Fault diagnostic apparatus for evaporated fuel purging system

• US 5,679,890 A
• Filed: 03/27/1996
• Issued: 10/21/1997
• Est. Priority Date: 03/29/1995
• Status: Expired due to Term

• Current Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Original Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Inventors: Teraoka, Katsuhiko, Shinohara, Susumu
• Primary Examiner(s): Dombroske, George M.
• Application Number:
  US08/624,009
• Time in Patent Office: 573 Days
• Field of Search: 73/115, 73/116, 73/117.2, 73/117.3, 73/118.1, 73/118.2, 73/40.5 R, 73/49.7, 123/518, 123/519, 123/520, 123/521
• US Class Current: 73/114.39
• CPC Class Codes: F02M 25/0809 Judging failure of purge control system

Abstract

The fault diagnostic apparatus of the present invention detects a failure (a leak) of a fuel tank of an engine. In this invention, space above the fuel level in the fuel tank is connected to a canister. The canister contains an adsorbent to adsorb evaporated fuel in the tank to prevent the evaporated fuel from being released to the atmosphere. Valves are provided to the canister to keep the internal pressure of the canister within a predetermined range. A control circuit of the engine employs a pressure sensor to monitor the internal pressure of the fuel tank, and determines whether the fuel tank has failed in accordance with a change in the internal pressure of the fuel tank. Since the change in the fuel level in the fuel tank varies in accordance with the fuel consumption rate, the change in the pressure in the fuel tank also varies in accordance with the fuel consumption rate. Therefore, the control circuit stops the determining operation when the fuel consumption rate of the engine is too large or too small, to avoid an error in the diagnosis of the fuel tank.

Claims

1. A fault diagnostic apparatus for an evaporative fuel purging system, comprising:

a vapor path connecting a space above a fuel level in a fuel tank of an internal combustion engine to an intake duct of the engine;

a purging unit disposed in the vapor path for purging evaporated fuel in the fuel tank into an intake duct through the vapor path;

an internal pressure control valve arranged in the vapor path between the purge unit and the fuel tank, for opening when the internal pressure of the fuel tank increases above a predetermined pressure higher than atmospheric pressure, to thereby keep the internal pressure of the fuel tank below said predetermined pressure;

pressure detecting means for detecting the internal pressure of the fuel tank;

failure determining means for performing a determining operation for determining whether the fuel tank has failed according to the internal pressure of the fuel tank detected by the detecting means after the engine is started;

fuel consumption detecting means for detecting the amount of fuel consumed by the engine after the start of the engine; and

control means for controlling the determining operation of the determining means in accordance with the fuel consumption detected by the fuel consumption detecting means;

wherein said control means prohibits the failure determining means from performing the determining operation when the amount of fuel consumed by the engine within a given period after the engine starts is smaller than a predetermined lower limit.

2. A fault diagnostic apparatus according to claim 1, wherein said failure determining means calculates the value of a failure determination parameter based on the internal pressure of the fuel tank detected within a predetermined period after the engine starts and determines whether the fuel tank has failed by comparing the value of the failure determination parameter with a predetermined reference value, and wherein said control means changes the reference value in accordance with the amount of fuel consumed by the engine within a given period after the engine starts.

3. A fault diagnostic apparatus for an evaporative fuel purging system, comprising:

a vapor path connecting a space above a fuel level in a fuel tank of an internal combustion engine to an intake duct of the engine;

a pursing unit disposed in the vapor path for purging evaporated fuel in the fuel tank into an intake duct through the vapor path;

an internal pressure control valve arranged in the vapor path between the purge unit and the fuel tank, for opening when the internal pressure of the fuel tank increases above a predetermined pressure higher than atmospheric pressure, to thereby keep the internal pressure of the fuel tank below said predetermined pressure;

pressure detecting means for detecting the internal pressure of the fuel tank;

failure determining means for performing a determining operation for determining whether the fuel tank has failed according to the internal pressure of the fuel tank detected by the detecting means after the engine is started;

fuel consumption detecting means for detecting the amount of fuel consumed by the engine after the start of the engine; and

control means for controlling the determining operation of the determining means in accordance with the fuel consumption detected by the fuel consumption detecting means;

wherein said control means prohibits the failure determining means from performing the determining operation when the amount of fuel consumed by the engine within a given period starting when a predetermined time has elapsed after the engine starts is higher than a predetermined upper limit.

