JP2929906B2 - Alcohol concentration sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an alcohol concentration sensor .
Concerning.

[0002]

2. Description of the Related Art In recent years, the development of methanol vehicles has been activated in order to reduce the pollution of automobile internal combustion engines and to save gasoline consumption. Particularly, a mixed fuel in which gasoline and alcohol are mixed at an arbitrary ratio (hereinafter referred to as a mixed fuel).
FFV (Flexible Fuel Vehicl)
e) has a high degree of freedom in fuel, and is being developed for practical use.

However, since the optimum air-fuel ratio of the mixed fuel varies depending on the alcohol concentration, it is necessary to control the air-fuel ratio and the ignition timing by measuring the alcohol concentration in the mixed fuel with an alcohol concentration sensor. Although two types of alcohol concentration sensors, an optical sensor and a capacitance sensor, have been proposed, the capacitance sensor is mainly used because of its simple structure.

That is, the capacitance type alcohol concentration sensor is
Using the fact that the dielectric constant varies depending on the alcohol concentration of the mixed fuel passing between the electrode plates immersed in the mixed fuel, the alcohol concentration of the mixed fuel is measured by measuring the capacitance between the electrodes. FIG. 11 is a sectional view of a conventional capacitance type alcohol concentration sensor, and FIG.
2 is a signal processing circuit diagram (see Japanese Utility Model Laid-Open No. 2-16054). The sensor electrode 151 has a pair of electrode plates 113a.
And the capacitor 113b, the capacitance 113 of which varies depending on the methanol concentration. The oscillation integrated circuit 153 charges the capacitor Cs up to a predetermined threshold value with a time constant determined by the charging resistance value R of the charging resistor 152 and the capacitance Cs, and varies the frequency according to the charging time (concentration). Output a signal. Frequency-voltage conversion circuit 15
Reference numeral 4 denotes a circuit for converting a frequency signal output from the oscillation integrated circuit 153 into an analog voltage, and outputting a predetermined voltage corresponding to the methanol concentration by the amplifier circuit 155.

[0005]

However, when ionic impurities are contained in the mixed fuel, it is inevitable that a current flows between the electrodes due to the conductance component. Therefore, when the capacitance, that is, the alcohol concentration of the mixed fuel is measured by using the charge and discharge of the electric charge accumulated in the capacitor constituted by the electrode plate immersed in the mixed fuel, the charging / discharging current is determined by the alcohol concentration. Even if it is constant, it differs depending on the content of ionic impurities, and an error occurs in the measured value of the alcohol concentration.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has a capacitance type alcohol capable of accurately measuring the alcohol concentration even when ionic impurities are contained in a mixed solution containing alcohol. An object is to provide a concentration sensor.

[0007]

Means for Solving the Problems] alcohol concentration sensor according to the first invention, a detection capacitor constituted by a pair of electrode plates which are immersed in a mixture containing A alcohol, pulsed electrode plate A pulse power supply for supplying power of
A discharge resistor that discharges the electric power stored in the pair of electrodes from the power supplied from the pulse power source, and a time period in which a discharge voltage generated across the discharge resistor as a signal proportional to the alcohol concentration is equal to or higher than a predetermined threshold voltage an output unit for outputting a voltage proportional to, compensation is a mixture other one of the electrodes to the output of one of the electrodes is constituted by the other pair of electrode plates were immersed pulse power supply in a containing a alcohol grounded Install a condenser.

[0008] In the alcohol concentration sensor according to the second invention, the housing of the alcohol concentration sensor is made of metal for electrostatic shielding, and is used as the other electrode of the compensating capacitor. Alcohol concentration sensor according to the third invention, a detection capacitor constituted by a pair of electrode plates which are immersed in a mixture containing A alcohol, a pulse power supply for supplying pulsed power to the electrode plates, A discharge resistor that discharges the electric power stored in the pair of electrodes from the power supplied from the pulse power source, and a time period in which a discharge voltage generated across the discharge resistor as a signal proportional to the alcohol concentration is equal to or higher than a predetermined threshold voltage An output section that outputs a voltage proportional to the resistance, a reference resistance connected in parallel with the detection capacitor, a known resistance value, a switch for controlling the connection / disconnection of the reference resistance, and a discharge resistance when the switch is in a disconnected state. First discharge time measuring means for measuring a first discharge time in which a discharge voltage generated at both ends is equal to or higher than a predetermined threshold voltage; A second discharge time measuring means for measuring a second discharge time in which the discharge voltage is equal to or higher than a predetermined threshold voltage; and a first discharge time measured by the first discharge time measuring means for controlling connection / disconnection of the switch. Discharge time and the second discharge time measured by the second discharge time measuring means.
First alcohol concentration determining means for determining the alcohol concentration of the mixed liquid based on the discharge time.

