JP2003074420A - Device for diagnosing failure of evaporator purging system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately diagnose a failure in a purging system by preventing an erroneous diagnosis. SOLUTION: Pressure rising speeds ΔP1, ΔP2 in the purging system composed of a canister 10, a fuel tank 11 and the like are measured by a pressure sensor 33 by keeping the system in negatively pressurized and hermetically sealed condition, and ΔP1, ΔP2 are compared with a prescribed determination map. Thereby, whether or not there is abnormality such as leakage or the like in the purging system is determined. When measuring an internal pressure rise, since a gas temperature in the fuel tank, which has once dropped by expansion when a pressure in the purging system has dropped, rises by heat exchange with the outside air through the wall surface of the tank, the internal pressure fluctuates, and an error is produced in the measured value of the internal pressure. In order to prevent it, the measured value of the internal pressure rising speeds ΔP1, ΔP2 are corrected based on a difference between the temperature of the outside air and a temperature in the fuel tank. Thereby, a failure can be accurately diagnosed without being influenced by temperature fluctuation in the fuel tank.

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 evaporated fuel from a fuel tank from being released into the atmosphere, the evaporated fuel from the tank is guided to a canister containing an adsorbent such as activated carbon so that the fuel vapor is adsorbed by the adsorbent. Generally, an evaporative purge system that prevents the release of fuel vapor into the atmosphere is 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 apparatus, Japanese Patent Laid-Open No. 8-2
There is one disclosed in Japanese Patent No. 40161. The device disclosed in the publication has a structure in which the purge system pressure changes when the internal pressure of the purge system is lowered to a predetermined pressure (negative pressure) lower than the atmospheric pressure.
Judge whether there is a leak in the purge system or a failure such as a hole. That is, in the device of the publication, the purge control valve is opened while the canister is shut off from the atmosphere during engine operation, and the negative pressure in the intake passage is introduced into the purge system. By this, the internal pressure of the purge system is reduced to a predetermined negative pressure, and when the predetermined negative pressure is reached, the purge control valve is closed to seal the purge system, thereby maintaining the purge system in a negative pressure sealed state. At the same time, the presence / absence of abnormality in the purge system is determined based on the amount of increase in the internal pressure of the purge system within the predetermined time period in which the negative pressure is sealed.

That is, the increase in the internal pressure of the purge system in the negative pressure sealed 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. Therefore, when the internal pressure increase rate of the purge system in the negative pressure closed state is larger than a predetermined upper limit value, it can be determined that the purge system is leaking and an abnormality such as a hole is generated.

[0006]

However, in the failure diagnosis device disclosed in Japanese Patent Laid-Open No. 8-240161, the pressure increase of the purge system is measured from the same negative pressure when the purge system is actually closed under negative pressure. However, the measurement results may vary. As a result of studies by the inventor, it has been found that this problem is caused by a temperature change in the fuel tank after the purge system is closed under a negative pressure.

For example, it is the space above the liquid level in the fuel tank that has the largest space volume in the purge system. When the internal pressure of the purge system is reduced to a predetermined negative pressure, the gas in the space above the liquid surface in the fuel tank expands due to the reduced pressure. For this reason,
The gas temperature (hereinafter referred to as "fuel tank internal temperature") in the space above the liquid surface of the fuel tank immediately after the internal pressure of the purge system is reduced to a predetermined negative pressure and the purge system is sealed is lower than that before the internal pressure was reduced. Becomes lower. That is, since the internal temperature of the fuel tank before the start of decreasing the internal pressure is substantially equal to the external air temperature, a temperature difference occurs between the internal temperature of the fuel tank immediately after the negative pressure is closed and the external temperature.

Since the gas in the space above the liquid surface of the tank exchanges heat with the outside air through the tank wall surface, the temperature inside the fuel tank once lowered after the negative pressure is closed and rises, and returns to the outside air temperature after a lapse of sufficient time. To do. In this case, the increase width and the increase speed of the temperature inside the fuel tank increase as the difference between the outside air and the temperature inside the fuel tank increases. Therefore, when the purge system is in a negative pressure sealed state, the tank internal pressure changes (increases) due to the change (increase) in the temperature inside the fuel tank.

Therefore, if it is judged whether or not there is a failure in the evaporative purge system based on the rate of increase in internal pressure of the purge system measured with the purge system in a negative pressure sealed state, the temperature change in the fuel tank after negative pressure sealing is large. In this case, even if there is no abnormality such as a leak or a hole, the internal pressure of the purge system increases at a high rate, and even if the evaporative purge system is normal, a failure may be erroneously determined. Furthermore, even if the predetermined negative pressure when closing the purge system under negative pressure is the same, if the range of decrease in internal pressure of the purge system and the speed of decrease until the predetermined negative pressure is different, the temperature inside the fuel tank during negative pressure sealing Changes greatly.

For example, the pressure of the purge system before introducing the negative pressure into the purge system may change greatly depending on the opening of the purge control valve and the intake passage pressure (negative pressure) of the engine. In addition, the time from when the introduction of the negative pressure is started until the predetermined negative pressure is reached, that is, the pressure decrease speed, changes greatly depending on the intake passage pressure (negative pressure). In this case, when the internal pressure of the purge system at the start of the introduction of the negative pressure is high, the pressure decrease range of the internal pressure of the purge system becomes large until the predetermined negative pressure is reached, and the expansion ratio of the gas in the fuel tank becomes large. The range of decrease in the temperature inside the fuel tank before and after is also large.

Further, even if the pressure drop width in the purge system is the same, the temperature in the fuel tank when the predetermined negative pressure is reached varies greatly depending on the rate of decrease in the purge system pressure. For example, when the rate of decrease in the internal pressure is relatively small, the gas in the tank expands while receiving heat from the outside air through the wall surface of the tank in the process of expansion, so the temperature decrease when the predetermined negative pressure is reached is relatively small. On the contrary, when the purge system internal pressure decrease rate is large, the gas in the tank expands without performing sufficient heat exchange with the outside air, so the temperature decrease in the fuel tank when the predetermined negative pressure is reached is relatively large. Become. Therefore, when the failure diagnosis of the evaporative purge system is performed based on only the pressure increase rate in the system at the time of closing the negative pressure of the purge system as in the apparatus disclosed in Japanese Patent Laid-Open No. 8-240161, erroneous diagnosis occurs. .

