JP2003065164A - Diagnostic system for evaporative emission purge system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a wrong diagnosis and conduct a correct failure diagnosis. SOLUTION: A purge system composed of a canister 10, a fuel tank 11, or the like is made in a negative pressure sealed state, a pressure rising speed ΔPL inside the system is measured with a pressure sensor 33, and if the ΔPL is a decision value or less, the purge system is decided as normal. If the ΔPL exceeds the decision value, the purge system is raised to the atmospheric pressure and kept in the atmospheric pressure sealed state, a pressure rising speed ΔPV inside the system is measured, and if the ΔPV is the specified decision value or more, the decision is reserved, and only when it is not more than the specified value, the purge system is decided as abnormal. By delaying the start of measurement of the ΔPV until the temperature inside the fuel tank approaches the atmospheric temperature and is stabilized, the generation of an error in the ΔPV measurement caused by temperature variation inside the tank is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an evaporative emission control device (evaporative purge system) for preventing evaporative fuel from being discharged from a fuel tank to the atmosphere, and more particularly to a canister, a fuel tank and connecting pipes for these. The present invention relates to a failure diagnostic device for an evaporative purge system, which determines an abnormality such as a leak or a hole in a purge system including the above.

[0002]

2. Description of the Related Art In order to prevent the vaporized fuel from a fuel tank from being released into the atmosphere, the vaporized fuel from the tank is introduced into a canister containing an adsorbent such as activated carbon to adsorb fuel vapor to the adsorbent. Evaporative purge systems that prevent atmospheric release of fuel vapors are generally known. In an evaporative purge system, normally, purge air is passed through the canister under the prescribed operating conditions of the engine to desorb the adsorbed vaporized fuel from the adsorbent, and at the same time, the air-fuel mixture of purge air and desorbed vaporized fuel (purge gas). Is supplied to the engine intake passage to be burned in the engine.

In such an evaporative purge system, if the apparatus fails, especially if the leak occurs in the purge system including the canister, the fuel tank, and the pipes connecting them, and the failure such as perforation occurs and the airtightness cannot be maintained, the fuel vapor is discharged. It may be released to the atmosphere without being supplied to the engine, which may cause air pollution. Further, even if such a failure of the evaporative purge system occurs, there is no hindrance to the operation of the engine, and therefore the driver may continue to operate the engine as it is without noticing the occurrence of the abnormality.

In order to solve the above problems, various failure detection devices have been devised which detect the occurrence of a failure in the evaporative purge system and inform the driver of the failure. For example, as an example of this type of device, Japanese Patent Laid-Open No. 5-1
There is one described in Japanese Patent No. 25997. The device disclosed in the same publication first closes the purge control valve provided in the purge pipe connecting the canister and the intake passage when the vehicle equipped with the engine is stopped and the engine is idle. Then, after the internal pressure of the purge system becomes equal to the atmospheric pressure, the shut-off valve arranged in the atmosphere introducing passage of the canister is closed to seal the internal pressure of the purge system at the atmospheric pressure state, and the purge system at this atmospheric pressure sealed state is closed. The rise width of the internal pressure within a predetermined time is measured. The range of increase in the internal pressure of the purge system at this time is a value representing the evaporation rate of the fuel.

After the measurement of the fuel evaporation rate is completed, the purge control valve is opened with the canister kept shut off from the atmosphere, and the negative pressure in the intake passage is introduced into the purge system to set the internal pressure of the purge system to a predetermined negative pressure. When the pressure is reduced to a predetermined negative pressure, the purge control valve is closed to close the purge system again. Then, the increase width of the internal pressure of the purge system within a predetermined time in the negative pressure closed state is measured, and the increase width of the internal pressure of the purge system in the atmospheric pressure closed state measured above and the increase width of the internal pressure of the purge system in the negative pressure closed state. Based on the above, whether or not there is an abnormality in the purge system is determined.

That is, the increase in the internal pressure of the purge system in the negative pressure closed state is caused only by the evaporation of the fuel in the fuel tank unless the purge system leaks and has no holes. On the other hand, if there is an abnormality such as a leak or a hole in the purge system,
Atmosphere enters the purge system through leaks, holes, etc.
The rate of increase in the internal pressure of the purge system is higher than that in the case where only the evaporation of fuel is used.

Further, in the measurement of the internal pressure rise of the purge system in the atmospheric pressure sealed state, which is performed before the internal pressure measurement in the negative pressure sealed state,
Since the pressure difference between the purge system and the atmosphere is small, the amount of air that enters the purge system through leaks, holes, etc. is small. Therefore, the rate of increase in the internal pressure of the purge system in the atmospheric pressure sealed state is a value that substantially corresponds to the evaporation rate of the fuel. In the apparatus of the above publication, when the internal pressure increase width in a predetermined time in the negative pressure closed state of the purge system is larger than the increase width (that is, the fuel evaporation rate) in the atmospheric pressure closed state to a certain extent or more, the purge system It is determined that an abnormality such as a leak or a hole has occurred.

[0008]

However, in the failure diagnosis apparatus disclosed in Japanese Patent Laid-Open No. 5-125997, the purge system must be kept in the atmospheric pressure sealed state before measuring the internal pressure rise in the purge system under the negative pressure sealed state. This may cause problems because it is necessary to measure the rise in internal pressure. That is, in order to seal the purge system, it is necessary to close the purge control valve regardless of whether it is a negative pressure seal or an atmospheric pressure seal. For this reason, the purge control valve cannot be opened to purge the canister while the purge system is sealed and a failure diagnosis is performed.

Therefore, as in the device of the above publication, both the measurement of the fuel evaporation rate by the atmospheric pressure sealing of the purge system and the measurement of the internal pressure rise by the negative pressure sealing of the purge system are always performed at the time of failure diagnosis. Then, the purge interruption time for the failure diagnosis becomes long and the purge of the evaporated fuel from the canister may become insufficient.

In order to solve this problem, for example, the internal pressure rise of the purge system is first measured by negative pressure sealing of the purge system during engine operation, and only when the measured internal pressure rise is large, then the atmospheric pressure sealing of the purge system is performed. It is also possible to measure the fuel evaporation rate according to. For example, when the internal pressure rise due to the negative pressure sealing of the purge system is large, the internal pressure rise is large due to actual leakage in the purge system, and there is no leakage in the purge system. The case where the internal pressure rise is large due to the high evaporation rate of
There are two possible cases. Therefore, it is necessary to actually measure the fuel evaporation rate and determine whether the increase in the internal pressure is due to the leakage or the fuel evaporation rate.

However, the internal pressure rise at the time of closing the negative pressure of the purge system becomes small only when there is no leakage in the purge system and the fuel evaporation rate is also small. Therefore, when the internal pressure increase rate is small. Can determine that the purge system is normal without measuring the fuel evaporation rate. Therefore, in such a case, it is possible to omit the measurement of the fuel evaporation rate and shorten the purge interruption time for failure diagnosis.

Therefore, during the engine operation, first, the internal pressure rise of the purge system when the negative pressure is closed is measured. If the internal pressure rise is small, the purge system is immediately judged to be normal and the fuel evaporation rate is not measured. Only when the internal pressure rise is large, if the atmosphere is introduced into the purge system after the internal pressure rise measurement is completed and the pressure is raised to atmospheric pressure and the fuel vaporization rate is measured by sealing the purge system at atmospheric pressure, the actual fuel The frequency at which the evaporation rate is measured becomes considerably lower, and the purge interruption time for failure determination can often be shortened.

However, actually, as described above, during the operation of the engine, first the internal pressure rise is measured by negative pressure sealing of the purge system,
Next, when the operation to detect the fuel evaporation rate by measuring the internal pressure rise in the atmospheric pressure sealed state after boosting the purge system to atmospheric pressure, even if the fuel temperature in the tank is the same, the detected fuel Experimental results have revealed that the evaporation rate may be greatly different and accurate failure diagnosis may not be possible.

Originally, if the fuel temperature in the fuel tank is the same, the fuel evaporation rate will be almost the same, and even if other conditions change, it should not change so much. However, in reality, if the history of changes in the pressure inside the fuel tank until the purge system is kept at the atmospheric pressure closed state in order to measure the fuel evaporation rate is different, the rate of increase in internal pressure at the subsequent atmospheric pressure closed state (fuel Evaporation rate) is significantly different. As a result of the study by the inventor, it has been found that this problem is caused by a temperature change in an atmospheric pressure sealed state after pressurization.

For example, it is the space above the liquid level in the fuel tank that has the largest space volume in the purge system. At the time of pressurization of the fuel tank, the gas in the liquid level upper space in the fuel tank is compressed by the inflowing atmosphere, but the gas temperature in the liquid level upper space rises due to this compression. In this case, the increased temperature in the tank decreases to the atmospheric temperature due to heat exchange with the outside air via the wall surface of the tank when the pressurization ends.

