Internal-combustion engines – Charge forming device – Having fuel vapor recovery and storage system
Reexamination Certificate
2000-06-28
2001-10-23
Miller, Carl S. (Department: 3747)
Internal-combustion engines
Charge forming device
Having fuel vapor recovery and storage system
C123S516000
Reexamination Certificate
active
06305362
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an evaporative emission control system for an internal combustion engine, and more particularly to such a system that the emission of evaporative fuel is prevented by maintaining the pressure in a fuel tank at a negative pressure.
For example, Japanese Patent Laid-open No. 11-50919 discloses an evaporative emission control system including a passage for connecting a fuel tank directly to an intake system of an internal combustion engine (this passage will be hereinafter referred to as “first evaporative fuel passage”) to maintain the pressure in the fuel tank at a negative pressure (a pressure lower than the atmospheric pressure). This conventional system further includes a canister for temporarily storing evaporative fuel, and a passage for connecting the fuel tank through the canister to the intake system of the internal combustion engine (this passage will be hereinafter referred to as “second evaporative fuel passage”). With this configuration, tank purge for purging the evaporative fuel from the fuel tank through the first evaporative fuel passage to the intake system and canister purge for purging the evaporative fuel stored in the canister through the second evaporative fuel passage to the intake system can be carried out in parallel.
In the above conventional system, however, the flow of the evaporative fuel in the tank purge and the canister purge is set to such an amount that having almost no effects on air-fuel ratio control for the engine. Accordingly, in the case that the pressure in the fuel tank is equal to the atmospheric pressure or in the case that the canister is in a full-charged condition, much time is required for each purge.
Further, in the above conventional system, a canister purge amount, i.e., an evaporative fuel amount to be supplied to the intake system by the canister purge, is first determined. Then, the canister purge amount is subtracted from a maximum evaporative fuel amount that can be purged to determine a tank purge amount, i.e., an evaporative fuel amount to be supplied to the intake system by the tank purge. As a result, the tank purge amount is relatively small, causing a delay of pressure reduction in the fuel tank. Conversely, in the case of adopting a method of preferentially determining the tank purge amount, there occurs another problem that the canister purge amount becomes lacking to cause a reduction in storage capacity of the canister (especially, the storage capacity required in refueling).
SUMMARY OF THE INVENTION
It is accordingly an object of the present invention to provide an evaporative emission control system which can properly control the ratio between the tank purge amount and the canister purge amount to realize quick pressure reduction in the fuel tank and ensuring the storage capacity of the canister in a well balanced manner.
In accordance with the present invention, there is provided in an evaporative emission control system for an internal combustion engine, including a first evaporative fuel passage for connecting a fuel tank and an intake system of said internal combustion engine, a first control valve provided in said first evaporative fuel passage for opening and closing said first evaporative fuel passage, first control means for controlling the opening degree of said first control valve so that the pressure in said fuel tank becomes lower than an atmospheric pressure, a second evaporative fuel passage for connecting said fuel tank and said intake system, a canister provided in said second evaporative fuel passage for temporarily storing evaporative fuel, a second control valve for opening and closing said second evaporative fuel passage, and second control means for controlling the opening degree of said second control valve; the improvement comprising target pressure setting means for setting a target pressure in said fuel tank; tank pressure detecting means for detecting the pressure in said fuel tank; and third control means for comparing said target pressure with said detected pressure in said fuel tank and controlling said first control means and said second control means according to the result of comparison between said target pressure and said detected pressure.
With this configuration, the first and second control means are controlled according to the result of comparison between the target pressure and the detected pressure in the fuel tank. Accordingly, when the detected pressure in the fuel tank is in the vicinity of the atmospheric pressure and much higher than the target pressure, tank purge through the first control valve is preferentially carried out. Conversely, when the detected pressure in the fuel tank is near the target pressure, canister purge through the second control valve is preferentially carried out. Accordingly, quick pressure reduction in the fuel tank and ensuring the storage capacity of the canister can be realized in a well balanced manner.
Preferably, the third control means controls the first and second control means so that the amount of evaporative fuel to be purged through the first evaporative fuel passage is decreased and the amount of evaporative fuel to be purged through the second evaporative fuel passage is increased with a decrease in the detected pressure toward the target pressure.
Preferably, the required fuel amount is determined according to an operating condition of the internal combustion engine, a corrective fuel amount is calculated according to the amount of evaporative fuel to be purged through the first evaporative fuel passage, and a fuel amount obtained by correcting the required fuel amount by the corrective fuel amount is supplied to the internal combustion engine.
Accordingly, it is possible to prevent the deviation of an air-fuel ratio from a target value due to the execution of the tank purge in which an evaporative fuel amount is large, and it is also possible to increase the maximum of a total purge amount as the sum of the tank purge amount and the canister purge amount, thereby allowing quicker pressure reduction in the fuel tank and quicker canister purge.
Preferably, the fuel amount control means calculates the corrective fuel amount according to the expected evaporative fuel amount and a delay of change in actual evaporative fuel amount from a change in the opening degree of the first control valve.
Preferably, the fuel amount control means calculates the expected evaporative fuel amount according to the difference between the pressure in the fuel tank and the pressure in the intake system, the opening degree of the first control valve, and the concentration of evaporative fuel generated in the fuel tank.
Preferably, the fuel amount control means calculates the concentration of the evaporative fuel according to the pressure in the fuel tank and the temperature of fuel in the fuel tank.
Preferably, the target pressure setting means corrects the target pressure according to the temperature of fuel in the fuel tank.
Preferably, the first control means sets an initial opening degree of the first control valve in the case of opening the first control valve from its closed condition, according to the difference between the pressure in the fuel tank and the pressure in the intake system.
Preferably, the first control means compares the expected evaporative fuel amount with a target evaporative fuel amount to be supplied through the first evaporative fuel passage to the intake system, and controls the opening degree of the first control valve according to the result of comparison between the expected evaporative fuel amount and the target evaporative fuel amount.
Preferably, the first control means corrects the opening degree of the first control valve according to the rotational speed of the internal combustion engine.
Other objects and features of the invention will be more fully understood from the following detailed description and appended claims when taken with the accompanying drawings.
REFERENCES:
patent: 5174265 (1992-12-01), Sekine
patent: 5353770 (1994-10-01), Osanai et a
Ishiguro Tetsuya
Kitamura Toru
Kurokawa Naohiro
Suzuki Norio
Arent Fox Kintner & Plotkin & Kahn, PLLC
Honda Giken Kogyo Kabushiki Kaisha
Miller Carl S.
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