Power plants – Internal combustion engine with treatment or handling of... – Methods
Reexamination Certificate
1999-08-10
2001-07-03
Denion, Thomas (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
Methods
C060S276000, C060S285000, C073S118040, C073S489000
Reexamination Certificate
active
06253541
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention generally relates to emission control systems and, more particularly, to oxygen sensor-based emission control systems for automotive vehicles.
2. Discussion
Operation of an internal combustion engine causes certain exhaust elements to be generated. For instance, hydrocarbons (HC) and nitrous oxide (NOx) emissions are produced. Certain air quality management plans dictate that such emissions be controlled to within pre-selected limits.
To reduce the amount of undesirable emissions passing through an engine exhaust system to the atmosphere, modern motor vehicles employ a catalytic converter. The catalytic converter fosters a reaction wherein undesirable emission elements are converted to different elements prior to their passage to the atmosphere. To monitor the efficiency of the catalytic converter, sensors are sometimes employed.
For example, an oxygen sensor may be disposed upstream of a catalyst in the catalytic converter so that the nature of the exhaust gasses entering the catalyst may be determined. If the constituents of the exhaust gas are not within a desirable range, the output of the oxygen sensor is used to modify the fuel-to-air ratio within the engine. Often, this entails increasing or decreasing the amount of fuel injected by the fuel injectors in the engine. As a result, the constituents within the exhaust gas are modified.
Similarly, by disposing an oxygen sensor downstream of the catalyst, the constituents of the exhaust gas exiting the catalyst can be learned. If the constituents are not within the desired range, the fuel-to-air ratio within the engine can be modified. Further, by placing a first oxygen sensor upstream of the catalyst and a second oxygen sensor downstream of the catalyst, the nature of the exhaust gas through the catalyst can be learned. As such, greater control of the fuel-to-air ratio within the engine may be exercised to modify the exhaust constituents.
In some automotive vehicles, a second catalyst brick is employed in the catalytic converter can downstream of the first catalyst brick. In combination with such an arrangement, a first oxygen sensor has been placed upstream of the first catalyst and a second oxygen sensor has been disposed downstream of the first catalyst and upstream of the second catalyst. This is the so-called “mid-brick” position. While this configuration has provided beneficial results for learning the constituents through the first catalyst and entering the second catalyst, there is room for improvement in the art.
For example, it would be desirable to provide a configuration that enables learning of the constituents through the second catalyst thereby enhancing control of the level of nitrous oxide passing through the system.
SUMMARY OF THE INVENTION
The above and other objects are provided by an exhaust system including two catalysts and three oxygen sensors. The second catalyst is disposed downstream of the first catalyst. The first oxygen sensor is disposed upstream of the first catalyst, the second oxygen sensor is disposed downstream of the first catalyst and upstream of the second catalyst, and the third oxygen sensor is disposed downstream of the second catalyst. A goal voltage corresponding to a desired level of nitrous oxide within the exhaust is provided for the third oxygen sensor. This goal voltage is based on engine RPM and MAP. The engine controller compares the goal voltage to an actual voltage generated by sensing the level of oxygen downstream of the second catalyst. Based on this comparisons an error value between the goal voltage and the actual voltage is obtained. This error value is converted into a goal voltage for the first oxygen sensor. An actual voltage generated by the first oxygen sensor sensing the a mount of oxygen upstream of the first catalyst is compared to the goal voltage derived from the third oxygen sensor. The difference between the goal voltage and actual voltage is used to modulate the pulse width of a signal sent to the fuel injectors of an engine such that the amount of fuel delivered by the fuel injectors is modified. The second oxygen sensor generates an actual voltage corresponding to the amount of oxygen the second oxygen sensor senses downstream of the first catalyst and upstream of the second catalyst. Changes in the actual voltage generated by the second oxygen sensor are compared to changes in the actual voltage generated by the first oxygen sensor. By monitoring the nature of these changes as they relate to one another, the performance of the first catalyst can be determined.
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DeGroot Kenneth P.
Reale Michael J.
Sullivan Raymond J.
Teague Bruce H.
Calcaterra Mark P.
DaimlerChrysler Corporation
Denion Thomas
Trieu Thai-Ba
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