This application is based upon and claims benefit of priority of Japanese Patent Application No. 2007-321225 filed on Dec. 12, 2007, the content of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a detector device for detecting a density of a component contained in mixture fuel.
2. Description of Related Art
An example of such a detector device is disclosed in JP-A-5-87764. A conventional detector device including this example will be briefly described. The detector device detects a density of a component such as ethanol contained in mixture fuel composed of, e.g., gasoline and ethanol. A pair of electrodes is immersed in the mixture fuel and alternating voltage is applied to the electrodes to thereby measure a permittivity of the mixture fuel. Since the permittivity of the mixture fuel is determined based on a frequency of the applied alternating voltage and densities of components contained in the mixture fuel, the density of one component (a focused component) can be calculated from the permittivity detected by applying alternating voltage having a known frequency. In this manner, a density of either gasoline or ethanol contained in the mixture fuel is detected.
However, the following problem is involved in the conventional detector device. It is known that some water is often mixed with the mixture fuel containing main components such as gasoline and ethanol. Water maybe mixed with the mixture fuel at a refinery stage or when the mixture fuel contacts atmospheric air containing water. Further, water may be inadvertently mixed with the mixture fuel by a person carrying or handling the mixture fuel. In the conventional detector device, the density of a component is detected without considering that water may be included in the mixture fuel. In other words, the density of a component is detected under an assumption that the mixture fuel is composed of only the main components. Therefore, the density of a component detected by the conventional detector device may include an error if water is contained in the mixture fuel. Although gasoline is usually composed of several-hundreds of ingredients, gasoline can be handled as a single component because the permittivity of all ingredients is substantially the same.
The present invention has been made in view of the above-mentioned problem, and an object of the present invention is to provide an improved detector device for accurately detecting a density of a component contained in mixture fuel.
Mixture fuel composed of gasoline and ethanol is used as a fuel for a gasoline engine. In order to control operation of the engine under optimum conditions, density of the mixture fuel has to be detected. According to the present invention, the density of the mixture fuel is detected by a detector device even when some water is contained in the mixture fuel.
The detector device includes a sensor having a pair of electrodes, an electronic device for calculating the density of the component in the mixture fuel and a memory device for storing permittivities of pure components. The pair of electrodes are immersed in the mixture fuel flowing through a fuel conduit, and alternating voltage having two frequencies f1 and f2, different from each other is applied to the electrodes. The permittivities of pure components are measured under the two frequencies f1, f2 and stored in the memory device.
The frequencies (a first frequency f1 and a second frequency f2) of the alternating voltage are chosen, so that the permittivities of gasoline and ethanol show no change between f1 and f2 while the permittivity of water shows a considerable change between f1 and f2. The first frequency f1 may be set in a frequency range from 50 kHz to 500 kHz, and the second frequency f2 may be set in a frequency range from 500 kHz to 10 MHz. The density of each component (gasoline, ethanol and water) in the mixture fuel is calculated based on a difference of the permittivities of the mixture fuel detected under f1 and f2 and permittivities of the pure components measured under f1 and f2 and stored in the memory device.
The mixture fuel is not limited to the mixture fuel composed of gasoline and ethanol as main components. The present invention may be applied to other mixture fuel such as mixture fuel for a Diesel engine containing light oil and fatty acid methyl ester as main components. A portion of the electrode contacting the mixture fuel may be covered with an insulating film to avoid chemical reactions between the electrode and the mixture fuel.
According to the present invention, the densities of components contained in the mixture fuel are accurately detected even if some water is included in the mixture fuel. Other objects and features of the present invention will become more readily apparent from a better understanding of the preferred embodiment described below with reference to the following drawings.
A preferred embodiment of the present invention will be described with reference to
The sensor 10 includes a pair of electrodes 12a, 12b and a detector circuit 11. An alternating voltage V is applied to the pair of electrodes 12a, 12b to measure a capacitance of the pair of electrodes to thereby detect a permittivity ε of the mixture fuel. Each electrode 12a, 12b is formed in a comb-shape, and the pair of electrodes is formed by combining the comb-shaped electrodes in a zigzag form.
