Leak diagnostic system of evaporative emission control system for internal combustion engines

• US 6,276,343 B1
• Filed: 08/06/1999
• Issued: 08/21/2001
• Est. Priority Date: 08/21/1998
• Status: Expired due to Fees

• Current Assignee: Nissan Motor Co., Ltd.
• Original Assignee: Nissan Motor Co., Ltd.
• Inventors: Kobayashi, Hideaki, Kawamura, Katsuhiko
• Primary Examiner(s): Yuen, Henry C.
• Assistant Examiner(s): Gimie, Mahmoud
• Application Number:
  US09/369,192
• Time in Patent Office: 746 Days
• Field of Search: 123/516, 123/518, 123/519, 123/520, 123/198.D, 123/521
• US Class Current: 123/520
• CPC Class Codes: F02M 25/0809 Judging failure of purge control system

Abstract

In a leak diagnostic system of an evaporative emission control system for an internal combustion system, which utilizes a change in internal pressure in a predetermined fluid-flow passage ranging from a fuel tank via a canister to a purge control valve, in addition to a relative-pressure sensor for sensing the internal pressure, an atmospheric-pressure sensor is provided for sensing atmospheric pressure. The leak diagnostic system includes a control module which samples the pressure in the predetermined fluid-flow passage as a first fluid-flow passage pressure at a first sampling time when a predetermined decompressing operation is completed, and samples the pressure in the predetermined fluid-flow passage as a second fluid-flow passage pressure at a second sampling time when a predetermined time interval has been elapsed from the first sampling time. The leak diagnostic system makes a leak diagnosis by comparing the pressure differential between the first and second fluid-flow passage pressures with a predetermined leak criterion. The control module compensates for the pressure differential by the atmospheric-pressure change occurring for a time interval from the first sampling time to the second sampling time.

Claims

1. A leak diagnostic system of an evaporative emission control system for an internal combustion engine having a canister with an air vent, comprising:

a first fluid-flow passage introducing fuel vapors emitted from a fuel tank into the canister;

a second fluid-flow passage through which the canister is connected to an intake pipe of an induction system;

a purge control valve opening and closing said second fluid-flow passage;

a drain cut-off valve opening and closing the air vent of the canister;

a relative-pressure sensor sensing a pressure in a predetermined fluid-flow passage ranging from the fuel tank via the canister to said purge control valve, relative to atmospheric pressure;

an atmospheric-pressure sensor sensing the atmospheric pressure; and

a control module configured to be connected to at least said purge control valve, said drain cut-off valve, said relative-pressure sensor, and said atmospheric-pressure sensor;

said control module comprising;

a leak-diagnosis permission condition decision section determining whether a predetermined leak-diagnosis permission condition is met;

a decompression section reducing the pressure in the predetermined fluid-flow passage, while adjusting both an opening of said drain cut-off valve and an opening of said purge control valve, only when the predetermined leak-diagnosis permission condition is met;

a first sampling section sampling the pressure in the predetermined fluid-flow passage as a first fluid-flow passage pressure at a first sampling time when a predetermined decompressing operation is completed by said decompression section, and sampling the pressure in the predetermined fluid-flow passage as a second fluid-flow passage pressure at a second sampling time when a predetermined time interval has been elapsed from the first sampling time;

a first arithmetic-calculation section calculating a pressure differential between the first and second fluid-flow passage pressures;

a second sampling section sampling the atmospheric pressure sensed by said atmospheric-pressure sensor as a first atmospheric pressure at the first sampling time and sampling the atmospheric pressure sensed by said atmospheric-pressure sensor as a second atmospheric pressure at the second sampling time;

a second arithmetic-calculation section calculating an atmospheric-pressure change between the first and second atmospheric pressures;

a compensation section compensating for the pressure differential calculated by said first arithmetic-calculation section by the atmospheric-pressure change calculated by said second arithmetic-calculation section to produce a compensated pressure differential; and

a leak-diagnosis section making a leak-diagnosis by comparing the compensated pressure differential with a predetermined threshold value.

9. A leak diagnostic system as set forth in claim 1, wherein said atmospheric-pressure sensor continuously monitors atmospheric air pressure proximate the engine.

