JPH0735718A - Alcoholic concentration sensor - Google Patents

Abstract

PURPOSE:To provide a concentration sensor for detecting the concentration of alcohol accurately even the fuel temperature is not settled. CONSTITUTION:Upon application of a square wave from a pulse oscillating section 21, a detecting capacitor 113 is charged instantaneously. Subsequently, current flows through a discharge resistor and the capacitor 113 is discharged. Since the capacitor 113 has a capacitance proportional to the concentration of alcohol, the concentration can be detected by detecting the time to be elapsed before the capacitor 113 is discharged to a predetermined threshold value. A resistance detecting capacitor 116 can elevate the threshold value as the fuel temperature lowers thus allowing accurate detection of alcoholic concentration even if the fuel temperature varies abruptly.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alcohol concentration sensor, and more particularly to an alcohol concentration sensor for measuring the alcohol concentration in a mixed fuel of gasoline and alcohol.

[0002]

2. Description of the Related Art In recent years, methanol vehicles have been actively developed in order to reduce pollution of internal combustion engines for automobiles and save gasoline consumption. In particular, a vehicle FFV ( F ule) capable of using a mixed fuel in which gasoline and alcohol are mixed at an arbitrary ratio (hereinafter, simply referred to as a mixed fuel)
xible F uel V ehicle) has a high degree of freedom of the fuel, it has been developed for practical use.

However, since the optimum air-fuel ratio of the mixed fuel differs depending on the alcohol concentration, it is necessary to control the fuel injection amount and ignition timing by measuring the alcohol concentration in the mixed fuel with an alcohol concentration sensor. Two types of alcohol concentration sensors, optical type and capacitance type, have been proposed, but the capacitance type is predominant because of its simple structure.

That is, the electrostatic capacitance type alcohol concentration sensor utilizes the fact that the permittivity of the mixed fuel differs depending on the alcohol concentration of the mixed fuel, so that the mixed fuel is passed between the electrode plates and the static electricity between the electrodes is maintained. The alcohol concentration in the mixed fuel is measured by measuring the electric capacity. By the way, since the permittivity of the mixed fuel has temperature dependency, it changes not only with the alcohol concentration (mixing ratio) but also with the fuel temperature. This is because the dielectric constant of methanol has temperature dependence. Therefore, the temperature of the fuel is measured by the temperature sensor, and the correct alcohol concentration is obtained by correcting the temperature according to the fuel temperature. The correction is performed based on the map data, and the map complements the voltage value in the steady state where the temperature of the entire sensor and the fuel temperature are equal. Therefore, a temperature sensor is provided in the alcohol concentration sensor in addition to the capacity detecting electrode to measure the fuel temperature.

Further, in Japanese Patent Laid-Open No. 3-215734, in order to prevent an alcohol concentration detection error due to a temperature difference between the sensor for detecting alcohol concentration and the detection circuit portion, the detection circuit portion is heat-exchanged with the fuel to detect the sensor. And an alcohol concentration sensor which eliminates the temperature difference between the detection circuit section and the detection circuit section.

[0006]

However, when the fuel temperature, which is represented by a high temperature restart, changes transiently, normal temperature correction is not performed and the circuit temperature characteristic of the sensor is large for map correction. Influence. This is because the circuit temperature of the sensor changes with the fuel temperature as a heating element, and it takes time for the circuit temperature to become equal to the fuel temperature. Therefore, there is no problem in the steady state in which the circuit temperature and the fuel temperature are equal, but in the transient state, there is a deviation between the circuit temperature and the fuel temperature, which deviates from the correction map. In other words, the circuit temperature characteristic does not become a problem when the sensor steady value is complemented by the map, but the influence of the circuit temperature characteristic becomes remarkable in the transient state of the sensor.

Also, in the alcohol concentration sensor disclosed in Japanese Patent Laid-Open No. 3-215734, heat exchange with the fuel is not carried out instantaneously, but when the fuel temperature sharply drops, such as during high temperature restart, the sensor There is a possibility that an alcohol concentration detection error may occur due to the temperature difference between the detection circuit and the detection circuit. As a result, there has been a problem that engine control such as fuel injection amount and ignition timing is not normally performed.

Therefore, an object of the present invention is to provide an alcohol concentration sensor capable of accurately detecting the alcohol concentration even during the transition period of the fuel temperature.

