JPH09264204A - Failure diagnostic device for evaporative fuel supply system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To determine leakage with high precision. SOLUTION: A control valve 24, a canister 22, and a purge valve 25 are connected to a purge passage 21 connecting a fuel tank 7 to an intake passage 2, and an atmospheric air releasing valve 28 is connected to the canister 22. While the control valve 24 is opened and the valve 28 is closed, the purge valve 25 is opened, so that the inside of a fuel tank 7 is sucked by means of an intake negative pressure. Then, the purge valve 25 is closed, and the purge passage 21 is cut off from the atmospheric air so as to be held in a sealed condition. After the lapse of the predetermined time, if a tank internal pressure (a pressure increase from the predetermined negative pressure) is within a determination threshold value, it is determined that leakage is not caused. The predetermined negative pressure in a start of leakage determination always takes the same value without respect to a difference in an operation condition of an engine. The predetermined negative pressure is always kept constant, but a leakage determining condition may be changed according to a dimension of the predetermined negative pressure in a start of leakage determination or according to a differential pressure between the predetermined negative pressure and the atmospheric pressure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an evaporative fuel supply system failure diagnosis device for detecting a leakage failure of an evaporative fuel supply system formed between a fuel tank and an intake passage.

[0002]

2. Description of the Related Art In engines, especially automobile engines,
In order to prevent the evaporative fuel from leaking from the fuel tank to the outside, an evaporative fuel recovery path called a page path is constructed. In this evaporative fuel recovery path, an evaporative fuel adsorber called a canister is provided in the middle of the purge passage connecting the fuel tank and the engine intake passage, and the evaporative fuel from the fuel tank is adsorbed by the canister. , The negative pressure of intake air generated in the intake passage while the engine is operating is used.
The evaporated fuel adsorbed by the canister is sucked into the intake passage.

By the way, the occurrence of a leak, that is, a leak in the purge path causes leakage of vaporized fuel to the atmosphere, and it is desirable to find out whether this leak has occurred. In order to detect a leak, the inside of the purge path is temporarily sucked to a predetermined negative pressure, and then the purge path is closed to the atmosphere, and the purge is performed when the closed status is reached. Whether or not a leak has occurred is detected by observing the degree of pressure increase in the passage (for example, see Japanese Patent Laid-Open No. 6-74106). And in the above publication,
Under environmental conditions where the amount of evaporative fuel generated is large,
It is difficult to judge whether the pressure rise is due to the pressure rise or the pressure rise due to the generation of a large amount of evaporative fuel.
It is also disclosed to prohibit the determination of a shock.

[0004]

For the above-mentioned leak determination, the inside of the fuel tank is sucked up to a predetermined negative pressure, but if an error occurs in this predetermined negative pressure, it may cause a leak erroneous determination. Become. That is, when there is a slight area leak in the purge passage, the degree of pressure increase in the closed purge passage changes due to a slight difference between the atmospheric pressure and the negative pressure in the purge passage. Therefore, it becomes easy to make an erroneous determination when making a leak determination based on the degree of pressure increase. On the other hand, the manner in which the negative pressure is generated in the intake passage, which is the suction source of the purge path, differs variously depending on the engine operating state.

The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide a failure diagnosis device for an evaporated fuel supply system which can accurately perform a leak judgment.

[0006]

In order to achieve the above object, the present invention has the following as a first structure thereof. That is, after the pressure path of the vaporized fuel that connects the fuel tank and the intake passage of the engine is reduced to a predetermined negative pressure, the purged path is closed in a closed state from the atmosphere.
In the failure diagnosis device for the evaporated fuel supply system, which performs a leak determination to determine whether or not a leak has occurred in the purge passage according to the degree of pressure increase in the purge passage, Regardless of the difference, the predetermined negative pressure at the start of execution of the leak determination is set to always be the same pressure. Preferred modes based on the above configuration are as described in claims 2 to 4 and claim 10 in the claims.

