1. Technical Field
This invention relates generally to a level sensor in a fuel system, and in particular, to an electro-static potential differential level sensor element for measuring fuel in a fuel system.
2. Related Art
Typical automotive fuel systems include an in-tank mounted fuel delivery system which includes a reservoir for containing fuel with the tank. A fuel pump located inside of the reservoir withdraws the fuel from the reservoir and delivers it to an internal combustion engine. As the fuel is withdrawn from the reservoir, a fuel detection device measures the level of fuel that remains in the tank by use of a sensor. Fluid level measuring mechanisms include, for example, floating arm mechanisms, pressure sensors, capacitive sensors and ultrasonic sensors.
Floating arm mechanisms require moving parts inside the reservoir, require time to install and are suspect to developing contact problems resulting in erroneous measurement. Typically a float is pivotally mounted to a fuel level assembly, which interacts with circuitry to develop a measurement of the level of fuel in the tank based on the buoyant position of the float.
Capacitive sensors use an electrical capacitor for measurement and another for reference. The capacitor used for measurement is normally present over the entire height of the tank, and the capacitance various varies according to the level of fuel in the tank. The reference capacitor is permanently immersed in the fuel and supplies a reference value of the dielectric constant of the fuel. An electronic circuit determines the level of the fuel in the tank. The capacitors can be flat or cylindrical plates between which fuel can fall and rise, thereby influencing the capacitance. These sensors may also be in the form of an interdigital electrode which interacts by interference effect.
U.S. Pat. No. 5,001,596 discloses a capacitor for a fluid level sensor that has elongated expandable capacitor plates mounted in spaced relationship with respect to one another to form a capacitor for measuring data representing liquid in a container. The capacitor plates are continuously expandable to accommodate any change in shape of the container.
U.S. Publication 2007/0240506 discloses a sensing assembly that senses the level of fluid in a reservoir. An excitation circuit is electrically connected to first and second ports for receiving voltage signals and to generate excitation signals. A receiving circuit is disposed adjacent to the excitation circuit and defines a variable capacitance with the excitation circuit. The receiving circuit produces an output voltage variable with the level of the fluid in a reservoir due to capacitance changes between the excitation circuit and receiving circuit due to dielectric changes created by the fluid.