JP2002310009A - Failure diagnosing device for evaporative emission purging system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correctly diagnose a purging system while shortening a purge interruption time. SOLUTION: A pressure rising speed ΔPL in the purging system is measured by a pressure sensor 33 in a state that the purging system composed of a canister 10, a fuel tank 11 and the like is sealed under negative pressure, and the normality of the purging system is determined when the ΔPL is below a determination value. When the ΔPL is above the predetermined value, the pressure rising speed ΔPV1 in the system is measured in a state that the purging system is sealed under atmospheric pressure, the determination is suspended when the ΔPV1 is above the predetermined determination value, and a pressure rising speed ΔPV2 in the system is measured again only when the ΔPV1 is below the predetermined value. When the ΔPV2 is above the predetermined value, the determination is suspended, and the abnormality of the purging system is determined only when both of ΔPV1 and ΔPV2 are below the predetermined value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an evaporative fuel emission control device (evaporation purge system) for preventing evaporative fuel from being released from the fuel tank into the atmosphere, and more particularly, to a canister, a fuel tank, and connecting pipes thereof. The present invention relates to a failure diagnosis device for an evaporative purge system for determining whether there is an abnormality such as leakage or perforation of a purge system including the above.

[0002]

2. Description of the Related Art In order to prevent the fuel vapor from a fuel tank from being released into the atmosphere, the fuel vapor from the tank is led to a canister containing an adsorbent such as activated carbon to adsorb fuel vapor onto the adsorbent. An evaporative purge system for preventing the release of fuel vapor to the atmosphere is generally known. In an evaporative purge system, purge air is usually passed through a canister under predetermined operating conditions of the engine to desorb absorbed fuel vapor from the adsorbent, and a mixture of purge air and desorbed fuel vapor (purge gas). Is supplied to the engine intake passage to be burned by the engine.

In such an evaporative purge system, when a failure of the apparatus, particularly a leakage of a purge system including a canister, a fuel tank, and a pipe connecting these, a failure such as a perforation, and the airtightness cannot be maintained, the fuel vapor is generated. It is released to the atmosphere without being supplied to the engine, and may cause air pollution. Further, even when such a failure of the evaporative purge system occurs, the operation of the engine is not hindered at all, and the driver may continue the engine operation without noticing the occurrence of the abnormality.

[0004] In order to solve the above problem, various failure detection devices have been devised which detect the occurrence of a failure in the evaporative purge system and notify the driver of the occurrence of the failure. For example, as an example of this type of apparatus, see Japanese Unexamined Patent Application Publication No.
There is one described in US Pat. The device disclosed in the publication is a system in which a vehicle equipped with an engine is stopped, and when the engine is idling, first, a purge control valve provided in a purge pipe connecting a canister and an intake passage is closed. After the internal pressure of the purge system becomes equal to the atmospheric pressure, the shut-off valve arranged in the air introduction passage of the canister is closed to close the internal pressure of the purge system at the atmospheric pressure. Then, the increase width of the purge system internal pressure within a predetermined time under the atmospheric pressure closed state is measured. The increase width of the purge system internal pressure at this time is a value representing the fuel evaporation rate.

After the measurement of the fuel evaporation rate is completed, the purge control valve is opened while the canister is kept off from the atmosphere, and the negative pressure in the intake passage is introduced into the purge system to reduce the internal pressure of the purge system to a predetermined negative pressure. The purge pressure is reduced to a predetermined pressure, and the purge control valve is closed in a state where the predetermined negative pressure is reached, and the purge system is closed again. Then, the purge system internal pressure rise width within a predetermined time in the negative pressure closed state is measured, and the purge system internal pressure rise width in the atmospheric pressure closed state and the purge system internal pressure rise width in the negative pressure closed state measured as described above are measured. The presence or absence of an abnormality in the purge system is determined based on the above.

That is, the increase in the internal pressure of the purge system in the negative pressure closed state is leaked to the purge system, and if there is no hole, it is caused only by evaporation of the fuel in the fuel tank. On the other hand, if there is an abnormality such as leakage or perforation in the purge system,
The atmosphere enters the purge system through leaks, holes, etc.
The increase width of the purge system internal pressure is larger than in the case where only the fuel is evaporated.

Further, in the measurement of the rise in the internal pressure of the purge system in the closed state of the atmospheric pressure performed before the measurement of the internal pressure in the closed state of the negative pressure,
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, and the like is small. For this reason, the increase width of the purge system internal pressure in the closed state of the atmospheric pressure is substantially caused only by the evaporation of the fuel.

In the apparatus disclosed in the above-mentioned publication, when the internal pressure increase width within a predetermined time in the negative pressure closed state of the purge system is larger than the increase width in the atmospheric pressure closed state (ie, the fuel evaporation rate) by a certain degree or more, In this case, it is determined that an abnormality such as leakage to the purge system or perforation has occurred.

[0009]

However, in the failure diagnosis apparatus disclosed in Japanese Patent Application Laid-Open No. 5-125997, the purge system must be closed at atmospheric pressure before measuring the rise in internal pressure of the purge system under negative pressure. This may cause a problem because it is necessary to measure the internal pressure rise. That is, in order to seal the purge system, it is necessary to close the purge control valve irrespective of negative pressure sealing or atmospheric pressure sealing. For this reason, the purge control valve cannot be opened and the canister cannot be purged during the failure diagnosis with the purge system closed.

Therefore, as in the apparatus disclosed in the above publication, both the measurement of the fuel evaporation rate by sealing the purge system at atmospheric pressure and the measurement of the increase in internal pressure by sealing the negative pressure of the purge system are always performed at the time of failure diagnosis. In this case, there is a problem in that the purge interruption time for the failure diagnosis becomes long, and the purge of the fuel vapor from the canister becomes insufficient.

[0011] In order to solve this problem, for example, during the operation of the engine, first, the internal pressure rise is measured by sealing the negative pressure of the purge system, and only when the measured increase in the internal pressure is large, the atmospheric pressure of the purge system is closed. It is also possible to measure the fuel evaporation rate by the following method. For example, when the internal pressure rise is large due to the negative pressure sealing of the purge system, the internal pressure rise becomes large because the purge system is actually leaking. And the case where the internal pressure rise is large due to the high evaporation rate of
There are two cases. For this reason, it is necessary to actually measure the fuel evaporation rate to determine whether the increase in the internal pressure is due to leakage or the fuel evaporation rate.

