JP2934999B2 - Leak diagnosis device in engine fuel vapor treatment system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a leak diagnostic device for an evaporative fuel treatment system for an engine, and more particularly to a technique for improving the diagnostic accuracy of a diagnostic device for diagnosing a leak state based on the pressure of an evaporative fuel supply system. About.

[0002]

2. Description of the Related Art Heretofore, after evaporative fuel generated in a fuel tank is once adsorbed and collected by a canister (adsorbing means), the evaporative fuel adsorbed and collected by the canister is newly collected by an engine suction negative pressure. A system has been proposed in which the intake system of the engine is purged (separated) and sucked together with the air and supplied to the intake system of the engine to prevent the evaporation of fuel vapor in the fuel tank into the atmosphere (Japanese Patent Laid-Open No. Sho 62-62). 7962
Reference).

[0003]

In the above-described evaporative fuel processing apparatus, if a crack is formed in the middle of the evaporative fuel pipe or if a seal failure occurs at the joint of the evaporative fuel pipe, the leaked portion may be formed. As a result, the evaporated fuel is radiated into the atmosphere, and the original radiation preventing effect cannot be sufficiently exhibited.

Accordingly, it is desired to provide a device for diagnosing the occurrence of a leak of the evaporated fuel as described above, and the presence or absence of the leak is diagnosed by utilizing the fact that the pressure state in the evaporated fuel pipe changes due to the leak. We examined the equipment to do. That is, with the air inlet of the canister closed,
If the suction negative pressure of the engine is introduced into the evaporative fuel pipe, the pressure in the evaporative fuel pipe will decrease, and then if the suction negative pressure is cut off, the pressure in the evaporative fuel pipe will gradually increase. However, if there is a leak, the rise rate becomes larger than normal when air is introduced from the leak portion, so that it is possible to diagnose whether or not a leak has occurred based on the pressure rise rate.

However, the atmospheric pressure and the state of generation of fuel vapor
Conditions affect the pressure rise rate, so atmospheric pressure conditions
Depending on the state of the fuel in the fuel tank or the like, the occurrence of leak may be erroneously diagnosed based on the pressure increase ratio.
The present invention has been made in view of the above problems, and in diagnosing the presence or absence of a leak based on the pressure of the evaporative fuel supply system, the reliability of the leak diagnosis is reduced due to the fuel state in the fuel tank and the atmospheric pressure state. The purpose is to be able to avoid doing.

[0006]

SUMMARY OF THE INVENTION Therefore, the present invention comprises an adsorbing means for adsorbing and trapping evaporated fuel in a fuel tank. A leak diagnostic device in an evaporative fuel processing device for an engine, which is configured to perform desorption suction by an intake system of the engine and to perform processing, and is configured as shown in FIG.

In FIG. 1, the negative pressure introduction switching means includes:
The switching control of the shutoff / introduction of fresh air to the adsorbing means is performed, and the switching means of fresh air introduction controls the switching of the shutoff / introduction of fresh air to the adsorbing means. Further, the pressure detecting means detects a pressure of an evaporative fuel supply system from the fuel tank to the engine intake system via the adsorbing means.

The diagnosing means selectively performs introduction / shutdown of the suction negative pressure by the negative pressure introduction switching means with respect to the suction means in which the fresh air introduction is blocked by the fresh air introduction switching means. Then, a leak state in the evaporative fuel supply system is diagnosed based on the pressure detected by the pressure detecting means at this time. On the other hand, the diagnostic condition detecting means detects the fuel temperature in the fuel tank and the atmospheric pressure.
It is detected, respectively.

[0009] The diagnostic condition judging means includes a diagnostic condition detecting means.
The atmospheric pressure detected by the discharge means is lower than a predetermined value,
The fuel temperature is lower than a predetermined temperature, and
Only when the degree does not show a rising change, the diagnosis of the leak state by the diagnosis means is permitted.

[0010]

According to this structure, the introduction and shutoff of the fresh air and the engine suction negative pressure to the adsorbing means are controlled to be switched. Introduce and shut off the negative pressure selectively. When the negative pressure of the engine intake is introduced in a state where the fresh air is shut off, the negative pressure of the engine intake is confined in the evaporative fuel supply system. Thereafter, when the negative pressure of the engine intake is shut off, the pressure in the evaporative fuel supply system gradually increases. But,
If there is a leak, the rate of increase becomes larger than normal, so that it is possible to diagnose whether or not a leak has occurred in the evaporative fuel supply system based on the rate of increase.

