JPH0580014A - Alcohol fuel ratio sensor - Google Patents

Abstract

PURPOSE:To obtain an alcohol fuel ratio sensor which can detect concentration of alcohol within a fuel highly accurately by compensating for influence of fuel temperature and water content. CONSTITUTION:A change in oscillation frequency due to fuel temperature, that of oscillation frequency due to water composition, and that of leakage resistance are taken out according to an electrostatic capacity for reference which consists of electrodes 11 and 12 where a dielectric which becomes a reference is filled and an electrostatic capacity for detection which consists of electrodes 1 and 2 where a fuel to be inspected is circulated and then temperature compensation according to an up/down counter and an identification of water composition according to a microcomputer table are performed, thus enabling the concentration of alcohol to be detected. Therefore, compensation of temperature and that of water content can be performed by combining a compact sensor element and a circuit, thus obtaining an alcohol fuel ratio sensor which is accurate, reliable, inexpensive, and used easily.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sensor for detecting an alcohol mixing ratio in a fuel of an internal combustion engine using an alcohol mixing fuel, and more particularly to detecting an alcohol mixing ratio in a gasoline / alcohol mixed fuel. It relates to a suitable alcohol fuel ratio sensor.

[0002]

2. Description of the Related Art In recent years, internal combustion engines that use alcohol such as methanol and ethanol as fuel have been attracting attention in order to prepare for the exhaustion of resources or to reduce air pollution. Prior to the transition, the internal combustion engine using so-called alcohol mixed fuel, in which gasoline and alcohol such as methanol and ethanol are mixed, is in the stage of commercialization.

By the way, in an internal combustion engine using such an alcohol mixed fuel, it is necessary to detect the alcohol mixing ratio in the mixed fuel when controlling the engine such as the air-fuel ratio control. Therefore, various types of sensors have been conventionally proposed as a sensor for detecting the alcohol mixing ratio in the mixed fuel, and one of them is a capacitance type alcohol fuel ratio sensor. For the conventional example of the sensor of the type, for example, the actual Kaihei 2-1129
No. 49, Utility Model No. 2-89354, or JP-A No. 2-1.
No. 90755 and the like.

[0004]

The above-mentioned prior art does not consider the following points necessary for practical use of the electrostatic capacity type alcohol fuel ratio sensor, and has a performance, reliability, cost and usability. There is a problem that it is impossible to provide a well-balanced alcohol fuel ratio sensor.

1) As a method for correcting the temperature dependence of capacitance, a sensor such as a metal thin film temperature sensor is used. The fuel temperature characteristic curve of this sensor is the same as the temperature dependence curve of electrostatic capacitance over the entire area. Since it cannot be said that they coincide with each other, the temperature correction coefficient is not constant. Therefore, for temperature correction, a temperature correction coefficient map is created in advance and C
Calculation processing by a PU (Central Processing Unit) is required, and therefore an increase in circuit scale cannot be avoided.

2) No consideration has been given to the detection error caused by the mixing of water into the fuel, and sufficient detection accuracy cannot be obtained. 3) No particular consideration was given to the measures for phase separation of alcohol and fuel due to the mixing of water into the fuel, and the detection accuracy is unavoidable.

An object of the present invention is to provide an alcohol fuel ratio sensor having sufficient practicality, which can directly obtain a temperature-corrected detection result by using a small-scale digital or analog circuit. Another object of the present invention is to provide an alcohol fuel ratio sensor capable of correcting a detection error due to mixing of water and capable of highly accurate detection. Still another object of the present invention is that even if phase separation due to water mixing occurs, detection can be performed with the required accuracy, and corrosion due to water mixing, resin swelling due to fuel, and fuel as these ripple effects (EN) An alcohol fuel ratio sensor capable of sufficiently preventing leakage.

[0008]

As means for correcting the water content and the fuel temperature of the fuel, in the present invention, two pairs of counter electrodes are first arranged in the fuel system, and one of the counter electrodes for alcohol concentration detection is arranged between the counter electrodes. Is a structure in which the test fuel is replaced as a dielectric, and the other reference counter electrode is filled with a known alcohol-mixed fuel that is not replaced as a dielectric or a liquid or solid dielectric.

