JP2002147293A - Failure diagnosis device for evaporation purge system - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To accurately detect whether or not there is a leak of fuel evaporative gas from the evaporative purge system even during low vehicle speed traveling, high vehicle speed traveling, high altitude traveling, or traveling on mountain roads. To A canister purge control (CPC) valve disposed in a purge passage is closed at a positive pressure and a negative pressure, respectively.
The evaporative purge system to zero is closed and the reference pressure detection chamber 11b of the relative pressure sensor 11 is closed to detect the amount of pressure change due to the fuel evaporation gas in the evaporative purge system. Then, the two pressure changes are corrected by the pressure change due to the atmospheric pressure change in the evaporative purge system to calculate the actual system pressure changes, and the two real system pressure changes are compared to determine whether there is a leak. . If there is a leak such as a crack in the evaporative purge system, the amount of pressure change is small at positive pressure because fuel evaporative gas leaks from the leak at the time of positive pressure, while at negative pressure, air enters the evaporative purge system from the leak point. Since the pressure changes due to the inflow, the differential pressure increases, and it is determined that there is a leak.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a failure diagnosis apparatus for an evaporative purge system capable of accurately detecting the presence or absence of a fuel vapor gas leak based on an actual pressure change in an evaporative purge system.

[0002]

2. Description of the Related Art Conventionally, as a failure diagnosis apparatus of this type, for example, Japanese Unexamined Patent Publication No. Hei 6-10779 discloses an on-off valve for opening and closing an air hole of a canister. By opening the valve, the purge control valve is closed in a state where the inside of the evaporative purge system including the fuel tank is at a negative pressure, and the pressure change when the inside of the evaporative purge system is sealed, the fuel vapor (evaporation) gas from the inside of the evaporative purge system is changed. There is disclosed a technique for diagnosing a leak of a gas.

[0003] For example, Japanese Patent Application Laid-Open No. 5-272417 discloses that a pressure switch detects a cycle in which the inside of an evaporative purge system is positively pressurized, and after returning a leak to a predetermined pressure after a certain amount of air is injected. There is disclosed a technique for diagnosing a leak of fuel evaporative gas from inside an evaporation purge system.

As described above, in the conventional failure diagnosis, when the presence or absence of leakage of the fuel evaporative gas from the evaporative purge system is detected, the evaporative purge system is hermetically sealed and any one of pressure reducing and pressurizing means is employed. In general, a method of examining a pressure change due to a leak of fuel evaporative gas based on a pressure difference from the atmospheric pressure is generally adopted.

Therefore, when the change in pressure is detected using a relative pressure sensor, if the atmospheric pressure changes, the presence or absence of a leak of fuel evaporative gas cannot be accurately detected.

As a countermeasure, conventionally, the presence or absence of a leak is diagnosed only in a low vehicle speed range where the atmospheric pressure change is small, or an atmospheric pressure sensor is separately provided as disclosed in Japanese Patent No. 2830628, for example. A change in the atmospheric pressure is detected by the atmospheric pressure sensor, and the pressure in the evaporative purge system detected by the relative pressure sensor is corrected based on the atmospheric pressure sensor, thereby diagnosing the presence or absence of a leak of the fuel evaporative gas.

Further, an on-off valve (for example, a solenoid valve) is provided on the reference pressure side of the relative pressure sensor for detecting a change in the internal pressure of the evaporative purge system. There has been proposed a technique for detecting a pressure change in an evaporative purge system without being affected by a change in the atmospheric pressure by detecting the pressure.

[0008]

However, in the diagnosis only in the low vehicle speed range, the frequency of diagnosis is low, and there is a limit to improving the accuracy of detecting the presence or absence of leakage of the fuel evaporative gas.

When detecting a change in atmospheric pressure, 1000
A considerably high-precision atmospheric pressure sensor that detects a minute change in atmospheric pressure of Pa or less is required. In addition, since a small change in atmospheric pressure that cannot be detected cannot be properly corrected, the accuracy of detecting a change in the internal pressure of the evaporation purge system decreases.