[0011] On the other hand, fuel temperature in the fuel tank, and, large
It is adapted to detect the atmospheric pressure as a diagnostic condition, the atmosphere
If the pressure is lower than the predetermined value and the fuel temperature is lower than the predetermined temperature,
Only when the fuel temperature does not show a rising change, the leak diagnosis using the pressure is permitted. If the fuel temperature in the fuel tank is high, the amount of evaporated fuel will increase, and
This will affect the detected pressure and the fuel temperature.
If the degree shows a rising change, a large amount of fuel
There may reach occurring temperature, further in, so that also the atmospheric pressure influences the detected pressure.

Therefore, when the atmospheric pressure is lower than a predetermined value and the fuel
The temperature is lower than the specified temperature and the fuel temperature shows a rising change.
The leak diagnosis is performed only when not performed, and the occurrence of the leak is erroneously diagnosed based on the change in the pressure characteristic due to a factor other than the leak.

[0013]

Embodiments of the present invention will be described below. FIG. 2 is a diagram illustrating the system configuration of the present embodiment. In FIG. 2, one end of an evaporative fuel pipe 2a is connected to a fuel tank 1 for storing fuel supplied to the engine, and the other end of the evaporative fuel pipe 2a is connected to the evaporative fuel generated in the fuel tank 1. It is connected to a canister 3 (adsorbing means) for temporarily adsorbing and collecting the fuel.

The fuel vapor pipe 2a is formed so as to branch into two branches in the middle and then join to the canister 3. A check valve 4 is provided at one of the branch pipe portions.
On the other hand, an electromagnetic bypass valve 5 is interposed. The check valve 4 and the bypass valve 5
In the evaporative fuel pipe 2a on the upstream side (on the side of the fuel tank 1),
A pressure sensor 6 (pressure detecting means) for detecting the pressure in the pipe 2a is provided.

A drain pipe 7 for introducing fresh air is connected to the canister 3, and an electromagnetic drain cut valve 8 (for selectively cutting off the introduction of fresh air) is connected to the drain pipe 7. A fresh air introduction switching means) is interposed.
On the other hand, an evaporative fuel pipe 2b for supplying the evaporative fuel temporarily adsorbed and collected to the canister 3 to an intake collector 9 (an intake system downstream of the throttle valve 10) of the intake manifold is connected to the canister 3 and the intake air. An electromagnetic purge cut valve 11 (negative pressure introduction switching means) is provided between the evaporative fuel pipe 2 b and the collector section 9.
Is interposed.

When the purge cut valve 11 and the drain cut valve 8 are open, the engine suction negative pressure is introduced into the canister 3 via the evaporative fuel pipe 2b, and is introduced into the canister 3 via the drain pipe 7. Along with the fresh air, the evaporated fuel desorbed (purged) from the canister 3 is sucked into the intake collector section 9 and provided for combustion in the engine.

The bypass valve 5, drain cut valve 8, and purge cut valve 11 are controlled to be opened and closed by a control unit 12 incorporating a microcomputer. The control unit 12 includes, in addition to the pressure signal from the pressure sensor 6, an opening signal from a throttle sensor 13 for detecting an opening TVO of the throttle valve 10, and a remaining amount for detecting a remaining fuel amount in the fuel tank 1. A fuel remaining amount signal from the sensor 14, a fuel temperature signal from a fuel temperature sensor 15 for detecting a fuel temperature in the fuel tank 1, and the like are input.

Then, the control unit 12
As shown in the flowchart of FIG.
A diagnosis is made as to whether or not there is a so-called leak state in which the fuel vapor is radiated into the atmosphere due to cracks in a and 2b and poor sealing at the pipe joint. In the present embodiment, the functions as the diagnostic means and the diagnostic condition determining means are provided by software in the control unit 12 as shown in the flowchart of FIG. Moreover, diagnosis condition detecting means in this embodiment, the pressure sensor 6, corresponds the fuel temperature sensor 15.

Before describing the leak diagnosis control in this embodiment in detail according to the flowchart of FIG. 3, a basic leak diagnosis method will be described below. In the configuration shown in FIG. 2, when the drain cut valve 8 is closed and the purge cut valve 11 is opened, the intake negative pressure of the engine is reduced to a state in which no fresh air is introduced into the canister 3.
a, 2b, the fuel vapor pipe 2
The pressure in a, 2b (fuel tank 1) gradually decreases.

On the other hand, as described above, the fuel vapor pipe 2
a, 2b with the engine suction negative pressure confined in
Purge cut valve with drain cut valve 8 closed
When the engine 11 is closed and the introduction of the engine negative pressure is shut off, the pressure in the fuel vapor pipes 2a and 2b gradually increases. However, if there is a crack or a seal failure, the rate of increase becomes larger than normal. Thus, it is possible to estimate the occurrence of a leak in the fuel vapor supply system (see FIG. 4).