A capacitance C of the pair of electrodes 12a, 12b is determined according to the frequency of the alternating voltage applied to the electrodes 12a, 12b, densities of the components contained in the mixture fuel and kinds of components contained in the mixture fuel. The capacitance C is expressed by the formula: C=α·ε, where α is a constant determined by a size and a shape of the pair of electrodes 12a, 12b. The detector circuit 11 calculates the permittivity ε of the mixture fuel base on the capacitance C and the constant α. Since the way of detecting the permittivity of the mixture fuel is well known, it is not explained here in detail.
The density of gasoline or ethanol contained in the mixture fuel is conventionally determined under an assumption that the mixture fuel is composed of gasoline and ethanol, without containing water therein. However, in an actual situation some water is usually contained in the mixture fuel for the reasons mentioned above. In this actual situation, it should be assumed that the mixture fuel is composed of gasoline, ethanol and water. In order to accurately detect a density of a component contained in the mixture fuel even if water is also contained therein, two frequencies, a first frequency f1 and a second frequency f2, are used in applying the alternating voltage to the pair of electrodes 12a, 12b. The frequencies f1, f2 are chosen, so that the permittivities of both gasoline and ethanol do not change between both frequencies f1, f2 while the permittivity of water changes between frequency f1 and frequency f2.
Generally, the permittivity of a substance uniquely changes according to frequencies due to polarization characteristics of molecules forming the substance, which is known as a dielectric alleviation phenomenon. For example, a peak of a dielectric loss appears when an alternating voltage in a high frequency region is applied to a substance. The permittivity of a substance also changes, due to its conductivity, ions and conductive impurity contained in the substance, when an alternating voltage in a low frequency region is applied thereto.
In this embodiment, a first frequency f1 is chosen from a frequency range from 50 kHz to 500 kHz where the permittivities of gasoline and ethanol show no change. A second frequency f2 is chosen from a frequency range from 500 kHz to 10 MHz where permittivities of all of gasoline, ethanol and water show no change. When the alternating voltages of frequency f1 and frequency f2 are applied to the pair of electrodes 12a, 12b, the permittivities of gasoline and ethanol do not change between f1 and f2, while the permittivity of water shows a considerable change between f1 and f2.
As shown in
It is known that the permittivity of the mixture fuel 51 becomes substantially equal to a sum of products of a density and permittivity of each component contained in the mixture fuel. In this particular embodiment (assumed that the mixture fuel is composed of gasoline, ethanol and water), the permittivity ε1 of the mixture fuel measured at f1 and the permittivity ε2 of the mixture fuel measured at f2 are expressed by the following formulae:
ε1=εa1·a+εb1·b+εc1·c
ε2=εa2·a+εb2·b+εc2·c
where εa1, εb1 and εc1 are permittivities of gasoline, ethanol and water, respectively, measured at frequency f1; εa2, εb2 and εc2 are permittivities of gasoline, ethanol and water, respectively, measured at frequency f2; and a, b and c are the densities of gasoline, ethanol and water, respectively. As shown in the graph of
(ε1−ε2)=(εc1−c2)·c
The density c of water (focused component) is expressed by:
c=(ε1−ε2)/(εc1−εc2)
This means that the density of the focused component water is calculated based on the detected permittivities ε1, ε2 of the mixture fuel and stored permittivities of water εc1, εc2. The density “a” of gasoline and the density “b” of ethanol are expressed by the following formulae:
a={ε1−εb1+(εb1−εc1)·c}/(εa1−εb1)
b=1−a−c
To calculate the density a, b, c of each component (gasoline, ethanol and water), at least εa1, εb1, εc1 and εc2 have to be known. Therefore, the permittivities of the pure components (gasoline, ethanol and water) are measured under frequencies f1, f2 beforehand and stored in the memory device 30.
As described above, the permittivity ε1 of the mixture fuel 51 is measured by applying the alternating voltage having frequency f1, and the permittivity ε2 of the mixture fuel is measured by applying the alternating voltage having frequency f2. The electronic device 20 calculates the density “c” of water (focused component) contained in the mixture fuel based on the measured permittivity ε1, ε2 and the permittivity of water memorized in the memory device 30. That is, the density of the water “c” is calculated according to the formula: c=(ε1−ε2)/(εc1−εc2). The density “a” of gasoline and the density “b” of ethanol are calculated based on “c” and the permittivities of each component memorized in the memory device 30 according to the formulae shown above.