Further, even if the reference pressure detecting side of the relative pressure sensor for detecting a change in the internal pressure of the evaporative purge system is shut off and the pressure change on the reference pressure detecting side during diagnosis is set to 0, the internal pressure of the evaporative purge system is reduced. In particular, it has been found that the material has a property of contracting when the atmospheric pressure in the fuel tank becomes high and expanding when the atmospheric pressure becomes low. Therefore, if the atmospheric pressure changes during the diagnosis, a pressure difference is generated between the inside of the evaporative purge system and the atmospheric pressure. Due to the influence of the contraction / expansion in the evaporative purge system, the presence or absence of a leak is accurately determined from the change in the internal pressure of the evaporative purge system. It is difficult to detect.

In view of the above circumstances, the present invention does not require an atmospheric pressure sensor for detecting a change in atmospheric pressure, and the diagnostic region is not limited to a low vehicle speed region. It is an object of the present invention to provide a failure diagnosis device for an evaporative purge system that can perform diagnosis even during traveling and that can increase the frequency of diagnosis to detect the presence or absence of leakage of fuel evaporative gas with high accuracy. .

[0012]

In order to achieve the above object, the present invention provides a fuel tank and a canister for adsorbing fuel evaporative gas generated in the fuel tank through an evaporative passage, and further connects the canister with the canister. An evaporative purge system that communicates with an intake system of an engine through a purge passage and purges fuel vapor adsorbed in the canister to the intake system when an evaporative purge condition is satisfied. Opening and closing means, a relative pressure sensor for detecting a pressure change in the evaporative purge system from the fuel tank to the purge passage based on the atmospheric pressure, and a reference pressure detection chamber for detecting the atmospheric pressure provided in the relative pressure sensor. A second opening / closing means for closing the inside of the evaporative purge system by the first opening / closing means when the inside of the evaporative purge system is at a positive pressure. The reference pressure detection chamber is closed by the opening / closing means, and the positive pressure change amount calculating means for calculating the pressure change amount in the evaporative purge system based on the detected pressure of the relative pressure sensor. The first opening / closing means closes the inside of the evaporative purge system, the second opening / closing means closes the reference pressure detection chamber, and calculates a pressure change amount in the evaporative purge system based on the detected pressure of the relative pressure sensor. Pressure-equalized pressure change amount calculating means, and leak determining means for comparing the pressure change amounts calculated by the two pressure change amount calculating means to determine whether or not a fuel evaporative gas leaks in the evaporative purge system. And

In such a configuration, when the inside of the evaporative purge system is at a positive pressure, the inside of the evaporative purge system is closed by the first opening / closing means and the reference pressure detecting chamber is closed by the second opening / closing means. Is read, and the amount of pressure change in the evaporative purge system is calculated based on the detected pressure. When the evaporative purge system is at a negative pressure, the inside of the evaporative purge system is closed by the first opening / closing means, and the reference pressure detection chamber is further opened by the second opening / closing means. Is closed, the detection pressure of the relative pressure sensor is read, and the pressure change amount in the evaporation purge system is calculated based on the detection pressure. If there is a leak such as a crack in the evaporative purge system, the amount of pressure change is small at positive pressure because fuel evaporative gas leaks from the leak at the time of positive pressure, while the air enters the evaporative purge system from the leak at negative pressure. Since the pressure changes due to the inflow, the pressure changes are compared to determine whether or not the fuel vapor gas leaks in the evaporative purge system.

In this case, it is preferable that the two pressure changes are corrected in accordance with the atmospheric pressure change.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic configuration diagram of an evaporation purge system.

In FIG. 1, reference numeral 1 denotes an intake passage communicating with an intake port (not shown) of the engine, and an air cleaner 2, a throttle valve 3, and an air chamber 4 are disposed on the intake passage 1 from the upstream side. An intake port (not shown) of the engine is connected downstream of the intake passage 1. still,
Reference numeral 5 denotes a pressure sensor that detects the intake pipe pressure downstream of the throttle valve 3.

