JPH0425752A - Electrical capacitance instrument for measuring alcohol concentration - Google Patents

Abstract

PURPOSE:To accurately detect alcohol concn. even at a time for voltage drop of a battery by providing the respective means for decision of voltage drop of the battery, calculation of correcting voltage at a time for voltage drop and addition thereof to the detection voltage. CONSTITUTION:A voltage detector 41 detects voltage VB of a battery and the detected value is inputted into a voltage correcting arithmetic device 43 provided with a voltage correcting map 43A and a memory circuit of built-in a voltage correcting program for the alcohol concn. The map 43A of built-in device 43 shows the fluctuating relation of both output voltage V0 correspondent to alcohol concn. and the voltage VB of the battery. When both voltage is known, the correcting voltage DELTAV0 is decided. The device 43 sets the correcting voltage DELTAV0 from the inputted both voltage and the map 43A. This is added to output voltage V0 and the device 43 outputs the detection voltage V0' to an injection amount arithmetic device 30. Thereby even when voltage V0 of the battery is lowered, the detection voltage V0' correspondent to the alcohol concn. is output and the alcohol concn. is accurately detected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a capacitive alcohol concentration measuring device that is applied to, for example, a fuel injection control device for an engine using methanol mixed fuel.

[Conventional technology]

Recently, alcohol-mixed gasoline containing methanol has come to be used as fuel for automobile engines instead of pure gasoline.

Naturally, the stoichiometric air-fuel ratio A/F differs between genuine gasoline and alcohol-mixed gasoline, so the fuel injection amount, ignition timing, etc. of the engine also differ.

Here, looking at the fuel injection amount T when using genuine gasoline with an alcohol concentration of 0%, T r = T
p X (X X α' X Coat + Tm ”
(1) However, TP: Basic injection amount α: Air-fuel ratio A/F feedback correction coefficient α': Basic air-fuel ratio A/F learning correction coefficient Coat: Various correction coefficients T, : Calculated as battery voltage correction coefficient. At this time, the air-fuel ratio A/F feedback correction coefficient α is corrected based on the oxygen concentration signal from the oxygen sensor, and the basic air-fuel ratio A/F learning correction coefficient α' is calculated from the basic injection amount Tp and the engine speed N. By performing learning correction, the theoretical air-fuel ratio A/F is controlled to be 14.7.

In this way, the air-fuel ratio A/F of genuine gasoline is 14.7, but when using methanol with an alcohol concentration of 100%, it is necessary to control the air-fuel ratio A/F to 6.5. Therefore, when the alcohol concentration is in the range of 0 to 100%, the stoichiometric air-fuel ratio A/F differs by about twice.

Therefore, when using alcohol-mixed gasoline,
From equation (1), the fuel injection amount Tl' is calculated as T I = MIl x
Tp × (2X Q' X Coat + Ts...
(2) However, MK: It is necessary to calculate it as a constant determined by the alcohol concentration.

For this reason, engines that use alcohol-mixed gasoline are equipped with an alcohol concentration measuring device called an alcohol sensor, which generates an output voltage corresponding to the alcohol concentration, and calculates equation (2) based on the output voltage value. It is now possible to do this. This type of alcohol concentration measurement device includes a resistance alcohol concentration measurement device that detects alcohol concentration from the electrical conductivity of gasoline and alcohol, and a capacitance alcohol concentration measurement device that uses changes in the dielectric constant of alcohol-mixed gasoline. An optical alcohol concentration measuring device that utilizes a change in refractive index is known.

Among the above-mentioned alcohol concentration measuring devices, the ones shown in FIGS. 5 to 11 are conventionally known as fuel injection control devices using capacitive alcohol concentration measuring devices.

First, in FIG. 5, reference numeral 1 denotes an automobile engine, and the engine 1 is provided with an injection valve 2 for injecting alcohol-mixed gasoline into a combustion chamber, an intake manifold 3 for taking in outside air, and an intake filter 4. An air flow meter 5 for measuring the amount of intake air is provided between the two. Further, the engine 1 is provided with an exhaust manifold 6, and the exhaust manifold 6 is provided with an oxygen sensor (not shown).

