JPH0552796A - Dielectric constant detection sensor of fuel - Google Patents

Abstract

PURPOSE:To enable an output for change in a dielectric constant to be increased and detection accuracy to be improved for reducing scattering by detecting the dielectric constant of fuel which passes a fuel passage between a coil and an electrode with an electrostatic capacity between a coil surface and an electrode surface. CONSTITUTION:A cylindrical single-layer winding coil 3 is provided at an outer periphery of a thin-wall portion 2 of a cylindrical case 2 which consists of a PPS resin, etc., with high dielectric constant and a pole-shaped electrode 6 is placed at a center of the case. A fuel is allowed to flow from an entrance/exit port 5 to a passage 4, a frequency which is applied to the electrode 6 is changed by a current controlled oscillation circuit, an induced voltage of the coil 3 is rectified by a full-wave rectification circuit, a maximum value of its output is detected by a peak detector, and a control input of a voltage-controlled oscillation circuit at this time is subjected to sample/hold by a sample/hold circuit and is output via a low-pass filter. Its voltage output becomes a value corresponding to a resonance frequency, namely a dielectric constant epsilon of fuel, and an amount of change becomes larger than that of a case where a coil and an electrode are provided at a same axis only by a parallel capacity, thus enabling a detection accuracy to be improved and a scattering to be reduced owing to ease of machining.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel permittivity detection sensor 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 particularly to an engine of an automobile or the like. The present invention relates to a method for measuring an alcohol content rate in a mixed alcohol fuel.

[0002]

2. Description of the Related Art In recent years, in countries such as the United States and Europe, in order to reduce the consumption of oil and the air pollution caused by automobile exhaust gas, fuel in which alcohol is mixed with gasoline is being introduced for automobiles. .. If such an alcohol-mixed fuel is used as it is in an engine that matches 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. Therefore, the alcohol content rate in the alcohol-mixed fuel is detected, and the air-fuel ratio, the ignition timing, etc. are adjusted according to the detected values.

Conventionally, in order to detect such an alcohol content, a method has been proposed in which the dielectric constant of an alcohol-mixed fuel is detected by a change in capacitance. In such a method, a coil is provided in the vicinity of the fuel flow path, and the capacitance is changed between the coil and another coil adjacent to the coil, or the capacitance between the coil and the electrode adjacent to the coil causes a change in dielectric. A method of detecting the rate is described in JP-A-62-25248 and JP-B-63-31734. This will be described with reference to FIGS.

FIG. 2 shows the structure of a conventional fuel dielectric constant detection sensor. 1 is an insulating tube made of an insulating material such as ceramic or oil resistant plastic, and has a fuel passage 4 inside, and 16 is an outer circumference of the insulating tube 1. The excitation electrode 3 wound in a ring shape on a part of the is a single layer winding coil which is also wound around the insulating tube 1 at a predetermined distance from the excitation electrode 16 and forms a sensor portion. Reference numeral 20 denotes a detection circuit connected to the sensor unit, the output of the sawtooth wave oscillation circuit 21 is connected to the voltage control oscillation circuit 22, the output of the voltage control oscillation circuit 22 is connected to the excitation electrode 16, and the single layer winding coil is provided. The opposite end of the excitation electrode 16 of 3 is grounded, the signal on the other end of the single-layer winding coil 3 is connected to the peak detector 24 via the full-wave rectifier circuit 23, and the output of the peak detector 24 is a sawtooth wave. The output of the oscillation circuit 21 is input to the sample-hold circuit 25 to which the output is input, and the output of the sample-hold circuit 25 is output to the outside via the low-pass filter 26. FIG. 3 is an explanatory diagram of an equivalent circuit of the sensor unit, and FIG. 4 is an output characteristic diagram of the sensor unit.

