JP2519116B2 - Capacitance type alcohol concentration measuring device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a capacitance type alcohol concentration measuring device applied to, for example, a fuel injection control device for an engine using a methanol mixed fuel.

[Conventional technology]

Recently, alcohol-mixed gasoline containing methanol has been used as a fuel for automobile engines instead of pure gasoline.

Since the theoretical air-fuel ratio A / F naturally changes between pure alcohol and alcohol-blended gasoline, the fuel injection amount, ignition timing, etc. of the engine will also differ.

Here, looking at the fuel injection amount T _i when using genuine gasoline having an alcohol concentration of 0%, T _i = T _P × α × α ′ × C _oef + T _S (1), and T _P : Basic injection amount α: Air-fuel ratio A / F feedback correction coefficient α ′: Basic air-fuel ratio A / F learning correction coefficient _Coef : Various correction coefficients T _S : 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 T _P 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.
The stoichiometric air-fuel ratio A / F is about twice different when the alcohol concentration is in the range of 0 to 100%.

Therefore, when alcohol-blended gasoline is used, the fuel injection amount T _i ′ can be calculated from the formula (1) as T _i ′ = M _K × T _P × α × α ′ × C _oef + T _S (2) where M _K : Must be calculated as a constant determined by alcohol concentration.

Therefore, an engine using alcohol-blended gasoline is equipped with an alcohol concentration measuring device called an alcohol sensor, generates an output voltage corresponding to the alcohol concentration, and calculates the equation (2) based on the output voltage value. Is designed to do. As this type of alcohol concentration measuring device, a resistance type alcohol concentration measuring device for detecting the alcohol concentration from the electric conductivity of gasoline and alcohol, a number capacitance type alcohol concentration measuring device utilizing the change of the dielectric constant of alcohol mixed gasoline An apparatus, an optical alcohol concentration measuring apparatus utilizing a change in refractive index, and the like are known.

Here, among the alcohol concentration measuring devices described above,
As a fuel injection control device using a capacitance type alcohol concentration measuring device, the one shown in FIGS. 7 to 13 is conventionally known.

First, in FIG. 7, reference numeral 1 denotes an automobile engine. The engine 1 is provided with an injection valve 2 for injecting alcohol-mixed gasoline into a combustion chamber, an intake manifold 3 for inhaling outside air, and an intake filter 4. An air flow meter 5 for measuring the amount of intake air is provided between them. Further, the engine 1 is provided with an exhaust manifold 6, and the exhaust manifold 6 is provided with an oxygen sensor (not shown).

A fuel tank 7 stores the alcohol-mixed gasoline 8, and a fuel pump 9 for discharging the alcohol-mixed gasoline 8 is provided in the fuel tank 7.

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

Reference numeral 14 denotes, for example, a capacitance type alcohol concentration measuring device provided in the middle of the fuel pipe 10. The alcohol concentration measuring device 14 is an alcohol mixed gasoline 8 flowing in the fuel pipe 10.
It is for detecting the alcohol concentration in the inside. Here, the alcohol concentration measuring device 14 comprises a pair of parallel plate type or coaxial cylindrical electrode plates provided in the fuel pipe 10 as shown in FIG. Capacitance C _S However, ε: permittivity S: electrode area d: capacitance detector 15 which detects as the distance between electrodes, and the capacitance detector
Based on the detection capacitance C _S by 15, the oscillation frequency f is However, L: inductance C ₀ : LC type oscillation circuit 16 that oscillates as a circuit capacitance, and a frequency that converts an oscillation frequency f from the oscillation circuit 16 into a detection voltage V −
Voltage conversion circuit 17 (hereinafter referred to as "f-V conversion circuit 17")
And an inverting amplifier circuit 18 that inverts and amplifies the detection voltage V from the f-V conversion circuit 17 and outputs it as an output voltage V ₀ .

That is, in the alcohol-blended gasoline 8, since the relationship between the alcohol concentration M and the dielectric constant ε has the characteristic shown in FIG. 9, the interelectrode capacitance C _S by the capacitance detector 15 and the alcohol concentration M are the tenth. In the relationship shown in the figure, the detected voltage V by the fV conversion circuit 17 through the oscillation circuit 16 has the characteristic as shown in FIG. 11, and by inverting and amplifying this by the inverting amplifier circuit 18,
The characteristic has an output voltage V ₀ as shown in FIG. Thus, the alcohol concentration measuring device 14 can obtain the output voltage V ₀ having the characteristic shown in FIG. 12 with respect to the alcohol concentration M.