The alcohol concentration detecting capacitance CC and the reference capacitance CR are used as an oscillation frequency determining element of an oscillator or an astable multivibrator, respectively. The obtained oscillation frequencies f _C and f _R are processed by an integrator or an up / down counter so as to correct the signal component depending on the fuel temperature from the alcohol concentration signal.

Furthermore, the leakage resistance R _L that enters in parallel with the alcohol concentration detecting capacitance CC due to the mixing of water
Therefore, the alcohol fuel ratio signal is corrected by the water content from the ratio of the rising or falling time constants of the rectangular wave outputs of the two oscillators for detection and reference or the up / down counter.

Moisture correction and temperature correction are performed serially,
The water composition signal and the fuel temperature signal are output as needed.
The alcohol / fuel ratio signal with corrected water content and temperature is used to select the optimum one from a plurality of maps prepared in advance in the engine control unit.

As a countermeasure for phase separation due to water mixture, two pairs of counter electrodes are vertically arranged in the entire area from the ceiling surface to the bottom surface in the container, and an outlet is provided near the bottom surface in the container to collect water due to a difference in specific gravity. Prevent.

As a measure against corrosion, swelling and sealing, a fluororesin film is provided on the surface between the opposed electrodes.

[0014]

[Function] Two pairs of counter electrodes are arranged in a metal container provided in the fuel system, one of which is a capacitance C for alcohol concentration detection.
C, the other is formed as a reference electrostatic capacity CR which is pre-filled with a fuel having a constant alcohol concentration and containing no water. These capacitances are used as the frequency determining element of the oscillator. Of the frequencies output from these, f _C is an alcohol concentration signal including an error due to moisture and an error due to temperature, and f _R is a temperature signal at a predetermined alcohol concentration including only an error due to temperature. Therefore, the temperature-corrected alcohol concentration can be detected by comparing these signals.

First, the temperature correction method will be described. Use the up-down counter to count up at fR, fC
When counting down at, a predetermined count-up time t
When 0 is determined, this becomes the reference temperature, and the count-up voltage V0 represents the normalized fuel temperature. This V
When 0 is counted down by fC, the countdown time tC has a correlation with the temperature-corrected alcohol concentration. Here, fC or fR, and t0 can be adjusted or optimized to improve temperature correction accuracy.

Next, the moisture correction will be described. The composition ratio of the mixed water has a correlation with the electrostatic capacity and the leakage resistance that enters in parallel with it. Therefore, the water composition ratio can be obtained from the oscillation frequency fC of the output of the unstable multivibrator. However, since the water composition ratio cannot be specified with one oscillation frequency f _C1 , for example, the frequency f _C2 when the electrostatic capacitance is connected in parallel to the detection capacitance is obtained as the other oscillation frequency, and the microcomputer frequency is calculated from these two types of frequencies. You can specify the alcohol concentration using the table in.

As another method for specifying the water composition ratio, the feedback resistance is replaced with a large value at the time of discharge to obtain the change Δτ / τ in the discharge time constant from the detection electrostatic capacitance, and f
The alcohol concentration can also be obtained from C1 and Δτ / τ using a table of the microcomputer.

When water is mixed in in a normal use state, the leakage resistance that enters in parallel with the capacitance is reduced by two to three digits. Therefore, the correction of the alcohol concentration by the leakage resistance is
Required as well as temperature correction.

When water is mixed in the alcohol mixed fuel,
Generally, since alcohol and water have a high affinity, alcohol and gasoline undergo phase separation in a stationary state. Even in such a case, in order to detect the average alcohol concentration, the counter electrode is arranged vertically from the ceiling surface to the bottom surface of the fuel container.
Further, regarding the positional relationship between the inlet passage and the outlet passage of the fuel container, the inlet is arranged near the bottom surface and the outlet is arranged near the ceiling surface so that the fuel in the container is quickly replaced.

As a method of signal processing the change in capacitance, it is effective to convert the signal into a frequency, process it with a digital logic circuit, and output it digitally. There is a method of using an up-down counter to process the temperature correction digitally. Note that analog output may be possible.

The mounting position of the alcohol fuel ratio sensor is
If it is placed near the pressure regulator and the injection valve on the fuel pump side of the fuel supply system of the engine, the consistency with the injected fuel is improved. Therefore, by incorporating the sensor in the pressure regulator, the mountability can be improved.