However, the rise of the internal pressure when the purge system negative pressure is closed is small only when no leak occurs in the purge system and the evaporation speed of the fuel is low. Can determine that the purge system is normal without measuring the fuel evaporation rate. Therefore, in such a case, the measurement of the fuel evaporation rate can be omitted to shorten the purge interruption time for failure diagnosis. For this reason, the internal pressure rise is first measured during the operation of the engine when the negative pressure of the purge system is closed. If the internal pressure rise is small, the purge system is immediately judged to be normal and the fuel evaporation rate is not measured. If the measurement of the fuel evaporation rate by closing the purge system at atmospheric pressure is performed only after the internal pressure rise measurement is completed, the frequency of the actual measurement of the fuel evaporation rate will be considerably reduced, and the failure judgment will be made. In many cases, it is possible to reduce the purge interruption time for cleaning.

However, actually, when the purge system is closed under negative pressure and the internal pressure rise is measured, and then the fuel vaporization rate is measured by increasing the pressure to near the atmospheric pressure, the measurement is performed even if the fuel temperature in the fuel tank is the same. It has been found that the evaporation rate varies. Further, it has been found that this variation is related to the variation in the internal pressure of the purge system before measuring the increase in the internal pressure by closing the purge system with a negative pressure, that is, before starting the introduction of the negative pressure to the purge system. I have.

Originally, the fuel evaporation rate depends only on the purge system internal pressure and the fuel temperature at the time of measurement, and if the internal pressure and the fuel temperature are constant, the fuel evaporation rate should be the same. However, when the pressure in the purge system is once maintained at a negative pressure and then raised to near the atmospheric pressure for measuring the fuel evaporation rate, it is necessary to introduce outside air into the purge system. Usually, the introduction of outside air to the purge system is performed through a canister. However, when air passes through the canister, the fuel vapor adsorbed by the adsorbent in the canister is desorbed and flows into the purge system together with the air, so-called back purge occurs.

On the other hand, in the purge system, fuel vapor generated by evaporating the fuel in the fuel tank while the internal pressure is being measured already exists. Therefore, when fuel vapor further flows into the purge system due to back purge from the canister, the fuel vapor pressure in the system is saturated depending on the amount of fuel vapor existing in the purge system and the amount of fuel vapor flowing through the back purge. In some cases, the vapor pressure may be reached. As described above, when the fuel vapor pressure in the system reaches the saturated vapor pressure due to the back purge, the fuel vapor condenses and liquefies in the system, and the pressure in the system is reduced by the liquefied fuel vapor. Will decrease.

Condensation of the fuel vapor by the back purge is more likely to occur when air is introduced into the purge system, that is, when the fuel vapor pressure in the purge system at the end of the internal pressure rise measurement due to negative pressure sealing is closer to the saturated vapor pressure, The pressure drop also increases. However, as described later, it has been found that the fuel vapor pressure in the purge system at the end of the internal pressure rise measurement varies not only with the fuel temperature but also with the purge system internal pressure at the time when the introduction of the negative pressure into the purge system starts. ing. On the other hand, before starting the introduction of the negative pressure, purging is normally performed, and the internal pressure of the purge system is a pressure determined by the intake passage pressure of the engine and the opening of the purge control valve. That is, the internal pressure of the purge system before the start of the introduction of the negative pressure changes according to the operating state of the engine and is not constant. For this reason, if the fuel evaporation rate is measured after the measurement of the internal pressure rise, the measurement result does not match the true fuel evaporation rate, causing a variation.

As described above, when the pressure in the system is increased to near atmospheric pressure and the fuel evaporation rate is measured after measuring the internal pressure rise while the purge system is closed under negative pressure, the fuel evaporation rate is measured to be smaller than the actual one. Therefore, there is a possibility that an erroneous diagnosis in which the purge system is determined to be abnormal, even though the purge system does not actually leak, may occur. For this reason, conventionally, performing the fuel evaporation rate after measuring the internal pressure rise due to the negative pressure sealing of the purge system lowers the reliability of the diagnosis result, although the purge interruption time can be reduced. There was a problem that could not be adopted.

SUMMARY OF THE INVENTION In view of the above problems, the present invention provides a failure diagnosis of an evaporative purge system which can perform an accurate abnormality diagnosis while measuring a fuel evaporation rate after measuring an internal pressure rise due to a negative pressure sealing of a purge system. The device is intended to provide.

[0019]

According to the present invention, a canister for adsorbing evaporated fuel in a fuel tank of an internal combustion engine, a vapor passage connecting a space above a fuel level in the fuel tank to the canister, A failure diagnosis device for an evaporative purge system including a purge passage connecting a canister and an engine intake passage, wherein the purge system including the fuel tank, the canister, the vapor passage, and the purge passage is hermetically closed and the purge system internal pressure is reduced. A rise in the internal pressure of the purge system after adjusting to a predetermined negative pressure is measured, and if the increase in the internal pressure of the purge system is larger than a predetermined reference value, the fuel after the internal pressure of the purge system is increased to a predetermined pressure. While detecting the evaporation rate of the fuel in the tank, it is determined whether the detected fuel evaporation rate is smaller than a predetermined value, and the detected fuel evaporation rate is Only when the fuel evaporation rate is smaller than the predetermined value, the fuel evaporation rate is continuously detected again, and only when the fuel evaporation rate detected again is smaller than the predetermined value, it is determined that an abnormality has occurred in the purge system. A failure diagnosis device is provided.

