JPH0534310A - Device for measuring dielectric constant of fuel - Google Patents

Abstract

PURPOSE:To obtain a device for measuring the dielectric constant of fuel to determine the content of a specific constituent of the fuel by adjusting apparent self-inductance of a detection coil. CONSTITUTION:The title item is provided with a conductive electrode 3, a single-layer winding coil 4 which is disposed away from the electrode 3 at a specified distance, fuel being introduced between the conductive electrode 3 and the single-layer winding coil 4, and a cylindrical conductor 8 nearly coaxially with the single-layer winding coil 4 on the opposite side of the fuel side of the single-layer winding coil 4. The dielectric constant of the fuel is detected by a coil periphery surface of the single-layer winding coil 4 and a periphery surface of the conductive electrode 3, thus enabling the content of a specific constituent of the fuel, for example, methanol, to be detected constantly and accurately.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel permittivity detector for detecting the permittivity of fuel supplied to a combustor or the like in a non-contact manner to determine the property of the fuel, and is particularly used for engines of automobiles and the like. The present invention relates to a device for measuring the alcohol content in alcohol-blended fuel.

[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 that matches the air-fuel ratio of gasoline fuel, the stoichiometric air-fuel ratio of alcohol is smaller than that of gasoline, making the air-fuel ratio lean and making operation difficult. The alcohol content rate of is detected, and the air-fuel ratio, ignition timing, etc. are adjusted according to the detected values.

Conventionally, a method of detecting the permittivity of alcohol-mixed fuel has been used to detect the alcohol content as described above.
A method of detecting the refractive index has been mainly proposed. As a conventional apparatus of the method of detecting the dielectric constant among such methods, for example, a method of detecting the dielectric constant of a liquid in a non-contact manner as described in JP-B-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 FIG.

FIG. 10 is a block diagram showing a conventional fuel dielectric constant detecting device. Reference numeral 101 is an insulating tube made of an insulating material such as ceramic or oil resistant plastic, and a fuel passage 102 is provided inside, and 103 is an insulating tube. A part of 101 is an excitation electrode wound in a ring shape, and 104 is a single-layer winding detection coil that is also wound around the insulating tube 101 at a predetermined distance from the excitation electrode 103. Are formed. A constant frequency oscillator 105 supplies a voltage of a constant frequency to the excitation electrode 103 via the amplifier 106, while one end of the detection coil 104 is grounded, and the signal at the other end is a high-pass filter 107 and a full-wave rectifier 108. , And is output as an output V _out via the amplifier 109.

The operation of the conventional device will be described below. When the frequency applied to the excitation electrode 103 of the sensor unit in FIG. 10 is changed, the induced voltage of the detection coil 104 shows the maximum value at different frequencies when the permittivity of the fuel is different. This is because LC resonance occurs due to the capacitance C _f corresponding to the permittivity ε of the fuel between the excitation electrode 103 and the detection coil 104 and the self-inductance L of the detection coil 104, and the induced voltage of the coil is maximum at the resonance frequency. Is because
This resonance frequency f is roughly expressed by the following equation.

[0006]

[Equation 1]

Here, k, a, and b are constants determined by the shape of the sensor section, and C _s is a capacitance determined by the shape of the sensor section. Since the resonance frequency f depends on the permittivity ε of the fuel as shown in Formula 1, the resonance frequency decreases as the permittivity ε of the fuel increases. For example, as a result of measurement with a predetermined sensor shape, the resonance frequency f _m is about 5 MHz when the fuel is methanol having a dielectric constant ε = 33, and the resonance frequency f _g is about 5.7 MHz when gasoline is the dielectric constant ε = 2. there were.

Therefore, methanol-mixed gasoline is caused to flow in the fuel passage 102, and the constant frequency oscillator 105 causes the resonance frequency f
_The amplifier 1 oscillates a signal having a frequency f _o slightly higher than _m.
When the excitation electrode 103 is excited with a constant voltage via 06, only the AC component of the induced voltage signal generated in the detection coil 104 is extracted by the high-pass filter 107, and the full-wave rectifier 108
Full-wave rectification is performed by the
At 9, the voltage is adjusted to a predetermined voltage range and output. At this time, the induced voltage of the frequency f _o is because the content of methanol is large increases, so that the output V _out is approximately proportional to the methanol content.

