JPH0552797A - Dielectric constant detection device - Google Patents

Abstract

PURPOSE:To enable a dielectric constant detection accuracy for temperature change of fuel which contains alcohol to be improved. CONSTITUTION:A dielectric constant detection device of a fuel is provided with a conductivity electrode 3, a single-layer winding coil 4 where a coil periphery surface which is covered with an insulation layer is placed opposingly at the conductive electrode 3 with a specified spacing, a fuel passage 2 where a fuel is introduced between the conductive electrode 3 and the single-layer winding coil 4, and a means for detecting a resonance frequency of the single- layer winding coil 4 and is constituted so that the resonance frequency corresponds to a dielectric constant of the fuel. A temperature-compensation capacitor 9 is provided at a position where a temperature change of the fuel can be detected, it is connected to the single-layer winding coil 4 in parallel, and then temperature characteristics of the resonance frequency are canceled out by the above temperature-compensation capacitor 9, thus obtaining the resonance frequency constantly and accurately regardless of temperature change of the fuel and the dielectric constant of the fuel to be detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device 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. The present invention relates to a dielectric constant detection device for measuring alcohol content.

[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 petroleum and the air pollution caused by automobile exhaust gas, fuel mixed with alcohol in gasoline is being introduced for automobiles. 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 value.

Conventionally, a method of detecting the dielectric constant of an 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. Among these methods, the applicant of the present invention has filed, for example, Japanese Patent Application No. 3-22488 as a method for detecting the dielectric constant. This method will be described below with reference to the drawings.

FIG. 12 shows an embodiment shown in Japanese Patent Application No. 3-22488. In the figure, C is a sensor portion, 1 is a cylindrical insulating tube with a bottom, which is made of an insulator such as ceramic or oil-resistant plastic, and into which fuel is guided, and 3 is provided inside this cylindrical insulating tube 1. Is a cylindrical conductive electrode whose outer peripheral surface is substantially parallel to the wall surface of the insulating tube 1 and is coaxial with the insulating tube 1, and 4 is the conductive electrode 3 outside the insulating tube 1.
Single-layer winding coil wound at a position opposed to 4a, 4b
Is a lead of the single-layer winding coil 4, 2 is a fuel passage formed between the inner peripheral surface of the single-layer winding coil 4 and the outer peripheral surface of the conductive electrode 3 across the tube wall of the insulating tube 1, and 5 is a conductive path. With a conductive electrode 3 attached to the insulating tube 1 via a fuel seal 7 to form a fuel container as a whole, in this case the conductive electrode 3
6 shows a nipple that guides fuel to the fuel passage 2.

Reference numeral B denotes a detection circuit section, 10 is a series resistor Rs which is connected to the lead 4a of the single-layer winding coil 4 to form a series circuit, and 11 is 0 ° to which signals at both ends of the resistor Rs10 are connected. A phase comparator, 12 is a low-pass filter to which the output of the phase comparator 11 is connected, and 13 is a low-pass filter 1.
2 is connected to a comparison integrator to which a predetermined reference voltage Vref corresponding to a phase of 0 ° is connected, 14 is a voltage controlled oscillator to which the output of the comparison integrator 13 is connected, and 15 is a voltage controlled oscillator 14
Output amplifier connected to the series circuit. Reference numeral 16 is a frequency divider for the output frequency of the voltage controlled oscillator 14.

Next, the operation of this device will be described. The sensor section c in FIG. 12 is roughly given by an equivalent circuit as shown in c of FIG. In FIG. 3, L is the inductance of the single-layer winding coil 4, and Cf is the single-layer winding coil 4 and the conductive electrode 3 that change according to the dielectric constant ε of the fuel in the fuel passage 2.
And Cs is a capacitance that uses the insulating material of the insulating tube 1 that protects the single-layer winding coil 4 from fuel as a dielectric,
Cp is a capacitance irrelevant to the permittivity ε of the fuel, such as a stray capacitance parasitic on the lead 4a and an input capacitance of the 0 ° phase comparator 11. Here, parallel LC resonance is exhibited when the frequency applied to the lead 4a of the sensor unit in FIG. 12 is changed. That is, the parallel resonance frequency f at this time is shown by the following equation.