Therefore, if the purge system is closed when the internal pressure of the tank becomes atmospheric pressure, the internal temperature of the tank is lowered and the fuel vapor in the tank is condensed accordingly, so that the increase rate of the internal pressure of the tank is higher than the actual fuel evaporation rate. In some cases, it becomes significantly small, and there arises a problem that the fuel evaporation rate in the purge system cannot be accurately measured when the air pressure is sealed. The pressure drop width after the atmospheric pressure is sealed becomes larger as the temperature drop width after the sealing becomes larger, that is, the tank temperature when the atmospheric pressure is reached becomes higher. Also, as the rate of increase in tank pressure increases, the time for heat exchange with the outside air during compression decreases and the amount of heat dissipated in the outside air decreases, so the tank temperature rises to the atmospheric pressure when the atmospheric pressure reaches the atmospheric pressure. The higher the speed, the higher the speed.

Further, as a result of the study by the inventor, in addition to the pressure increase rate at the time of increasing the internal pressure to the atmospheric pressure after the negative pressure is sealed, there are factors that influence the temperature decrease in the tank after the atmospheric pressure is sealed. There was found. That is, before measuring the internal pressure increase rate (fuel evaporation rate) due to atmospheric pressure sealing, the internal pressure increase rate (leakage detection) is always measured due to negative pressure sealing of the purge system. However, the internal pressure of the purge system at the time of this leak detection, the rate of decrease of the internal pressure when making the purge system a negative pressure, and the time to keep the purge system at a negative pressure at the time of leak detection are also after the atmospheric pressure is closed. It affects the temperature drop in the tank.

For example, when the internal pressure of the purge system is reduced to seal the purge system under negative pressure, the gas in the fuel tank expands and the temperature decreases. As with boosting,
The temperature decrease range depends on the decrease rate and the decrease range of the fuel tank internal pressure. Further, the temperature inside the fuel tank that has once dropped due to the pressure drop rises due to heat exchange with the outside air, but this temperature rise width changes depending on the time period during which the fuel tank is hermetically held in the negative pressure state.

For this reason, when the internal pressure of the purge system is increased to the atmospheric pressure to detect the fuel evaporation rate after the leakage is detected by the negative pressure sealing of the purge system, the temperature in the tank at the start of the increase in pressure is not constant, and the above conditions are satisfied. It will change. That is, even if the pressure increase rate at the time of increasing the atmospheric pressure is the same, if the temperature in the fuel tank at the start of the pressure increase is higher, the temperature in the fuel tank after the pressure increase becomes higher, and the temperature decrease range in the tank after the atmospheric pressure is closed ( The internal pressure decrease width) becomes larger.

The temperature inside the fuel tank immediately after the purge system is closed under negative pressure becomes higher as the width of pressure drop when the internal pressure drops becomes smaller and as the time required for the pressure drop becomes longer. The temperature inside the fuel tank before the internal pressure of the purge system is lowered is almost atmospheric temperature. For this reason, the smaller the pressure drop width in the fuel tank when the internal pressure decreases and the longer the pressure decrease time, the smaller the difference between the temperature in the fuel tank immediately after the negative pressure sealing and the atmospheric temperature. Also, after the fuel tank is closed under negative pressure, the temperature inside the tank approaches the atmospheric temperature due to heat exchange with the outside air, so the longer the time to keep the purge system closed in a negative pressure state, the more the difference between the internal temperature of the fuel tank and the atmospheric temperature. Becomes smaller.

For this reason, the temperature in the fuel tank at the time of starting pressure increase after the negative pressure is closed is smaller as the pressure decrease width at the time of pressure decrease is longer and the time required for the pressure decrease is longer, and further the negative pressure is kept closed. The longer the time, the higher (close to the atmospheric temperature). Conversely, the larger the pressure drop width, the shorter the pressure drop required time, and the shorter the negative pressure closed holding time, the lower (the temperature difference from the atmosphere is large). Become. Therefore, the temperature inside the fuel tank immediately after the purge system is pressurized after the negative pressure is closed and closed to the atmospheric pressure is also changed by the above factors, and a large error occurs in the fuel evaporation rate detected during the atmospheric pressure closing.

In view of the above problems, the present invention is to seal the purge system in a negative pressure state and measure the internal pressure rise (leakage detection), and then increase the internal pressure of the purge system to the atmospheric pressure to keep the internal pressure in the atmospheric pressure sealed state. To provide a failure diagnostic device for an evaporative purge system that enables accurate failure diagnosis by preventing an error in the detected fuel evaporation rate when performing measurement (fuel evaporation rate detection). It is an object.

[0023]

According to the first aspect of the present invention, a canister for adsorbing evaporated fuel in a fuel tank of an internal combustion engine and a fuel liquid upper space in the fuel tank are connected to the canister. Adjusting the internal pressure of a purge system including the fuel tank, the canister, the vapor passage, and the purge passage of the evaporative purge system including the vapor passage and the purge passage connecting the canister and the engine intake passage to a predetermined negative pressure After that, the purge system is hermetically closed, and the leak detection means for detecting the purge system internal pressure increase rate in the negative pressure closed state, and the purge system internal pressure increase rate detected by the leak detection means is larger than a predetermined reference value, A fuel vaporization rate detecting means for detecting the rate of increase of the internal pressure of the purge system in the atmospheric pressure sealed state after closing the purge system after increasing the internal pressure of the purge system to the atmospheric pressure; A failure diagnosis device for an evaporation purge system, comprising: an abnormality determination means for determining that a failure has occurred in the evaporation purge system when the purge system internal pressure increase rate detected by the fuel evaporation rate detection means is smaller than a predetermined determination value. The fuel evaporation rate detecting means,
A means for determining whether or not the internal temperature of the fuel tank after the internal pressure of the purge system has risen to atmospheric pressure is stable, and starts detecting the rate of increase in internal pressure of the purge system after the internal temperature of the fuel tank has stabilized. A failure diagnostic device for an evaporative purge system is provided.

That is, in the invention of claim 1, the fuel evaporation rate detecting means detects the increase rate of the internal pressure of the purge system,
After the internal pressure is raised to the atmospheric pressure, the temperature inside the fuel tank is reduced and the temperature is stabilized, that is, when the internal temperature of the fuel tank becomes almost atmospheric temperature, the detection of the increase rate of the internal pressure of the purge system is started. Therefore, when the purge system internal pressure increase rate is detected, an accurate purge system internal pressure increase rate (fuel vaporization rate) that is not affected by the change in the fuel tank internal temperature to the fuel tank internal pressure is detected, and accurate failure diagnosis is possible. Become. A temperature sensor may be provided in the fuel tank to directly detect the temperature inside the fuel tank to determine whether the temperature inside the fuel tank has stabilized. It is also possible to make an indirect determination based on this.

According to the second aspect of the present invention, the canister for adsorbing the evaporated fuel in the fuel tank of the internal combustion engine, the vapor passage for connecting the fuel liquid level upper space in the fuel tank to the canister, and the canister. Of the evaporative purge system including a purge passage connecting the engine and the intake passage of the engine, including the fuel tank, the canister, the vapor passage, and the purge passage, the internal pressure of the purge system is adjusted to a predetermined negative pressure, and then the purge system is closed. However, if the leak detection means for detecting the internal pressure increase rate of the purge system in the negative pressure closed state and the increase rate of the internal pressure of the purge system detected by the leakage detection means are larger than a predetermined reference value, the internal pressure of the purge system is increased. After elevating the pressure to atmospheric pressure, the purge system is closed, and the fuel evaporation rate detecting means for detecting the increase rate of the internal pressure of the purge system in the atmospheric pressure closed state; A failure diagnosis device for the evaporative purge system, comprising: an abnormality determination device for determining that a failure has occurred in the evaporative purge system when the purge system internal pressure increase speed detected by the means is smaller than a predetermined determination value. The speed detection means starts detecting the increase rate of the internal pressure of the purge system after a lapse of a predetermined delay time after the internal pressure of the purge system rises to the atmospheric pressure, and the internal pressure of the purge system after the adjustment of the internal pressure of the purge system by the leak detection means is started. There is provided a failure diagnostic device for an evaporative purge system, wherein the delay time is set longer as the time required to decrease to the predetermined negative pressure is longer.