Reference numeral 6 denotes a fuel tank. The upper portion of the fuel tank 6 communicates with the canister 7 through an evaporative passage 8, and the canister 7 communicates with the air chamber 4 through a purge passage 9. Have been. The canister 7 is filled with an adsorbent 7a, and one end of the canister 7 is connected to an air introduction passage 7b. The air introduction passage 7b is opened and closed via an electromagnetic on-off valve 7c. Further, a first on-off valve 10 is interposed in the purge passage 9.

In this embodiment, the first on-off valve 10 also serves as a canister purge control (CPC) valve for controlling the purge ratio of fuel evaporative gas to intake air, but is independent of the CPC valve. May be provided. When the first on-off valve is provided independently, it is preferable to dispose this first on-off valve on the downstream side of the purge passage 9 as much as possible. In the following description, for convenience, the first on-off valve 10
Will be described as a CPC valve 10.

A pressure detecting chamber 11a of a relative pressure sensor 11 is connected to the fuel tank 6. This pressure detection chamber 11
a and a reference pressure detection chamber 11b are partitioned via a diaphragm type pressure detection section 11c.
An atmosphere passage 11d is communicated with the valve b, and the atmosphere passage 11d is opened / closed via an atmosphere opening / closing valve 12 as a second opening / closing valve.

The solenoid on-off valve 7c, the CPC valve 10, and the atmospheric on-off valve 12 are operated in accordance with a drive signal output from an electronic control unit (ECU) 13. In the electronic control unit 13, in the normal evaporative purge control mode, the atmosphere introduction passage 7 of the canister 7 is output based on parameters indicating the operating state of the engine output from the sensors and switches.
b in a state where the electromagnetic on-off valve 7c interposed in b is opened.
The valve opening of the C valve 10 is controlled so that the effect of the fuel evaporative gas purged to the intake system on the air-fuel ratio becomes substantially constant.

On the other hand, at the time of failure diagnosis, the CPC valve 10 is first fully closed with the solenoid on-off valve 7c closed, and if the internal pressure of the evaporative purge system is within a predetermined value, the failure diagnosis execution condition It is determined that the condition is satisfied, the atmosphere on-off valve 12 is closed, and the evaporation generation amount measurement mode is executed. Next, after once opening the atmosphere on-off valve 12 and the CPC valve 10,
Close and execute the leak generation amount measurement mode.The fuel evaporation is performed based on the pressure change in the evaporation purge system measured when the evaporation generation amount measurement mode is executed and the pressure change in the evaporation purge system measured when the leak generation amount measurement mode is executed. Check if gas is leaking.

An alarm lamp 14 is connected to the ECU 13, and when a leak of fuel evaporative gas is detected,
The alarm lamp 14 is turned on. Also, the diagnosis result is E
By connecting the serial monitor 15 to the CU 13, reading can be performed easily.

The failure diagnosis process executed by the ECU 13 is specifically performed according to a failure diagnosis routine shown in FIGS. During execution of the failure diagnosis processing,
The electromagnetic on-off valve 7c is closed, and the air introduction passage 7b of the canister 7 is closed.

When the failure diagnosis condition is satisfied, first, in step S1, the CPC valve 10 is closed and the fuel tank 6
Then, the inside of the evaporative purge system that reaches the CPC valve 10 interposed in the purge passage 9 through the evaporative passage 8 and the canister 7 is closed.

Next, the process proceeds to step S2, where it is determined whether or not the internal pressure of the evaporative purge system detected by the relative pressure sensor 11 is within a set positive pressure region (for example, 0 to 1400 Pa). Determines that the failure diagnosis execution condition is not satisfied, and exits the routine as it is. Also, when the internal pressure of the evaporative purge system falls within the set positive pressure range,
It is determined that the failure diagnosis execution condition is satisfied, and the process proceeds to step S3.

When the process proceeds to step S3, steps S3 to S
At 11, an evaporation generation amount measurement mode is executed.