In order to achieve the above object, the present invention has the following second construction. That is, a fuel vapor fuel line connecting the fuel tank and the intake passage of the engine.
After reducing the pressure in the purge passage to a predetermined negative pressure, is there a leak in the purge passage depending on the degree of pressure increase in the purge passage in a closed state in which the purge passage is shut off from the atmosphere? In a failure diagnosis device for an evaporated fuel supply system, which performs a leak determination to determine whether or not the leak determination condition is changed according to the difference in the predetermined negative pressure at the start of execution of the leak determination. It is configured as follows. A preferred mode based on the above configuration is as described in claims 6 and below in the claims. This

[0008]

According to the first aspect of the present invention, since the same negative pressure is constantly maintained in the purge path at the start of the leak determination execution, the leak execution at the start of the leak determination is started. It is possible to prevent erroneous determination of leak due to negative pressure fluctuation.

With the structure as described in claim 2, while the start of execution of the leak determination is delayed, the pressure in the purge path is gradually increased by the evaporated fuel, and a desired predetermined value is obtained. It can be negative pressure.

With the configuration as described in claim 3, it is possible to shorten the time to wait for the start of the execution of the leak determination until the predetermined negative pressure is reached.

With the structure as described in claim 4, the predetermined negative pressure can be promptly set by introducing the atmospheric pressure into the purge passage using the atmosphere release valve.

According to the invention described in claim 5,
It is possible to prevent the erroneous determination of the leak by changing the leak determination condition according to the fluctuation of the negative pressure in the purge path at the start of the execution of the leak determination.

According to the sixth aspect of the present invention, the leak determination can be accurately performed in response to the fluctuation of the negative pressure in the purge path at the start of the execution of the leak determination. A more specific method is provided. With the structure as described in claim 7, the differential pressure between the atmospheric pressure and the negative pressure in the purge path that affects the degree of pressure increase for the leak determination is dealt with. , The leak determination can be performed more accurately.

With the structure as described in claim 8 or claim 9, a concrete method for changing the leak determination condition is provided.

With the structure described in claim 10, by using a plastic tank which is resistant to pressure fluctuations (a plastic tank having a larger plate thickness than a steel plate fuel tank has a larger tank internal pressure). Deformation due to fluctuation is unlikely to occur), and a control valve that prevents a large negative pressure in the fuel tank due to intake negative pressure (two-way valve that prevents transmission of negative pressure above a predetermined level to the fuel tank side) becomes unnecessary. . Along with this, it is not necessary to separately provide a bypass valve for bypassing the control valve in order to suck up the inside of the fuel tank to a predetermined negative pressure for leak determination, which reduces the number of parts as a whole. It will be preferable from the above.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, reference numeral 1 denotes an engine body, 2 denotes an intake passage, and an air cleaner 3, a throttle valve 4,
A surge tank 5 is provided, and the intake passage 2 from the surge tank 5 to the engine body 1 is an independent intake passage 2a independent for each cylinder. A fuel injection valve 6 is arranged in the independent intake passage 2a.

Reference numeral 7 denotes a fuel tank. The fuel in the fuel tank 7 drawn from the fuel pump 8 is supplied to the fuel injection valve 6 via the fuel supply passage 9, and the surplus fuel is supplied to the return passage 10. The fuel is then returned from the fuel injection valve 6 to the fuel tank 7. In the figure, reference numeral 11 denotes a fuel filter connected to the fuel supply passage 9, and reference numeral 12 denotes a pressure regulator connected to the return passage 10.

The evaporated fuel in the fuel tank 7 is collected in the surge tank 5. For this reason, the fuel tank 7 and the surge tank 5 are connected by a purge passage 21, and a canister 22 as an evaporative fuel adsorbing means (adsorber) is connected in the middle of the purge passage 21. . That is, of the purge passage 21, the fuel tank 7 and the canister 22 are connected by the upstream purge passage 21a on the fuel tank 7 side, and the canister 22 and the surge tank 5 are connected by the downstream purge passage 21a. And are connected.

A pressure sensor 23 as a pressure detecting means for detecting the pressure in the fuel tank 7 and a control valve 24, which will be described later, are sequentially connected to the upstream purging passage 21a from the fuel tank 7 side. A purge valve 25 is connected to the downstream purge passage 21b. The purge valve 25 is of an electromagnetic type, which can selectively take a fully closed state and a fully opened state, and its opening degree can be changed continuously by duty control, for example. The canister 22 has an atmosphere release passage 26, and the atmosphere release passage 26 is connected with a filter 27 and an atmosphere release valve 28 composed of an electromagnetic on-off valve. A roll passage for preventing fuel from leaking into the purge passage 21 at the time of overturning is provided at a connection portion of the purge passage 21 to the fuel tank 7.
The valve 29 is connected to the roll valve 29.
Has a throttle resistance even when fully opened (full opening is small).

