
Pc (−19) = (p3−p1) / T is calculated.

Based on the pressure change rate ΔPc (−19), it is determined whether there is an abnormality such as a hole in the canister path group. Specifically, in step 121, the ECU
Determines whether ΔPc (−19) is less than a predetermined threshold speed γ (γ> 0). If the determination in step 121 is YES, it is determined in step 122 that there is no abnormality such as a hole in the canister path group. On the other hand,
If the determination in step 121 is NO, step 123
It is determined that there is an abnormality such as a hole in the canister route group in.

After making a determination in either step 122 or 123, the ECU ends the processing of FIGS. If it is determined in step 119 that the tank is abnormal, or if it is determined in step 123 that the canister route group is abnormal, a warning display or a buzzer sounds to notify the person of the abnormality. Or

When it is determined in step 104 that the fuel tank 20 is normal, the ECU performs steps 131 and subsequent steps in order to perform abnormality diagnosis on the canister path group excluding the fuel tank 20 in the evaporative path. Execute.

Steps 131 to 134 and step 1
Processes 20 to 123 show the outline of the procedure for diagnosing the abnormality of the canister route group by the negative pressure method. The timing chart in FIG. 8 corresponds to the procedure for diagnosing the abnormality of the canister path group by the negative pressure method.

In performing the leak diagnosis of the canister path group, if the cooling water temperature of the engine 10 has reached the purge start water temperature (80 ° C. in this embodiment), the ECU opens the air introduction valve 35a in step 131. Under circumstances, the purge of the fuel vapor by the system is initiated by opening the purge control valve 34a. (Time t1 in FIG. 8)
1). At this time, it is not necessary to consider the stability of the canister internal pressure Pc because the volume of the canister 40 is small, the amount of generated fuel vapor is small, and the pressure change associated therewith is small.

Next, at step 132, the ECU keeps the refueling valve 60 closed and closes the air introduction valve 35a while keeping the purge control valve 34a open (FIG. 8).
At time t12). As a result, the canister 40 is cut off from the atmosphere, and the intake passage 1 is provided in the canister path group.
A negative pressure is led from 2 through a purge passage 34. The internal pressure of the canister path group is detected by a pressure sensor 32 attached to the canister 40.

During this time, the ECU determines that the canister internal pressure Pc has reached a predetermined target low pressure level (for example, -2.67 kPa =-
It is monitored whether the pressure has dropped to 20 mmHg) (step 133). Then, when the canister internal pressure Pc decreases to a predetermined target low pressure level (the determination in step 133 is Y
ES, at time t13 in FIG. 8, the ECU closes the purge control valve 34a in step 134. Since the refueling valve 60 is held in the closed state, the canister path group is closed in a negative pressure state by closing the purge control valve 34a.

At this time, if there is no abnormality such as a hole in the canister path group, the pressure change of the canister internal pressure Pc should be small (that is, increase slowly). On the other hand, when there is a leak in the canister path group, the canister internal pressure Pc rapidly approaches the external pressure (atmospheric pressure). Also in this case, the canister internal pressure Pc becomes the predetermined pressure p3 (for example, −2.53 kPa = −19 mmHg) based on this concept.
Pressure change rate ΔPc (−19) (kPa / sec or m
mHg / sec) (step 120). Specifically, the pressure p3 after a predetermined time T (for example, 5 seconds) from the time t14 is measured, and the pressure change rate ΔPc (−1
9) = (p3-p1) / T is calculated.

Based on the pressure change rate ΔPc (−19), it is determined whether there is an abnormality such as a hole in the canister path group. Specifically, in step 121, the ECU
Determines whether ΔPc (−19) is less than a predetermined threshold speed γ (γ> 0). If the determination in step 121 is YES, it is determined in step 122 that there is no abnormality such as a hole in the canister path group. On the other hand,
If the determination in step 121 is NO, step 123
It is determined that there is an abnormality such as a hole in the canister route group in.

After making a determination in either step 122 or 123, the ECU ends the processing in FIGS. If it is determined in step 123 that the canister route group is abnormal, a warning display for notifying a person of this is turned on or a warning buzzer sounds.

(Effects) According to the present embodiment, the following effects can be obtained.・ The abnormality diagnosis can be performed by separating only the fuel tank part from other parts of the entire evaporation path to be subjected to the abnormality diagnosis. Therefore, when there is an abnormality in the fuel tank 20, the fuel tank 20 can be specified as a location where abnormality is found. Further, abnormality diagnosis of the evaporation path (canister path group) excluding the fuel tank 20 can be separately performed, and it is possible to narrow down an abnormal part of the fuel vapor purge system to some extent.

According to the present embodiment, although the fuel tank 20 is a part of the evaporation path, the first diagnosis of the abnormality of the purge system can be promptly completed immediately after the engine is started.

Further, immediately after the cold start of the engine 10, the fuel tank 20 is determined based on the comparison result between the absolute value of the internal pressure (residual pressure) of the fuel tank 20 and the determination value α (α> 0).
Can be determined early and with high reliability. That is, various valves (particularly, the refueling valve 60)
Before (or without) performing the opening / closing operation of the fuel tank 20, it is possible to quickly determine whether there is any abnormality in the fuel tank 20 based only on the tank internal pressure Pt detected by the pressure sensor 31. As described above, since the abnormality diagnosis of the fuel tank 20 can be performed earlier than other parts, not only the reliability of the purge system is improved, but also the abnormality diagnosis becomes easier thereafter.