[0009]

However, in such a conventional device, when the self-inductance L of the detection coil changes due to a dimensional change due to a change in environment such as temperature and humidity, the detection coil manufactured due to a dimensional error during coil production. If the self-inductance L of the fuel fluctuates, the resonant frequency f of the fuel changes and the methanol content of the fuel changes, as is clear from the above formula 1, although the dielectric constant ε, that is, the methanol content changes little. There is a problem that it becomes difficult to accurately detect

The present invention has been made to solve the above-mentioned problems, and even if the environment of the sensor unit changes,
An object of the present invention is to obtain a fuel dielectric constant detection device capable of accurately detecting the content rate of a specific component in fuel even if the coil has a dimensional error.

[0011]

In a fuel permittivity detection apparatus according to the present invention, a fuel is introduced between a conductive electrode provided in the middle of a fuel passage and the conductive electrode, and A single-layer winding coil arranged to be separated from a conductive electrode by a predetermined distance, a means for detecting a resonance frequency of the single-layer winding coil, and the single-layer winding coil on the side opposite to the fuel side of the single-layer winding coil. A columnar conductor is provided substantially coaxially.

[0012]

In the fuel dielectric constant detecting device according to the present invention, the apparent self-inductance L of the detection coil is adjusted by the columnar conductor substantially coaxial with the single layer winding coil on the side opposite to the fuel side of the single layer winding coil. Then, by adjusting the resonance frequency of the single-layer winding coil depending on the ε of the fuel, the dielectric constant in the fuel, that is, the methanol content is accurately detected.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram showing an embodiment of a fuel dielectric constant detection device according to the present invention, FIG. 2 is a structural diagram of a sensor portion of this embodiment, FIG. 3 is a diagram showing apparent changes in inductance, and FIG. Is the frequency characteristic diagram of the sensor impedance,
FIG. 5 is a diagram showing a specific example of the detection circuit unit, FIG. 6 is a time chart diagram in a specific circuit, and FIG. 7 is an output characteristic diagram in an embodiment using a specific circuit example.

In FIGS. 1 and 2, A is a sensor portion, 1 is formed of an insulating material such as oil-resistant plastic,
A cylindrical container-shaped insulator 4 having a single-layer winding coil 4 inside and in which a columnar conductor 8 is guided substantially coaxially with the single-layer winding coil 4 on the side opposite to the fuel side, 4 is a detector coil of the insulator 1. Single-layer winding coils 4a, 4b embedded in the conductive electrode 3 to be described later and separated from each other by a predetermined distance so that the pillar surfaces of the coil are opposed to each other.
Is a lead of the single-layer winding coil 4, and 3 is a conductive electrode which is provided outside the insulator 1 and whose pillar surface is substantially parallel to the pillar surface of the insulator 1 and is substantially coaxial with the insulator 1. Aluminum whose surface is anodized is preferable in terms of resistance to fuel.

Reference numeral 2 denotes an outer peripheral surface side of the single-layer winding coil 4 and the insulator 1.
A cylindrical container-shaped insulator 1 is attached to a fuel passage 5 formed between the conductive electrode 3 and the inner circumferential surface of the column with a space therebetween.
Reference numeral 6 denotes a flange that is joined to the conductive electrode 3 through the fuel seal 7 to form a fuel container as a whole, and 6 is a nipple that guides the fuel to the fuel passage 2.

Reference numeral B denotes a detection circuit portion, 10 is a series resistor having a resistance value R _s which is connected in series with the single-layer winding coil 4 by leads 4a to form a series circuit, and 11 is the single-layer winding coil 4. The 0 ° phase comparator to which the signal at the connection with the resistor 10 and the signal at the other end of the resistor 10, that is, the signal applied to the series circuit are connected, 12 is the low voltage to which the output of the 0 ° phase comparator 11 is connected. A pass-pass filter, 13 is a comparator / integrator to which the output of the low-pass filter 12 and a predetermined reference voltage V _ref corresponding to a phase of 0 ° are connected, 14 is a voltage-controlled oscillator to which the output of the comparator / integrator 13 is connected, 15 Is an amplifier of the output of the voltage controlled oscillator 14, the output of which is connected to the series circuit;
Is a frequency divider for the output frequency of the voltage controlled oscillator 14.

