Abstract:
A fluid level sensor for a fluid storage tank including a mounting surface having a heating element mounted thereto, the heating element mounted in close proximity to a thermal sensor and a circuit for controlling power to the heating elements and receiving a signal from the thermal sensors sensing the change in temperature of the heating element to indicate whether or not the heating element is submersed in liquid, wherein the circuit intermittently energizes the heating element for a first period of time and de-energizes the heating element for a second period of time.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     The present application claims priority to U.S. Provisional Patent Application No. 60/756,923 filed Jan. 6, 2006, the contents of which are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     The invention relates to fluid level sensors, and in particular to a non-mechanical solid state fluid level sensor for automobiles having no moving parts.  
         [0003]     When driving an automobile, it is important that the driver know how much fuel remains within the gas tank so that he or she can refuel the vehicle before it runs out of fuel. Various types of level sensors are used to monitor the fuel level within the fuel tank and communicate the current level to the driver. The majority of these sensors utilize a mechanical action associated with a float or level disposed within the fuel tank. Mechanical sensors suffer from a variety of inadequacies, including sensitivity to fuel types, fuel sloshing and mechanical breakdowns.  
         [0004]     Available level sensors fail to perform adequately enough to meet the standards in today&#39;s competitive auto industry. Currently available sensors are either not accurate enough or able to meet current quality standards under the broad range of operating conditions, such as temperature ranges, fuel types, and fuel sloshing, as is required by the industry.  
         [0005]     Therefore, what is needed is a non-mechanical fuel level sensor that can accurately monitor and communicate the fuel level under the broad range of operating conditions that exist in automobiles.  
       SUMMARY OF THE INVENTION  
       [0006]     Briefly stated, the invention is a fuel sensor apparatus, comprising an external power source, a housing adapted for immersion within a fuel storage container, and at least one sensor array mounted within the housing. The sensor array comprises at least one microprocessor operatively connected to the power source, a plurality of thermal diodes operatively connected to the microprocessor, and at least one controlled heating element associated with each thermal diode. The microprocessor is configured to monitor an output signal from each of the thermal diodes in response to a heating or cooling cycle, with the output signal varying over time in response to immersion of the thermal diode within a liquid or fuel. By identifying whether a thermal diode is immersed in fuel or exposed to air, the fuel sensor apparatus of the present invention provides an indication of a fuel level within a fuel storage container.  
         [0007]     The foregoing and other features, and advantages of the invention as well as embodiments thereof will become more apparent from the reading of the following description in connection with the accompanying drawings. 
     
    
     DESCRIPTION OF THE DRAWINGS  
       [0008]     In the accompanying drawings which form part of the specification:  
         [0009]      FIG. 1  is a plan view of a level sensor apparatus in an extended position according to an embodiment of the present invention;  
         [0010]      FIG. 2  is a plan view of the level sensor apparatus in a retracted position according to an embodiment of the present invention;  
         [0011]      FIG. 3  is a perspective view of an upper half of the housing according to an embodiment of the present invention;  
         [0012]      FIG. 4  is a side view of the upper half of the housing according to an embodiment of the present invention;  
         [0013]      FIG. 5  is a perspective view of an upper flange of the housing according to an embodiment of the present invention;  
         [0014]      FIG. 6  is another perspective view of the upper half of the housing according to an embodiment of the present invention;  
         [0015]      FIG. 7  is an end view of the upper half of the housing according to an embodiment of the present invention;  
         [0016]      FIG. 8  is a side view of the upper half of the housing according to an embodiment of the present invention;  
         [0017]      FIG. 9  is a perspective view of the upper half of the housing with connectors attached to the flange according to an embodiment of the present invention;  
         [0018]      FIG. 10  is a perspective view of the lower half of the housing according to an embodiment of the present invention;  
         [0019]      FIG. 11  is another perspective view of the lower half of the housing according to an embodiment of the present invention;  
         [0020]      FIG. 12  is a end view of the lower half of the housing according to an embodiment of the present invention;  
         [0021]      FIG. 13  is a plan view of a sensor circuit board according to an embodiment of the present invention;  
         [0022]      FIG. 14  is a side view of the sensor circuit board according to an embodiment of the present invention;  
         [0023]      FIG. 15  is an enlarged view of the sensor circuit board according to an embodiment of the present invention;  
         [0024]      FIG. 16  is a schematic of the sensor circuit board; according to an embodiment of the present invention  
         [0025]      FIG. 17  is a graph illustrating the temperature response of a sensor during heating and cooling cycles according to an embodiment of the present invention;  
         [0026]      FIG. 18  is a diagram of a sensor according to an embodiment of the present invention; and  
         [0027]      FIG. 19  is a diagram of a sensor according to another embodiment of the present invention. 
