JP2018100932A - Concentration sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the accuracy of measurement by a sensor for measuring an alcohol concentration in liquid by measuring a capacitance, if ambient temperatures change.SOLUTION: The concentration sensor includes an AC voltage source 1, a capacitor 2, a detector circuit 4, and a timing generation circuit 5. The timing generation circuit 5 includes an AD converting circuit 10 connected to the AC voltage source 1, a DA converting circuit 12 connected to the AD converting circuit 10, a voltage control oscillation circuit 14 connected to the DA conversion circuit 12, and a frequency divider circuit 15 connected to the voltage control oscillation circuit 14. A sampling timing signal of the AD converting circuit 10 is a clock signal φ0 output from the voltage control oscillation circuit 14, a sampling timing signal of the DA converting circuit 12 is an output signal φ1 from the frequency divider circuit 15, and a detection timing signal of the detector circuit 4 is an output signal φ2 from the frequency divider circuit 15.SELECTED DRAWING: Figure 2

Description

  The present disclosure relates to a capacitance type density sensor.

  In recent years, alcohol-mixed fuels in which alcohol such as methanol or ethanol is mixed with gasoline have been studied as alternative fuels for internal combustion engines such as automobile engines. Since the combustion efficiency of the alcohol-mixed fuel changes according to the alcohol concentration, it is important to detect the alcohol concentration of the alcohol-mixed fuel supplied to the internal combustion engine when controlling the output of the internal combustion engine.

  As a concentration sensor for detecting the alcohol concentration in such a measurement liquid, a capacitor composed of a pair of electrodes is immersed in an alcohol mixed fuel, and a static electricity between electrodes in a gasoline and alcohol mixed liquid having different dielectric constants is immersed. A capacitance detection type concentration sensor that detects an alcohol concentration by observing a change in capacitance is generally used.

  Note that it is the conductivity of alcohol that must be taken into account when using a capacitance detection type concentration sensor. The conductivity (resistance component) is greatly changed by mixing conductive ions, and an electrical conduction component between the electrodes due to the conductivity (resistance component) is generated as an error in capacitance detection.

  Conventionally, as a technique for suppressing such an error component, Patent Document 1 proposes a structure in which an electrode forming a capacitor is covered with an insulator to prevent electrical conduction between the electrodes. Patent Document 2 proposes a configuration in which a reference capacitor is separately provided in addition to the detection capacitor, and the true value of the alcohol concentration is obtained by comparing both phase differences.

JP 2004-125464 A JP 2005-121428 A

  Since such a concentration sensor is a component related to output control of an internal combustion engine as described above, further improvement in detection accuracy is required.

  In view of this, the present disclosure responds to such a demand and aims to improve the detection accuracy of the density sensor.

  The concentration sensor in one embodiment of the present disclosure includes an AC voltage source, a capacitor, a detection circuit, and a timing generation circuit, and the timing generation circuit is connected to the AD conversion circuit connected to the AC voltage source and the AD conversion circuit. A DA conversion circuit; a voltage control oscillation circuit connected to the DA conversion circuit; and a frequency division circuit connected to the voltage control oscillation circuit. A sampling timing signal of the AD conversion circuit is output from the voltage control oscillation circuit. The sampling timing signal in the DA converter circuit is an output signal from the frequency divider circuit, and the detection timing signal in the detector circuit is the output signal φ2 from the frequency divider circuit.

  With this configuration, the detection accuracy of the density sensor can be improved.

FIG. 1 is a diagram illustrating a usage pattern of the concentration sensor of the present disclosure. FIG. 2 is a circuit diagram of the concentration sensor of the present disclosure. FIG. 3 is a diagram illustrating an output signal from the AC voltage source in the present disclosure. FIG. 4 is a diagram illustrating an output signal from the current-voltage conversion circuit according to the present disclosure. FIG. 5 is a diagram illustrating a signal processing operation in the detection circuit according to the present disclosure. FIG. 6 is a diagram illustrating a signal processing operation in the timing generation circuit according to the present disclosure. FIG. 7 is a diagram illustrating a signal processing operation in the timing generation circuit according to the present disclosure. FIG. 8 is a diagram illustrating a signal processing operation in the timing generation circuit according to the present disclosure.

  Hereinafter, the concentration sensor according to the embodiment of the present disclosure will be described with reference to the drawings. Note that each of the embodiments described below shows a preferred specific example of the present disclosure. Accordingly, the shapes, components, arrangement of components, connection forms, and the like shown in the following embodiments are merely examples, and are not intended to limit the present disclosure. Therefore, among the constituent elements in the following embodiments, constituent elements that are not described in the independent claims showing the highest concept of the present invention are described as optional constituent elements.

