JP2012185074A - Alcohol concentration detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an alcohol concentration detector capable of accurately detecting alcohol concentration.SOLUTION: An alcohol concentration detector 1 includes: an electrode part 65; a switched capacitor circuit 70; a standard voltage generation circuit 80; an amplifier circuit 90; and a control part 100. The switched capacitor circuit 70 converts capacitance Cp at the electrode part 65 into detection voltage Vb. The amplifier circuit 90 amplifies the detection voltage Vb to be output. The control part 100 acquires output voltage Voutγ amplified by an amplification degree γ, and output voltage Voutβ amplified by an amplification degree β, and corrects the amplification degree β based on the output voltage Voutγ, Voutβ, and the amplification degree γ. By correcting the amplification degree, generation of difference in alcohol concentration to be calculated by the amplification degree due to influences by an error, etc. can be avoided, and the alcohol concentration in liquid can be accurately detected.

Description

  The present invention relates to an alcohol concentration detection device that detects an alcohol concentration in a liquid.

Conventionally, for example, an alcohol concentration detection device that detects an ethanol concentration in a mixed liquid in which gasoline and ethanol are mixed is known. In the alcohol concentration detection device, a capacitance body is formed by two electrodes and a liquid between the electrodes to form a concentration sensor, and the alcohol concentration is detected based on the capacitance.
The dielectric constant of the mixed liquid of gasoline and ethanol has a strong non-linearity especially in the region where the ethanol concentration is low. For this reason, in Patent Document 1, the ethanol concentration detection accuracy is increased by increasing the gain in a region where the change in voltage corresponding to the ethanol concentration is small.

JP 2010-133930 A

By the way, when a plurality of resistors having different resistance values are provided and the gain is switched by switching the resistors to be used as in Patent Document 1, for example, there is a possibility that an error may occur in the alcohol concentration detected due to individual variation of the resistance.
This invention is made | formed in view of the above-mentioned subject, The objective is to provide the alcohol concentration detection apparatus which can detect alcohol concentration accurately.

  The alcohol concentration detection apparatus according to claim 1 includes an electrode unit, a voltage conversion unit, a voltage application unit, an amplification unit, an amplification degree switching unit, a voltage acquisition unit, and a correction unit. The electrode portion detects a capacitance that is immersed in the liquid and changes in accordance with the alcohol concentration in the liquid. The voltage conversion unit converts the capacitance in the electrode unit into a detection voltage. The voltage application unit applies a voltage to the voltage conversion unit. The amplifying unit amplifies and outputs the detection voltage. The amplification degree switching means switches the amplification degree of the detection voltage. The voltage acquisition means is a first output voltage that is a detection voltage amplified with a reference first amplification factor, and a detection voltage that is amplified with a second amplification factor different from the first amplification factor. A second output voltage is obtained. The correcting means outputs the first output so that the alcohol concentration in the liquid calculated based on the first output voltage matches the alcohol concentration in the liquid calculated based on the second output voltage. The second amplification degree is corrected based on the voltage, the second output voltage, and the first amplification degree.

  In the present invention, since the amplification degree can be switched, for example, when the alcohol concentration is low, the detection voltage can be appropriately amplified by increasing the amplification degree, and the alcohol concentration can be detected with high accuracy. In addition, by correcting the second amplification degree based on the first amplification degree as a reference, it is possible to avoid a difference in the alcohol concentration calculated by the amplification degree due to the influence of an error or the like. It is possible to calculate an accurate alcohol concentration regardless of the amplification degree. Therefore, the alcohol concentration in the liquid can be detected with high accuracy. In addition, for example, if the alcohol concentration at the first amplification degree that is a reference at the time of product shipment inspection is confirmed, the second amplification degree can be corrected, so that the number of inspection steps can be reduced.

  In the invention according to claim 2, the amplifying unit includes an operational amplifier and a plurality of gain resistors having different resistance values that can be connected in parallel to the operational amplifier. The amplification degree switching means switches the amplification degree by switching a gain resistor connected to the operational amplifier. Thereby, the amplification degree can be easily switched. Even if there is an error between the actual resistance value and the set value of the gain resistor, the alcohol concentration can be detected with high accuracy by correcting the amplification degree.

  In a third aspect of the present invention, the voltage application unit includes a first resistor and a plurality of second resistors having different resistance values. The second resistor can be connected in series with the first resistor, and constitutes a voltage dividing resistor by being connected to the first resistor. The amplification degree switching means switches the amplification degree by switching the second resistance connected to the first resistance. That is, in the present invention, the amplification degree is changed by changing the voltage applied to the voltage conversion unit by the voltage application unit. Thereby, the amplification degree can be easily switched. Even if there is an error between the actual value and the set value of the ratio between the first resistance value and the second resistance value constituting the voltage dividing resistor, the alcohol concentration can be accurately corrected by correcting the amplification degree. Can be detected.

It is a mimetic diagram explaining a fuel supply system by a 1st embodiment of the present invention. It is sectional drawing which shows the sensor part of the alcohol concentration detection apparatus by 1st Embodiment of this invention. It is a circuit diagram which shows the structure of the alcohol concentration detection apparatus by 1st Embodiment of this invention. It is a graph which shows the relationship between the ethanol concentration and detection voltage in 1st Embodiment of this invention. It is a graph which shows the relationship between the ethanol concentration and output voltage in 1st Embodiment of this invention. It is a flowchart explaining the correction process by 1st Embodiment of this invention. It is a flowchart explaining the correction process by 1st Embodiment of this invention. It is a circuit diagram which shows the structure of the alcohol concentration detection apparatus by 2nd Embodiment of this invention.

Hereinafter, an alcohol concentration detection apparatus according to the present invention will be described with reference to the drawings.
Hereinafter, in a plurality of embodiments, substantially the same configuration is denoted by the same reference numeral, and description thereof is omitted.
(First embodiment)
The alcohol concentration detection device according to the first embodiment of the present invention is used to detect the ethanol concentration in a mixed liquid of gasoline and ethanol as fuel supplied to a vehicle engine.

  First, FIG. 1 shows a fuel supply system in which the alcohol concentration detection device of this embodiment is used. As shown in FIG. 1, the alcohol concentration detection device 1 is provided in a fuel supply system of an engine (not shown). The alcohol concentration detection device 1 is provided in a fuel pipe 4 that connects a fuel tank 2 and a delivery pipe 5. The fuel tank 2 stores a fuel in which gasoline and ethanol are mixed. The fuel tank 2 can be optionally supplied with a mixed liquid of gasoline and ethanol, gasoline, and ethanol. Therefore, the ethanol concentration in the fuel in the fuel tank 2 may fluctuate from the time of refueling. The fuel in the fuel tank 2 is pumped by a fuel pump 3 through a fuel pipe 4 to a delivery pipe 5 and injected from an injector 6 into an intake pipe or a cylinder (not shown). The injector 6 is electrically driven and controlled by an ECU (electronic control unit) 7 of the engine. The ECU 7 is composed of a microcomputer or the like, and receives a detection signal from the alcohol concentration detection device 1 and various detection signals related to the engine. In the present embodiment, in order to operate the engine under the optimum conditions (for example, the amount of harmful substances contained in the exhaust gas is minimum and the fuel saving condition), the alcohol concentration detection device 1 detects the ethanol concentration of the fuel supplied to the engine. In accordance with the detected ethanol concentration, various control parameters such as the air-fuel ratio, the fuel injection amount, and the ignition timing are appropriately controlled. In order to operate the engine under optimum conditions, it is preferable to provide the alcohol concentration detection device 1 so as to detect the ethanol concentration at a position as close as possible to the injector 6.