In view of the above-mentioned problems of the prior art, the present invention considers the influence of the fluctuation in the tank internal pressure due to the temperature change in the fuel tank when the failure diagnosis of the evaporative purge system is performed based on the internal pressure increase speed when the purge system is closed with a negative pressure. It is an object of the present invention to provide a failure diagnosis device for an evaporative purge system, which enables accurate failure diagnosis without receiving the failure.

[0013]

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. In an evaporative purge system having a vapor passage and a purge passage connecting the canister and the engine intake passage, the internal pressure of a purge system including the fuel tank, the canister, the vapor passage, and the purge passage is reduced to a predetermined negative pressure. The leak detection means for detecting the increase rate of the internal pressure of the purge system in the negative pressure closed state, and the failure of the evaporative purge system based on the increase rate of the internal pressure of the purge system detected by the leakage detection means. In the failure diagnostic device for the evaporative purge system, which comprises a determining means for determining the presence or absence of The determining means comprises a correcting means for correcting the purge system internal pressure increasing speed detected by the leak detecting means based on the difference between the outside air temperature and the fuel tank internal temperature when reaching a constant negative pressure. There is provided a failure diagnosis device for an evaporative purge system, which determines whether or not there is a failure in the evaporative purge system based on the rate of increase in internal pressure of the purge system after correction by the means.

That is, in the first aspect of the present invention, there is provided the correction means for correcting the increase rate of the internal pressure of the purge system detected by the leak detection means based on the difference between the outside air temperature and the internal temperature of the fuel tank when the internal pressure decreases. . As described above, the rate of increase in the internal pressure of the purge system at the time of leak detection is affected by the temperature difference between the outside air and the gas inside the fuel tank when the internal pressure drops, and accurate leak detection is not always possible if the temperature difference is large. Can not. In the present invention, the purge system internal pressure increase rate detected by the leak detection means is corrected based on the difference between the outside air temperature and the fuel tank internal temperature. It is possible to calculate the increase rate of the internal pressure of the purge system. Therefore, according to the present invention, it is possible to perform accurate failure diagnosis of the evaporative purge system regardless of the difference between the outside air temperature and the fuel tank internal temperature when the internal pressure decreases.

According to the second aspect of the present invention, the correction means detects the purge system so that the increase rate of the internal pressure of the purge system decreases as the difference between the outside air temperature and the internal temperature of the fuel tank increases. The failure diagnosis device for an evaporative purge system according to claim 1, which corrects an internal pressure increase rate.

That is, according to the second aspect of the present invention, the increase rate of the internal pressure of the purge system detected by the leak detecting means is corrected so as to decrease as the difference between the outside air temperature and the internal temperature of the fuel tank increases. At the start of leak detection, the temperature inside the fuel tank rises due to heat exchange with the outside air, and the pressure inside the fuel tank rises accordingly.However, the greater the difference between the outside air temperature at the start of leak detection and the temperature inside the fuel tank, the greater the fuel The rise width and rise speed of the temperature in the tank become large, and the pressure rise speed due to temperature change becomes large. In the present invention, the larger the difference between the outside air temperature and the fuel tank internal temperature, the smaller the purge system internal pressure increase rate detected by the leak detection means is corrected to eliminate the influence of the change in the fuel tank internal temperature on the internal pressure increase rate. Since it is possible to perform fault diagnosis using the accurate internal pressure rise speed, it is possible to perform accurate fault diagnosis of the evaporative purge system regardless of the difference between the outside air temperature and the fuel tank internal temperature when the internal pressure drops. Becomes The difference between the outside air temperature and the temperature inside the fuel tank can also be obtained by directly detecting the outside air temperature and the temperature inside the fuel tank by providing a temperature sensor, for example, the pressure decrease width when the internal pressure decreases, You may make it indirectly based on time etc.

According to the third aspect of the present invention, the correction means is based on the space volume above the liquid level in the fuel tank when the leak is detected, in addition to the difference between the outside air temperature and the temperature inside the fuel tank. A failure diagnosis device for an evaporative purge system according to claim 1, wherein the increase rate of the internal pressure of the purge system detected by the leak detection means is corrected.

That is, in the third aspect of the invention, the correction means corrects the purge system internal pressure increase rate based on the difference between the outside air temperature and the fuel tank internal temperature, and further based on the volume of the fuel tank internal liquid level upper space. The temperature change in the fuel tank occurs when the gas in the fuel tank, the temperature of which has decreased due to the decrease in the internal pressure, exchanges heat with the outside air through the wall surface of the tank to increase the temperature. The amount of heat given per unit volume of gas in the fuel tank due to heat exchange with the outside air increases as the heat exchange area per unit volume of gas in the fuel tank (wall surface area of the fuel tank in contact with gas in the fuel tank) increases. Become.
On the other hand, the heat exchange area changes according to the upper space volume in the fuel tank. For example, when the amount of remaining fuel in the fuel tank is large and the upper space volume in the fuel tank is small, the heat exchange area per unit volume of gas is large and the amount of heat exchange per unit volume of gas is large. The speed increases, and the increase rate of the internal pressure of the purge system increases accordingly. In the present invention, in addition to the temperature difference between the inside and outside of the fuel tank, the purge system internal pressure increase rate detected by the leak detection means is further corrected based on the upper space volume (heat exchange area per unit volume of gas) inside the fuel tank. As a result, it is possible to more accurately determine the true increase rate of the internal pressure of the purge system, and thus it is possible to perform more accurate failure diagnosis of the evaporative purge system.

According to the fourth aspect of the present invention, the correction means includes a pressure until the internal pressure of the purge system is reduced to the predetermined negative pressure by the leak detection means until the predetermined negative pressure is reached. The failure diagnosis device for an evaporative purge system according to claim 1, wherein the difference between the outside air temperature and the fuel tank temperature is estimated based on at least one of the decrease width and the required time.