That is, according to the second aspect of the present invention, the delay time is set based on the time required for the internal pressure of the purge system to decrease when a leak is detected before the fuel evaporation rate is detected. First, after the delay time elapses after the internal pressure of the purge system has risen to the atmospheric pressure, the detection of the increase in the internal pressure of the purge system is started. When the internal pressure of the purge system was adjusted to a negative pressure when a leak was detected, the longer the time required to reduce the internal pressure, the higher the temperature inside the fuel tank after the leak was detected, and after the leak was detected, the internal pressure of the purge system was raised to atmospheric pressure. At this time, the temperature inside the fuel tank also rises accordingly. Therefore, the longer the time required to reduce the internal pressure of the purge system is, the longer the temperature of the fuel tank after the atmospheric pressure rises is reduced to near atmospheric pressure and becomes stable. In the present invention, the longer the time required to decrease the internal pressure of the purge system is, the longer the delay time for starting the fuel evaporation rate detection is set, so that the fuel evaporation rate is detected after the temperature in the fuel tank is stabilized. Thus, when the fuel evaporation rate is detected, an accurate purge system internal pressure increase rate (fuel evaporation rate) that is not affected by the change in the fuel tank internal temperature to the fuel tank internal pressure is detected, and accurate failure diagnosis can be performed.

According to the third aspect of the present invention, the canister for adsorbing the evaporated fuel in the fuel tank of the internal combustion engine, the vapor passage for connecting the fuel liquid level upper space in the fuel tank to the canister, and the canister. Of the evaporative purge system including a purge passage connecting the engine and the intake passage of the engine, including the fuel tank, the canister, the vapor passage, and the purge passage, the internal pressure of the purge system is adjusted to a predetermined negative pressure, and then the purge system is closed. However, if the leak detection means for detecting the internal pressure increase rate of the purge system in the negative pressure closed state and the increase rate of the internal pressure of the purge system detected by the leakage detection means are larger than a predetermined reference value, the internal pressure of the purge system is increased. After elevating the pressure to atmospheric pressure, the purge system is closed, and the fuel evaporation rate detecting means for detecting the increase rate of the internal pressure of the purge system in the atmospheric pressure closed state; A failure diagnosis device for the evaporative purge system, comprising: an abnormality determination device for determining that a failure has occurred in the evaporative purge system when the purge system internal pressure increase speed detected by the means is smaller than a predetermined determination value. The speed detecting means starts detecting the rate of increase in the internal pressure of the purge system after a lapse of a predetermined delay time after the internal pressure of the purge system rises to the atmospheric pressure, and the internal pressure of the purge system rises from the predetermined negative pressure to the atmospheric pressure. There is provided a failure diagnostic device for an evaporative purge system in which the delay time is set to be longer as the required time until it becomes shorter.

That is, according to the third aspect of the invention, the delay time is set based on the time required to raise the internal pressure of the purge system to the atmospheric pressure after the leak detection, and when the fuel evaporation rate is detected, the internal pressure of the purge system is set. After the delay time elapses after the pressure rises to the atmospheric pressure, the detection of the increase in the purge system internal pressure is started. After the leak is detected, when the internal pressure of the purge system is raised to atmospheric pressure, the shorter the required time (that is, the faster the pressure rise rate).
The temperature inside the fuel tank rises when the internal pressure of the purge system is raised to atmospheric pressure. Therefore, the shorter the time for raising the internal pressure of the purge system to the atmospheric pressure, the longer the time until the internal temperature of the fuel tank drops to near atmospheric pressure and stabilizes after the atmospheric pressure rises. In the present invention, the shorter the time required to increase the internal pressure of the purge system is, the longer the delay time for starting the fuel evaporation rate detection is set, so that the fuel evaporation rate is detected after the temperature in the fuel tank is stabilized. Thus, when the fuel evaporation rate is detected, an accurate purge system internal pressure increase rate (fuel evaporation rate) that is not affected by the change in the fuel tank internal temperature to the fuel tank internal pressure is detected, and accurate failure diagnosis can be performed.

According to a fourth aspect of the present invention, the fuel evaporation rate detecting means further seals the purge system after the predetermined delay time has elapsed after the internal pressure of the purge system has risen to atmospheric pressure. A failure diagnosis device for an evaporative purge system according to claim 2 or claim 3 is provided.

That is, according to the invention of claim 4, in the invention of claim 2 or 3, the purge system is not closed immediately after the internal pressure of the purge system reaches the atmospheric pressure, and the purge system is maintained until the above delay time elapses. Keep open to the atmosphere. If the system is closed immediately after the internal pressure of the purge system reaches atmospheric pressure,
At the time when the purge system internal pressure rise (fuel evaporation rate) is detected after the delay time elapses, the system internal pressure may be negative due to the temperature decrease in the fuel tank, which may lead to leakage or holes in the purge system. There is a possibility that the increase rate of the internal pressure of the purge system may not accurately correspond to the fuel evaporation rate if there is an abnormality. On the other hand, in the present invention, the internal pressure of the purge system is always the atmospheric pressure at the time when the detection of the increase in the internal pressure of the purge system is started after the delay time has elapsed. Therefore, in the present invention, not only the influence on the fuel tank internal pressure due to the change in the fuel tank internal temperature at the time of detecting the fuel evaporation rate but also the accurate purge system internal pressure increase excluding the effect of the purge system internal pressure at the start of the internal pressure increase detection is detected. The speed (fuel evaporation speed) can be detected, and more accurate failure diagnosis can be performed.

According to a fifth aspect of the present invention, the fuel evaporation rate detecting means further corrects the delay time in accordance with the amount of fuel remaining in the fuel tank, and the purge system is set after the corrected delay time has elapsed. 3. The detection of the internal pressure rising speed is started.
5. The failure diagnostic device for an evaporative purge system according to claim 4.

That is, according to the invention of claim 5, claim 2
In any one of the inventions 1 to 4, the delay time until the detection of the fuel evaporation rate is started is corrected according to the remaining amount of fuel in the fuel tank. As described above, the delay time until the start of the fuel evaporation rate detection is the temperature inside the fuel tank (gas temperature in the space above the liquid level in the tank) that has risen due to the atmospheric pressure increase due to heat exchange with the outside air through the tank wall surface. It is necessary to set the time until the temperature drops. However, in reality, the amount of heat exchanged between the gas in the liquid level upper space in the fuel tank and the outside air per unit time varies depending on the tank inner wall area in contact with the gas. For example, when the tank inner wall contact area per unit volume of gas is small, the heat exchange amount per unit time between the outside air and the tank gas is smaller than when the tank inner wall contact area per unit volume of gas is large. . For this reason, even if the temperature inside the tank is the same immediately after the atmospheric pressure is increased, the time required for the temperature inside the tank to fall to the atmospheric temperature becomes longer when the contact area is smaller than when the contact area is large. . The contact area of the tank inner wall changes depending on the remaining amount in the fuel tank. In the present invention, the delay time preset based on the predetermined relationship is corrected according to the remaining fuel amount in the fuel tank, so that the temperature in the fuel tank is reliably stabilized after the delay time elapses. At the time of detection, it is possible to detect the accurate increase rate of the internal pressure of the purge system (fuel evaporation rate), which reliably excludes the influence of the change in the temperature inside the fuel tank on the internal pressure of the fuel tank, and it is possible to perform more accurate failure diagnosis. .

[0033]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a diagram showing a schematic configuration of an embodiment in which the present invention is applied to an automobile fuel tank.
In FIG. 1, 100 is an internal combustion engine body, 1 is an internal combustion engine 1.
The intake passage 0, 3 indicates an air cleaner arranged in the intake passage 1. In the intake passage 1, there is a throttle valve 6 that opens according to the operation of an accelerator pedal (not shown) by the driver.
Is provided.

Reference numeral 11 in FIG. 1 denotes an engine fuel tank. The fuel oil in the tank 11 is pressurized by the fuel pump 70 and is pressure-fed to the fuel injection valve 101 of each cylinder of the engine 100 via the feed pipe 71. Fuel tank 11
Is provided with a pressure sensor 33 that detects the pressure in the space above the liquid level in the fuel tank. At the top of the tank 11,
A breather pipe 13 that connects a fuel oil liquid level upper space in a tank 11 is connected to a canister 10 described later.

At the connection between the breather pipe 13 and the tank 11, a COV (CUT
OFF VALVE 132 and ROV (ROLL OV)
ERVALVE) 133 is provided. ROV1
The valve 33 closes due to the rise of the liquid level during refueling, and disconnects the breather pipe 13 and the fuel tank 11. Also, RO
The V133 has a function of closing a connecting portion between the breather pipe 13 and the tank 11 when the vehicle falls or the like and preventing a large amount of fuel oil from leaking to the outside through the breather pipe 13.