4. A fault diagnostic apparatus for an evaporated fuel purging system, comprising:

a vapor path connecting a space above a fuel level in a fuel tank of an internal combustion engine to an intake duct of the engine;

a purging unit disposed in the vapor path for purging evaporated fuel in the fuel tank into an intake duct through the vapor path;

an internal pressure control valve arranged in the vapor path between the purge unit and the fuel tank, for opening when the internal pressure of the fuel tank increases above a predetermined pressure higher than atmospheric pressure, to thereby keep the internal pressure of the fuel tank below said predetermined pressure;

pressure detecting means for detecting the internal pressure of the fuel tank;

failure determining means for performing a determining operation for determining whether the fuel tank has failed according to the internal pressure of the fuel tank detected by the pressure detecting means after the engine is started;

temperature detecting means for detecting the temperature of a wall of the fuel tank; and

prohibiting means for prohibiting said failure determining means from performing the determining operation when the wall temperature of the fuel tank changes more than a predetermined amount within a given period after the engine starts.

5. A fault diagnostic apparatus for an evaporative fuel purging system, comprising:

a vapor path connecting a space above a fuel level in a fuel tank of an internal combustion engine to an intake duct of the engine;

a purging unit disposed in the vapor path for purging evaporated fuel in the fuel tank into an intake duct through the vapor path;

valve means arranged in the vapor path between the purge unit and the fuel tank, for opening when the internal pressure of the fuel tank increases becomes a predetermined pressure, to thereby keep the internal pressure of the fuel tank within a predetermined pressure range;

pressure detecting means for measuring the internal pressure of the fuel tank;

failure determining means for performing a determining operation for determining whether the fuel tank has failed based on the internal pressure of the fuel tank measured by the pressure detecting means after the engine is started;

wherein said failure determining means performs a determining operation in such a manner that an error in the measurement of the internal pressure of the fuel tank due to a measurement tolerance of the pressure detecting means is corrected,

wherein said valve means opens when the internal pressure of the fuel tank increases above a predetermined reference pressure higher than atmospheric pressure, to thereby keep the interval pressure of the fuel tank below said reference pressure, and said failure determining means determines whether the fuel tank has failed by comparing the internal pressure of the fuel tank detected at the start of the engine with the internal pressure of the fuel tank detected within a predetermined period after the engine starts.

6. A fault diagnostic apparatus for an evaporative fuel purging system, comprising:

a vapor path connecting a space above a fuel level in a fuel tank of an internal combustion engine to an intake duct of the engine;

a purging unit disposed in the vapor path for purging evaporated fuel in the fuel tank into an intake duct through the vapor path;

valve means arranged in the vapor path between the purge unit and the fuel tank, for opening when the internal pressure of the fuel tank becomes a predetermined pressure, to thereby keep the internal pressure of the fuel tank within a predetermined pressure range wherein, said valve means opens when the difference between the internal pressure of the fuel tank and atmospheric pressure becomes more than a predetermined amount, to thereby keep the pressure difference between the fuel tank and the atmosphere within the predetermined amount;

pressure detecting means for detecting a difference between the internal pressure of the fuel tank and the atmospheric pressure;

failure determining means for performing a determining operation for determining whether the fuel tank has failed based on the pressure difference measured by the pressure detecting means after the engine is started wherein said failure determining means comprises first determining means for determining whether the fuel tank has failed by comparing the pressure difference when the engine starts with a first reference value, and a second determining means for determining whether the fuel tank has failed by comparing an amount of change in the pressure difference within a predetermined period after the engine starts with a predetermined second reference value;

wherein said failure determining means performs a determining operation in such a manner that an error in the measurement of the internal pressure of the fuel tank due to a measurement tolerance of the pressure detecting means is corrected,

wherein, said predetermined amount of the pressure difference at which the valve means opens is set at a larger value than a total of a measuring tolerance of said pressure detecting means and said first reference value and said second reference value.

