JPH04318267A - Abnormality detecting device for evaporation purge system - Google Patents

Abstract

PURPOSE:To surely detect abnormality even in the case that fuel adsorbed to a canister is in a small amount, relating to an abnormality detecting device for an evaporation purge system constituted such that the abnormality is detected based on a change of air-fuel ratio before and after execution of a purge. CONSTITUTION:In an abnormality detecting device for an evaporation purge system provided in the evaporation purge system 20 for purging fuel through a purge passage 15 by a canister 11 relating to an intake pipe 14 of an engine and for detecting abnormality of the evaporation purge system 20 by detecting a change of air-fuel ratio at purge execution time by an ECU21, an atmospheric opening pipe 19 for introducing the atmosphere to the purge passage 15 is provided. A VSVl6 for selectively introducing fuel and the atmosphere to the purge pipe 15 is provided further to constitute the ECU21 to detect abnormality of the evaporation purge system 20 based on air-fuel ratio at atmospheric air supply time and air-fuel ratio at purge execution time.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an abnormality detection device for an evaporative purge system, and more particularly to an abnormality detection device for an evaporative purge system configured to detect abnormalities based on changes in air-fuel ratio before and after purge execution.

0002

[Prior Art] Generally, fuel evaporated in a fuel tank is
The vaporized fuel (hereinafter also simply referred to as fuel) is adsorbed in a canister filled with activated carbon or the like, so that the evaporated fuel (hereinafter also simply referred to as fuel) is not released into the atmosphere. In addition, since the capacity of the canister is limited and the amount of fuel that can be adsorbed is limited, in order to prevent canister overflow, the fuel adsorbed in the canister is purged into the engine intake pipe and burned. There is an evaporative purge system.

[0003] Furthermore, if this evaporative purge system malfunctions, there is a risk that the canister may overflow or the fuel may be released into the atmosphere. system is proposed.

[0004] Conventionally, as an abnormality detection device for this evaporative purge system, there is one disclosed in, for example, Japanese Patent Laid-Open No. 2-136558. The abnormality detection device disclosed in the publication uses an internal pressure detection means to detect the internal pressure of the fuel tank, and when the internal pressure of the fuel tank exceeds a predetermined pressure, controls the opening/closing means to open and close the discharge passage. By doing so, the purge is executed and stopped, and the presence or absence of an abnormality is determined based on changes in the air-fuel ratio before and after the purge is executed.

[0005]

[Problems to be Solved by the Invention] However, in the conventional device described above, in which the presence or absence of an abnormality is determined based on changes in the air-fuel ratio before and after purge is executed, if there is a large amount of adsorbed fuel adsorbed in the canister, the system may not function properly. Although abnormality detection can be performed, a problem arises because even if the internal pressure of the fuel tank at the time of abnormality detection is equal to or higher than a predetermined value, the adsorbed fuel actually adsorbed in the canister may be small. In other words, if there is little adsorbed fuel in the canister, only a small amount of fuel will be supplied to the engine's intake pipe even if purge is performed, so the change in air-fuel ratio due to purge will be small, indicating that an abnormality has occurred. There was a problem in that it was not possible to determine whether the fuel being adsorbed in the canister was simply insufficient.

The present invention has been made in view of the above points, and provides an abnormality detection device for an evaporative purge system that can reliably detect an abnormality even when there is little adsorbed fuel in a canister. The purpose is to

[0007]

[Means for Solving the Problems] In order to solve the above problems, the present invention provides an evaporative purge system that purges fuel from a canister to an intake system of an internal combustion engine through a purge passage, and is provided with an evaporative purge system that purges fuel from a canister through a purge passage. An abnormality detection device for an evaporative purge system that detects an abnormality in the evaporative purge system by detecting changes in the air-fuel ratio during purge execution is configured to allow atmospheric air to be introduced into the purge passage, and to selectively purge fuel and atmospheric air. A selective introduction means is provided to be introduced into the piping, and the abnormality detection means is configured to detect an abnormality in the evaporative purge system based on the air-fuel ratio at the time of atmospheric supply and the air-fuel ratio at the time of purge execution. It is.