[0009] the alcohol concentration sensor according to the fourth invention, the pulse supplies a detection capacitor constituted by a pair of electrode plates which are immersed in a mixture containing A alcohol, the pulsed power to the electrode plate A power supply, a discharge resistor that discharges electric power supplied from the pulse power supply to the pair of electrodes, and a discharge voltage generated across the discharge resistor as a signal proportional to the alcohol concentration is equal to or higher than a predetermined threshold voltage. An output unit for outputting a voltage proportional to time,
And a second switch connected to one terminal of the detection capacitor having a second terminal to which the pulse power supply is connected, and a second terminal connected to the first terminal and the discharge resistor. A second switch connected to the other terminal of the detection capacitor; a constant voltage source connected to the first terminal of the first switch; and a constant voltage source connected to the first terminal of the second switch. A voltage dividing resistor, a first switch and a second switch are switched and controlled, and a first voltage generated at both ends of the voltage dividing resistor when both the first switch and the second switch are connected to the first terminal. And a second voltage generated at both ends of the discharge resistor when both the first switch and the second switch are connected to the second terminal is measured to obtain the first voltage and the second voltage. determine the alcohol concentration of the mixture based on A second alcohol concentration determining means for comprises a.

The alcohol concentration sensor according to a fifth aspect of the present invention includes a concentration measurement switch that is brought into contact only when measuring the alcohol concentration between the pulse power supply and the detection capacitor.

[0011]

[Action] In the first alcohol concentration sensor according to the invention, due to the ionic impurities voltage pulses proportional to the ionic impurities concentration in the mixture is in mixed fuel is supplied to the detecting capacitor containing alcohol Is compensated for. In the alcohol concentration sensor according to the second aspect, the structure is simplified because the housing itself is used as one electrode of the compensation capacitor.

In the alcohol concentration sensor according to a third aspect of the present invention, when a discharge voltage and a resistance whose resistance value is known by a discharge circuit including a detection capacitor and a discharge resistor are connected in parallel with the detection capacitor. by determining the alcohol concentration based discharge voltage and the Al
Dielectric constant due to the ionic impurities in the liquid mixture containing the call is compensated.

[0013] In the alcohol concentration sensor according to the fourth invention, by connecting a detecting capacitor to a constant voltage source, the dielectric constant due to the ionic impurities in the liquid mixture containing the alcohol is measured. In the alcohol concentration sensor according to the fifth invention, a pulse voltage is applied to the detection capacitor only when measuring the alcohol concentration.

[0014]

1 is a top view and a front view of an alcohol concentration sensor, FIG. 2 is a sectional view taken along line XX and YY, and FIG.
Is a ZZ sectional view. That is, an arc-shaped outer electrode 104 is provided in a fuel pipe 101 via a cylindrical center electrode 102 and a first fuel flow channel 103. Further, the space between the outer electrode 104 and the fuel pipe 101 is filled with an insulating material 105.

The center electrode 102 and the outer electrode 104 extend upward and are directly connected to the substrate 110. Substrate 11
In 0, a signal processing circuit described later is configured. The fuel pipe 101 and the substrate 110 are covered with a metal casing 120 and function as an electrostatic shield. FIG. 4 is a circuit diagram of a signal processing circuit for an alcohol concentration sensor according to the first and second inventions formed on a substrate 110,
It comprises a pulse generator 41, a detector 42 and an output unit 43.