7 is a fuel tank that stores alcohol-mixed gasoline 8;
A fuel pump 9 for discharging the alcohol-mixed gasoline 8 is provided within the fuel tank 7 .

10 is a fuel pipe; one end of the fuel pipe 10 is connected to the discharge side of the fuel pump 9 via a fuel filter 11, and the other end is connected to the inlet side of the injection valve 2 and the pressure regulator 12; The outflow side of the fuel tank 7 is connected to the fuel tank 7 via a return pipe 13.

Reference numeral 14 denotes a capacitive alcohol concentration measuring device installed, for example, in the middle of the fuel pipe 10, and the alcohol concentration measuring device 14 detects the alcohol concentration in the alcohol-mixed gasoline 8 flowing inside the fuel pipe 10. . Here, as shown in FIG. 6, the alcohol concentration measuring device 14 consists of a pair of parallel plate-shaped or coaxial co-cylindrical electrode plates provided in the fuel pipe 10. In the case of parallel plate-shaped electrodes, , the capacitance C8 is S...(3) C・''8d, where C: dielectric constant S: electrode area d: distance between electrodes; Based on the capacitance C3 detected by the capacitance detector 15, the oscillation frequency f is determined.
a frequency divider circuit 17 that divides the oscillation frequency f from the frequency divider circuit 17 and converts it into a frequency f' to remove noise; and a frequency-voltage conversion circuit 18 that converts the frequency f' from the frequency divider circuit 17 as a detection voltage ■. (hereinafter referred to as "rf-V conversion circuit 18"), an inverting amplifier circuit 19 that inverts and amplifies the detected voltage (2) from the f-V conversion circuit 18 and outputs it as an output voltage v0, and each of the circuits 17, 18 . 19 and a constant voltage circuit 20 that supplies a constant voltage to the circuit 19.

Here, the constant voltage circuit 20 will be explained with reference to FIG. 7. The constant voltage circuit 20 converts the battery voltage ■8 from the battery 21 mounted on the automobile into a constant voltage ■A (for example, rated voltage 5V), and supplies each of the circuits 16, 17 .
18, which includes a constant voltage element 22 consisting of a three-terminal regulator, a protective resistor 23, and a Zener diode 24.
and capacitors 25 and 26 for preventing oscillation. The protective resistor 23 is connected in series between the positive side of the battery 21 and the input terminal 22A of the constant voltage element 22, and the Zener diode 24 and the capacitor 25 are connected between the input terminal 22A of the constant voltage element 22 and the ground 27. connected in parallel. Furthermore, constant voltage element 22
A capacitor 2 is connected between the output terminal 22B and the ground 27.
6 is connected to supply a stable constant voltage VA. The Zener diode 24 and the protective resistor 23
A protection circuit 28 is configured to prevent damage to electronic components due to inductive surge, reverse connection, etc. of the battery 21. Further, the protective resistor 23 has a high resistance value, and is used to lower the battery voltage 8 and regulate the input voltage of the constant voltage element 22.

That is, the alcohol concentration measuring device 1 configured in this way
4, the alcohol mixed gasoline 8 has the relationship between the alcohol concentration M and the dielectric constant ε as shown in FIG. With the relationship shown in Figure 9, the oscillation circuit 169
The detected voltage V by the fV conversion circuit 18 after passing through the frequency dividing circuit 17 has the characteristics as shown in FIG. 10, and by inverting and amplifying this in the inverting amplifier circuit 19, the output voltage v0 as shown in FIG. It has a unique characteristic. Thus, the alcohol concentration measuring device 14 outputs an output voltage (■) with the characteristics shown in FIG. 11 for the alcohol concentration M. can be obtained.