[0009]

In order to achieve the above object, the present invention provides a detection capacitor comprising a pair of electrode plates dipped in a mixed fuel in which gasoline and alcohol are mixed, and A pulse power supply that supplies square-wave pulsed power to the detection capacitor, a discharge resistance that discharges the charge accumulated in the pair of detection capacitors by the pulse power supply, and a signal proportional to the alcohol concentration of the mixed fuel, An output section that outputs a voltage proportional to the time when the discharge voltage is equal to or higher than a predetermined threshold value, a temperature sensor that measures the temperature of the mixed fuel, and the predetermined value when the mixed fuel temperature detected by the temperature sensor decreases. An alcohol concentration sensor having a threshold value setting means for increasing the threshold value is adopted.

[0010]

According to the alcohol concentration sensor of the present invention, the electric charge accumulated in the detection capacitor by the pulse power supply is discharged by the discharge resistance. The output unit outputs a voltage proportional to the time when the discharge voltage is equal to or higher than a predetermined threshold value. When the fuel temperature drops, the discharge voltage shifts to the high voltage side, but the threshold value setting means raises the predetermined threshold value, so that even if the fuel temperature sharply drops as in a high temperature restart, the alcohol concentration can be accurately measured. Can be detected.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The alcohol concentration sensor of the present invention will be described below with reference to the drawings. FIG. 1 shows the structure of the alcohol concentration sensor of the present invention. The housing 11 is hollow, and the fuel discharged from the fuel pump (not shown) enters the housing 11 through the supply side fuel passage 111 and is supplied to the fuel engine (not shown) through the discharge side fuel flow path 112. To be done.

A holder 13 is mounted on the top of the housing 11, and a substrate 1 forming an electronic circuit is provided in the holder 13.
31 is stored. The temperature sensor 132 and the temperature sensor 133 attached to the substrate 131 for compensating the alcohol concentration by the temperature change of the mixed fuel are the case 134.
Is installed in such a manner that the temperature detecting portion penetrates the holder 13 and the housing 11 and is immersed in the mixed fuel.

A pair of electrode plates 11 for detecting alcohol concentration
Detection capacitor 1 composed of 3a and 113b
13 is installed on a stud 114 made of an insulating material via a spacer 115 also made of an insulating material. Similarly, a pair of electrode plates 116 for detecting fuel resistance
The resistance detecting capacitor 116 composed of a and 116b is also installed on the stud 117 made of an insulating material via a spacer 118 also made of an insulating material. The resistance detecting capacitor 116 has the same structure and the same shape as the pair of electrodes 113 of the detecting capacitor.

A pair of lead wires 119 and 120 are drawn out to the detection capacitor 113 and connected to the substrate 131, and a pair of terminals 1 penetrating the holder 13 and the housing 11 are connected.
35 and 136. That is, the detection capacitor 113 is used to measure the dielectric constant depending on the alcohol concentration existing between the electrode plates. Similarly, the pair of lead wires 1 is connected to the resistance detecting capacitor 116.
21 and 122 are pulled out, connected to the substrate 131, and pass through the holder 13 and the housing 11. A pair of terminals 137.
And 138. That is, the resistance detecting capacitor 116 is used to measure the resistivity depending on the alcohol concentration existing between the electrode plates.

The electronic circuit output on the substrate 131 is taken out by a cable 125 as an electric signal to the outside. FIG. 2 is a circuit diagram of the alcohol concentration sensor formed on the substrate 131, which includes a pulse generation unit 21, a detection unit 22, and an output unit 23. The pulse generator 21 is
A CR oscillation circuit composed of the inverters 211, 212, 213, the resistor 214 and the capacitor 215 applies a square wave pulse having a frequency of 500 kHz or more to the detection unit 22.

The detection unit 22 includes a detection capacitor 113, a resistance detection capacitor 116, a discharge resistor 221, a clamp diode 222, and a threshold control diode 223, 2.
24, comparator 225, threshold adjustment resistor 226,
227, 230, parasitic fuel resistance 22 of capacitor 113
8 and a parasitic fuel resistance 229 of the capacitor 116, which converts the capacitance generated between the detection electrodes into an electric (voltage) signal.

