Power plants – Internal combustion engine with treatment or handling of... – Having sensor or indicator of malfunction – unsafeness – or...
Reexamination Certificate
2000-11-28
2003-11-25
Denion, Thomas (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
Having sensor or indicator of malfunction, unsafeness, or...
C060S274000, C060S284000, C060S285000
Reexamination Certificate
active
06651422
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to catalytic conversion of exhaust gases for internal combustion engines, and more particularly of heating a catalytic converter using cyclic fuel control and to detecting deterioration of efficiency of catalysts.
2. The Related Art
Catalysts for engine exhausts are used to convert unburned or partially reacted gases that are mostly made up of hydrocarbon (HC), carbon monoxide (CO), and nitrogen oxides (NO
x
) components. Gases leaving the exhaust manifold of an internal combustion engine enter the inlet of a device called a catalytic converter. A catalytic converter is the device that provides an expansive area where these gas components are oxidized to carbon dioxide (CO
2
), nitrogen (N
2
), and water vapor (H
2
O) by catalyst materials such as platinum (Pt), palladium (Pd), and rhodium (Rh). The conversion of these gases to CO
2
N
2
and H
2
O results in an exothermic chemical reaction at the catalyst surface that causes an increase in the temperature of the gases leaving the outlet side of the catalyst element. Increasing the concentrations of unburned or partially reacted gases entering the catalyst will result in a temperature rise that can be used to determine the catalyst's conversion efficiency as well as to heat it. A catalytic converter can be made up of several catalyst bed elements (CE) that provide a large effective surface area for the catalyst material. Each catalyst element may have different oxidation characteristics for the gases entering from the engine's exhaust manifold.
Other methods for determining the catalyst's conversion efficiency by monitoring the level of the chemical or exothermic reactions occurring within a catalytic converter have been proposed in the past. Detection of the catalyst's efficiency with a chemical method usually incorporates the use of two oxygen sensors placed at the inlet and the outlet portions of the catalytic converter catalyst elements being monitored. The voltage versus time characteristics of the two oxygen sensor's output signals provides an indication of the catalyst's ability for storing oxygen for chemical oxidation reactions. The catalyst's oxygen storage capacity causes a difference between the catalyst's inlet and outlet oxygen sensor signals. Since the catalyst's oxygen storage capacity decreases after extended high temperature operation, the sensors output voltage versus time characteristics become more similar as the catalyst's ability to store oxygen drops to zero.
However, the method using two oxygen sensors suffers from at least two problems. First, the accuracy of the oxygen sensor deteriorates over time thus creating sources of errors in detecting the actual deterioration in catalyst capability. For example, chemical factors such as fuel additives or sulfur concentrations can adversely affect the dual oxygen sensor method of catalyst efficiency monitoring. Second, the oxygen sensor method is dependent on the amount of active ceria in the catalyst rather than the catalyst's oxidation conversion efficiency that is dependent on the other active precious metals. This results in a highly nonlinear relationship between catalyst efficiency and oxygen storage capacity that decreases the accuracy of catalyst efficiency monitoring. Catalyst efficiency durability characteristics sometimes are compromised to improve the correlation with the oxygen storage capacity and allow adequate catalyst monitoring accuracy.
Exothermic energy is also released at the catalyst's surface during the chemical oxidation of hydrocarbons, carbon monoxide and nitrogen oxides (NO
x
) gases as they are converted into water vapor and carbon dioxide. The exothermic energy released in the catalyst causes a temperature increase at the surface of the catalyst's substrate and in the exhaust gases flowing past this surface. Monitoring this temperature increase, caused by the exothermic energy release at the catalyst's surface, provides a second method for measuring the catalytic converter's overall chemical conversion performance.
Two primary methods have been proposed that monitor the catalyst's gas conversion capability by using the catalyst's temperature characteristics for determining its level of exothermic energy release. The first method uses two or more temperature sensors to monitor the temperatures of both the gases entering and exiting the desired portion of catalyst elements of the catalytic converters to be monitored. While flowing through the catalytic converter, each catalyst element's outlet gas temperatures increase to a steady state level above its inlet exhaust gas temperatures depending on the exothermic energy released at the catalyst's surface. Under some relatively steady state vehicle operating conditions, the temperature differences between the gases entering and exiting the portion of the catalytic converter being monitored provides an indication of the catalyst's condition. U.S. Pat. Nos. 5,592,815 and 5,630,315 apply this first method of catalyst temperature detection during periods of steady state engine operating conditions. The steady state temperature difference between the inlet and outlet catalyst temperature sensors in a properly functioning catalytic converter can be about 50-80° C. This compares with a catalyst having insufficient conversion efficiency with an indicated temperature sensor difference (outlet minus inlet) of 10-40° C.
The second method of temperature based catalyst monitoring uses a momentary disabling of the ignition system voltage to the engine's spark plugs to cause an unburned fuel and air mixture to exit the engine's exhaust. The time period of disabling the ignition system must be short in order to prevent the torque change from the engine to be noticed by the vehicle's driver. This pulse of unburned fuel and air mixture subsequently enters the catalyst and causes a sudden, momentary temperature rise of the catalyst's temperature for a short time period. Quick responding temperature sensors are required to monitor this sudden and brief temperature rise at various portions within the catalyst where the unburned fuel and air mixture are oxidized. Temperature sensors must also be placed at the proper location where the unburned exhaust pulse will be oxidized since most catalytic converters have multiple catalyst elements with differing precious metal catalyst makeup. The location where the pulse will be oxidized is dependent on the instantaneous temperatures of each catalyst element. Identification of the instantaneous catalyst element temperatures and the location where the unburned exhaust pulse is oxidized can require multiple temperature sensors to be placed at various locations within the catalytic converter. This second method and related systems are shown in, for example, U.S. Pat. Nos. 5,339,628, 5,435,172, 5,355,671 and 5,610,844.
These two methods are dependent upon the ability of temperature detection devices or temperature sensors to accurately detect small temperature differences with magnitudes between 10-50° C. Monitoring of the catalyst's condition is performed during short time periods between 5-30 seconds when engine speed and load conditions are relatively stable. Normal temperature fluctuations caused by exhaust gases entering the catalyst during the catalyst efficiency monitoring time period are difficult to be accurately discerned from temperature changes caused by the catalyst's exothermic reactions. Multiple temperature sensors are sometimes required with these methods to more accurately discern only temperature changes associated with the test for catalytic efficiency and its related exothermic chemical activity.
In the first method of monitoring, both the catalyst's inlet and outlet temperature sensor's error characteristics must remain very stable over the life of the engine in order to provide adequate detection of catalyst performance. This stabili
Tran Diem
Wolff Kevin Alan
Wolff Law Offices
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