[0008]

[Operation] According to the abnormality detection device configured as described above, the air-fuel ratio can be determined in a state where the atmosphere is introduced into the purge passage. This air-fuel ratio at the time of air introduction is equivalent to the air-fuel ratio in a state where an abnormality such as a pipe disconnection occurs in the evaporative purge system. Therefore, since abnormality detection can be performed based on the air-fuel ratio at the time of occurrence of the abnormality, it is possible to perform highly accurate abnormality detection.

[0009]

Embodiments Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram showing an abnormality detection device 10 for an evaporative purge system, which is an embodiment of the present invention.

In the figure, 11 is a canister, and the inside thereof is filled with an adsorbent 11a such as activated carbon. This canister 11 is communicated with a fuel tank 13 through a vapor passage 12 . Therefore, the evaporated fuel generated in the fuel tank 13 is introduced into the canister 11 through the vapor passage 12, and is absorbed into the canister 1 by being adsorbed by the adsorbent 11a.
It is kept within 1.

A purge passage 15 is provided between the canister 11 and the intake pipe 14 of the engine (not shown), and the purge passage 15 is equipped with a switching valve 16 (which is the essential part of the present invention). (hereinafter referred to as VSV) is provided. The evaporative purge system 20 is composed of the above-mentioned components.

[0012] The VSV16 will now be described in more detail. The VSV 16 is, for example, a three-way solenoid valve, and is connected to a purge passage 15, a connection pipe 17 connected to the canister 11, and an atmosphere release pipe 19 that is opened to the atmosphere via an air filter 18. This VSV 16 is driven by being supplied with an electric signal, and selectively connects the purge passage 15 to the connection pipe 17 or the atmosphere release pipe 19 (
In the following explanation, the state in which the VSV 16 connects the connecting pipe 17 and the purge passage 15 is referred to as an "OFF" state, and the state in which the VSV 16 connects the atmosphere release pipe 19 and the purge passage 15 is referred to as an "ON" state. ” state).

Therefore, when the VSV 16 is OFF, the fuel adsorbed in the canister 11 passes through the connection pipe 17 and the purge passage 15 and is purged into the intake pipe 14. Also, when VSV16 is ON,
Atmosphere (air) is passed through the air filter 18, atmosphere release pipe 19,
It passes through the purge passage 15 and is introduced into the intake pipe 14. Therefore, fuel or air is selectively introduced into the purge passage 15 by the ON/OFF operation of the VSV 16.

Reference numeral 21 in the figure is an engine control unit (ECU) to which various sensors (not shown) such as an oxygen sensor, water temperature sensor, and air flow meter are connected. Based on this, various controls for driving the engine are performed, including fuel injection control and ignition timing control. In addition, the above-mentioned VSV16 is also connected to the ECU21, and the ECU
It opens and closes based on the signal supplied from 21.

[0015] This ECU 21 is a central processing circuit (C
PU), read-only memory (ROM), random access memory (RAM), etc. The abnormality detection process of the abnormality detection device 10 according to the present invention is also carried out by this ECU.
21, and the ROM of ECU 21
An anomaly detection processing program is stored in . The above abnormality detection means is configured as software processing of the ECU 21.

Next, the abnormality detection device 1 having the above configuration will be described.
The principle of detecting 0 abnormality will be explained using FIG. 2 in addition to FIG. 1.

When the fuel adsorbed in the canister 11 is purged into the intake pipe 14, the air-fuel ratio of the air-fuel mixture supplied to the engine changes. In this embodiment, the ECU 21 is configured to calculate the air-fuel ratio based on an oxygen concentration signal from an oxygen sensor disposed in the exhaust manifold of the engine.