     
    
       [0028]     Corresponding reference numerals indicate corresponding parts throughout the several figures of the drawings.  
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0029]     The following detailed description illustrates the invention by way of example and not by way of limitation. The description clearly enables one skilled in the art to make and use the invention, describes several embodiments, adaptations, variations, alternatives, and uses of the invention, including what is presently believed to be the best mode of carrying out the invention. Additionally, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting.  
         [0030]     As shown in  FIGS. 1-15 , an embodiment of the present invention, generally referred to as a level sensor  1 , includes a sensor circuit board  10  mounted within a housing  12 .  
         [0031]     The housing  12  comprises an upper half  14  and a lower half  16  that is slidably mounted within the upper half  14  so that the housing can be extended and retracted by sliding the lower half  16  within the upper half  14 . The housing  12  includes a flange  18  at an upper end  20  of the upper half  14  that mounts to the top of a fuel tank and comprises electrical connections  22  that operatively connect to a power supply. The lower half  16  comprises an electrical connector opening  23 .  
         [0032]     The sensor circuit board  10  mounts within the lower half  16  of the housing  12  and operatively connects to the electrical connections  22  of the upper half  14  of the housing  12  via a wiring harness. A plurality of discrete sensors  24  are mounted and spaced apart along the board in a linear fashion and operatively connected through a multiplexer to a microprocessor or other suitable logic circuit. The discrete sensors  24  each include a thermal diode  26  operatively connected to, and located in close proximity to, a controlled heating element  28  (shown diagrammatically in  FIG. 18 ). The controlled heating element  28  is preferably a resistor.  FIG. 16  is a schematic of the sensor circuit board.  
         [0033]     In operation, the microprocessor or logic circuit  29  cycles the controlled heating elements  28  over a predetermined period of time, alternately heating and cooling the thermal diodes  26  of each discrete sensor  24 . The output signal from each thermal diode  26 , in the form of a voltage level, is sampled by the microprocessor or logic circuit over a period of time during the heating and/or cooling phase of the cycle to identify the change in temperature (ΔT) in response to the application or extraction of heat over a given period of time. Discrete sensors  24  which are immersed within the fuel stored in the fuel storage container will respond differently to the heating and cooling cycle as compared with those which are not. Accordingly, the value for ΔT for each discrete sensor  24  immersed within the fuel will differ from the value of ΔT for those discrete sensors which are not.  
         [0034]     Accordingly, the microprocessor or logic circuit is configured to identify a level of fuel within the fuel storage container based upon a determination of which discrete sensors  24  are immersed in fuel and which are not. Preferably, the sensors  24  are arranged in a linear array, disposed vertically within the fuel storage container, however, those of ordinary skill in the art will recognize that the sensors need not be disposed in this manner, but rather, may be disposed as required about the fuel storage container, so as to accommodate any of a variety of container geometries.  
         [0035]     In the preferred embodiment, the temperature difference is greater when the sensor is exposed to air, as shown in  FIG. 17 .  
         [0036]     While the sensors  24  are described above as thermal diode/resistor pairs, it should be understood by one of ordinary skill in the art that this arrangement is exemplary and the sensors may comprises any combination of a heating element and a heat sensing element. For example, the resistor may be omitted and merely a thermal diode used as by the heating element and a heat sensing element by utilizing the internal resistance of the thermal diode for heat generation, as diagrammatically illustrated in  FIG. 19 . Moreover, the thermal diode may comprise a NPN or PNP transistor wherein the base and collector are connected or simply by using a standard PN junction-type diode.  
         [0037]     Moreover, the present invention can use the sensors  24  in any manner to determine the level of a liquid within a storage container, such as fuel within a fuel tank. Described above, the microprocessor investigates heating times in order to determine the sensors  24  that are submerged. However, one of ordinary skill in the art, from reading the present disclosure, would readily understand that one could also supply a voltage or current to the sensors  24  and determine absolute temperatures to determine fuel level or heating times and absolute temperatures could be used in alternating fashion, or a first method upon startup and a second method upon continued operation. For determining a fuel level based upon absolute temperature of the sensors  24 , it may be advantageous to include reference sensors that are always submerged and/or always not submerged in order to determine the ambient temperature of the fuel and/or the air.  
         [0038]     Furthermore, while it is described above to directly submerge the sensors, it has been found that coating the sensors and circuit board in a polymeric protective coating protects the device from the corrosive effects of certain liquids, for example, the corrosive effect of fuel containing 10% or more alcohol.  
         [0039]     Changes can be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.