Next, the operation of the above-mentioned conventional sensor will be described. The frequency of the signal applied from the voltage controlled oscillator circuit 22 to the excitation electrode 16 is sweep-controlled by the output of the sawtooth wave oscillator circuit 21. At this time, the induced voltage of the single-layer winding coil 3 shows the maximum value at different frequencies when the permittivity ε of the fuel is different. This is the excitation electrode 16 and the single layer winding coil 3.
LC by the electrostatic capacitance C _f corresponding to the dielectric constant ε of the fuel in the fuel passage 4 between them and the self-inductance L of the single-layer winding coil 3.
This is because resonance occurs and the induced voltage of the single-layer winding coil 3 becomes maximum at the resonance frequency.

[0006] schematic equivalent circuit of the sensor unit is as shown in FIG. 3, it is the series resonance frequency _{f o f o = 1 / [} 2π√L√ {C f / (1 + C f / C s) + C p + C pa }] (1). Here, L is the self-inductance of the single-layer winding coil 3, C _f is the capacity in the fuel passage 4 between the excitation electrode 16 and the single-layer winding coil 3, and corresponds to the permittivity ε of the fuel. .. C _s is the capacity of the wall of the insulating tube 1, C _p is the axial capacity of the insulating tube 1 between the electrode 16 and the coil 3, and C _pa
Is an external stray capacitance between the electrode 16 and the coil 3, and C _pc is a stray capacitance existing in parallel with the coil 3.

The resonance frequency f _o decreases as the capacity C _{f, that} is, the permittivity ε of fuel increases, as shown in the equation (1). The induced voltage of the coil 3 is converted into a DC signal by the full-wave rectifying circuit 23, and the maximum value is detected by the peak detector 24,
The peak detect pulse is output to the sample hold circuit 25, and the sweep output of the sawtooth wave oscillator circuit 21 is sampled and held. Therefore, the hold voltage at this time corresponds to the resonance frequency f _o, the voltage output is outputted as V _out to the outside through the low-pass filter 26.

[0008]

However, the above-mentioned conventional sensor has the following problems because the electrode 16 is coaxially arranged on the end face of the coil 3. For example, L = 20 μH, outer diameter of insulating tube 1 = 10 m
Assuming that m is m, the thickness of the tube wall of the insulating tube 1 is t = 1 mm, and the distance d between the end surface of the coil 3 and the end surface of the electrode 16 is d = 2 mm, the fuel is ε =
In the case of gasoline of 2 and methanol of ε = 33, both the resonance frequencies f _o are about 8 MHz, but there are large parallel capacitances C _p and C _pa with respect to the capacitance C _f that changes depending on the permittivity ε of the fuel. to change the resonant frequency f _o was about 5% only be obtained as shown in FIG.

Further, since d is the distance between the end faces, it is difficult to ensure accuracy, the resonance frequency f _o varies greatly, and the stray capacitance C _pa changes depending on the surface condition of the insulating tube 1 such as dirt and the external humidity. However, there is a problem that output reproducibility is poor. Also, increasing the distance d in order to ensure accuracy, capacitance C _p, C _pa is reduced is also small capacitance C _f, the rate of change of only f _o resonance frequency f _o increases on average is rather Fell. That is, the conventional sensor has a problem that the output change rate with respect to the change of the dielectric constant ε cannot be large, the output variation between the sensors is large, the sensor output is easily influenced by the external state, and the accuracy of the sensor is poor.

The present invention has been made in order to solve the above problems, and it is possible to increase the output change with respect to the change of the dielectric constant ε, and to reduce the influence of the output variation and the external condition. It is an object of the present invention to obtain a fuel permittivity detection sensor with high accuracy.

[0011]

A fuel dielectric constant detection sensor according to the present invention is a tubular or flat surface provided with an insulating thin wall having a high dielectric constant in close contact with a peripheral surface or a flat surface on the side in contact with fuel. The single-layer winding coil, a metal electrode facing the coil and forming a fuel passage between the coil and a means for detecting the permittivity of the fuel from the capacitance between the coil and the electrode are provided.

[0012]

In the present invention, the fuel is caused to flow in the fuel passage formed between the single-layer coil and the metal electrode, and the dielectric constant of the fuel is detected by the capacitance between the coil and the electrode.

