JPH0572165A - Dielectric constant detecting device for fuel - Google Patents

Abstract

PURPOSE:To accurately detect methanol content rate in fuel by compensating temperature characteristic of dielectric constant of the fuel through temperature characteristic of dielectric constant of insulating material. CONSTITUTION:A conductive electrode 3 provided on the way of a fuel passage 2, and a single-layer-winding coil 4 which fuel is introduced between it and the electrode 3, it is molded with insulating material, and the coil cylindrical face is oppositely arranged and spaced by a decided distance against the electrode 3, are provided. Under the condition in which gasoline mixed with methanol is let flow in the passage 2, a series circuit of series resistance 10 and the coil 4 is input from an amplifier 15 to a 0 phase comparator 11, and both phase differences are compared with each other. Because dielectric constant of fuel is monotonously decreased as temperature rise and reversely dielectric constant of mold material is monotonously increased as temperature rise, resonance frequency of the coil 4 depending upon the dielectric constant of fuel is compensated, and hence alcohol content rate is accurately detected by detecting dielectric constant of fuel.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention detects the permittivity of fuel supplied to a combustor or the like in a non-contact manner to determine the property of the fuel. Particularly, the alcohol-containing fuel used in engines for automobiles contains alcohol. The present invention relates to a fuel dielectric constant detection device for measuring a rate.

[0002]

2. Description of the Related Art In recent years, fuel mixed with alcohol in gasoline is being introduced for automobiles in various countries such as the United States and Europe in order to reduce consumption of oil and air pollution caused by automobile exhaust gas. is there.

If such an alcohol-mixed fuel is used as it is in an engine matched to the air-fuel ratio of gasoline fuel, the theoretical air-fuel ratio of alcohol is smaller than that of gasoline, so the air-fuel ratio becomes lean and operation becomes difficult.
By detecting the alcohol content in the alcohol-blended fuel,
The air-fuel ratio, ignition timing, etc. are adjusted according to the detected values.

Conventionally, as a method of detecting the alcohol content as described above, a method of detecting the dielectric constant of the alcohol mixed fuel and a method of detecting the refractive index have been mainly proposed.

Among these methods, as a conventional device for detecting the dielectric constant, for example, a device for detecting the dielectric constant in a liquid without contact as described in Japanese Patent Publication No. 63-31734 can be used. A case where this conventional device is used to detect the alcohol content in the alcohol-blended fuel will be described with reference to FIGS.

FIG. 10 is a block diagram showing a conventional fuel dielectric constant detecting device. A is a sensor section, 1 is a ceramic,
An insulating tube made of an insulating material such as oil-resistant plastic and provided with a fuel passage 2 inside, 8 is an exciting electrode wound around a part of the insulating tube 1 in a ring shape, and 4 is a predetermined distance from the exciting electrode 8. It is also a single-layer winding detection coil wound around the insulating tube 1.

A sensor section A is formed by the insulating tube 1, the fuel passage 2, the single-layer winding detection coil 4, and the excitation electrode 8.

On the other hand, B is a detection circuit of the sensor, the output of the sawtooth wave oscillation circuit 21 is connected to the voltage control oscillation circuit 22, and the output of the voltage control oscillation circuit 22 is connected to the excitation electrode 8 to detect the single layer winding. The side of the coil 4 farther from the excitation electrode 8 is grounded, and the signal on the side closer to the excitation electrode 8 is connected to the peak detector 24 via the full-wave rectifier circuit 23.

The output of the peak detector 24 and the output of the sawtooth wave oscillating circuit 21 are input to the sample hold circuit 25, and the output of the sample hold circuit 25 is output to the outside as the output V _out via the low pass filter 26. It

FIG. 11 is a sectional view of the sensor section A, which is shown in FIG.
2 is an explanatory diagram of an equivalent circuit of the sensor unit A.

Next, the operation of this conventional fuel dielectric constant detecting device will be described. The frequency applied from the voltage controlled oscillator circuit 22 to the excitation electrode 8 of the sensor unit A in FIG.
Sweep control is performed by the output of the sawtooth wave oscillation circuit 21. At this time, the induced voltage of the detection coil 4 shows the maximum value at different frequencies when the permittivity ε of the fuel is different.

This is because LC resonance is caused by the capacitance C _f corresponding to the induction ratio ε of fuel between the excitation electrode 8 and the detection coil 4 and the self-inductance L of the detection coil 4, and the induced voltage of the coil is generated at the resonance frequency. Is the maximum.

A schematic equivalent circuit of the sensor unit A is as shown in FIG. 12, and its series resonance frequency f ₀ is expressed by (Equation 1).