The pulse generation section 41 functions as a pulse power supply for supplying power to the detection section.
Second and third inverters 411, 412 and 41
3 and a feedback resistor 414 that feeds back the output of the first inverter 411 to the input of the first inverter 411 and a capacitor 415 that feeds back the output of the second inverter 412 to the input of the first inverter 411. Is done. Note that the oscillation frequency of the pulse power supply is desirably 500 kHz or more.

The third inverter 413 includes a voltage dividing resistor 416
Is connected to the outer electrode 104 via the. Outer electrode 104
And the center electrode 1 constituting the detection capacitor 421
02 is the discharge resistor 422 and the clamp diode 42
3 and a fourth inverter 424
Connected to.

The output of the fourth inverter is a filter resistor 4
Transistor 433 filtered by a low-pass filter composed of
Supplied to the base. In FIG. 4, a detection resistor 425 connected in parallel with the detection capacitor 421 is an equivalent resistor that determines the magnitude of leakage current flowing through ionic impurities present in the mixed fuel.

Since the resistance value of the detection resistor 425 decreases in inverse proportion to the increase in the concentration of ionic impurities in the mixed fuel, the discharge current supplied from the detection capacitor 421 to the discharge resistor 422 apparently increases. This results in a measurement error of the alcohol concentration. To compensate for this measurement error, a compensation capacitor 417 is provided between the output terminal of the third inverter 413 and the ground.

An external electrode 104 can be used as one electrode of the compensation capacitor 417. As another electrode of the compensating capacitor 417, another electrode can be provided. However, an insulator is inserted between the outer electrode 104 and the metal housing 120 of the alcohol concentration sensor, and the metal housing 120 itself is inserted. May be the other terminal.

In FIG. 4, a compensating resistor 418 connected in parallel to a compensating capacitor 417 is an equivalent resistor that determines the magnitude of a leakage current flowing through ionic impurities present in the mixed fuel. It decreases in inverse proportion to the increase in the concentration of ionic impurities. Therefore, the charging current for the detection capacitor 421 decreases in inverse proportion to the increase in the concentration of the ionic impurity, and therefore, it is possible to compensate for the discharge current that increases in proportion to the increase in the concentration of the ionic impurity.

FIG. 5 is an explanatory diagram of a method for compensating the ionic impurity concentration, in which the horizontal axis represents time and the vertical axis represents voltage Vc. However, the pulse voltage of the pulse generator 41 is Vp, and the threshold voltage for measuring the discharge time is Vp / 2. The solid line is the discharge current when no ionic impurities are contained, and reaches the threshold voltage at Td after the start of discharge.

However, when ionic impurities are contained, the discharge current apparently increases and becomes the current indicated by the broken line unless a fuel dielectric constant compensating capacitor is provided. Therefore, the time To to reach the threshold voltage Vp / 2 is: To> Td.

If the compensating capacitor 417 is additionally provided, the charging voltage for the detecting capacitor decreases in proportion to the ionic impurity concentration, so that the discharge current is indicated by a dashed line and reaches the threshold voltage Vp / 2. The time for performing is Td, and the ionic impurity concentration can be compensated. In other words, the main purpose of the compensating capacitor 417 is to measure the leakage resistance, and the capacitance needs to be as small as possible. Therefore, the distance between the external electrode 104 and the metal housing 120 is increased while being inserted. The dielectric constant of the insulator.

According to the above configuration, the fourth inverter 42
The output of 4 is a pulse train having a duty ratio proportional to the alcohol concentration in the fuel. This pulse train is filtered by the filter resistor 431 and the filter capacitor 432, and by controlling the collector current of the transistor 433, an analog voltage signal proportional to the alcohol concentration in the fuel can be obtained from the output unit 43.

FIG. 6 is a signal processing circuit diagram of the alcohol concentration sensor according to the third invention, wherein the same elements as those of the alcohol concentration sensors according to the first and second invention are denoted by the same reference numerals. . The difference from the alcohol concentration sensor according to the first and second inventions is that instead of the compensation capacitor 417, a series connection of the reference resistor 426 and the switch 427 is provided in parallel with the detection capacitor 421 and the transistor 433. Is provided with a microcomputer 434 (corresponding to the first discharging time measuring means, the second discharging time measuring means and the first alcohol concentration determining means in the third invention) in place of.