That is, in the fourth aspect of the invention, the difference between the outside air temperature when the internal pressure decreases and the fuel tank internal temperature is estimated based on the pressure change history when the internal pressure decreases. The temperature inside the fuel tank before the start of the decrease in internal pressure is approximately equal to the outside air temperature. Further, the width of decrease in temperature inside the tank when the internal pressure decreases changes depending on the expansion ratio (pressure decrease width) of the gas in the fuel tank and the time of heat exchange with the outside air (time required for pressure decrease). For example, the larger the pressure drop width, the lower the temperature inside the fuel tank when the internal pressure drops, and the shorter the pressure drop time, the gas inside the fuel tank expands without being warmed by heat exchange with the outside air, so the fuel tank when the internal pressure drops. The internal temperature becomes low. Therefore, it is possible to estimate the temperature difference between the inside and the outside of the fuel tank when the internal pressure decreases, based on at least one of the pressure decrease width and the pressure decrease required time. According to the present invention, by estimating the temperature difference between the inside and outside of the fuel tank based on at least one of the pressure drop width and the pressure drop required time, it is possible to accurately diagnose the failure of the evaporative purge system without using a temperature sensor. Becomes

According to the fifth aspect of the present invention, the correction means is based on the difference between the outside air temperature and the fuel tank internal temperature, and further based on the remaining fuel amount in the fuel tank when the leak is detected. A failure diagnosis device for an evaporative purge system according to claim 4, wherein the purge system internal pressure increase rate detected by the leak detection means is corrected.

That is, in the fifth aspect of the invention, the rate of increase in the internal pressure of the purge system is corrected based on the temperature difference between the inside and outside of the fuel tank and the remaining amount of fuel in the fuel tank. The volume of the upper space in the fuel tank, that is, the heat exchange area per unit volume of gas changes depending on the remaining amount of fuel in the fuel tank. Therefore, by correcting the purge system internal pressure increase rate based on the fuel tank internal / external temperature difference and the fuel remaining amount in the fuel tank, the true internal pressure increase rate can be obtained more accurately, and the accurate evaporation rate can be obtained. It is possible to diagnose the failure of the purge system.

[0023]

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 connecting portion of 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. The atmosphere communication pipe 18 is opened in the vicinity of the oil supply port of the tank 11, and an air filter 19 is provided on the atmosphere communication pipe 18. The air filter 19 is connected from the atmosphere communication pipe 18 to the canister 1 when purging is performed.
The foreign matter in the air flowing into 0 is removed. C
The CV 17 is provided with 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 according 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 pressure rises in the space above the liquid level in the fuel tank 11 due to the rise in the liquid level in the fuel tank. 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, a mixture of fuel vapor and air flows into the canister 10 from the space above the liquid surface of the fuel tank 11 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 the present embodiment, purging is performed 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 is 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
And CCV 17 are 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
Signals representing the engine speed, the engine intake air amount, the engine cooling water temperature, etc. are input to the input port of the CU 30 from sensors (not shown), respectively, and also from the pressure sensor 33 via an AD converter (not shown). A signal indicating the internal pressure of the fuel tank 11 is input.

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.

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 first pressure (for example, a pressure of about 740 mmHg) for a predetermined time after the internal pressure of the purge system rises while maintaining the negative pressure closed state. (For example, about 5 seconds) Purge system internal pressure increase width (that is, internal pressure increase rate) ΔP1,
A second pressure higher than the first pressure (eg 745 mmHg
After reaching a certain pressure), the increase width ΔP2 of the internal pressure of the purge system within a predetermined time (for example, about 5 seconds) is measured. Then, based on the measured values of ΔP1 and ΔP2, it is determined whether or not there is a leak in the purge system and a failure such as a hole has occurred.

In this state, the rate of increase in the internal pressure of the purging 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 purging 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, when the internal pressure increase speeds ΔP1 and ΔP2 measured by the purge system internal pressure increase measurement (hereinafter referred to as “leakage detection”) when the negative pressure is closed are large, an abnormality such as leakage occurs in the purge system. It may have occurred. Actually, in the present embodiment, the abnormality determination at the time of leakage detection is performed not only based on the magnitude of ΔP1 and ΔP2 but also based on the relationship between ΔP1 and ΔP2. The abnormality determination when the leak is detected will be described later.

Actually, the rate of increase in the internal pressure of the purge system at the time of leak detection is large when the fuel evaporation rate during 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 leak detection.

Therefore, in the present embodiment, ΔP is set when a leak is detected.
When the abnormality determination is made based on the values of 1 and ΔP2, the fuel evaporation rate in the fuel tank is continuously detected, and it is verified whether or not the abnormality determination is reliable. That is, in this case, after the leak detection is completed, the CCV 17 is opened with the purge control valve 15 kept closed, and the atmosphere is introduced to raise 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 the vicinity of the atmospheric pressure, the CCV 17 is closed to close the inside of 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.

Therefore, the increase in the internal pressure of the purge system which occurs in the atmospheric pressure sealed state is only due to 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 increase in internal pressure is a predetermined value or more in the leak detection operation. In this case, when the fuel evaporation rate is low, it can be determined that the increase in the internal pressure at the time of the leak detection operation is due to the actual leakage in the purge system. Also,
When the fuel evaporation rate is high, the increase in internal pressure of the purge system at the time of leak detection may have occurred due to the high fuel evaporation rate, so it cannot always be determined that a leak has occurred in the purge system. Suspend the determination of whether or not there is a leak and stop the abnormality diagnosis.

However, in actuality, when the pressure increase rate of the fuel tank internal pressure is measured by the pressure sensor 33 in order to detect a leak in a state where the purge system is hermetically sealed with a negative pressure, there is no leakage in the purge system, there is no abnormality such as holes, and fuel evaporation Even under conditions where the velocity should be low, the internal pressure rise rate may increase. in this way,
If the increase rate of the internal pressure at the time of leak detection becomes larger than the original value, there is a problem that an abnormality is determined at the time of leak detection until the evaporative purge system should be normally judged to be normal. Also, in this case, the fuel evaporation rate is measured after the leak detection is completed, but if the detected fuel evaporation rate is small, the purging system is abnormal until the normal judgment should be made. It may be judged and a false diagnosis may occur.

As described above, the problem that the increase rate of the internal pressure of the purge system at the time of leak detection becomes larger than the original value is that the pressure decrease width and the predetermined negative pressure are reached when the internal pressure of the fuel tank is made a predetermined negative pressure at the time of leak detection. It has been found to be related to the history of fuel tank pressure changes such as pressure drop time to.