The COV 132 is arranged in parallel with the ROV 133 and shuts off the communication between the breather pipe 13 and the tank 11 when the liquid level further rises above the ROV 133.
The COV 132 is a ROV 133 when the liquid level rises during refueling.
Even after the valve is closed, the valve is opened and the tank 11 and the breather pipe 13 are communicated with each other, but the COV1
When the liquid level reaches the 32nd position, or when the vehicle falls, it has a function of closing the valve to prevent the fuel oil from entering the breather pipe 13.

Reference numeral 10 in FIG. 1 denotes a canister for adsorbing the fuel vapor in the fuel tank. Canister 10
Is an adsorbent 50 such as activated carbon that adsorbs fuel vapor inside.
Is stored and is connected to the breather pipe 13 via a refueling valve 131. The refueling valve 131 opens when the internal pressure of the fuel tank 11 becomes slightly higher than the atmospheric pressure, and allows the air containing the evaporated fuel in the tank 11 to flow to the canister 10 through the breather pipe 13.

The canister 10 further includes a purge pipe 14
Is connected to the intake passage 1, and a purge control valve 15 is provided at a connecting portion between the purge pipe 14 and the intake passage 1. The purge control valve 15 is provided with an actuator of an appropriate type such as a solenoid actuator, is opened by a signal from an electronic control unit (ECU) 30 described later, and connects the canister 10 with the intake passage 1.

Further, the canister 10 has a CCV (CAN
It is connected to the atmosphere communication pipe 18 through an ISTER CLOSE VALVE) 17. Atmosphere communication pipe is tank 1
An air filter 19 is provided on the atmosphere communication pipe 18 and is open in the vicinity of the fuel filler port 1. Air filter 19
Is for removing foreign matters in the air flowing into the canister 10 from the atmosphere communication pipe 18 when the purge is executed. CCV
Reference numeral 17 includes an actuator of an appropriate type such as a solenoid actuator, and cuts off the communication between the atmosphere communication pipe 18 and the canister 11 in response to a control signal from the ECU 30.

When the purge gas cannot be supplied to the intake passage 1 such as when the engine is stopped, the purge control valve 15 is closed and the CCV 17 of the canister 10 is kept open. In this case, the canister 10 communicates with the atmosphere through the CCV 17, and the internal pressure of the canister 10 becomes atmospheric pressure. In this state, the fluctuation of the fuel tank internal pressure is mainly due to the change of the vapor pressure of the fuel inside the tank due to the change of the outside air temperature, and therefore the fluctuation of the tank internal pressure becomes relatively gentle. Further, the oil supply valve 131 is provided with a small-diameter communication hole that communicates the breather pipe 13 and the canister 10 even when the valve is closed. Therefore, in this state, the tank internal pressure is equalized with the internal pressure of the canister 10 through the communication hole of the fuel supply valve 131, so that the fuel tank internal pressure is maintained at substantially atmospheric pressure.

Next, when refueling is performed in this state, the liquid level in the fuel tank rises and the pressure in the space above the liquid level in the fuel tank 11 rises. The internal pressure of the fuel tank 11 is the canister 1
When the pressure becomes higher than 0, the refueling valve 131 opens, and the fuel tank 11 and the canister 10 communicate with each other via the refueling valve 131.

As a result, the mixture of fuel vapor and air flows from the space above the liquid surface of the fuel tank 11 into the canister 10 through the breather pipe 13, passes through the adsorbent 50 in the canister 10, and then from the CCV 17. It flows into the atmosphere communication pipe 18. Since the fuel vapor in the air-fuel mixture is adsorbed by the adsorbent when passing through the adsorbent 50, only the air after the fuel vapor is removed by the adsorbent 50 in the canister 10 is discharged from the atmosphere communication pipe 18. become. Therefore, it is possible to prevent the fuel vapor from being released into the atmosphere at the time of refueling, and to prevent the internal pressure of the fuel tank 11 from rising and making refueling difficult.

When the amount of the fuel vapor adsorbed on the adsorbent 50 increases, the adsorbent 50 is saturated with the fuel vapor, and evaporation cannot be adsorbed any more. Therefore, in this embodiment, the adsorbent is purged during engine operation. The fuel vapor adsorbed from 50 is desorbed (purged). The canister 10 is purged by the CCV 17 and the purge control valve 1 during the operation of the engine 100.
This is done by opening both valves 5 and 5 and introducing air into the canister 10. That is, in a normal engine, a negative pressure is generated on the downstream side of the throttle valve 6 in the intake passage 1 during the engine operation. Therefore, if the purge control valve 15 is opened during the engine operation, the purge pipe 14 in the canister 10 is opened. A negative pressure in the intake passage 1 acts via the, and the internal pressure of the canister becomes lower than the atmospheric pressure.

Therefore, when the purge control valve 15 is opened, the clean air from which foreign matter has been removed by the filter 19 from the atmosphere communication pipe 18 via the CCV 17 canister 1.
It flows into 0. When this air passes through the adsorbent 50 in the canister 10, it separates the fuel vapor from the adsorbent, and becomes a mixed gas (purge gas) of the fuel vapor and air, from the purge pipe 14 through the purge control valve 15 and the engine intake passage. Flow into 1. As a result, the purge gas is purged from the adsorbent 50 and burned in the engine combustion chamber, so that the adsorbent 50 is prevented from being saturated with the fuel vapor.

Reference numeral 30 in FIG. 1 denotes an electronic control unit (ECU) of the engine. The ECU 30 includes a ROM (read only memory), a RAM (random access memory), a CPU (microprocessor), and a microcomputer having a known configuration in which input / output ports are connected to each other by a bidirectional bus. Purge control is performed during engine operation. Valve 15
The CCV 17 is controlled to purge the canister 10 described above. Further, in the present embodiment, the ECU 30 closes the purge system in a negative pressure state by opening / closing the purge control valve 15 and the CCV 17 during engine operation, and determines whether there is a leak, a hole, or the like abnormality based on a change in internal pressure. Perform fault diagnosis operation.

For the above control, the output port of the ECU 30 is connected to the actuator of the purge control valve 15 and the actuator of the CCV 17 via a drive circuit (not shown) to control the operation of these valves. Also, E
To the input port of the CU 30, signals representing the engine speed, the engine intake air amount, the engine cooling water temperature, etc. are input from sensors (not shown), respectively, and a signal representing the internal pressure of the fuel tank 11 is input from the pressure sensor 33. It has been entered.

Next, the failure diagnosis operation of the evaporation purge system of the present invention will be described. In the present invention, when the predetermined purge execution condition is satisfied after the engine operation is started and the purge is being executed, the purge system is brought into a negative pressure sealed state and the internal pressure increase speed is measured. During execution of the purge, the purge control valve 15 is opened, and the negative pressure of the intake passage 1 acts on the canister 10 via the purge passage 14. However, since the CCV 17 is open, the inside of the canister 10 communicates with the atmosphere through the atmosphere communicating pipe 18, and the pressure inside the canister 10 is maintained at the pressure determined by the intake passage pressure and the opening degree of the purge control valve 15. ing. When the CCV 17 is closed in this state, the inflow of air from the atmosphere communication pipe 18 is stopped, and the pressure in the canister 10 decreases.

Further, the negative pressure in the canister is due to the oil supply valve 131.
Since it is introduced into the breather pipe 13 and the fuel tank 11 through the communication hole of the canister 1 through the refueling valve 131.
The internal pressure of the purge system of the fuel tank 11, the breather pipe 13, etc. communicating with 0 decreases. When the purge control valve 15 is closed when the pressure in the purge system has dropped sufficiently,
The purge system is closed under negative pressure. When the purge system is closed, the internal pressure of the purge system starts rising due to the evaporation of the fuel in the fuel tank 11. In the present invention, as described above, the internal pressure of the purge system reaches a predetermined negative pressure (for example, a pressure of about 745 mmHg) due to the pressure increase in a state where the purge system is maintained in the negative pressure sealed state, and then a predetermined time (for example, about 5 seconds). ) Inside the purge system, the increase width of the internal pressure (that is, the internal pressure increase rate) is measured.

In this state, the rate of increase in the internal pressure of the purge system is relatively slow because it is only due to the evaporation of the fuel in the fuel tank 11 if there is no leakage or holes in the purge system. When there is a leak or a hole in the system, air intrudes into the system from the outside through the leak portion, and the rate of pressure increase becomes larger than that in the case where only fuel vaporizes. Therefore, if the internal pressure increase rate measured by the internal pressure increase measurement of the purge system (hereinafter referred to as "leak detection") at the time of negative pressure sealing is large, an abnormality such as leakage may occur in the purge system. .