The connection and disconnection of the switch 427 is controlled by the microcomputer 434. FIG. 7 is a flowchart of a first processing routine executed by the microcomputer. In step 71, an initial value is set. In step 72, a disconnection command of the switch 427 is output,
In step 73, the switch-off output voltage Vo proportional to the time required for the terminal voltage of the detection capacitor 421 to reach a predetermined threshold voltage is measured.

When the threshold voltage is set to 1/2 of the output voltage Vp of the pulse generator 41, the output voltage Vo at the time of switching off is expressed by the following equation (1).

[0029]

(Equation 1)

At step 74, a contact command for the switch 427 is output, and at step 75, a switch contact output voltage Vc proportional to the time required for the terminal voltage of the detection capacitor 421 to reach a predetermined threshold voltage is measured. When the threshold voltage is set to の of the output voltage Vp of the pulse generator 41, the output voltage Vc at the time of switch contact is expressed by the following equation (2).

[0031]

(Equation 2)

Therefore, the expressions (1) and (2) indicate the capacitance Cs of the detecting capacitor 421 and the detecting capacitor 4.
This is a simultaneous equation in which the resistance value Rs of the detection resistor 425, which is the leakage resistance of No. 21, is unknown. Therefore, in step 76, it is possible to determine the capacitance Cs of the detection capacitor 421 by equation (3).

[0033]

(Equation 3)

The capacitance Cs can be determined by solving simultaneous equations, or can be determined from a two-dimensional map of the output voltage Vo when the switch is turned off and the output voltage Vc when the switch is turned on. The capacitance C of the detection capacitor 421
Since s is proportional to the alcohol concentration of the mixed fuel, it is possible to output the alcohol concentration in step 77.

FIG. 8 is a signal processing circuit diagram of the alcohol concentration sensor according to the fourth invention, wherein the same elements as those of the alcohol concentration sensors according to the first and second invention are denoted by the same reference numerals. . The difference from the alcohol concentration sensor according to the first and second inventions is that the compensation capacitor 417 is removed, the switches 428 and 429 are provided at both ends of the detection capacitor 421, and the microcontroller is used instead of the transistor 433. This is the point that a computer 434 (corresponding to a second alcohol concentration determining means in the fourth invention) is provided.

The disconnection of the switches 428 and 429 is controlled by the microcomputer 434. The terminal a of the switch 428 is connected to the constant voltage source 801, and the terminal b is connected to the output of the pulse generator 41. Also, switch 429
The terminal a is connected to the microcomputer 434 via a reference resistor 802 (corresponding to a voltage dividing resistor in the fourth aspect of the present invention), and the terminal b is connected via a discharge resistor 422 and a clamp diode 423. Connected to the fourth inverter 424.

FIG. 9 is a flowchart of a second processing routine executed by the microcomputer. In step 91, an initial value is set. In step 92, a command to switch the switches 428 and 429 to the a side is output. In step 93, the voltage Vb of the constant voltage source 801 is changed to the detection resistance 42 equal to the leakage resistance of the detection capacitor 421.
5 and the divided voltage Vd divided by the reference resistor 802 are read into the microcomputer 434.

Since the voltage Vb of the constant voltage source 801 and the resistance value Rx of the reference resistor 802 are known, the divided voltage Vd
Is proportional to the ionic impurity concentration in the mixed fuel. Note that the divided voltage Vd is represented by the following equation (4).

[0039]

(Equation 4)

At step 94, switches 428 and 42
9 is output to the b side. In step 95, an output voltage Vc proportional to the time required for the terminal voltage of the detection capacitor 421 to drop to a predetermined threshold voltage by discharging is measured. Note that the output voltage Vc when the threshold voltage is set to 1/2 of the output voltage Vp of the pulse generator 41 is represented by Expression (5).

