Capacitive fuel composition sensor with ground isolation
First Claim
1. A fuel composition sensor for a fuel mixture in a fuel supply line for a combustion engine wherein the fuel mixture comprises two fuels of different dielectric constants in unknown relative concentrations, one of the fuels being electrically conductive, the combustion engine having a control computer comprising an electric power supply defining a computer analog reference voltage ECM referenced to a computer ground voltage EGD and an input adapted to receive a fuel composition signal VOUT from the sensor varying in a range between the computer analog reference voltage ECM and the computer ground voltage EGD, the sensor comprising, in combination:
- a capacitive sensor in the fuel line provided with a sensor analog reference voltage VREF referenced to a sensor ground voltage GND, which sensor ground voltage GND may differ from the computer ground voltage EGD, for providing a fuel composition responsive sensor voltage VSIG referenced to the sensor ground voltage GND, the sensor voltage VSIG having a minimum possible value VSIGmin corresponding to a sensed fuel composition of only one of the fuels;
an input isolation amplifier generating the sensor analog reference voltage VREF referenced to the sensor ground voltage GND ratiometrically from the computer analog reference voltage ECM referenced to the computer ground voltage EGD; and
an output isolation amplifier generating the fuel composition signal VOUT relative to the computer ground voltage EGD, less a constant, ratiometrically from the difference between the sensor voltage VSIG and the minimum possible value of the sensor voltage VSIGmin.
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Accused Products
Abstract
A fuel composition sensor for a fuel line carrying a mixture of two fuels provides a fuel composition signal VOUT to an engine control computer having a computer analog reference voltage ECM referenced to a computer ground EGD. The sensor has a sensor analog reference voltage VREF referenced to a sensor ground GND, which may differ from the computer ground EGD. An input isolation amplifier derives the sensor analog reference voltage VREF relative to GND ratiometrically from the computer analog reference voltage ECM referenced to EGD; and an output isolation amplifier derives the fuel composition signal VOUT referenced to EGD ratiometrically from the difference between a fuel composition responsive sensor signal VSIG and its minimum possible value, corresponding to a sensed fuel composition of only one of the fuels, relative to GND. The sensor may comprise a capacitive voltage divider and provide sensor voltage VSIG also having a maximum value corresponding to a sensed fuel composition of only the other fuel. If the range of possible values of VSIG is compressed, the isolation amplifier may provide a gain greater than one to better match the available input range of the computer. The minimum value of the fuel composition signal may be set detectably greater than EGD so that a value of EGD signals a sensor fault.
47 Citations
10 Claims
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1. A fuel composition sensor for a fuel mixture in a fuel supply line for a combustion engine wherein the fuel mixture comprises two fuels of different dielectric constants in unknown relative concentrations, one of the fuels being electrically conductive, the combustion engine having a control computer comprising an electric power supply defining a computer analog reference voltage ECM referenced to a computer ground voltage EGD and an input adapted to receive a fuel composition signal VOUT from the sensor varying in a range between the computer analog reference voltage ECM and the computer ground voltage EGD, the sensor comprising, in combination:
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a capacitive sensor in the fuel line provided with a sensor analog reference voltage VREF referenced to a sensor ground voltage GND, which sensor ground voltage GND may differ from the computer ground voltage EGD, for providing a fuel composition responsive sensor voltage VSIG referenced to the sensor ground voltage GND, the sensor voltage VSIG having a minimum possible value VSIGmin corresponding to a sensed fuel composition of only one of the fuels; an input isolation amplifier generating the sensor analog reference voltage VREF referenced to the sensor ground voltage GND ratiometrically from the computer analog reference voltage ECM referenced to the computer ground voltage EGD; and an output isolation amplifier generating the fuel composition signal VOUT relative to the computer ground voltage EGD, less a constant, ratiometrically from the difference between the sensor voltage VSIG and the minimum possible value of the sensor voltage VSIGmin. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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Specification