That is, in the present invention, the purge system is closed at a negative pressure and the internal pressure rise is measured. Only when the internal pressure rise is large, the internal pressure of the purge system is adjusted to near atmospheric pressure after the measurement of the internal pressure rise, and the fuel evaporation rate is measured. Is measured. As a result of the first measurement of the fuel evaporation rate, if the fuel evaporation rate is larger than the predetermined value, it can be determined that the fuel evaporation rate at the time of the measurement of the increase in the internal pressure is large irrespective of the variation, so that the abnormality determination is not performed. If the fuel evaporation rate is lower than the predetermined value in the first measurement, it is determined whether the fuel evaporation rate during the internal pressure rise measurement is actually low or the measurement result is small due to back purge from the canister. I can't judge. Therefore, if the first measurement result of the fuel evaporation rate is smaller than the predetermined value, the second fuel evaporation rate measurement is continuously performed. Condensation of the fuel vapor flowing in by the back purge occurs in a short time. For this reason, when a certain period of time has elapsed after the purge system is closed and there is no more fuel vapor newly flowing in, the condensation of the fuel vapor has ended even if the condensation of the fuel vapor has occurred. Therefore, in the second fuel evaporation rate measurement performed after the end of the first fuel evaporation rate measurement, the measurement result is a value close to the fuel evaporation rate at the time of the internal pressure rise measurement. For this reason, if the speed measurement result is smaller than the predetermined value during the second fueling, it is determined that an abnormality such as leakage has occurred in the purge system.

In the present invention, first, when the internal pressure rise at the time of the negative pressure sealing is small, the normal judgment is immediately made, so that the subsequent measurement of the fuel evaporation rate can be stopped. When the internal pressure rise is large, the first measurement of the fuel evaporation rate is performed after the internal pressure rise measurement is completed. However, when the evaporation rate is large in the first fuel evaporation rate measurement, the fuel evaporation rate at the time of the internal pressure rise measurement is measured. No abnormality diagnosis is performed because the evaporation rate can be estimated to be high. In this case, since the second measurement of the fuel evaporation rate is not performed, the second measurement of the fuel evaporation rate is performed because the internal pressure rise is large and the first fuel evaporation rate measurement result is smaller than a predetermined value. Only when.

In the second measurement of the fuel evaporation rate, the influence of the variation and the like is reduced, so that the accurate fuel evaporation rate is measured and the diagnostic accuracy is improved. The probability is extremely low except when the purge system is truly abnormal, and in most cases, the normality is determined before the second fuel evaporation rate measurement, or the failure diagnosis is stopped. For this reason, in fact, there is a higher probability that the purge interruption time is reduced as compared with the case where the fuel evaporation rate is measured for each failure diagnosis. Thus, in the present invention, the purge interruption time is reduced in most cases without reducing the failure diagnosis accuracy.

[0023]

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 evaporative purge system for a vehicle. In FIG. 1, reference numeral 1 denotes an intake passage of an internal combustion engine (not shown), and reference numeral 3 denotes an air cleaner arranged in the intake passage 1. The intake passage 1 is provided with a throttle valve 6 having an opening in accordance with an operation of an accelerator pedal (not shown) by a driver. Reference numeral 11 in FIG. 1 denotes a fuel tank of the engine. The fuel oil in the tank 11 is pressurized by a fuel pump 70 and is fed to a fuel injection pump (not shown) of the engine through a feed pipe 71. Also, the fuel pump 70
Among the fuel pumped from the fuel tank, the fuel not injected into the engine from the fuel injection valve is returned to the fuel tank 11 through the return pipe 73.

The fuel tank 11 is provided with a fuel supply pipe 111 for refueling the tank. Also, tank 1
A vapor pipe 12 and a breather pipe 13 that connect a space above the fuel oil level in the tank 11 to a canister 10 described later are connected to an upper portion of the tank 1. In FIG. 1, reference numeral 121 denotes a COV (CUT OF) comprising a float valve disposed at a connection between the vapor pipe 12 and the tank 11.
F VALVE), 123 is a check valve. C
The OV 121 prevents the fuel oil from entering the vapor pipe 12 by closing the vapor pipe 12 when the liquid level in the fuel tank 11 reaches the connection of the vapor pipe 12 when the vehicle turns. It is. In addition, the check valve 123
For example, when the pressure in the fuel tank 11 becomes higher than the pressure in the vapor pipe 12 by a predetermined value or more when the COV 121 or the like is stuck at the valve closing position, the valve is opened to release the pressure in the tank to the vapor pipe 12. belongs to.

The connecting portion between the breather pipe 13 and the tank 11 has a differential pressure valve 131 and an RO
V (ROLL OVER VALVE) 133 is provided. The differential pressure valve 131 includes a diaphragm 131a urged in a direction to close the breather pipe 13 opening, and a pressure chamber 131b provided on the opposite side of the diaphragm 131a from the breather pipe opening.
1b communicates with the upper part of the oil supply pipe 111 via a pipe 111a. When the fuel oil is injected through the oil supply pipe during refueling, a negative pressure is generated in the pipe 111a due to the entrainment by the flow of the fuel oil, so that the pressure in the pressure chamber 131b is negative. On the other hand, the pressure above the fuel level in the tank 11 rises due to the rise in the liquid level due to the flowing fuel. For this reason,
The diaphragm 131a of the differential pressure valve 131 is a pressure chamber 131b.
And the opening of the breather pipe 13 is opened. For this reason, when the pressure rises rapidly during refueling or the like, the fuel tank 1
The space above the liquid surface in 1 communicates with the atmosphere via the canister 10, so that an excessive increase in pressure in the fuel tank 11 is prevented. Also, the ROV 133 closes the connection between the breather pipe 13 and the tank 11 when the vehicle falls, etc.
This prevents a large amount of fuel oil from leaking outside through the breather pipe 13.

In FIG. 1, reference numeral 30 denotes an electronic control unit (ECU) of the engine. The ECU 30 includes a microcomputer having a known configuration in which a ROM (read only memory), a RAM (random access memory), a CPU (microprocessor), and an input / output port are connected to each other via a bidirectional bus. In addition to performing the basic control described above, the present embodiment performs a failure diagnosis of the evaporative purge system described later.

For the above control, an output port of the ECU 30 is connected to a fuel injection valve of the engine via a drive circuit (not shown) to control the fuel injection amount from the fuel injection valve.
Actuators 15a, C of the purge control valve 15 described later
CV (CANISTER CLOSURE VALV)
E) 17 actuator 17a, bypass valve 20
Are connected to control valves around the canister 10, such as the actuator 20a, and control the operation of these control valves. The input port of the ECU 30 receives signals representing the engine speed, the intake air amount, the engine coolant temperature, etc. from sensors (not shown), and a pressure sensor 33 provided above the fuel tank 11. A signal representing the pressure in the upper space of the fuel level in the tank from is input through an A / D converter (not shown).