When a square wave pulse having a constant frequency generated from the pulse generator 21 is applied to a differentiating circuit composed of a detecting capacitor 113 having a capacitance proportional to the alcohol concentration and a discharge resistor 221, the capacitance is increased. A differential waveform corresponding to is obtained. This waveform shows the detection capacitor 11
3 is a voltage obtained by converting the discharge current when the charge charged in No. 3 is discharged by the discharge resistor 221. Then, since the time required for the comparator 225 to reach the predetermined voltage is proportional to the electrostatic capacitance, the electrostatic capacitance is converted into an electric signal (pulse width). At this time, the electric signal having the information of the detection capacity is a rectangular wave pulse, and the pulse width represents the detection capacity, that is, the alcohol concentration. However, the threshold value of the comparator 225 is variable depending on the size of the parasitic fuel resistance 229, and the voltage between the power supply voltage and the ground GND is controlled by the parasitic fuel resistance 229 and the threshold value control diode 223.
The value obtained by dividing the voltage by the resistors 226 and 227 with the voltage divided by the resistor 224 and the adjusting resistor 230 as the reference voltage.

The output unit 2 outputs the pulse signal thus obtained.
It is converted into an analog voltage by 3 and output. The conversion circuit is
The FET 23 and the integrating circuit which is composed of the resistor 231 and the capacitor 232 and has a sufficiently large time constant with respect to the signal frequency.
3 and resistors 234 and 235. Next, the alcohol concentration output when the fuel temperature transiently changes, as represented by high temperature restart, will be described with reference to FIG.

When the pulse oscillator 21 applies a square wave having a voltage Vcc and a signal width τ to the detecting capacitor 113,
The capacitor 113 is instantly charged and the potential at the point A is Vcc.
(H level). However, a current flows through the discharge resistor 221, the charge of the capacitor is discharged, and the potential at the point A gradually drops. The rate of decrease of this voltage is determined by the product of the detection capacitor 113 and the discharge resistance 221 (CR time constant), and the discharge resistance is fixed, resulting in a differential waveform proportional to the capacity. Then, after the time τ, when the voltage becomes the L level, the potential at the point A becomes V1−Vcc, where V1 is the voltage at the time when the potential is inverted, and thereafter, this negative voltage (charge) is reduced by the clamp diode 222 in a short time. It is discharged (almost instantly) and returns to the GND level. Strictly speaking, however, the clap by the clamp diode 222 is not discharged to the GND level and settles down to the magnitude of the forward voltage Vf as shown in the following expression 1.

[0020]

[Equation 1] However, m: constant, k: Boltzmann constant, T: absolute temperature, q0: electron charge, Is: reverse saturation current, Id:
Forward current.

This forward voltage Vf is determined by the magnitude of the forward current Id, and this forward current Id depends on the magnitude of the parasitic fuel resistance 228 of the detection capacitor 113. Further, the parasitic fuel resistance 228 has a size proportional to the fuel temperature as shown in FIG. Therefore, the fuel temperature suddenly rises to T1.
When the temperature changes from (high temperature) to T2 (low temperature), the parasitic fuel resistance value greatly changes from R1 to R2, and the forward current changes from (V1-Vcc) / R1 to (V1-Vcc) / R2, and the clamp The forward voltage due to the diode 222 is V
It becomes smaller by ΔVf from f1 to Vf2.

As a result, the differential waveform at the point A is Vf1.
-Vf2 is shifted in the positive direction, and the comparator 22
Calculate the pulse width with reference to the threshold value Vth1 of 5 Δ
An output error of t occurs. Therefore, in order to correct this output error, a resistance detection capacitor having the same structure and shape as the detection capacitor 113 is provided in the housing 11, and the differential waveform is shifted using the fuel resistance 229 parasitic on this capacitor. The threshold value is shifted by the amount.

FIG. 5 shows the resistance detecting capacitor 11 described above.
6, parasitic fuel resistance 229, threshold control diode 22
3 shows a variable threshold circuit composed of 3, 224, adjustment resistors 226, 227 and a comparator 225. The threshold value of the converter 225 becomes a voltage division value of the voltage between the point B and GND by the adjusting resistors 226 and 227, and the voltage of the point B changes the voltage between the power supply voltage Vcc and GND to the parasitic fuel resistance 229 and the threshold control. The voltage divided by the diodes 223 and 224 and the adjustment resistor 230 is obtained.

Since the resistance detecting capacitor 116 has the same structure as the detecting capacitor 113 and is immersed in the fuel in the housing 11, the size of the parasitic fuel resistance 229 is the same as that of the parasitic fuel resistance 228. The forward current becomes equal (id1 = id2), and the threshold adjustment diode 2
23 and 224 have the same forward voltage effect as the clamp diode 222. As a result, the potential at point B is 2 ^*
Since it is increased by ΔVf, the adjustment resistors 226 and 22 are
By setting 7 to be the same, the threshold value of the converter 225 can be shifted in the positive direction by ΔVf.