A temperature sensor 19 is provided, for example, in the middle of the fuel pipe 10 and includes a thermistor or a posistor for detecting the fuel temperature of the alcohol-blended gasoline 8 (hereinafter referred to as "fuel temperature"). The temperature t detected by the temperature sensor 19 is t. Is input into the alcohol concentration temperature correction device 21 described later, and the alcohol concentration M
Is temperature-corrected.

Reference numeral 20 denotes a control unit composed of, for example, a microcomputer. The control unit 20 is for performing electronic injection control, and includes an alcohol concentration temperature correction device 21 and an injection amount calculation device 22. Has been done.

Here, the electrostatic capacitance type alcohol concentration measuring device 14 focuses on the fact that the dielectric constant ε increases as the alcohol concentration M increases, as described above with reference to FIG.
It is detected as a change in C _S and output as a voltage value. However, the dielectric constant ε not only changes as the alcohol concentration M increases, but also changes with temperature. As a result, the output voltage V _{0 from the} capacitance type alcohol concentration measuring device 14 has temperature dependency and has characteristics as shown in FIG. 13 with respect to the fuel temperature t. That is, the output voltage V ₀ of the alcohol concentration measuring device 14 is generated as the output voltage becomes larger as the temperature becomes lower for the same alcohol concentration M.

Therefore, the alcohol concentration temperature correction device 21 is realized in the control unit 20 by software,
The input side of the alcohol concentration temperature correction device 21 is connected to the alcohol concentration measuring device 14 and the temperature sensor 19, the output side is connected to the injection amount calculation device 22, and the output voltage V ₀ from the inverting amplifier circuit 18 is sensed. The temperature is corrected based on the temperature detected by the sensor 19, and a temperature correction map 21A is provided inside a storage element such as a RAM or a ROM. In addition, temperature correction map 21A
The relationship between the alcohol concentration M and the output voltage V ₀ is stored as a map for each detected temperature t, and the corrected standard output voltage or the corrected standard alcohol concentration corresponding to, for example, 20 ° C. is output. There is.

Furthermore, the injection amount calculation device in the control unit 20
The input side of the injection valve 22 is connected to the alcohol concentration temperature correction device 21, the crank angle sensor 23, the air flow meter 5, the oxygen sensor, the water temperature sensor (all not shown), and the output side is an injection valve for injecting fuel into the engine. It is connected to 2.
Here, the injection amount calculation device 22 calculates the basic injection amount T _P from the engine speed N from the crank angle sensor 23 and the intake air amount Q from the air flow meter 5, and at the same time from the alcohol concentration temperature correction device 21. other standard output voltage or standard alcohol concentration after correction, based on signals from various sensors, (2) 'is calculated, and the fuel injection amount T _i' fuel injection amount T _i by formula with a pulse duty corresponding to The injection pulse is output to the injection valve 2.

When the alcohol concentration measuring device 14 according to the prior art is applied to the fuel injection control device, it is configured as described above, but the electrostatic capacitance detector 15 corresponds to the alcohol concentration M and the electrostatic capacitance by the formula (3) is used. detecting a C _S, corresponding to the alcohol concentration M in the oscillator circuit 16 (4) oscillates a frequency f by an equation, and outputs a detection voltage V corresponding to the frequency f in f-V conversion circuit 17, inverting amplifier circuit 18 is the output voltage after inverting amplification
Output V ₀ .

On the other hand, on the control unit 20 side, the alcohol concentration temperature correction device 21 performs temperature correction of the alcohol concentration based on the output voltage V ₀ from the alcohol concentration measurement device 14 and the detected temperature t from the temperature sensor 19, for example, 20
The standard output voltage or standard alcohol concentration corresponding to ° C is output to the injection amount calculation device 22. As a result, the injection amount calculation device 22 can calculate the fuel injection amount T _i ′ according to the equation (2) based on the standard alcohol concentration that is not affected by temperature, and highly accurate injection control can be performed.