  Each figure is a mimetic diagram and is not necessarily illustrated strictly. In each figure, substantially the same structure is denoted by the same reference numeral, and redundant description is omitted or simplified.

  FIG. 1 is a schematic diagram showing a usage pattern of the density sensor 100. The concentration sensor 100 includes an AC voltage source 1, a capacitor 2, a detection circuit 4, and a timing generation circuit 5 as a basic configuration. An output signal of the AC voltage source 1 is connected to the capacitor 2 and the timing generation circuit 5. The output of the capacitor 2 is connected to the detection circuit 4. The output of the timing generation circuit 5 is connected to the detection circuit 4. Although the current-voltage conversion circuit 3 is disposed between the capacitor 2 and the detection circuit 4, the current-voltage conversion circuit 3 is not necessarily disposed. The capacitor 2 is composed of a pair of opposing conductive plates. The capacitor 2 is disposed in the measurement object 6. The concentration sensor 100 is a capacitance type sensor that detects a change in capacitance of the capacitor 2 due to a change in concentration of the measurement target 6. Each processing circuit excluding the AC voltage source 1 and the capacitor 2 can be formed using an IC or a microcomputer.

  In addition, the measuring object 6 in this embodiment is a mixed fuel obtained by mixing gasoline and alcohol. Since gasoline and alcohol have different dielectric constants, the dielectric constant of the mixed fuel changes depending on the proportion of alcohol contained in the mixed fuel. By detecting the change in the dielectric constant of the mixed fuel with the capacitor 2, the concentration of alcohol in the mixed fuel is detected.

  FIG. 2 shows a circuit diagram of the density sensor 100. The timing generation circuit 5 includes an AD conversion circuit 10, an arithmetic circuit 11, a DA conversion circuit 12, a filter circuit 13, a voltage control oscillation circuit 14, a frequency divider circuit 15, and a compensation circuit 16.

The AD conversion circuit 10 converts the output signal from the AC voltage source 1 into a digital value. The arithmetic circuit 11 calculates the difference between the output value output from the compensation circuit 16 and the digital value output from the AD conversion circuit 10. The DA conversion circuit 12 converts the output value output from the arithmetic circuit 11 into an analog signal. The filter circuit 13 integrates the analog signal output from the DA conversion circuit 12. The voltage controlled oscillation circuit 14 outputs a clock signal φ0 having a frequency corresponding to the output voltage from the filter circuit 13. The clock signal φ0 is input to the AD conversion circuit 10 and the frequency dividing circuit 15. The clock signal φ0 becomes a sampling timing signal of the AD conversion circuit 10. The frequency dividing circuit 15 divides the clock signal φ0 by 8 and outputs output signals φ1 and φ2. The phases of the output signal φ1 and the output signal φ2 are different by 90 °. The output signal φ1 is a sampling timing signal of the DA conversion circuit 12. The output signal φ2 is a detection timing signal of the detection circuit 4. The compensation circuit 16 includes a temperature detection circuit 17 and an arithmetic circuit 18. The temperature detection circuit 17 detects the temperature of the measurement object 6. The arithmetic circuit 18 calculates a target value corresponding to the detection result of the temperature detection circuit 17 based on a predetermined arithmetic expression. The target value is an output value corresponding to the temperature of the output signal of the AC voltage source 1.

  As described above, since the AD conversion circuit 10 and the DA conversion circuit 12 are arranged in the timing generation circuit 5, the digital processing section 19 is arranged before the voltage controlled oscillation circuit 14. By providing the digital processing section 19 in the timing generation circuit 5, it is possible to suppress an increase in circuit scale when adding compensation information for variable elements such as temperature and humidity.

  Next, the detection process in the detection circuit 4 will be described.

  FIG. 3 shows an output signal 20 from the AC voltage source 1. The vertical axis in FIG. 3 indicates voltage, and the horizontal axis indicates time. The output signal 20 is a sine wave signal and is represented by V (t) = Vsinωt. Times t0, t2, t3, and t4 indicate timings when the output signal 20 crosses 0V.

  FIG. 4 shows an output signal 30 from the current-voltage conversion circuit 3. The vertical axis in FIG. 4 indicates voltage, and the horizontal axis indicates time. Times t0 to t4 in the figure coincide with the times t0 to t4 shown in FIG. The output signal 30 is obtained by converting the current signal output from the capacitor 2 into a voltage signal by the current-voltage conversion circuit 3. The output signal 30 is represented by I (t) = (V / R) sinωt + (VωC) cosωt.

  Signal 31 indicates the resistance component current in the output signal 30. The resistance component current is represented by (V / R) sinωt. The signal 31 varies depending on the conductivity of the measurement object 6. The phase of the signal 31 matches the phase of the output signal 20 from the AC voltage source 1 shown in FIG.