[0013]

【Example】

Example 1. Embodiments of the present invention will be described below with reference to the drawings. 1A and 1B are a perspective view and a sectional view taken along the line AA of the dielectric constant detection sensor according to the first embodiment, FIG. 5 is an explanatory diagram of an equivalent circuit of the sensor, and FIG. 4 is an output characteristic diagram. ..

In FIG. 1, reference numeral 2 denotes a cylindrical container-like case which is formed of an insulating material such as plastic and has a thin wall portion 2a at the center thereof. As plastic, an oil resistant epoxy resin or PPS having a relatively high dielectric constant is used. Use of a resin or the like is preferable in terms of improvement in output change rate and resistance to fuel, but PPS resin is particularly preferable in that injection molding is possible. Reference numeral 3 denotes a tubular single-layer winding coil wound in a tubular shape on the outer periphery of the thin wall portion 2a of the case 2.
Is a fuel passage formed inside the case 2, 5 is a pair of fuel inlets and outlets provided at both ends of the fuel passage 4, and 6 is a coil 3
Is a columnar electrode coaxially arranged with the coil 3 at a position opposed to the inner peripheral surface of, and is formed of stainless steel, titanium, copper, brass, iron or the like plated with nickel, and Use a resistant one.

It is advantageous that the diameter of the columnar electrode 6 is smaller than the inner diameter of the thin wall portion 2a around which the coil 3 is wound in terms of improving the output change rate of the sensor. The columnar electrode 6 is fitted with an O-ring 8 so that the diameter of one end thereof matches the inner diameter of the case 2, and the other end is inserted and fixed in the recess 2b provided in the case 2 to seal the fuel. The stopper 7 is crimped and fixed to the case 2 to press one end of the columnar electrode 6, and the columnar electrode 6 is fixed to the case 2. 9 is attached to the case 2 by insert molding,
A pair of coil terminals with both ends of the coil 3 soldered,
Reference numeral 10 is an electrode terminal formed by protruding a part of the columnar electrode 6 to the outside through the central hole of the stopper 7, and 11 is a reinforcing beam provided on the outer periphery of the thin wall portion 2a to reinforce the strength of the case 2. is there.

Next, the operation of the above sensor will be described. The detection circuit 20 of the sensor is equivalent to the conventional one shown in FIG. 2, and the output of the voltage controlled oscillation circuit 22 is the electrode terminal 10 of the columnar electrode 6.
And the one coil terminal 9 of the coil 3 is grounded, and the other coil terminal 9 and the full-wave rectifier circuit 23 are connected. Unlike the conventional case, either of the coil terminals 9 may be grounded.

FIG. 5 shows an outline of an equivalent circuit of the sensor in the case of such a connection, where C _f is the permittivity ε of the fuel passage 4 between the outer circumference of the columnar electrode 6 and the inner circumference of the thin wall portion 2a. Capacitance when the fuel flows, C _s is the capacitance in the thickness direction of the thin wall portion 2a, C _pc is the stray capacitance existing in parallel with the coil 3, and C _f is As in the conventional case, a series resonance circuit is formed with the self-inductance L of the coil 3, and the resonance frequency f _m is f _m = 1 / [2π√L√ {C _f / (1 + C _f / C _s )}] (2) Given that, the resonance frequency f _m decreases as the permittivity ε of the fuel increases.

Therefore, the frequency applied to the columnar electrode 6 is changed by the voltage controlled oscillator circuit 22, the induced voltage of the coil 3 at this time is rectified by the full wave rectifier circuit 23, and the maximum value of the output is peak detector 24. By detecting and controlling the control input of the voltage controlled oscillator 22 at this time by the sample hold circuit 25 and outputting it through the low pass filter 26, the voltage output V _out is the resonance frequency f _{m of the} sensor, that is, The value corresponds to the permittivity ε of the fuel. In this case, the resonance frequency f _{m with} respect to the change of the dielectric constant ε
The rate of change of is large because there is no contribution of the parallel capacitances C _p and C _pa to C _f as shown in the equation (2) or the equivalent circuit of FIG. Further, by increasing the dimension of the case 2 and the dimensional accuracy of the columnar electrodes 6, the geometric capacitance accuracy of C _f and C _s can be increased, and the output variation of the sensor can be reduced.