F = 1 / [2π√ {L (Cp + 1 / (1 / Cs + 1 / Cf))] = K / √ {a + b * ε (t)} (1) where K, a, b is a constant determined by the shape of the sensor unit. For example, it depends on the diameter and thickness of the insulating tube 1, the dielectric constant of the material of the insulating tube 1, the distance between the conductive electrode 3 and the single-layer winding coil 4, the self-inductance of the single-layer winding coil 4, and the like. Since the resonance frequency f depends on the permittivity ε of the fuel as shown in the equation (1), the resonance frequency becomes lower as the permittivity ε of the fuel increases. In addition, in an arbitrary mixed fuel of methanol and gasoline, the resonance frequency f changes as shown in FIG. 13 according to the content ratio of methanol. That is, by detecting the signal corresponding to the resonance frequency f, the permittivity ε of the fuel, and thus the methanol content in the methanol mixed fuel, can be detected.

The circuit section B in FIG. 12 is constructed so as to detect the resonance frequency f.
Continue to explain. A high frequency signal is applied from the amplifier 15 to the series circuit of the resistor Rs10 and the single-layer winding coil 4 with the methanol mixed fuel flowing in the fuel passage 2, and the high frequency voltage signal applied to both ends of the resistor Rs10, that is, the series circuit. The high frequency voltage signal applied to the single-layer winding coil 4 is input to the phase comparator 11 and the phases of the both are compared. Now, assuming that a high frequency voltage signal having the same frequency as the resonance frequency f is applied to the series circuit, the current-voltage phase of the sensor unit C becomes 0 °, so the phase difference of the high frequency voltages across the resistor Rs10 is 0 °. Becomes On the other hand, if a high-frequency voltage signal having a frequency lower than the resonance frequency f is applied to the series circuit, the current-voltage phase of the sensor unit C leads 0 °, so that the phase difference of the high-frequency voltage across the resistor Rs10 is When the phase of the high frequency signal applied to the series circuit is used as a reference, it becomes larger than 0 °.

Therefore, the output of the phase comparator 11 is converted into a DC voltage corresponding to the phase difference via the low pass filter 12,
DC voltage Vref corresponding to the DC voltage and a phase difference of 0 °
Are input to the comparison integrator 12, the difference between the two is integrated, and the output of the comparison integrator 12 is input to the voltage controlled oscillator applying a high frequency signal to the series circuit via the resistor Rs10. A phase locked loop is formed. The voltage controlled oscillator 13 has a resistor Rs10 by the phase locked loop.
Since the phase difference between the high-frequency voltage signals at both ends of is controlled to be 0 °, the oscillation frequency of the voltage controlled oscillator 13 is always the parallel resonance frequency f. Therefore, the output frequency of the voltage controlled oscillator 12 is divided into an appropriate frequency via the frequency divider 16, and the frequency output foo corresponding to the parallel resonance frequency f is obtained.
t is obtained. Further, noting that the oscillation frequency of the voltage controlled oscillator 13 and the control input voltage have a one-to-one correspondence, the output of the low pass filter 11 can be taken out as the voltage output Vout.

[0010]

However, in this conventional device, the dielectric constant of the fuel and the insulating tube 1 are changed due to the temperature change of the fuel even though the methanol content does not change.
There is a problem in that the dielectric constant of No. 1 changes and the frequency output fout greatly changes as indicated by the alternate long and short dash line in FIG. 13, making it difficult to accurately detect the methanol content.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a dielectric constant detecting device capable of accurately detecting dielectric constant with respect to temperature change of alcohol-containing fuel.

[0012]

SUMMARY OF THE INVENTION A dielectric constant sensing device according to the present invention is a single layer winding coil in which a conductive electrode and a coil pillar surface which is separated from the conductive electrode by a predetermined distance and is covered with an insulating layer are arranged to face each other. And a fuel passage through which fuel is introduced between the conductive electrode and the single-layer winding coil, and means for detecting the resonance frequency of the single-layer winding coil. The resonance frequency corresponds to the dielectric constant of the fuel. A device for detecting the permittivity of fuel, which is provided with a temperature compensating capacitor at a position where the temperature change of the fuel can be detected, and is connected in parallel with the single-layer winding coil to cancel the temperature characteristic of the resonance frequency by the temperature compensating capacitor. It was done like this.