Therefore, by using the variable threshold value comparator 225 of the present invention, even if the fuel temperature (fuel resistance) changes abruptly, the differential waveform shifted by the magnitude of the fuel resistance is interlocked. It can be corrected by changing the value. In addition, the temperature sensor 132 and the clamp diode 2
22 and the threshold value adjusting diodes 223 and 224 are housed in the case 34, and the temperature detecting portion is immersed in the fuel, so that the temperature responsiveness to the temperature sensing element does not matter.

A structure as shown in FIG. 6 may be used as a method for improving the temperature responsiveness to the warm (sensing) element. Reference numeral 10 in the drawing is a case of the sensor, through which the mixed fuel passes. The cylindrical electrode 20 is made of an insulating resin to fix and insulate the electrode.
The inner electrode 22 is attached and configured. The outer electrodes and 21 are provided with holes orthogonal to the axis, which guide the mixed fuel between the electrodes. And this cylindrical electrode 2
0 is mounted in the passage of the case 10 via the insulating resin 31. On the other hand, the holder 40 to which the case 10 is fixed
Accordingly, the circuit board 50 on which the alcohol detection circuit having the capacity conversion function and the capacity temperature dependency correction function is arranged is mounted. Then, a cover 60 for protecting the components including the circuit board 50 is attached. (Note that the cover 6
0 and the case 10 also have the function of an electrostatic shield. )
Here, when the inner electrode 22 is thermally viewed, it is surrounded by insulating resins 30 and 31 for electrical insulation between the outer electrode 21 and the case 10 and electrical insulation between the electrodes.
This resin material is an electrically insulating material and also has good thermal insulation.
Alternatively, it is thermally insulated from the circuit board 50. Then, the temperature of the inner electrode 22 can be made substantially the same as the fuel temperature. Therefore, the fuel temperature can be easily measured by attaching the temperature measuring element 70 to the inner electrode 22 and measuring the temperature of the electrode. Therefore, the temperature responsiveness to the temperature sensitive element does not matter.

With the above structure, the fuel temperature response of the temperature sensing element is improved, and even when the fuel temperature changes abruptly, such as when restarting at high temperature, the sensor circuit temperature time instantly changes to the fuel temperature. With the matched characteristics, the sensor output is intolerant and enters a steady state (the fuel temperature and the circuit temperature are equal), and accurate fuel temperature correction by the map becomes possible.

[0028]

As is apparent from the above description, according to the alcohol concentration sensor of the present invention, the alcohol concentration can be accurately detected even when the fuel temperature changes abruptly such as when restarting at high temperature.

[Brief description of drawings]

FIG. 1 is a structural diagram showing an embodiment of an alcohol concentration sensor of the present invention.

FIG. 2 is a circuit diagram showing an embodiment of an alcohol concentration sensor of the present invention.

FIG. 3 is a signal waveform diagram showing the circuit operation of the embodiment of the alcohol concentration sensor of the present invention.

FIG. 4 is a diagram showing a fuel temperature-resistance value characteristic in the alcohol concentration sensor of the present invention.

FIG. 5 is a detection unit circuit diagram showing an embodiment of an alcohol concentration sensor of the present invention.

FIG. 6 is a structural diagram of a temperature sensing (temperature measuring) section showing another embodiment of the alcohol concentration sensor of the present invention.

[Explanation of reference numerals]

 11 Housing 113 Detection Capacitor 116 Resistance Detection Capacitor 131 Substrate 132 Temperature Sensor 21 Pulse Oscillator (Pulse Power Supply) 22 Detector 221 Discharge Resistor 222 Clamp Diode 223, 224 Threshold Control Diode 225 Comparator (Threshold Setting Unit) 23 Output section

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

[Procedure amendment]

[Submission date] August 6, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] Full text

[Correction method] Change

[Correction content]

[Document name] Statement

Title of the invention Alcohol concentration sensor

[Claims]

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alcohol concentration sensor, and more particularly to an alcohol concentration sensor for measuring the alcohol concentration in a mixed fuel of gasoline and alcohol.

