Patent Application
20100132431
The present invention relates generally to sensors, more particularly to a fuel sensor having sensing plates that do not obstruct a fuel passage, and still more particularly to a method for testing and calibrating such sensors.
Due to the fact that ethanol is a renewable fuel, and for other reasons as well, the use of ethanol and ethanol blends (i.e., ethanol and gasoline) continues to grow. 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). Properties of such fuels, such as its conductivity or dielectric constant, can be used to determine the concentration of ethanol (or other alternate fuel) in the gasoline/alternate fuel blend and can also be used to determine the amount of water mixed in with the fuel. Experimental data shows that the fuel dielectric constant is directly proportional to the ethanol concentration but relatively insensitive to water contamination, provided that the water concentration is below about 1% since the dielectric constant of water is around 80 at 25° C. (i.e., surveys show that the water concentration on most U.S. Flex fuel stations is below 1%). On the other hand, fuel conductivity is very sensitive to water concentration. For example, ethanol has a dielectric constant of around 24 at 25 degrees Celsius while gasoline has a dielectric constant of around 2 at the same temperature. Determining the properties of such fuels is important for operation of a motor vehicle since an engine controller or the like can use the information regarding the composition, quality, temperature and other properties of the fuel to adjust air/fuel ratio, ignition timing and injection timing, among other things. Additionally, increasingly strict emissions-compliance requirements have only further strengthened the need for an accurate flexible fuel sensor.
Fuel passage obstruction is a shortcoming of conventional fuel sensors, particularly capacitance-based approaches. More specifically, to measure the capacitance of the fuel, conventional sensors are known to use plates with different shapes, but in all such applications these plates are inside the fuel line (i.e., the fuel passage). This makes the construction of such sensors more complex and poses a potential for obstructing the fuel flow. Additionally, this approach imposes stricter requirements to protect the plates from corrosion by the ethanol.
Co-pending application (Attorney Docket No. DP-317807) disclose an obstruction-less fuel property sensor that measures, for example, the ethanol concentration in the fuel, which is then used by the engine control unit for controlling the engine to accommodate the fuel with the varying ethanol levels. As known, different blends have varying energy content levels. The sensor in the co-pending application measures capacitance across the fuel that flows through the sensor and from which a corresponding dielectric constant can be derived. The sensor then correlates the dielectric constant with an ethanol concentration. The output of the sensor may be, in one embodiment, proportional to the dielectric constant of the media under measurement, and which may vary between about 2 and 24 (as described above).
In the manufacturing process of this kind of flex fuel sensor, important steps involve calibration and final testing. To perform the calibration, one approach involves exposing the sensor to a series of different fuel formulations containing varying (but known) ethanol concentrations, like what which would be encountered during the service life of the sensor. For each fuel formulation, a respective reading would be taken from the sensor. The readings would be used to arrive at a calibration factor (or a curve or a map in some instances) that could be used to interpret or convert the actual sensor readings into a more accurate indication of ethanol concentration. However, a drawback of such an approach is that using fuels in the manufacturing process (even for testing) complicates the handling and the cleaning of the sensor, as well as requires increased levels of care (e.g., safety measures) in the handling of the fuels. Overall, this introduces extra expensive.
Another approach involves the use of other liquids to simulate different gasoline and ethanol blends of fuels (e.g., like various oils). However, a drawback of this approach is that it will still require a special step to clean the sensor and/or related parts after the calibration and test phases. The step of cleaning itself may involve or require the use of solvents, which can complicate the overall process as much as the use of fuel blends. In sum, the use of oils or the like do not provide any appreciable improvement over use of fuels.
There is therefore a need for a method for calibration and testing of a fuel property sensor that minimizes and/or eliminates one or more of the problems described above.
The present invention solves one or more of the problems described above in connection with calibrating/testing a fuel sensor by employing a test blank formed of a solid material having a known dielectric constant. The test blank is formed with a size and shape configured to match that of the fuel passageway in the fuel sensor and is used in place of actual fuel during calibration and final testing. The invention reduces the cost of the equipment needed for calibration/testing, its operating cost, as well as eliminating previously required related costs pertaining to safety measures and sensor cleaning.
A method of calibrating a fuel property sensor having a fuel passage includes a number of steps. The first step involves inserting a test blank into the fuel passage wherein the blank comprises material having a predetermined dielectric constant. Preferably, the test blank is configured in size and shape to correspond to the fuel passage, thereby substantially occupying the passage. The next step involves calibrating the fuel property sensor while the blank remains in the fuel passage.
In an alternate embodiment, the method further includes the step of compressing the test blank while it is in the fuel passage so as to substantially eliminate “air gaps” due to irregularities in either the inner surface of the fuel passage or the outer surface or geometry and/or size of the test blank. Minimizing or eliminating these “air gaps” allows for a more accurate calibration.
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,
The output signal 16 is indicative of one or more sensed physical properties of the fuel, such as dielectric constant or conductivity. The output signal 16 may then be provided to, for example only, an electronic engine controller 18 or the like for use in engine control, as described above. The sensing apparatus 10 further includes a tube 20 formed of fuel resistant material (e.g., acetal) having a fuel inlet 22, a fuel outlet 24 and a fuel passage 26 formed therebetween. Further details of the kind of fuel sensing apparatus to which the inventive method for calibrating and final testing may find useful application may be seen by reference to co-pending U.S. patent application entitled “FUEL SENSOR” (attorney docket no. DP-317807) referenced above.
In addition,
In sum, the test blank 30 fits in the fuel passage 26 of the sensing apparatus 10 to simulate the different fuel blends required in the calibration and test. This inventive approach using a solid test blank greatly simplifies the process while at the same time provides an approach that eliminates the need for extensive post-calibration cleaning.
In step 44, the test blank 30 (or 30′) is inserted in the fuel passage 26 of the fuel sensing apparatus 10. The test blank 30 (or 30′) is preferably solid and comprises material having a predetermined, known dielectric constant. The method proceeds to step 46.
In step 46, the controller 36 is configured to calibrate the fuel sensing apparatus 10 while the test blank 30 (or 30′) is in the fuel passage 26. In one embodiment, the calibrating step includes the step of applying an excitation signal of a predetermined, known character while measuring the resulting, induced signal. From the excitation and induced signals, a capacitance can be derived, from which a test-based dielectric constant of the media-under-test (i.e., test blank 30 or 30′) can be computed, all as previously described in the U.S. application entitled “FUEL SENSOR” (docket no. DP-317807), referred to above and incorporated herein by reference. The controller 38 may be further configured to calculate a calibration factor based on the test-based dielectric constant of the media-under-test, on the one hand, and the predetermined, known dielectric constant of the media-under-test, on the other hand. Finally, the method may involve storing the calculated calibration factor (or curve/map as the case may with multiple test blanks of different dielectric constants), in accordance with at least one calibration usage strategy known in the art. Two exemplary approaches were described above, however, it should be understood that those are exemplary only and not limiting in nature.
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
This application is related to co-pending U.S. application Ser. No. ______ filed ______, 2008 entitled “FUEL SENSOR (Docket No. DP-317807), now pending, owned by the common assignee of the present invention, the disclosure of which is hereby incorporated by reference herein in its entirety.