FIG. 4 shows L = 30 μH, the thin wall portion 2 of the case 2.
The outer diameter φ of a is 10 mm, the thickness t of the thin wall portion 2 a is 1 mm, the width d of the fuel passage 4 between the inner circumference of the thin wall portion 2 a and the outer circumference of the columnar electrode 6.
This is a comparison of the output characteristics of the sensor in the case of = 2 mm with the output characteristics of the conventional sensor of the same size. Fuel is ε
In the case of = 2 gasoline and ε = 33 methanol, the change of the resonance frequency f _m is about 20% or more in this embodiment, and the change range is greatly improved as compared with the conventional case.

Example 2. FIG. 6 is a sectional view of a sensor portion according to Embodiment 2 of the present invention, in which 12 is a coil bobbin and 13
Is a coil molded body in which the coil 3 is integrally molded so that the wound portion of the coil 3 becomes the thin wall portion 13a, and 14 is a cylindrical case electrode which also serves as a case. The coil molded body 13 is
After winding the single-layer winding coil 3 around the outer circumference of the columnar or tubular coil bobbin 12, both ends of the coil 3 are soldered to a pair of coil terminals 9 insert-molded in the coil bobbin 12, and further plastic is injection-molded around this. It was then molded. This mold material is PP
S resin or the like is suitable.

Since the coil bobbin 12 does not come into contact with fuel,
Although it is not always necessary to use plastic that is resistant to fuel, it is preferable to use the same material as the coil molded body 13 because thermal deformation can be avoided. Except for the thin wall portion 13a on which the coil 3 is wound, the coil molded body 13 has its both ends having a diameter substantially matched with the inner diameter of the tubular case electrode 14, and a pair of O-rings 8 are provided here to provide a fuel seal. The cylindrical case electrodes 14 are bent and fixed at both ends by crimping.

The fuel passage 4 is formed between the inner periphery of the cylindrical case electrode 14 and the outer periphery of the coil molded body 13, and a pair of fuels connected to the cylindrical case electrode 14 by welding or the like at both ends thereof. A doorway 5 is provided to allow the fuel to flow. In the second embodiment, unlike the cylindrical container-shaped case 2 of FIG. 1, the thin wall portion 13a does not need to bear the fuel pressure only by the thin wall portion 13a. Therefore, the thin wall portion 13a can be made thinner,
The capacitance C _s of the thin wall portion 13a connected in series with the capacitance C _f can be further increased, and the change in the resonance frequency with respect to the change in the dielectric constant of the fuel can be further increased.

Cylindrical case electrode 14 and one coil terminal 9
Is grounded, the output of the voltage controlled oscillation circuit 22 of the detection circuit 20 is applied to the other coil terminal 9 via the resistor R, and the voltage at the connection between the coil 3 and the resistor R is input to the full-wave rectifier circuit 23. FIG. 7 shows an equivalent circuit of the sensor part of FIG. in this case,
The sensor section constitutes a parallel resonance circuit, and its resonance frequency f _n
Is given by f _n = 1 / [2π L {C _f / (1 + C _f / C _s ) + C _pc }] (3), and the resonance frequency f _n decreases as the permittivity ε of the fuel increases.

At the resonance frequency f _n , the impedance of the LC parallel resonance circuit becomes maximum, and the voltage at the connection between the coil 3 and the resistor R also becomes maximum. Therefore, the frequency applied to the coil 3 via the resistor R is changed by the voltage controlled oscillator circuit 22, and the connection voltage between the coil 3 and the resistor R is changed to the full-wave rectifier circuit 2.
The maximum value of the output is rectified by the peak detector 24.
By detecting the control input of the voltage controlled oscillator circuit 22 at this time by the sample hold circuit 25 and outputting it through the low pass filter 26, the voltage output V _out is the resonance frequency, that is, the fuel dielectric. The value corresponds to the rate ε.