Further, 29 indicates a control unit constituted by, for example, a microcomputer, and the control unit 29 is for performing electronic injection control, and is constituted by including an injection amount calculation device 30, etc., and is configured to control the injection amount. The input side of the calculation device 3° is the crank angle sensor 3.
1. Air flow meter5. It is connected to an oxygen sensor, a water temperature sensor (none of which are shown), and the output side is connected to an injection valve 2 that injects fuel into the engine. Here, the injection amount calculation device 30 calculates the engine speed N from the crank angle sensor 31 and the intake air amount Q from the air flow meter 5.
Based on the output voltage V0 from the alcohol concentration measuring device 14 or signals from various sensors, the basic injection amount Tp is calculated by formula (2).
+' is calculated, and an injection pulse having a pulse duty corresponding to this fuel injection amount Tl' is output to the injection valve 2.

When the alcohol concentration measuring device 14 according to the prior art is applied to a fuel injection control device, it is configured as described above.
In the capacitance detector 15, (
3) is detected, the oscillation circuit 16 oscillates the frequency f according to the equation (4) in accordance with the alcohol concentration M, and the fV conversion circuit 18 converts the frequency via the frequency dividing circuit 17. The detection voltage ■ corresponding to f' is outputted, and the inverting amplifier circuit 19 outputs the output voltage ■ after being inverted and amplified. Output.

On the other hand, on the control unit 29 side, the fuel injection amount T+' can be calculated according to equation (2) using the output voltage v0 from the alcohol concentration measuring device 14, making it possible to perform highly accurate injection control.

[Problem to be solved by the invention]

However, in the above-mentioned conventional technology, when the engine is started at a low temperature, etc., the battery voltage Va drops due to a decrease in the capacity of the battery 21, making it impossible to input a predetermined voltage (for example, 8■) or more to the constant voltage circuit 20. Each of the circuits 16.1
There is a problem in that the constant voltage VA supplied to 7, 18, and 19 becomes lower than the rated voltage, and the output voltage v0 also decreases, making it impossible to accurately detect the alcohol concentration. To solve this problem, it is possible to ensure a constant voltage by reducing the voltage drop across the protective resistor 23 of the protective circuit 28, but in this case, the resistance value of the protective resistor 23 must be reduced. Inductive surge and battery 2
This results in a reduction in the durability of protection due to the reverse connection of 1 and the like.

The present invention has been made in view of the problems of the prior art, and is a capacitive alcohol method that enables accurate detection of alcohol concentration even when the battery voltage drops due to deterioration of battery performance. The purpose of the present invention is to provide a concentration measuring device.

[Means to solve the problem]

In order to solve the above problems, the capacitive alcohol concentration measuring device according to the present invention, as shown in FIG. A capacitance detector 101, an oscillation circuit 102 that oscillates a frequency based on the capacitance detected by the capacitance detector 101, and a frequency that converts the oscillation frequency by the oscillation circuit 102 into a detection voltage corresponding to the alcohol concentration. -Voltage conversion circuit 103 and battery 10
In the capacitive alcohol concentration measuring device, the capacitance type alcohol concentration measuring device includes a constant voltage circuit 105 that supplies the power supply voltage from 4 to the oscillation circuit 102 and the frequency-voltage conversion circuit 103 as a constant voltage, respectively. A voltage drop determining means 106 determines whether the voltage from the battery 104 has dropped below a predetermined voltage, and when the voltage drop determining means 106 determines that the voltage has dropped below the predetermined voltage,
A correction voltage calculation means 107 calculates a correction voltage from the detected voltage from the frequency-voltage conversion circuit 103 and the dropped voltage value, and a correction voltage calculation means 107 calculates the correction voltage from the frequency-voltage conversion circuit 103. The present invention is comprised of an adding means 108 for adding to the detected voltage.

[Effect]

With the above configuration, when the battery voltage applied to the constant voltage circuit drops, the detection voltage of alcohol concentration can be accurately detected by adding a correction value to the detection voltage according to this voltage drop. .

〔Example〕

Embodiments of the present invention will be described below with reference to FIGS. 2 to 4. In the embodiment, the same components as those in the prior art described above are given the same reference numerals, and their explanations will be omitted.