The fuel supply valve 60 separates the fuel tank 20 in the evaporative path from the other canister path groups to perform abnormality diagnosis. In the canister path group, since the volume of the canister 40 is small, the amount of generated fuel vapor is small, and the pressure change of the canister internal pressure Pc is small, the judgment value for abnormality diagnosis can be appropriately set. Abnormality diagnosis can be performed.

(Another Example) The above embodiment may be modified as follows. -Although the processing of steps 102, 103, and 104 of FIG. 5 was performed at the time of the cold start, the diagnostic program may be modified so that a series of these processing is performed before the start of the engine.

As far as the invention is concerned, the canister 40
It is not necessary to provide the internal pressure sensor 32. Also, when monitoring the pressures at two observation points in the fuel tank 20 and the canister 40, only one pressure sensor is used, and a three-way valve is interposed between the single pressure sensor and the two observation points. Then, one of the two observation points may be selectively communicated with the pressure sensor by operating the three-way valve.

In the above-described embodiment, the negative pressure method is employed in the diagnosis of the tank and the diagnosis of the entire evaporative path. However, instead of this, the area to be inspected is once pressurized, and the presence or absence of an abnormality is determined based on the subsequent pressure transition. A pressure method may be employed.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a fuel vapor purge system and a diagnostic device therefor.

FIG. 2 is an enlarged cross-sectional view of a part of a path connecting a fuel tank and a canister.

FIG. 3 is an enlarged sectional view of a part of a path connecting a fuel tank and a canister.

FIG. 4 is a block diagram showing an outline of an electrical configuration relating to abnormality diagnosis.

FIG. 5 is a flowchart showing an outline of a fuel tank abnormality diagnosis procedure.

FIG. 6 is a flowchart showing an outline of a fuel tank abnormality diagnosis procedure.

FIG. 7 is a timing chart of abnormality diagnosis of a fuel tank by a negative pressure method.

FIG. 8 is a timing chart of an abnormality diagnosis of only the canister path group by the negative pressure method.

[Explanation of symbols]

10 engine, 12 intake passage, 20 fuel tank,
31: pressure sensor (internal pressure measuring means), 33: vapor passage, 34: purge passage, 40: canister, 60: oil supply valve (forcible on-off valve), ECU: electronic control unit (diagnosis control means).

Claims (7)

[Claims] 1. A method for diagnosing the presence or absence of an abnormality in a fuel tank configured to be capable of communicating with an engine intake passage in a gas phase via a path including a forced open / close valve, wherein the forced open / close valve is closed. Measures the tank internal pressure in a closed tank state, compares the absolute value of the difference between the tank internal pressure and the atmospheric pressure with a predetermined determination value, and determines whether the fuel tank is abnormal based on the comparison result. A method for diagnosing a fuel tank abnormality. 2. When the absolute value of the difference between the tank internal pressure and the atmospheric pressure is equal to or greater than the predetermined determination value, it is determined that there is no abnormality such as leakage in the fuel tank. Item 3. The abnormality diagnosis method for a fuel tank according to Item 1. 3. The fuel tank abnormality diagnosis method according to claim 1, wherein the measurement of the tank internal pressure in the closed state of the fuel tank is performed at the time of cold start or before the start of the engine. 4. An apparatus for diagnosing the presence or absence of an abnormality in a fuel tank configured to be able to communicate with an engine intake passage in a gas phase through a path having a forced open / close valve, the internal pressure being used to measure the internal pressure of the fuel tank. Measuring means, and diagnostic control means for controlling the opening and closing of the forcible on-off valve and for obtaining information on the internal pressure of the fuel tank from the internal pressure measuring means, wherein the diagnostic control means comprises a fuel for which the forcible on-off valve is closed. Obtain the tank internal pressure in the tank closed state from the internal pressure measuring means, compare the absolute value of the difference between the tank internal pressure and the atmospheric pressure with a predetermined judgment value, and based on the comparison result, there is an abnormality in the fuel tank. An abnormality diagnosis device for a fuel tank, which determines whether or not the abnormality is detected. 5. The diagnostic control means according to claim 1, wherein the absolute value of the difference between the tank internal pressure and the atmospheric pressure is equal to or greater than a predetermined determination value.
The abnormality diagnosis device for a fuel tank according to claim 4, wherein it is determined that the fuel tank has no abnormality such as leakage. 6. The fuel tank according to claim 4, wherein the diagnostic control means measures the tank internal pressure in the closed state of the fuel tank during or before a cold start of the engine. Abnormal diagnostic device. 7. A path that allows the fuel tank and the engine intake passage to communicate with each other in a gas phase includes a canister, a purge passage connecting the canister and the engine intake passage, and a vapor passage connecting the canister and the fuel tank. The abnormality diagnosis device for a fuel tank according to any one of claims 4 to 6, wherein the forcible on-off valve is a refueling valve provided in the middle of the vapor passage.