As shown in FIG. 2, the alcohol concentration detection apparatus 1 includes a first housing 10, connection pipes 20, 21, a first electrode 31, a second electrode 32, a thermistor 40, a second housing 50, a circuit unit 60, and the like. It is configured.
The first housing 10 is formed in a substantially cylindrical shape from a metal such as stainless steel. A fuel chamber 11 is formed inside the first housing 10. Connection pipes 20 and 21 are screwed to both ends of the first housing 10 in the axial direction (left and right direction in FIG. 2) with the seal members 12 and 13 interposed therebetween. The connecting pipes 20 and 21 are formed in a cylindrical shape from a metal such as stainless steel. A passage 22 is formed inside the connection pipe 20, and a passage 23 is formed inside the connection pipe 21. The passages 22 and 23 communicate with the fuel chamber 11. A claw 24 that protrudes radially outward is formed in the middle of the connecting pipe 20 in the axial direction, and a claw 25 that protrudes radially outward is formed in the middle of the connecting pipe 21 in the axial direction. The connecting pipes 20 and 21 are connected to the fuel pipe 4 (see FIG. 1) via connectors (not shown) connected to the claws 24 and 25. As a result, fuel is supplied to the passage 22 of the connection pipe 20, the passage 23 of the connection pipe 21, and the fuel chamber 11 of the first housing 10.

The first electrode 31 is formed in a substantially cylindrical shape with a metal such as stainless steel, for example, and is substantially perpendicular to the axial direction of the first housing 10 from the opening 14 formed on one side in the radial direction of the first housing 10. It is inserted into the fuel chamber 11 of the first housing 10. The second electrode 32 is formed in a bottomed cylindrical shape from a metal such as stainless steel, and is accommodated in a space 35 formed on the radially inner side of the first electrode 31. A glass seal 36 is provided between the radially inner wall of the first electrode 31 and the radially outer wall of the second electrode 32. Thereby, the 1st electrode 31 and the 2nd electrode 32 are fixed. The glass seal 36 electrically insulates the first electrode 31 and the second electrode 32 from each other.
The first electrode 31 has fuel holes 33 and 34 communicating with the radial direction. The fuel in the fuel chamber 11 of the first housing 10 flows into the space 35 between the first electrode 31 and the second electrode 32 via the fuel holes 33 and 34. Thereby, the first electrode 31 and the second electrode 32 function as a capacitor by using the fuel flowing into the space 35 as a dielectric. Although details will be described later, this capacitor is referred to as “capacitor 66” in the circuit diagram of FIG.

  The thermistor 40 is a temperature detection element whose electrical resistance changes with temperature changes. The thermistor 40 is accommodated inside the second electrode 32 and is in contact with the inner wall of the bottom of the second electrode 32. Thereby, the temperature of the fuel in the space 35 between the first electrode 31 and the second electrode 32 is conducted to the thermistor 40 via the bottom of the second electrode 32. A heat conductive member such as heat radiation grease may be filled between the inner wall at the bottom of the second electrode 32 and the thermistor 40.

The second housing 50 is formed into a bottomed cylindrical shape, for example, with resin or the like, and the bottom 51 is fixed at a position corresponding to the opening 14 of the first housing 10. The bottom 51 of the second housing 50 is provided with an accommodation hole 57 for accommodating the end of the second electrode 32 that is not immersed in fuel.
An annular packing 52 and a plate-like elastic member 53 are provided between the second housing 50 and the first housing 10. The packing 52 prevents water or the like from entering between the second housing 50 and the first housing 10 from the outside. The elastic member 53 has an opening substantially in the center, and the second electrode 32 is fitted in this opening.

  A plate-like lid 54 is provided at the opening of the second housing 50 opposite to the first housing 10 to prevent water and the like from entering the second housing 50 from the outside. The lid 54 is fixed by a plate-like spring 56 that is locked to a locking portion 55 that protrudes radially outward of the second housing 50. Accordingly, the first electrode 31 is pressed against the first housing 10 via the elastic member 53.

  The circuit unit 60 is composed of a plurality of electronic components provided on the printed wiring board, and is accommodated inside the second housing 50. The circuit unit 60 and the first electrode 31 are connected by a first conductor 37. The circuit unit 60 and the second electrode 32 are connected by a second conductor 38. The circuit unit 60 and the thermistor 40 are connected by a third conductor 41 and a fourth conductor 42.

Here, the circuit configuration of the alcohol concentration detection apparatus 1 will be described with reference to FIG. In FIG. 3, the configuration related to temperature detection by the thermistor 40 is omitted.
The alcohol concentration detection apparatus 1 is supplied with power from the battery 111 via the ignition switch 110. The output terminal 115 of the alcohol concentration detection device 1 is connected to the ECU 7. Thereby, an ethanol concentration detection signal related to the ethanol concentration in the fuel detected by the alcohol concentration detection device 1 is output to the ECU 7.
A constant voltage regulator 116 is provided between the alcohol concentration detection device 1 and the battery 111. The constant voltage regulator 116 converts the voltage from the battery 111 into a predetermined voltage and stabilizes it. In the present embodiment, the battery voltage (for example, 12V) is converted to 5V by the constant voltage regulator 116 and applied to the alcohol concentration detection apparatus 1.

  The alcohol concentration detection apparatus 1 includes an electrode unit 65, a switched capacitor circuit 70 as a voltage conversion unit, a standard voltage generation circuit 80 as a voltage application unit, an amplification circuit 90 as an amplification unit, a control unit 100, and the like. . In the present embodiment, the electrode portion 65 is configured by the first electrode 31, the second electrode 32, and the fuel that flows into the space 35 between the first electrode 31 and the second electrode 32. In addition, electronic components such as the switched capacitor circuit 70, the standard voltage generation circuit 80, the amplifier circuit 90, and the control unit 100 are provided in the circuit unit 60.

  As described above, the electrode portion 65 is configured by the first electrode 31, the second electrode 32, and the fuel that flows into the space 35 between the first electrode 31 and the second electrode 32. The fuel flowing into the space 35 acts as a dielectric, and a capacitance body is formed by the first electrode 31, the second electrode 32, and the fuel flowing into the space 35. This capacitance body is described as a capacitor 66 in FIG. The capacitance of the capacitor 66 has a correlation with the ethanol concentration at a constant temperature. Specifically, at a certain temperature, the capacitance increases as the ethanol concentration increases. In the present embodiment, this characteristic is used to measure the ethanol concentration in the fuel based on the capacitance of the capacitor 66. Further, since the fuel temperature and the capacitance have a correlation at a constant ethanol concentration, the temperature characteristic correction is performed based on the fuel temperature detected by the thermistor 40.

  Further, between the first electrode 31 and the second electrode 32, there is a leakage resistance that is an electrical resistance via the fuel flowing into the space 35. This leakage resistance can be regarded as being connected in parallel with the capacitor 66 on the electric circuit, and is described as a leakage resistance 67 connected in parallel with the capacitor 66 in FIG. The leak resistance 67 varies depending on fuel properties such as moisture content.