[0013]

In the dielectric constant detecting device according to the present invention, the dielectric constant of the fuel is measured by the resonance frequency, and the temperature compensation capacitor cancels the change in the resonance frequency due to the temperature.
It always detects an accurate methanol content regardless of the temperature change of the device.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the dielectric constant detecting device according to the present invention will be described in detail below with reference to the drawings. FIG. 1 is a configuration diagram showing an embodiment of a fuel dielectric constant detecting device according to the present invention, FIG.
Is a structural diagram of the sensor portion of this embodiment, FIGS. 3 and 4 are equivalent circuit diagrams and configuration diagrams of the sensor portion, FIG. 5 is an output characteristic diagram of an embodiment using a concrete circuit example, and FIG. FIG. 7 and FIG. 8 are various capacitance characteristic diagrams with respect to temperature, and FIG. 9 is a parallel resonance frequency characteristic diagram of the conventional example and the example with respect to temperature.

In the figure, the detection circuit is the same as that of the conventional example, but the sensor section A is different. Therefore, the sensor section A will be described. Reference numeral 1 denotes a bottomed cylindrical insulating tube made of an insulator such as ceramic or oil-resistant plastic, into which fuel is guided, and 3 is provided inside the cylindrical insulating tube 1, and the outer peripheral surface of the insulating tube 1 is an insulating tube. 1 is a cylindrical conductive electrode substantially parallel to the wall surface of 1 and coaxial with the insulating tube 1. Titanium, stainless steel, aluminum whose surface is anodized, or the like is preferable in terms of resistance to fuel. 4 is a conductive electrode 3 outside the insulating tube 1.
Single-layer winding coil wound at a position opposed to 4a, 4b
Is a lead of the single-layer winding coil 4, 2 is a fuel passage formed between the inner peripheral surface of the single-layer winding coil 4 and the outer peripheral surface of the conductive electrode 3 across the tube wall of the insulating tube 1, and 5 is a conductive path. A flange that is connected to an insulating tube 1 to which a conductive electrode 3 is attached via a fuel seal 7 to form a fuel container as a whole. Here, an example in which the conductive electrode 3 is integrally formed is shown. Fuel passage 2
A nipple 9 for guiding the fuel to is provided at a position where the fuel temperature can be detected, and a temperature compensating capacitor connected in parallel to the single-layer winding coil 4.

3 and 4 are an equivalent circuit diagram and a configuration diagram showing the sensor section A in a simple manner. Cp is a line capacitance and an input capacitance generated in the single-layer winding coil 4, and Cs is a single-layer winding coil 4. The parallel resonance frequency f is represented by the following equation, where Cf is a capacity of a fuel dielectric and Ct is a capacity of a temperature compensation capacitor.

F = 1 / [2π√ {L (Ct (t) + Cp + 1 / (1 / Cs (t) + 1 / Cf (ε, t)))}] ... (2) Parallel The resonance frequency f depends on the permittivity ε of the fuel, and the permittivity ε
Becomes larger, it decreases. Moreover, as shown in FIG. 6, the permittivity ε of the fuel depends on the temperature change of the fuel, and monotonously decreases as the temperature rises.

Next, with respect to the above equation (2), the series combined capacitance showing the temperature dependence of the sensor portion is given by the following equation.

1 / C (t) = 1 / Cs (t) + 1 / Cf (t) = a / εs (t) + b / εf (t) (3) where a and b are insulators A is a geometric capacitance of Cs, b is a geometric capacitance of Cf, and is not simply determined by a change in the dielectric constant, but each geometric capacitance acts as a coefficient. Since the permittivity of fuel monotonically decreases with temperature, and conversely, the permittivity of insulator monotonically increases with temperature, the temperature dependence tends to be canceled in the series connection of the corresponding capacitances of these permittivities. The influence of the permittivity of the fuel on the temperature shows a slightly different temperature coefficient depending on the fuel content, but the influence of the temperature coefficient of the insulator is large. The temperature characteristics when the sensor shape is fixed and the insulator is changed are shown in FIGS. 7 and 8 in the form of series combined capacitance. Here, the difference between FIG. 7 and FIG. 8 shows the state when the insulator is changed, where a is nylon and b is PPS. Although Cs varies depending on the material of the insulator as described above, there is a limit to the selection of the material of the insulator in consideration of oil resistance. At this time, when a temperature compensation capacitor is provided at a position where the fuel temperature can be detected and the temperature compensation capacitor is connected in parallel to the single-layer winding coil, the combined capacity is given by the following equation.