In FIG. 5 showing a more specific circuit example of FIG. 1, 17a to 17c are inverter circuits, and 18a and 18c.
Reference numeral b is a D flip-flop circuit, 19 is an exclusive OR circuit, 20 is a DC offset circuit by the operational amplifier OP2, and 21 is a DC cut capacitor having a capacitance C _p .

FIG. 2 is a structural view of the sensor portion of this embodiment, which has a structure in which the central portion of the insulator 1 is threaded so as to form a cylindrical container shape, and the columnar conductor 8 can be screwed in. The position of the columnar conductor 8 with respect to the axial direction of the detection coil can be made variable. In this embodiment, the single layer winding coil 4 is used as the detection coil. FIG. 3B shows the apparent distance d from the upper end of the detection coil to the lower end of the columnar conductor when the columnar conductor is gradually inserted from the upper end of the detection coil as shown in FIG. 3 shows a change in self-inductance L of the above. By inserting a columnar conductor and changing its position, L ₀ to L ₁
The apparent self-inductance can be adjusted during.

Next, the operation of the embodiment will be described by taking the case of detecting the methanol content in methanol-blended gasoline as an example. FIG. 4 shows the impedance Z of the single-layer winding coil 4 when the fuel flowing in the fuel passage 2 in FIG. 2 is gasoline or methanol and the frequency of the high-frequency signal applied between the leads 4a and 4b of the single-layer winding coil 4 is variable. It is a figure which shows the frequency characteristic of. Single layer winding coil 4
When the frequency of the high-frequency signal applied to the single-layer winding coil 4 is changed, the impedance becomes maximum at a specific frequency and the electric current − by the self-inductance L of the single-layer winding coil 4 and the capacitance C between the single-layer winding coil 4 and the conductive electrode 3. An LC parallel resonance having a voltage phase of 0 ° is generated. The resonance frequency f is approximately the same as the equation 1 and is the following equation 2 and the single-layer winding coil 4 and the conductive electrode 3 are
Depending on the permittivity ε of the fuel flowing in the fuel passage 2 between the two, the larger the permittivity ε, that is, in the mixed fuel of gasoline with permittivity ε = 2 and methanol with permittivity ε = 33, the content ratio of methanol is The higher it is, the lower it is.

[0020]

[Equation 2]

Here, k, a, and b are constants determined by the shape of the sensor portion A, as in the conventional device, for example, the insulator 1
Or the diameter of the single-layer winding coil 4, the dielectric constant of the material of the insulator 1, the distance between the conductive electrode 3 and the single-layer winding coil 4, the L of the single-layer winding coil 4.
Etc.

Next, referring to FIG. 1, the method of detecting the resonance frequency will be described in detail. With the methanol-blended gasoline flowing in the fuel passage 2, a resistor 10 is
And a high-frequency signal is applied to the series circuit of the single-layer winding coil 4,
The signal across the resistor 10, that is, the voltage signal applied to the series circuit and the voltage signal applied to the single-layer winding coil 4 are input to the 0 ° phase comparator 11, and the phase difference between them 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, if 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, and the low pass filter 12 outputs a DC voltage signal proportional to the phase difference.
The comparator / integrator 13 uses the reference voltage V _ref corresponding to the output of the low-pass filter 12 having a phase of 0 °, and the low-pass filter 12
The output of is compared and integrated. The voltage output of the comparator / integrator 13 determines the frequency of the high frequency signal applied to the series circuit via the amplifier 15 by the voltage controlled oscillator 14.

That is, such a series circuit and 11 to 15
A phase-locked loop is formed by this circuit, and the oscillation frequency of the voltage controlled oscillator 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 coil 4 is 0 °. Therefore, the voltage output V _out of the comparator / integrator 13 or the frequency output of the voltage controlled oscillator 14 is the parallel resonance frequency of the sensor unit, that is, the permittivity ε of the fuel,
In other words, the value corresponds to the methanol content.