In FIG. 1, reference numeral 10 denotes a canister for adsorbing fuel vapor in a fuel tank. The canister 10 is connected to a space above the fuel level of the fuel tank 11 by a vapor pipe 12, and to a portion of the intake passage 1 on the downstream side of the throttle valve 6 by a purge pipe 14. Reference numeral 15 in FIG. 1 denotes a purge control valve 15 that opens and closes the purge passage 14. The purge control valve 15 is opened in response to a signal from the ECU 30, and purges the canister 10 by communicating the canister 10 with a portion of the intake passage 1 downstream of the throttle valve 6. The reference numeral 15a in FIG.
, And an appropriate type of actuator such as a solenoid or a negative pressure actuator.

Next, the structure of the canister 10 of the present embodiment will be described. The canister 10 is a housing 10a
And an evaporative fuel adsorbent 50 such as activated carbon filled in the housing. In the housing 10a,
A partition 10b extending from an upper portion of the housing is provided, and divides the inside of the housing 10a into a main chamber 10c and a sub chamber 10d. The adsorbent 50 is filled between two holding plates 50a and 50b made of a permeable material such as a filter material and a perforated plate provided in the main chamber 10c and the sub chamber 10d, respectively. Lower end of partition 10b, main room 10c, sub room 1
A space 10e is formed below the lower holding plate 50b in Od.

The upper space 10f of the upper holding plate 50a in the main chamber 10c of the housing 10a is connected to the vapor passage 12 via the internal pressure control valve 16 and the equalizing valve 21. The upper space 10g of the upper holding plate 50a of the sub chamber 10d.
Is connected to the air cleaner 3 via an atmosphere introduction pipe 18e via an atmosphere valve 18 and communicates with the atmosphere via an atmosphere release valve 19.

The internal pressure control valve 16 opens when the internal pressure of the fuel tank 11 becomes higher than the atmospheric pressure by a predetermined pressure, and connects the canister 10 to the fuel tank 11. In addition, equalizing valve 2
The valve 1 opens when the internal pressure of the fuel tank 11 becomes lower than the internal pressure of the canister 10 by a predetermined pressure, and similarly connects the canister 10 and the fuel tank 11. On the other hand, the atmosphere valve 18
The valve opens when the pressure inside the canister 10 becomes lower than the atmospheric pressure by a predetermined pressure, and the inside of the canister 10 communicates with the atmosphere via the atmosphere introduction pipe 18e and the air cleaner 3. Also,
On the other hand, when the internal pressure of the canister 10 becomes higher than the atmospheric pressure by a predetermined pressure, the atmosphere release valve 19 communicates the inside of the canister 10 with the atmosphere to prevent an excessive rise in the pressure of the canister 10.

Next, the function of the canister 10 in this embodiment will be described. When the pressure in the fuel tank 11 rises and reaches the opening pressure of the internal pressure control valve 16 during the closing of the purge control valve 15 on the purge passage 14 connecting the canister 10 and the intake passage 1, the internal pressure control valve 16 Open the valve. As a result, a mixture of fuel vapor and air flows from the space above the liquid surface of the fuel tank 11 through the vapor pipe 12 to the main chamber 10.
c, passes through the adsorbent 50 in the main chamber, passes through the lower space 10e, passes through the adsorbent 50 in the sub-chamber 10d, and is released from the atmosphere release valve 19 to the atmosphere. From 19, only the air after the fuel vapor is removed by the adsorbent 50 in the main chamber 10c and the sub chamber 10d is released. Therefore, the internal pressure of the fuel tank 11 is maintained at or below the valve opening pressure of the internal pressure control valve 16, and the release of evaporated fuel to the atmosphere is prevented.

When the purge control valve 15 is opened during operation of the engine, a negative pressure on the downstream side of the throttle valve 6 in the intake passage 1 acts on the canister 10 via the purge passage 14, and the canister internal pressure is reduced. Becomes lower than atmospheric pressure. Therefore, when the purge control valve 15 is opened, the atmosphere valve 18 is opened, and clean air flows into the canister 10 from the atmosphere introduction pipe 18e. This air releases the evaporated fuel adsorbed from the adsorbent 50 in the sub-chamber 10d and the main chamber 10c, becomes a mixed gas (purge gas) of the evaporated fuel and air, flows into the engine intake passage 1 from the purge passage 14, and enters the engine. Burns in the combustion chamber. This prevents the adsorbent 50 from being saturated with the fuel vapor.

Further, after the engine stops, the fuel temperature in the fuel tank 11 decreases, and the pressure in the tank 11 decreases
When the pressure becomes lower than the zero pressure by a predetermined pressure, the pressure equalizing valve 21 is opened, and the fuel tank 11 communicates with the inside of the canister 10 via the vapor pipe 12. Thereby, the fuel tank 1
The pressure difference between the internal pressure 1 and the internal pressure of the canister 10 is equalized by the pressure equalizing valve 2
It is kept below the valve opening differential pressure of 1. Here, canister 1
Since the internal pressure of the fuel tank 11 does not drop below the atmospheric pressure by a predetermined pressure or more by the atmospheric valve 18, the internal pressure of the fuel tank 11 is maintained at a pressure near the atmospheric pressure by the equalizing valve 21 and the atmospheric valve 18. In the present embodiment, the canister 10 and the air cleaner 3 are used to diagnose the failure of the evaporation purge system.
The CCV 17 is provided in the atmosphere introduction pipe 18e connecting the air passage and the bypass passage 20e and the bypass valve 20 connecting the space 10f above the holding plate 50a of the sub chamber 10d of the canister 10 and the vapor pipe 12 are provided. .

