Diagnosis for evaporative emission control system
First Claim
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1. A diagnostic apparatus for an evaporative emission control system, the diagnostic apparatus comprising:
- a first passage conveying evaporative fuel vapor from a fuel tank to a canister;
a second passage extending between the canister and an intake passage section downstream of a throttle valve;
a purge control valve opening and closing the second passage;
a drain cut valve opening and closing an atmospheric port of the canister;
a pressure sensor sensing a pressure in a fluid passage from the fuel tank to the purge control valve; and
a controller holding the fluid passage from the fuel tank to the purge control valve in a state of a closed space by closing the purge control valve and the drain cut valve when an engine is out of operation, and performing a leak diagnosis by checking a pressure decrease due to condensation of the fuel vapor in the fluid passage held in the state of a closed space when the engine is started.
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Abstract
At the time of a stop of an engine, a diagnostic control unit shuts off a purge line with a purge control valve and an atmospheric port of a canister with a drain cut valve, and thereby holds an evaporative emission control circuit inclusive of a fuel tank and the canister in a state of a closed space during an off period of the engine. At the time of a next start of the engine, the diagnostic control unit measures a pressure in the closed circuit with a pressure sensor and checks a pressure decrease due to condensation of fuel vapors in the closed circuit to determine the existence or nonexistence of leakage.
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Citations
15 Claims
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1. A diagnostic apparatus for an evaporative emission control system, the diagnostic apparatus comprising:
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a first passage conveying evaporative fuel vapor from a fuel tank to a canister;
a second passage extending between the canister and an intake passage section downstream of a throttle valve;
a purge control valve opening and closing the second passage;
a drain cut valve opening and closing an atmospheric port of the canister;
a pressure sensor sensing a pressure in a fluid passage from the fuel tank to the purge control valve; and
a controller holding the fluid passage from the fuel tank to the purge control valve in a state of a closed space by closing the purge control valve and the drain cut valve when an engine is out of operation, and performing a leak diagnosis by checking a pressure decrease due to condensation of the fuel vapor in the fluid passage held in the state of a closed space when the engine is started. - View Dependent Claims (2, 3, 4)
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5. An evaporative emission control system comprising:
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a fuel tank for storing fuel for an engine;
a canister;
a first passage conveying evaporative fuel vapor from the fuel tank to the canister;
a second passage extending from the canister to an intake passage of the engine;
a valve system for putting a fuel vapor recovery passage defined by the fuel tank, the first passage, the canister and the second passage in a closed state in which the fuel vapor recovery passage is in a state of a closed space;
a pressure sensor sensing a fluid pressure in the vapor recovery passage; and
a diagnostic controller for holding the vapor recovery passage in the closed state by controlling the valve system during an off period of the engine, for determining a first pressure value of the fluid pressure sensed by the pressure sensor at a start of the engine, for calculating, from the first pressure value, a pressure decrease due to condensation of the fuel vapor in the vapor recovery passage held in the closed state during the off period of the engine, and for producing a leak diagnostic signal indicating existence of a leak in the vapor recovery passage when the pressure decrease is smaller than a predetermined pressure decrease value. - View Dependent Claims (6, 7, 8, 9, 10, 11, 12)
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13. An evaporative emission control system comprising:
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a first passage conveying evaporative fuel vapor from a fuel tank to a canister;
a second passage extending from the canister to an intake passage;
a valve system for putting an evaporative fuel vapor recovery passage formed by the fuel tank, the first passage, the canister and the second passage in a closed state in which the vapor recovery passage is in a state of a closed space;
pressure sensing means for sensing a fluid pressure in the vapor recovery passage;
holding means for holding the vapor recovery passage in the closed state by controlling the valve system during an off period of the engine; and
diagnosing means for determining a pressure decrease in the vapor recovery passage during the off period of the engine by sampling the fluid pressure sensed by the pressure sensor at a start of the engine, and for producing a leak diagnostic signal indicating existence of a leak in the vapor recovery passage when the pressure decrease is smaller than a predetermined pressure decrease value.
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14. A diagnostic process for an evaporative emission control system comprising a first passage conveying evaporative fuel vapor from a fuel tank to a canister, and a second passage extending from the canister to an intake passage for an engine, the diagnostic process comprising:
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holding a fuel vapor recovery passage extending from the fuel tank through the canister to the second passage in a closed state to confine fuel vapor in the fuel vapor recovery passage during an off period of the engine; and
detecting leakage in the fuel vapor recovery passage at an end of the off period by checking a pressure decrease in the fuel vapor recovery passage held in the closed state during the off period. - View Dependent Claims (15)
inhibiting a diagnostic judgment based on the pressure degrease in the fuel vapor recovery passage when the off period of the engine ends with a restart of the engine before the engine cools down.
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Specification