Internal-combustion engines – Charge forming device – Including exhaust gas condition responsive means
Reexamination Certificate
2001-09-13
2003-07-08
Argenbright, Tony M. (Department: 3747)
Internal-combustion engines
Charge forming device
Including exhaust gas condition responsive means
C123S491000, C123S687000
Reexamination Certificate
active
06588409
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a fuel control for an internal combustion engine designed to operate with a lean air/fuel ratio, and more particularly to a control that detects combustion instability due to the use of low volatility fuel during cold start operation, and for compensating the fuel control to alleviate detected instability.
BACKGROUND OF THE INVENTION
It is well known that motor vehicle fuels contain a variety of different compounds, and that the fuel volatility can therefore vary significantly from tank to tank. In an effort to quantify this variation, the industry has developed a driveability index (DI) based on a summation of specified distillation measurements, weighted to reflect their relative effect on combustion stability an internal combustion engine. In general, high volatility fuels have a relatively low DI value, whereas low volatility fuels have a relatively high DI value.
In an engine fuel control, the volatility of the injected fuel is most critical during cold starting and warm-up, since the internal surfaces of the engine may not be hot enough to vaporize a sufficient quantity of high DI fuel. For this reason, automotive fuel controls have traditionally been designed to enrich the cold calibration to ensure that the engine will start and run acceptably with high DI fuel. This enrichment to compensate for high DI fuel causes the air/fuel to be richer than optimum with medium and low DI fuel, resulting in higher hydrocarbon emissions than if the appropriate calibration were used. Thus, low emission engines designed to operate at leaner air/fuel ratios during cold starting and warm-up may experience degraded driveability due to combustion instability if a high DI fuel is being used. Accordingly, what is needed is a control method that permits the use of lean air/fuel ratio control during cold starting and warm-up while minimizing degraded driveability due to the use of high DI fuel.
SUMMARY OF THE INVENTION
The present invention is directed to an improved engine fuel control that detects combustion instability due to the use of high DI fuel during cold start and warm-up and that compensates the fuel control for detected combustion instability through temporary enrichment of the delivered air/fuel ratio. According to the present invention, the usage of high DI fuel is detected during engine cranking by measuring the time required for the engine speed to increase from a lower reference speed to an upper reference speed, provided the engine run time is less than a calibrated value. A timer is started when the lower reference speed is achieved, and the timer value is compared to a crank time threshold determined as a function of the initial engine coolant temperature. If the timer value exceeds the crank time threshold before the engine speed reaches the upper reference speed, the presence of high DI fuel is indicated, and the air/fuel ratio is temporarily enriched to alleviate the instability and to ensure acceptable driveability without unnecessarily increasing hydrocarbon emissions in the engine exhaust gases.
REFERENCES:
patent: 6079396 (2000-06-01), Ament et al.
patent: 6360726 (2002-03-01), Javaherian
Breidenbach Hallett D.
Carlson Craig A.
Herman Andrew D.
Maloney Peter James
Yoo Deog H.
Argenbright Tony M.
Chichosz Vincent A.
Delphi Technologies Inc.
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