CCV17 is a solenoid actuator,
An appropriate type of actuator 17a such as a negative pressure actuator is provided, and when performing a failure diagnosis of the evaporative purge system, the valve is closed by a signal from the ECU 30, and together with the purge control valve 15, the canister 10, the pipes 12, 13, 14,
20, the purge system including the fuel tank 11 and the like is maintained in a closed state. The bypass valve 20 includes an actuator 20a similar to the CCV 17, and is opened by a signal from the ECU 30 when the failure diagnosis of the evaporative purge system is completed, so that the air flowing from the air introduction passage 18e is supplied to the sub chamber 10a.
d Directly lead to the vapor pipe 12 from the upper space to reduce the time required for the internal pressure of the fuel tank 11 to return to near atmospheric pressure. This makes it possible to restart the purge in a short time after the failure diagnosis ends.

Next, a failure diagnosis method for the evaporative purge system according to the present invention will be described. In the present invention, when a predetermined purge execution condition is satisfied after the engine operation is started and the purge is being performed, the purge system is placed in a negative pressure closed state, and the internal pressure rise rate is measured. During the execution of the purge, the purge control valve 15 is opened, and the negative pressure of the intake passage 1 is acting on the canister 10 via the purge passage 14. However, since the CCV 17 is opened, the housing 10a of the canister The inside communicates with the atmosphere through an atmosphere introduction pipe 18e, and the pressure in the housing 10a, the vapor pipe 12, and the fuel tank 11 is maintained at a pressure determined by the intake passage pressure and the opening degree of the purge control valve 15. In this state, when the CCV 17 is closed, the inflow of air from the atmosphere introduction pipe 18e stops, and the canister 10 and the fuel tank 1 communicating with the canister are stopped.
1. The internal pressure of the purge system such as the vapor pipe 12 decreases. When the purge control valve 15 is closed when the pressure in the purge system has sufficiently decreased, the purge system is closed in a negative pressure state. When the purge system is closed, the purge system internal pressure starts to increase due to the evaporation of the fuel in the purge system internal pressure fuel tank 11. In the present invention, a predetermined time (for example, 5 seconds) after the internal pressure of the purge system reaches a predetermined negative pressure (for example, a pressure of about -15 mmHg) due to an increase in the pressure while the purge system is maintained in the negative pressure closed state as described above. The degree of increase in the internal pressure of the purge system is measured.

In this state, the purge system internal pressure rise width (rise speed) is relatively gradual since the fuel in the fuel tank 11 only evaporates if there is no leakage or perforation in the purge system. However, if the purge system is leaked or perforated, air enters the system from the outside through the leaked portion, so that the pressure increase width (speed) is larger than that in the case where only the fuel is evaporated. Therefore, the pressure increase in the purge system when the negative pressure is sealed (hereinafter, “leakage detection”
If the internal pressure rise rate measured in
An abnormality such as leakage may occur in the purge system.

However, the purge system internal pressure increasing speed at the time of detection of a leak increases when the fuel evaporation speed during the detection of the leak is high, even if the purge system does not leak. For this reason, it is not possible to determine whether the internal pressure increasing speed has increased due to leakage or the internal pressure increasing speed has increased due to the high fuel evaporation speed, simply by increasing the internal pressure increasing speed at the time of leak detection.

Therefore, in the present embodiment, when the internal pressure rise rate at the time of leak detection is higher than a predetermined value, after the leak detection is completed, the CCV 17 is opened and the atmosphere is introduced while the purge control valve 15 is kept closed. Then, the purge system internal pressure is increased to near the 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 keep the inside of the purge system at atmospheric pressure. In this atmospheric pressure closed state, even if a leak occurs in the purge system, the atmosphere does not enter the purge system because the differential pressure between the purge system internal pressure and the atmosphere is small. For this reason, the increase in the internal pressure of the purge system that occurs in the closed state of the atmospheric pressure is caused only by the evaporation of the fuel in the fuel tank 11. Therefore, the purge system is closed in the atmospheric pressure state for a predetermined time (for example, 15 hours).
The fuel evaporation rate can be measured by detecting the increase width of the purge system internal pressure in about 2 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 the internal pressure is equal to or greater than a predetermined value in the leak detection operation. For this reason, when the fuel evaporation rate is low, it can be determined that the increase in the internal pressure during the leak detection operation is due to the fact that a leak has actually occurred in the purge system. Further, when the fuel evaporation rate is high, the increase in the purge system internal pressure upon detection of the leak may have occurred due to the high fuel evaporation rate, so it cannot always be determined that the leak has occurred in the purge system. Therefore, the determination of the presence or absence of leakage is suspended and the abnormality diagnosis is stopped.

However, actually, when the fuel evaporation rate is measured after the leak detection is performed in the negative pressure sealed state, depending on the internal pressure of the purge system at the start of the leak detection, the pressure from the canister when the atmosphere is introduced into the purge system is determined. Due to the back purge, the measurement result of the fuel evaporation rate may be smaller than the true fuel evaporation rate.

Hereinafter, other problems will be described in detail with reference to FIGS. FIG. 2 is a diagram schematically showing a change in the pressure in the purge system at the time of the above-described failure diagnosis. FIG. 2, (A),
2 (B) shows a case where there is no leakage in the purge system, FIG. 2 (A) shows a case where the pressure in the system at the start of introduction of the negative pressure is near atmospheric pressure, and FIG. The cases where the pressure is low at around -20 mmHg are shown. FIG.
(A), as shown in FIG. 2 (B), in both cases, the pressure in the system decreases with the start of negative pressure introduction (negative pressure introduction period),
When the pressure drops to a predetermined negative pressure (−20 mmHg) and the purge system is in a negative pressure sealed state, the pressure in the system gradually increases due to evaporation of fuel (leakage detection period). Then, after the end of the leak detection period, when the atmosphere is introduced from the canister, the pressure in the system rises sharply (pressure rising period), and when the pressure becomes close to the atmospheric pressure, the CCV 17 is closed and the system is hermetically sealed at the atmospheric pressure. .

In this state, the pressure in the system increases again due to the evaporation of the fuel (fuel evaporation rate measurement period),
When the negative pressure is introduced from the vicinity of mHg (FIG. 2 (B)), the pressure increase in the system during the fuel evaporation measurement period (ΔP) is lower than when the negative pressure is introduced from the atmospheric pressure (FIG. 2 (A)).
V ₁ ) is smaller. As described above, the rise in the system pressure during the fuel evaporation measurement period is changed by the system pressure at the start of the introduction of the negative pressure because the fuel vapor pressure in the system at the start of the fuel evaporation measurement period is at the start of the introduction of the negative pressure. This is considered to be due to the change due to the system pressure.