Although the output frequency of the voltage controlled oscillator 14 depends on the size of the sensor portion, in the embodiment having a small shape as shown in FIG. 2, it is a high frequency of several MHz as shown in FIG. Therefore, the frequency is divided by the frequency divider 16 to a frequency suitable for output measurement, and the frequency output f _out
To be done.

In FIG. 5, the phase difference between the voltage signal applied to the series circuit and the voltage signal applied to the single layer winding coil 4 is 0 ° by using the exclusive OR circuit 19 as the 0 ° phase comparator.
FIG. 6 shows a specific circuit example of the detection circuit B in which the phase-locked loop is formed as described above, and FIG. 6 shows a time chart of signals of respective portions P1 to P6 of the circuit.

In FIG. 5, the high frequency rectangular wave signal (P1) output from the voltage controlled oscillator 14 is input to the CK port of the first D flip-flop circuit 18a and the CK port of the second D flip-flop circuit 18b. A signal obtained by inverting the phase of the rectangular wave signal (P1) by the inverter circuit 17a is input to. Here, the signal of the inverting output port of the first D flip-flop circuit 18a is input to the D port of the second D flip-flop circuit 18b, and the first D
The signal of the output port Q of the second D flip-flop circuit 18b is input to the D port of the flip-flop circuit 18a.

Therefore, the first D related to the series circuit is
The signal at the output port Q of the flip-flop circuit 18a (P
In 2), the data is updated at the rising of the rectangular wave signal (P1), and becomes a signal obtained by dividing the signal (P1) by 1/2.
On the other hand, the signal (P3) at the output port Q of the second D flip-flop circuit 18b, which is input to one side of the exclusive OR circuit 19 via the inverter circuit 17b, has its data updated at the trailing edge of the signal (P1). Signal (P
The signal has the same frequency as 2) but has a phase difference of 90 °.

At the other input of the exclusive OR circuit 19, a voltage signal (P4) applied to the connection point between the resistor 10 and the single-layer winding coil 4, that is, the voltage applied to the single-layer winding coil 4 (P5) via the inverter circuit 17c. ) And compared with the phase inversion signal of the signal (P3). Here, since the voltage signal (P4) generated in the single-layer winding coil 4 is sinusoidal as shown in FIG. 6, its DC level is set to the power supply voltage V _s and the resistance R
The voltage is divided into 1/2 and controlled by the DC offset circuit 20 by the operational amplifier OP2, and only the DC component is separated from the ground portion by the DC cut capacitor 21, and the inverter circuit 17
Control to the judgment level of c.

As a result, the inverter circuit 17c acts as a waveform shaper, and therefore the inverter circuit 17c.
The output (P5) of c is a signal (P5) at the LC resonance frequency.
It is a rectangular wave signal that is 90 ° out of phase with the opposite phase signal of the signal (P3), that is, the opposite phase signal of 2). Therefore, in the output (P6) of the exclusive OR circuit 19, the phase difference between the signal applied to the series circuit and the voltage signal applied to the single-layer winding coil 4 is 0 °.
50% duty at the time of LC resonance frequency
Becomes FIG. 6 shows changes in each waveform when the phase difference between the two is not 0 °.

Output of the exclusive OR circuit 19 (P
6) is input to the low pass filter 12. Since the DC output voltage becomes 1/2 of the power supply voltage at the resonance frequency, such output is set to the reference potential V _ref of 1/2 of the power supply voltage.
Comparing integrator (having operational amplifier OP1) 13
To enter. By controlling the frequency of the voltage-controlled oscillator 14 with its output, the detection circuit B causes the phase difference between the signal applied to the series circuit and the voltage signal applied to the single-layer winding coil 4 to be 0 °. Acts as a phase-locked loop whose frequency is controlled. Therefore, the frequency output f _{out obtained} by dividing the frequency of the voltage controlled oscillator 14 by the frequency divider 16 is a function that monotonically decreases with respect to the resonance frequency, that is, the permittivity ε of the fuel.

FIG. 7 shows the frequency output f _out with respect to the alcohol content in the alcohol blended gasoline of the embodiment of such a device using the detection circuit of FIG.
The methanol content increases, the dielectric constant ε increases, and the output monotonously decreases.