[0002]

2. Description of the Related Art In recent years, methanol vehicles have been actively developed in order to reduce pollution of internal combustion engines for automobiles and save gasoline consumption. Especially gasoline and mixed mixed fuel and alcohol in any proportion (hereinafter, simply referred to as mixed fuels.) The possibility of using a F FV (F lexibl
e F uel V ehicle) has a high degree of freedom of the fuel, it has been developed for practical use.

However, since the optimum air-fuel ratio of the mixed fuel differs depending on the alcohol concentration, it is necessary to control the fuel injection amount and ignition timing by measuring the alcohol concentration in the mixed fuel with an alcohol concentration sensor. Two types of alcohol concentration sensors, optical type and capacitance type, have been proposed, but the capacitance type is predominant because of its simple structure.

That is, the electrostatic capacitance type alcohol concentration sensor utilizes the fact that the permittivity of the mixed fuel differs depending on the alcohol concentration of the mixed fuel, so that the mixed fuel is passed between the electrode plates and the static electricity between the electrodes is maintained. The alcohol concentration in the mixed fuel is measured by measuring the electric capacity. By the way, since the permittivity of the mixed fuel has temperature dependency, it changes not only with the alcohol concentration (mixing ratio) but also with the fuel temperature. This is because the dielectric constant of methanol has temperature dependence. Therefore, the temperature of the fuel is measured by the temperature sensor, and the correct alcohol concentration is obtained by correcting the temperature according to the fuel temperature. The correction is performed based on the map data, and the map complements the voltage value in the steady state where the temperature of the entire sensor and the fuel temperature are equal. Therefore, a temperature sensor is provided in the alcohol concentration sensor in addition to the capacity detecting electrode to measure the fuel temperature.

Further, in Japanese Patent Laid-Open No. 3-215734, in order to prevent an alcohol concentration detection error due to a temperature difference between the sensor for detecting alcohol concentration and the detection circuit portion, the detection circuit portion is heat-exchanged with the fuel to detect the sensor. And an alcohol concentration sensor which eliminates the temperature difference between the detection circuit section and the detection circuit section.

[0006]

However, when the fuel temperature, which is represented by a high temperature restart, changes transiently, normal temperature correction is not performed and the circuit temperature characteristic of the sensor is large for map correction. Influence. This is because the circuit temperature of the sensor changes with the fuel temperature as a heating element, and it takes time for the circuit temperature to become equal to the fuel temperature. Therefore, there is no problem in the steady state in which the circuit temperature and the fuel temperature are equal, but in the transient state, there is a deviation between the circuit temperature and the fuel temperature, which deviates from the correction map. In other words, the circuit temperature characteristic does not become a problem when the sensor steady value is complemented by the map, but the influence of the circuit temperature characteristic becomes remarkable in the transient state of the sensor.

Also, in the alcohol concentration sensor disclosed in Japanese Patent Laid-Open No. 3-215734, heat exchange with the fuel is not carried out instantaneously, but when the fuel temperature sharply drops, such as during high temperature restart, the sensor There is a possibility that an alcohol concentration detection error may occur due to the temperature difference between the detection circuit and the detection circuit. As a result, there has been a problem that engine control such as fuel injection amount and ignition timing is not normally performed.

Therefore, an object of the present invention is to provide an alcohol concentration sensor capable of accurately detecting the alcohol concentration even during the transition period of the fuel temperature.

[0009]

In order to achieve the above object, according to the present invention, a detection capacitor composed of a pair of electrode plates immersed in a mixed fuel in which gasoline and alcohol are mixed, and this detection capacitor. Power supply for supplying square wave pulsed power to the capacitor for discharge, discharge resistance for discharging the electric charge accumulated in the pair of detection capacitors by the pulse power supply, and discharge as a signal proportional to the alcohol concentration of the mixed fuel. and threshold setting means for voltage raises the predetermined threshold value with an output unit for outputting a voltage proportional to the which time more than a predetermined threshold value, the decrease in temperature <br/> degree of the mixed fuel, An alcohol concentration sensor equipped with is used.

[0010]

According to the alcohol concentration sensor of the present invention, the electric charge accumulated in the detection capacitor by the pulse power supply is discharged by the discharge resistance. The output unit outputs a voltage proportional to the time when the discharge voltage is equal to or higher than a predetermined threshold value. During reduction of the fuel temperature, the discharge voltage will be shifted to the high voltage side, the predetermined threshold is raised by the threshold value setting means.

