Measuring and testing – With fluid pressure – Leakage
Reexamination Certificate
2001-06-06
2004-07-13
Williams, Hezron (Department: 2856)
Measuring and testing
With fluid pressure
Leakage
C073S049700
Reexamination Certificate
active
06761058
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a leakage determination system for an evaporative fuel processing system of an internal combustion engine, for determining whether or not there is a leak in the evaporative fuel processing system which causes a canister to temporarily store evaporative fuel generated from a fuel tank, and supplies the same to an intake system of the engine with proper timing.
2. Description of the Prior Art
Conventionally, a leakage determination system of the above-mentioned kind was proposed e.g. in Japanese Laid-Open Patent Publication (Kokai) No. 9-291854. The evaporative fuel processing system includes a canister, a fuel tank, a charge passage, and a purge passage. The canister is connected to the fuel tank via the charge passage. The charge passage is provided with a pressure sensor that detects pressure within the charge passage (hereinafter referred to as “the tank internal pressure” because the pressure within the charge passage is approximately equal to pressure within the fuel tank in a steady state of the system). In a bypass passage bypassing the charge passage, there is arranged a bypass valve for opening and closing the bypass passage. Further, the canister is connected to an atmosphere passage which is open to the atmosphere, and in the atmosphere passage, there is arranged a vent shut valve for opening and closing the same. In the purge passage, there is arranged a purge control valve for opening and closing the same.
The leakage determination system determines whether or not there is a leak in the evaporative fuel processing system, by carrying out a pressure-reducing mode process and a leakage-checking mode process sequentially as described below. First, in the pressure-reducing mode process, the bypass valve and the purge control valve are opened, and the vent shut valve is closed, whereby the pressure within the evaporative fuel processing system is reduced until the tank internal pressure is lowered to a predetermined negative pressure.
Then, in the leakage-checking mode process, the bypass valve, the purge control valve and the vent shut valve are all closed to maintain the evaporative fuel processing system in a sealed state over a predetermined time period, and in this state, changes in the tank internal pressure are monitored. Through this monitoring, if a change in the tank internal pressure becomes equal to or larger than a predetermined value, it is determined that there is a leak in the system, whereas if the changes in the tank internal pressure are held below the predetermined value, it is determined that there is no leak.
In the above conventional leakage determination system, however, e.g. when the vehicle is jolted with only a small amount of fuel remaining in the fuel tank or when the outside temperature is high, the amount of evaporative fuel within the fuel tank can be increased to raise the tank internal pressure in a short time, which makes it impossible to effect an accurate leakage determination. In short, the leakage-checking mode process is only executed for checking changes in the tank internal pressure within the predetermined time period, and hence if the tank internal pressure is temporarily increased for some reason as mentioned above, it can be erroneously determined that there is a leak, even though there is no leak.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a leakage determination system for an evaporative fuel processing system, which, even when pressure within the evaporative fuel processing system is temporarily increased e.g. due to an increase in the amount of evaporative fuel in a fuel tank, is capable of performing an accurate leakage determination by eliminating the influence of the temporary rise in the pressure within the evaporative fuel processing system.
To attain the above object, according to a first aspect of the invention, there is provided a leakage determination system for an evaporative fuel processing system that causes a canister to absorb evaporative fuel generated from a fuel tank and supplies the evaporative fuel absorbed in the canister to an intake system of an internal combustion engine,
the leakage determination system comprising:
pressure detection means for detecting pressure within the evaporative fuel processing system;
pressure reduction means for reducing the pressure within the evaporative fuel processing system until the detected pressure within the evaporative fuel processing system becomes equal to a predetermined negative pressure, by introducing negative pressure from the intake system;
negative pressure introduction means for introducing the negative pressure from the intake system into the evaporative fuel processing system under predetermined conditions after the pressure reduction by the pressure reduction means; and
leakage determination means for determining whether or not there is a leak in the evaporative fuel processing system, based on a state of the pressure within the evaporative fuel processing system, which has been detected during the introduction of the negative pressure from the intake system by the negative pressure introduction means.
Preferably, the negative pressure introduction means introduces the negative pressure from the intake system at a predetermined constant negative pressure introduction flow rate.
According to this leakage determination system for an evaporative fuel processing system, in a leakage determination process, first, negative pressure is introduced from the intake system into the evaporative fuel processing system, whereby the pressure within the evaporative fuel processing system is reduced to the predetermined negative pressure. Then, after the pressure reduction is terminated, negative pressure is introduced again from the intake system into the evaporative fuel processing system at the predetermined constant negative pressure introduction flow rate, and whether or not there is a leak in the evaporative fuel processing system is determined based on a pressure within the evaporative fuel processing system, which has been detected during the introduction of the negative pressure at the constant flow rate. According to the first aspect of the invention, since the pressure within the evaporative fuel processing system is detected while introducing the negative pressure as described above, the detected pressure represents an offset between an increment of a pressure increased by leakage and a decrement of the same reduced by the introduction of the negative pressure. Therefore, leakage determination for the evaporative fuel processing system can be carried out based on the pressure within the evaporative fuel processing system.
Further, since the pressure within the evaporative fuel processing system is detected while continuously introducing the negative pressure, even when the pressure within the evaporative fuel processing system is temporarily increased e.g. due to an increase in the amount of evaporative fuel generated in the fuel tank, it is possible to carry out leakage determination while reducing the temporary rise in the pressure. Consequently, the influence of the temporary rise in the pressure caused by other factors than leakage on the leakage determination can be eliminated, which enables accurate determination of whether or not there is a leak in the evaporative fuel processing system.
More preferably, the negative pressure introduction means includes pressure re-reduction means for holding the evaporative fuel processing system in a closed state and introducing the negative pressure from the intake system whenever the pressure within the evaporative fuel processing system rises to a predetermined pressure higher than the predetermined negative pressure, to thereby repeatedly reduce the pressure within the evaporative fuel processing system to a second predetermined negative pressure lower than the predetermined pressure,
the leakage determination system further comprising pressure reduction cycle detection means for detecting a pressure red
Isobe Takashi
Yamaguchi Takashi
Arent & Fox PLLC
Garber Charles D.
Honda Giken Kogyo Kabushiki Kaisha
Williams Hezron
LandOfFree
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