  A signal 32 indicates the capacitance component current in the output signal 30. The capacitance component current is represented by (VωC) cosωt. The signal 32 varies depending on the dielectric constant of the measurement target 6. The dielectric constant of the measurement object 6 is proportional to the concentration of the measurement object 6. The phase of the signal 32 is 90 ° different from the phase of the output signal 20 from the AC voltage source 1 shown in FIG.

  FIG. 5 shows a signal processing operation in the detection circuit 4. In FIG. 5, the vertical axis represents voltage, and the horizontal axis represents time. Note that the times t0 to t4 coincide with the times t0 to t4 shown in FIG. Times j0, j1, j2, and j3 indicate timings at which the signal 32 shown in FIG. 4 crosses 0V.

  The signal 40 is a detection timing signal of the detection circuit 4. That is, the signal 40 is the output signal φ2 of the frequency dividing circuit 15 in FIG. The phase difference between the output signal 20 and the signal 40 from the AC voltage source 1 shown in FIG. 3 is 90 °. The formation of the detection timing signal in the timing generation circuit 5 will be described later.

  The detection processing in the detection circuit 4 performs inversion processing on the output signal 30 from the current-voltage conversion circuit 3 in the section of time j0 to j1 and the section of time j2 to j3. Then, the integration processing is performed on the signal subjected to the inversion processing at timings j0 to j4.

  As described above, the output signal 30 from the current-voltage conversion circuit 3 includes the signal 31 that is a resistance component current and the signal 32 that is a capacitance component current.

  The resistance component current signal 31 is inverted between the time j0 to j1 and the time j2 to j3 to form an inverted signal 31a. The inversion signal 31a is integrated at the timing of times j0 to j4, so that the voltage 41 becomes a signal 41. That is, the resistance component current is canceled by the detection process.

  The signal 32 of the capacitance component current is inverted in the interval from time j1 to j2 and in the interval from time j3 to j4 to form an inverted signal 32a. The inversion signal 32a is integrated at the timings of time j0 to j4, thereby becoming a signal 42 having a voltage of v1V.

  That is, since the influence of the resistance component current is canceled in the signal output from the detection circuit 4, the concentration sensor 100 with high detection accuracy can be realized.

  Next, generation of a detection timing signal in the timing generation circuit 5 will be described.

  6 to 8 show signal processing operations in the timing generation circuit 5. The vertical axis in FIG. 3 indicates voltage, and the horizontal axis indicates time.

  A signal 50 is a sampling timing signal of the AD conversion circuit 10. That is, the signal 50 is the clock signal φ0 output from the voltage controlled oscillation circuit 14. The signal 50 is a pulse wave obtained by multiplying the output signal 20 of the AC voltage source 1 by eight. The AD conversion circuit 10 outputs a digital value obtained by sampling the output signal 20 at the falling times s0 to s7 of the signal 50. Times s0 and s4 coincide with the timing when the output signal 20 of the AC voltage source 1 becomes 0V. A signal 51 is a sampling timing signal of the DA conversion circuit 12. The signal 51 is the frequency dividing circuit 15 output signal φ1. The frequency of the signal 51 matches the frequency of the output signal 20 from the AC voltage source 1. The DA conversion circuit 12 samples the digital value at the falling timing of the signal 51 and outputs it as an analog signal. Therefore, clock signal φ0 is controlled to synchronize with output signal 20 of AC voltage source 1 at the timing of time s0. The signal 52 is the output signal φ2 of the frequency dividing circuit 15. The phase difference between the signal 51 and the signal 52 is 90 °.

  FIG. 6 shows a signal processing operation in a state where the phases of the signal 50 and the output signal 20 match at the time s0. In this case, since the voltage 20a of the output signal 20 at time s0 is 0V, the AD conversion circuit outputs 0 as a digital value. Therefore, the state of the output clock φ0 of the voltage controlled oscillation circuit 14 arranged in the subsequent stage is maintained.

  FIG. 7 shows a signal processing operation in a state where the phase of the output signal 20 has advanced at the timing of time s0. In this case, since the voltage 20b of the output signal 20 at time s0 is a negative value, the AD conversion circuit 10 outputs a negative value as a digital value. Therefore, the filter circuit 13 disposed in the subsequent stage outputs a signal having a polarity that decreases the frequency of the output clock of the voltage controlled oscillation circuit 14 in accordance with the digital value. In the voltage controlled oscillation circuit 14, the frequency of the output clock is reduced according to the output of the filter circuit 13.