In equation (3), the parallel capacitance C _pc of the coil 3
Can be made smaller than the capacitance C _f , and since the coil 3 is molded, it is not affected by external factors such as humidity. Also, the cylindrical case electrode 14 with the coil 3 grounded
Since the cylindrical case electrode 14 is covered with a magnetic substance such as iron whose inner surface is nickel-plated to ensure fuel resistance, the effect of the external magnetic field on the coil 3 can be eliminated. As described above, in the second embodiment, not only the change in the resonant frequency with respect to the change in the dielectric constant of the fuel can be made large, but also the influence of the external environment on the sensor output can be removed more completely.

Example 3. FIG. 8 is a sectional view of the sensor unit according to the third embodiment, and 15 is a coating member. The coil bobbin 12 is insert-molded with a pair of coil terminals 9 via an O-ring 81 for fuel sealing, the coil 3 is wound around the outer circumference of the coil bobbin 12, and both ends of the coil 3 are soldered to the coil terminals 9. And the like, and then the coil 3 is dipped to form the coating member 1
5, the bobbin 12 is finally inserted into the tubular case electrode 14 with the O-ring 8 attached, and the end of the tubular case electrode 14 is bent and fixed by caulking. As the coating member 15, an oil resistant epoxy resin or PPS resin is used. According to this configuration, since the thin wall portion can be configured by the coating member 15, the thickness thereof can be further reduced, and the capacitance C _s can be further increased, so that the resonance frequency change can be further increased and The manufacturing process can be simplified and the sensor can be made cheaper.

In each of the above embodiments, the coil 3
The columnar electrode 6 and the cylindrical case electrode 14 are coaxial, but they are not necessarily coaxial as long as the outer circumference of the coil 3 and the inner circumference of the electrode 14 or the inner circumference of the coil 3 and the outer circumference of the electrode 6 face each other. Alternatively, it may be substantially parallel to the axis. Further, although the case of using it for measuring the dielectric constant of fuel has been described, it can be generally used for measuring the dielectric constant of liquid.

Example 4. 9A and 9B show the fourth embodiment.
FIG. 10 shows a perspective view of a sensor part of the sensor according to FIG. 1 and a sectional view taken along line BB thereof, and FIGS. 10A and 10B show perspective views of the coil part. Reference numeral 17 denotes a round plate container-like member formed of an insulator such as plastic. Among the plastics, an oil-resistant epoxy resin or PPS resin having a relatively high dielectric constant is preferable for improving the output change rate and resistance to fuel. , PP
It is advantageous in that S resin can be injection molded. Reference numeral 18 denotes a coil substrate on which a planar single-layer winding coil 19 is patterned, and 27 denotes a pair of coil terminals penetrating the coil substrate 18 and connected to both ends of the coil 19.
8, the coil 19 and the coil terminal 27 form a coil portion.

As shown in FIG. 10A, the coil portion is a round plate-shaped plastic laminated substrate 18 such as glass epoxy.
A round spiral coil 19 is arranged on the above, through holes are provided in the lead connecting portions at both ends thereof, and the coil terminals 27 are soldered. A ceramic substrate may be used as the coil substrate 18. Further, as shown in FIG. 10B, a square spiral coil 19 may be arranged on the square plate substrate 18. The coil portion is insert-molded on the bottom portion of the round dish container-shaped member 17 from the inner bottom surface, leaving the thin wall portion 17a.

Reference numeral 28 denotes a cylindrical case-shaped metal case electrode in which the flat single-layer winding coil 19 is arranged and is spaced a predetermined distance from the inner bottom surface of the round dish container-shaped member 17 so that the flat portions of the bottom surface face each other. The fuel passage 4 is formed between the facing surfaces. The thickness of the portion of the electrode 28 facing the thin wall portion 17a is thicker than the thickness of the thin wall portion 2a by about 5 times or more, which is advantageous in improving the output change rate of the sensor.

A pair of nipples 29 for supplying and discharging the fuel to the fuel passage 4 are attached to the bottom surface of the metal case electrode 28 by welding, brazing or the like so as to communicate with the fuel passage 4. The metal case electrode 28 is made of stainless steel, titanium, or the like as a material, or is made of iron or the like and has a nipple 29 attached thereto, and then nickel plating is applied to the inner surface thereof to secure fuel resistance. The O-ring 8 is arranged on the outer circumference of the round plate container-shaped member 17 to form the metal case electrode 2
8 is inserted into the cylindrical portion to secure a fuel seal, and the end of the cylindrical portion is bent and fixed by caulking. Reference numeral 10 denotes an electrode terminal formed by leaving the crimped portion without bending it.