[Problems to be Solved by the Invention]

However, in the above-mentioned conventional technology, the LC type oscillator circuit 16
Since the low frequency (100KHz or less) is used as the oscillating frequency f, the oscillating frequency varies due to the influence of the conductive substances (metal ions, etc.) deposited in the fuel, and the detection voltage is unstable. There is a problem that becomes. Therefore, there is a problem in that the fuel injection amount T _i ′ of the injection amount calculation device 22 cannot be calculated accurately and the air-fuel ratio A / F cannot be controlled accurately.

The present invention has been made in view of the above-mentioned problems of the prior art. The oscillation frequency of the oscillation circuit is high, a predetermined frequency range is used, and noise and the like generated in the circuit are removed. Accordingly, it is an object of the present invention to provide a capacitance type alcohol concentration measuring device capable of performing stable and accurate alcohol concentration detection.

[Means for Solving the Problems]

In order to achieve the above object, the present invention provides a capacitance detector for detecting the alcohol concentration in a liquid mixed with alcohol as a capacitance between electrodes, and a capacitance detector detected by the capacitance detector. The present invention relates to a capacitance type alcohol concentration measuring device, comprising: an oscillation circuit that oscillates a frequency based on the above; and a frequency-voltage conversion circuit that converts the oscillation frequency of the oscillation circuit into a voltage.

And the characteristic of the configuration adopted by the present invention is that when the alcohol concentration is in the range of 0 to 100%, the oscillation frequency of the oscillation circuit is set in the range of 10 to 60 MHz, and the oscillation circuit and the frequency-voltage are set. A frequency dividing circuit that divides the oscillation frequency of the oscillation circuit and then outputs the frequency to the frequency conversion circuit is provided between the conversion circuit and the conversion circuit.

[Action]

Since the electrostatic capacitance detector is present in the alcohol mixed liquid, the electrostatic capacitance between the electrodes corresponding to the alcohol concentration is detected. The oscillator circuit oscillates a frequency based on the detected capacitance. Then, the frequency-voltage conversion circuit converts this oscillation frequency into a voltage, and this voltage signal is input to a computing device or the like and used for fuel injection control or the like.

At this time, by setting the oscillation frequency of the oscillation circuit to 10 to 60 MHz, it is possible to stably output the oscillation frequency of the oscillation circuit without the electrode loss of the capacitance detector being affected by temperature.

Further, by providing the frequency dividing circuit between the oscillation circuit and the frequency-voltage conversion circuit, noise such as ringing generated due to ringing or the like in the oscillation circuit or the frequency-voltage conversion circuit which constitutes the alcohol concentration measuring device is caused. The effect can be eliminated.

〔Example〕

As a result of investigating and researching the cause of the variation of the oscillation frequency f, which is the problem of the above-mentioned conventional technique, the present applicant has found the following.

The capacitance detector 15 appears as an equivalent circuit in FIG. 1 regardless of whether it is a coaxial cylinder type or a parallel plate type, and is configured as a parallel circuit of an internal resistance R and a capacitance C _S. When the electrode loss caused by the internal resistance R and the capacitance C _{S of the} capacitance detector 15 is D, and the relationship between the electrode loss D and the oscillation frequency f of the oscillation circuit is focused, the electrode loss D is It has been found that the oscillation frequency f varies in the low frequency region where it changes greatly, and the experimental results shown in FIGS. 2 and 3 can be obtained.

The electrode loss D of the capacitance detector 15 is However, R is calculated as the internal resistance of the electrode.

That is, FIG. 2 shows, for example, an alcohol concentration of 85% (hereinafter,
M85), the characteristics of the electrode loss D with respect to the frequency f with and without the metal ion are shown for the fuel having a fuel temperature of 20 ° C. The solid line in the figure shows the characteristic line when metal ions are not contained, and the dotted line shows the characteristic line when metal ions are contained.

As is clear from FIG. 2, when the frequency f is in the range of 10 MHz or less, the changes in the electrode loss D change rapidly with each other. In particular, in the frequency range of 100 KHz or less, which has been used in the past, the change becomes sharp when metal ions are included and when it is not included.On the other hand, each characteristic line also has a small change in the frequency range of 100 KHz or less. It can be seen that the electrode loss D changes drastically. For this,
It has been clarified that the detection voltage becomes unstable due to variations in the oscillation frequency f depending on the set frequency range of the oscillation frequency f.