  The switched capacitor circuit 70 includes an inverter 71 and two switches 72 and 73. At the point A of the switched capacitor circuit 70, as the two types of pulse wave voltages having different frequencies from the control unit 100, the first frequency pulse wave voltage having the first frequency f1 and the frequency having the second frequency f2 are used. A second frequency pulse wave voltage is applied. The two switches 72 and 73 are both closed when the applied pulse wave voltage is at a high level and open when the pulse wave voltage is at a low level. The pulse wave voltage from the control unit 100 is directly applied to one switch 72, and the pulse wave voltage from the control unit 100 is applied to the other switch 73 via the inverter 71. Thereby, a pulse wave voltage having the same frequency and opposite phase is applied to the switch 72 and the switch 73. Therefore, when the pulse wave voltage applied to the switch 72 is at a high level, the pulse wave voltage applied to the switch 73 is at a low level. At this time, the switch 72 is closed and the switch 73 is opened. When the pulse wave voltage applied to the switch 72 is at a low level, the pulse wave voltage applied to the switch 73 is at a high level. At this time, the switch 72 is opened and the switch 73 is closed. That is, the opening / closing operation of the switch 72 and the opening / closing operation of the switch 73 are opposite in timing. Accordingly, when the first frequency pulse voltage is applied from the control unit 100 to the switched capacitor circuit 70, the switches 72 and 73 are opened and closed at the first frequency f1 and at the opposite timing. Further, when the second frequency pulse voltage is applied from the control unit 100 to the switched capacitor circuit 70, the switches 72 and 73 are opened and closed at the second frequency f2 and at the opposite timing.

  The standard voltage generation circuit 80 includes an operational amplifier 81, resistors 82 and 83, and the like. The standard voltage generation circuit 80 divides the voltage stabilized by the constant voltage regulator 116 into the ratio of the resistors 82 and 83 and applies the divided voltage to the switched capacitor circuit 70.

  The amplifier circuit 90 includes an operational amplifier 91, gain resistors 92, 94, 96, gain resistor changeover switches 93, 95, 97, and the like. The gain resistors 92, 94, and 96 are configured by resistors having different resistance values, and are provided in parallel. In the present embodiment, the gain resistors 92, 94, and 96 are in order from the smaller resistance value. That is, the resistance value of the gain resistor 92 is the smallest and the resistance value of the gain resistor 96 is the largest. In addition, the gain resistor 92 and the gain resistor selector switch 93 are connected in series, the gain resistor 94 and the gain resistor selector switch 95 are connected in series, and the gain resistor 96 and the gain resistor selector switch 97 are connected in series. . The gain resistance changeover switches 93, 95, and 97 are controlled to be opened and closed by a drive signal from the control unit 100. Thus, by switching the open / closed state of the gain resistance changeover switches 93, 95, 97, the resistance value of the resistor connected to the operational amplifier 91 and functioning as a gain resistor, that is, the amplification degree in the amplifier circuit 90 can be switched.

  The controller 100 operates when a voltage stabilized by the constant voltage regulator 116 is applied. The control unit 100 is configured by a known microcomputer, for example. The control unit 100 acquires the output voltage Vout amplified by the amplifier circuit 90, and calculates the ethanol concentration in the fuel based on the acquired output voltage Vout. In the present embodiment, the ethanol concentration in the fuel is calculated after the output voltage Vout is converted into a capacitance. Then, an ethanol concentration signal related to the ethanol concentration calculated by the control unit 100 is output to the ECU 7 via the output terminal 115.

Here, the ethanol concentration detection by the alcohol concentration detection apparatus 1 will be described.
When the operation of the alcohol concentration detection device 1 is started, the control unit 100 alternately applies the first frequency pulse wave voltage and the second frequency pulse wave voltage to the point A of the switched capacitor circuit 70. As described above, when the first frequency pulse wave voltage and the second frequency pulse wave voltage are applied to the point A of the switched capacitor circuit 70, the switches 72 and 73 are synchronized with the frequency of the applied pulse wave voltage. And it opens and closes at the opposite timing.

  When the switch 72 is open and the switch 73 is closed, the standard voltage E is applied to the electrode portion 65 from the standard voltage generation circuit 80 via the switch 73. At this time, the current i1 flows through the capacitor 66, and the current i2 flows through the leak resistor 67. The current i1 flowing through the capacitor 66 rises immediately after the standard voltage E is applied, and becomes zero when the capacitor 66 is completely charged. In addition, the current i <b> 2 flowing through the leak resistor 67 that is considered to be connected in parallel with the capacitor 66 has a constant value while the standard voltage E is applied to the electrode portion 65.

On the other hand, when the switch 72 is closed and the switch 73 is open, the standard voltage E is not applied to the electrode portion 65 from the standard voltage generation circuit 80 via the switch 73, and is charged via the switch 72. A current i1 flows from the capacitor 66 to the ground side. The direction in which the current i1 flows is opposite to the case where the switch 72 is open and the switch 73 is closed. When the discharge of the capacitor 66 ends, the current i1 becomes zero. Further, the current i2 flowing through the leak resistance 67 is zero.
That is, by switching the opening and closing of the switches 72 and 73, the charging state in which the charge is stored in the capacitor 66 and the discharging state in which the charge is discharged from the capacitor 66 are switched.

Next, a voltage output from the operational amplifier 81 when the opening and closing of the switches 72 and 73 are switched at the first frequency f1 or the second frequency f2, that is, a point B voltage Vb that is a voltage at the point B in FIG. Will be described.
First, the average value of the current i2 flowing through the leak resistor 67 is expressed by the following equation (1).
i2 = 0.5 × E × Rp (1)
Here, Rp is the resistance value of the leak resistor 67.

Further, the electric charge ΔQ stored in the capacitor 66 is expressed by the following equation (2), where Cp is the capacitance of the capacitor 66.
ΔQ = Cp × E (2)
Since the average value of the current i1 is a time derivative of the charge ΔQ, it is expressed by the following formula (3).
i1 = ΔQ / T
= Cp x E / T
= Cp × T × f (3)
However, T is a period and is the reciprocal (1 / f) of the frequency T.
Here, as is apparent from the equation (3), the magnitude of the current i 1 discharged from the capacitor 66 is proportional to the frequency f of the pulse wave voltage applied to the point A of the switched capacitor circuit 70.

Further, the point B voltage Vb is expressed by the following expression (4) from the expressions (1) and (3).
Vb = E + Rg × (i1 + i2)
= E + Rg × {(Cp × E / T) + 0.5 × E / Rp}
= E * {1+ (0.5 * Rg / Rp) + Rg * Cp + f} (4)
However, Rg is the resistance value of the resistor 86.

  Here, the equation (4) representing the B point voltage Vb that changes according to the ethanol concentration in the fuel includes Rp that is the resistance value of the leak resistor 67. The resistance value Rp of the leak resistance 67 varies depending on the ratio of conductive impurities such as water contained in the fuel. For this reason, the resistance value Rp of the leak resistor 67 changes depending on the ratio of impurities in the fuel, so that the ethanol concentration detection accuracy decreases.