However, the rate of increase in the internal pressure of the purge system at the time of detecting a leak becomes large when the rate of fuel evaporation during the leak detection is high even if there is no leak in the purge system. For this reason, it is not possible to determine whether the internal pressure increase rate is large due to the leakage or whether the internal pressure increase rate is increased due to the high fuel evaporation rate, simply by increasing the internal pressure increase rate at the time of detecting the leak.

Therefore, in this embodiment, when the internal pressure increase rate at the time of leak detection is higher than a predetermined value, the CCV 17 is opened and the atmosphere is introduced after the leak detection is completed while the purge control valve 15 is kept closed. , Increase the internal pressure of the purge system to near atmospheric pressure. When the pressure sensor 33 detects that the internal pressure of the purge system has risen to near atmospheric pressure, the CCV 17
Is closed to close the purge system while maintaining the atmospheric pressure. In this atmospheric pressure closed state, even if a leak occurs in the purge system, the atmospheric pressure does not enter the purge system because the differential pressure between the internal pressure of the purge system and the atmosphere is small.

For this reason, the increase in the internal pressure of the purge system which occurs in the atmospheric pressure sealed state is caused only by the evaporation of the fuel in the fuel tank 11. Therefore, the fuel vaporization rate can be measured by keeping the purge system in the atmospheric pressure sealed state and detecting the increase width of the purge system internal pressure within the predetermined time (for example, about 15 seconds) by the pressure sensor 33 of the fuel tank 11. .

In the present embodiment, the fuel evaporation rate is measured only when the internal pressure rise is above a predetermined value in the leak detection operation. Therefore, when the fuel evaporation rate is low, it can be determined that the increase in the internal pressure during the leakage detection operation is due to the actual leakage in the purge system. Further, when the fuel evaporation rate is high, it is possible that the increase in the purge system internal pressure at the time of leakage detection may have occurred due to the high fuel evaporation rate, so it cannot always be determined that the purge system is leaking. Therefore, the determination of the presence or absence of leakage is suspended and the abnormality diagnosis is stopped.

However, in reality, after the leak detection is completed, the internal pressure of the purge system is increased to the atmospheric pressure and the pressure sensor 33
When the increase rate of the internal pressure of the fuel tank is measured, the internal pressure increase rate may become small even under the condition that the fuel evaporation rate should be high. In this way, if the fuel evaporation rate is detected to be smaller than it actually is, it is determined that an abnormality has occurred in the purge system until the judgment should be suspended because the fuel evaporation rate is originally high, resulting in a false diagnosis. There is.

The problem is that the pressure decrease width when the fuel tank internal pressure is set to a predetermined negative pressure when a leak is detected, the time until the predetermined negative pressure is reached, the negative pressure holding time, and the fuel tank internal pressure when the fuel evaporation rate is detected. It has been found to be related to the history of pressure change in the fuel tank, such as the rate of increase in internal pressure of the purge system when returning to atmospheric pressure.

First, let us consider a case where the tank internal pressure is reduced when a leak is detected. As will be described later, the failure diagnosis operation of the evaporation purge system is executed while the purge control valve 15 is open. Therefore, the internal pressure of the purge system (tank) has a value according to the opening degree of the purge control valve 15 and the intake negative pressure.
Therefore, the tank internal pressure before the purge control valve 15 is fully opened to start the system internal pressure decrease varies depending on the operating conditions.

Therefore, the internal pressure of the purge system (internal pressure of the tank) is the above-mentioned predetermined negative pressure (for example, 740 mm) from the start of the pressure decrease.
The width (P1) of decrease in tank pressure before reaching Hg) is
It depends on engine operating conditions. Further, the time (T1) from the start of the pressure decrease until the tank internal pressure reaches the predetermined negative pressure is shortened if the pressure in the intake passage is low (that is, if the negative pressure is high), and is high if the intake passage pressure is high ( It becomes longer if the negative pressure is small. That is, the pressure drop width P1
And the lowering time T1 change depending on various conditions.

However, when the tank internal pressure reaches the predetermined negative pressure, the tank internal temperature greatly changes depending on the pressure decrease width P1 and the decrease time T1. For example, the pressure drop width P
When 1 is large and the decrease time T1 is short,
The temperature drops greatly due to the expansion of the gas in the tank,
The time for warming the gas in the tank by heat exchange with the outside is shortened, and the temperature in the tank when the predetermined negative pressure is reached is lowered.
On the other hand, when P1 is small and when the pressure decrease time T1 is long, the temperature decrease due to the expansion of the gas in the tank is small and the time for the gas in the tank to exchange heat with the outside air becomes long, so that when the predetermined negative pressure is reached. The temperature inside the tank becomes high (the temperature difference from the atmosphere is small).

After the predetermined negative pressure is reached, the purge control valve 15 is closed and the purge system is hermetically held in a negative pressure state. Since it is warmed by heat exchange, the gas temperature in the tank becomes higher as the negative pressure closed holding time (T2) becomes longer. When the leak detection due to the negative pressure sealing is completed, the purge control valve 15 is closed and the CCV 17 is once fully opened to increase the internal pressure of the purge system to the atmospheric pressure. When the atmospheric pressure is reached, the temperature inside the tank rises. In this case, the temperature increase width in the tank becomes larger as the increase speed of the pressure in the tank becomes higher, in other words, as the time (T3) required to increase the pressure to the atmospheric pressure becomes shorter.

However, as described above, the temperature in the tank at the end of the negative pressure sealing differs depending on the case. Therefore, when the temperature in the tank at the end of the negative pressure sealing is high, the temperature in the tank at the atmospheric pressure reaches the atmospheric pressure. It may be higher. In this case, the gas in the tank is cooled by the heat exchange with the outside after reaching the atmospheric pressure, and the temperature in the tank is reduced to the atmospheric pressure. Therefore, a phenomenon occurs in which the internal pressure of the tank is reduced in the sealed state. In this case, the range of decrease in the tank internal pressure changes depending on the temperature inside the tank when the atmospheric pressure is reached, but the higher the temperature inside the tank when the atmospheric pressure reaches, the more the tank internal temperature decreases to the atmospheric temperature and stabilizes. It will take a long time.

In this embodiment, the start of the purge system internal pressure increase rate measurement (fuel evaporation rate detection) in the atmospheric pressure sealed state is delayed until the tank internal temperature drops to the atmospheric temperature and becomes stable. This prevents pressure fluctuations due to temperature changes in the tank from affecting the detected fuel evaporation rate, but the time until the temperature in the tank stabilizes
That is, the delay time required before the start of the fuel evaporation rate detection changes due to various factors as described above.

FIG. 2 is a schematic diagram showing the above-described change in tank pressure from the start to the end of the evaporative purge system failure diagnosis. In FIG. 2, the vertical axis represents the tank pressure and the horizontal axis represents time. In FIG. 2, P1 represents the tank pressure decrease width when the negative pressure is introduced after the start of the failure diagnosis, and T1 represents the time until the tank internal pressure reaches the predetermined negative pressure after the introduction of the negative pressure (negative pressure arrival time). Also, T
2 is the time required to keep the purge system airtight under a negative pressure after the predetermined negative pressure is reached, that is, the time required for leak detection, and T3 is the time required to return the atmosphere in the purge system to atmospheric pressure after the leak is detected (pressurization time). ing.

As described above, the time until the temperature inside the tank stabilizes after the atmospheric pressure is restored is P1, T1, T2, and T3.
Change according to. The tendency of this change is described below again.

(1) Pressure drop width P1 The larger the pressure drop width P1, the lower the temperature inside the tank when the predetermined negative pressure is reached, and the smaller P1 the higher the temperature inside the tank when the predetermined negative pressure is reached. Therefore, if the other conditions are the same, the temperature inside the tank immediately after returning to atmospheric pressure becomes lower as P1 becomes larger, and becomes higher as P1 becomes smaller. For this reason,
The delay time until the start of fuel evaporation rate detection (the time required for the temperature in the tank to stabilize after returning to atmospheric pressure) needs to be longer as P1 is smaller.

(2) Negative pressure arrival time T1 If the negative pressure arrival time T1 is short, the gas in the tank expands without sufficiently exchanging heat with the outside, so the temperature in the tank when the predetermined negative pressure is reached becomes low, On the contrary, when T1 is long, the temperature in the tank becomes high when the predetermined negative pressure is reached. Therefore, it is necessary to lengthen the delay time as T1 is longer.

(3) Negative pressure sealed holding time T2 The longer the negative pressure sealed holding time T2, the more the gas in the tank is warmed up by heat exchange with the outside, so the temperature inside the tank after the negative pressure sealing is finished becomes higher. Therefore, the delay time is T2.
The longer is the longer it needs to be.

