Abstract:
A method of controlling operation of a compressed natural gas vehicle as a function of a predetermined level of methane in the ambient. Vehicle ignition is turned off when a predetermined level of methane is sensed in the ambient.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to the operation of vehicles fueled by compressed natural gas (CNG). 
     2. Prior Art 
     Even though natural gas is in universal use as a household and commercial fuel, the acceptance of compressed natural gas as fuel for motor vehicles, in particular those for personal transportation, has been hampered by its low volumetric energy density as compared with that of the common liquid fuels, gasoline and diesel fuel. This manifests itself in lower power and performance, a more expensive and heavier fuel storage, shorter range, and a larger share of the useful vehicle space occupied by the fuel system as compared to vehicles fueled by liquids. The developments of the last 20 years have largely minimized these drawbacks such that vehicles powered by internal combustion engines designed for natural gas combustion approximate, in their overall performance, those powered by liquid fuels. 
     In the past there have been instances where in times of extreme scarcity of liquid fuels, local availability of natural gas made it the fuel of choice. An example is the Po valley of Italy in the years after the 2nd World War, 1947-9. There the majority of vehicular traffic was powered by the abundant, locally produced natural gas. 
     While presently there is no mass production of CNG vehicles, local availability of cheap natural gas results in some low level conversion of vehicles, primarily light trucks, to this fuel. At present the price of liquid hydrocarbons is low and their availability is high so that the market impetus for wider implementation of natural gas is absent. This condition can change in the future and the ample domestic resources of natural gas might be drawn upon for fueling personal transportation vehicles. Also, environmental constraints, both localized as in the Los Angeles Basin and global, as related to the climate change concerns, may promote the use of natural gas for vehicular transport since it presents a practical, large volume, alternative to gasoline and diesel fuel. 
     Any widespread use of vehicles using a gaseous fuel may lead to various alerting devices located on the vehicle itself as well as in parking garages. These are some of the problems this invention overcomes. 
     SUMMARY OF THE INVENTION 
     This invention comprises a system that responds to a predetermined level of methane and controls operation of a CNG vehicle as a function of such level. For example, the ignition of the CNG vehicle may be turned off when such a predetermined level of natural gas is present in the surrounding atmosphere. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The FIGURE is a block diagram of logic flow of a method of vehicle operation in accordance with an embodiment of this invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     This invention teaches a method of operating a vehicle in response to a predetermined content of methane (CH 4 ) in the surroundings. For example, under certain conditions, the method may include automatically turning off the ignition of a CNG powered vehicle parked in a closed space such as a garage, when a predetermined level of natural gas (methane) is present in this space. The system uses a sensor which can sense and measure the concentration of natural gas in the ambient. Advantageously, the sensor must be selective to methane as not to provide false alarms. Since people store organic, flammable materials in their garages such as gasoline and solvents, it is undesirable to turn on the alarm in response to small concentrations of such organic fumes. 
     Several types of gas sensors which respond to CH 4  exist, for example, the SnO 2  sensors produced by Figaro Engineering Inc. and the pellistors produced by, for example, Neotronics of North America, Inc. and others. However, these sensors are not selective, that is, they respond not only to CH 4  but even more strongly to gasoline, ethanol, and many other solvents and combustibles. Consequently, if a non-selective sensor is used, the mere presence in the garage of gasoline vapors in small quantities may turn on an alarm and affect vehicle operation even in the absence of CH 4  in the ambient. 
     This invention uses a selective sensor to avoid false alarms. A sensor of this type has been described in U.S. Pat. No. 4,870,025 assigned to Ford Motor Company, the disclosure of which is incorporated herein by reference. It has two electrically connected catalysts, one being a palladium catalyst and the other being a platinum catalyst heated at a temperature of about 350° to 450° C. When the ambient gas atmosphere contains CH 4  and other interfering combustibles, the methane and the other combustibles, are oxidized by the palladium catalyst, whereas the second platinum catalyst oxidizes only the other combustibles. Consequently, the palladium catalyst will be heated to a higher temperature than the platinum catalyst. The difference in temperature of the two catalysts provides a measure of the concentration of methane. The sensor response is advantageously matched to the ambient concentration of CH 4  i.e., at ca. 2.5 volume % which is 1/2 of the lower flammability limit. 
     Referring to the FIGURE, a logic flow diagram shows a sequence of operations in accordance with an embodiment of this invention. Logic flow starts at a start block 20 and then goes to a decision block 21 where it is asked whether the CH 4  level is high (e.g. &gt;2.5 volume %). If YES, logic flow goes to a block 22 wherein an alarm is turned on. Logic flow then goes to a block 23 where a switch N is set to &#34;1&#34;. Logic flow then goes to a decision block 24 where it is asked whether the vehicle engine is running. If YES, the logic flow goes to a decision block 25 where it is asked whether the vehicle transmission is in neutral or park. If YES, logic goes to a block 26 where the ignition switch is turned off. Logic flow then goes to a block 27, where a switch M is set to &#34;2&#34;, and then goes to an END block 28. Returning to decision block 25, if NO, logic flow goes to END block 28. Returning to decision block 24, if NO, logic flow goes to block 26. 
     Returning to decision block 21, if NO, logic flow goes to a decision block 30 where it is asked whether the switch N has a value of &#34;1&#34; (that is, if the alarm is on). If YES, the logic flow goes to a block 31, where the alarm is turned off, and then goes to a block 32, where the switch N is set to &#34;2&#34;. The logic flow then goes to a decision block 33 where it is asked whether the switch M has the value &#34;2&#34; (that is, if the ignition switch is turned off and locked). If YES, the logic flow goes to a block 34, where the ignition switch is turned on (unlocked), then goes to a block 35, where the switch M is set to &#34;1&#34;, and finally goes to END block 28. Returning to decision block 33, if NO, the logic block goes to END block 28. Returning to decision block 30, if NO, the logic flow goes to END block 28. 
     Various modifications and variations will no doubt occur to those skilled in the arts to which this invention pertains. For example, instead of, or in addition to, turning off the ignition switch, an alarm device, such as the horn or lights, can be activated. Such variations which generally rely on the teachings through which this disclosure has advanced the art are properly considered within the scope of this invention.