FIG. 3 is a diagram for explaining the effect of the internal pressure at the start of the introduction of the negative pressure on the change in the fuel vapor pressure after the introduction of the negative pressure. FIG. 3A is a diagram illustrating a case where the introduction of the negative pressure from the atmospheric pressure is started (FIG. 2A). Before the introduction of the negative pressure, the pressure in the system is near the atmospheric pressure. From this state, the pressure in the system is reduced by -20 mm from atmospheric pressure by introducing negative pressure.
It is assumed that the pressure has decreased to Hg and then increased to the atmospheric pressure again. Also, it is assumed that the fuel temperature does not change and the saturated vapor pressure of the fuel is kept constant during this time.

Each bar graph of a, b, and c in FIG.
The pressures in the system before the introduction of the negative pressure, at the start of the negative pressure sealing, and at the start of the fuel evaporation rate measurement, respectively. Note that FIG.
In (A), to simplify the explanation, the atmospheric pressure is set to 100,
The pressure at the start of the negative pressure sealing is represented as 20, and the proportional relationship with the actual pressure is ignored. A of FIG.
Assuming that the fuel temperature does not change in b and c, the saturated vapor pressure of the fuel in these three cases becomes constant. In FIG. 3A, this saturated vapor pressure is tentatively set to 30 for the atmospheric pressure of 100 (a value irrelevant to the actual fuel saturated vapor pressure).

Before the introduction of the negative pressure, the system is in an equilibrium state, so that the system pressure at this time is 100, and the partial pressure of the fuel vapor is 30 (the shaded portion in FIG. 3A). When negative pressure is introduced from this state, the air and fuel vapor in the system are discharged from the purge control valve at the same ratio. Therefore, if the pressure in the system is reduced to 20 after the introduction of the negative pressure, the partial pressure of the fuel vapor in the system at this time is 30 × (20/100)
= 6 (the shaded portion in FIG. 3A). Further, air is introduced into the system from this state, and the pressure in the system becomes 1
When the pressure returns to 00 (atmospheric pressure), if only air is introduced into the system, there is no change in the partial pressure of the fuel vapor, so the fuel vapor partial pressure remains the same as b (6 in FIG. 3 ( A) c
Shaded area).

The measurement of the fuel evaporation rate is performed in the state of c. In this state, a relatively large difference (30-6) between the actual fuel vapor partial pressure (6) and the saturated vapor pressure (30) is obtained. =
24) has occurred. Therefore, in this case, the fuel evaporation rate increases, and the pressure rise rate in the system at the time of measuring the fuel evaporation rate also increases relatively (FIG. 2 (A) ΔPV ₁ ). On the other hand, when the pressure at the start of negative pressure introduction is low (for example, atmospheric pressure
Considering the case where the pressure is 40 with respect to 00), in this case as well, if the inside of the system is in an equilibrium state, the partial pressure of the fuel vapor becomes the saturated vapor pressure of 30 (the oblique line in FIG. 3B). part). Further, when the whole pressure is reduced to 20 at the time of the negative pressure sealing, the partial pressure of the fuel vapor becomes 30 × (20/40) = 15.
(The shaded portion in FIG. 3B). Therefore, the difference between the saturated vapor pressure and the fuel vapor pressure at the start of the fuel evaporation rate measurement is 30
-15 = 15 (FIG. 3B).

That is, when the pressure in the system at the start of the introduction of the negative pressure is low (FIGS. 2B and 3B), it is higher than that when the pressure is high (FIGS. 2A and 3A). Thus, the fuel evaporation rate at the time of measurement becomes small (FIG. 2 (A) ΔPV ₁ ).

Further, as described above, when the internal pressure of the purge system is increased from the closed state of the negative pressure to the atmospheric pressure, the air that has passed through the canister is supplied into the system. In this case, when the back purge occurs, fuel vapor is supplied from the canister into the system, but when the difference between the vapor pressure in the system and the saturated vapor pressure is small (for example, FIG. 3B). In the case (c), the fuel vapor flowing into the system due to the back purge may cause the fuel vapor partial pressure to rise and exceed the saturated vapor pressure. In this case, the fuel vapor exceeding the saturated vapor pressure is condensed into a liquid, so that the pressure in the system at the time of atmospheric pressure sealing is reduced.

Further, when the difference between the vapor pressure in the system and the saturated vapor pressure is small, the fuel evaporation rate is originally small, and the pressure rise during the measurement of the evaporation rate is small. For this reason, when the fuel vapor is saturated by the back purge, a case may occur in which the pressure in the system hardly rises during the measurement of the evaporation rate (FIG. 2B).

In this embodiment, when the internal pressure increase width (increase speed) in the system measured at the time of measuring the fuel evaporation speed is smaller than a predetermined judgment value, it is determined that a leak has occurred in the purge system and an abnormality judgment is made. When the difference between the partial pressure of the fuel vapor and the saturated vapor pressure is sufficiently large, the fuel vapor is not condensed even if the fuel vapor is supplied by the back purge, or the pressure drop becomes small even if the condensation occurs. Therefore, there is no significant influence on the determination. However, in the case where the fuel evaporation rate is actually low, if the fuel vapor is condensed by the back-purge, the measured fuel evaporation rate is actually higher than the determined value even though the fuel evaporation rate is actually larger than the determination value. The value may fall below the determination value due to the condensation of the steam, and the abnormality may be determined even though the abnormality should not actually be determined.

Therefore, in this embodiment, when the fuel evaporation rate measurement result is smaller than the predetermined value, the second fuel evaporation rate measurement is continuously performed without releasing the atmospheric pressure closed state of the purge system. Condensation of the fuel vapor that has flowed in due to the back purge ends in a relatively short time even if it occurs. For this reason, in the second measurement of the fuel evaporation rate, it is possible to measure the accurate fuel evaporation rate while eliminating the influence of the condensation of the fuel vapor.