Further, FIG. 3 shows the same experimental results as in FIG. 2 when the fuel temperature is different, the solid line in the figure is the characteristic line when the fuel temperature is −30 ° C., and the dotted line is the case when the fuel temperature is 60 ° C. The characteristic line of is shown.

Also in this case, as is clear from FIG. 3, the electrode loss D changes rapidly in both characteristic lines in the range where the frequency f is 10 MHz or less. For this reason, it was previously used.
At a frequency of 0 KHz or less, the oscillation frequency f varies. Furthermore, the oscillation frequency f
In the region where the temperature is high, the electrode loss D changes although the slope is gentle.

Furthermore, FIG. 4 shows the same experimental results as in FIG. 3 when metal ions are included. The solid line in the figure is the characteristic line when the fuel temperature is −30 ° C., and the dotted line is the fuel temperature of 60 ° C. The characteristic line at the time of is shown. As is apparent from the figure, in the case of containing metal ions of alcohol, the electrode loss D is greatly affected by the fuel temperature in the frequency region of 10 KHz or less.

Based on these results, the configuration of the oscillator circuit is designed so that the electrode loss D is not significantly affected by the fuel temperature in the high frequency region (10 MHz
By improving so that the oscillation frequency f can be obtained at z or more), the variation of the oscillation frequency f can be prevented, and the alcohol concentration can be accurately detected. Also,
Further, by setting the oscillation frequency f in the vicinity of 50 MHz, for example, 40 to 60 MHz, the electrode loss D becomes stable and an accurate output can be obtained. That is, when the fuel temperature is low, the resonance frequency of the molecules of methanol decreases, so the electrode loss D accompanying resonance (dispersion) increases slightly, and due to the effect, the electrode loss D increases slightly on the high frequency side. As shown in, the electrode loss D is particularly stable near 50 MHz.

Here, a specific example of the alcohol concentration measuring apparatus of the present embodiment is shown in FIG. 5 and will be described. It should be noted that the same components as those of the above-described conventional technique are designated by the same reference numerals, and the description thereof will be omitted.

In the figure, 31 is a capacitance type alcohol concentration measuring device, the alcohol concentration measuring device 31 is configured almost the same as the alcohol concentration measuring device 14 described above, the specific configuration is shown in JP-A-1-196557. The capacitance detector 15 provided in the fuel pipe 10 detects the alcohol concentration in the alcohol-blended gasoline 8. Reference numeral 32 denotes the oscillation circuit of the present embodiment, which is configured to oscillate the oscillation frequency f shown in equation (4) by the electrostatic capacitance C _S of the electrostatic capacitance detector 15. Especially when the alcohol concentration changes in the range of 0 to 100%, the oscillation frequency f
Oscillates a frequency of 10 MHz or higher, for example, a frequency within the range of 10 to 60 MHz.

Reference numeral 33 denotes a frequency dividing circuit for dividing the oscillation frequency of the oscillation circuit 32, and the frequency dividing circuit 33 includes the oscillation circuit 32 and the fV conversion circuit.
17 is provided between the oscillation circuit 32 and the oscillation frequency by the oscillation circuit 32 and outputs the frequency to the fV conversion circuit 17,
Noise such as ringing generated in the oscillation circuit 32 and the fV conversion circuit 17 is removed to eliminate the influence of the noise,
It is designed to accurately detect alcohol concentration.

The operation of the alcohol concentration measuring device 31 of the present embodiment having such a configuration is almost the same as that of the conventional technique.

Therefore, in the alcohol concentration measuring apparatus 31 of the present embodiment, the oscillation frequency f of the oscillation circuit 32 is in the range of 10 MHz or higher, for example, 10 MHz.
Since the oscillation is performed in the range of -60 MHz, the influence of the electrode loss D on the change of the fuel temperature is reduced, the variation of the oscillation frequency f is effectively prevented, and the stable frequency can be obtained.

Further, a frequency divider circuit 33 is provided between the oscillator circuit 32 and the f-V converter circuit 17, and the oscillation frequency f of the oscillator circuit 32 is frequency-divided and then output to the f-V converter circuit 17.
It is possible to remove noise such as ringing generated in the 32, f-V conversion circuit 17, eliminate the influence of the noise, and detect an accurate alcohol concentration.