FIG. 8 shows a signal processing operation in a state where the phase of the output signal 20 is delayed at the timing of time s0. In this case, since the voltage 20c of the output signal 20 at time s0 is a positive value, the AD conversion circuit 10 outputs a positive value as a digital value. Therefore, the filter circuit 13 disposed in the subsequent stage outputs a signal having a polarity that increases the frequency of the output clock of the voltage controlled oscillation circuit 14 in accordance with the digital value. In the voltage controlled oscillation circuit 14, the frequency of the output clock is increased according to the output of the filter circuit 13.

  The timing generation circuit 5 finally converges to the target signal processing operation state shown in FIG. 6 by repeating the signal processing operation in FIG. 7 and the signal processing operation in FIG. Note that such a timing generation circuit 5 can be set in units of resolution of the AD conversion circuit 10, and therefore can be set finely regardless of the clock frequency of the voltage controlled oscillator 25.

  Further, a portion between the AD conversion circuit 10 and the DA conversion circuit 12 is a digital processing section. In the digital section, expansion of the circuit scale when additional signal processing is performed is suppressed. In the timing generation circuit 5 described above, the arithmetic circuit 11 is disposed between the AD conversion circuit 10 and the DA conversion circuit 12. A compensation circuit 16 is connected to the arithmetic circuit 11. The compensation circuit 16 outputs a target value corresponding to environmental changes such as temperature conditions and humidity conditions. In the arithmetic circuit 11, the difference between the target value output from the compensation circuit 16 and the digital value output from the AD conversion circuit 10 is calculated and output to the DA conversion circuit 12. Therefore, the timing generation circuit 5 can suppress the influence of environmental changes.

  In the timing generation circuit 5, the compensation circuit 16 includes a temperature detection circuit 17 and an arithmetic circuit 18. The temperature detection circuit 17 detects the temperature. The arithmetic circuit 18 determines and outputs a target value corresponding to the detected temperature using a preset function. As a result, the concentration sensor 100 can perform detection with high accuracy while suppressing the influence of temperature change.

  For example, when the temperature of the measurement object 6 is detected by the temperature detection circuit 17, the output fluctuation accompanying the temperature change of the measurement object 6 can be suppressed. In particular, if the measurement object 6 is a mixed fuel in which gasoline and alcohol are mixed as described above, the output fluctuation accompanying the temperature change becomes large, so that the suppression of the output fluctuation accompanying the temperature change is effective. Further, when the temperature detection circuit 17 detects the temperature of the processing circuit that constitutes the concentration sensor 100 such as the voltage controlled oscillation circuit 14 and the detection circuit 4, it is possible to suppress the output fluctuation accompanying the temperature change of the processing circuit. In particular, in the case of using an IC in which a plurality of processing circuits are integrated, the output fluctuation accompanying the temperature change becomes large, so it is effective to suppress the output fluctuation accompanying the temperature change.

  The concentration sensor of the present disclosure is particularly effective in an internal combustion engine application such as an automobile.

DESCRIPTION OF SYMBOLS 1 AC voltage source 2 Capacitor 4 Detection circuit 5 Timing generation circuit 6 Measurement object 10 AD conversion circuit 11 Calculation circuit (1st calculation circuit),
12 DA converter circuit 14 Voltage controlled oscillation circuit 15 Frequency divider circuit 16 Compensation circuit 17 Temperature detection circuit 18 Calculation circuit (second calculation circuit)
20 Output signal 100 Concentration sensor φ0 Clock signal φ1 Output signal φ2 Output signal

Claims (3)

A capacitor placed in the measurement object;
An AC voltage source for applying an AC voltage to the capacitor;
A detection circuit for detecting an output signal from the capacitor;
A timing generation circuit that generates a detection timing signal of the detection circuit from the AC voltage,
The timing generation circuit includes:
An AD conversion circuit for converting an output signal from the AC voltage source into a digital value;
A DA conversion circuit that converts a digital value output from the AD conversion circuit into an analog signal; a voltage-controlled oscillation circuit that outputs a clock signal corresponding to the analog signal output from the DA conversion circuit;
A frequency dividing circuit that divides the clock signal output from the voltage controlled oscillation circuit,
The sampling timing signal in the AD conversion circuit is a clock signal output from the voltage controlled oscillation circuit,
The sampling timing signal in the DA converter circuit is an output signal from the frequency divider circuit,
The detection timing signal of the detection circuit is an output signal from the frequency divider circuit.
Concentration sensor. A first arithmetic circuit connected between the AD conversion circuit and the DA conversion circuit;
A compensation circuit connected to the first arithmetic circuit,
The concentration sensor according to claim 1. The compensation circuit includes:
A temperature detection circuit;
A second arithmetic circuit that calculates an output value based on a detection result of the temperature detection circuit;
In the first arithmetic circuit, a difference between an output value from the second arithmetic circuit and an output value from the AD converter circuit is calculated.
The concentration sensor according to claim 2.

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