(4) Pressure rising time T3 As the pressure rising time T3 is shorter, the gas in the tank is compressed without sufficiently exchanging heat with the outside, so that the temperature in the tank becomes higher when the atmospheric pressure is reached. Therefore, the delay time is T3.
The shorter is the longer it needs to be.

As described above, in this embodiment, the start of the purge system internal pressure increase rate measurement (fuel evaporation rate detection) in the atmospheric pressure sealed state after the tank internal pressure returns to the atmospheric pressure is delayed until the temperature in the tank stabilizes. However, this delay time must be long enough to stabilize the temperature in the tank. Further, although the tank temperature stabilizes as the delay time is lengthened, there is a problem that if the delay time is set longer than necessary, the time required for failure diagnosis becomes long.

Therefore, in the present embodiment, this delay time (time T in FIG. 2) is calculated based on the pressure drop width P1, the negative pressure arrival time T1, the negative pressure closed holding time T2, and the boosting time T3. The minimum time that does not affect the temperature change in the tank when the fuel evaporation rate is detected is set.
In this embodiment, the delay time T is set by the following formula.

T = α × (PK1 + TK1 + TK2) × TK3 (A) Here, α is a coefficient determined by the shape and size of the fuel tank and the type of vehicle and engine. α is a reference value (second) of the delay time. For example, when the values of P1, T1, T2, and T3 are set to certain reference values P1 ₀ , T1 ₀ , T2 ₀ , and T3 ₀ , respectively, the temperature in the fuel tank is Represents the minimum delay time required to stabilize. The value of α is determined by an experiment using an actual fuel tank, a vehicle, and an engine under the conditions where P1, T1, T2, and T3 are the above-mentioned reference values.

Further, PK1, TK1, TK2, TK3
Are the actual P1, T1, T2, and T at the time of failure diagnosis, respectively.
The correction coefficient is determined according to the value of 3. FIG. 3 to FIG. 6 are diagrams showing examples of the relationships between PK1 and P1, TK1 and T1, TK2 and T2, and TK3 and T3, respectively.

As shown in FIG. 3, the coefficient PK1 decreases substantially linearly as the pressure decrease width P1 increases, and PK1
= P1 ₀ (reference value), PK1 = 1 is set.

Further, as shown in FIG. 4, the coefficient TK1 increases exponentially as the negative pressure arrival time T1 becomes longer.
Further, TK1 is also TK1 when T1 = P1 ₀ (reference value)
= 1 is set.

Further, as shown in FIG. 5, the coefficient TK2 is also T
Similar to K1, it shows an exponential change that increases as the negative pressure sealing holding time T2 becomes longer, and T2 = T2 ₀ (reference value)
Is set so that TK2 = 1.

In this embodiment, (PK1 + TK1 +
If the value of TK2) is smaller than 1, then (A) above
In the formula, calculation is performed with (PK1 + TK1 + TK2) = 1, and α × (PK1 + TK1 + TK2) is restricted so as not to be smaller than α.

[0076] The coefficient TK3 represents exponential change becomes smaller as the boosting time T3 is longer as shown in FIG. 6, the TK3 = 1 when T3 = T3 _0.

The relations of FIGS. 3 to 6 are described in detail by changing P1, T1, T2 and T3 respectively while keeping other conditions constant by using the actual fuel tank, vehicle and engine. It is set based on an experiment to measure the change of. In the above formula (A), the boost time correction coefficient TK
3 is directly multiplied, and has a greater influence on the delay time than other coefficients. In the actual failure diagnosis operation, the boosting time T3 has the greatest influence on the temperature in the tank when the atmospheric pressure is restored. This is because.

FIG. 7 is a flow chart for concretely explaining the above-mentioned evaporative purge system failure diagnosis operation of the present embodiment. This operation is executed by the ECU 30. In the operation of FIG. 7, first, in step 701, it is determined whether or not the execution condition of the abnormality diagnosis operation is satisfied. Step 70
The abnormality detection operation execution condition determined in 1 is a. Failure diagnosis of the evaporative purge system has not been completed after engine start, b. Purging is currently being performed (the purge control valve 15 is open), c. The atmospheric pressure is equal to or higher than a predetermined value, d. For example, the pressure fluctuation in the fuel tank is not more than a predetermined value (for example, the liquid level in the tank is not greatly changed due to traveling on a slope, turning, traveling on a bad road, etc.).

Condition a. This is because this failure diagnosis operation is accompanied by interruption of purging, so that it is possible to prevent the interruption of purging from being lengthened by repeating failure diagnosis even though it has already been completed. In this failure diagnosis operation, it is necessary to open the purge control valve 15 to introduce a negative pressure into the purge system, and the evaporated fuel in the canister flows into the intake passage at the time of failure diagnosis. This is because if this failure diagnosis is performed when there is no such situation, the operating state of the engine may be affected. In addition, the above condition c. And d. Is a condition for preventing noise from being mixed in the measurement result and performing highly reliable failure diagnosis.

If all the conditions in step 701 are satisfied, then in steps 703 and 705, the internal pressure increase rate ΔPL of the purge system in the negative pressure closed state is measured (leakage detection), and the pressure decrease width P1 and the negative pressure described above are detected. The arrival time T1 is measured. That is, in step 703, the CCV 17 is maintained while the purge is being executed (the purge control valve 15 is still open).
Perform the negative pressure introduction operation to close the valve. As a result, the negative pressure in the intake passage 1 is introduced into the purge system, and the canister 10,
The pressure in the purge system such as the fuel tank 11 decreases.

In step 703, the purge control valve 15 is closed when the negative pressure is introduced into the purge system as described above and the internal pressure of the fuel tank detected by the pressure sensor 33 drops to a predetermined negative pressure (for example, 740 mmHg). Speak. At this time, the time required from the closing of the CCV 17 (at the start of introduction of negative pressure) to the closing of the purge control valve 15 (at the start of closing of negative pressure) is stored as the negative pressure arrival time T1, and at the start of introduction of negative pressure. And the difference in the tank internal pressure detected by the pressure sensor 33 at the start of the negative pressure sealing is stored as the pressure decrease width P1.

Then, in step 705, the leak (ΔPL) of the purge system closed under negative pressure is detected as described above. When the purge system is closed, the internal pressure of the purge system starts rising due to the evaporation of the fuel in the fuel tank 11. If there is no leakage in the purge system, this pressure increase will be caused by the fuel tank 11
Since it is generated only by the evaporation of the fuel inside, the rate of pressure increase is relatively slow, and after a sufficient time has elapsed, it reaches a value determined by the saturated vapor pressure of the fuel. On the other hand, when there is a leak in the purge system, the pressure inside the purge system rises relatively quickly due to the air entering from outside the system through the leak.
After a sufficient time has elapsed, the pressure becomes close to atmospheric pressure.

In step 705, after the purge control valve 15 is closed and the purge system is closed under negative pressure, time measurement is started when the system internal pressure reaches the second predetermined pressure (for example, 745 mmHg), and thereafter. The pressure rise width detected by the pressure sensor 33 within a predetermined time (for example, about 5 seconds) is adopted as ΔPL.

According to the above, after the leak detection operation is completed,
At step 707, a temporary determination is made as to whether or not there is an abnormality in the purge system. In the temporary determination in step 707, it is determined whether the pressure increase rate ΔPL measured by the leak detection operation is equal to or less than the determination value ΔPL ₀ . Here, when ΔPL ≦ ΔPL ₀ , the pressure increase in the system is small, and it can be determined that the purge system has not leaked regardless of the fuel evaporation rate. Therefore, the routine proceeds to step 709, and the purge system is normal. Is judged as normal. ΔPL ₀ is set to a value of about several mmHg / 5 seconds. When the normal determination is made, the purge control valve 15 and the CCV 17 are immediately opened, and the purging of the canister 10 is restarted.

On the other hand, in step 707, ΔPL> ΔPL ₀
If so, the increase in internal pressure at the time of leak detection is large and there is a possibility that a leak has actually occurred, so it is necessary to determine the magnitude of the fuel evaporation rate. Therefore, in this case, the fuel evaporation rate detection operation in and after step 711 is performed.

That is, in step 711, the CCV 17 is first opened while the purge control valve 15 is closed to start the introduction of the atmosphere into the purge system, and the step 70
CCV17 is closed at 3 and then CCV at step 711
The elapsed time until the valve 17 is opened is the negative pressure closed holding time T2.
Memorize as. Then, in step 713, when the fuel tank internal pressure detected by the pressure sensor 33 rises to the atmospheric pressure, the CCV 17 is closed to close the purge system at the atmospheric pressure, and the CCV 17 is opened in step 711 before the step The elapsed time until the valve is closed at 713 is stored as the boosting time T3.

