Fuel control for a variable cam phase engine

Details Fuel control for a variable cam phase engine Fuel control for a variable cam phase engine

1999-11-29

2001-09-11

Kwon, John (Department: 3747)

Internal-combustion engines

Charge forming device

Fuel injection system

C123S480000

Reexamination Certificate

active

06286487

ABSTRACT:

TECHNICAL FIELD
The present invention relates in general to an engine fuel control, and more specifically to a method of compensating the fuel control of an engine in which the camshaft phase angle is changed for control purposes.
BACKGROUND OF THE INVENTION
Accurate control of engine air/fuel ratio requires knowledge of the quantity of fresh air drawn into the engine cylinders -in each engine cycle. Ordinarily, this can be determined either by sensing the mass air flow in the intake manifold of the engine or through a computation involving the engine speed and a measure of the manifold absolute pressure. The fuel pulse width so determined can then be adjusted to account for other factors that influence the air charge. With variable cam phase engines, for example, the phase angle of the cam must be taken into account since changing the cam angle changes the degree of overlap between the cylinder intake and exhaust valves. One way of compensating for the variable cam phasing is to simply measure the actual cam position, and adjust the fuel pulse width to account for the corresponding degree of valve overlap. However, in transient operation, the cam phase continues to change in the interval between fuel pulse width computation and the corresponding combustion cycle, resulting in fueling errors that adversely affect emissions. Accordingly, what is needed is a fuel compensation method that more accurately accounts for the air charge changes due to cam phase angle, even during transient operation.
SUMMARY OF THE INVENTION
The present invention is directed to an improved fuel compensation method for a variable cam phase engine which predicts the phase of the cam at the midpoint of valve overlap and uses the predicted cam phase to compensate a base fuel pulse for the corresponding amount of diluent. If the cam phase is in transition to a desired value, the cam phase for purposes of compensation is predicted based on the current cam phase and its rate of change; otherwise, the cam phase is predicted based on the current cam phase. In a first interval of cam phase transition characterized by nonlinear change in cam phase, the cam phase is predicted by applying a nonlinear offset to the measured cam phase. In a second interval of cam phase transition characterized by substantially linear variation of cam phase, the cam phase is predicted by linear extrapolation of the measured cam phase, and limited to a range bounded by the measured cam phase and the desired cam phase.


REFERENCES:
patent: 5245968 (1993-09-01), Kolias et al.
patent: 5492101 (1996-02-01), Saito et al.
patent: 5507265 (1996-04-01), Ichikawa et al.
patent: 5730105 (1998-03-01), McGinnity
patent: 5918582 (1999-07-01), Itoyama et al.
patent: 6085729 (2000-07-01), Kondo et al.

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