The control valve 24 basically switches between a state in which the upstream side purge passage 21a is fully opened and a state in which the upstream side purge passage 21a is fully closed. In addition, in the fully closed state, the pressure in the fuel tank 7 is basically reduced. When the pressure becomes lower than the canister 22 side pressure by a predetermined amount, it functions as a breathing plug that connects the fuel tank 7 side and the canister 22 side.

An example of the control valve 24 is shown in FIG. In FIG. 2, reference numeral 31 denotes a valve seat opened upward,
Reference numeral 32 is a movable valve body that is seated on and off the valve seat 31. The movable valve body 32 is a cylindrical member 33 which also becomes a covered cylindrical movable iron core.
And an elastic member 34 such as rubber integrated with the lower end of the tubular member 33. The elastic member 34 is attached to and detached from the valve seat 31, and a pair of left and right lip-shaped valve bodies 35A and 35B are formed integrally with the elastic member 34. Further, the cylindrical member 33 has a small hole 3 for communication on a side surface thereof.
6 are formed.

The tubular member 33 is integrally held by the diaphragm 37, and is urged downward by the return spring 38, that is, in the direction in which the elastic member 34 is seated on the valve seat 31. A fixed iron core 39 is provided above the cylindrical member 33 as a movable iron core, and a coil 40 is provided around the fixed iron core 39.

In the state of FIG. 2 in which the coil 40 is demagnetized, the return spring 38 causes the elastic member 34 to move to the valve seat 3
1 (closed state). In this state, when a negative pressure acts on the canister 22, that is, when the pressure on the canister 22 side is lower than the pressure on the fuel tank 7 side, the lip-shaped valve bodies 35 </ b> A and 35 </ b> B close, and the inside of the fuel tank 7 has a large negative pressure. Pressure is prevented. Conversely, when the negative pressure in the fuel tank 7 exceeds a predetermined value, that is, when the pressure in the fuel tank 7 becomes lower than the pressure on the canister 21 side by a predetermined amount, the lip-shaped valve bodies 35A and 35B open, and the The fuel tank 7 and the canister 22 communicate with each other through the small hole 36,
A large negative pressure in the fuel tank 7 is prevented (respiration function). However, the effective opening area of the small hole 36 is set to be small, and has a diaphragm resistance. In this way, the control valve 24 functions as a two-way valve that prevents a large negative pressure from acting in the fuel tank 7 (valve element 35).
A, 35B and the function of the small hole 36) and a bypass valve (function of the valve seat 31 and the movable valve body 32) that bypasses the two-way valve.

When the coil 40 is excited from the state shown in FIG. 2, the cylindrical member 33 as a movable iron core is attracted to the fixed iron core 39, the elastic member 34 is largely separated from the valve seat 31, and the upstream purging passage is formed. 21a is fully opened (large opening, no throttling resistance).

The evaporated fuel from the fuel tank 7 is supplied to the control valve 2
4 (small holes 36 and lip-shaped valve bodies 35A, 35B) and are adsorbed to the canister 22. The atmosphere release valve 28 is normally open, and during a predetermined operation of the engine, the purge valve 25 is opened, and the fuel adsorbed by the canister 22 is released by the intake negative pressure generated in the intake passage 2. (Purge).

In FIG. 3, U is a control unit constituted by using a microcomputer, and as is known, a CPU as a calculation means and a ROM as a storage means.
And a RAM. In addition to the signal from the pressure sensor 23, signals from various sensors (detection means) S1 to S7 are input to the control unit U. From the control unit U, the control valve 24, the purge valve 25,
In addition to outputting a control signal to the atmosphere release valve 28, it is also output to an alarm device 41 such as a lamp or buzzer.

The sensor S1 detects the amount of fuel in the fuel tank 7, that is, the residual fuel amount. Sensor S2
Is for detecting atmospheric pressure. The sensor S3 detects the engine cooling water temperature, that is, the engine temperature. The sensor S4 detects an engine speed. The sensor S5 detects an engine load such as an accelerator opening. The sensor S6 detects the vehicle speed. The sensor S7 detects the intake air temperature.