[0041]

(Equation 5)

Therefore, equations (4) and (5) indicate the capacitance Cs of the detecting capacitor 421 and the detecting capacitor 4.
This is a simultaneous equation in which the resistance value Rs of the detection resistor 425, which is the leakage resistance of No. 21, is unknown. Therefore, in step 96, it is possible to determine the capacitance Cs of the detection capacitor 421 by the equation (6).

[0043]

(Equation 6)

The capacitance Cs can be determined by solving simultaneous equations, or can be determined from a two-dimensional map of the divided voltage Vd and the output voltage Vc. Since the capacitance Cs of the detection capacitor 421 is proportional to the alcohol concentration of the mixed fuel, the alcohol concentration can be output in step 97. If the mixed fuel contains ionic impurities, the mixture between the center electrode 102 and the outer electrode 104 or between the outer electrode 104 and the casing 120
Current flows between the electrodes and electric erosion occurs.

On the other hand, since the alcohol concentration of the mixed fuel does not fluctuate with time, it is not necessary to constantly measure the alcohol concentration.
It is sufficient to measure intermittently at predetermined time intervals. Therefore, by providing a switch at the output end of the pulse power supply and connecting the switch only for the alcohol concentration measurement time, it becomes possible to prevent electrolytic corrosion of the electrode. FIG. 10 is a circuit diagram in the case where a switch is provided for the alcohol concentration sensor according to the first or second invention. An alcohol concentration measurement switch is provided between the output of the third inverter 413 and the voltage dividing resistor 416. Is installed.

The disconnection of the switch 419 can be controlled by a microcomputer or the like. In this embodiment, the amount of electrolytic corrosion is reduced to 1/100 by setting the switch 419 to indirect for 2 milliseconds every 200 milliseconds. Became possible. Note that 200 milliseconds is selected as a value sufficiently larger than the sampling period of the microcomputer for controlling the internal combustion engine, and 2 milliseconds is selected as a time during which the output of the detection unit is stabilized.

Note that adding the switch 419 is second
Needless to say, the invention can be applied to the fourth invention.

[0048]

According to the alcohol concentration sensor according to the first aspect of the present invention, by additionally providing a compensating capacitor ,
The measurement error of the alcohol concentration caused by the ionic impurities in the mixed solution containing alcohol can be compensated, and the measurement accuracy of the alcohol concentration can be improved.

According to the alcohol concentration sensor of the second invention, the structure can be simplified by using the metal housing of the sensor as one electrode of the compensating capacitor. According to the alcohol concentration sensor according to the third invention, by measuring the discharge time of the contact state and disconnection state of the reference resistor, the alcohol concentration due to the ionic impurities in the mixed solution <br/> containing alcohol The measurement error can be compensated, and the measurement accuracy of the alcohol concentration can be improved.

According to the alcohol concentration sensor of the fourth aspect , the alcohol is controlled by the constant voltage source and the voltage dividing resistor.
By measuring the discharge time after measuring the ionic impurity concentration in the mixed solution containing, it is possible to compensate for the measurement error of the alcohol concentration caused by the ionic impurity in the mixed solution , and to improve the measurement accuracy of the alcohol concentration. Can be improved. According to the alcohol concentration sensor of the fifth aspect, it is possible to reduce the electrolytic corrosion of the electrodes by intermittently supplying power from the pulse power supply.

[Brief description of the drawings]

FIG. 1 is a top view and a front view of an alcohol concentration sensor.

FIG. 2 is a cross-sectional view taken along line XX and a line YY of the alcohol concentration sensor.

FIG. 3 is a ZZ cross-sectional view of the alcohol concentration sensor.

FIG. 4 is a signal processing circuit diagram of the alcohol concentration sensor according to the first and second inventions.

FIG. 5 is an explanatory diagram of a method for compensating the ionic impurity concentration.

FIG. 6 is a signal processing circuit diagram of the alcohol concentration sensor according to the third invention.

FIG. 7 is a flowchart of a first processing routine.

FIG. 8 is a signal processing circuit diagram of an alcohol concentration sensor according to a fourth invention.

FIG. 9 is a flowchart of a second processing routine.

FIG. 10 is a signal processing circuit diagram of an alcohol concentration sensor according to a fifth invention.

FIG. 11 is a longitudinal sectional view of a conventionally used alcohol concentration sensor.