In the system closed at atmospheric pressure as described above, the temperature in the fuel tank that has risen when the atmospheric pressure is increased is reduced by heat exchange with the outside air through the tank wall. An error occurs when measuring the speed). Therefore, in the present embodiment, the pressure drop width P1, the negative pressure arrival time T1, the negative pressure closed holding time T2, and the pressure rising time T3 stored in the above respective steps are used to describe the above (A).
The time (delay time) T until the temperature inside the tank becomes sufficiently close to the atmospheric temperature and stabilizes is calculated based on the equation, and the detection of the fuel evaporation rate is started after the elapse of this delay time.

That is, in step 715, the correction values PK1, TK1, TK2, and TK3 are respectively determined from the relationships of FIGS. 2 to 6 using the stored values of P1, T1, T2, and T3, and in step 717. The delay time is calculated as T = α × (PK1 + TK1 + TK2) × TK3.

Then, in step 719, step 71
Wait until the delay time T has elapsed since the CCV 17 was closed in step 3, and after the time T has elapsed, step 721
Proceed to and the detection of the fuel evaporation rate is started. That is, in step 721, the pressure sensor 33 determines the purge system internal pressure increase width ΔPV during a predetermined time (about 15 seconds) in the atmospheric pressure sealed state.
To measure. The value of ΔPV is a value corresponding to the fuel evaporation rate ΔPV.

In step 723, Δ measured as above
PV is compared with a predetermined judgment value ΔPV _0, and ΔPV ≧ ΔPV ₀
If it is, it is determined that the increase rate of the internal pressure of the purge system at the time of detecting the leak is large because the fuel evaporation rate is large. Therefore, in step 723, ΔPV ≧ ΔPV ₀
If it is, the process proceeds to step 725 to suspend the determination and end the abnormality diagnosis. ΔPV ₀ is a value of about several mmHg.

In step 723, ΔPV <ΔPV ₀
If it is, the fuel evaporation rate is low and step 7
It can be determined that the reason of ΔPL> ΔPL ₀ in 07 is that the purge system is leaking. Therefore, in this case, the process proceeds to step 727, and it is determined that an abnormality has occurred in the purge system, and the abnormality determination is performed and the diagnostic operation ends.

When the abnormality determination is made in step 727, the warning light arranged near the driver's seat of the vehicle is turned on by an operation separately executed by the ECU 30 to notify the driver of the abnormality of the purge system.

As described above, in this embodiment, when the fuel evaporation rate is detected by increasing the pressure to the atmospheric pressure, the time required for ending the decrease in the temperature in the tank increased by the pressure increase, that is, the temperature in the fuel tank. Since the fuel evaporation rate is detected after the minimum delay time required for the temperature to stabilize, it is possible to prevent the detected fuel evaporation rate from being affected by temperature changes in the tank. It is possible to perform various failure diagnosis.

Further, in this embodiment, when the normal determination is made in step 709, the purge is immediately restarted without measuring the fuel evaporation rate. In reality, in most cases, the normal determination is made in step 709, and the fuel evaporation rate is detected (step 711 and thereafter) less frequently. Therefore, according to the present embodiment, when the fuel evaporation rate is detected for each diagnosis. In comparison, the time required for diagnosis can be shortened as a whole.

In the failure diagnosis operation of FIG. 7, the delay time T is calculated as a function of all of the pressure drop width P1, the negative pressure arrival time T1, the negative pressure closed holding time T2 and the boosting time T3 ( (Equation (A)), the greatest influence on the delay time is the boosting time T3 and the negative pressure reaching time T1 among the above.
Is. Therefore, the delay time T is approximately calculated using only the boosting time T3 or only the negative pressure reaching time T1 and using the following formula (B) or (C) instead of the formula (A). It is also possible to do so.

T = α × TK3 (B) T = α × TK1 (C) where TK3 is TK1 using T3 from the relationship of FIG.
Are coefficients that are respectively obtained from the relationship of FIG. 4 using T1.

Next, an embodiment of the fault diagnosis operation of the present invention different from that of FIG. 7 will be described. Also in this embodiment,
The point where the fuel evaporation rate detection is started after waiting for the delay time T calculated by the formula (A) after the internal pressure of the purge system is increased to the atmospheric pressure when the fuel evaporation rate is detected is the same as in the embodiment of FIG. 7. .

However, in the embodiment of FIG. 7, when the fuel evaporation rate is detected, the internal pressure of the purge system reaches the atmospheric pressure, and at the same time CC
While the valve V17 is closed and the delay time T elapses while the purge system is closed, in the present embodiment, the CCV17 is kept open even after the internal pressure of the purge system reaches atmospheric pressure. 7 is different from the embodiment of FIG. 7 in that the CCV 17 is closed at the same time as the delay time T elapses, that is, the delay time is waited for while the purge system is open to the atmosphere.

As described above, the temperature in the fuel tank changes during the delay time T, but in the embodiment of FIG. 7, the purge system is kept closed during the delay time T, so When the temperature changes, the internal pressure of the purge system changes, and the internal pressure of the purge system is lower than the atmospheric pressure when the fuel evaporation rate detection is started after the delay time ends. As previously explained, when the fuel evaporation rate is detected, it leaks to the purge system,
It is necessary that the atmosphere does not enter the system even if holes or the like are formed. For this purpose, it is preferable that the internal pressure of the purge system be as close to the atmospheric pressure as possible at the start of detecting the fuel evaporation rate.

Therefore, in the embodiment of FIG. 7, if the fuel tank temperature change within the delay time is large, the internal pressure of the purge system at the start of the fuel evaporation rate detection may become a relatively large negative pressure, resulting in leakage or holes. In some cases, the accurate fuel evaporation rate may not be detected.

In this embodiment, the CCV 17 is kept open until the delay time T elapses, and the CCV 17 is closed after the delay time elapses. Therefore, even if the temperature in the fuel tank changes within the delay time, the internal pressure of the purge system at the start of the fuel evaporation rate detection is always atmospheric pressure. Therefore, according to the present embodiment, the fuel evaporation rate can be detected more accurately, and accurate failure diagnosis can be performed.

Next, still another embodiment of the present invention will be described. The present embodiment is different from the embodiment of FIG. 7 only in that correction is performed in consideration of the remaining amount of fuel in the fuel tank when calculating the delay time T. In the embodiment of FIG. 7,
3 to 6 by using the pressure drop width P1, the negative pressure arrival time T1, the negative pressure closed holding time T2, and the pressure rising time T3, respectively.
Correction factors PK1, TK1, T set based on the relationship
The delay time T is calculated from the equation (A) using K2 and TK3 as they are. However, the temperature change in the tank is greatly affected by heat exchange with the outside air through the wall surface of the tank.
The gas in the space above the liquid level in the tank is also in contact with the liquid level of the fuel, but the heat transfer coefficient between the fuel and the gas is relatively small. on the other hand,
The fuel tank is usually made of metal, and the heat transfer coefficient between the gas in the space above the liquid level inside the tank and the tank wall surface is relatively large.
The temperature change of the gas in the tank is greatly affected by the heat exchange with the outside air through the wall surface of the tank. On the other hand, the effect of heat exchange with the outside air changes in proportion to the tank wall surface area per unit volume of the gas in the tank.

It is assumed that the fuel tank is shaped like a rectangular parallelepiped having a bottom area C × D and a height A as shown in FIG. Further, when the height of the liquid level in the tank is B, the volume V of the space above the liquid level in the tank is V = (A−B) × C × D. Also, in this case, the tank wall surface area AW in contact with the gas
Becomes AW = 2 × (A−B) × (C + D) + C × D. Therefore, the contact wall surface area AW /
V is

AW / V = (2 × (A−B) × (C + D)
+ C × D) / ((A−B) × C × D). here,
When the remaining fuel amount is expressed by F = B / A, the above formula is AW / V = (A (1-F) × (C + D) + C × D) / A
X (1-F) xCxD. Since A, C, and D are constant values, AW / V = (K1 (1-F) + K2) / (K3 × (1-F)) = (K1 + K2 / (1-F)) / K3 Becomes

That is, as understood from the above equation, the contact wall surface area AW / V per unit volume of gas increases as the fuel quantity F in the tank increases. Therefore, for example, when the amount of remaining fuel is large, the amount of heat exchange with the outside air per unit volume of the gas in the tank becomes large, so that even if the pressure drop width P1 and the negative pressure arrival time T1 are the same, The temperature inside the fuel tank when the pressure reaches is higher than when the remaining fuel amount is small. Similarly, even if the negative pressure sealing holding time T2 is the same,
The temperature in the fuel tank becomes high at the end of the negative pressure sealed holding, and the temperature rise width at the time of pressurization becomes low.