Therefore, in the present embodiment, by alternately applying two types of pulse wave voltages having different frequencies to the switched capacitor circuit 70, the influence of the leak resistor 67 is eliminated and the ethanol concentration detection accuracy is improved.
Specifically, it is as follows.
The point B voltage Vb1 when the switches 72 and 73 are opened and closed at the frequency f1 is expressed by the following equation (5).
Vb1 = E × {1+ (0.5 × Rg / Rp) + Rg × Cp + f1} (5)

Further, the point B voltage Vb2 when the switches 72 and 73 are opened and closed at the frequency f2 is expressed by the following equation (6).
Vb2 = E × {1+ (0.5 × Rg / Rp) + Rg × Cp + f2} (6)

The difference between the point B voltage Vb1 when the switches 72 and 73 are opened and closed at the frequency f1 and the point B voltage Vb2 when the switches 72 and 73 are opened and closed at the frequency f2 is expressed by the following equation (7). Is done.
Vb1-Vb2 = E * (f1-f2) * Rg * Cp (7)

  As described above, by using the point B voltage Vb1 when the switches 72 and 73 are opened / closed at the frequency f1 and the point B voltage Vb2 when the switches 72 and 73 are opened / closed at the frequency f2, the detection of the ethanol concentration is performed. The resistance value Rp of the leak resistor 67 is eliminated from the equation, and the influence of the leak resistor 67 in detecting the ethanol concentration can be eliminated. Thereby, the detection precision of ethanol concentration improves.

  Hereinafter, the difference between the frequency f1 and the frequency f2 is referred to as “difference frequency Δf”, and in this embodiment, the difference frequency Δf is 400 kHz. Further, the B point voltage Vb1−Vb2 calculated by the above equation (7) is a value obtained by converting the electrostatic capacitance Cp of the electrode portion 65, and changes according to the alcohol concentration in the fuel. Therefore, in the present embodiment, when the difference frequency Δf is 400 kHz, the alcohol concentration in the fuel is detected based on Vb1−Vb2 calculated by the above equation (7). Hereinafter, the above equation (7) is detected. Vb1−Vb2 calculated in the above is simply referred to as “detection voltage Vb”.

Here, the relationship between the detection voltage Vb and the ethanol concentration in the fuel will be described with reference to FIG.
As shown in FIG. 4, the detection voltage Vb and the ethanol concentration in the fuel have a correlation. When the ethanol concentration in the fuel is greater than or equal to a certain value Xa, the relationship between the detection voltage Vb and the ethanol concentration in the fuel is substantially linear. On the other hand, when the ethanol concentration in the fuel is less than a certain value Xa, the relationship between the detection voltage Vb and the ethanol concentration in the fuel is exponential. That is, when the ethanol concentration in the fuel is low, the change amount of the detection voltage Vb with respect to the ethanol concentration change amount is smaller than in the case where the ethanol concentration in the fuel is high. In other words, the resolution related to ethanol concentration detection based on the detection voltage Vb is low.

Therefore, in this embodiment, the detection accuracy of the ethanol concentration in the fuel is increased by switching the amplification degree. In the present embodiment, the amplification degree is switched by switching the gain resistors 92, 94, 96 connected to the operational amplifier 91 in the amplifier circuit 90.
Referring to the relationship between the resistance value of the gain resistor connected to the operational amplifier 91 in the amplifier circuit 90 and the amplification factor, the greater the resistance value of the gain resistor, the greater the amplification factor and the smaller the resistance value of the gain resistor. Amplification is small. That is, in this embodiment, the gain is the highest when the gain resistor 96 having the largest resistance value is used, and the amplification is the smallest when the gain resistor 92 having the smallest resistance value is used. In the present embodiment, the amplification factor when the gain resistor 96 is used is α, the amplification factor when the gain resistor 94 is used is β, the amplification factor when the gain resistor 92 is used is γ, and the amplification factors α, β , Γ is α>β> γ.

  Here, switching of the amplification degree will be described with reference to FIG. In FIG. 5, the horizontal axis represents the ethanol concentration in the fuel, and the vertical axis represents the output voltage Vout output from the amplifier circuit 90. The output voltage Vout is a voltage applied to the point H in FIG. In FIG. 5, the solid line represents the relationship between the output voltage Vout and the ethanol concentration when the resistance values of the gain resistors 92, 94, and 96 are as set values.

As shown in FIG. 5, when the ethanol concentration in the fuel is X2 or less, the ethanol concentration can be calculated using the gain resistor 96. At this time, the output voltage Voutα output from the amplifier circuit 90 is amplified with the amplification degree α and becomes as indicated by the solid line Lα.
Further, when the ethanol concentration in the fuel is not less than X1 and not more than X4, the ethanol concentration can be calculated using the gain resistor 94. At this time, the output voltage Voutβ output from the amplifier circuit 90 is amplified with the amplification degree β and is as indicated by the solid line Lβ.
Furthermore, when the ethanol concentration in the fuel is X3 or more, the ethanol concentration can be calculated using the gain resistor 92. At this time, the output voltage Voutγ output from the amplifier circuit 90 is amplified with the amplification degree γ, as shown by the solid line Lγ.

  In this embodiment, the amplification degree is switched by switching the gain resistor connected to the operational amplifier 91 according to the ethanol concentration in the fuel. That is, when the ethanol concentration in the fuel is low and the output voltage Vout is small, the resolution is improved by connecting the gain resistor 96 having a large resistance value to the operational amplifier 91 to increase the amplification degree. This increases the detection accuracy of the ethanol concentration in the fuel.

  In the present embodiment, the ethanol concentration can be calculated using either the concentration region R1 in which the ethanol concentration can be calculated using either the gain resistor 96 or the gain resistor 94, and the gain resistor 94 or the gain resistor 92. A high density region R2 is provided. Specifically, in the concentration region R1 where the ethanol concentration is X1 or more and X2 or less, the ethanol concentration can be calculated using either the gain resistor 96 or the gain resistor 94, and the ethanol concentration is X3 or more and X4 or less. In the region R2, the ethanol concentration can be calculated using either the gain resistor 94 or the gain resistor 92.

When the ethanol concentration is in the concentration region R1 that is not less than X1 and not more than X2, the ethanol concentration can be calculated using the gain resistor 96 or the gain resistor 94. When the ethanol concentration is X1, the output voltage Voutα when using the gain resistor 96 is V _{[alpha] 1,} the output voltage Voutβ when using the gain resistor 94 is V _.beta.1. Further, when the ethanol concentration is X2, the output voltage Voutα when using the gain resistor 96 is V _{[alpha] 2,} the output voltage Voutβ when using the gain resistor 94 is V _.beta.2. Here, when the output voltage Voutα when the gain resistor 96 is used is V _α1 or more and V _α2 or less, it can be said that the ethanol concentration can also be calculated using the gain resistor 94. Further, when the output voltage Voutβ when using the gain resistor 94 is not less than V _{β1 and not} more than V _β2 , it can be said that the ethanol concentration can also be calculated using the gain resistor 96.

Similarly, in the concentration region R2 where the ethanol concentration is X3 or more and X4 or less, the ethanol concentration can be calculated using the gain resistor 94 or the gain resistor 92. When the ethanol concentration is X3, the output voltage Voutβ when using the gain resistor 94 is V _.beta.3, the output voltage Voutγ when using the gain resistor 92 is V _.gamma.1. Further, when the ethanol concentration is X4, the output voltage Voutβ when using the gain resistor 94 is V _beta4, the output voltage Voutγ when using the gain resistor 92 is V _.gamma.2. Here, when the output voltage Voutβ when the gain resistor 94 is used is V _β3 or more and V _β4 or less, it can be said that the ethanol concentration can also be calculated using the gain resistor 92. Further, when the output voltage Voutγ when the gain resistor 92 is used is not less than V _{γ1 and not} more than V _γ2, it can be said that the ethanol concentration can be calculated even if the gain resistor 94 is used.