[0014]

[Equation 1]

In this (Equation 1), L is the self-inductance of the single-layer winding detection coil 4, C _f is the capacity of the fuel passage between the excitation electrode 8 and the single-layer winding detection coil 4, and the permittivity ε of the fuel is C _S is the capacitance of the wall of the insulating tube 1, and C _P is the external stray capacitance between the excitation electrode 8 and the single-layer winding detection coil 4. C _Pa is a stray capacitance existing in parallel with the single-layer winding detection coil 4.

The resonance frequency f ₀ is C _f as shown in (Equation 1).
In other words, since it depends on the permittivity ε of the fuel, the permittivity ε of the fuel
Becomes larger, the resonance frequency decreases.

The induced voltage of the single-layer winding detection coil 4 is converted into a DC signal by the full-wave rectification circuit 23, and the peak detector 24.
Then, the maximum value is detected, the peak detect pulse is output to the sample hold circuit 25, and the sweep output of the sawtooth wave oscillation circuit 21 is sampled and held.

Therefore, the hold voltage at this time corresponds to the resonance frequency f ₀ , and this voltage output is output as the external sensor output V _out via the low pass filter 26.

[0019]

Since the conventional fuel permittivity detecting device is constructed as described above, since the permittivity of the fuel has a temperature characteristic, even if the fuel has the same concentration depending on the measurement temperature. There is a problem that the resonance frequency changes.

As a method for temperature compensation, generally, a thermistor is installed in the fuel passage and connected to a temperature compensation circuit. However, not only is the device enlarged, but a new circuit is added. However, there is a problem that the device becomes expensive.

The present invention has been made in order to solve the above problems. By compensating the temperature characteristic of the permittivity of the fuel with the temperature characteristic of the permittivity of the insulator, the methanol content in the fuel is accurately contained. An object of the present invention is to obtain a device for detecting the permittivity of fuel that can detect the rate.

[0022]

SUMMARY OF THE INVENTION A fuel dielectric constant sensing device according to the present invention includes a conductive electrode provided in the middle of a fuel passage and a fuel introduced between the conductive electrode and a mold formed by an insulator. In addition, the outer peripheral surface of the coil is provided with a single-layer winding detection coil which is arranged opposite to the conductive electrode by a predetermined distance.

[0023]

The dielectric constant detecting device according to the present invention compensates the temperature characteristic of the permittivity of the fuel by the temperature characteristic of the permittivity of the insulator, so that the resonance frequency of the single-layer winding detecting coil depending on the permittivity of the fuel is determined. Compensation is performed and the dielectric constant in the fuel is detected to accurately detect the alcohol content.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a fuel dielectric constant detecting device of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram showing an embodiment thereof, and FIG. 2 is a diagram showing a configuration of a sensor portion of the embodiment, and is a perspective view showing a perspective view of the inside with a part cut away,
FIG. 3 is a schematic sectional view of the sensor portion of this embodiment, and FIG. 4 is an explanatory diagram of its equivalent circuit.

First, in FIGS. 1 to 4, A is a sensor portion, 1 is an insulator made of oil-resistant plastic or the like, and a cylindrical insulator having a single-layer winding detection coil 4 inside. The single-layer winding detection coil 4 is molded in the insulator 1.

The leads 4a, 4 of the single-layer winding detection coil 4
b is led out from the upper surface of the insulator 1, the lead 4b is grounded in the detection circuit B, and the lead 4a is connected to the input end of the 0 ° phase comparator 11 in the detection circuit B. And is connected to the output terminal of the amplifier 15 via the series resistor 10.

A conductive electrode 3 is provided outside the insulator 1.
Is provided. The conductive electrode 3 is provided on the outside of the insulator 1, the inner peripheral surface of which is substantially parallel to the outer peripheral surface of the insulator 1 and coaxial with the insulator 1, and titanium, stainless steel, and the surface thereof are alumite. Treated aluminum or the like is preferable in terms of resistance to fuel.

A fuel passage 2 is formed between the outer peripheral surface of the single-layer winding detection coil 4 and the inner peripheral surface of the cylinder of the conductive electrode 3 with the insulator 1 interposed therebetween.

The upper end surface of the cylindrical insulator 1 is attached to the flange 5, and the lower surface of the flange 5 is joined to the flange portion of the conductive electrode 3 via the fuel seal 7. .. Thus, the insulator 1, the conductive electrode 3, and the flange 5 form a fuel container.

A pair of nipples 6a and 6b are projected on the upper surface of the flange 5 so as to penetrate the flange 5.
The nipples 6a and 6b are for guiding the fuel into the fuel passage 2, and the nipple 6b is for discharging.

Next, the configuration of the detection circuit B will be described with reference to FIG. The series resistor 10 has a resistance value RS and is connected in series by the single-layer winding detection coil 4 and the lead 4a to form a series circuit.

