Catalytic converter temperature control system and method

Details Catalytic converter temperature control system and method Catalytic converter temperature control system and method

1998-12-08

2001-08-14

Denion, Thomas (Department: 3748)

Power plants

Internal combustion engine with treatment or handling of...

Having sensor or indicator of malfunction, unsafeness, or...

C060S274000, C060S286000, C060S285000

Reexamination Certificate

active

06272850

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a catalytic converter temperature control system and method for controlling the delivery of fuel to an internal combustion engine to protect the catalytic converter from degradation due to high temperature exposure.
BACKGROUND OF THE INVENTION
Modern automotive engines typically utilize a catalytic converter to reduce regulated exhaust gases produced by the engine. Such converters operate to chemically alter the exhaust gas composition produced by the engine. Catalytic converters typically operate at peak efficiency when the temperature of the catalytic material within the converter is within a certain specified range. Continued operation of the converter at a temperature greater than the specified temperature range, however, leads to degradation of the catalytic converter material within the converter. Such degradation leads to reduced converter operating life.
One method to limit the converter temperature is to ramp the engine air/fuel ratio injected into the engine to a value rich of stoichiometry that will maintain the temperature at the maximum when the conditions are such that normal stoichiometric operation would cause the temperature to exceed the maximum allowable temperature. The ramping rate of the air/fuel ratio that is injected is a fixed value and is large enough that the converter temperature does not exceed the maximum allowable temperature. Further, a single predetermined temperature limit is used. Such a system is described in U.S. Pat. No. 5,414,994.
The inventors herein have recognized a disadvantage with the above approach. During certain operating conditions, especially high load and high speed operation, the necessary enrichment to maintain the converter temperature at or below the predetermined temperature limit causes an increase in certain regulated exhaust gases. Further, the enrichment also decreases fuel economy.
SUMMARY OF THE INVENTION
An object of the invention claimed herein is to provide a system and method to control the temperature of a catalytic converter such that catalytic converter efficiency is maintained while minimizing the regulated exhaust gases caused by fuel enrichment.
In one particular aspect of the invention, this object is achieved, and disadvantages of prior approaches overcome by a method for preventing degradation of efficiency of an emission control device due to temperature exposure by controlling air/fuel ratio of an air/fuel ratio mixture inducted into an internal combustion engine having an exhaust coupled to the emission control device. The method comprises the steps of determining temperature within said the emission control device, generating a desired rich air/fuel ratio reference value that will maintain the emission control device near a predetermined temperature, ramping the air/fuel ratio to said desired rich air/fuel ratio reference value at a first ramping rate when said temperature is greater than a first predetermined threshold, and ramping the air/fuel ratio to said desired rich air/fuel ratio reference value at a second ramping rate when said temperature is greater than a second predetermined threshold and less than said first predetermined threshold.
By using two temperature regions and a different ramping rate in each, the converter temperature is controlled to the same temperature limit as attempted by prior approaches, but momentarily exceeds this limit while never exceeding a higher limit. This is an acceptable solution because the lower temperature limit represents a temperature at which the converter can operate at indefinitely while incurring no degradation. However, the converter can tolerate higher temperatures without degradation, provided the exposure is only for a short period of time. Therefore, employing multiple temperature bands with varying ramping rates allows for optimization of fuel economy and emissions, while maintaining the integrity of the converter.
An advantage of the above aspect of the invention is improved fuel economy.
Another advantage of the above aspect of the invention is improved emission control.
Other objects, features and advantages of the present invention will be readily appreciated by the reader of this specification.


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