The leak diagnosis will be described with reference to the flowchart of FIG. 3. First, step 1 (S1 in the figure)
There is. In the following), it is determined whether or not the fuel temperature detected by the fuel temperature sensor 15 is equal to or higher than a predetermined temperature. If the fuel temperature in the fuel tank 1 is high, the amount of evaporated fuel increases, which affects the pressure detected in the leak diagnosis. Therefore, when it is determined that the fuel temperature is equal to or higher than the predetermined temperature, the leak diagnosis is performed. Without doing
Proceeding to step 14, the bypass valve 5 is controlled to close, and the drain cut valve 8 and the purge cut valve 11 are controlled to open.

When it is determined in step 1 that the fuel temperature is lower than the predetermined temperature, the process proceeds to step 2, where it is determined whether the fuel temperature is increasing at a predetermined speed or more. That is, even if the fuel temperature is equal to or lower than the predetermined temperature, if the fuel temperature is increasing, the temperature may reach a temperature at which a large amount of evaporative fuel is generated during the execution of the leak diagnosis. Proceed to and do not perform leak diagnosis.

If it is determined in step 2 that the fuel temperature has not risen, the process proceeds to step 3, in which it is determined whether the vehicle is running at high altitude (atmospheric pressure is lower than a predetermined value). The highland determination can be made based on the pressure detected by the pressure sensor 6 in a state where the leak diagnosis is not performed. Since the determination of the pressure rise rate in the leak diagnosis is performed using a determination level that is appropriate in low altitudes, the accuracy of the leak diagnosis deteriorates in high altitudes where the atmospheric pressure is low and affects the pressure rise rate. . Therefore, when the high altitude is determined, the process proceeds to step 14, and the leak diagnosis is not performed.

Even if it is determined in step 3 that it is not a high altitude (altitude above a predetermined level), if it is determined in step 4 that there is a change in atmospheric pressure, the temperature rise is not changed. Similarly, the leak diagnosis may not be performed because the environment (altitude) may deteriorate the diagnostic accuracy during the leak diagnosis. On the other hand, if it is determined in step 4 that there is no change in the atmospheric pressure, the process proceeds to step 5, where it is determined whether the remaining fuel amount in the fuel tank 1 detected by the remaining fuel sensor 14 is within a predetermined range. .

The space of the fuel tank 1 and the fuel vapor pipe 2
When the volume of the evaporative fuel supply system consisting of a and 2b changes,
This affects the pressure change in the leak diagnosis, and the space in the fuel tank 1 can be known from the remaining fuel amount. Therefore, the condition for leak diagnosis is set to be within a predetermined range with respect to the standard remaining amount of fuel, so that the diagnosis can be avoided when the space volume in the fuel tank 1 is significantly different.

If it is determined in step 5 that the remaining fuel amount is within the predetermined range, the process proceeds to step 6, where it is determined whether the vehicle is in a rapid acceleration / deceleration operation. This is because when the vehicle is suddenly accelerated and decelerated and acceleration in the vehicle longitudinal direction occurs,
This is because the fuel level in the fuel tank 1 undulates and fluctuates the pressure detected by the pressure sensor 6, which makes it difficult to accurately determine the pressure increase rate in the leak diagnosis.

In this embodiment, when the absolute value of the rate of change of the throttle valve opening TVO detected by the throttle sensor 13 is equal to or larger than a predetermined value, it is assumed that the vehicle is in a rapid acceleration / deceleration operation state. I have to. However, the acceleration in the front-rear direction may be detected by a G sensor or the like, or the acceleration in the front-rear direction may be detected based on a change in the vehicle speed. In addition, the lateral acceleration due to turning or the like may be detected. It is good.

If it is determined in step 6 that the vehicle is not in the rapid acceleration / deceleration operation state, it is determined that the condition for permitting the leak diagnosis is satisfied, and the leak diagnosis in step 7 and thereafter is executed.
That is, that the fuel temperature in the fuel tank 1 is lower than a predetermined temperature, that the fuel temperature has not risen and changed, that the vehicle is running on a lowland, that there is no change in the atmospheric pressure, that the remaining fuel amount in the fuel tank 1 is low. The leak diagnosis is executed only when all of the six conditions of being within a predetermined range and being not in a rapid acceleration / deceleration operation state of the vehicle are satisfied.
As a result, the diagnosis is performed under the condition where the reliability of the leak diagnosis based on the pressure increase rate is reduced, and it is possible to avoid giving an erroneous diagnosis result.

[0029] When the 6 conditions for pre-Symbol leakage diagnosis proceeds to step 7 are met, the detected pressure by the pressure sensor 6, and determines whether or not it is a predetermined negative pressure (20~50mmHg) ( (See FIG. 4).

