Measuring and testing – Specific gravity or density of liquid or solid – Hydrostatic pressure type
Reexamination Certificate
2000-05-12
2001-09-04
Williams, Hezron (Department: 2856)
Measuring and testing
Specific gravity or density of liquid or solid
Hydrostatic pressure type
C073S03200R, C073S299000, C073S149000
Reexamination Certificate
active
06282953
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not Applicable
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable
MICROFICHE APPENDIX
Not Applicable
BACKGROUND OF THE INVENTION
The present invention relates to techniques for sensing and indicating the fuel reserve in a tank and particularly vehicle fuel tanks containing volatile fuel such as gasoline or mixtures of gasoline and methanol. Where vapor pressure is accumulated in the tank above the liquid fuel level, and particularly at elevated ambient temperature conditions in closed fuel vapor vent systems, the increased vapor pressure can significantly increase the effective density of the fuel. Where a float type sensor is employed for sending a fuel level signal from the tank to a remote indicator for the vehicle operator, the increased buoyancy, without any change in the liquid level of the fuel in the tank, can result in an increased buoyancy force on the float raising the float and thus providing an erroneous liquid level signal. Furthermore, float type sensors are unique or distinct for different fuel tank configurations, and thus require a variety of sensors in inventory for the various configurations in a manufacturers line of vehicle products, which is quite cumbersome and costly in mass production.
Accordingly, it has been desired to provide a simple, low cost yet effective technique or system for sensing the level of volatile liquid fuel in a fuel tank and particularly a fuel tank employed on a motor vehicle which will provide an accurate indication of the fuel level irrespective of the change in ambient temperature conditions and vapor pressure in the tank. It has further been desired to provide a single design liquid level sensor which can accommodate different fuel tank depth configurations.
BRIEF SUMMARY OF THE INVENTION
The present invention provides a system for indicating the fuel reserve in a tank by means of solid state sensors disposed within the fuel tank and eliminates the need for a float type device for sensing the liquid level of the remaining fuel in the tank. The system of the present invention employs a pair of solid state sensors disposed at a predetermined vertical increment and located near the bottom of the tank, with a third sensor disposed near the top of the tank for sensing the vapor pressure above the liquid level within the tank.
The system computes the apparent hydrostatic pressure by subtracting the measured vapor pressure from the pressure reading of the lowest sensor in the tank. The difference in the pressure readings for the two sensors located near the bottom of the tank is then normalized for the known distance between the sensors to enable a calculation of the liquid fuel density. From the computed apparent hydrostatic pressure and the computed density, the height of the liquid level in the tank is then computed; and, from a lookup table of fluid level height as a function of the tank volume at various liquid heights, the volume of fuel reserve is computed and an indication thereof provided to a remote indicator for the vehicle operator. In the event that the fuel level computed indicates that the liquid fuel has dropped below the level of the upper of the two sensors near the bottom of the tank, the system proceeds to set the density at the previously determined value and computes the fuel level based on a fixed density. In the event of a loss of signal to the remote indicator, the system may be reset by the vehicle operator upon refueling.
The present invention thus provides a simple and relatively low cost system for measuring the fuel reserve in a fuel tank without the need for a float type sensor, and is based upon pressure readings from a pair of sensors disposed near the bottom of the tank spaced at a predetermined vertical increment and a third sensor disposed near the top of the tank for reading the vapor pressure above the liquid fuel level. The present invention thus provides a system particularly useful for closed vent systems employed in fuel tanks in high volume, mass produced motor vehicles. The present invention provides a single fuel level sensor which can be used in a variety of tank configurations and depths.
REFERENCES:
patent: 4043193 (1977-08-01), Bailey
patent: 4625553 (1986-12-01), Charter
patent: 4949572 (1990-08-01), Wilen et al.
patent: 5157968 (1992-10-01), Zfira
patent: 5261276 (1993-11-01), Gifford
patent: 5351725 (1994-10-01), Suthergreen et al.
patent: 5604315 (1997-02-01), Briefer et al.
patent: 5900547 (1999-05-01), Bartkiewicz
Eaton Corporation
Johnston Roger A.
Williams Hezron
Wilson Katina M
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