The second frequency f2 is set in the frequency range from 500 kHz to 10 MHz where the permittivities of all of the components (gasoline, ethanol and water) do not change even if the frequency f2 fluctuates. Therefore, the permittivity ε2 of the mixture fuel detected by the sensor 10 is stable, and influence of temperature changes in the sensor 10 on the detected permittivity can be minimized.
Though the first frequency f1 and the second frequency f2 are chosen from the frequency range from 50 kHz to 500 kHz and the frequency range from 500 kHz to 10 MHz, respectively, in the embodiment described above, it is possible to choose both frequencies f1 and f2 from the same range, e.g., the range from 50 kHz to 500 kHz. The alternating voltage is applied to the sensor electrodes 12a, 12b to avoid formation of electric double layers around the electrodes. If the polarities of the electrodes were not alternate, plus or minus irons in the mixture fuel would be attracted to the electrodes, thereby forming the electric double layers. The permittivity of the mixture fuel can be accurately detected by applying the alternating voltage.
The pair electrodes 12a, 12b is formed by comb-shaped electrodes as shown in
The present invention is not limited to the embodiment described above, but it maybe variously modified. For example, The detector circuit 11 may be disposed outside of the sensor 10, and it may be disposed somewhere in the detector device 1. Though the electronic device 20 and the memory device 30 are disposed outside of the sensor 10 in the foregoing embodiment, they may be included in the sensor 10. The shape of the electrodes 12a, 12b is not limited to the comb-shape. The electrodes 12a, 12b may be made in a form of flat plates or in a co-axial cylindrical form.
As shown in
The alternating voltage applied to the sensor electrodes is not limited to the sinusoidal wave voltage. It may be a rectangular wave voltage or a triangular wave voltage, for example. Though the alternating voltage is preferable to avoid formation of electric double layers, it may be possible to use a voltage other than the alternating voltage if the permittivity of the mixture fuel is quickly detected before the electric double layers are formed.
As shown in
The density “a” of the gasoline contained in the mixture fuel and the density “b” of the ethanol contained in the mixture fuel may be calculated according to the following formulae in place of the formulae shown above:
a=1−b−c
b={εa2−(εa2−εc2)·c−ε2}/(εa2−εb2)
In this case, at least permittivity εa2 of gasoline measured at frequency f2, permittivity εb2 of ethanol measured at frequency f2, permittivity εc1 of water measured at frequency f1 and permittivity εc2 of water measured at frequency f2 have to be memorized in the memory device 30 (or 30a).
In the foregoing embodiment, it is assumed that the mixture fuel is composed of gasoline, ethanol and water. It is possible, however, to assume that the mixture fuel is composed of gasoline and ethanol (water is not included). In this case, the densities (a, b) of gasoline and ethanol are calculated according to the following formulae: b=1−a; a=1−b
The present invention may be applied to mixture fuel composed of other than three components, gasoline, ethanol and water. In any case, two different frequencies have to be set, so that permittivities of components other than a focused component do not change between two frequencies, and a permittivity of the focused component changes between two frequencies. The density of the focused component is calculated based on permittivities of the mixture fuel detected under the two frequencies and permittivities of the focused component measured under the two frequencies and stored in the memory device.
The present invention is applied to the mixture fuel composed of mainly gasoline and ethanol that is used in a gasoline engine in the embodiment described above. The present invention may be applied to mixture fuel mainly composed of light oil and fatty acid methyl ester that is used in a Diesel engine. The present invention may be widely applied to other mixture fuels such as those containing flex fuel or biochemical light oil.
In the foregoing embodiment, a density of a focused component such as water contained in mixture fuel is detected. In this case, the focused component is known as water. If a kind of a focused component is unknown, the permittivity of the focused component cannot be measured beforehand. In this case, the density of the focused component cannot be detected. However, it is possible to detect that an unknown component is mixed with the mixture fuel by continuously monitoring changes in the permittivity (ε1 or ε2) of mixture fuel.
While the present invention has been shown and described with reference to the foregoing preferred embodiment, it will be apparent to those skilled in the art that changes in form and detail may be made therein without departing from the scope of the invention as defined in the appended claims.
Number | Date | Country | Kind |
---|---|---|---|
2007-321225 | Dec 2007 | JP | national |