C = Ct (t) + 1 / (1 / Cs (t) + 1 / Cf (t)) (4) At the stage when the material and shape of the sensor, that is, the value of the geometrical capacitance is determined, the above ( The capacity and temperature coefficient of the temperature compensation capacitor and the temperature coefficient tolerance are determined so that the equation 4) becomes a function independent of temperature. From the above results, FIG. 9 shows a comparison of the temperature characteristic of the parallel resonance frequency with that of the conventional example. Thus, the temperature characteristic of the parallel resonance frequency is compensated for as compared with the conventional example.

FIG. 5 schematically shows the frequency output fout with respect to the alcohol content rate in the alcohol blended gasoline of the embodiment of the apparatus of FIG. 1 by the detection circuit of FIG. 12 as in the conventional example, in which the methanol content rate increases. However, the dielectric constant ε becomes large and the output monotonously decreases regardless of the temperature change of the fuel.

In the above embodiment, the single layer winding coil of the sensor portion A and the conductive electrode are coaxial, but they are not necessarily coaxial, and the electrostatic capacitance due to the fuel is present between the single layer winding coil and the conductive electrode. Just make it exist.

FIG. 10 shows another embodiment of the present invention, in which the temperature compensating capacitor 9 is molded in an insulating layer for protecting the single-layer winding coil 4 from the fuel, and the temperature compensating capacitor 9 is used. The terminals are connected near the four terminals of the single-layer winding coil. With such a structure, the additional capacitance such as the lead of the temperature compensating capacitor 9 can be reduced, and the effect is that the compensation becomes more accurate. Further, as shown in FIG. 11, the arrangement of the single-layer winding coil 4 and the conductive electrode 3 is reversed, and the single-layer winding coil 4 is molded with the insulating tube 1 and the temperature compensation capacitor 9 is also molded with the insulating tube 1, and inside the insulating tube. By connecting the terminals, the single-layer winding coil can be effectively protected from disturbance.

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

[0025]

As described above, according to the present invention,
A single-layer winding coil covered with a conductive electrode and an insulating layer was provided in the middle of the fuel passage with a fuel sandwiched between them, and a temperature compensation capacitor was connected in parallel with the single-layer winding coil to compensate for the resonance frequency due to fuel temperature changes. The alcohol content 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 partially cutaway perspective view of a sensor unit according to an embodiment of the present invention.

FIG. 3 is an equivalent circuit diagram of a sensor unit according to an embodiment of the present invention.

FIG. 4 is a configuration diagram of an equivalent circuit of a sensor unit according to an embodiment of the present invention.

FIG. 5 is an output characteristic diagram of a specific circuit example according to the present invention.

FIG. 6 is a dielectric constant characteristic diagram of fuel with respect to temperature in the present invention.

FIG. 7 is a capacitance characteristic diagram with respect to temperature.

FIG. 8 is a capacitance characteristic diagram with respect to temperature.

FIG. 9 is a parallel resonance frequency characteristic diagram of a conventional example and an example with respect to temperature.

FIG. 10 is a configuration diagram of a sensor unit of a dielectric constant detection device according to another embodiment of the present invention.

FIG. 11 is a configuration diagram of a sensor unit of a dielectric constant detection device according to still another embodiment of the present invention.

FIG. 12 is a configuration diagram showing a conventional fuel dielectric constant detection device.

FIG. 13 is an output characteristic diagram of a conventional dielectric constant detection device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Insulation tube 2 Fuel passage 3 Conductive electrode 4 Single layer winding coil 4a, 4b Lead 9 Temperature compensation capacitor 10 Series resistance Rs 11 0 ° Phase comparator 12 Low pass filter 13 Comparator / integrator 14 Voltage controlled oscillator 15 Amplifier 16 minutes Circulator

Claims (1)

[Claims] 1. A conductive electrode, a single-layer winding coil in which a coil pillar surface which is isolated from the conductive electrode by a predetermined distance and is covered with an insulating layer is arranged to face the conductive electrode, and the conductive electrode and the single-layer winding coil. A fuel dielectric constant detection device having a fuel passage through which fuel is introduced, and means for detecting the resonance frequency of the single-layer winding coil, wherein the resonance frequency corresponds to the dielectric constant of the fuel. Therefore, a temperature compensation capacitor is provided at a position where the temperature change of the fuel can be detected, and it is connected in parallel with the single-layer winding coil so that the temperature characteristic of the resonance frequency is canceled by the temperature compensation capacitor. Permittivity detector.