  Incidentally, the output voltage Voutβ when the gain resistor 94 is used is as indicated by a solid line Lβ in design, but is different from the design value as indicated by a broken line M due to individual variation of the gain resistor 94, for example. There is a risk of becoming. As described above, when the actual resistance values of the gain resistors 92, 94, and 96 are different from the designed resistance values, an error may occur in the calculated alcohol concentration by switching the gain resistor to be used. .

  Therefore, in the present embodiment, when the ethanol concentration in the fuel is a concentration region that can be calculated by two gain resistors, the gain to be used is learned by learning the characteristics of the other amplification based on the reference amplification. The amplification degree is corrected so that an error does not occur in the alcohol concentration calculated with the resistance switching. Hereinafter, the concentration region R1 in which the ethanol concentration can be calculated by the gain resistor 96 and the gain resistor 94 is referred to as a “first learning region R1”, and the concentration region R2 in which the ethanol concentration can be calculated by the gain resistor 94 and the gain resistor 92. Is referred to as "second learning region R2".

Here, the correction process executed by the control unit 100 will be described with reference to FIGS. In the present embodiment, it is assumed that an inspection is performed with the gain γ using the gain resistor 96 before product shipment, and it is confirmed that the characteristic is within the standard.
In the first step S101 (hereinafter, “step” is omitted and is simply indicated by the symbol “S”), the control unit 100 is initialized.

  In S102, the gain resistance changeover switches 93 and 97 are opened, the gain resistance changeover switch 95 is closed, and the gain resistance 94 is connected to the operational amplifier 91 to obtain the output voltage Voutβ. Since the gain resistor 94 is selected, the detected output voltage Vb of the acquired output voltage Voutβ is amplified with the amplification factor β. Here, since the ethanol concentration in the fuel is unknown, the output voltage Voutβ is first obtained by using the gain resistor 94, but the gain resistor used first may be another gain resistor.

In S103, output voltage Voutβ acquired in S102 it is determined whether V _.beta.3 or more. V _β3 is a voltage corresponding to the lower limit value of the first learning region, in other words, a voltage corresponding to a region in which the ethanol concentration can be calculated using the gain resistor 92. When it is determined that the output voltage Voutβ is smaller than V _β3 (S103: NO), the process proceeds to S111 in FIG. When it is determined that the output voltage Voutβ is equal to or higher than V _β3 (S103: YES), the process proceeds to S104.

In S104, the gain resistance changeover switches 95 and 97 are opened, the gain resistance changeover switch 93 is closed, and the gain resistance 92 is connected to the operational amplifier 91. The amplification degree at this time is γ.
In S105, the output voltage Voutγ is acquired. Note that the detected output voltage Vb of the acquired output voltage Voutγ is amplified with the amplification degree γ.

In S106, it is determined whether the output voltage Voutγ acquired in S105 is V _γ1 or more and V _γ2 or less. V _γ1 is a voltage corresponding to the lower limit value of the second learning region R2, and V _γ2 is a voltage corresponding to the upper limit value of the second learning region R2. That is, in this step, it can be said that it is determined whether or not the ethanol concentration in the fuel is within the second learning region R2. If it is determined that the output voltage Voutγ is smaller than V _γ1 or the output voltage Voutγ is larger than V _γ2 (S106: NO), that is, if the ethanol concentration in the fuel is not within the second learning region R2, go to S109. Transition. If it is determined that the output voltage Voutγ is not less than V _{γ1 and not} more than V _γ2 (S106: YES), that is, if the ethanol concentration in the fuel is within the second learning region R2, the process proceeds to S107.

In S 107, the gain resistance changeover switches 93 and 97 are opened, the gain resistance changeover switch 95 is closed, and the gain resistance 94 is connected to the operational amplifier 91. The amplification degree at this time is β.
In S108, the output voltage Voutβ is acquired. Note that the detected output voltage Vb of the acquired output voltage Voutβ is amplified with the amplification degree β.

In S109, the correction coefficient Kβ related to the correction of the output voltage Voutβ is learned based on the output voltages Voutγ and Voutβ and the amplification degree γ.
Here, a learning method of the correction coefficient Kβ will be described. The actual amplification degree β when the gain resistor 94 is used is expressed by the following equation (8).
β = Voutβ / Voutγ × γ (8)
If the designed amplification degree when using the gain resistor 94 is βt, a correction coefficient Kβ for the amplification degree β is expressed by the following equation (9).
Kβ = βt / β (9)
If the equation (8) is substituted into the equation (9), the correction coefficient Kβ is expressed by the following equation (10) and is calculated as a constant.
Kβ = (Voutγ × βt) / (Voutβ × γ) (10)
When the output voltage Voutβ is corrected using the correction coefficient Kβ and converted into the capacitance Cpβ, the capacitance Cpβ is expressed by the following equation (11). Cβ in the equation is a conversion factor from the output voltage Voutβ to the capacitance Cpβ.
Cpβ = Voutβ / (βt × Kβ) × Cβ (11)

  In the present embodiment, the ethanol concentration in the fuel is calculated based on the capacitance Cpβ calculated by Expression (11). Since the amplification factor β is corrected, the ethanol concentration in the fuel calculated based on the capacitance Cpγ when the gain resistor 92 is used as the amplification factor γ, and the amplification factor β using the gain resistor 94 The ethanol concentration in the fuel calculated on the basis of the capacitance Cpβ at this time coincides. As a result, the ethanol concentrations calculated irrespective of the gain resistance to be used coincide with each other, and a step due to switching of the amplification degree does not occur.

In S110, it is determined whether or not the output voltage Voutγ is V _γ1 or less. V _γ1 is a lower limit value of the output voltage at which the ethanol concentration can be calculated using the gain resistor 92. When it is determined that the output voltage Voutγ is larger than V _γ1 (S110: NO), the process proceeds to S105. When it is determined that the output voltage Voutγ is equal to or lower than V _γ1 (S110: YES), the process proceeds to S112 in FIG.

When it is determined that the output voltage Voutβ is smaller than V _β3 (S103: NO), in S111 in FIG. 7, it is determined whether or not the output voltage Voutβ is equal to or lower than V _β1 . V _β1 is the lower limit value of the output voltage at which the alcohol concentration can be calculated using the gain resistor 94. When it is determined that the output voltage Voutβ is equal to or lower than V _β1 (S111: YES), the process proceeds to S121. When it is determined that the output voltage Voutβ is greater than V _β1 (S111: NO), the process proceeds to S112.

In S112, the gain resistance changeover switches 93 and 97 are opened, the gain resistance changeover switch 95 is closed, and the gain resistance 94 is connected to the operational amplifier 91. The amplification degree at this time is β.
In S113, the output voltage Voutβ is acquired.