If the detected pressure has not reached the predetermined negative pressure, the routine proceeds to step 8, where the bypass valve 5 and the purge cut valve 11 are opened and the drain cut valve 8 is closed. In a state where the bypass valve 5 and the purge cut valve 11 are opened and the drain cut valve 8 is closed, the engine suction negative pressure is introduced in a state where the introduction of fresh air to the canister 3 is cut off. The pressure in the evaporative fuel supply system including the pipe 2b, the canister 3, the evaporative fuel pipe 2a, and the fuel tank 1 decreases.

When the detected pressure gradually decreases in accordance with the valve opening / closing control in step 8 and approaches the negative pressure determined in step 7, the process proceeds to step 9, where the bypass cut valve 5 is opened, and the drain cut valve 8 is opened. While maintaining the closed state, the purge cut valve 11 is controlled to be closed to cut off the introduction of the engine suction negative pressure. Then, in the next step 10, the rate of increase in the pressure detected by the pressure sensor 6 is calculated.

That is, if the introduction of the engine suction negative pressure is interrupted in a state where the pressure in the evaporative fuel supply system has reached the predetermined negative pressure, the pressure in the evaporative fuel supply system gradually changes toward the atmospheric pressure. The change rate ΔP of the pressure toward the atmospheric pressure is calculated in step 10 (see FIG. 4). Here, if there is a crack in the fuel vapor pipes 2a, 2b, or if there is a poor seal at the joint of the fuel vapor pipes 2a, 2b, the pressure rise rate due to the introduction of the atmosphere from the leak portion is determined as follows. It is larger than.

Therefore, in step 11, the aforementioned step 10
By comparing the pressure increase ratio ΔP calculated in the above with a predetermined value,
The presence / absence of a leak is diagnosed based on whether or not the pressure rise rate ΔP is greater than the state without a leak. If the pressure rise rate ΔP is larger than the predetermined value, the process proceeds to step 12, where it is determined that a leak has occurred. If the pressure increase rate ΔP is equal to or less than the predetermined value, the process proceeds to step 13 and determines a normal state (a state in which no leak occurs).

If it is determined in step 12 that a leak has occurred, the driver may be warned of the result of the determination by a warning means provided in the driver's seat or the like of the vehicle.

[0035]

As described above, according to the present invention, in a diagnostic apparatus for diagnosing the presence or absence of a leak based on the pressure of an evaporative fuel supply system, a leak diagnosis is performed based on a fuel state in a fuel tank and an atmospheric pressure state. It is possible to prevent the reliability from being lowered, and it is possible to improve the reliability of the leak diagnosis.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a basic configuration of the present invention.

FIG. 2 is a system configuration diagram of an embodiment.

FIG. 3 is a flowchart showing a leak diagnosis according to the embodiment.

FIG. 4 is a time chart showing characteristics of a pressure change at the time of leak diagnosis.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fuel tank 2a, 2b Evaporated fuel pipe 3 Canister 4 Check valve 5 Bypass valve 6 Pressure sensor 7 Drain pipe 8 Drain cut valve 9 Intake collector section 10 Throttle valve 11 Purge cut valve 12 Control unit 13 Throttle sensor 14 Fuel level sensor 15 Fuel Temperature sensor

Claims (1)

(57) [Claims] 1. An adsorbing means for adsorbing and collecting vaporized fuel in a fuel tank, wherein the vaporized fuel adsorbed and collected by the adsorbing means is desorbed and sucked together with fresh air into an intake system of the engine together with fresh air by an intake negative pressure of the engine. In the evaporative fuel processing apparatus for an engine configured to perform processing by performing the process, negative pressure introduction switching means for controlling the introduction / shutdown of the engine suction negative pressure to the adsorption means, and shutting off / introducing fresh air to the adsorption means. New air introduction switching means for performing switching control; pressure detection means for detecting the pressure of an evaporative fuel supply system from the fuel tank to the engine intake system via the adsorption means; and fresh air introduction by the fresh air introduction switching means. The suction means in the cut-off state is selectively introduced and cut off by the negative pressure introduction switching means, and the pressure detection at this time is performed. Diagnosing means for diagnosing a leak state in the evaporative fuel supply system based on the pressure detected by the discharging means ; and a fuel temperature in the fuel tank , and an atmospheric pressure, respectively.
Given a diagnosis condition detecting means for detecting the said atmospheric pressure is detected more in the diagnosis condition detecting means
Below, and the fuel temperature is less than a predetermined temperature, and
A diagnostic condition determining means for permitting a diagnosis of a leak state by the diagnostic means only when the fuel temperature does not show a rise change; and a leak diagnostic apparatus for an evaporative fuel processing apparatus for an engine, comprising: .