The control unit U determines whether or not there is a leak in the purge path including the fuel tank 7, the purge passage 21 and the canister 22, that is, the leak determination. The basic method of judgment will be described with reference to FIG. First, while the purge valve 25 is open, the atmosphere release valve 28 is closed and the control valve 2 is closed.
4 is opened (at time t1). This allows the purge passage 2
The intake negative pressure acts in the fuel tank 7 via the valve 1, and the negative pressure in the fuel tank 7 gradually increases.

At the time when the negative pressure in the fuel tank 7 becomes a predetermined negative pressure, for example, -200 mmAq (water level) (at time t2) and becomes slightly higher than this (at time t3), the purge valve 25. Is closed. When the purge valve 25 is closed, the purge path is sealed off from the atmosphere. After a lapse of a short time from the time point t3, the pressure detected by the pressure sensor 23 is increased to the predetermined negative pressure (for example, -200 mmAq) (at the time point t4, the influence of the throttle resistance of the roll-over valve 29). Elimination of the delay in the transmission of the negative pressure of the intake air to the fuel tank 7).

At the time t4 when the predetermined negative pressure is reached,
The negative pressure detected by the pressure sensor 23 is set as a first detected negative pressure TP1. The negative pressure detected by the pressure sensor 23 is the second detected pressure TP2 at a point in time when a predetermined time, for example, 30 seconds has elapsed from the point in time of detecting TP1 (point in time t5).

The leak is determined by the above two detected pressures TP1.
This is performed by comparing the deviation between the TP2 and TP2 with a predetermined determination threshold value. In other words, when the degree of pressure increase from TP1 to TP2 is large, it is considered that leakage such as a small hole in the purge path is considered, and in this case, it is determined that leakage has occurred. That is, a failure determination is made. Conversely, if the degree of pressure rise is small,
Is determined not to have been clicked.

The degree of pressure increase from TP1 to TP2 is changed by the amount of evaporated fuel generated in the fuel tank 7, and the judgment condition of the leak judgment is appropriately changed in accordance with the amount of evaporated fuel generated. -A lot of chances of being judged are secured as much as possible.

Next, including the change of the leak judgment condition,
The details of the leak determination by the control unit U will be described with reference to the flowcharts in FIG. In the following description, Q indicates a step, and control is started immediately after the engine is started.

First, the engine is started by starting the engine, and it is determined by Q1 to Q10 whether or not the conditions for performing the leak determination are satisfied. This leak determination is premised on that the engine operating condition satisfies the condition for purging, but the purging execution condition is Q
It is set according to the engine temperature at 4, the engine speed at Q6, the engine load at Q7, the vehicle speed at Q8, and the intake air temperature at Q9. Also, in Q10, the actual
It is confirmed that it is being executed.

Q1 to Q3 and Q5 determine whether or not the conditions for performing the leak determination are satisfied. That is,
It was confirmed in Q1 that the residual fuel amount was in a predetermined range between a predetermined lower limit value and a predetermined upper limit value, in Q2 that the fuel tank internal pressure was below a predetermined pressure, and in Q3 the atmospheric pressure. Is determined to be equal to or higher than a predetermined pressure, and in Q5, it is confirmed that the engine cooling water temperature at engine start is within a predetermined temperature range. Is done.

In Q1, the upper limit value for the residual fuel amount is set because if the residual fuel amount is too large, too much evaporated fuel will be generated and the leak determination will be erroneously determined.
The lower limit value of the residual fuel amount is set in consideration that the volume of the space portion of the purge path is too large and the pressure change for leak determination is too small.

In Q2, the upper limit value regarding the tank internal pressure is set to confirm that the amount of vaporized fuel produced is too large due to various factors. In Q5, the upper limit value regarding the cooling water temperature at the time of starting, that is, the engine temperature is set because the fuel returned from the return passage 10 to the fuel tank 7 is too hot, which causes too much evaporated fuel to be generated. It The lower limit value of the cooling water temperature at the time of starting is set because the purged fuel vapor into the intake passage 2 is not preferable.

If NO in any of the determinations from Q1 to Q10, the process returns to Q1 without performing a leak determination. Q1
When the determinations in Q10 are all YES, the process proceeds to Q21 in FIG. In Q21, it is judged whether or not the tank internal pressure is lower than -100 mmAq.
In the case of S, in Q22, the opening amount of the purge valve 25 is reduced or fully closed to reduce the purge amount, and then the process returns to Q21. The processing of Q22 is performed to prevent the negative pressure in the fuel tank 7 from becoming too large.