2. A leak diagnostic system of an evaporative emission control system for an internal combustion engine having a canister with an air vent, comprising:

a first fluid-flow passage introducing fuel vapors emitted from a fuel tank into the canister;

a second fluid-flow passage through which the canister is connected to an intake pipe of an induction system;

a purge control valve opening and closing said second fluid-flow passage;

a drain cut-off valve opening and closing the air vent of the canister;

a relative-pressure sensor sensing a pressure in a predetermined fluid-flow passage ranging from the fuel tank via the canister to said purge control valve, relative to atmospheric pressure;

an atmospheric-pressure sensor sensing the atmospheric pressure; and

a control module configured to be connected to at least said purge control valve, said drain cut-off valve, said relative-pressure sensor, and said atmospheric-pressure sensor;

said control module comprising;

a leak-diagnosis permission condition decision section determining whether a predetermined leak-diagnosis permission condition is met;

a decompression section reducing the pressure in the predetermined fluid-flow passage, while adjusting both an opening of said drain cut-off valve and an opening of said purge control valve, only when the predetermined leak-diagnosis permission condition is met;

a first sampling section sampling the pressure in the predetermined fluid-flow passage as an initial pressure just before a predetermined decompressing operation is started by said decompression section, the pressure in the predetermined fluid-flow passage as a first fluid-flow passage pressure at a first sampling time when the predetermined decompressing operation is completed, and sampling the pressure in the predetermined fluid-flow passage as a second fluid-flow passage pressure at a second sampling time when a predetermined time interval has been elapsed from the first sampling time;

a first arithmetic-calculation section calculating a first pressure differential between the initial pressure and the first fluid-flow passage pressure, and calculating a second pressure differential between the initial pressure and the second fluid-flow passage pressure;

a second sampling section sampling the atmospheric pressure sensed by said atmospheric-pressure sensor as a first atmospheric pressure at the first sampling time and sampling the atmospheric pressure sensed by said atmospheric-pressure sensor as a second atmospheric pressure at the second sampling time;

a second arithmetic-calculation section calculating an atmospheric-pressure change between the first and second atmospheric pressures;

a compensation section compensating for the second pressure differential calculated by said first arithmetic-calculation section by the atmospheric-pressure change calculated by said second arithmetic-calculation section to produce a compensated pressure differential;

a third arithmetic-calculation section calculating a leak area on the basis of the first pressure differential and the compensated pressure differential; and

a leak-diagnosis section making a leak-diagnosis by comparing the leak area calculated by said third arithmetic-calculation section with a predetermined leak criterion.

3. The leak diagnostic system as claimed in claim 2, wherein said third arithmetic-calculation section calculates the leak area AL2 from the following expression:

10. A leak diagnostic system as set forth in claim 2, wherein said atmospheric-pressure sensor continuously monitors atmospheric air pressure proximate the engine.

4. In an internal combustion engine equipped with an evaporative emission control system having at least a canister having an air vent and temporarily adsorbing fuel vapors emitted from a fuel tank, a fuel-tank vapor vent line introducing the fuel vapors into the canister, a purge line through which the canister is connected to an intake pipe of an induction system, a purge control valve disposed in the purge line, and a drain cut-off valve opening and closing the air vent of the canister, a leak diagnostic system of the evaporative emission control system, comprising:

a relative-pressure sensing means for sensing a pressure in a predetermined fluid-flow passage ranging from the fuel tank via the canister to the purge control valve, relative to atmospheric pressure;

an atmospheric-pressure sensing means for sensing the atmospheric pressure; and

control means configured to be connected to at least the purge control valve, the drain cut-off valve, said relative-pressure sensing means, and said atmospheric-pressure sensing means;

said control means comprising;

a leak-diagnosis permission condition decision means for determining whether a predetermined leak-diagnosis permission condition is met;

a decompression means for reducing the pressure in the predetermined fluid-flow passage, while adjusting both an opening of the drain cut-off valve and an opening of the purge control valve, only when the predetermined leak-diagnosis permission condition is met;