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 and the system internal pressure reduction is started 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 (eg, 740 m) from the start of the pressure decrease.
The width (P1) of decrease in the tank internal pressure until the pressure reaches mHg or less) varies depending on the 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 decrease width P1 and the decrease time T1 will change depending on various conditions.

However, when the tank internal pressure reaches the above-mentioned predetermined negative pressure, the tank internal temperature greatly changes depending on the pressure decrease width P1 and the pressure decrease required time T1. For example, when the pressure drop width P1 is large, and the pressure drop required time T1
When is short, the temperature in the tank is greatly decreased 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 short, and the temperature in the tank when the predetermined negative pressure is reached is low. For this reason, the difference between the outside air and the temperature inside the fuel tank becomes large, the temperature change (rise) due to heat exchange with the outside air becomes large, and the purge system internal pressure rise speed at the time of leak detection is high even if there are no leaks or holes. It is significantly higher than the internal pressure rise rate due to evaporation. 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 is high (the temperature difference from the outside air is small). In this case, the temperature rise in the fuel tank at the time of leak detection is small,
The increase rate of the internal pressure of the purge system becomes substantially equal to the fuel evaporation rate.

In this embodiment, in order to eliminate the influence of the change in the temperature inside the fuel tank on the increase rate of the internal pressure when a leak is detected, the detected increase rate of the internal pressure is corrected to a value in the state where there is no temperature change in the fuel tank. Then, the presence / absence of abnormality is determined based on the corrected internal pressure increase rate. Further, as described above, the change in the temperature inside the fuel tank when the leak is detected is determined by the difference between the outside air temperature and the temperature inside the fuel tank when the predetermined negative pressure is reached. The difference between the outside air temperature and the temperature inside the fuel tank when the predetermined negative pressure is reached may be detected by using a temperature sensor to detect the outside air temperature and the temperature inside the fuel tank, respectively. The difference between the outside air temperature at that time and the temperature inside the fuel tank is determined by the pressure decrease width P1 when the predetermined negative pressure is reached and the pressure decrease required time T1. Therefore, in the present embodiment, instead of directly detecting the outside air temperature and the fuel tank internal temperature using the temperature sensor, the detected internal pressure increase rate is corrected based on the pressure decrease width P1 and the pressure decrease required time T1. I have to.

Further, in this embodiment, when an abnormality is determined at the time of leak detection, the internal pressure of the purge system is increased to atmospheric pressure, and the fuel evaporation rate is detected at the atmospheric pressure with the purge system sealed. In this case, contrary to the case where the internal pressure of the purge system is lowered to detect a leak, the gas in the space above the liquid surface in the fuel tank is compressed and the temperature rises due to the increase in the internal pressure of the purge system. Also in this case, if the temperature inside the fuel tank is higher than the outside air temperature when the atmospheric pressure is restored, the temperature in the fuel tank decreases after the atmospheric pressure is closed because the gas in the fuel tank exchanges heat with the outside air through the wall surface of the fuel tank. The internal pressure tends to decrease. Therefore, if the purge system internal pressure increase rate (fuel evaporation rate) is detected immediately after the atmospheric pressure is restored, the detected internal pressure increase rate may be lower than the true fuel evaporation rate.

Therefore, in the present embodiment, in order to eliminate the influence of the temperature change in the fuel tank even when the fuel evaporation rate is detected, after the purge system is sealed at atmospheric pressure, the temperature in the fuel tank becomes stable (fuel tank After waiting until the inside temperature becomes close enough to the outside temperature, the increase in internal pressure of the purge system (fuel evaporation rate) is measured. As described above, the temperature in the tank when the internal pressure of the tank decreases to the predetermined negative pressure when the leak is detected changes depending on the pressure decrease width P1 and the decrease time T1, and when the pressure decrease width P1 is large and the decrease time. When T1 is short, the temperature in the tank becomes low when the predetermined negative pressure is reached. Conversely, when P1 is small and when the pressure drop time T1 is long, the temperature inside the tank when the predetermined negative pressure is reached is high (the temperature difference from the outside air 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 longer the negative pressure closed holding time (T2) is, the higher the gas temperature in the tank at the end of the leak detection is. When the leak detection due to the negative pressure sealing is completed, the purge control valve 15 is closed and once the CC is closed.
When V17 is fully opened, the internal pressure of the purge system is raised to atmospheric pressure. However, since the gas in the tank is compressed by this, the temperature in the tank rises when the atmospheric pressure is reached. In this case, as the temperature rise rate in the tank increases,
In other words, the shorter the time (T3) required to raise the pressure to the atmospheric pressure, the larger the time.

However, when the temperature in the tank is high at the end of the negative pressure sealing, the temperature in the tank at the time of reaching the atmospheric pressure after pressurization may be higher than the atmospheric pressure. 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 atmospheric pressure sealed state. in this case,
The higher the temperature inside the tank when the atmospheric pressure is reached, the longer it takes for the temperature inside the tank to drop to the outside air temperature and stabilize.

In the present embodiment, the start of the purge system internal pressure rise rate measurement (fuel evaporation rate detection) in the atmospheric pressure closed state is delayed until the temperature inside the tank drops to the outside air 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 diagram schematically 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 is the width of the pressure drop in the tank when the negative pressure is introduced after the start of the failure diagnosis, and T1 is the time until the tank pressure reaches a predetermined negative pressure after the start of the negative pressure introduction (time required for the pressure decrease). Represents Further, T2 is a time period in which the purge system is hermetically maintained in a negative pressure state after reaching a predetermined negative pressure (negative pressure hermetically maintaining time T
2), that is, the time required for leak detection, T3 represents the time required for returning the inside of the purge system to atmospheric pressure after leak detection (pressurization time).

In the present embodiment, the purge system internal pressure measurement value at the time of leak detection is corrected on the basis of the fuel tank internal pressure decrease width P1 and the pressure decrease required time T1 when the negative pressure is introduced.
In addition to correcting the fuel tank internal pressure change due to the fuel tank internal temperature change at the time of leak detection, when measuring the fuel evaporation rate, after increasing the purge system internal pressure to atmospheric pressure, the pressure decrease width P1, the pressure decrease required time T1, and the negative pressure. The fuel evaporation rate is detected after the delay time T (FIG. 2) determined based on the sealing holding time T2 and the pressurization time T3 has elapsed, so that the fuel evaporation rate is detected while the temperature in the fuel tank is stable. I'm trying to do. The delay time T is the minimum time required for the temperature in the fuel tank to stabilize (close to the outside air temperature), and is calculated based on P1, T1, T2, T3 by the method described later.