When the determination in Q21 is NO, in Q23, the atmosphere release valve 28 is closed and the control valve 24 is opened. As a result, the inside of the fuel tank 7 is sucked by the intake negative pressure, and the negative pressure is gradually increased. Q
After 23, in Q24, the tank internal pressure was -190 mm
It is determined whether or not it is smaller than Aq. This Q2
If the result of the determination in No. 4 is NO, in Q25, the purge flow rate is set to a relatively large value such as 10 liters / minute, and the negative pressure is increased at a high speed. After Q25, in Q26, it is determined whether or not a predetermined time (25 seconds in the embodiment) has elapsed from the time of Q23. The process of Q26 is set to forcibly shift to the next step when the inside of the fuel tank 7 does not rise to a predetermined negative pressure (-200 mmAq in the embodiment). If NO in this Q26, the process returns to Q24.

When the determination in Q24 is YES, Q2
7, the internal pressure of the tank is -200 m as a predetermined negative pressure.
It is determined whether it is smaller than mAq. When the determination in Q27 is NO, in Q28, it is determined whether or not a predetermined time (20 seconds in the embodiment) has elapsed from the time point of Q23. When the determination in Q28 is NO, the state is in the vicinity of passing -200 mmAq as the predetermined negative pressure.
Since there is a margin up to the predetermined time in Q26, the purge flow rate is set to a relatively small value such as 5 liters / minute, and then the process proceeds to Q26. In addition, it becomes YE by the judgment of Q28.
At the time of S, in Q29, the state has approached 25 seconds as the predetermined time set in Q26, so in order to reach -200 mmAq as the predetermined negative pressure early, the power is reached.
The flow rate is relatively large, such as 10 liters / minute.

When the determination in Q27 is YES, or the determination in Q26 is YES, the Q of FIG.
Move to 41. In this Q41, the purge valve 25 is closed, so that the purge path is in a closed state in which the purge path is shut off from the atmosphere, and the pressure change is as long as there is no leakage.
The state depends only on the pressure change according to the generation of the evaporated fuel.

After Q41, in Q42, after a short predetermined time (2 seconds in the embodiment) has elapsed from the time of Q41, the process proceeds to Q43. The process of Q42 corresponds to the state of shifting from t3 to t4 in FIG.

After Q42, in Q43, from the map set with the atmospheric pressure and the starting water temperature as parameters,
The threshold value SP1 is set. This threshold SP1 is
In the standard state, for example, it is set as -130 mmAq,
As shown in FIG. 9, the larger the atmospheric pressure (lowland) and the higher the starting water temperature, the smaller the negative pressure (the direction closer to the atmospheric pressure). The above-mentioned SP1 is a confirmation in the case where suction is not possible up to -200 mmAq as a predetermined negative pressure. In addition to when there is a leak in the purge path, the atmosphere release valve 28 is stuck open and the purge valve 25 is stuck closed. Can be considered.

At Q44, it is judged if the current tank internal pressure is smaller than the threshold value SP1. If the determination in Q44 is YES, the current tank internal pressure is stored as TP1 in Q45 (at time t4 in FIG. 4). After that, in Q46, after waiting a predetermined time (30 seconds in the embodiment) from the time point Q41, that is, waiting the time point t5 in FIG. 4, the process proceeds to Q47.

In Q47, the threshold value S for determination is calculated from the map set with the atmospheric pressure and the water temperature at startup as parameters.
P2 is set. This SP2 is t4 in FIG.
It is the upper limit value of the pressure increase that can be considered when there is no leak from the tank internal pressure TP1 at the time point to the time point t5, and it is, for example, 50 mmAq equivalent in the standard state. The threshold value SP2 is also changed to a direction in which the negative pressure becomes smaller (a direction closer to the atmospheric pressure) as the atmospheric pressure becomes larger (lowland) and the starting water temperature becomes higher (determination condition change).

After Q47, in Q48, it is judged whether or not the value obtained by subtracting the current tank internal pressure from the stored tank internal pressure TP1 is smaller than the threshold value SP2. When the determination in Q48 is YES, it is considered that there is no leak in the purge path. At this time, in Q49, the tank internal pressure TP at the time t4.
2 is stored.