7. A fault diagnostic apparatus for an evaporative fuel purging system, comprising:

a vapor path connecting a space above a fuel level in a fuel tank of an internal combustion engine to an intake duct of the engine;

a purging unit disposed in the vapor path for purging evaporated fuel in the fuel tank into an intake duct through the vapor path, said purge unit comprising a canister connected to the space above a fuel level in the fuel tank and to the intake duct of the engine by the vapor path for adsorbing the evaporated fuel from the fuel tank and for purging the adsorbed fuel into the intake duct, and a purge control valve for alternately opening and blocking the vapor path;

valve means arranged in the vapor path between the purge unit and the fuel tank, for opening when the internal pressure of the fuel tank increases becomes a predetermined pressure, to thereby keep the internal pressure of the fuel tank within a predetermined pressure range wherein said valve means opens when the difference between the internal pressure of the fuel tank and atmospheric pressure becomes more than a predetermined amount, to thereby keep the pressure difference within the predetermined amount;

pressure detecting means for detecting an internal pressure of the fuel tank and an internal pressure of the canister;

failure determining means for performing a determining operation for determining whether the fuel tank has failed based on the internal pressure of the fuel tank measured by the pressure detecting means after the engine is started wherein said failure determining means determines whether the fuel tank has failed by comparing the internal pressure of the fuel tank at the start of the engine with the internal pressure of the canister at the start of the engine;

wherein said failure determining means performs a determining operation in such a manner that an error in the measurement of the internal pressure of the fuel tank due to a measurement tolerance of the pressure detecting mean is corrected.

8. A fault diagnostic apparatus for an evaporative fuel purging system, comprising:

a vapor path connecting a space above a fuel level in a fuel tank of an internal combustion engine to an intake duct of the engine;

a purging unit disposed in the vapor path for purging evaporated fuel in the fuel tank into an intake duct through the vapor path;

valve means arranged in the vapor path between the purge unit and the fuel tank, for opening when the internal pressure of the fuel tank increases becomes a predetermined pressure, to thereby keep the internal pressure of the fuel tank within a predetermined pressure range;

pressure detecting means for sensing both an internal pressure of the fuel tank and an atmospheric pressure;

failure determining means for determining whether the fuel tank has failed by comparing the internal pressure of the fuel tank at the start of the engine with the atmospheric pressure;

wherein said pressure detecting means comprises a pressure sensor and a switching valve which selectively connects the pressure sensor to the space above the fuel level in the fuel tank and to the vapor path, and wherein said pressure detecting means detects the atmospheric pressure by connecting the pressure sensor to the vapor path before the engine is started.

9. A fault diagnostic apparatus for an evaporative fuel purging system, comprising:

a vapor path connecting a space above a fuel level in a fuel tank of an internal combustion engine to an intake duct of the engine;

a purging unit disposed in the vapor path for purging evaporated fuel in the fuel tank into an intake duct through the vapor path;

an internal pressure control valve arranged in the vapor path between the purge unit and the fuel tank, for opening when the internal pressure of the fuel tank increases above a predetermined pressure higher than atmospheric pressure, to thereby keep the internal pressure of the fuel tank below said predetermined pressure;

pressure detecting means for detecting an internal pressure of the fuel tank and an atmospheric pressure;

failure determining means for determining whether the fuel tank has failed based on the internal pressure of the fuel tank, wherein the failure detecting means determines that the fuel tank is normal when the internal pressure of the fuel tank detected by the detecting means before the engine starts is outside a predetermined pressure range, the predetermined pressure range extending from a predetermined lower limit to a predetermined upper limit.