When the fuel vapor has been condensed, the fuel vapor pressure in the system is close to the saturated vapor pressure at the time when the second fuel evaporation rate measurement is started. It should not evaporate, and it is considered that the internal pressure of the purge system does not increase during the second fuel evaporation rate measurement.
However, actually, the fuel in the fuel tank is gradually rising due to the inflow of high-temperature return fuel from the fuel injection valve. For this reason, the saturated vapor pressure also increases with time, and in fact, even in the second measurement, the pressure in the purge system increases due to a change in the saturated vapor pressure accompanying the increase in the fuel temperature. Also, since the fuel temperature actually rises during the leak detection, the increase in the internal pressure measured at the time of the leak detection is caused by the change in the fuel vapor generated by the pressure change of the entire purge system shown in FIGS. 3 (A) and 3 (B). Both fuel evaporation due to the difference between the pressure and the saturated vapor pressure (fuel evaporation due to pressure change) and fuel evaporation due to the change in saturated vapor pressure caused by temperature change (fuel evaporation due to temperature change) occur. When the pressure at the start of the introduction of the negative pressure is low as in the case of FIG. 3B, the pressure rise caused by the fuel evaporation due to the pressure change is originally small during the leak detection. If the pressure rise during leak detection is large even though there is no leak, it is considered that the pressure rise is due to large fuel evaporation due to temperature change.

As described above, in the second measurement of the fuel evaporation rate, the influence of the fuel evaporation due to the pressure change is reduced.
The fuel evaporation rate due to the temperature change can be measured more accurately.
Therefore, by comparing the result of the second measurement of the fuel evaporation rate with the increase in the internal pressure at the time of detecting the leak, erroneous abnormality determination is prevented.

FIG. 4 is a flowchart for specifically explaining the above-described abnormality diagnosis operation of the purge system according to the present embodiment. This operation is performed as a routine executed by the ECU 30 at regular intervals. In the operation of FIG. 4, first, at step 401, it is determined whether or not the execution condition of the abnormality diagnosis operation is satisfied. The abnormality detection operation execution conditions determined in step 401 include: a. Failure diagnosis of the evaporative purge system has not been completed after the engine is started, b. Purging is currently being performed (purge control valve 15 is open); c. Atmospheric pressure is equal to or higher than a predetermined value, d. For example, the pressure fluctuation in the fuel tank is equal to or less than a predetermined value (for example, the liquid level in the tank is not largely shaken due to running on a slope, turning, or running on a bad road).

The above conditions a. Is to prevent the purge interruption period from being extended by repeating the failure diagnosis because the failure diagnosis operation involves interruption of the purge. This means that the failure diagnosis operation requires opening the purge control valve 15 and introducing a negative pressure into the purge system. This is to prevent adverse effects on the system. The above condition c. And d. Is a condition for preventing noise from being mixed in the measurement result and performing a highly reliable failure diagnosis.

If all of the conditions in step 401 are satisfied, then in step 403 it is determined whether or not the leak detection operation has already been completed, that is, the measurement of the purge system internal pressure increase width ΔPL in the negative pressure closed state is completed. Is determined. If the measurement of ΔPL has already been completed in step 403, the process proceeds directly to the provisional abnormality determination operation in step 407. If not completed, the measurement of the internal pressure increase width ΔPL is performed in step 405 before executing step 407. Is executed.

In step 405, while the purge is being executed (that is, the purge control valve 15 is kept open), C
Close CV17. Thereby, a 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 rapidly decreases. In the present embodiment, the purge control valve 15 is closed when a negative pressure is introduced into the purge system and the pressure in the purge system decreases to a first predetermined pressure (for example, −20 mmHg). Thereby, the purge system is sealed in a negative pressure state. When the purge system is closed,
The purge system internal pressure starts to rise due to evaporation of the fuel in the fuel tank 11. If there is no leakage in the purge system, this pressure rise is caused only by evaporation of the fuel in the fuel tank 11, so that the pressure rise speed is relatively slow, and after a sufficient time has passed, the saturated vapor of the fuel A value determined by pressure is reached. On the other hand, if there is a leak in the purge system, the pressure inside the purge system rises relatively quickly due to air entering from outside the system through the leak, and after a sufficient time has passed, it becomes a pressure near the atmospheric pressure.

In the present embodiment, after the purge control valve 15 is closed and the purge system is closed under negative pressure, timing is started when the pressure in the system reaches a second predetermined pressure (for example, -15 mmHg). Thereafter, the pressure increase width detected by the pressure sensor 33 within a predetermined time (for example, about 5 seconds) is adopted as ΔPL. Therefore, the measured value of ΔPL indicates the rate of pressure rise in the system. As described above, after completing the leak detection operation (measurement of the pressure increase width in the system at the time of closing the negative pressure), in step 407, a temporary determination is made as to whether there is an abnormality in the purge system. Step 4
The tentative decision 07, leakage measured pressure rise in the detection operation (speed)? PL whether the determination value? PL ₀ or less is determined. Here, when ΔPL ≦ ΔPL ₀ , the pressure increase in the system is small, and it can be determined that the purge system does not leak regardless of the fuel evaporation speed.
Then, it is determined that the purge system is normal. When the normality is determined, the purge control valve 15 and the CCV 17 are immediately opened, and the purge of the canister 10 is restarted.

On the other hand, at step 407, ΔPL> ΔPL ₀
In this case, it is necessary to determine the magnitude of the fuel evaporation rate because the internal pressure rises at the time of detection of the leak is large and the leak may actually occur. Therefore, the process proceeds to step 411 in this case, already determined whether the measurement of the fuel evaporation rate Pv ₁ has been completed, the process proceeds directly to step 415 if it is finished. Further, when the measurement of Pv ₁ is not finished the process proceeds to step 413 to perform the fuel evaporation measurements 1st.