After Q49, the routine moves to Q51 in FIG. 8 where the atmosphere release valve 28 is opened and the control valve 24 is closed (time t5 in FIG. 4). After this, in Q52, after waiting for a short time (3 seconds in the embodiment) to elapse, the tank internal pressure T stored from the current tank internal pressure T is stored.
It is determined whether or not the value obtained by subtracting P2 is larger than a predetermined value, for example, 5 mmAq. This determination of Q53 is a determination as to whether or not the atmosphere release valve 28 has failed in the closed state (if the atmosphere release valve 28 is stuck in the closed state, the pressure rise from time t5 in FIG. 4). The degree will be small).

When the determination in Q53 is YES, it is determined in Q54 whether the value obtained by subtracting TP2 from the current tank internal pressure is smaller than a predetermined value, for example, 100 mmAq. This determination of Q54 is to determine whether or not the control valve 24 has an open failure (when the control valve 24, which should be closed, is open, atmospheric pressure is detected through the atmosphere release valve 28 as a pressure sensor. 23, the degree of pressure increase after the time point t5 in FIG. 4 becomes extremely large).

When the determination in Q54 is YES, each valve 2
Assuming that there is no failure in Nos. 4 and 28, and there is no leak in the page route, the normal condition is set in Q55.
Return to control.

When the determination in Q44 is NO, or the determination in Q48 is NO, the process proceeds to Q56, and it is determined whether or not the shaking of the fuel tank 7 is small.
Whether or not this swing is small is determined to be small, for example, when the deviation between the maximum residual fuel amount and the minimum residual fuel amount detected within a predetermined time (for example, 10 seconds) is within 10%. . When the shaking of the fuel tank 7 is large, the fuel is agitated in the fuel tank 7 so much that the amount of evaporated fuel generated becomes extremely large. In such a state, it is determined that the fuel tank is leaking. This is a process to prohibit. In addition to this, as is known, a method for detecting that the vehicle is traveling on a bad road or a method for detecting a turn can be used to determine whether or not the shake of the fuel tank 7 is small (whether it is large or not). (When shaking on a rough road or turning, there is a large amount of shaking.)

When the determination in Q56 is NO, the process directly returns to Q1. Also, when the determination in Q56 is YES,
In Q57, it is determined whether or not a predetermined time (corresponding to the predetermined period in claim 1, for example, 600 seconds) has elapsed since the engine was started. Even if NO in this determination in Q57, the process returns to Q1 (prohibition of determination that the leak is occurring).
If YES in the determination in Q57, it is determined in Q58 whether or not the determination in Q57 is YES twice in succession, that is, if NO in the determination in Q44 for two consecutive times, or Q48. It is determined whether or not the determination is NO. If YES in the determination in Q58, the alarm device 41 is activated in Q59 to warn that there is a leak, and then in Q60,
The fact that a leak is detected is stored as a failure code (for diagnostic check during maintenance).

It should be noted that, by the processing of Q58, it is determined that the leak is finally made on the condition that the leak is detected twice in succession (several times in succession).
Even in an environment where a large amount of evaporated fuel is generated, it is preferable for increasing the chances of making a leak judgment and for preventing a situation in which an erroneous judgment is made that a leak is occurring.

FIG. 11 shows another embodiment of the present invention. When the inside of the purge path has a negative pressure larger than a predetermined negative pressure (-200 mmAq as described above in the embodiment). The pressure can be quickly raised to the predetermined negative pressure. In the present embodiment, when the determination in Q27 is YES, the process in Q11 of FIG.
71, Q72 processing is performed. That is, in Q71, it is determined whether or not the actual tank internal pressure is lower than -210 mmAq. If the determination in this Q71 is NO, the actual tank internal pressure is within the error range of the predetermined negative pressure. Then, the process shifts to Q41.

If YES in the determination in Q71, in Q72, the atmosphere release valve 28 is slightly opened to introduce atmospheric pressure into the purge passage, and positively increase the pressure in the purge passage. (Move closer to atmospheric pressure). After Q71, return to 71 again. After Q72, Q27 or Q24
You may return to (check if the atmospheric pressure is too high). Moreover, -210 mmAq set in Q71
Can be set to an appropriate numerical value as long as it does not substantially cause an error in the leak determination with respect to a predetermined negative pressure of, for example, -200 mmAq such as -205 mmAq.