a first sampling means for sampling the pressure in the predetermined fluid-flow passage as a first fluid-flow passage pressure at a first sampling time when a predetermined decompressing operation is completed by said decompression means, and sampling the pressure in the predetermined fluid-flow passage as a second fluid-flow passage pressure at a second sampling time when a predetermined time interval has been elapsed from the first sampling time;

a first arithmetic-calculation means for calculating a pressure differential between the first and second fluid-flow passage pressures;

a second sampling means for sampling the atmospheric pressure sensed by said atmospheric-pressure sensing means as a first atmospheric pressure at the first sampling time and sampling the atmospheric pressure sensed by said atmospheric-pressure sensing means as a second atmospheric pressure at the second sampling time;

a second arithmetic-calculation means for calculating an atmospheric-pressure change between the first and second atmospheric pressures;

a compensation means for compensating for the pressure differential calculated by said first arithmetic-calculation means by the atmospheric-pressure change calculated by said second arithmetic-calculation means to produce a compensated pressure differential; and

a leak-diagnosis means for making a leak-diagnosis by comparing the compensated pressure differential with a predetermined threshold value.

11. A leak diagnostic system as set forth in claim 4, wherein said atmospheric-pressure sensor continuously monitors atmospheric air pressure proximate the engine.

5. In an internal combustion engine equipped with an evaporative emission control system having at least a canister having an air vent and temporarily adsorbing fuel vapors emitted from a fuel tank, a fuel-tank vapor vent line introducing the fuel vapors into the canister, a purge line through which the canister is connected to an intake pipe of an induction system, a purge control valve disposed in the purge line, and a drain cut-off valve opening and closing the air vent of the canister, a leak diagnostic system of the evaporative emission control system, comprising:

a relative-pressure sensing means for sensing a pressure in a predetermined fluid-flow passage ranging from the fuel tank via the canister to the purge control valve, relative to atmospheric pressure;

an atmospheric-pressure sensing means for sensing the atmospheric pressure; and

control means configured to be connected to at least the purge control valve, the drain cut-off valve, said relative-pressure sensing means, and said atmospheric-pressure sensing means;

said control means comprising;

a leak-diagnosis permission condition decision means for determining whether a predetermined leak-diagnosis permission condition is met;

a decompression means for reducing the pressure in the predetermined fluid-flow passage, while adjusting both an opening of the drain cut-off valve and an opening of the purge control valve, only when the predetermined leak-diagnosis permission condition is met;

a first sampling means for sampling the pressure in the predetermined fluid-flow passage as an initial pressure just before a predetermined decompressing operation is started by said decompression means, the pressure in the predetermined fluid-flow passage as a first fluid-flow passage pressure at a first sampling time when the predetermined decompressing operation is completed, and sampling the pressure in the predetermined fluid-flow passage as a second fluid-flow passage pressure at a second sampling time when a predetermined time interval has been elapsed from the first sampling time;

a first arithmetic-calculation means for calculating a first pressure differential between the initial pressure and the first fluid-flow passage pressure, and calculating a second pressure differential between the initial pressure and the second fluid-flow passage pressure;

a second sampling means for sampling the atmospheric pressure sensed by said atmospheric-pressure sensing means as a first atmospheric pressure at the first sampling time and sampling the atmospheric pressure sensed by said atmospheric-pressure sensing means as a second atmospheric pressure at the second sampling time;

a second arithmetic-calculation means for calculating an atmospheric-pressure change between the first and second atmospheric pressures;

a compensation means for compensating for the second pressure differential calculated by said first arithmetic-calculation means by the atmospheric-pressure change calculated by said second arithmetic-calculation means to produce a compensated pressure differential;

a third arithmetic-calculation means for calculating a leak area on the basis of the first pressure differential and the compensated pressure differential; and

a leak-diagnosis means for making a leak-diagnosis by comparing the leak area calculated by said third arithmetic-calculation means with a predetermined leak criterion.

12. A leak diagnostic system as set forth in claim 5, wherein said atmospheric-pressure sensing means continuously monitors atmospheric air pressure proximate the engine.