In the figure, 41 indicates a voltage detector connected between the battery 21 and the constant voltage circuit 20, and the voltage detector 41 is
The battery voltage Vs is detected by a detection resistor or the like and inputted to a voltage correction calculation device 43, which will be described later. 42
2 shows a control unit composed of a microcomputer or the like, and the control unit 42 is composed of the injection amount calculation device 30 and the voltage correction calculation device 43 described in the above-mentioned prior art. A storage circuit comprised of ROM and RAM in the voltage correction arithmetic unit 43 stores a voltage correction map 4 analyzed through experiments as shown in FIG.
3A and an alcohol concentration voltage correction program shown in FIG. 4 are stored.

Here, the characteristic diagram of the voltage correction map 43A shown in FIG. 3 will be explained. The characteristic diagram in Figure 3 shows, for example, alcohol concentration M of 0.20, 40, 60.80, 100% (
Below, this is MO.

M20. ..., Mloo), battery 2
Output voltage V for battery voltage ■8 applied from 1
This shows the variation of o. The characteristic diagram shown in FIG. 3 was obtained through experiments; when the battery voltage 6 becomes 8V or less, the output voltage V. was also found to decrease.

Conversely, if the battery voltage ■ and the output voltage v0 are known, the correction voltage Δ■o can be detected. For example, the battery voltage v3 is 7■, and the output voltage is ■. is 2.3■, the alcohol concentration is Mloo
When the correction voltage Δ■. becomes 0.43V.

Next, the voltage correction processing operation of the alcohol concentration by the voltage correction calculation device 43 in the control unit 42 will be explained with reference to FIG.

First, when the processing operation is started, in step 1, the battery voltage ``8'' is read from the voltage detector 41, and in step 2, it is determined whether the battery voltage ``8'' is equal to or higher than a predetermined voltage (for example, 8.3V), rYES'', the process moves to step 5, and in the case of rNOJ, the process moves to step 3. That is, when it is determined in step 2 that the battery voltage is rNOJ, the battery voltage 8 is lower than 8,3 2, so the process moves to step 3.

Now, in step 3, the output voltage V. Inverting amplifier circuit 19
In step 4, with reference to the voltage correction map 43A stored in the voltage correction calculation device 43, a correction voltage Δ■ is calculated from the battery voltage ■6 and the output voltage vo. Read out the correction voltage △■. Set.

On the other hand, in the case of rYESJ in step 2, since the battery voltage ■8 is in a normal state, the process moves to step 5, and in step 5, the correction voltage Δ■o is set to Ov.

Furthermore, in step 6, the correction voltage △■ set in steps 4 and 5 is applied. is added to the output voltage vo,
Detection voltage■. ' is obtained, and in step 7, the injection amount calculation device 3
0, the detection voltage V0' is output, and the process returns from step 8.

Here, step 2 is a voltage drop determination means according to the present invention,
Steps 3 to 5 constitute correction voltage calculation means, and step 6 constitutes addition means.

Thus, the operation of the alcohol concentration measuring device 14 of this embodiment configured as described above is almost the same as that of the prior art.

However, in this embodiment, even if the battery voltage (■8) applied to the constant voltage circuit 20 drops, the output voltage (■) is maintained by the voltage correction calculation device 43. Correction voltage Δ■. Add and
Detection voltage corresponding to alcohol concentration■. ′ can be output, allowing accurate detection of alcohol concentration,
The detection performance of the alcohol concentration measuring device 14 can be improved. Furthermore, since it is no longer necessary to reduce the resistance value of the protective resistor 23 of the protective circuit 28, it is possible to prevent damage to various electronic components due to inductive surges, reverse connection of the battery 21, etc., and the life of the alcohol concentration measuring device 14 can be reduced. can be extended. Furthermore, when the capacitive alcohol concentration measuring device of this embodiment is used as a fuel injection control device, it is possible to calculate the fuel injection amount T,' according to equation (2), which is accurate and highly accurate. Injection control becomes possible.

Although the explanation was omitted in the above embodiment, when the battery voltage ゎ becomes 6V or less, it is determined that it is impossible to start the car itself, it is determined that there is no need to detect the alcohol concentration, and the detected voltage is ■. The correction is now canceled.