  In S114, it is determined whether or not the correction coefficient Kβ has been learned in S109 in FIG. When it is determined that the correction coefficient Kβ has not been learned (S114: NO), the process proceeds to S119. When it is determined that the correction coefficient Kβ has been learned (S114: YES), the process proceeds to S115.

In S115, it is determined whether or not the output voltage Voutβ acquired in S113 is V _β1 or more and V _β2 or less. V _β1 is a voltage corresponding to the lower limit value of the first learning region R1, and V _β2 is a voltage corresponding to the upper limit value of the first learning region R1. That is, in this step, it can be said that it is determined whether or not the ethanol concentration in the fuel is within the first learning region R1. Output voltage Voutβ is V _.beta.1 smaller, or when the output voltage Voutβ is determined to be greater than _V β2 (S115: NO), i.e. if the ethanol concentration in the fuel is not in the first learning region R1, to S119 Transition. When it is determined that the output voltage Voutβ is V _β1 or more and V _β2 or less (S115: YES), that is, when the ethanol concentration in the fuel is within the first learning region R1, the process proceeds to S116.

In S 116, the gain resistance changeover switches 93 and 95 are opened, the gain resistance changeover switch 97 is closed, and the gain resistance 96 is connected to the operational amplifier 91. The amplification degree at this time is α.
In S117, the output voltage Voutα is acquired. The acquired output voltage Voutα is obtained by amplifying the detection voltage Vb with the amplification degree α.

In S118, the correction coefficient Kα related to the correction of the output voltage Voutα is learned based on the output voltage Voutβ, the output voltage Voutα, the amplification degree β, and the correction coefficient Kβ.
Here, a learning method of the correction coefficient Kα will be described. The actual amplification degree α when the gain resistor 96 is used is expressed by the following equation (12).
α = Voutα / Voutβ × β × Kβ (12)
When the designed amplification degree when using the gain resistor 96 is αt, the correction coefficient Kα of the amplification degree α is expressed by the following equation (13).
Kα = αt / α (13)
If the equation (12) is substituted into the equation (13), the correction coefficient Kα is expressed by the following equation (14) and is calculated as a constant.
Kα = (Voutβ × αt) / (Voutα × β × Kβ) (14)
When the output voltage Voutα is corrected using the correction coefficient Kα and converted into the capacitance Cpα, the capacitance Cpα is expressed by the following equation (15). Cα in the equation is a conversion coefficient from the output voltage Voutα to the capacitance Cpα.
Cpα = Voutα / (αt × Kα) × Cα (15)

  In the present embodiment, the ethanol concentration in the fuel is calculated based on the capacitance Cpα calculated by the equation (15). Since the amplification degree α is corrected, the ethanol concentration in the fuel calculated based on the capacitance Cpβ when the gain resistance 94 is used as the amplification degree β, and the amplification degree α using the gain resistance 96 The ethanol concentration in the fuel calculated on the basis of the capacitance Cpα at this time coincides. As a result, the ethanol concentrations calculated irrespective of the gain resistance to be used coincide with each other, and a step due to switching of the amplification degree does not occur.

In S119, it is determined whether or not the output voltage Voutβ is V _β1 or less. When it is determined that the output voltage Voutβ is smaller than V _β1 (S119: YES), the process proceeds to S121. V _β1 is the lower limit value of the output voltage at which the ethanol concentration can be calculated using the gain resistor 94. When it is determined that the output voltage Voutβ is equal to or lower than V _β1 (S119: NO), the process proceeds to S120.

In S120, the output voltage Voutβ determines whether V _beta4 or more. V _β4 is the upper limit value of the output voltage at which the ethanol concentration can be calculated using the gain resistor 94. When it is determined that the output voltage Voutβ is smaller than V _β4 (S118: NO), the process proceeds to S113. When it is determined that the output voltage Voutβ is equal to or higher than V _β4 (S118: YES), the process proceeds to S104 in FIG.

When the output voltage Voutβ is equal to or lower than V _β1 (S111: YES or S119: YES), in S121, the gain resistor changeover switches 93 and 95 are opened, the gain resistor changeover switch 97 is closed, and the gain resistor 96 is an operational amplifier. 91 is connected. The amplification degree at this time is α.
In S122, the output voltage Voutα is acquired.

  In S123, it is determined whether or not the correction coefficient Kβ has been learned in S109 in FIG. When it is determined that the correction coefficient Kβ has not been learned (S123: NO), the process proceeds to S128. When it is determined that the correction coefficient Kβ has been learned (S123: YES), the process proceeds to S124.

In S124, it is determined whether or not the output voltage Voutα acquired in S122 is V _α1 or more and V _α2 or less. V _α1 is a voltage corresponding to the lower limit value of the first learning region R1, and V _α2 is a voltage corresponding to the upper limit value of the first learning region R1. That is, in this step, it can be said that it is determined whether or not the ethanol concentration in the fuel is within the first learning region R1. Output voltage Voutα is V _{[alpha] 1} is smaller than, or, if the output voltage Voutα is determined to be greater than _V α2 (S124: NO), i.e. if the ethanol concentration in the fuel is not in the first learning region R1, to S128 Transition. If it is determined that the output voltage Voutα is V _α1 or more and V _α2 or less (S124: YES), that is, if the ethanol concentration in the fuel is within the first learning region R1, the process proceeds to S125.

In S125, the gain resistance changeover switches 93 and 97 are opened, the gain resistance changeover switch 95 is closed, and the gain resistance 94 is connected to the operational amplifier 91. The amplification degree at this time is β.
In S126, the output voltage Voutβ is acquired.
In S127, the correction coefficient Kα related to the correction of the output voltage Voutα is learned based on the output voltage Voutβ, the output voltage Voutα, the amplification degree β, and the correction coefficient Kβ. Note that the learning method of the correction coefficient Kα is as described in S118.

In S128, the output voltage Voutα determines whether V _{[alpha] 2} or more. V _α2 is the upper limit value of the output voltage at which the ethanol concentration can be calculated using the gain resistor 96. If the output voltage Voutα is determined to V _{[alpha] 2} is smaller than (S128: NO), the process proceeds to S122. If the output voltage Voutα is determined to be V _{[alpha] 2} or more (S128: YES), the process proceeds to S113.

  In this embodiment, since the ethanol concentration calculated based on the output voltage Voutγ when the gain resistor 92 is selected is confirmed to be within the specification, the amplification factor when the gain resistor 94 is selected. By learning the correction coefficient Kβ for correcting β based on the output voltage Voutγ, the ethanol concentration calculated based on the output voltage Voutβ is also corrected to be within the standard. Further, as the gain resistor 92 and the gain resistor 94 are switched, there is no step in the calculated ethanol concentration.

  In addition, since the ethanol concentration calculated based on the output voltage Voutβ and the correction coefficient Kβ when the gain resistor 94 is selected is corrected to be within the standard, amplification when the gain resistor 96 is selected. By learning the correction coefficient Kα for correcting the degree α based on the output voltage Voutβ and the correction coefficient Kβ, the ethanol concentration calculated based on the output voltage Voutα is also corrected to be within the standard. Further, when the gain resistor 94 and the gain resistor 96 are switched, there is no step in the calculated ethanol concentration.

