Abstract:
The composition of a fluid is measured with a sensor with a tube having: (i) a cavity for holding contents therein; and (ii) at least one opening in the tube being in communication with the cavity of the tube and the content held therein. The sensor further includes a sensor body attached to the tube having: (i) a circuit board; and (ii) a header, the header comprising a plurality of contacts that are electrically coupled to the circuit board; wherein the plurality of contacts of the header are in communication with the cavity of the tube. A method for measuring the composition of the fluid using the sensor is also described.

Description:
BACKGROUND 
       [0001]    1. Field 
         [0002]    The present invention relates generally to sensors, and more particularly, to a method and apparatus for sensing composition of flexible fuels. 
         [0003]    2. Background 
         [0004]    Flexible fuel, which is a blend of ethanol and gasoline, is becoming more common as a viable alternative energy source for vehicle operation. Flexible fuel vehicles (FFVs) are designed to run on gasoline or a blend of up to 85% ethanol (commonly referred to as “E85” with the number behind the “E” designating the percentage of ethanol that is in the fuel). 
         [0005]    FFVs have been produced since the  1980 s, and dozens of models are currently available. FFVs experience no loss in performance when operating on flex fuel. However, since a gallon of ethanol contains less energy than a gallon of gasoline, FFVs typically get about 20-30% fewer miles per gallon when fueled with E85. Except for a few engine and fuel system modifications, FFVs are identical to gasoline-only models. 
         [0006]    For example, with flex fuel, there is a need to determine the content of the fuel; 
         [0007]    more specifically, the ratio of the blend of ethanol to gasoline in the fuel. This information is required to calculate the correct air/fuel ratio for fuel metering and other parameters to optimize engine performance. The information may also be used as an indicator to warn the user regarding the content of the fuel. It would be desirable to be able to determine the content information to be used for automotive and other industrial applications. 
       SUMMARY OF THE PREFERRED EMBODIMENTS 
       [0008]    In one preferred embodiment of the present invention, the composition of a fluid is measured with a sensor with a tube having: (i) a cavity for holding contents therein; 
         [0009]    and (ii) at least one opening in the tube being in communication with the cavity of the tube and the content held therein. The sensor further includes a sensor body attached to the tube having: (i) a circuit board; and (ii) a header, the header comprising a plurality of pins that are electrically coupled to the circuit board; wherein the plurality of pins of the header are in communication with the cavity of the tube. 
         [0010]    In another preferred embodiment of the present invention, a method is provided for determining the composition of a fluid having a first component and a second component, each component having a respective dielectric property. The method includes the steps of providing a sensor having a capacitative sense element; putting the fluid in contact with the capacitative sense element; determining a dielectric property of the fluid based on the capacitance of the capacitative sense element; and, determining the proportion of at least one of the first component and the second component. 
         [0011]    In yet another embodiment of the present invention, an apparatus for determining the composition of a fluid having a first component and a second component, each component having a respective dielectric property, comprises a container for holding the fluid; a capacitative sense element, the capacitative sense element having a plurality of pins placed in contact with the fluid in the container; and, a circuit coupled to the capacitative sense element, the circuit configured to determine a dielectric property of the fluid based on a capacitance of the capacitative sense element. 
         [0012]    Other objects, features and advantages will become apparent to those skilled in the art from the following detailed description. It is to be understood, however, that the detailed description and specific examples, while indicating exemplary embodiments, are given by way of illustration and not limitation. Many changes and modifications within the scope of the following description may be made without departing from the spirit thereof, and the description should be understood to include all such variations. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The invention may be more readily understood by referring to the accompanying drawings in which: 
           [0014]      FIG. 1  is a first perspective view of a fuel sensor configured in accordance with one preferred embodiment of the present invention; 
           [0015]      FIG. 2  is a second perspective view of the fuel sensor of  FIG. 1 ; 
           [0016]      FIG. 3  is a front plan view of the fuel sensor of  FIG. 1 ; 
           [0017]      FIG. 4  is a side plan view of the fuel sensor of  FIG. 1 ; 
           [0018]      FIG. 5  is a top plan view of the fuel sensor of  FIG. 1 ; 
           [0019]      FIG. 6  is a cross-sectional view of the fuel sensor of  FIG. 1 , taken along line VI-VI of  FIG. 5 ; 
           [0020]      FIG. 7  is a cross-sectional view of the fuel sensor of  FIG. 1 , taken along line VII-VII of  FIG. 5 ; 
           [0021]      FIG. 8  is a detailed top plan view of a sensor electronics housing portion of the fuel sensor of  FIG. 1 , configured in accordance with one preferred embodiment of the present invention; 
           [0022]      FIG. 9  is a perspective view of a header of the fuel sensor of  FIG. 1 , configured in accordance with one preferred embodiment of the present invention; 
           [0023]      FIG. 10  is a top plan view of the header of the fuel sensor of  FIG. 1 ; 
           [0024]      FIG. 11  is a cross-sectional view of the header of  FIG. 10 , taken along line XI-XI of  FIG. 10 ; 
           [0025]      FIG. 12  is a cross-sectional view of the header of  FIG. 10 , taken along line XII-XII of  FIG. 10 ; 
           [0026]      FIG. 13  is a top plan view of a circuit board of the fuel sensor of  FIG. 1 , configured in accordance with one preferred embodiment of the present invention; 
           [0027]      FIG. 14  is a bottom plan view of the circuit board of  FIG. 13  ; and, 
           [0028]      FIG. 15  is a side view of the circuit board of  FIG. 13 . 