[0011]

EXAMPLES Hereinafter, a first example of the alcohol concentration sensor of the present invention will be described .
Examples will be described with reference to the drawings. FIG. 1 shows the structure of the alcohol concentration sensor of the present invention. Housing 11 is hollow, to a fuel pump (not shown) from the discharged fuel fuel engine via the discharge-side fuel passage 112 enters the housing 11 through the supply-side fuel passage 111 (not shown) Supplied.

A holder 13 is mounted on the top of the housing 11, and a substrate 1 forming an electronic circuit is provided in the holder 13.
31 is stored. The temperature sensor 132 and the temperature sensor 133 attached to the substrate 131 for compensating the alcohol concentration by the temperature change of the mixed fuel are the case 134.
Is installed in such a manner that the temperature detecting portion penetrates the holder 13 and the housing 11 and is immersed in the mixed fuel.

A pair of electrode plates 11 for detecting alcohol concentration
Detection capacitor 1 composed of 3a and 113b
13 is installed on a stud 114 made of an insulating material via a spacer 115 also made of an insulating material. Similarly, a pair of electrode plates 116 for detecting fuel resistance
The resistance detecting capacitor 116 composed of a and 116b is also installed on the stud 117 made of an insulating material via a spacer 118 also made of an insulating material. The resistance detecting capacitor 116 has the same structure and the same shape as the pair of electrodes 113 of the detecting capacitor.

A pair of lead wires 119 and 120 are drawn out to the detection capacitor 113 and connected to the substrate 131, and a pair of terminals 1 penetrating the holder 13 and the housing 11 are connected.
35 and 136. That is, the detection capacitor 113 is used to measure the dielectric constant depending on the alcohol concentration existing between the electrode plates. Similarly, the pair of lead wires 1 is connected to the resistance detecting capacitor 116.
21 and 122 are pulled out, connected to the substrate 131, and pass through the holder 13 and the housing 11. A pair of terminals 137.
And 138. That is, the resistance detecting capacitor 116 is used to measure the resistivity depending on the alcohol concentration existing between the electrode plates.

The electronic circuit output on the substrate 131 is taken out by a cable 125 as an electric signal to the outside. Figure 2 is a circuit diagram of the alcohol concentration sensor which is formed on the substrate 131, the pulse oscillation section 21, and a detecting unit 22 and the output unit 23. Pulse oscillation unit 21,
A CR oscillation circuit composed of the inverters 211, 212, 213, the resistor 214 and the capacitor 215 applies a square wave pulse having a frequency of 500 kHz or more to the detection unit 22.

The detection unit 22 includes a detection capacitor 113, a resistance detection capacitor 116, a discharge resistor 221, a clamp diode 222, and a threshold control diode 223, 2.
24, comparator 225, threshold adjustment resistor 226,
227, 230, parasitic fuel resistance 22 of capacitor 113
8 , parasitic fuel resistance 229 of capacitor 116 , and power supply
236, and converts the capacitance generated between the detection electrodes into an electric (voltage) signal.

When a square wave pulse having a constant frequency generated from the pulse oscillating section 21 is applied to a differentiating circuit composed of a detecting capacitor 113 having a capacitance proportional to the alcohol concentration and a discharge resistor 221, the capacitance is increased. A differential waveform corresponding to is obtained. This waveform shows the detection capacitor 11
3 is a voltage obtained by converting the discharge current when the charge charged in No. 3 is discharged by the discharge resistor 221. Then, since the time required for the comparator 225 to reach the predetermined voltage is proportional to the electrostatic capacitance, the electrostatic capacitance is converted into an electric signal (pulse width). At this time, the electric signal having the information of the detection capacity is a rectangular wave pulse, and the pulse width represents the detection capacity, that is, the alcohol concentration. However, the threshold of the comparator 225 is a by <br/> the magnitude Ri variable parasitic fuel resistance 229, the power supply voltage and the voltage between the ground GND and parasitic fuel resistance 229 Threshold control diode 22
The voltage divided by the resistors 3 and 224 and the adjusting resistor 230 is used as a reference voltage and further divided by the resistors 226 and 227.

The output unit 2 outputs the pulse signal thus obtained.
It is converted into an analog voltage by 3 and output. The conversion circuit is
The FET 23 and the integrating circuit which is composed of the resistor 231 and the capacitor 232 and has a sufficiently large time constant with respect to the signal frequency.
3 and resistors 234 and 235. Next, the alcohol concentration output when the fuel temperature transiently changes, as represented by high temperature restart, will be described with reference to FIG.