Therefore, the fuel injection amount calculation device 22 can calculate the fuel injection amount T _i ′ according to the equation (2) and perform appropriate air-fuel ratio A / F control, and highly accurate injection control is possible. Become. As a result of mounting the alcohol concentration measuring device 31 of this embodiment on a vehicle and performing a durability test, stable output is obtained as shown in FIG. 6 with almost no output error over a long time (long-distance running). I was able to confirm that.

Further, in the above-described embodiment, the temperature is corrected by the alcohol concentration temperature correction device 21 as in the prior art, but this temperature correction is omitted by appropriately limiting the region of the oscillation frequency f. It is also possible to do so.

Further, the oscillation frequency f of the oscillation circuit 32 is set to 1321 MHz in the alcohol concentration range of 0 to 100% and the alcohol concentration in the fuel is measured to control the fuel injection amount T _i ′ with extremely high accuracy. You can

〔The invention's effect〕

As described in detail above, according to the present invention, when the alcohol concentration is in the range of 0 to 100%, the oscillation frequency of the oscillation circuit is set to 10
By setting it within the range of ~ 60MHz,
Even if metal ions or the like are dissolved in the alcohol-mixed liquid, the electrode loss can be stabilized and an accurate oscillation frequency can be obtained, and the oscillation circuit is provided between the oscillation circuit and the frequency-voltage conversion circuit. Since the frequency dividing circuit outputs the frequency-voltage conversion circuit after dividing the oscillation frequency, noise such as ringing generated in the circuit can be removed and accurate alcohol concentration can be measured. .

[Brief description of drawings]

1 to 6 show an embodiment of the present invention, FIG. 1 is an equivalent circuit diagram of a capacitance detector, and FIG. 2 is an alcohol concentration.
Diagram showing the relationship between oscillation frequency and electrode loss at 85%, No. 3
The figure shows the relationship between the oscillation frequency and the electrode loss at temperatures of -30 ° C and 60 ° C when metal ions are not included. Figure 4 shows the same oscillation frequency as in Figure 3 when metal ions are included. FIG. 5 is a diagram showing a relationship of electrode loss, FIG. 5 is a circuit configuration diagram of a capacitance type alcohol concentration measuring device, FIG. 6 is a diagram showing a result of a durability test of the alcohol concentration measuring device, FIG. 7 to FIG.
FIG. 13 shows a conventional technique, FIG. 7 is an overall configuration diagram when a capacitance type alcohol concentration measuring device according to the conventional technique is applied to a fuel injection control device, and FIG. 8 is a block diagram showing a circuit configuration of the conventional technique. , FIG. 9 is a diagram showing the relationship between alcohol concentration and dielectric constant, FIG. 10 is a diagram showing the relationship between alcohol concentration and detected capacitance, and FIG. 11 is alcohol concentration and f
Fig. 12 is a diagram showing the relationship between the detected voltage from the -V conversion circuit, Fig. 12 is a diagram showing the relationship between the alcohol concentration and the output voltage from the inverting amplifier circuit, and Fig. 13 is the alcohol concentration at each fuel temperature and the inverting amplification. It is a diagram which shows the relationship with the output voltage from a circuit. 15 ... Capacitance detector, 31 ... Alcohol concentration measuring device, 32 ... Oscillation circuit, 33 ... Dividing circuit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masahiko Shimamura 1671, Kasukawa-cho, Isesaki-shi, Gunma Japan Electronic Equipment Co., Ltd. (72) Inventor Kiyoshi Takeuchi, 2 Takara-cho, Kanagawa-ku, Yokohama, Japan Nissan Motor Co., Ltd. Within (56) References: Kaikaihei 2-17650 (JP, U)

Claims (1)

(57) [Claims] 1. A capacitance detection path for detecting the alcohol concentration in a liquid mixed with alcohol as a capacitance between electrodes, and a frequency based on the capacitance detected by the capacitance detector is oscillated. In an electrostatic capacitance type alcohol concentration measuring device comprising an oscillation circuit and a frequency-voltage conversion circuit for converting the oscillation frequency of the oscillation circuit into a voltage,
When the alcohol concentration is in the range of 0 to 100%, the oscillation frequency of the oscillation circuit is set in the range of 10 to 60 MHz, and the oscillation between the oscillation circuit and the frequency-voltage conversion circuit is generated by the oscillation circuit. A capacitance type alcohol concentration measuring device, characterized in that a frequency dividing circuit for dividing the frequency and outputting it to the frequency-voltage conversion circuit is provided.