In such a structure, as shown by the broken line in FIG. 4, the Q at the resonance point is lowered due to the increase in the conductivity of the fuel due to the impurities in the fuel and the decrease in the insulation resistance due to the change in the temperature and humidity environment of the sensor section. However, as shown by the broken line in FIG. 4, since there is almost no effect on the resonance point frequency at which the phase becomes 0 °, there is an advantage that output fluctuation does not occur.

In the adjustment of the apparent self-inductance L in the structure of the sensor portion of this embodiment as shown in FIG. 2, the environment for adjustment is always the same, and the test liquid whose components do not change (primary reagent methanol, etc.) is used. ) Is introduced into the fuel passage and, for example, the circuit shown in the above embodiment is used, the columnar conductor 8 is screwed in until V _out or f _{out at} that time shows a certain value, and a certain value is shown. By the way, the columnar conductor 8 is fixed.

FIG. 8 shows a specific example of a method of fixing the columnar conductor 8. If the upper end surface of the columnar conductor 8 is located below the upper surface of the flange 5 as shown in FIG. 8A, the columnar conductor 8a is filled with resin 8a as shown by the meshes in the figure to form a columnar shape. The conductor 8 is fixed. If the upper end surface of the columnar conductor 8 is located above the upper surface of the flange 5 as shown in FIG. 8B, it may be fixed with a nut 8b and then with an adhesive 8c.

FIG. 9 is a sectional view of a sensor portion of another embodiment, in which the same or corresponding portions as those in the first embodiment are designated by the same reference numerals 1 to 8. In this embodiment, columnar conductive materials are used. The body 8 has a burr on the side surface, and the columnar conductor 8 is inserted and fixed by press fitting.

In the above embodiment, the example in which the single-layer winding coil of the sensor section and the conductive electrode are coaxial is shown. However, they are not necessarily coaxial, and electrostatic discharge due to fuel is provided between the pillar surface of the single-layer winding coil and the conductive electrode. It suffices if there is capacity. Further, although the case where the present device is used for detecting the methanol content is shown in the above-mentioned embodiment, it can be widely applied for detecting the dielectric constant in other liquids.

[0038]

As described above, according to the present invention, a conductive electrode, a single-layer winding coil, and a means for detecting the resonance frequency of the single-layer winding coil are provided with the fuel interposed in the middle of the fuel passage, Further, a columnar conductor can be installed on the side of the single-layer winding coil opposite to the fuel side substantially coaxially with the single-layer winding coil, and the columnar conductor can be moved and fixed in the length direction of the single-layer winding coil. By doing so, the apparent self-inductance of the single-layer winding coil can be made variable, so that the alcohol content in the fuel can always be detected accurately.

[Brief description of drawings]

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

FIG. 2 is a structural diagram of a sensor unit according to an embodiment of the present invention.

FIG. 3 is an explanatory diagram showing changes in apparent inductance according to an embodiment of the present invention.

FIG. 4 is a frequency characteristic diagram of sensor impedance according to an embodiment of the present invention.

FIG. 5 is a diagram showing a specific example of a detection circuit unit according to an embodiment of the present invention.

FIG. 6 is a time chart diagram in a specific circuit according to an embodiment of the present invention.

FIG. 7 is an output characteristic diagram in a specific circuit example according to an embodiment of the present invention.

FIG. 8 is a diagram showing each specific example of the method of fixing the columnar conductor according to the embodiment of the present invention.

FIG. 9 is a sectional view of a sensor unit according to another embodiment of the present invention.

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Insulator 2 Fuel passage 3 Conductive electrode 4 Single layer winding coil 8 Columnar conductor A Sensor part B Detection circuit part

Claims (1)

Claim: What is claimed is: 1. A fuel is introduced between a conductive electrode provided in the middle of a fuel passage and the conductive electrode, and is separated from the conductive electrode by a predetermined distance. A single-layer winding coil, and a device for detecting a dielectric constant of the single-layer winding coil, which corresponds to the dielectric constant of the fuel, for detecting the resonance frequency of the single-layer winding coil. A columnar conductor is installed substantially coaxially with the single-layer winding coil on the side, and the resonance frequency is adjusted by varying the end face position of the columnar conductor with respect to the axial direction of the single-layer winding coil. A fuel dielectric constant detection device characterized by the above.