Next, the operation of the sensor according to the fourth embodiment will be described. The detection circuit of the sensor is the same as the conventional one shown in FIG. 2, and the output of the voltage controlled oscillation circuit 22 is the metal case electrode 28.
Of the coil terminal 27 is grounded, and the other coil terminal 27 is connected to the full-wave rectifier circuit 23. Either of the coil terminals 27 may be grounded. FIG. 11 shows an equivalent circuit of the sensor portion having the above-mentioned configuration, and C _f is the static passage between when the fuel of permittivity ε flows through the fuel passage 4 between the bottom surface of the metal case electrode 28 and the surface of the thin wall portion 17a. The capacitance, C _s is the capacitance in the thickness direction of the thin wall portion 17a, C _pc is the stray capacitance existing in parallel with the single-layer coil 19, and C _f is the self-inductance L of the coil 19.
And a resonance frequency f _m thereof is given by the above equation (2), and the resonance frequency f _m decreases as the permittivity ε of the fuel increases.

Therefore, the frequency applied to the metal case electrode 28 is changed by the voltage controlled oscillator circuit 22, and the coil 1
The induced voltage of 9 is rectified by the full-wave rectifier circuit 23, and the maximum value of its output is detected by the peak detector 24. The control input of the voltage controlled oscillator circuit 22 at this time is sample-held by the sample-hold circuit 25, and the low range By outputting through the pass filter 26, the voltage output V _out becomes a value corresponding to the resonance frequency f _m of the sensor unit, that is, the permittivity ε of the fuel.

In this case, as for the rate of change of the resonance frequency f _m with respect to the change of the dielectric constant ε, as shown in the equation (2) or FIG. 11, the contribution of the parallel capacitances C _p and C _pa to the conventional C _f is shown. You can take big because there is no. Further, since the surface distance between the bottom surface of the metal case electrode 28 and the thin wall portion 17a and the thickness of the thin wall portion 17a can secure dimensional accuracy by increasing the working precision of each member, C _f , C _s It is possible to improve the geometric capacity accuracy of the sensor and reduce variations in the output of the sensor. The output characteristic of the fourth embodiment is also shown in FIG.
As shown in Fig., The fuel is gasoline with ε = 2 and ε = 33.
The change of the resonance frequency f _{m in} the case of methanol is significantly improved as compared with the conventional sensor.

FIG. 12 shows an equivalent circuit in the case where the connection with the detection circuit of the sensor portion having the above-mentioned configuration is changed. In this case, the metal case electrode 28 and one coil terminal 27 are grounded, and the other coil terminal 27 is connected. It is connected to the voltage controlled oscillator circuit 23 via the resistor R, and the coil terminal 27 is connected to the full-wave rectifier circuit 22. The sensor portion forms a parallel resonance circuit, and its resonance frequency f _n is as shown in the equation (3), and the resonance frequency f _n decreases as the permittivity ε of fuel increases.

When the frequency reaches the resonance frequency f _n , the impedance of the LC parallel resonance circuit becomes maximum and the coil 19
The voltage at the connection between the resistor R and the resistor R also becomes maximum. Therefore, the frequency of the signal applied from the voltage controlled oscillator circuit 22 to the coil 19 via the resistor R is changed, the connection voltage is rectified by the full-wave rectifier circuit 23, and the maximum value of its output is detected by the peak detector 24. Then, the control input of the voltage controlled oscillation circuit 22 at this time is sampled and held by the sample and hold circuit 25, and is output through the low pass filter 26, so that the voltage output V _out is the resonance frequency f _n of the sensor unit, that is, It corresponds to the dielectric constant ε of the fuel.

