Patent Application
20090079445
The present invention relates generally to sensors and more particularly to a fuel sensor having sensing elements and electronics that are isolated from the fuel.
Properties of gasoline, such as its conductivity or dielectric constant, are often important for operation of a motor vehicle. For example, flexible fuel vehicles are known that are designed to run on gasoline as a fuel or a blend of up to 85% ethanol (E85). Such properties can be used to determine the concentration of ethanol in a gasoline and can also determine the amount of water mixed in with the fuel. For example, experimental data shows that the fuel dielectric constant is directly proportional to the ethanol concentration but relatively insensitive to water contamination, while fuel conductivity is very sensitive to water concentration. Thus, for these applications and others, there is a need for a fuel sensor that precisely measures the impedance of fuel. More generally, therefore, engine controllers benefit from sensors that provide information regarding the composition, quality, temperature and other properties of the fuel that is delivered to the combustion chamber.
Most sensor technologies for fuel property sensing require in-situ signal processing electronics to convert the relatively small sensing signals to a suitably strong electrical signal that can be used by an external circuit, such as an engine controller, to define the measured fuel property of interest. For example only, a capacitive sensor that is configured to apply an excitation signal to spaced apart sensing plates induces a relatively small induced signal, thus requiring local electronics to preserve the signal-to-noise ratio.
Furthermore, it is known that most in-situ sensors use capacitive, inductive or magnetic technologies, which do not require direct contact or exposure to the fuel in order to assess the relevant fuel properties. In fact, these sensors generally require physical isolation from the fuel, since contact with the fuel can often degrade the performance of the sensor. While it is known to use coatings to isolate various sensor components from contact with the fuel, such coatings may induce stress and/or degrade the signal-to-noise ratio of the sensing approach.
There is therefore a need for a fuel sensor that minimizes or eliminates one or more of the problems set forth above.
The invention achieves isolation of the sensing elements and signal processing electronics from any contact with a fuel, without the use of any coatings, encapsulants or other potting materials that would be resistant to fuel and benign to the various sensor components. This eliminates a source of performance degradation over the service life of such a fuel sensor.
An apparatus for use in sensing characteristics of fuel includes a unitary (i.e., one-piece) body having a fuel inlet, a fuel outlet and a fuel passage between the inlet and outlet. The unitary body further includes at least first and second, spaced-apart holders extending into the fuel passage. First and second sensing elements are disposed in the first and second holders. The holders, being integral with the main body, isolate the sensing elements from contact with any fuel in or flowing through the fuel passage.
In a preferred embodiment, a fuel sensor includes a unitary, cylindrical body extending along a main axis, with a fuel inlet, a fuel outlet and a fuel passage in between. The body further includes at least a pair of spaced-apart first and second sensing element holders extending into the fuel passage, and which contain first and second sensing elements.
The unitary body also contains a cavity that is adapted to house an electrical circuit. The electrical circuit is configured to produce the output signal. Each sensing element has a respective lead extending into the cavity for connection to the electrical circuit. The cavity is isolated from the fuel passage, isolating the electrical circuit from exposure to fuel. The sensor further includes a cover configured to close the cavity and seal it against outside environmental influences (e.g., water).
The unitary body also contains an interface connector having at least power, ground and output signal terminals. Finally, the sensor includes a ground shield that is disposed radially-outwardly of the cylindrical body, located around the sensing elements. The shield reduces electromagnetic emissions and also reduces the effect of any external electromagnetic interference.
Other features, aspects and advantages are presented.
The present invention will now be described by way of example, with reference to the accompanying drawings:
Referring now to the drawings wherein like reference numerals are used to identify identical components in the various views,
Apparatus 10 includes a body 20, which in the illustrated embodiment includes a generally cylindrical tube portion 21 that extends along a main, longitudinal axis labeled “A” in
Unitary body 20 includes an inlet 22, an outlet 24 and a fuel passage 26 formed in between. Inlet 22 and outlet 24 each include a respective interface that is suitable for connection to a fuel hose or tube or other mechanism, as per the requirements of any particular application.
Body 20 also includes an interface connector 28, which may include a plurality of electrical terminals (best shown in
It should be appreciated that while the illustrated embodiment shows three sensing plates 321, 322 and 323, two plates may be sufficient for certain application and an even greater number of plates may be provided in other applications. The operating principle being that two sensing plates that have fuel between them may be used to ascertain one or more physical properties or characteristics. The sensing plates 321, 322 and 323 are preferably substantially parallel to each other, and the holders 301, 302 and 303 are configured to achieve this orientation. Moreover, the sensing plates 321, 322 and 323 are substantially perpendicular to longitudinal axis “A” (best shown in
Typical embodiments of the present invention use a copper-based terminal, such as brass, that is tin-plated at the PCB interface for optimization of the solder interface.
It should be understood that in the present disclosure, a pair of sensing plates, with fuel present in between, will appear to the electronics on PCB 46 as a complex load (e.g., a parallel combination of a resistor and a capacitor). This complex impedance comprises a real component part (resistive) and an imaginary component part (capacitive), which can be correlated to conductivity and a dielectric constant, useful physical properties of the fuel. The art is replete with approaches for measuring the complex impedance, or components thereof, for purposes of ascertaining one or more physical properties of the fuel, for example, as seen by reference to U.S. application Ser. No. 10/199,651 filed Jul. 19, 2002, now U.S. Pat. No. 6,693,444 B2 entitled “CIRCUIT DESIGN FOR LIQUID PROPERTY SENSOR” issued Feb. 17, 2004 to Lin et al., owned by the common assignee of the present invention, and hereby incorporated by reference in its entirety herein, or as seen by reference to U.S. provisional application Ser. No. 60/890,112 filed 15 Feb. 2007, now pending, entitled “LIQUID PROPERTIES SENSOR CIRCUIT” to Lin et al., owned by the common assignee of the present invention and hereby incorporated by reference in its entirety herein.
While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiments but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as is permitted under the law.
