Internal-combustion engines – Charge forming device – Having fuel vapor recovery and storage system
Reexamination Certificate
1999-06-24
2001-05-08
Moulis, Thomas N. (Department: 3747)
Internal-combustion engines
Charge forming device
Having fuel vapor recovery and storage system
C123S399000
Reexamination Certificate
active
06227177
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for controlling an internal combustion engine equipped with an evaporative emission control system that captures or traps any fuel vapors coming from a fuel tank mainly when the engine is not running and prevents them from escaping into atmosphere.
2. Description of the Prior Art
As is generally known, a typical evaporative emission control system for an internal combustion engine, has a carbon or charcoal canister filled with activated carbon or charcoal for temporarily storing, trapping or adsorbing fuel vapors emitted from a fuel tank, and a purge control valve disposed in a purge line connecting an induction system with the canister. Generally, the action of clearing or removing the trapped fuel vapor from the canister is called “purging”. An electronic air-fuel mixture ratio control system for an internal combustion engine equipped with an evaporative emission control system as discussed above, has been disclosed in Japanese Patent Provisional Publication No. 63-55357. In the air-fuel ratio control system disclosed in the Japanese Patent Provisional Publication No. 63-55357, a flow rate of air passing through a throttle valve is detected, a basic value of a desired fuel-injection amount is, first of all, set on the basis of the air flow rate detected. On the other hand, during a so-called closed-loop mode, an engine control unit (ECU) executes engine air/fuel ratio feedback control in response to a voltage signal from an oxygen sensor, to set a final desired fuel injection amount and to maintain the engine air/fuel ratio almost at a constant value (that is, at as close to stoichiometric as possible), regardless of the presence or absence of fuel vapors escaping from the fuel tank.
SUMMARY OF THE INVENTION
In the presence of excessively increased amount of fuel vapors, there is a tendency that the air/fuel ratio control mode deviates from the closed-loop feedback control zone. In such a case, the air/fuel ratio will become excessively rich (too much fuel), thereby increasing harmful exhaust emissions, and deteriorating vehicle driveability. For the reasons set out above, when the air/fuel ratio control mode is out of the feedback control zone, the opening of the purge control valve would be decreasingly compensated for. In other words, when the engine is operating out of the closed-loop feedback control operating mode, the decreased opening of the purge control valve limits the amount of purging to a small amount. In hot weather (at high ambient temperatures), there is a large amount of fuel vapor from the fuel tank. Thus, if the canister is insufficiently purged of fuel vapor owing to the undesiredly decreased opening of the purge control valve and additionally the canister has a small capacity, there is a possibility of fuel vapor leakage from the canister into the atmosphere. Depending on variations in the flow rate of purge air and variations in the quantity of purge fuel vapor, correction of a fuel-injection amount would be made through only the air/fuel ratio closed-loop feedback control. The response delay of the feedback control system may lower the accuracy of the air/fuel ratio control system or the follow-up performance of the system, thus resulting in undesirable system hunting (that is, fluctuations in the air/fuel ratio).
Accordingly, it is an object of the invention to provide an apparatus for controlling an internal combustion engine equipped with an evaporative emission control system which avoids the aforementioned disadvantages of the prior art.
It is another object of the invention to provide an integrated engine control apparatus of an internal combustion engine equipped with an evaporative emission control system, which is capable of executing high-precision A/F ratio control of an enhanced follow-up performance even in the presence of remarkable variations in the purge air flow rate and purge fuel-vapor quantity, without undesiredly limiting canister purging to a small amount of purging.
In order to accomplish the aforementioned and other objects of the present invention, an apparatus for controlling an internal combustion engine equipped with an evaporative emission control system having at least a canister temporarily adsorbing fuel vapor emitted from a fuel tank, a purge line through which the fuel vapor adsorbed by the canister flows to an induction system, and a purge control valve disposed in the purge line, the apparatus comprises a control unit configured to be connected to at least an electronically-controlled throttle and an electronic fuel injection system having a fuel injector provided for each engine cylinder, the control unit comprising a desired air flow rate setting section setting a desired air flow rate on the basis of at least an opening of an accelerator, a desired fuel-flow quantity setting section setting a desired quantity of fuel flow on the basis of at least the opening of the accelerator, a purge-air flow rate detection section detecting a purge-air flow rate of purge air flowing through the purge line via the purge control valve to the induction system, a purge fuel-flow quantity detection section detecting a purge fuel-flow quantity of purge fuel vapor flowing through the purge line via the purge control valve to the induction system, a desired throttle air flow rate arithmetic-calculation section arithmetically calculating a corrected air flow rate by subtracting the purge-air flow rate from the desired air flow rate, a throttle control section controlling an opening of the electronically-controlled throttle on the basis of the corrected air flow rate, a desired fuel-injection quantity arithmetic-calculation section arithmetically calculating a corrected fuel-injection quantity by subtracting the purge fuel-flow quantity from the desired quantity of fuel flow, and a fuel-injection control section controlling a fuel-injection quantity of fuel to be injected from the fuel injector on the basis of the corrected fuel-injection quantity.
According to another aspect of the invention, in an internal combustion engine equipped with an evaporative emission control system having at least a canister temporarily adsorbing fuel vapor emitted from a fuel tank, a purge line through which the fuel vapor adsorbed by the canister flows to an induction system, and a purge control valve disposed in the purge line, an integrated engine control apparatus for electronically controlling an air/fuel ratio, comprises an electronically-controlled throttle whose opening is changeable arbitrarily in response to an opening of an accelerator, an electronic fuel injection system having a fuel injector provided for each engine cylinder, control means configured to be connected to at least the electronically-controlled throttle, the electronic fuel injection system, and the purge control valve, for controlling the air/fuel ratio, the control means comprising a desired air flow rate setting means for setting a desired air flow rate on the basis of at least the opening of the accelerator, a desired fuel-flow quantity setting means for setting a desired quantity of fuel flow on the basis of at least the opening of the accelerator, a purge-air flow rate estimation means for estimating a purge-air flow rate of purge air flowing through the purge line via the purge control valve to the induction system on the basis of both an opening of the purge control valve and a negative pressure in the induction system, a purge fuel-flow quantity estimation means for estimating a purge fuel-flow quantity of purge fuel vapor flowing through the purge line via the purge control valve to the induction system on the basis of both the purge air flow rate estimated by the purge-air flow rate estimation means and a concentration of hydrocarbon contained within purge gas consisting of the purge air and the purge fuel vapor flowing through the purge line, a desired throttle air flow rate arithmetic-calculation means for arithmetically calculating a corrected air flow rate by subtra
Kouda Yasuo
Yamafuji Takahiro
Foley & Lardner
Moulis Thomas N.
Nissan Motor Co,. Ltd.
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