Further, in the equation (3), the parallel capacitance C _pc can be made smaller than the capacitance C _f because the coil 19 is extremely thin and the facing area between the coil turns is small. Since it is molded, it is not affected by external factors such as humidity as in the past.
Further, since the coil 19 is covered with the grounded metal case electrode 28, by using a magnetic material such as iron whose inner surface is nickel-plated and fuel resistance is secured as the metal case electrode 28, an external effect on the coil 19 is exerted. The influence of the magnetic field can be reduced. That is, in the fourth embodiment, not only can the resonance frequency change with respect to the fuel dielectric constant change be large, but the influence of the external environment on the sensor output can be further reduced.

Example 5. FIG. 13 shows a cross section of the sensor section according to the fifth embodiment, and 15 is a coating section, in which a planar single-layer winding coil 19 is patterned on a coil substrate 18, and coil terminals 27 are connected to both ends of the coil 19. In the coil portion, the coil 19 is formed by coating a plastic having fuel resistance and a large dielectric constant by printing or dipping. After the O-ring 30 is inserted into the coil terminal 27 for the fuel seal of the coil portion having such a structure, it is attached to the bottom surface of the round dish container-shaped member 17. In this case, the coil portion may be fixed by adhering the coil substrate 18 to a concave portion on the bottom surface of the round dish container-shaped member 17 with a fuel-resistant adhesive, or after aligning the coil substrate 18 with the concave portion, It may be fixed by melting and caulking around, or may be fixed by adhesion and caulking simultaneously. It is not necessary to consider the dielectric constant of the round plate container-shaped member 17. According to the fifth embodiment, since the thickness of the coating portion 15 can be made thinner than that of the thin wall portion 17a formed by the molding of the fourth embodiment, the series capacitance C _s with C _f can be further increased, and the dielectric constant of the fuel can be increased. The change in the resonance frequency with respect to the change can be further increased.

Example 6. FIG. 14 is a cross-sectional view of the sensor unit according to the sixth embodiment, and 31 is a cylindrical container-shaped plastic case in which a metal electrode plate 32 is insert-molded on the bottom surface and a nipple 29 is integrally molded, and a coil part is insert-molded in a circular shape. The dish container-shaped member 17 is fitted with an O-ring 8 and inserted into the cylindrical portion of the cylindrical container-shaped plastic case 31 for alignment, and then the end of the cylindrical portion is fixed by melting caulking, or by ultrasonic welding or the like. Weld and fix with.
The material of the plastic case 31 may be the same as that of the round plate container-shaped member 17.

Although the coils 19 are patterned on the coil substrate 18 in the fourth to sixth embodiments,
Any coil may be used as long as it is a substantially flat single-layer winding coil. Further, although the case of using it for measuring the dielectric constant of fuel has been described, it can also be used for measuring the dielectric constant of liquids in general.

[0041]

As described above, according to the present invention, the fuel passage is formed between the coil and the electrode, and the permittivity of the fuel flowing through the fuel passage is determined by the capacitance between the coil surface and the electrode surface. Since the capacitance is hardly affected by the parallel capacitance, the capacitance is significantly changed and detected by the change of the dielectric constant, and the detection accuracy can be improved. Further, since the distance between the coil and the electrode can be accurately determined, it is possible to reduce the detection variation.

[Brief description of drawings]

FIG. 1 is a perspective view and a sectional view of a sensor unit of a sensor according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram of a conventional sensor.

FIG. 3 is an equivalent circuit diagram of a sensor unit of a conventional sensor.

FIG. 4 is an output characteristic diagram of the sensor of the present invention and the conventional sensor.

FIG. 5 is an equivalent circuit diagram of the sensor unit of the sensor according to the first embodiment of the present invention.

FIG. 6 is a sectional view of a sensor portion of a sensor according to a second embodiment of the present invention.

FIG. 7 is an equivalent circuit diagram of a sensor section of a sensor according to a second embodiment of the present invention.

FIG. 8 is a sectional view of a sensor portion of a sensor according to a third embodiment of the present invention.

9A and 9B are a perspective view and a sectional view of a sensor portion of a sensor according to a fourth embodiment of the present invention.

FIG. 10 is a perspective view of a coil part of a sensor according to a fourth embodiment of the present invention.