In FIG. 2, (A) shows the air-fuel ratio when an abnormality has occurred in the evaporative purge system 19, and (B) shows the air-fuel ratio when the evaporative purge system 19 is normal and the canister 11 is adsorbed. (C) shows the air-fuel ratio when the evaporative purge system 19 is normal and sufficient fuel is adsorbed in the canister 11, and (D) shows the air-fuel ratio when there is little fuel in the tank.
indicates the state of VSV16. Furthermore, the above (A) ~
For convenience of explanation, in (C), both air-fuel ratio changes are shown side by side so that the air-fuel ratio change caused by the conventional abnormality detection device and the air-fuel ratio change caused by the abnormality detection device 10 of the present invention can be compared.

As described above, the conventional abnormality detection device cannot introduce atmospheric air into the purge passage, and only has the function of purging the fuel adsorbed in the canister into the intake pipe. In the figure, time t1 is the time when purge is started in the conventional abnormality detection device. Moreover, the time t2 is the abnormality detection device 10 according to the present invention.
This is the time when VSV16 was turned ON at time t.
3 is the time when VSV16 was turned off. Therefore, between times t2 and t3, atmospheric air is introduced into the intake pipe 14 through the purge passage 15, and after time t3, purge fuel is introduced into the intake pipe 14 through the purge passage 15.

First, a case where an abnormality has occurred in the evaporative purge system 20 shown in FIG. 3(A) will be described.

When an abnormality occurs in the evaporative purge system 20, for example, the vapor passage 12 or the purge passage 1
5 has come off or a hole or crack has formed. When such an abnormality occurs, VSV16
When turned on, air is introduced from the purge passage 15 into the intake pipe 14, and the air-fuel ratio becomes lean.

Subsequently, at time t3, VSV16 becomes O.
When switched to the FF state, the connection pipe 17 and the purge passage 15 are connected. Therefore, Evapo purge system 2
If 0 were normal, purge gas containing fuel would be introduced into the intake pipe 14, but the evaporative purge system 2
If there is an abnormality in purge passage 1, the fuel will flow to purge passage 1.
5, and the state in which air flows in from the location where the abnormality has occurred is maintained. Therefore, if an abnormality occurs in the evaporative purge system 20, the air-fuel ratio remains lean even after time t3. Therefore, time t2 ~
Based on the air-fuel ratio during time t3 (the value of this air-fuel ratio is assumed to be A), the air-fuel ratio after time t3 (the value of this air-fuel ratio is assumed to be B) is equal to this air-fuel ratio A, or If it becomes even leaner, it can be determined that an abnormality has occurred in the evaporative purge system 20.

On the other hand, in the conventional abnormality detection device as well, air from the abnormality location flows in when the VSV opens at time t1, so that the air-fuel ratio becomes lean for the same reason as above. Therefore, in the conventional abnormality detection device, the air-fuel ratio after time t1 is determined based on the air-fuel ratio before time t1 (indicated by arrow X in the figure).
If the air-fuel ratio is lean compared to the previous air-fuel ratio X, it is determined that an abnormality has occurred in the evaporative purge system 20.

Next, a change in the air-fuel ratio when the evaporative purge system 20 shown in FIG. 3B is normal and there is little fuel adsorbed in the canister 11 will be described.

In the case shown in FIG. 1B, since there is little fuel adsorbed in the canister 11, the canister 1
Only a small amount of fuel is purged from 1. Therefore, what is introduced into the intake pipe 14 is purge gas with a large amount of air and low fuel concentration relative to the amount of fuel. In this way, when purge gas with a low fuel concentration flows into the intake pipe 14, in other words, when a large amount of air (although some amount of fuel is included) is introduced from the evaporative purge system 20, the air-fuel ratio becomes lean. ).

In the conventional abnormality detection device, as described above, the air-fuel ratio X before time t1 is used as the reference, and
If the air-fuel ratio after 1 is lean compared to the air-fuel ratio Even when the air-fuel ratio becomes lean due to a small amount of fuel being used, the abnormality detection device may incorrectly determine that an abnormality has occurred in the evaporative purge system.