As described above, in the present embodiment, when leak detection is performed by sealing the purge system under negative pressure, the internal pressure of the purge system rises after sealing and the first predetermined negative pressure (for example, 740 mmH).
It is determined whether or not there is an abnormality such as a hole or the like based on an internal pressure increase rate ΔP1 when passing a pressure of about g) and an internal pressure increase rate ΔP2 when passing a second predetermined negative pressure (for example, a pressure of about 745 mmHg). Then, the internal pressure increase rates ΔP1 and ΔP2 at the time of detecting the leak are corrected based on the pressure decrease width P1 and the pressure decrease required time T1 (FIG. 2) to eliminate the influence of the temperature change in the tank.

Below, the internal pressure increase rate ΔP1 at the time of leak detection,
The correction based on the pressure decrease width P1 of ΔP2 and the pressure decrease time T1 will be described. As described above, as the pressure drop width P1 at the time of leak detection is larger, the pressure drop required time T
The shorter 1 is, the lower the temperature in the fuel tank is when the pressure reaches a predetermined negative pressure, and the rate of increase in internal pressure when the temperature in the fuel tank rises to the outside air temperature increases.

Therefore, in the present embodiment, correction coefficients K1P and K2P are added to the detected internal pressure increase rates ΔP1 and ΔP2, respectively.
The internal pressure increase speed is corrected by multiplying by. In this embodiment, Δ
For P1 and ΔP2, correction coefficients (pressure decrease width correction coefficient) αP1 and αP for the influence of the pressure decrease width P1
2 and correction factors (pressure reduction required time correction factors) βP1 and βP2 for the influence of the pressure reduction required time T1 are obtained,
The larger value of αP1 and βP1 is adopted as the correction coefficient K1P, and the larger value of αP2 and βP2 is adopted as the correction coefficient K2P.

3 and 4 show the relationship between the pressure decrease width P1 and the correction coefficients αP1 and αP2, and the pressure decrease time T1 and the correction coefficients βP1 and βP2, respectively. As previously mentioned,
When the pressure decrease width P1 is large, the detected values of the internal pressure increase rates ΔP1 and ΔP2 are correspondingly larger than the true values. Therefore, as shown in FIG. 3, the correction coefficients αP1 and αP
The value of 2 is set to 1 when the pressure decrease width P1 is 0, and is set to a smaller value as P1 increases. Also, the rate of temperature rise in the fuel tank after the pressure drop is
It becomes smaller as the temperature inside the fuel tank rises (as the pressure inside the fuel tank rises). Therefore, the measured value of the internal pressure increase rate ΔP1 measured at the first predetermined negative pressure is higher than the internal pressure increase rate ΔP2 measured at the second predetermined negative pressure higher than the first predetermined negative pressure. Will be greatly affected by. Therefore, the value of the pressure decrease correction coefficient αP1 for ΔP1 is set to be smaller than the pressure decrease correction coefficient αP2 for ΔP2.

Further, when the time T1 required for pressure decrease is short, the detected values of the internal pressure increase rates ΔP1 and ΔP2 become larger than the true values accordingly. Therefore, as shown in FIG. 4, the values of the correction coefficients βP1 and βP2 are set so as to increase and approach 1 as the pressure reduction required time becomes longer. For the same reason as αP1 and αP2, the correction coefficient βP
The value of 1 is set to be smaller than the correction coefficient βP2.

In this embodiment, the internal pressure increase rate ΔP1 and ΔP2 as well as the internal pressure decrease width P1 and the required time T1 are measured when a leak is detected, and αP1 and αP2 are calculated based on P1 in FIG.
4 and βP2 based on the relationship of FIG.
The correction coefficient K1P for ΔP1 and the correction coefficient K2P for ΔP2 are calculated based on the relationship
K1P = max (αP1, βP1), K2P = max
It is calculated as (αP2, βP2). However, in the above equation, max (αP1, βP1), max (αP2,
βP2) means the larger value of αP1 and βP1, and the larger value of αP2 and βP2, respectively.

In this embodiment, the correction coefficients K1P and K2P calculated above are multiplied by ΔP1 and ΔP2 to correct the internal pressure increasing rates ΔP10 and ΔP20 (that is, ΔP1).
0 = K1P × ΔP1, ΔP20 = K2P × ΔP2) is used to determine whether there is an abnormality such as a leak or a hole from the determination map of FIG.

The abscissa of the determination map of FIG. 5 is (ΔP10 / Δ
P20), ΔP20 is plotted on the vertical axis, and (ΔP20
10 / ΔP20) and the value of ΔP20 are combined to divide into three areas: abnormality determination, determination suspension, and normal determination. In the present embodiment, the two internal pressure rise rates ΔP10 and ΔP20 measured at different internal pressures are used to determine whether or not there is a hole and whether there is a hole or not. Accurate failure determination is performed in consideration of the shape of the internal pressure rise curve of the purge system. This is because.

FIGS. 6 (A) and 6 (B) show internal pressure rise curves when a leak is detected. The vertical axis represents the purge system internal pressure and the horizontal axis represents time. Further, FIG. 6A shows a pressure rise curve when there is no abnormality in the purge system such as a hole, and FIG. 6B shows a pressure rise curve when there is leakage in the purge system and there is an abnormality such as a hole. Shown respectively.

When there is no abnormality such as leakage in the purge system (FIG. 6 (A)), the rate of pressure increase at the time of leakage detection is high at the beginning and decreases as the pressure increases. For this reason,
The corrected ΔP10 becomes larger than ΔP20, and ΔP10
The value of / ΔP20 becomes larger than 1. On the other hand, when the purge system has a leak or an abnormality such as a hole (FIG. 6 (B)), the pressure increase rate at the time of leak detection is substantially uniform, and the corrected value of ΔP10 / ΔP20 is It is close to 1. Therefore, in the determination map of FIG. 5, the shape of the pressure rise curve is shown in FIG.
When the value of ΔP10 / ΔP20 is large, the normal determination is performed even if the internal pressure increase rate ΔP20 is large to some extent, and as the value of ΔP10 / ΔP20 approaches 1 (the shape of the pressure increase curve is shown in FIG. The value of the internal pressure increase rate ΔP20 for making the normal determination is set to decrease as the value approaches B).