In addition, in the alcohol concentration voltage correction process of the embodiment, when the battery voltage 6 has not fallen below a predetermined voltage, that is, when the battery voltage VB is normal, the correction voltage Δ■ is set in step 5. is set to Ov, but in this case, the detected voltage V0 may be output as is without performing voltage correction processing.

Further, in the above embodiment, the inverting amplifier circuit 19 is provided at the next stage of the f-V conversion circuit 18, but the inverting amplifier circuit 19 does not necessarily need to be provided.On the other hand, a non-inverting amplifier circuit may also be used. good. Further, the frequency dividing circuit 17 may be provided as necessary.

[Effects of the Invention] As detailed above, according to the present invention, the voltage from the battery applied to the constant voltage circuit is detected, and the voltage drop determination means detects whether the battery voltage has dropped below a predetermined voltage. When the voltage drop determining means determines that the voltage has dropped below a predetermined voltage, the corrected voltage calculating means calculates a correction voltage corresponding to the detected voltage and the dropped voltage value. The corrected voltage is applied to the frequency -
By adding the detection voltage to the detected voltage from the voltage conversion circuit, the alcohol concentration can be accurately detected even when the voltage from the battery drops, and high-performance alcohol concentration detection can be performed. Furthermore, since the constant voltage circuit is equipped with a protection circuit, protection against inductive surges, reverse battery connections, etc. can be achieved at low cost and in a small size, as in the past.

[Brief explanation of drawings]

FIG. 1 is a functional block diagram showing the basic configuration of a capacitive alcohol concentration measuring device according to the present invention, FIGS. 2 to 4 show embodiments of the present invention, and FIG. Circuit configuration diagram of capacitive alcohol concentration measuring device, Part 3
The figure is a diagram showing the relationship between the battery voltage applied to the constant voltage circuit and the output voltage corresponding to the alcohol concentration, Figure 4 is a flowchart showing the voltage correction calculation process, and Figures 5 to 11 show the conventional technology. 5 is an overall configuration diagram when a capacitive alcohol concentration measuring device according to the prior art is applied to a fuel injection control device, FIG. 6 is a block diagram showing the circuit configuration of the prior art, and FIG. Electrical circuit diagram of the voltage circuit, Figure 8 is a diagram showing the relationship between alcohol concentration and dielectric constant, Figure 9 is a diagram showing the relationship between alcohol concentration and detected capacitance, and Figure 10 is a diagram showing the relationship between alcohol concentration and dielectric constant. A diagram showing the relationship between the detected voltage from the fV conversion circuit, and FIG. 11 is a diagram showing the relationship between the alcohol concentration and the output voltage from the inverting amplifier circuit. 14... Alcohol concentration measuring device, 15... Capacitance detector, 16... Oscillation circuit, 18... Frequency-voltage conversion circuit, 20... Constant voltage circuit, 21... Battery, 42... Control unit, 43... Voltage correction calculation device. Patent Applicant Japan Electronics Co., Ltd. Agent Patent Attorney Kazuhiko Hirose Figure 1.7 Voltage Vs (V) Figure 10 Alcohol Concentration M ('/,) Figure Alcohol Concentration M ( '/,)

Claims (1)

[Claims] a capacitance detector that detects the alcohol concentration in a liquid containing alcohol as a capacitance between electrodes; an oscillation circuit that oscillates a frequency based on the capacitance detected by the capacitance detector; A frequency-voltage conversion circuit that converts the oscillation frequency of the oscillation circuit into a detection voltage corresponding to the alcohol concentration, and a constant voltage circuit that supplies the power supply voltage from the battery as a constant voltage to the oscillation circuit and the frequency-voltage conversion circuit, respectively. A capacitive alcohol concentration measuring device comprising: a voltage drop determining means for determining whether a voltage from a battery applied to the constant voltage circuit has dropped below a predetermined voltage; When it is determined that the voltage has dropped below the voltage, a correction voltage calculation means for calculating a correction voltage from the detected voltage from the frequency-voltage conversion circuit and the dropped voltage value; 1. A capacitance-type alcohol concentration measuring device comprising: an addition means for adding to a detected voltage from a frequency-voltage conversion circuit.