In contrast, the abnormality generating device 10 of the present invention
In this case, only air can be introduced into the intake pipe 14 between time t2 and t3.
The air-fuel ratio at is leaner than the conventional air-fuel ratio after time t1 (leaner by the amount indicated by arrow a in the figure). This is because even purge gas with a low fuel concentration contains some fuel. Subsequently, when the VSV 16 is turned off after time t3, the purge passage 1
5, a purge gas having a low fuel concentration is introduced, so that the air-fuel ratio changes slightly to the rich side by the amount of fuel contained in the purge gas, as shown in the figure. Therefore, time t2 to t3
If the air-fuel ratio B after time t3 becomes rich with respect to this air-fuel ratio A, it can be determined that no abnormality has occurred in the evaporative purge system 20. .

Next, a change in the air-fuel ratio when the evaporative purge system 20 shown in FIG. 3(C) is normal and sufficient fuel is adsorbed in the canister 11 will be described.

In the case shown in FIG. 2C, since sufficient fuel is adsorbed in the canister 11, a large amount of fuel is purged from the canister 11. After t3, purge gas with a high fuel concentration is introduced into the intake pipe 14, and the air-fuel ratio changes greatly to become richer. Therefore, in the present invention, with respect to the air-fuel ratio A between times t2 and t3 as a reference, the time t
If the air-fuel ratio B becomes rich after 3,
It can be determined that no abnormality has occurred in the evaporative purge system 20.

Furthermore, in the conventional abnormality detection device, the time t1
Based on the previous air-fuel ratio (indicated by arrow X in the figure), if the air-fuel ratio after time t1 is richer than the air-fuel ratio X before time t1, the evaporative purge system 20 is determined to be normal. It had been.

As is clear from the above explanation, the conventional abnormality detection device may make an erroneous determination when there is little fuel adsorbed in the canister. On the other hand, in the abnormality detection device 10 according to the present invention, the VS
Based on the air-fuel ratio A between time t2 and t3 when V16 is in the ON state, VSV after time t3
16 is in the OFF state, it is determined that an abnormality occurs in the evaporative purge system 20 when the air-fuel ratio B is equal to the air-fuel ratio A or lean, and the air-fuel ratio B is rich with respect to the air-fuel ratio A. In some cases, the configuration is determined to be normal. With this configuration, highly reliable abnormality detection without misjudgment is possible, and even when there is little fuel adsorbed in the canister 11, an abnormality in the evaporative purge system 20 can be reliably detected. The reliability of the abnormality detection device 10 can be improved.

Next, based on the principle of abnormality detection described above, the abnormality detection operation executed by the ECU 21 will be explained using FIG. This figure is a flowchart showing the abnormality detection operation performed by the ECU 21.

When the abnormality detection operation shown in the figure is started, the ECU 21 first determines whether the execution flag is set (
(Step 100. Hereinafter, step will be abbreviated as S). This execution flag is a flag that is set when the abnormality detection process described below is executed. Further, the abnormality detection process is a process that can sufficiently ensure safety if it is executed only once after the engine is started. Therefore, if the execution flag is set, the process is terminated without executing the abnormality detection process again.

On the other hand, if it is determined in S100 that the execution flag is not set, the process proceeds to S110, and it is determined whether the execution conditions are met. Here, the execution conditions include that the engine is being warmed up, that the engine is not under feedback control, and so on. If the execution conditions are not met, accurate abnormality detection may not be possible, or abnormality detection may adversely affect engine control, resulting in deterioration of drivability. Therefore, if the execution conditions are not met, abnormality detection is not performed and the process is terminated.

If it is determined in S110 that the execution conditions are met, the process proceeds to S120, where it is determined whether the current state of the engine is in the purge area. As shown in FIG. 1, the purge system of this embodiment is a so-called port purge, and the negative pressure applied to the purge passage 15 varies depending on the opening degree of the throttle valve 22. Further, the canister 11 is provided with a check valve (not shown), and the fuel is not purged from the canister 11 unless the negative pressure in the purge passage 15 exceeds a predetermined value. Therefore, in S120, it is determined whether the canister 11 is ready to be purged of fuel. Therefore, when the engine is in a state where purge is not possible, abnormality detection cannot be performed and the process is terminated.