First, in step S3, the relative pressure sensor 11
Is operated to close the atmosphere on-off valve 12 provided adjacent to. Then, the reference pressure detection chamber 11b is closed, and the relative pressure sensor 1
No. 1 detects a change in the internal pressure of the evaporative purge system using the pressure at the time of closing the valve as a reference pressure without being affected by a change in the atmospheric pressure.

Then, the process proceeds to step S4, and the system pressure (pressure at the start of the evaporative emission amount measurement mode) PEVPST at the start of the evaporative emission amount measurement mode in the evaporative purge system is measured based on the output signal from the relative pressure sensor 11. Then, the process proceeds to step S5, and a predetermined time (for example, 10 seconds)
c) elapses, and after a predetermined time elapses, the process proceeds to step S6, and based on the output signal from the relative pressure sensor 11, the system pressure (evaporation amount measurement mode) at the end of the evaporation generation amount measurement mode in the evaporative purge system. End pressure) PEVP
Measure E.

Thereafter, the flow advances to step S7 to calculate a command pressure change amount PEVPI from the difference between the mode end pressure PEVPE and the mode start pressure PEVPST (PEVP).
I ← PEVPE-PEVPST).

As shown in FIG. 5, if there is no abnormality in the evaporative purge system, in the evaporative emission amount measurement mode, the CP
The pressure in the evaporative purge system in the section where the C valve 10 is closed is considered to increase in accordance with the amount of generated fuel evaporative gas. For example, if there is a leak such as a crack in the evaporative purge system, Therefore, it is considered that the pressure rise becomes gentle or the pressure does not rise because the fuel evaporative gas leaks from. As a result, the indicated pressure change amount PE
VPI will show a small value.

Next, the routine proceeds to step S8, where the atmospheric opening / closing valve 12 is opened. Then, since the reference pressure detection chamber 11b of the relative pressure sensor 11 communicates with the atmosphere, the relative pressure sensor 11 detects a pressure change based on the current atmospheric pressure.

Thereafter, the process proceeds to step S9, in which the evaporative purge system internal pressure (system relative pressure) PEVP0 is measured based on the output signal from the relative pressure sensor 11, and step S10 is performed.
To the system relative pressure PEVP0 and the mode end pressure P
From the difference with EVPE, the differential pressure PEVPS due to atmospheric pressure change
Calculate W (PEVPSW ← PEVP0−PEVP)
E).

Then, the process proceeds to a step S11, wherein the actual system pressure change amount PEVPB is calculated based on the following equation. PEVPB ← K1 · PEVPSW + PEVPI Here, K1 is an atmospheric pressure correction value. As shown in FIG. 4, the atmospheric pressure correction value K1 is obtained from the ratio between the amount of pressure change due to contraction or expansion caused by the change in atmospheric pressure in the evaporative purge system when the CPC valve 10 is fully closed and the amount of change in atmospheric pressure. In the present embodiment, the calculated value is set to K1 = 0.5 as an experience value.

As described above, the instructed pressure change PEVPI in the evaporative purge system is corrected by the pressure change due to the atmospheric pressure change in the evaporative purge system, and the actual system pressure change PEVPB is corrected.
Is calculated, the actual system pressure change PEVP
B can be calculated accurately.

Therefore, if there is no leak in the evaporative purge system, the amount of evaporative generation can be accurately calculated from the actual in-system pressure change amount PEVPB. The description of the procedure for calculating the evaporation amount from the actual system pressure change amount PEVPB is omitted.

Next, the process proceeds to step S12, in which the internal pressure of the evaporative purge system is temporarily reduced in order to shift to the leak amount measurement mode in steps S12 to S14.

First, in step S12, the CPC valve 10 is opened to open the evaporative purge system. Then
An intake pipe negative pressure is introduced into the evaporative purge system, and the evaporative purge system is in a negative pressure state as shown in FIG.

Meanwhile, in step S13, the relative pressure sensor 1
1 and waits until the internal pressure of the evaporative purge system decreases to the measurement permission pressure (set negative pressure). When the internal pressure of the evaporation purge system decreases to the measurement permission pressure, the process proceeds to step S14, and the CPC valve 10
Is operated to close the evaporative purge system to a negative pressure state.

