Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – With indicator or control of power plant
Reexamination Certificate
2001-02-27
2004-02-17
Dolinar, Andrew M. (Department: 3747)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
With indicator or control of power plant
C073S118040, C060S276000
Reexamination Certificate
active
06694243
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to an onboard system for monitoring vehicular emissions and more particularly to a diagnostic system for monitoring such emissions.
BACKGROUND
Government regulations require vehicles equipped with internal combustion engines to have emission monitoring systems conventionally known as OBD (On-board Diagnostic Systems) to advise the operator of the vehicle when the gaseous pollutants or emissions produced by such vehicles exceed government regulatory standards. Government regulatory standards set emission threshold levels which the vehicle cannot exceed when operated pursuant to a specified driving cycle such as that set forth in a FTP (Federal Test Procedure). The FTP requires the vehicle be operated at various acceleration/deceleration modes as well as at steady state or constant velocity at various specified speeds.
One of the principal components of the vehicle's emission system is the catalytic converter, typically a TWC (Three Way Catalyst—NOx, hydrocarbons and oxides, i.e., CO). TWCs store oxygen when the engine operates lean and release stored oxygen when the engine operates rich to combust gaseous pollutants such as hydrocarbons or carbon monoxide. As the catalyst ages, its ability to store oxygen diminishes and thus the efficiency of the catalytic converter decreases.
In order to determine the efficiency of the catalytic converter, systems monitor the ability of TWCs to store oxygen to determine failure of the catalyst. Typically an EGO (exhaust gas oxygen sensor) is placed upstream of the TWC and an oxygen sensor is placed either within or downstream of the TWC to sense the oxygen content in the exhaust gas. The signals are adjusted for the time it takes the exhaust gas to travel from the precatalytic converter sensor to the postcatalytic converter oxygen sensor. The adjusted signals are then compared to ascertain the storage capacity of the TWC when the engine is in a lean or stoichiometric mode.
The principal disadvantage of this method is simply that the oxygen storage capacity of the TWC has been demonstrated to poorly correlate with hydrocarbon conversion efficiencies. See J. S. Hepburn and H. S. Gandhi “The Relationship Between Catalyst Hydrocarbon Conversion Efficiency and Oxygen Storage Capacity”, SAE paper 920831, 1992 and G. B. Fischer, J. R. Theis, M. V. Casarella and S. T. Mahan “The Roll of Ceria in Automotive Exhaust Catalysis and OBD-II Catalyst Monitoring”, SAE paper 931034, 1993. Another significant disadvantage of current monitoring systems is that for such methods to be applied to low emission vehicles and ultra-low emission vehicles, it will be necessary to monitor increasingly smaller portions of the TWC leading to less reliable correlations to total TWC performance. Finally, any system which attempts to evaluate the efficiency of the catalytic converter by ascertaining the gas composition of an exhaust stream before and after the TWC is inherently flawed because i) the speed of the gas has to be precisely determined even though the gas stream passes through a tortuous path within the converter conducive to producing uneven flow for various gas stream slips and ii) the gaseous reactions within the TWC are fundamentally kinetic in nature and vary in a complex manner depending on the speed and particular composition of the exhaust gas at any given instant.
Vehicles are equipped with engine microprocessors or ECMs (engine control modules) that are sophisticated, high powered devices capable of processing input from any number of sensors depicting operating conditions of the vehicle and rapidly issuing engine control signals in response thereto. An ECM can be programmed to perform on-board monitoring of the emissions system. U.S. Pat. No. 5,490,064 to Minowa illustrates such a control unit which includes in its functions an on-board self diagnostic emissions monitoring process using conventional pre and postcatalytic O.sub.2 sensors, digital filtering and exhaust gas speed to correlate the sensor readings to one another to determine failure of the catalytic converter. U.S. Pat. No. 5,431,011 to Casarella et al. likewise illustrates precatalytic and postcatalytic converter O.sub.2 sensors whose signals are processed by the CPU in the ECM along with other vehicle operational signals. In Casarella, a two-stage analyzing technique is utilized. Filtered signals are collected in a first stage and analyzed. If the first stage analysis indicates a failure, then a more thorough or rigorous second stage scrutiny of a number of signals which can affect performance of the catalytic converter is conducted before indicating failure of the converter. Despite the sophistication employed in the computer program and the ECM, the aforementioned system is inherently flawed because of the defects in the sampling system discussed above.
Catalysts are commonly used as part of exhaust systems to treat motor vehicle exhaust in order to minimize air pollution. The reduction of pollution from motor vehicles is mandated by the Environmental Protection Agency through the Environmental Protection Act. As part of the process to assure compliance, it is common for various motor vehicle regulatory bodies to mandate tailpipe testing of automobiles on a regular basis. In order to avoid the expense of such emissions, inspection and to assure that automobiles on the road are complying with the environmental laws and regulations, there are efforts to develop a system which can sense when the exhaust system is not compliant and signal the vehicle operator accordingly.
It is the goal to monitor the exhaust gas of a motor vehicle during normal operation to determine whether the catalytic converter is performing as required. The apparatus and method to accomplish this is commonly referred to as on-board diagnostics (OBD). The strategy which is contemplated is that the performance. of the catalyst is determined based on sensing the exhaust gases to determine whether the catalyst is performing as specified and required. Different sensing means have been proposed but all are required to signal the motor vehicle operator if the catalyst is failing to operate as required.
Sensors useful to measure various components in gaseous exhaust streams such as motor vehicle exhaust streams are known. Useful sensors include oxygen sensors and NOx sensor assemblies. Such oxygen sensors include on/off sensors known as heated exhaust gas oxygen sensors (HEGO) and universal exhaust gas oxygen sensors (UEGO) which is an on/off sensor plus a linear signal which is a function of the air to fuel ratio. Various oxygen sensors have been used and are disclosed in the art including the above referenced sensors.
Other approaches to sense whether the catalyst is performing include the use of dual oxygen sensors. In accordance with this method, one oxygen sensor is located upstream of the catalyst and the other downstream of the catalyst. The signals from the upstream and downstream sensors are compared and correlated to the emissions, typically hydrocarbon emissions, to determine whether the catalyst is functioning to reduce hydrocarbon emissions to achieve compliance with the regulations. If the amount of emissions is calculated to exceed a specific amount, a signal can be sent to the motor vehicle console to alert the operator that the system to treat exhaust has failed and repair is required.
The use of a dual oxygen sensor system has been reported in SAE Technical Paper Series No. 900062, Clemmens, et al., “Detection of Catalyst Performance Loss Using On-Board Diagnostics”, presented at the International Congress and Exposition, Detroit, Mich., Feb. 26-Mar. 2, 1990. This paper reviews the history of such systems which are commonly referred to as On-Board Diagnostic Systems (OBD). This early study was indicated to be a proof of concept testing study to identify serious losses in catalyst efficiency with a dual oxygen sensor method. In accordance with this disclosure, testing was conducted at steady state conditions. The results showed that this approach resu
Benton David N.
Dempsey David W.
Kao Minghui
Shi Guojun
Singh Sharanjit
Dolinar Andrew M.
General Motors Corporation
Simon Anthony Luke
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