       
    
    
       [0029]    Like numerals refer to like parts throughout the several views of the drawings. 
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0030]    The present invention is directed to a fuel sensor for determining the composition of flexible fuel. In one preferred embodiment, the flex fuel sensor determines the composition of the flex fuel (i.e., mixture of how much ethanol versus gasoline is in the mixture) via the use of a dielectric measurement. The flex fuel sensor incorporates a header, which consists of a metal, glass, and pin assembly, that is immersed in the flex fuel as a capacitive probe. Specifically, the pins of the header function as the electrodes. As the fluid passes through the pins of the header, the capacitance will change in proportion to the dielectric of the fluid and used to determine the composition of the flex fuel. 
         [0031]    The dielectric constant (DC) of gasoline and ethanol is 2.2 and 24.2 respectively. This large difference between the two fluids, and in conjunction with their non-conductive properties, lends itself to utilize a dielectric measurement method as the viable means to discriminate between the amount of the components of the two. In one preferred embodiment of the present invention, a linear transfer function can be used to determine the constituents. Any value of DC between the two extremes (2.2 and 24) can then be used as an indicator to determine the fuel&#39;s respective constituents. As discussed herein, the shorthand of “E%” will be used to represent the percentage of ethanol that is in the flexible fuel, where the “%” is the number. Thus, E85 represents a flexible fuel mixture of 85% ethanol and 15% gasoline. Any proportion between E0 to E100 can be interpolated using a linear transfer function. For example, a DC value of 5.5 will represent E15, and 20.9 will represent E85. In one preferred embodiment of the present invention, the formula used to determine DC based on the percentage of ethanol, or 
         [0000]        DC= 0.22 E +2.2 
         [0000]    where E represents ethanol content and it will vary from 0 for E0, to 100 for E100. 
         [0032]      FIGS. 1 and 2  illustrate two perspective views of a fuel sensor  100 . In one preferred embodiment of the present invention, the fuel sensor  100  is configured so that it can be mounted directly in the path through which the fuel travels, such as in a fuel line, fuel tank, fuel rail, etc. The fuel sensor  100  includes a fuel tube  150  having a pair of inlet/outlet tubes  104 ,  114  and a center portion  118 . In one preferred embodiment of the present invention, the tubes  104 ,  114  are used to attach to a fuel line. The fuel flows through a tube openings  102  in tube  104  and a tube opening  202  in tube  114 . In one preferred embodiment of the present invention, the tube is a cylindrical structure, as illustrated in the figure. In other preferred embodiments, the tube may be a structure with other cross-sectional shapes such that it is a hollow body that may be used for conveying or containing liquids or gases. A sensor body  106  having a cover  108  is attached to the center portion  118 . The sensor body  106  also includes a connector  110  with a connector opening  112 . 
         [0033]      FIG. 3  illustrates a front plan view of the fuel sensor  100  where a plurality of contact pins  304  is accessible through the connector opening  112 .  FIG. 4  illustrates a side plan view of the fuel sensor  100  where a plurality of pins  402  may be accessible through the tube  104  of the opening  102 . As further described herein, the plurality of pins  402  are submerged in the fuel that flows through the fuel tube  150 . In one preferred embodiment of the present invention, the length, and the diameter of the plurality of pins  402  can be adjusted to thereby increase or decrease the capacitance pick up as desired. 
         [0034]      FIG. 5  illustrates a top plan view of the fuel sensor  100  that includes cross-section delineation lines VI-VI and VII-VII that are shown in  FIG. 6  and  FIG. 7 , respectively. In  FIG. 6 , a header  604  coupled to a circuit board  602  contained in the sensor body  106 . The header  604  also includes a header body  606 .  FIG. 7  illustrates how the plurality of contact pins  304  is attached to circuit board  602  through a plurality of connector wires  702 . In one preferred embodiment of the present invention, the header  604  is used as a capacitive probe, where each pin in the plurality of pins  402  functions as an electrode. As illustrated in  FIG. 6 , as well as  FIGS. 9-12 , the plurality of pins  402  is attached to header body  606  with a plurality of insulators  608 . In one preferred embodiment of the present invention, each pin in the plurality of pins  402  also includes a protruded portion  902  to support the circuit board  602  so that the circuit board  602  will have a place to rest when it is being assembled into fuel sensor  100 . In other preferred embodiments of the present invention, each pin in the plurality of pins  402  does not include the protruded portion  902 . 
