Internal-combustion engines – Charge forming device – Fuel injection system
Reexamination Certificate
2000-06-30
2002-10-15
Kwon, John (Department: 3754)
Internal-combustion engines
Charge forming device
Fuel injection system
C701S115000, C701S105000, C123S478000, C123S480000, C123S436000
Reexamination Certificate
active
06463913
ABSTRACT:
TECHNICAL FIELD
This invention relates to fuel control systems and, more particularly, to a system that is insensitive to the timing inaccuracy of a low cost microcontroller timing source.
BACKGROUND ART
The vast majority of engine fuel control systems are based on either manifold absolute pressure (MAP), mass air flow (MAF), or MAP+MAF. The basic objective is to measure air flow or air flow rate into the engine and meter a corresponding fuel amount to achieve either a cumulative or instantaneous fuel/air composition.
Fueling error has disadvantageous consequences for emissions control. One potential source of error is the timing sources in the microcontroller. Fuel amount injected is controlled by the time the fuel injector is open. Thus, time measurement influences fueling amount. A clock source that is 1% slower than design intent results in usage of approximately 1% more fuel than intended.
Historically, the manner in which this problem is addressed is to provide the Powertrain Control Module (PCM) with a high-accuracy, high-cost timing source, using a quartz crystal instead of a relatively low accuracy, low-cost timing sources using a ceramic resonator.
DISCLOSURE OF INVENTION
In accordance with the present invention, a fuel control method is provided that uses a MAP sensor output that is encoding to render fueling computations insensitive to microprocessor clock accuracy. More particularly, the signal output of the MAP sensor is encoded as a pulse width modulated signal, the cylinder air mass is calculated as a function of the encoded MAP signal and the engine is fueled according to the calculated cylinder air mass. Because the same time scale is used to decode the pulse width of the MAP PWM signal as is used to time injector duration, the time scale becomes irrelevant to the actual fuel/air ratio attained. A further improvement may be achieved by shaping either the fuel injector transfer function (fuel delivered versus injector driver on-time) or the MAP transfer function (MAP versus pulse width). Preferably, the MAP sensor's PWM encoding is arranged such that the period is affine with MAP, meaning high MAP, long period, and low MAP, short period. Period encoding is of interest for capacitor-based pressure sensors because a change in frequency is a common way to sense capacitance change.
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Crosby Paul A.
Kotwicki Allan Joseph
Pursifull Ross Dykstra
Ford Global Technologies Inc.
Kwon John
Lippa Allan J.
Russell John D.
Vo Hieu T.
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