Thereafter, the flow advances to step S15, and a leak occurrence amount measurement mode is executed in steps S15 to S20.

First, in step S15, the atmosphere on-off valve 12
Is closed, and the reference pressure detecting chamber 11 of the relative pressure sensor 11 is operated.
Close b. Therefore, the relative pressure sensor 11 detects a change in the internal pressure of the evaporative purge system based on the pressure at the time of closing the valve without being affected by the change in the atmospheric pressure.

Then, the process proceeds to step S16, and the system pressure (pressure at the start of the leak generation amount measurement mode) PLERKST at the start of the leak generation amount measurement mode is measured based on the output signal from the relative pressure sensor 11. Then, step S1
7 and waits until a predetermined time (for example, 10 seconds) elapses. After the predetermined time elapses, the flow proceeds to step S18, and based on the output signal from the relative pressure sensor 11, the system pressure (leakage) at the end of the leak generation amount measurement mode. The pressure at the end of the generation amount measurement mode) PLERKE is measured.

Then, in step S19, the command pressure change amount PLERKI is calculated from the difference between the mode end pressure PLERKE and the mode start pressure PLERKST (PL
ERKI ← PLERKE-PLERKST).

As shown in FIG. 5, if there is no abnormality in the evaporative purge system, in the leak generation amount measurement mode, the CP
The pressure in the evaporative purge system in the section in which the C valve 10 is closed is considered to increase in accordance with the amount of generated fuel evaporative gas. For example, when there is a leak point such as a crack in the evaporative purge system, Is in a negative pressure state,
Contrary to the evaporation amount measurement mode, it is considered that the pressure rises steeply when the air flows into the evaporation purge system from the leak location, and the indicated pressure change amount PLERKI shows a large value.

Next, the routine proceeds to step S20, where the atmospheric opening / closing valve 12 is opened. Then, since the reference pressure detection chamber 11b of the relative pressure sensor 11 is communicated with the atmosphere, the relative pressure sensor 11 detects a relative pressure based on the current atmospheric pressure.

Thereafter, the process proceeds to step S21, in which the pressure (relative pressure in the system) PLERKO in the evaporative purge system is measured based on the output signal from the relative pressure sensor 11, and the process proceeds to step S21.
22, the difference between the relative pressure PLERKO in the system and the pressure PLERKE at the end of the mode is calculated as the differential pressure PL corresponding to the change in the atmospheric pressure.
Calculate ERKSW (PLERKSW ← PLERKO)
-PLERKE).

In step S23, the actual system pressure change amount PLERKB is calculated based on the following equation. PLERKB ← K1 · PLERKSW + PLERKI Here, K1 is an atmospheric pressure correction value, and in this embodiment, as in step S11 described above, K1 = 0.5 is set uniformly as an experience value.

As described above, the instructed pressure change PLERKI in the evaporative purge system is corrected by the pressure change due to the atmospheric pressure change in the evaporative purge system, and the actual system pressure change PLER is corrected.
Since KB is calculated, the actual system pressure change PL
ERKB can be accurately calculated.

Thereafter, the flow advances to step S24, and the presence or absence of a leak is determined based on the following leak determination condition. PLERKB-K2 · PEVPB> set value ... “failure (with leak)” PLERKB-K2 · PEVPB ≦ set value… “normal (no leak)” where K2 is the fuel evaporative gas generated by the difference between positive pressure and negative pressure Is a coefficient for correcting the difference in the amount of occurrence, and in the present embodiment, K2 = 1.5.

Therefore, when there is no leak, theoretically, P
LERKB = K2 · PEVPB, and the set value is a value indicating the permissible error.

As described above, when a leak has occurred, the actual system pressure change amount PEVPB calculated in the evaporation amount measurement mode shows a small value, and the actual system pressure change amount calculated in the leak generation amount measurement mode is small. System pressure change P
Since LERKB indicates a large value, it is determined that a failure has occurred (leakage has occurred).

