Leakage diagnosis apparatus and method for diagnosing purge apparatus for internal combustion engine

Abstract

A leakage diagnosis apparatus is applied to a purge apparatus of an internal combustion engine. The purge apparatus includes a canister accommodating an adsorbent for temporarily absorbing fuel vapor produced in a fuel tank. The fuel vapor is desorbed from the adsorbent and purged into an intake passage of the internal combustion engine. A diagnosis unit performs a leakage diagnosis to detect leakage in the purge apparatus. A state measurement unit measures a fuel vapor state of mixture containing the fuel vapor, which is desorbed from the adsorbent. A command unit commands the diagnosis unit to perform the leakage diagnosis at a predetermined time. An evaluating unit evaluates the leakage diagnosis to be performed in an appropriate state on the basis of a change between the fuel vapor state before the leakage diagnosis and the fuel vapor state after the leakage diagnosis.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings. In the drawings:

FIG. 1 is a schematic diagram showing a purge apparatus;

FIG. 2 is a flow chart showing a purge control;

FIG. 3 is a time chart showing an operation of the purge control;

FIG. 4 is a flow chart showing a leakage diagnosis operation;

FIG. 5 is a flow chart showing a leakage diagnosis routine; and

FIGS. 6, 7 are schematic diagrams showing the purge apparatus in a concentration measurement.

Claims

1. A leakage diagnosis apparatus for a purge apparatus of an internal combustion engine, the purge apparatus including a canister accommodating an adsorbent for temporarily absorbing fuel vapor produced in a fuel tank and for purging the fuel vapor desorbed from the adsorbent into an intake passage of the internal combustion engine, the leakage diagnosis apparatus comprising: a diagnosis unit for performing a leakage diagnosis to detect leakage in the purge apparatus;a state measurement unit for measuring a fuel vapor state of mixture containing the fuel vapor desorbed from the adsorbent;a command unit for commanding the diagnosis unit to perform the leakage diagnosis at a predetermined time; andan evaluating unit for evaluating the leakage diagnosis to be performed in an appropriate state on the basis of a change between the fuel vapor state before the leakage diagnosis and the fuel vapor state after the leakage diagnosis.

2. The leakage diagnosis apparatus according to claim 1, wherein the state measurement unit includes: a measurement passage that includes a throttle;a stream generating unit for generating a gas stream in the measurement passage;a pressure detecting unit for detecting pressure in a downstream of the throttle;a first switching unit for switching between a first measurement state, in which air flows through the measurement passage by opening the measurement passage to the atmosphere, and a second measurement, in which the mixture flows through the measurement passage by communicating the measurement passage with the canister; anda fuel-vapor-state calculating unit for calculating the fuel vapor state on the basis of a first pressure, which is detected in the first measurement state, and a second pressure, which is detected in the second measurement state,wherein the diagnosis unit includes a second switching unit for facilitating a third measurement state, in which the mixture flows from the canister into the downstream of the throttle while bypassing the throttle, andthe diagnosis unit performs the leakage diagnosis on the basis of the first pressure and a third pressure, which is detected in the third measurement state.

3. The leakage diagnosis apparatus according to claim 1, wherein the command unit commands the diagnosis unit to perform the leakage diagnosis when a first time period lapses after stop of the internal combustion engine; andthe command unit commands the diagnosis unit to perform the leakage diagnosis again when a second time period lapses after the previous leakage diagnosis under a condition where the evaluating unit performs the previous leakage diagnosis in a state other than the appropriate state.

4. The leakage diagnosis apparatus according to claim 3, wherein the command unit repeatedly commands the diagnosis unit to perform the leakage diagnosis each time the second time period lapses, till the evaluating unit determines the leakage diagnosis to be performed in the appropriate state.

5. The leakage diagnosis apparatus according to claim 3, the second time period is greater than the first time period.

6. The leakage diagnosis apparatus according to claim 1, wherein the evaluating unit determines the leakage diagnosis to be performed in a state other than the appropriate state under the following conditions:the fuel vapor state after the leakage diagnosis is greater than the fuel vapor state before the leakage diagnosis by a threshold.

7. A leakage diagnosis apparatus for a purge apparatus of an internal combustion engine, the purge apparatus including an adsorbent for temporarily absorbing fuel vapor and desorbing the fuel vapor into an intake passage of the internal combustion engine, the leakage diagnosis apparatus comprising: a diagnosis unit for performing a leakage diagnosis to detect leakage in the purge apparatus on the basis of pressure in the purge apparatus;a state measurement unit for measuring a fuel vapor concentration in mixture containing the fuel vapor; andan evaluating unit for evaluating the leakage diagnosis to be performed in an appropriate state on the basis of a change between the fuel vapor concentration before the leakage diagnosis and the fuel vapor concentration after the leakage diagnosis.

8. A method for diagnosing a purge apparatus for purging fuel vapor into an intake passage of an internal combustion engine, the method comprising: desorbing fuel vapor, which is temporarily absorbed into an adsorbent of the purge apparatus, from the adsorbent;measuring a fuel vapor state of mixture containing the fuel vapor;detecting leakage in the purge apparatus; andevaluating whether the detecting of leakage is in an appropriate state on the basis of a change between the fuel vapor state before the detecting of leakage and the fuel vapor state after the detecting of leakage.

9. A method for diagnosing a purge apparatus for purging fuel vapor into an intake passage of an internal combustion engine, the method comprising: desorbing fuel vapor, which is temporarily absorbed into an adsorbent of the purge apparatus, from the adsorbent;measuring a fuel vapor concentration in mixture containing the fuel vapor;detecting leakage in the purge apparatus on the basis of pressure in the purge apparatus;evaluating whether the detecting of leakage is in an appropriate state on the basis of a change between the fuel vapor concentration before the leakage diagnosis and the fuel vapor concentration after the leakage diagnosis; andrepeating the detecting of leakage when the leakage diagnosis is in a state other than the appropriate state.