In the present embodiment, as described above, the internal pressure increase width ΔPV ₁ within a predetermined time of the purge system in the atmospheric pressure closed state is set.
Is measured to estimate the fuel evaporation rate. In the operation of step 413, the CCV 17 of the air introduction passage 18e and the bypass valve 20 of the bypass passage 20e are kept open while the purge control valve 15 is kept closed.
As a result, outside air flows into the purge system that has been under negative pressure for leak detection through the CCV 17 and the canister 10, and the internal pressure of the purge system quickly returns to atmospheric pressure. C
When it is confirmed that the purge system internal pressure measured by the pressure sensor 33 provided in the fuel tank 11 has become the atmospheric pressure after the CV 17 is opened, the CCV 17 is then closed and the purge system is set to the atmospheric pressure. Keep tightly closed.

As a result, the internal pressure of the purge system is
The internal pressure rises with the evaporation of the fuel in the fuel cell 1, and the internal pressure rising speed increases as the fuel evaporation speed increases. In this embodiment,
The purge system internal pressure increase width ΔPV ₁ is measured for a predetermined time (about 15 seconds) from when the CCV 17 is closed. The internal pressure increase width (that is, the increase speed) ΔPV ₁ is a value corresponding to the fuel evaporation speed in the fuel tank 11.

When the measurement of the fuel evaporation rate ΔPV ₁ is completed in step 413, it is next determined in step 415 whether or not the measured fuel evaporation rate ΔPV ₁ is equal to or more than a predetermined determination value ΔPV ₀ . In step 415 ΔPV ₁ ≧ ΔPV ₀
In this case, it means that the fuel evaporation rate is high regardless of whether or not the fuel vapor has been condensed due to back purge from the canister. Likely to be. Therefore, in this case, without making a normal determination or an abnormality determination, the determination is suspended in step 425 and the abnormality diagnosis is terminated. Note that, when the determination is suspended, the CCV
The valve 17 is opened immediately, and the purging of the canister 10 is restarted.

In step 415, ΔPV₁<ΔPV₀So
If the measured fuel evaporation rate is actually small,
Or it is smaller than the actual size due to the back purge
It is necessary to judge whether or not. Therefore, in step 417
Second fuel evaporation rate ΔPV _TwoHas been measured
It is determined whether or not the processing has been completed.
1 or if not finished, at step 419
ΔPV_TwoThen, the process proceeds to step 419.

In the second measurement of the fuel evaporation rate in step 419, the purge system internal pressure increase width Δ for a predetermined time (about 15 seconds) from the end of the _first measurement of the fuel evaporation rate ΔPV _1.
To measure the PV _2. The internal pressure increase width (that is, the increase speed) ΔPV ₂ is a more accurate fuel evaporation speed that is less affected by the back purge.

In step 421, 2
The second fuel evaporation rate ΔPV2 is set to the same determination value ΔPV as the previous time.
Compare with ₀ . In step 421, if ΔPV ₂ ≧ ΔPV ₀ , the fuel evaporation rate Δ in the first measurement
Since PV ₁ has a large error and it can be determined that the fuel evaporation rate was actually large, the process also proceeds to step 425 to suspend the determination and terminate the abnormality diagnosis. If ΔPV2 <ΔPV0 in step 421, the fuel evaporation rate is actually low, and in step 407, ΔPL> ΔP0
Since it can be determined that L ₀ is a a is given because the leak in the purge system has occurred, the process proceeds to step 423, and ends the diagnosis operation performed abnormality determination.

When an abnormality is determined in step 423, a warning lamp arranged near the vehicle driver's seat is turned on by an operation separately executed by the ECU 30, and the driver is notified of the abnormality of the purge system. As described above, in the present embodiment, when the normality is determined in step 409, the purge is immediately restarted without measuring the fuel evaporation rate. In addition, even when the normality is not determined in step 409, the fuel evaporation rate ΔPV ₁ measured at the first time is used.
Is large, the purge is restarted immediately. For this reason, the frequency at which the second fuel evaporation rate measurement is performed becomes extremely low, and the purge interruption time can be shortened as a whole.

When the value of the fuel evaporation rate ΔPV ₁ measured at the first time is small, the fuel evaporation rate is measured at the second time without performing the abnormality determination immediately. Since the abnormality determination is made only when both the measured fuel evaporation rates ΔPV ₁ and ΔPV ₂ are smaller than the predetermined value, it is possible to prevent the purge system having no leakage from being erroneously determined to be abnormal.

[0069]

According to the present invention, a high-precision abnormality judgment is performed while reducing the purge interruption time by measuring the fuel evaporation rate after measuring the internal pressure rise due to the negative pressure sealing of the purge system. This has the effect that it becomes possible.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of a general automotive evaporative purge system to which the present invention is applied.

FIG. 2 is a diagram illustrating a change in system pressure when a failure diagnosis of a purge system is performed.

FIG. 3 is a diagram illustrating a change in a fuel evaporation rate due to a purge system internal pressure at the start of negative pressure introduction.

FIG. 4 is a flowchart illustrating an embodiment of a failure diagnosis operation according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Intake passage 10 ... Canister 11 ... Fuel tank 12 ... Vapor piping 14 ... Purge piping 15 ... Purge control valve 17 ... CCV 30 ... Electronic control unit (ECU) 33 ... Fuel tank pressure sensor

Continued on the front page (72) Inventor Toshihiro Ozaki 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation F-term (reference) 3G044 BA22 EA08 EA32 FA04 FA38 FA39

Claims (1)

[Claims] 1. A canister for adsorbing evaporated fuel in a fuel tank of an internal combustion engine, a vapor passage connecting a space above a fuel level in the fuel tank to the canister, and a purge connecting the canister to an engine intake passage. A failure diagnosis device for an evaporative purge system including a passage, wherein a purge system including the fuel tank, the canister, the vapor passage, and the purge passage is hermetically sealed and purged after adjusting a purge system internal pressure to a predetermined negative pressure. The system pressure rise is measured, and when the pressure increase range of the purge system is larger than a predetermined reference value, the evaporation rate of the fuel in the fuel tank after the purge system pressure is increased to a predetermined pressure is detected. And determining whether the detected fuel evaporation rate is smaller than a predetermined value, and only when the detected fuel evaporation rate is smaller than the predetermined value. A failure diagnosis device for an evaporative purge system that determines again that an abnormality has occurred in the purge system only when the fuel evaporation rate is again detected and the detected fuel evaporation rate is also smaller than the predetermined value.