Air/fuel ratio control responsive to catalyst window locator

Details Air/fuel ratio control responsive to catalyst window locator Air/fuel ratio control responsive to catalyst window locator

2000-05-02

2002-04-02

Denion, Thomas (Department: 3748)

Power plants

Internal combustion engine with treatment or handling of...

By means producing a chemical reaction of a component of the...

C060S274000, C060S277000, C060S276000

Reexamination Certificate

active

06363715

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an air/fuel ratio control system for an internal combustion engine coupled to a catalytic converter.
2. Description of the Related Art
Three-way catalytic converters (TWC) are commonly used to remove pollutants such as NO
x
, HC, and CO components in the exhaust gas of an internal combustion engine. NO
x
is removed from the exhaust gas by reduction using the CO, HC and H
2
in the exhaust gas. There is also typically enough O
2
present to oxidize the CO and HC. Generally, however, the catalyst used in such converters is able to remove the pollutants from the exhaust gas simultaneously only when the air/fuel ratio of the exhaust gas is kept in a narrow range near the stoichiometric air/fuel ratio.
FIG. 1
shows the conversion efficiency of a typical TWC as a function of measured exhaust gas air/fuel ratio. As can be seen in
FIG. 1
, TWCs require that the air/fuel ratio of the engine be held in a relatively narrow range, such as window
10
, to assure high conversion efficiencies. Therefore, in order to reduce undesirable emissions within the exhaust gas, it is important to keep the air/fuel ratio of the engine in the region where the TWC has high efficiency. Typically, this is near the stoichiometric air/fuel ratio or at a predetermined offset near stoichiometric. Component drifting or aging can result in an altered air/fuel ratio and, hence, less than optimum efficiency of the TWC.
SUMMARY OF THE INVENTION
An object of the invention herein is to provide a method of locating the peak TWC efficiency window. Another object is to maintain engine air/fuel operation within the peak efficiency window of a catalytic converter.
An air/fuel control method for an engine including a NO
x
sensor in operative relationship to a catalytic converter. The method comprises the steps of providing a base fuel signal related to a quantity of air inducted into the engine and generating a bias signal for biasing the base fuel signal towards a leaner air/fuel ratio. The output of the NO
x
sensor is monitored to detect a predetermined exhaust gas NO
x
value representing a predefined NO
x
conversion efficiency. The base fuel signal is then modified as a function of the bias signal corresponding to the predetermined exhaust gas NO
x
value to maintain the catalytic converter within a desired efficiency range. In one aspect of the invention, the process of detecting the edge of the NO
x
conversion efficiency window is executed at predetermined time periods measured by the distance the vehicle has traveled, or the elapsed time since last base fuel value modification.
One advantage of the present invention is that it suppresses fluctuation in the air/fuel ratio. Another advantage is that it improves the efficiency of the catalytic converter.
Other objects and advantages of the invention will become apparent upon reading the following detailed description and appended claims, and upon reference to the accompanying drawings.


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