Here, as a modification of FIG. 11, the following can be performed. First, the atmosphere release valve 28 in Q72
Instead of opening, a transition to Q41 may be waited until the pressure is increased to −200 mmAq as a predetermined negative pressure. In this case, in order to shorten the waiting time,
The opening of the purge valve 25 may be reduced (including zero opening).

Instead of setting the purge path to the same predetermined negative pressure and starting the execution of the leak determination, the following procedure can be performed. That is, if the negative pressure in the purge path is set to such an extent that the leak can be determined, the leakage is determined according to the negative pressure in the purge path at the start of the leak determination. The judgment condition may be changed. That is, Lee
When the negative pressure in the purge path at the start of the judgment is large, the reference pressure (SP2) as the judgment threshold value is closer to the atmospheric pressure than when it is small, that is, the leak pressure. You may change to the value of the direction where it is hard to be judged that it is performing. In this case, the reference pressure as the determination threshold value can be changed to a continuously variable type or a stepwise type according to the magnitude of the negative pressure in the purge path at the start of execution of the leak determination.

Similarly, the leak determination condition may be changed according to the differential pressure between the negative pressure and the atmospheric pressure in the purge path at the start of the leak determination. That is, when the differential pressure between the negative pressure and the atmospheric pressure in the purge path at the start of the execution of the leak determination is large, the reference pressure (SP2) as the determination threshold is larger than when it is small. The value may be changed to a value closer to the atmospheric pressure, that is, a value in a direction in which it is difficult to determine that a leak is occurring.
In this case, the reference pressure as the determination threshold value can be changed to a continuously variable type or a step type according to the differential pressure.

When the leak judgment condition is changed according to the negative pressure in the purge path at the start of the execution of the leak judgment or the differential pressure between the negative pressure and the atmospheric pressure, the judgment is made. The reference pressure as the threshold value may be set to a constant value, and the timing of detecting the actual tank internal pressure with which the reference pressure is compared, that is, the predetermined time between t4 and t5 in FIG. 4, may be changed. . Of course, in this case, as the negative pressure is larger or the differential pressure is larger, the predetermined time is changed to a continuously variable type or a stepwise type.

Although the embodiments have been described above, the present invention is not limited to this, and includes, for example, the following cases. First, in the case of changing the judgment threshold value for checking whether or not a leak is occurring according to the atmospheric pressure or the like, for example, as shown in FIG.
A first correction coefficient (a coefficient indicating the amount of evaporated fuel generated) is determined from the map shown in FIG. 10, and a second correction coefficient is set according to the residual fuel amount as shown in FIG. It is also possible to multiply each coefficient by a standard decision threshold value to obtain a corrected decision threshold value. In FIG. 10, Y1 represents the pressure increase divided pressure with respect to the residual fuel amount in the fuel tank. Further, Y2 is a correction coefficient considering the amount of evaporated fuel, and Y3 is a correction coefficient considering the space volume in the fuel tank.

The control valve 24 may not be provided, and in this case, the fuel tank 7 is preferably a plastic tank capable of withstanding pressure fluctuations and large negative pressure.

The steps shown in the flowchart are:
The function can be described with the name of the means attached thereto, and implicitly includes what is regarded as a higher concept of the function.

The object of the present invention is not limited to the explicit ones, and it is also implicitly provided that the contents described in the effects of the invention and the contents substantially preferred or advantageous are provided. It includes. Further, the present invention can be understood not only as an apparatus invention but also as a leak detection method.

[Brief description of drawings]

FIG. 1 shows an embodiment of the present invention and is an overall system diagram showing a configuration example of a purge path for an engine.

FIG. 2 is a sectional view showing an example of a control valve connected to a purge path.

FIG. 3 is a diagram showing an example of a control system used in the present invention.

FIG. 4 is a time chart showing a control example of the present invention.

FIG. 5 is a flowchart showing a control example of the present invention.

FIG. 6 is a flowchart showing a control example of the present invention.

FIG. 7 is a flowchart showing a control example of the present invention.

FIG. 8 is a flow chart showing a control example of the present invention.