Note that the alcohol concentration detection apparatus 1 can also be regarded as correcting the output voltage Voutβ using the correction coefficient Kβ and calculating the ethanol concentration in the fuel based on the corrected output voltage. The corrected output voltage VoutβR is expressed by the following equation (16).
VoutβR = Voutβ × Kβ (16)
In addition, the alcohol concentration detection apparatus 1 can also be regarded as correcting the output voltage Voutα using the correction coefficient Kα and calculating the ethanol concentration in the fuel based on the corrected output voltage. The corrected output voltage VoutαR is expressed by the following equation (17).
VoutαR = Voutα × Kα (17)

  As described above in detail, the alcohol concentration detection apparatus 1 includes the electrode unit 65, the switched capacitor circuit 70, the standard voltage generation circuit 80, the amplification circuit 90, and the control unit 100. In the electrode part 65, the electrostatic capacitance which is immersed in the liquid and changes according to the alcohol concentration in the liquid is detected. The switched capacitor circuit 70 converts the electrostatic capacitance Cp in the electrode portion 65 into a detection voltage Vb. The standard voltage generation circuit 80 applies a voltage to the switched capacitor circuit 70. The amplifier circuit 90 amplifies and outputs the detection voltage Vb. In the control unit 100, the gain resistance changeover switches 93, 95, and 97 are controlled, and the gain resistors 92, 94, and 96 connected to the operational amplifier 91 are switched to switch the amplification degree of the detection voltage Vb.

The control unit 100 obtains the output voltage Voutγ that is the detection voltage Vb amplified at the amplification degree γ and the output voltage Voutβ that is the detection voltage Vb amplified at the amplification degree β (S105 and S108 in FIG. 6). The output voltages Voutγ, Voutβ, and the amplification degree γ are set so that the alcohol concentration in the liquid calculated based on the output voltage Voutγ matches the alcohol concentration in the liquid calculated based on the output voltage Voutγ. Based on this, the amplification degree β is corrected. Specifically, a correction coefficient Kβ for correcting the amplification degree β is calculated (S109).
Further, the output voltage Voutβ that is the detection voltage Vb amplified at the amplification degree β and the output voltage Voutα that is the detection voltage amplified at the amplification degree α are acquired (S113, S117, S122, and S126 in FIG. 7). The output voltage Voutβ, the output voltage Voutα, and the amplification degree so that the alcohol concentration in the liquid calculated based on the output voltage Voutβ matches the alcohol concentration in the liquid calculated based on the output voltage Voutα. Based on β, the amplification degree α is corrected. Specifically, a correction coefficient Kα for correcting the amplification degree α is calculated (S118, S127).

  In the present embodiment, since the amplification degree can be switched, the detection voltage Vb can be appropriately amplified. In particular, the resolution can be increased by increasing the amplification degree in a region where the alcohol concentration is low, and the alcohol concentration can be detected with high accuracy. In addition, by correcting other amplification levels based on the reference amplification level, it is possible to avoid the difference in alcohol concentration calculated by the amplification level due to the influence of errors and the like. Regardless, it is possible to calculate an accurate alcohol concentration. Therefore, the alcohol concentration in the liquid can be detected with high accuracy. In this embodiment, the alcohol concentration at the amplification factor γ that is a reference at the time of product shipment is confirmed, and the amplification factors β and α are corrected based on the amplification factor γ, so the alcohol concentration at all amplification factors is confirmed. Compared with the case where it does, inspection man-hours can be reduced.

  The amplifier circuit 90 includes an operational amplifier 91 and a plurality of gain resistors 92, 94, and 96 having different resistance values that can be connected in parallel to the operational amplifier. In the control unit 100, the gain is switched by switching the gain resistors 92, 94, and 95 connected to the operational amplifier 91. Thereby, the amplification degree can be easily switched. Even if there is an error between the actual resistance value and the set value of the gain resistors 92, 94, 96, the alcohol concentration can be detected with high accuracy by correcting the amplification degree.

  In addition, the switched capacitor circuit 70 includes switches 72 and 73 that switch between a charge state for storing charges and a discharge state for discharging charges in the capacitor 66 of the electrode unit 65. In the control unit 100, the detection voltage Vb1 when the switches 72 and 73 are driven at the first frequency f1 and the detection voltage Vb2 when the switches 72 and 73 are driven at the first frequency f2 The alcohol concentration is calculated.

  In the present embodiment, the control unit 100 constitutes “amplification degree switching means”, “voltage acquisition means”, and “correction means”. Further, S104, S107 in FIG. 6 and S112, S116, S121, S125 in FIG. 7 correspond to processing as a function of “amplification degree switching means”, and S105, S108, S113, S117, S122, S126 are “ S109, S118, and S127 correspond to processing as the function of “correction means”.

  Further, in the present embodiment, in FIG. 6, the amplification degree γ corresponds to the “reference first amplification degree”, the output voltage Voutγ corresponds to the “first output voltage”, and the amplification degree β is “ The output voltage Voutβ corresponds to the “second output voltage” corresponding to the “second amplification degree different from the first amplification degree”. In FIG. 7, the amplification factor β corresponds to the “first amplification factor as a reference”, the output voltage Voutβ corresponds to the “first output voltage”, and the amplification factor α corresponds to the “first amplification factor”. The output voltage Voutα corresponds to the “second output voltage”.

(Second Embodiment)
Since the circuit configuration of the present embodiment is mainly different from that of the first embodiment, the description will focus on the circuit configuration, and the description relating to other configurations and processing will be omitted.
The circuit configuration of the alcohol concentration detection apparatus 200 according to the present embodiment is different from that of the first embodiment in the configurations of the standard voltage generation circuit 280 and the amplification circuit 290.
The amplifier circuit 290 includes an operational amplifier 91 and a gain resistor 292. That is, unlike the above embodiment, the gain resistor 292 is the only gain resistor connected to the operational amplifier 91.

  Incidentally, the detection voltage Vb is proportional to the standard voltage E applied to the switched capacitor circuit 70 as shown in the above equation (7). Therefore, in the alcohol concentration detection apparatus 200 according to the present embodiment, the amplification degree is switched by switching the voltage applied to the switched capacitor circuit 70 by the standard voltage generation circuit 280.

  Specifically, the standard voltage generation circuit 280 includes a resistor 82 and three resistors 283, 284, and 285 having different resistance values. In the present embodiment, the resistors 283, 284, and 285 are in order from the one having the smallest resistance value. The resistors 283, 284, and 285 can be connected to the resistor 82, respectively, and constitute a voltage dividing resistor by being connected to the resistor 82. In addition, a voltage dividing resistor changeover switch 287 for switching a resistor connected to the resistor 82 is provided between the resistors 283, 284, 285 and the resistor 82. The voltage dividing resistor changeover switch 287 is switched by a drive signal from the control unit 100. In the standard voltage generation circuit 280, the voltage stabilized by the constant voltage regulator 116 is divided into the ratio of the resistor 82 and the resistors 283, 284, 285 connected to the resistor 82, and applied to the switched capacitor circuit 70. Yes. Thereby, the magnitude of the voltage applied to the switched capacitor circuit 70 can be changed by switching the resistance value of the resistor functioning as the voltage dividing resistor.