         [0035]    In one preferred embodiment of the present invention, the header  604  is a metal, glass, and pin assembly wherein the header body  606  is comprised of metal or composite materials. The metal or composite materials of the header body  606  provides structural support for the header  604 . In one preferred embodiment, a material referred to as NiCo 2918, which is a composite comprised of 29% nickel (Ni), 18% cobalt (Co) and 53% iron (Fe), is used. Further, in one preferred embodiment of the present invention, the plurality of insulators  608  is comprised of glass and provides a hermetic seal for and insulation of the plurality of pins  402  from the header body  606 . In one preferred embodiment of the present invention, the specific materials are chosen because they provide immunity from corrosion. 
         [0036]    Glass-to-metal seals, which are assemblies of glasses with metals that are used to feed electrical conductors through the walls of hermetically-sealed packages, are vacuum tight. They have proven successful in electronic and electrical engineering and cover a wide range of applications in which the sealing glass serves as an excellent insulator. A typical glass-to-metal seal consists of an external metal part into which a pre-formed sintered glass element is sealed. The sintered glass element in turn encloses one or more metal leads that are sealed into it. 
         [0037]    In one preferred embodiment, the header  604  performs two fundamental functions: a) acts as a capacitor, and b) provides a hermetic seal. As the fluid (i.e., fuel) passes through the plurality of pins  402  of the header  604 , the capacitance measured by the plurality of pins  402  will change in proportion to the dielectric of the fluid. The capacitance signal is then converted through the electronics contained on the circuit board  602  to an output format suitable for the application—which could be a voltage, current, frequency, pulse width modulation (PWM), digital frame, etc. 
         [0038]    In one preferred embodiment of the present invention, it is anticipated that the use of a forest of pins for electrodes will at least partially eliminate any sensing errors due to the flow of liquid past the electrodes. There is a wide variety of possible electrode configurations possible and each might have its advantages. For example, an even number of pins in the plurality of pins  402  could be arranged in a circle with alternate pins being opposite electrodes. Or a single central pin could be the “+” electrode and the surrounding pins could all be “−” or ground potential. The surrounding metal structure provided by the header body  606  is grounded and therefore provides an electromagnetic interference (EMI) shield for the electrodes. 
         [0039]    In one preferred embodiment of the present invention, large gaps between the plurality of pins  402  and the metal, and the short run of the plurality of pins  402  through the header body  606  (i.e., post height), result in very low parasitic capacitance, which is a highly desirable feature for a capacitive sense element. The gap between the plurality of pins  402  allows fluid to pass through and flow freely without any adverse effect, or restriction. The post height of the header provides for easier mounting of the electronics (PCB, and other circuit materials). Specifically, in one preferred embodiment of the present invention, a smaller post height allows the electronics to be mounted very close to the sense element. Further, a shorter length of the header  604  and the resulting sturdiness keeps the capacitance signal stable (less changing with time) and also provides immunity to vibration. 
         [0040]    In one preferred embodiment of the present invention, the header  604  is bonded to a structure through brazing, welding, soldering, or any other means that provides “metal-to-metal” seal and maintains the integrity of the seal. The post height (extension on the non fluid side) of each pin of the plurality of pins  402  is used to connect to the electronics on the circuit board  602 . As illustrated in  FIGS. 13-15 , the circuit board  602  include a plurality of openings  1304  so that the plurality of pins  402  pokes through the circuit board  602  so that the plurality of pins  402  may be electrically coupled to the electronics and circuitry on the circuit board  602 . The circuit board  602  also includes a plurality of mounting holes  1302  so that the circuit board  602  can be mounted to sensor body  106 . 
         [0041]    Although the fuel sensor described herein is to be used for flexible fuel based on ethanol, the principles and features disclosed may be applied to other types of fluids where there exists a difference between the DC of the fluid components. 
         [0042]    The embodiments described above are exemplary embodiments. Those skilled in the art may now make numerous uses of, and departures from, the above-described embodiments without departing from the inventive concepts disclosed herein. Various modifications to these embodiments may be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments, e.g., in fuel production applications, without departing from the spirit or scope of the novel aspects described herein. Thus, the scope of the invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein. The word “exemplary” is used exclusively herein to mean “serving as an example, instance, or illustration.” Any embodiment described herein as “exemplary” is not necessarily to be construed as the most preferred or advantageous over other embodiments. Accordingly, the present invention is to be defined solely by the scope of the following claims.