Further, the abnormality judgment is made by ΔP10 / Δ
It is limited to the case where the value of P20 is relatively close to 1 (the shape of the pressure rise curve is close to that of FIG. 6B) and the value of ΔP20 is large. Further, in FIG. 5, (ΔP10 / ΔP2
When the values of 0) and ΔP20 do not fall within the normal determination region or the abnormality determination region, the determination is suspended to prevent erroneous diagnosis due to the fluctuation of the liquid surface.

Since the relationship between FIGS. 3 and 4 and the determination map shown in FIG. 5 differ depending on the size and shape of the fuel tank, it is preferable to set them by an experiment using an actual fuel tank.

Next, the setting of the fuel evaporation rate detection delay time T will be described. As described above, the time required for the temperature in the tank to stabilize after returning to atmospheric pressure changes depending on P1 and T1, T2, and T3. 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) Time required for pressure decrease T1 If the time required for pressure decrease T1 is short, the gas in the tank expands without sufficient heat exchange with the outside, and the temperature in the tank becomes low when a predetermined negative pressure is reached. 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 sealing holding time T2 The longer the negative pressure sealing holding time T2, the more the gas in the tank is warmed up by heat exchange with the outside, so the temperature in the tank after the negative pressure sealing ends becomes higher. Therefore, the delay time is T2.
The longer is the longer it needs to be.

(4) Boosting time T3 As the boosting 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 the present 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 tank internal temperature 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 decrease width P1, the pressure decrease required time T1, the negative pressure sealing holding time T2, and the pressure increasing 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.

Also, 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. 7 to 10 show PK1 and P1, TK1 and T1, TK2, respectively.
It is a figure which shows an example of the relationship of T2 and T2, and TK3 and T3.

As shown in FIG. 7, 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. 8, the coefficient TK1 increases exponentially as the time T1 required for pressure decrease increases. TK1 is also T when T1 = P1 ₀ (reference value)
It is set so that K1 = 1.

Further, as shown in FIG. 9, 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.

[0085] The coefficient TK3 represents exponential change becomes smaller as the boosting time T3 is longer as shown in FIG. 10, the TK3 = 1 when T3 = T3 _0.

The relationships of FIGS. 7 to 10 are described in detail by changing P1, T1, T2 and T3 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. 11 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. 11, first, at step 1101, it is determined whether or not the condition for executing the abnormality diagnosis operation is satisfied. The abnormality detection operation execution conditions determined in step 1101 are 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. The pressure fluctuation in the fuel tank is less than a predetermined value (for example, the liquid level in the tank does not shake significantly due to running on a slope, turning, running on a bad road, etc.)
And so on.

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 of step 1101 are satisfied, then in steps 1103 and 1105, the measurement (leakage detection) of the purge system internal pressure increase rates ΔP1 and ΔP2 in the negative pressure closed state and the pressure decrease width P1 described above are performed. The measurement with the pressure drop required time T1 is performed. That is, in step 1103, a negative pressure introducing operation is performed in which the CCV 17 is closed while the purge is being executed (while the purge control valve 15 is open).
As a result, the negative pressure in the intake passage 1 is introduced into the purge system, and the pressure in the purge system such as the canister 10 and the fuel tank 11 decreases.

In step 1103, when the negative pressure is introduced into the purge system and the internal pressure of the fuel tank detected by the pressure sensor 33 is reduced to a predetermined negative pressure (for example, pressure of 740 mmHg or less), the purge control valve is operated. Close valve 15. Then, at this time, when the CCV 17 is closed (at the time of introducing the negative pressure) to when the purge control valve 15 is closed (at the time of closing the negative pressure).
Is stored as the pressure decrease required time T1, and the difference between the tank internal pressures detected by the pressure sensor 33 at the start of the introduction of the negative pressure and the start of the negative pressure sealing is stored as the pressure decrease width P1.

Then, in step 1105, a leak (increase in internal pressure) of the purge system closed under negative pressure as described above is detected. 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. That is, in step 1105, after the purge control valve 15 is closed to seal the purge system under negative pressure, timing is started when the system internal pressure reaches the first predetermined negative pressure (for example, 740 mmHg), and then predetermined The pressure rise width detected by the pressure sensor 33 within the time (for example, about 5 seconds) is stored as ΔP1,
When the internal pressure further rises and the system internal pressure reaches a second predetermined negative pressure (for example, 745 mmHg) higher than the first predetermined negative pressure, the system internal pressure increase width within a predetermined time (for example, about 5 seconds) is set. Store as ΔP2.

According to the above, after the leak detection operation is completed,
In step 1107, based on the pressure decrease width P1 and the pressure decrease required time T1 stored in step 1103, αP1, αP2, and βP1, βP are obtained from the relationships shown in FIGS.
2 is calculated, and the correction coefficient K1P for ΔP1 and the correction coefficient K2P for ΔP2 are calculated as K1P = max (αP1,
βP1), K2P = max (αP2, βP2).

Then, in step 1109, ΔP10
= K1P × ΔP1, ΔP20 = K2P × ΔP2), the corrected internal pressure increase rates ΔP10 and ΔP20 are calculated. Further, in step 1111, the corrected internal pressure increase rates ΔP10 and ΔP20 are used to obtain (ΔP10 / ΔP
20) and the value of ΔP20 are determined in which region of the three regions of “abnormality determination”, “determination pending”, and “normality determination” on the determination map of FIG.

Then, in steps 1113 and 1115, it is judged whether the judgment result in step 1111 is "abnormal judgment" or "judgment pending", respectively.
If neither "abnormality determination" nor "judgment pending", that is, "normality determination", normality determination is made in step 1117, and this operation is ended. In addition, step 1
When the normal determination is made in 117, the purge control valve 15 and C
The valve with the CV 17 is immediately opened to restart the purging of the canister 10.

If the determination result of step 1111 is "determination pending", the process proceeds from step 1115 to step 1133, and "diagnosis pending" is stored as the diagnosis result. If the judgment is suspended, step 11 is executed again.
When the diagnosis execution condition of 01 is satisfied, the failure diagnosis operation of FIG. 11 is executed.