When the pulse oscillator 21 applies a square wave having a voltage Vcc and a signal width τ to the detecting capacitor 113,
The capacitor 113 is instantly charged and the potential at the point A is Vcc.
(H level). However, a current flows through the discharge resistor 221, the charge of the capacitor is discharged, and the potential at the point A gradually drops. The rate of decrease of this voltage is determined by the product of the detection capacitor 113 and the discharge resistance 221 (CR time constant), and the discharge resistance is fixed, resulting in a differential waveform proportional to the capacity. Then, after the time τ, when the voltage becomes the L level, the potential at the point A becomes V1−Vcc, where V1 is the voltage at the time when the potential is inverted, and thereafter, this negative voltage (charge) is reduced by the clamp diode 222 in a short time. It is discharged (almost instantly) and returns to the GND level. However, clan flop by the clamp diode 222 is strictly not discharged to GND level settles to the magnitude of the forward voltage Vf as shown in the following equation.

[0020]

[Equation 1] However, m: constant, k: Boltzmann constant, T: absolute temperature, q0: electron charge, Is: reverse saturation current, Id:
Forward current.

This forward voltage Vf is determined by the magnitude of the forward current Id, and this forward current Id depends on the magnitude of the parasitic fuel resistance 228 of the detection capacitor 113. Further, the parasitic fuel resistance 228 has a size proportional to the fuel temperature as shown in FIG. Therefore, the fuel temperature suddenly rises to T1.
When the temperature changes from (high temperature) to T2 (low temperature), the parasitic fuel resistance value greatly changes from R1 to R2, and the forward current changes from (V1-Vcc) / R1 to (V1-Vcc) / R2, and the clamp The forward voltage due to the diode 222 is V
It becomes smaller by ΔVf from f1 to Vf2. In addition, in FIG.
M0 means that the alcohol concentration in the mixed fuel is 0%
Meaning, M100 means that the alcohol concentration is 100%.
Means and.

As a result, the differential waveform at the point A is Vf1.
-Vf2 is shifted in the positive direction, and the comparator 22
Calculate the pulse width with reference to the threshold value Vth1 of 5 Δ
An output error of t occurs. Therefore, in order to correct this output error, a resistance detection capacitor 116 having the same structure and shape as the detection capacitor 113 is provided in the housing 11,
Utilizing the fuel resistance 229 parasitic on this capacitor,
The threshold value is shifted by the amount by which the differential waveform is shifted.

FIG. 5 shows the resistance detecting capacitor 11 described above.
6, parasitic fuel resistance 229, threshold control diode 22
3 shows a variable threshold circuit composed of 3, 224, adjustment resistors 226, 227 and a comparator 225. The threshold value of the converter 225 is a voltage divided value by the voltage adjusting resistors 226 and 227 between the point B and GND, and the voltage at the point B is the parasitic fuel resistance of the voltage between the power source voltage Vcc and GND. 229, the threshold control diodes 223 and 224, and the adjustment resistor 230 provide a divided voltage value.

Since the resistance detecting capacitor 116 has the same structure as the detecting capacitor 113 and is immersed in the fuel in the housing 11, the size of the parasitic fuel resistance 229 is the same as that of the parasitic fuel resistance 228. The forward current becomes equal (id1 = id2), and the threshold adjustment diode 2
23 and 224 have the same forward voltage drop as that of the clamp diode 222. As a result, the potential at point B is 2Δ
Since it is increased by Vf, the adjustment resistors 226 and 227
To make the threshold of the converter 225 Δ
It can be shifted in the positive direction by Vf.

Therefore, by using the variable threshold value comparator 225 of the present invention, even if the fuel temperature (fuel resistance) changes abruptly, the differential waveform shifted by the magnitude of the fuel resistance is interlocked. It can be corrected by changing the value. In addition, the temperature sensor 132 and the clamp diode 2
22 and the threshold value adjusting diodes 223 and 224 are housed in the case 34, and the temperature detecting portion is immersed in the fuel, so that the temperature responsiveness to the temperature sensing element does not matter.