Then, in step S24, the normal (PLE)
If it is determined that RKB−K2 · PEVPB ≦ set value, the process proceeds to step S25, where a failure determination flag (not shown) is cleared, and the process exits.

In addition, failure (PLERKB-1.5.PEV)
When it is determined that (PB> set value), the process proceeds to step S26, in which a failure determination flag (not shown) is set, and the process exits.

When this failure determination flag is set, E
The drive signal is output from the CU 13 to the alarm lamp 14, and the alarm lamp 14 is turned on or blinks to notify the driver of the failure of the evaporative purge system.

As described above, in the present embodiment, when detecting the presence or absence of leakage of the fuel evaporative gas in the evaporative purge system, the relative pressure sensor caused by the atmospheric pressure change in the evaporative emission amount measuring mode and the leak amount measuring mode. Considering the influence of the reference pressure change of No. 11 and the effect of contraction or expansion in the evaporative purge system, the actual system pressure change amount PEVPB, PLE
Since the RKB is detected, it is possible to diagnose the presence or absence of a leak not only during low-speed running, but also during high-speed running, high-altitude running, or mountain running, greatly improving the frequency of fault diagnosis.

Further, an atmospheric opening / closing valve 12 is provided in the reference pressure detecting chamber 11b of the existing relative pressure sensor 11, and the atmospheric opening / closing valve 12 is opened and closed before and after the diagnosis mode, so that the atmospheric pressure change amount during the diagnosis can be reduced. Since detection is performed, highly accurate diagnosis can be performed without newly adding an atmospheric pressure sensor.

[0056]

As described above, according to the present invention,
An atmospheric pressure sensor for detecting a change in atmospheric pressure is not required, and diagnosis can be performed not only in a low vehicle speed region but also in a high vehicle speed region, high altitude traveling, or traveling on a mountainous road. In addition, the frequency of diagnosis is improved, and the presence or absence of leakage of fuel evaporative gas can be detected with high accuracy.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an evaporation purge system.

FIG. 2 is a flowchart showing a failure diagnosis routine (part 1);

FIG. 3 is a flowchart showing a failure diagnosis routine (part 2);

FIG. 4 is an explanatory diagram of an atmospheric pressure correction value.

FIG. 5 is a waveform diagram showing a pressure change in an evaporative purge system due to opening and closing of an atmospheric on-off valve and a canister purge control valve.

[Description of Signs] 6 Fuel tank 7 Canister 8 Evaporation passage 9 Purge passage 11 Relative pressure sensor 11b Reference pressure detection chamber 10 Canister purge control valve (first opening / closing means) 12 Atmospheric opening / closing valve (second opening / closing means)

Claims (2)

[Claims] 1. A fuel tank communicates with a canister for adsorbing fuel evaporative gas generated in the fuel tank via an evaporative passage, and further communicates the canister with an intake system of an engine via a purge passage. An evaporative purge system for purging fuel vapor adsorbed in the canister to the intake system when the evaporative purge condition is satisfied; a first opening / closing means for opening and closing the purge passage; and A relative pressure sensor for detecting a pressure change in the evaporative purge system reaching the purge passage; a second opening / closing means for opening and closing a reference pressure detection chamber provided in the relative pressure sensor for detecting atmospheric pressure; At the time of pressure, the inside of the evaporative purge system is closed by the first opening / closing means, and the reference pressure detection chamber is closed by the second opening / closing means. Positive pressure change amount calculating means for calculating the pressure change amount in the evaporative purge system based on the detection pressure of the pressure sensor; and closing the evaporative purge system by the first opening / closing means when the evaporative purge system is negative pressure. Further, the second opening / closing means closes the reference pressure detection chamber and calculates a pressure change amount in the evaporative purge system based on the detected pressure of the relative pressure sensor. A failure diagnosis device for an evaporative purge system, comprising: a leak determination device that determines whether or not a fuel evaporative gas leaks in the evaporative purge system by comparing the pressure change amount calculated by the amount calculation device. 2. A failure diagnosis apparatus for an evaporative purge system according to claim 1, wherein said both pressure change amounts are corrected in accordance with an atmospheric pressure change amount.