6. A method for making a leak diagnosis on an evaporative emission control system for an internal combustion engine, wherein the evaporative emission control system includes at least a canister having an air vent and temporarily adsorbing fuel vapors emitted from a fuel tank, a fuel-tank vapor vent line introducing the fuel vapors into the canister, a purge line through which the canister is connected to an intake pipe of an induction system, a purge control valve disposed in the purge line, and a drain cut-off valve opening and closing the air vent of the canister, the method comprising:

sensing a pressure in a predetermined fluid-flow passage ranging from the fuel tank via the canister to the purge control valve, relative to atmospheric pressure,

sensing the atmospheric pressure,

determining whether a predetermined leak-diagnosis permission condition is met,

reducing the pressure in the predetermined fluid-flow passage, while adjusting both an opening of the drain cut-off valve and an opening of the purge control valve, only when the predetermined leak-diagnosis permission condition is met,

sampling the pressure in the predetermined fluid-flow passage as a first fluid-flow passage pressure at a first sampling time when the pressure in the predetermined fluid-flow passage is reduced to a predetermined value,

sampling the pressure in the predetermined fluid-flow passage as a second fluid-flow passage pressure at a second sampling time when a predetermined time interval has been elapsed from the first sampling time,

calculating a pressure differential between the first and second fluid-flow passage pressures,

sampling the atmospheric pressure as a first atmospheric pressure at the first sampling time,

sampling the atmospheric pressure as a second atmospheric pressure at the second sampling time,

calculating an atmospheric-pressure change between the first and second atmospheric pressures,

compensating for the pressure differential between the first and second fluid-flow passage pressures by the atmospheric-pressure change to produce a compensated pressure differential, and

making a leak-diagnosis by comparing the compensated pressure differential with a predetermined threshold value.

13. A leak diagnostic system as set forth in claim 6, wherein said step of sensing atmospheric-pressure is continuously carried out proximate the engine.

7. A method for making a leak diagnosis on an evaporative emission control system for an internal combustion engine, wherein the evaporative emission control system includes at least a canister having an air vent and temporarily adsorbing fuel vapors emitted from a fuel tank, a fuel-tank vapor vent line introducing the fuel vapors into the canister, a purge line through which the canister is connected to an intake pipe of an induction system, a purge control valve disposed in the purge line, and a drain cut-off valve opening and closing the air vent of the canister, the method comprising:

sensing a pressure in a predetermined fluid-flow passage ranging from the fuel tank via the canister to the purge control valve, relative to atmospheric pressure,

sensing the atmospheric pressure,

determining whether a predetermined leak-diagnosis permission condition is met,

reducing the pressure in the predetermined fluid-flow passage, while adjusting both an opening of the drain cut-off valve and an opening of the purge control valve, only when the predetermined leak-diagnosis permission condition is met,

reducing the pressure in the predetermined fluid-flow passage, while adjusting both an opening of the drain cut-off valve and an opening of the purge control valve, only when the predetermined leak-diagnosis permission condition is met,

sampling the pressure in the predetermined fluid-flow passage as an initial pressure just before starting to reduce the pressure in the predetermined fluid-flow passage,

sampling the pressure in the predetermined fluid-flow passage as a first fluid-flow passage pressure at a first sampling time when the pressure in the predetermined fluid-flow passage is reduced to a predetermined value,

sampling the pressure in the predetermined fluid-flow passage as a second fluid-flow passage pressure at a second sampling time when a predetermined time interval has been elapsed from the first sampling time,

calculating a first pressure differential between the initial pressure and the first fluid-flow passage pressure,

calculating a second pressure differential between the initial pressure and the second fluid-flow passage pressure,

sampling the atmospheric pressure as a first atmospheric pressure at the first sampling time,

sampling the atmospheric pressure as a second atmospheric pressure at the second sampling time,

calculating an atmospheric-pressure change between the first and second atmospheric pressures,

compensating for the second pressure differential by the atmospheric-pressure change to produce a compensated pressure differential,

calculating a leak area on the basis of the first pressure differential and the compensated pressure differential, and

making a leak-diagnosis by comparing the leak area with a predetermined leak criterion.

8. The method as claimed in claim 7, wherein the leak area AL2 is arithmetically calculated from the following expression:

14. A leak diagnostic system as set forth in claim 7, wherein said step of sensing atmospheric-pressure is continuously carried out proximate the engine.