FIG. 12 is a signal processing circuit diagram of a conventionally used alcohol concentration sensor.

[Explanation of symbols]

 41 ... Pulse generation part 417 ... Compensation capacitor 42 ... Detection part 421 ... Detection capacitor 43 ... Output part 102 ... Center electrode 104 ... External electrode 120 ... Case

──────────────────────────────────────────────────続 き Continued from the front page (72) Inventor Ichiro Hosoya 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (56) References JP-A-5-133926 (JP, A) (58) Fields investigated (Int.Cl. ⁶ , DB name) G01N 27/22 G01R 27/26

Claims (5)

(57) [Claims] 1. A detection capacitor constituted by a pair of electrode plates which are immersed in a mixture containing A alcohol, a pulse power supply for supplying pulsed power to the electrode plate, supplied from the pulse power supply And a discharge resistor for discharging the electric charge stored in the pair of electrodes, and a signal proportional to the alcohol concentration is proportional to the time during which the discharge voltage generated across the discharge resistor is equal to or higher than a predetermined threshold voltage. in the alcohol concentration sensor comprising an output unit for outputting a voltage, and is configured on the other pair of electrode plates were immersed in a mixture containing a alcohol while one electrode of the other output of the pulse power supply An alcohol concentration sensor, wherein a compensating capacitor whose electrode is grounded is provided. 2. A method according to claim 1, wherein the housing of the alcohol concentration sensor is made of metal for electrostatic shielding, and is used as another electrode of the compensating capacitor.
4. An alcohol concentration sensor according to claim 1. 3. A detection capacitor constituted by a pair of electrode plates which are immersed in a mixture containing A alcohol, a pulse power supply for supplying pulsed power to the electrode plate, supplied from the pulse power supply And a discharge resistor for discharging the electric charge stored in the pair of electrodes, and a signal proportional to the alcohol concentration is proportional to the time during which the discharge voltage generated across the discharge resistor is equal to or higher than a predetermined threshold voltage. An output unit that outputs a voltage, wherein: a reference resistor connected in parallel with the detection capacitor and having a known resistance value; a switch controlling disconnection of the reference resistor; and the switch. A first discharge time measuring means for measuring a first discharge time in which a discharge voltage generated across the discharge resistor when the is in a disconnected state is equal to or higher than the predetermined threshold voltage; A second discharge time measuring means for measuring a second discharge time in which a discharge voltage generated across the discharge resistor when the switch is in a contact state is equal to or higher than the predetermined threshold voltage; And the alcohol concentration of the mixed liquid based on the first discharge time measured by the first discharge time measuring means and the second discharge time measured by the second discharge time measuring means. A first alcohol concentration determining means for determining the alcohol concentration. A detection capacitor constituted by a pair of electrode plates which are immersed in 4. A mixture containing A alcohol, a pulse power supply for supplying pulsed power to the electrode plate, supplied from the pulse power supply And a discharge resistor for discharging the electric charge stored in the pair of electrodes, and a signal proportional to the alcohol concentration is proportional to the time during which the discharge voltage generated across the discharge resistor is equal to or higher than a predetermined threshold voltage. An output unit for outputting a voltage, wherein the first switch is connected to one terminal of the detection capacitor having a first terminal and a second terminal to which the pulse power supply is connected. A second switch connected to the other terminal of the detection capacitor, the second switch having a first terminal and a second terminal connected to the discharge resistor; A constant voltage source connected to a first terminal of the switch; a voltage dividing resistor connected to a first terminal of the second switch; and switching control of the first switch and the second switch. Measuring a first voltage generated across the voltage dividing resistor when both the first switch and the second switch are connected to a first terminal;
Measuring the second voltage generated across the discharge resistor when both the switch and the second switch are connected to the second terminal, and based on the first voltage and the second voltage, the liquid mixture is measured. And a second alcohol concentration determining means for determining the alcohol concentration. 5. A concentration measuring switch provided between the pulse power supply and the detection capacitor, the switch being in a contact state only when alcohol concentration is measured.
5. The alcohol concentration sensor according to any one of items 1 to 4.