When the ethanol concentration in the fuel is less than or equal to X2 (see FIG. 5), the ethanol concentration can be calculated using the resistor 285. When the resistor 285 and the resistor 82 are connected, the output voltage Voutα output from the amplifier circuit 290 can be regarded as being amplified with the amplification factor α.
When the ethanol concentration in the fuel is greater than or equal to X1 and less than or equal to X4, the ethanol concentration can be calculated using the resistor 284. When the resistor 284 and the resistor 82 are connected, the output voltage Voutβ output from the amplifier circuit 290 can be regarded as being amplified with the amplification factor β.
When the ethanol concentration in the fuel is X3 or more, the ethanol concentration can be calculated using the resistor 283. When the resistor 283 and the resistor 82 are connected, the output voltage Voutγ output from the amplifier circuit 290 can be regarded as being amplified with the amplification degree γ.
Note that the amplification degrees α, β, and γ are the largest and the smallest γ, as in the above embodiment. That is, α>β> γ.

  In the present embodiment, similarly to the above-described embodiment, the ethanol concentration can be calculated using the resistor 285 or the resistor 284 when the ethanol concentration is in the concentration region R1 of X1 or more and X2 or less. In addition, when the ethanol concentration is in the concentration region R2 that is greater than or equal to X3 and less than or equal to X4, the ethanol concentration can be calculated using the resistor 284 or the resistor 283.

  In the present embodiment, the amplification degrees α and β are corrected by a process substantially similar to the correction process described with reference to FIGS. 6 and 7. Specifically, in S104 in FIG. 6, the voltage dividing resistor changeover switch 287 is switched so that the resistor 82 and the resistor 283 are connected to obtain the amplification degree γ. In S102 and S107 in FIG. 6 and S112 and S125 in FIG. 7, the voltage dividing resistor changeover switch 287 is switched so that the resistor 82 and the resistor 284 are connected to obtain an amplification factor β. In S116 and S121, the voltage dividing resistor changeover switch 287 is switched so that the resistor 82 and the resistor 285 are connected to obtain the amplification degree α.

In the present embodiment, the standard voltage generation circuit 280 includes a resistor 82 and resistors 283, 284, and 285 having different resistance values. The resistors 283, 284, and 285 can be connected in series with the resistor 82, and constitute a voltage dividing resistor by being connected to the resistor 82. In the control unit 100, the amplification factor is switched by switching the voltage dividing resistor switch 287 and switching the resistors 283, 284, and 285 connected to the resistor 82. That is, in this embodiment, the amplification degree is changed by changing the voltage applied to the switched capacitor circuit 70 by the standard voltage generation circuit 280. Thereby, the amplification degree can be easily switched. Further, even if there is an error between the actual value and the set value of the ratio of the resistor 82 constituting the voltage dividing resistor and the resistors 283, 284, 285, by correcting the amplification degree as in the above embodiment, The alcohol concentration can be detected with high accuracy.
In addition, the same effects as those of the above embodiment can be obtained.
In the present embodiment, the resistor 82 corresponds to the “first resistor”, and the resistors 283, 284, and 285 correspond to the “second resistor”.

(Other embodiments)
In the above embodiment, the amplification degree is set in three stages by switching three resistors having different resistance values. In other embodiments, the degree of amplification may be two or four or more as long as it is two or more. Further, the switching of the amplification degree may be realized by connecting a plurality of resistors in series as a gain resistor and short-circuiting a part of the resistors. The amplification degree may be switched by another method such as switching the difference frequency Δf.
In the above embodiment, an inspection is performed with the amplification degree γ before product shipment, and it is confirmed that the characteristics are within the standard. In another embodiment, the test is performed at the amplification factor α or the amplification factor β to confirm that the specification is within the standard, and based on the tested amplification factor α or the amplification factor β, other amplification factors are used. May be corrected.

In the above embodiment, the learning of the amplification degree is configured to be continued. However, in the other embodiments, the correction process is terminated when the correction coefficients relating to all the amplification degrees are calculated. May be. Specifically, after an affirmative determination is made in S114 in FIG. 7, it is determined whether or not the correction coefficient Kα has been learned. If a negative determination is made, the process proceeds to S115, and if an affirmative determination is made. The correction process ends. Further, after an affirmative determination is made in S123 in FIG. 7, it is determined whether or not the correction coefficient Kα has been learned. If a negative determination is made, the process proceeds to S124, and if an affirmative determination is made, correction processing is performed. finish.
Further, the processing related to S123 to S127 in FIG. 7 may be omitted, and the process may be shifted to S128 after S122.

In the above embodiment, when the difference frequency Δf is 400 kHz, Vb1−Vb2 calculated by the above equation (7) is used as the detection voltage, and the ethanol concentration is calculated based on the detection voltage. Other embodiments may have any number of differential frequencies. Alternatively, the point B voltage when a pulse wave voltage having a certain frequency is applied may be used as the detection voltage.

In the above-described embodiment, the alcohol concentration detection device detects the concentration of ethanol in the fuel. However, the alcohol concentration detection device is not limited to ethanol, and may detect other alcohols such as methanol and propanol. Further, the present invention may be applied to other than the engine fuel supply system.
As mentioned above, this invention is not limited to the said embodiment at all, In the range which does not deviate from the meaning of invention, it can implement with a various form.

DESCRIPTION OF SYMBOLS 1 ... Alcohol concentration detection apparatus 31 ... 1st electrode (electrode part)
32 ... 2nd electrode (electrode part)
40 ... Thermistor 60 ... Circuit part 65 ... Electrode part 70 ... Switched capacitor circuit (voltage converter)
80 ... Standard voltage generation circuit (voltage application unit)
81... Operational amplifier 82... Resistor (first resistor)
90... Amplifier circuit (amplifier)
91... Operational amplifier 92, 94, 96... Gain resistor 93, 95, 97... Gain resistance changeover switch 100... Control unit (amplification degree switching means, voltage acquisition means, correction means)
200: alcohol concentration detection device 280: standard voltage generation circuit (voltage application unit)
283, 284, 285 ... resistor (second resistor)
290 ... Amplifier circuit (amplifier)
α, β, γ ・ ・ ・ Amplification degree

Claims (3)

An electrode portion that detects a capacitance that is immersed in a liquid and changes according to an alcohol concentration in the liquid;
A voltage conversion unit that converts the capacitance in the electrode unit into a detection voltage;
A voltage application unit for applying a voltage to the voltage conversion unit;
An amplifying unit for amplifying and outputting the detection voltage;
Amplification degree switching means for switching the amplification degree of the detection voltage;
The first output voltage, which is the detection voltage amplified with the first amplification degree as a reference, and the second detection voltage, which is amplified with a second amplification degree different from the first amplification degree Voltage acquisition means for acquiring the output voltage of
The first output voltage so that the alcohol concentration in the liquid calculated based on the first output voltage matches the alcohol concentration in the liquid calculated based on the second output voltage. Correcting means for correcting the second amplification degree based on the second output voltage and the first amplification degree;
An alcohol concentration detection device comprising: The amplification unit has an operational amplifier and a plurality of gain resistors having different resistance values that can be connected in parallel to the operational amplifier.
The alcohol concentration detection apparatus according to claim 1, wherein the amplification degree switching unit switches the amplification degree by switching the gain resistor connected to the operational amplifier. The voltage application unit can be connected in series with a first resistor and the first resistor, and when connected to the first resistor, a plurality of second resistance values constituting a voltage dividing resistor are different. Having a resistance of 2;
The alcohol concentration detection device according to claim 1, wherein the amplification degree switching unit switches the amplification degree by switching the second resistor connected to the first resistor.

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