On the other hand, if the determination result in step 1111 is "abnormality determination", it is possible that the abnormality determination was made because the fuel evaporation rate was high, and therefore the magnitude of the fuel evaporation rate is determined. There is a need to. Therefore, in this case, the fuel vaporization rate detection operation from step 1119 onward is performed.

That is, in step 1119, first, the CCV 17 is opened with the purge control valve 15 kept closed,
Start the introduction of air into the purge system and step 1
After closing CCV1 at 103, C at step 1119
The elapsed time until the CV 17 is opened is stored as the negative pressure closed holding time T2. Then, in step 1121, when the pressure in the fuel tank detected by the pressure sensor 33 rises to atmospheric pressure, the CCV 17 is closed to close the purge system at atmospheric pressure, and the CCV 17 is opened in step 1119 before the step The elapsed time until the valve is closed at 1121 is stored as the boosting time T3.

As described above, in the system closed at atmospheric pressure, 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 temperature inside the tank is calculated based on the above equation (A) by using the pressure decrease width P1, the pressure decrease required time T1, the negative pressure sealing holding time T2, and the pressure increasing time T3 stored in each of the above steps. The time (delay time) T until the temperature becomes sufficiently close to the atmospheric temperature and stabilizes is calculated, and after the delay time elapses, detection of the fuel evaporation rate is started.

That is, in step 1123, the stored values of P1, T1, T2, and T3 are used, and the values shown in FIGS.
From the relationship of 0, the correction coefficients PK1, TK1, TK2, TK3
Respectively, and further, in step 1125, the delay time is calculated as T = α × (PK1 + TK1 + TK2) × TK3.

Then, in step 1127, step 1
Wait until the elapsed time after closing the CCV 17 at 121 reaches the delay time T, and after the time T elapses, step 1
Proceeding to 129, the fuel evaporation rate detection is started. That is,
In step 1129, a predetermined time (1
The pressure sensor 33 measures the increase width ΔPV of the internal pressure of the purge system during about 5 seconds. This value of ΔPV is a value corresponding to the fuel evaporation rate.

At step 1131, ΔPV measured as described above is compared with a predetermined judgment value ΔPV _0, and ΔPV ≧ ΔP
If it is V ₀ , step 1111 is performed when a leak is detected.
It is judged that there is a high possibility that the abnormality determination was made because the fuel evaporation rate was high and not because the abnormality really occurred. Therefore, in step 1131 ΔPV ≧
If ΔPV ₀ , the process proceeds to step 1133 and the determination is suspended and the abnormality diagnosis is finished. ΔPV ₀ is several mm
It is a value of about Hg.

In step 1131, ΔPV <ΔPV
If it is ₀ , the fuel evaporation rate is low, and it can be determined that the abnormality determination is made in step 1111 because the purge system is truly abnormal. Therefore, in this case, the process proceeds to step 1135, 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 1135, the warning light arranged near the driver's seat of the vehicle is turned on by the operation separately executed by the ECU 30 to notify the driver of the abnormality of the purge system.

As described above, in the present embodiment, when the abnormality of the purge system is judged based on the internal pressure increase rate measured with the purge system in the negative pressure closed state, the influence of the internal pressure change due to the temperature change in the fuel tank is affected. Since the true internal pressure increase rate corrected for is used, it is possible to accurately perform the failure diagnosis regardless of the temperature change in the fuel tank after the negative pressure is closed.

In this embodiment, when the normal determination is made in step 1111, the purge is immediately restarted without measuring the fuel evaporation rate. In reality, in most cases, the normal determination is made in step 1111 and the fuel evaporation rate is detected (step 1119 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.

Next, an embodiment different from that of FIG. 11 of the failure diagnosis operation of the present invention will be described. Also in the present embodiment, the internal pressure increase rates ΔP1 and ΔP2 at the time of leak detection are corrected based on the difference between the outside air temperature and the fuel tank internal temperature at the time when a predetermined negative pressure is reached, and the internal pressure of the purge system at the time of fuel evaporation rate detection. 11 is similar to the embodiment of FIG. 11 in that the fuel evaporation rate detection is started after waiting until a predetermined delay time T elapses after increasing the pressure to atmospheric pressure.

However, the present embodiment is different from the embodiment of FIG. 11 in that the correction of ΔP1 and ΔP2 and the correction in consideration of the remaining fuel amount in the fuel tank when the delay time T is calculated. . In the embodiment of FIG. 11, the correction of ΔP1 and ΔP2 and the calculation of the delay time T are performed only on the basis of the difference between the outside air temperature and the fuel tank internal temperature. 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, since the fuel tank is usually made of metal, and the heat transfer coefficient between the gas in the tank upper liquid level space and the tank wall surface is relatively large, the temperature change of the gas in the tank is due to heat exchange with the outside air through the tank wall surface. It will be greatly affected. 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 has a rectangular parallelepiped shape 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 represented by F = B / A, the above formula becomes AW / V = (A (1-F) * (C + D) + C * D) / A * (1-F) * C * D. 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 can be seen 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 is large, so that even if the pressure drop width P1 and the pressure drop required 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 closed holding time T2 is the same, the temperature in the fuel tank at the end of the negative pressure closed holding becomes high and the temperature rise width at the time of negative pressure closed becomes low. On the other hand, when the amount of remaining fuel is large and the amount of heat exchange with the outside air per unit volume of gas is large, the temperature inside the fuel tank approaches the outside air temperature in a short time after the negative pressure is closed. Becomes larger, and the rate of change in fuel tank internal pressure also increases accordingly.

Therefore, in the present embodiment, the coefficients αP1, αP2, βP1, and βP2 obtained from FIGS. 3 and 4 are corrected according to the fuel tank remaining amount F, and the corrected values are used to make correction coefficients. K1P and K2P are calculated.

That is, in the present embodiment, a value obtained by multiplying each coefficient of αP1, βP1, and αP2, βP2 obtained from FIGS. 3 and 4 by the fuel remaining amount correction coefficient KV1, KV2, (KV1 × αP1), Using (KV1 × βP1) and (KV2 × αP2), (KV2 × βP2), the correction coefficients K1P and K2P in step 1107 of FIG. And K2P = max ((KV2 × αP2), (KV2 × βP2)).