On the other hand, if it is determined in S120 that the engine condition is in the purge region, the process proceeds to S130, and the E
CU21 turns on VSV16 and opens air release pipe 1.
9 and the purge passage 15 are communicated with each other. As a result, only air is introduced into the intake pipe 14 through the purge passage 15. In the subsequent S140, the average air-fuel ratio A when the VSV 16 is in the ON state is calculated. This average air-fuel ratio A corresponds to the air-fuel ratio during the time period t2 to t3 described using FIG. 2, and is the air-fuel ratio that will be a reference in the abnormality detection process below. Note that the average air-fuel ratio is calculated by calculating the air-fuel ratio multiple times within a predetermined period of time, and then taking the average of the calculated air-fuel ratios. In this way, by finding the average air-fuel ratio,
Detection accuracy can be improved.

After the average air-fuel ratio A is determined in S140, the ECU 21 then turns the VSV 16 to O in S150.
Switching to the FF state, connecting the connecting pipe 17 and the purge passage 15, and in the subsequent S160, the average air-fuel ratio B
Calculate. The average air-fuel ratio B obtained in S160 corresponds to the air-fuel ratio after time t3 described using FIG. 2. Average air-fuel ratio B found here
is an air-fuel ratio that reflects the state of the evaporative purge system 20 (ie, whether it is in a normal state or an abnormal state).

As described above, when the average air-fuel ratio A, which serves as a reference for abnormality detection processing, and the average air-fuel ratio B, which reflects the state of the evaporative purge system 19, are determined, the ECU 21
70, the value of each average air-fuel ratio A and the average air-fuel ratio B
Compare the values of . As is clear from the above description of the detection principle, when the average air-fuel ratio B is equal to the average air-fuel ratio A or is lean, it means that an abnormality has occurred in the evaporative purge system 20. On the other hand, when the average air-fuel ratio B is richer than the average air-fuel ratio A, the evaporative purge system 20 is normal.

Therefore, if the average air-fuel ratio B is richer than the average air-fuel ratio A in S170, the ECU 21 determines that the evaporative purge system 20 is normal, and the ECU 21 determines that the evaporative purge system 20 is normal.
At 0, the execution flag is set and the process ends. On the other hand, if the average air-fuel ratio B is equal to the average air-fuel ratio A or is lean in S170, the ECU 21 determines that an abnormality has occurred in the evaporative purge system 20, and turns on the warning lamp 2 in S180.
3 is turned on to notify the driver that an abnormality has occurred in the evaporative purge system 20. Note that when the warning lamp 23 is turned on in S180, an execution flag is set in S190, and the process ends.

[0040]

As described above, according to the present invention, it is possible to reliably detect an abnormality in the evaporative purge system even when the amount of fuel adsorbed in the canister is small, thereby improving the reliability of the abnormality detection device. It has features such as:

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of an abnormality detection device according to a first embodiment of the present invention.

FIG. 2 is a diagram for explaining the principle of abnormality detection in the present invention.

FIG. 3 is a flowchart showing an abnormality detection processing operation executed by the ECU.

[Explanation of symbols]

10 Abnormality detection device 11 Canister 12 Vapor passage 13 Fuel tank 14 Intake pipe 15 Purge passage 16　Switching valve (VSV) 17 Connection piping 18 Air filter 19 Atmospheric release piping 20 Evapo purge system

Claims (1)

[Claims] [Claim 1] An evaporative purge system that purges fuel from a canister to an intake system of an internal combustion engine through a purge passage. An abnormality detection device for an evaporative purge system that detects an abnormality is configured to allow atmospheric air to be introduced into the purge passage, and is provided with a selective introduction means for selectively introducing the fuel and the atmospheric air into the purge piping. An abnormality detection device for an evaporative purge system, characterized in that the means is configured to detect an abnormality in the evaporative purge system based on the air-fuel ratio during air supply and the air-fuel ratio during purge execution.