Further, it may have a structure of the second embodiment, such as shown in FIG. 6 as a method of Ru improve the temperature response of the temperature sensitive (temperature measurement) device. 10 in the figure is a case of the sensor,
The mixed fuel passes through the portion where the cylindrical electrode 20 is arranged . The cylindrical electrode 20 includes an electrode stay 30 made of an insulating resin for fixing and insulating the electrode, an outer electrode 21 and an inner electrode 22.
Is installed and configured. The outer electrodes and 21 are provided with holes orthogonal to the axis, which guide the mixed fuel between the electrodes. The cylindrical electrode 20 is used in the case 1
It is attached to the passage of 0 through the insulating resin 31. on the other hand,
The fixed holder 40 of the case 10 mounts a circuit board 50 on which an alcohol detection circuit having a capacity conversion function and a capacity temperature dependency correction function is arranged. Then, a cover 60 for protecting the components including the circuit board 50 is attached. (Note that the cover 60 and the case 10
Also has the function of an electrostatic shield. Here, when the inner electrode 22 is thermally viewed, it is surrounded by insulating resins 30 and 31 for electrical insulation between the outer electrode 21 and the case 10 and electrical insulation between the electrodes. This resin material
In addition to being an electrically insulating material, it also has good thermal insulation, and is thermally insulated from the case 10, that is, the sensor mounting environment, or the circuit board 50. Then, the inner electrode 22
The temperature can be about the same as the fuel temperature. Therefore,
The fuel temperature can be easily measured by attaching the temperature measuring element 70 to the inner electrode 22 and measuring the temperature of the electrode. Therefore, the temperature responsiveness to the temperature sensitive element does not matter. The second embodiment also has the same structure as the first embodiment.
By arranging two detection capacitors like
Accurately, even if there is a sudden temperature change.
Concentration can be detected.

The more fuel temperature response of the temperature sensitive element is improved by the configuration, even at the case where the fuel temperature, such as hot restart suddenly changes, the circuit temperature characteristics of the sensor in the fuel temperature instantly With the matched characteristics, the sensor output is intolerant and enters a steady state (the fuel temperature and the circuit temperature are equal), and accurate fuel temperature correction by the map becomes possible.

[0028]

As is apparent from the above description, according to the alcohol concentration sensor of the present invention, the fuel temperature is lowered and the discharge
When the voltage shifts to the high voltage side, the threshold setting means
Since more threshold is increased, it is possible to fuel temperature such as during hot restart to accurately detect <br/> alcohol concentration change rapidly.

[Brief description of drawings]

FIG. 1 is a structural diagram showing an embodiment of an alcohol concentration sensor of the present invention.

FIG. 2 is a circuit diagram showing an embodiment of an alcohol concentration sensor of the present invention.

FIG. 3 is a signal waveform diagram showing the circuit operation of the embodiment of the alcohol concentration sensor of the present invention.

In the alcohol concentration sensor of the present invention; FIG, fuel temperature - is a view showing resistance value characteristics.

FIG. 5 is a detection unit circuit diagram showing an embodiment of an alcohol concentration sensor of the present invention.

FIG. 6 is a structural diagram of a temperature sensing (temperature measuring) section showing another embodiment of the alcohol concentration sensor of the present invention.

[Explanation of Codes] 11 Housing 113 Detection Capacitor 116 Resistance Detection Capacitor 131 Substrate 132 Temperature Sensor 21 Pulse Oscillator (Pulse Power Supply) 22 Detector 221 Discharge Resistor 222 Clamp Diode 223, 224 Threshold Control Diode 225 Comparator Threshold setting means) 23 Output unit

[Procedure Amendment 2]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 2

[Correction method] Change

[Correction content]

[Fig. 2]

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshikazu Ina 14 Iwatani, Shimohakaku-cho, Nishio-shi, Aichi Japan Auto Parts Research Institute (72) Inventor Ichiro Hosoya 1 Toyota-cho, Toyota-shi, Aichi Toyota Automobile Within the corporation

Claims (1)

[Claims] 1. A detection capacitor composed of a pair of electrode plates immersed in a mixed fuel in which gasoline and alcohol are mixed, and a pulse power supply for supplying square-wave pulsed power to the detection capacitor. A discharge resistance for discharging the electric charge accumulated in the pair of detection capacitors by the pulse power supply, and a voltage proportional to the time when the discharge voltage is equal to or higher than a predetermined threshold as a signal proportional to the alcohol concentration of the mixed fuel. An output section for outputting the temperature, a temperature sensor for measuring the temperature of the mixed fuel, and a threshold setting means for increasing the predetermined threshold value as the temperature of the mixed fuel detected by the temperature sensor decreases. Alcohol concentration sensor.