FIG. 11 is an equivalent circuit diagram of a sensor part of a sensor according to a fourth embodiment of the present invention.

FIG. 12 is an equivalent circuit diagram in the case where the connection with the detection circuit of the sensor unit of the sensor according to the fourth embodiment of the present invention is changed.

FIG. 13 is a sectional view of a sensor portion of a sensor according to a fifth embodiment of the present invention.

FIG. 14 is a sectional view of a sensor portion of a sensor according to a sixth embodiment of the present invention.

[Explanation of symbols]

 2 Cylindrical container case 2a, 13a, 17a Thin wall part 3 Cylindrical single layer winding coil 4 Fuel passage 6 Columnar electrode 13 Coil molded body 14 Cylindrical case electrode 15 Coating member 17 Round plate container member 19 Planar single layer winding Coil 20 Detection circuit 28 Metal case electrode 31 Metal electrode plate 32 Cylindrical container-shaped plastic case

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] July 30, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0008

[Correction method] Change

[Correction content]

[0008]

However, the above-mentioned conventional sensor has the following problems because the electrode 16 is coaxially arranged on the end face of the coil 3. For example, L = 20 μH, outer diameter of insulating tube 1 = 10 m
Assuming that m is m, the thickness of the tube wall of the insulating tube 1 is t = 1 mm, and the distance d between the end surface of the coil 3 and the end surface of the electrode 16 is d = 2 mm, the fuel is ε =
For methanol 2 of gasoline and epsilon = 33, since a large parallel capacitance C _p with respect to capacitance C _f which varies by the dielectric constant of the fuel epsilon, is C _pa exists, the resonant frequency f _o are both about 8
In MHz, the difference was only about 5% as shown in Fig. 4.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] 0030

[Correction method] Change

[Correction content]

Reference numeral 28 denotes a cylindrical container-like member provided with the flat surface portions of the bottom surface facing each other at a predetermined distance from the inner bottom surface of the round plate container-shaped member 17 on which the flat single-layer winding coil 19 is arranged . It is a metal case electrode, and the fuel passage 4 is formed between the facing surfaces. The thickness of the portion of the electrode 28 facing the thin wall portion 17a is thicker than the thickness of the thin wall portion 2a by about 5 times or more, which is advantageous in improving the output change rate of the sensor.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0034

[Correction method] Change

[Correction content]

In this case, as for the rate of change of the resonance frequency f _m with respect to the change of the dielectric constant ε, as shown in the equation (2) or FIG. 11, the contribution of the parallel capacitances C _p and C _pa to the conventional C _f is shown. You can take big because there is no. Further, since the surface distance between the bottom surface of the metal case electrode 28 and the thin wall portion 17a and the thickness of the thin wall portion 17a can secure dimensional accuracy by increasing the working precision of each member, C _f , C _s Accuracy of the sensor can be increased, and
The key can be reduced. The output characteristic of the fourth embodiment is also shown in FIG.
As shown in Fig., The fuel is gasoline with ε = 2 and ε = 33.
The change of the resonance frequency f _{m in} the case of methanol is significantly improved as compared with the conventional sensor.

Claims (2)

[Claims] 1. A tubular single-layer winding coil having a high-dielectric-constant insulating thin wall in close contact with a peripheral surface on the side in contact with fuel; and a peripheral surface coaxial with or axially parallel to the single-layer winding coil. A columnar or cylindrical metal electrode that is provided so as to face the coil circumferential surface and forms a fuel passage between the coil and the single-layer winding coil, and a capacitance between the circumferential surface of the single-layer winding coil and the circumferential surface of the metal electrode. A fuel permittivity detection sensor comprising means for detecting the permittivity of fuel flowing through a fuel flow path. 2. A flat single-layer winding coil having a high-dielectric-constant insulating thin wall provided in close contact with the surface in contact with fuel, and a single-layer winding coil provided so as to face the single-layer winding coil. And a means for detecting the permittivity of the fuel flowing through the fuel passage by the electrostatic capacitance between the single-layer winding coil and the metal electrode. Sensor for detecting permittivity of fuel.