Therefore, in this embodiment, the coefficients PK1, TK1, TK2, and TK3 set using FIGS. 3 to 6 are corrected in accordance with the remaining amount F of the fuel tank. That is, in this embodiment, step 717 in FIG.
Instead of the equation (A) of the above, the delay time T is calculated by using the following equation (D).
To calculate.

T = α × (PK1 / VP1 + TK1 / VT1 + TK2 / VT2) × TK3 / VT3 (D) Here, VP1, VT1, VT2, and VT3 are correction coefficients determined according to the remaining fuel amount.

Considering the correction coefficients VP1 and VT1, for example, as described above, as the remaining fuel amount increases, the temperature in the fuel tank when the negative pressure is reached is the same even if the pressure drop width P1 and the negative pressure arrival time T1 are the same. Get higher Therefore, the delay time T
Needs to be longer as the remaining fuel amount is larger, and VP1, V
It is necessary to reduce T1 as the remaining fuel amount increases.

Actually, the relationship between VP1 and VT1 and the remaining fuel amount F is as shown in FIG. 9, and is substantially constant (VP1 = VT1 = 1) in the region where the remaining fuel amount is small, and the remaining fuel amount F
The value is smaller than 1 in a region where there are many. VT2, VT3
Also has the same relationship as in FIG. In this embodiment,
A coefficient PK based on the remaining amount F of fuel using an actual tank in advance
The changes in 1, TK1, TK2, and TK3 are obtained by actual measurement, and the relationship between the values of VP1, VT1, VT2, and VT3 and the remaining fuel amount F is obtained in the same manner as in FIG.

In this embodiment, step 71 in FIG.
5, the coefficients PK1, TK1, TK2, and TK3 are calculated, and the correction coefficients VP1, VT1, VT2, and VT3 are calculated according to the remaining fuel amount F from the same relationship as in FIG. 9, and these coefficients are used in step 177. The delay time T is calculated from the equation (D).

As a result, in this embodiment, the influence of the remaining amount of fuel is corrected, so that the fuel evaporation rate can be calculated more accurately.

[0112]

According to the invention described in each of the claims, after the purge system is hermetically sealed in a negative pressure state and the internal pressure rise is measured (leak detection), the internal pressure of the purge system is increased to atmospheric pressure. When performing internal pressure measurement (fuel vaporization rate detection) in a sealed state, it is possible to prevent an error from occurring in the detected fuel vaporization rate, and to have a common effect of enabling accurate failure diagnosis.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of an embodiment in which the present invention is applied to an evaporative purge system for an internal combustion engine for automobiles.

FIG. 2 is a diagram schematically showing changes in tank pressure from the start to the end of the evaporative purge system failure diagnosis.

FIG. 3 is a diagram illustrating setting of a fuel evaporation rate detection delay time according to the present invention.

FIG. 4 is a diagram illustrating setting of a fuel evaporation rate detection delay time according to the present invention.

FIG. 5 is a diagram illustrating setting of a fuel evaporation rate detection delay time according to the present invention.

FIG. 6 is a diagram illustrating setting of a fuel evaporation rate detection delay time according to the present invention.

FIG. 7 is a flowchart for explaining an embodiment of a failure diagnosis operation by the evaporation purge system failure diagnosis device of the present invention.

FIG. 8 is a diagram illustrating a change in delay time depending on the remaining fuel amount.

FIG. 9 is a diagram illustrating correction of a delay time depending on the remaining amount of fuel.

[Explanation of symbols]

1 ... Intake passage 10 ... Canister 11 ... Fuel tank 15 ... Purge control valve 17 ... CCV 30 ... Electronic control unit (ECU) 33 ... Pressure sensor 100 ... Internal combustion engine body 131 ... Refueling valve

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Naoya Takagi             1 Toyota Town, Toyota City, Aichi Prefecture Toyota Auto             Car Co., Ltd. F term (reference) 2G087 AA27 BB25 CC31 EE21 FF23                 3G044 BA22 DA03 EA32 EA53 EA55                       EA57 FA04 FA38 FA39 GA02                       GA03 GA04

Claims (5)

[Claims] 1. A canister for adsorbing evaporated fuel in a fuel tank of an internal combustion engine, a vapor passage for connecting an upper space of a fuel liquid level in the fuel tank to the canister, and a purge for connecting the canister and an engine intake passage. In an evaporative purge system having a passage, the internal pressure of the purge system including the fuel tank, the canister, the vapor passage, and the purge passage is adjusted to a predetermined negative pressure, and then the purge system is closed, and the purge system is in a negative pressure closed state. Leak detection means for detecting the internal pressure rise rate, and the purge system after raising the internal pressure of the purge system to atmospheric pressure when the internal pressure rise rate of the purge system detected by the leak detection means is larger than a predetermined reference value. A fuel evaporation rate detecting means for detecting an increase rate of the internal pressure of the purge system which is hermetically sealed and at an atmospheric pressure closed state; In the failure diagnosis device of the evaporation purge system, which comprises an abnormality determination means for determining that a failure has occurred in the evaporation purge system when the system internal pressure increase speed is smaller than a predetermined determination value, the fuel evaporation rate detection means is Evaporation means for determining whether or not the internal temperature of the fuel tank is stable after the internal pressure of the purge system has risen to atmospheric pressure, and starts detecting the rate of increase of the internal pressure of the purge system after the internal temperature of the fuel tank has stabilized Purge system failure diagnostic device. 2. A canister for adsorbing evaporated fuel in a fuel tank of an internal combustion engine, a vapor passage for connecting an upper space of a fuel liquid level in the fuel tank to the canister, and a purge for connecting the canister and an engine intake passage. In an evaporative purge system having a passage, the internal pressure of the purge system including the fuel tank, the canister, the vapor passage, and the purge passage is adjusted to a predetermined negative pressure, and then the purge system is closed, and the purge system is in a negative pressure closed state. Leak detection means for detecting the internal pressure rise rate, and the purge system after raising the internal pressure of the purge system to atmospheric pressure when the internal pressure rise rate of the purge system detected by the leak detection means is larger than a predetermined reference value. A fuel evaporation rate detecting means for detecting an increase rate of the internal pressure of the purge system which is hermetically sealed and at an atmospheric pressure closed state; In the failure diagnosis device of the evaporation purge system, which comprises an abnormality determination means for determining that a failure has occurred in the evaporation purge system when the system internal pressure increase speed is smaller than a predetermined determination value, the fuel evaporation rate detection means is After the internal pressure of the purge system rises to the atmospheric pressure, detection of the rate of increase in the internal pressure of the purge system is started after a lapse of a predetermined delay time, and the internal pressure of the purge system becomes the predetermined negative pressure after the adjustment of the internal pressure of the purge system by the leak detection means is started. A failure diagnostic device for an evaporative purge system, wherein the delay time is set longer as the time required to decrease the delay becomes longer. 3. A canister for adsorbing evaporated fuel in a fuel tank of an internal combustion engine, a vapor passage for connecting an upper space of a fuel liquid level in the fuel tank to the canister, and a purge for connecting the canister and an engine intake passage. In an evaporative purge system having a passage, the internal pressure of the purge system including the fuel tank, the canister, the vapor passage, and the purge passage is adjusted to a predetermined negative pressure, and then the purge system is closed, and the purge system is in a negative pressure closed state. Leak detection means for detecting the internal pressure rise rate, and the purge system after raising the internal pressure of the purge system to atmospheric pressure when the internal pressure rise rate of the purge system detected by the leak detection means is larger than a predetermined reference value. A fuel evaporation rate detecting means for detecting an increase rate of the internal pressure of the purge system which is hermetically sealed and at an atmospheric pressure closed state; In the failure diagnosis device of the evaporation purge system, which comprises an abnormality determination means for determining that a failure has occurred in the evaporation purge system when the system internal pressure increase speed is smaller than a predetermined determination value, the fuel evaporation rate detection means is After the purge system internal pressure rises to the atmospheric pressure, the detection of the purge system internal pressure increase rate is started after a predetermined delay time, and the time required for the purge system internal pressure to rise from the predetermined negative pressure to the atmospheric pressure. A failure diagnostic device for an evaporative purge system, wherein the shorter the delay time, the longer the delay time is set. 4. The evaporation system according to claim 2 or 3, wherein the fuel evaporation rate detecting means further seals the purge system after the predetermined delay time has elapsed after the internal pressure of the purge system has risen to atmospheric pressure. Purge system failure diagnostic device. 5. The fuel evaporation rate detecting means further corrects the delay time according to the remaining amount of fuel in the fuel tank, and starts detecting the purge system internal pressure increase rate after the corrected delay time has elapsed. The failure diagnostic device for the evaporative purge system according to claim 2.