The signal at the connection between the single-layer winding coil 4 and the series resistor 10 and the signal at the other end of the series resistor 10, that is, the signal applied to the series circuit are input to the 0 ° phase comparator 11, and The output of the amplifier 15 is also input to the 0 ° phase comparator 11.

As a result, the 0 ° phase comparator 11 compares the phase difference between the output of the single-layer winding detection coil 4 and the output of the amplifier 15, and outputs the comparison result to the low pass filter 12. ..

Output of low-pass filter 12 and reference voltage V
_{The ref} is compared by the comparison integrator 13, and the comparison result is added to the output terminal T1 and the input terminal of the voltage controlled oscillator 14. This reference voltage V _ref is a voltage corresponding to a phase of 0 °.

The output of the voltage controlled oscillator 14 is the amplifier 1 described above.
It is designed to be amplified by 5 and the frequency divider 16
The frequency is divided by and output from the output terminal T2 as the output frequency f _out .

5 and 6 are temperature characteristic diagrams of the permittivity of fuel and various molding materials, FIG. 7 and FIG. 8 are temperature characteristic diagrams for explaining temperature compensation according to the present invention, and FIG. 9 is conventional. It is a comparison figure of the resonance frequency of this invention which performed temperature compensation with the example.

Next, the operation of the present invention will be described with reference to FIGS. In the description of this operation, detection of the resonance frequency will be described. With the methanol-blended gasoline flowing through the fuel passage 2, the series resistance 10
And a high-frequency signal is applied to the series circuit of the single-layer winding detection coil 4, and the signals across the series resistor 10, that is, the voltage signal applied to the series circuit and the voltage signal applied to the single-layer winding detection coil 4 are phase-compared by 0 °. It is input to the device 11, and the phase difference between the two is compared.

If a sine wave amplifier is used as the amplifier 15 and the high frequency signal applied to the series circuit is a sine wave, the voltage signal also becomes sinusoidal. Therefore, a multiplier is used as the 0 ° phase comparator 11. Good.

The 0 ° phase comparator 11 outputs a signal corresponding to the phase difference between the two, the low pass filter 12 outputs a DC voltage signal proportional to the phase difference, and the comparison / integrator 13 is in the low band. The reference voltage V _ref , which corresponds to the output of phase 0 ° of the pass filter 12, and the output of the low pass filter 12 are compared and integrated, and the voltage output of the comparison integrator 13 is applied to the series circuit via the amplifier 15. The frequency of the high frequency signal is determined by the voltage controlled oscillator 14.

That is, a phase locked loop is formed by this series circuit, and a series circuit of the 0 ° phase comparator 11, the low-pass filter 12, the comparison integrator 13, the voltage controlled oscillator 14 and the amplifier 15 to form a voltage controlled oscillator. Since the oscillation frequency of 14 is controlled so that the phase difference between the voltage signal applied to the series circuit and the voltage signal applied to the single-layer winding detection coil 4 is 0 °, the voltage output V _out of the comparator / integrator 13 or the voltage control is performed. The frequency output of the oscillator 14 has a value corresponding to the parallel resonance frequency of the sensor unit A, that is, the dielectric constant of the fuel, in other words, the methanol content rate.

The output frequency of the voltage controlled oscillator 14 is
Although it depends on the size of the sensor unit A, since it is a high frequency of several MHz, it is frequency-divided by the frequency divider 16 to a frequency suitable for the output characteristic and output as a frequency output f _out .

FIG. 2 shows the structure of the sensor portion A of this embodiment, but it has a structure in which a single layer winding detection coil 4 is molded inside a cylindrical insulator 1. As shown in FIG. FIG. 4 is a schematic cross-sectional view thereof, FIG. 4 is a view showing an outline of an equivalent circuit thereof, and in these FIGS. 2 to 4, C _f is a capacitance when fuel flows through the fuel passage 2, and C _s is an insulation. A capacitance in the thickness direction, C _pc , which contributes to the outer portion of the single-layer winding detection coil 4 of the body 1, C _pc is a stray capacitance existing in parallel with the detection coil 4.

At this time, the sensor unit A constitutes a parallel resonance circuit, the resonance frequency f _n thereof is given by (Equation 2), and the resonance frequency f _n decreases as the permittivity of fuel increases.

[0044]

[Equation 2]

Next, a method of determining the sensor size for compensating the temperature characteristic of the dielectric constant of the fuel with the temperature characteristic of the molding material will be described with reference to this embodiment. In the equivalent circuit of FIG. 4, it is considered that C _pc has no temperature dependence, so the combined capacitance C having temperature dependence is expressed by (Equation 3).