Here, the remaining fuel amount correction coefficients KV1 and KV2
Is a correction coefficient determined according to the remaining fuel amount F, and is set as shown in FIG. 13 in the present embodiment. For example, as described above, as the remaining fuel amount F increases, the heat exchange area per unit volume of gas increases, and even if the pressure drop width P1 and the pressure drop required time T1 are the same, the temperature in the fuel tank at the time of pressure drop is Although it becomes higher, the temperature increase rate in the fuel tank after negative pressure sealing becomes higher. Therefore, in the present embodiment, KV1,
The value of KV2 is set so as to approach 1 in a region where the fuel remaining amount F in the fuel tank is small, and becomes smaller as the fuel remaining amount F increases. In this way, by correcting ΔP1 and ΔP2 according to the remaining fuel amount, it is possible to eliminate the influence of the remaining fuel amount and perform more accurate failure diagnosis.

When the heat exchange area per unit volume of gas changes depending on the remaining amount of fuel, not only the correction of ΔP1 and ΔP2 but also the delay time T until the temperature in the fuel tank stabilizes when the fuel evaporation rate is detected. Change. Therefore, in the present embodiment, the correction coefficients PK1, TK1, TK2, TK3 obtained in step 1123 based on the relationships of FIG. 7 to FIG.
Is corrected according to the correction coefficient KV that is determined according to the remaining amount of fuel, and in step 1125 of FIG. 11, the delay time T is calculated using the following equation instead of the above equation (A).

T = α × (PK1 / KV + TK1 / KV +
TK2 / KV) x TK3 / KV

FIG. 14 is a diagram showing the relationship between the correction coefficient KV and the remaining fuel amount F. As shown in FIG. 14, the correction coefficient K
The value of V approaches 1 in the region where the remaining fuel amount is small, and becomes smaller as the remaining fuel amount F increases, similar to the change in FIG. 13. In this way, by correcting the delay time T of the fuel evaporation rate detection based on the remaining fuel amount as well, it is possible to perform accurate failure diagnosis without the influence of the remaining fuel amount on the fuel evaporation rate.

[0117]

According to the invention described in each of the claims, when the failure diagnosis of the evaporative purge system is performed based on the internal pressure increase rate at the time of closing the negative pressure of the purge system, the fluctuation of the tank internal pressure due to the temperature change in the fuel tank is detected. There is a common effect that the failure diagnosis can be performed accurately without being affected.

[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 showing a relationship between a pressure decrease width P1 and correction coefficients αP1 and αP2.

FIG. 4 is a pressure reduction required time T1 and correction coefficients βP1 and βP.
It is a figure which shows the relationship of 2.

FIG. 5 is a diagram illustrating an abnormality determination map based on an internal pressure increase rate.

FIG. 6 is a diagram illustrating an internal pressure increase curve (FIG. 6 (A)) when there is no leakage in the purge system and an internal pressure increase curve (FIG. 6 (B)) when there is leakage.

FIG. 7 is a diagram illustrating an example of setting a fuel evaporation rate detection delay time according to the present invention.

FIG. 8 is a diagram illustrating an example of setting a fuel evaporation rate detection delay time according to the present invention.

FIG. 9 is a diagram illustrating an example of setting a fuel evaporation rate detection delay time according to the present invention.

FIG. 10 is a diagram illustrating an example of setting a fuel evaporation rate detection delay time according to the present invention.

FIG. 11 is a flowchart illustrating an embodiment of a failure diagnosis operation by the evaporation purge system failure diagnosis apparatus of the present invention.

FIG. 12 is a diagram illustrating a change in heat exchange of gas in the fuel tank through the wall surface of the fuel tank depending on the remaining fuel amount.

FIG. 13 is a diagram illustrating setting of a correction coefficient for the internal pressure increase rate when a leak is detected based on the remaining fuel amount.

FIG. 14 is a diagram illustrating setting of a correction coefficient for the fuel evaporation rate based on the remaining fuel amount.

[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) 3G044 BA22 CA03 CA13 DA02 DA09                       EA55 FA02 FA14 FA15 FA23                       GA02 GA04 GA08 GA11 GA22

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 including a passage, the internal pressure of the purge system including the fuel tank, canister, vapor passage, and purge passage is reduced to close the purge system after reaching a predetermined negative pressure, and the negative pressure is closed. Of the evaporative purge system, which comprises a leak detecting means for detecting an increase rate of the internal pressure of the purge system, and a determining means for determining the presence or absence of a failure of the evaporative purge system based on the increase rate of the internal pressure of the purge system detected by the leak detecting means. In the failure diagnosis device, the outside air temperature and the fuel tank when the internal pressure of the purge system reaches the predetermined negative pressure by the leak detection means. Compensation means for compensating the purge system internal pressure increase rate detected by the leak detection means based on the difference with the internal temperature is provided, and the determination means is based on the purge system internal pressure increase rate corrected by the compensation means. A failure diagnostic device for the evaporative purge system that determines whether or not there is a failure in the purge system. 2. The correction means corrects the detected increase rate of the internal pressure of the purge system such that the increase rate of the internal pressure of the purge system decreases as the difference between the outside air temperature and the internal temperature of the fuel tank increases. 1. A failure diagnostic device for the evaporative purge system according to 1. 3. The leak correction means detects the leak based on the difference between the outside air temperature and the temperature inside the fuel tank, and further based on the space volume above the liquid level in the fuel tank when the leak is detected. The failure diagnosis device for an evaporative purge system according to claim 1, which corrects an increase rate of the internal pressure of the purge system. 4. The correction means, when the internal pressure of the purge system is reduced to the predetermined negative pressure by the leak detection means, at least one of a pressure decrease width and a required time until the predetermined negative pressure is reached. The failure diagnosis device for the evaporative purge system according to claim 1, wherein the difference between the outside air temperature and the fuel tank temperature is estimated based on the above. 5. The purge means detected by the leak detecting means based on the remaining amount of fuel in the fuel tank when the leak is detected, in addition to the difference between the outside air temperature and the temperature inside the fuel tank. The system pressure rising rate is corrected,
A failure diagnostic device for the evaporative purge system according to item 1.