FIG. 9 is a diagram showing the relationship between atmospheric pressure, water temperature at start-up, and amount of evaporated fuel.

FIG. 10 is a diagram showing a relationship between a residual fuel amount, a pressure increase rate, and a correction coefficient.

FIG. 11 is a main part flow chart showing another control example of the present invention.
G.

[Explanation of symbols]

 1: Engine body 2: Intake passage 5: Surge tank 6: Fuel injection valve 7: Fuel tank 21: Purging passage 22: Canister 23: Pressure sensor 24: Control valve 25: Purging valve 28: Atmosphere release valve 41 : Alarm device U: Control unit S2: Sensor (atmospheric pressure)

Claims (10)

[Claims] Claim: What is claimed is: 1. A purge path for vaporized fuel, which connects a fuel tank to an intake passage of an engine, is pressure-reduced to a predetermined negative pressure, and then the purge is performed in a closed state in which the atmosphere is cut off. Differences in engine operating states in a failure diagnosis device for an evaporated fuel supply system, which performs a leak determination to determine whether or not a leak has occurred in the purge route in accordance with the degree of pressure increase in the route. Regardless of the above, the failure diagnosis apparatus for the evaporated fuel supply system is characterized in that the predetermined negative pressure at the start of execution of the leak determination is always set to be the same pressure. 2. The predetermined negative pressure according to claim 1, wherein the actual negative pressure in the purge path at the start of execution of the leak determination is a negative pressure that is higher than the predetermined negative pressure. A failure diagnosis device for an evaporated fuel supply system, characterized in that the start of execution of leak judgment is waited until the pressure reaches a pressure. 3. The opening of a purge valve for adjusting the degree of communication between the purge passage and the intake passage while waiting for the start of a leak determination until the predetermined negative pressure is reached. A failure diagnosis device for an evaporated fuel supply system, which is characterized in that it is made small. 4. The purging according to claim 1, wherein when the purging path is sucked to a predetermined negative pressure,
An atmospheric release valve that closes the atmospheric release port of the canister provided in the purge path is provided, and the actual negative pressure in the purge path at the start of execution of the leak determination is a negative pressure that is larger than the predetermined negative pressure. When the above is established, the failure diagnosis device for the evaporated fuel supply system is characterized in that the atmosphere release valve is opened to set the purge path to the predetermined negative pressure. 5. A purge path for the evaporated fuel, which connects the fuel tank and the intake passage of the engine, is pressure-reduced to a predetermined negative pressure, and then the purge is performed in a closed state in which the atmosphere is cut off. Leak determination is performed in a failure diagnosis device for an evaporated fuel supply system, which is configured to perform a leak determination that determines whether or not a leak has occurred in the purge route in accordance with the degree of pressure increase in the route. Depending on the difference in the predetermined negative pressure at the start,
A failure diagnosis device for an evaporated fuel supply system, characterized in that a leak determination condition is changed. 6. The leak determination condition according to claim 5, wherein the larger the predetermined negative pressure at the start of execution of the leak determination, the more difficult it is to determine that the leak is being made. A failure diagnosis device for an evaporated fuel supply system. 7. The leak judgment condition according to claim 5, wherein the larger the differential pressure between the predetermined negative pressure and the atmospheric pressure at the start of execution of the leak judgment, the more difficult it is to judge that the leak is occurring. A failure diagnosis device for an evaporated fuel supply system, wherein: 8. The leak determining method according to claim 5, wherein the leak determination determines the actual pressure in the purge path after a predetermined time has elapsed after the predetermined negative pressure. It is set so as to be performed by comparing with a reference pressure as a threshold value, and the change of the leak determination condition is performed by changing the reference pressure. Diagnostic device. 9. The leak judgment according to claim 8, wherein the actual pressure of the purge path after a lapse of a predetermined time from the predetermined negative pressure is compared with a reference pressure as a judgment threshold value. The failure diagnosis device for an evaporated fuel supply system is characterized in that the leak determination condition is changed by changing the predetermined time. 10. The fuel tank according to any one of claims 1 to 9, wherein the fuel tank is a plastic tank, and an upstream side pad between the canister provided in the page passage and the fuel tank is provided. A failure diagnosis device for an evaporated fuel supply system, characterized in that a control valve for preventing a large negative pressure from acting on the fuel tank is not connected to the passage.