[0046]

[Equation 3]

However, (K · K) is the geometrical capacity of C _s , K is the geometrical capacity of C _f , and if the value α in [] of (Equation 3) is a constant, the dielectric constant of the fuel in one embodiment will be described. It can be seen that temperature compensation of the rate sensing device is achieved.

FIG. 5 shows the temperature characteristics of the dielectric constant of the fuel and the various molding materials, and FIG. 6 shows the vertical axis with the reciprocal of the dielectric constant.

As is clear from FIG. 5, the permittivity of the fuel monotonously decreases with temperature, and as is clear from FIG. The temperature dependence tends to be canceled in the series connection of the corresponding capacitances of the dielectric constants.

On the other hand, FIG. 7 shows a plot of α when the molding material is fixed and K is varied, and FIG. 8 is a plot of the α when K is fixed and the molding material is varied. From FIGS. 7 and 8, K and a molding material when α is a constant are selected, and since K is a geometrical capacity, temperature compensation is performed by determining the sensor size from this value.

FIG. 9 shows the temperature characteristics of the resonance frequency f _n of the sensor in methanol with nylon 66 used as the molding material and K being a predetermined value in comparison with the conventional example. As described above, it can be seen that the compensation of the resonance frequency temperature characteristic is achieved in this embodiment as compared with the conventional example.

In the above embodiment, the case where the present apparatus is used for detecting the methanol content is shown, but it can be widely applied for detecting the dielectric constant in other liquids.

[0053]

As described above, according to the present invention, the single-layer winding detection coil and the single-layer winding which are molded by the conductive material and the molding material which is the insulator while sandwiching the fuel in the middle of the fuel passage. Since the means for detecting the resonance frequency of the coil is provided and the temperature characteristic of the dielectric constant of the fuel can be compensated by the temperature characteristic of the coil mold material, the alcohol content rate can always be detected accurately.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a fuel dielectric constant detection device according to an embodiment of the present invention.

FIG. 2 is a perspective view showing a structure of a sensor unit applied to the embodiment.

FIG. 3 is a schematic cross-sectional view of the same sensor unit.

FIG. 4 is an equivalent circuit diagram of the same sensor unit.

FIG. 5 is a temperature characteristic diagram of the dielectric constant of various mold materials for explaining the above-mentioned embodiment.

FIG. 6 is a temperature characteristic diagram of various molding materials in which the vertical axis represents the reciprocal of the dielectric constant for explaining the embodiment.

FIG. 7 is an explanatory diagram of a temperature compensation method in the case of fixing a molding material for explaining the embodiment.

FIG. 8 is an explanatory diagram of a temperature compensation method when a mold material is changed to explain the embodiment.

FIG. 9 is a comparison diagram of the resonance frequency when temperature compensation is performed with the present invention and the conventional example.

FIG. 10 is a configuration diagram showing a conventional fuel dielectric constant detection device.

FIG. 11 is a schematic cross-sectional view of a sensor unit in a conventional fuel dielectric constant detection device.

FIG. 12 is an equivalent circuit diagram of a sensor unit in a conventional fuel dielectric constant detection device.

[Explanation of symbols]

 1 Cylindrical Insulator 2 Fuel Passage 3 Conductive Electrode 4 Single Layer Winding Detection Coil 11 0 ° Phase Comparator 12 Low Pass Filter 13 Comparator / Integrator 14 Voltage Controlled Oscillator 15 Amplifier 16 Divider A Sensor Section B Detection Circuit

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[Procedure amendment]

[Submission date] June 22, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Claim 1

[Correction method] Change

[Correction content]

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] 0022

[Correction method] Change

[Correction content]

[0022]

SUMMARY OF THE INVENTION A fuel dielectric constant sensing device according to the present invention includes a conductive electrode provided in the middle of a fuel passage and a fuel introduced between the conductive electrode and a mold formed by an insulator. while being, it is provided with a facing arrangement monolayer wound detection coil cylindrical surface of the coil in isolation between the conductive electrode and a predetermined.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0044

[Correction method] Change

[Correction content]

[0044]

[Equation 2]

[Procedure amendment 4]

[Document name to be corrected] Drawing

[Name of item to be corrected] Fig. 11

[Correction method] Change

[Correction content]

FIG. 11

Claims (1)

[Claims] 1. A cylindrical conductive electrode, an insulator coaxially arranged in the conductive electrode with a predetermined gap, and introduced between the conductive electrode and the columnar insulator. Resonance frequency dependent on the permittivity of the fuel and the fuel, and a mold material capable of compensating the temperature characteristic of the permittivity of the fuel with the temperature characteristic of the permittivity and being molded in the insulator and facing the conductive electrode. A single-layer winding detection coil having: and a detection unit for detecting the resonance frequency of the single-layer winding detection coil.