[0022]

The alcohol fuel ratio sensor according to the present invention will be described in detail below with reference to the embodiments shown in the drawings. FIG. 1 is a sectional structural view showing an embodiment of the present invention.
Is an inner electrode forming an electrostatic capacitance element for alcohol concentration detection, 2 is also an outer electrode, both of which are made of a metal tube and are held by insulating support members 4 and 5 so as to maintain a concentric gap. , The capacitance formed between them becomes the detected capacitance value CC.

The outer electrode 2 is provided with a plurality of flow holes 3 so that fuel can easily flow in and out. The inner electrode 1 is connected to a lead-out terminal 6 which is sealed to the flange 15 with glass, so that a conductive path to the outside is drawn out, while the outer electrode 2 is formed by a recess 7 provided in a metal container 8. It is held and electrically connected to the metal container 8. On the other hand, the fuel inflow pipe 13 and the outflow pipe 14 are connected to the metal container 8 and are connected to the fuel supply path of the engine.
It is sealed from the outside.

On the other hand, 10 is an inner electrode forming the reference capacitance element, 11 is also an outer electrode, and these are also the inner electrodes 1 forming the alcohol concentration detecting electrostatic capacitance element.
And has the same configuration as the outer electrode 2, except that the outer electrode 11 has no through holes, and a dielectric 12 having a known relative permittivity is filled between these electrodes. The capacitance formed between them becomes the reference capacitance CR.

As the dielectric 12, a fuel which does not contain water and has a known alcohol concentration is used, but as another embodiment, a dielectric whose temperature characteristic of relative permittivity is similar to that of the test fuel is used. You may do it.

These two sets of electrostatic capacitances CC and CR are taken out by the connection fittings 9 and processed by the signal processing circuit 20 mounted on the printed circuit board 19 and then corrected by temperature and water. Is output from the lead 22. Reference numeral 17 is a fixing screw for the printed circuit board, 18 is a mounting bracket for the sensor, and 21 is a housing for the signal processing circuit.

In this embodiment, as is clear from the figure, the inner electrodes 1 and 10 and the outer electrodes 2 and 11 which form the two sets of electrostatic capacitances CC and CR are vertically arranged in the metal container 8. The fuel cell is arranged so as to reach from the ceiling surface to the bottom surface, so that even if phase separation occurs in the fuel, the alcohol concentration can be detected on average without being affected by it.

Next, in this embodiment, the surfaces of the inner electrodes 1 and 10 and the outer electrodes 2 and 11 constituting these two sets of electrostatic capacitances CC and CR are covered with a fluororesin coating material. This prevents corrosion due to moisture in the fuel. Further, in this embodiment, the electronic circuit module is integrally arranged in the storage case adjacent to the outside of the fuel container containing the two sets of electrostatic capacities CC and CR, thereby providing a space for mounting on the engine. You can improve the factor.

FIG. 2 shows an example of an engine control system using an alcohol fuel ratio sensor. In the figure, 26 is an alcohol fuel ratio sensor and 33 is an engine control microcomputer. Fuel is pressurized by the pump 27, regulator (fuel injection pressure control valve)
The pressure is adjusted by 30, and the fuel is injected from the injectors 28, 29. The air-fuel mixture compressed in the cylinder of the engine is ignited by the spark discharge generated in the spark plug by the high voltage supplied from the ignition control unit 34 through the ignition coil 35.

At this time, the microcomputer 33
When the signal from the alcohol fuel ratio sensor 26 is taken in together with the signals from the water temperature sensor 31 and the oxygen sensor 32, and when alcohol is mixed with gasoline, the concentration is detected,
Accordingly, the air-fuel ratio at the time of starting or in the power range is appropriately controlled.

FIG. 3 shows an embodiment of a signal processing circuit of an alcohol fuel sensor according to the present invention, which is a static capacitance for detection formed by an alcohol concentration detecting electrostatic capacitance element composed of an inner electrode 1, an outer electrode 2 and a flow hole 3. The capacitance CC is connected to the detecting oscillator 46, and is formed by a reference capacitance element including the inner electrode 10 and the outer electrode 11, and the reference capacitance CR.
Is connected to the reference oscillator 47 and is used as a frequency determining element of each oscillator. Then, at this time, the inner electrode 10 and the outer electrode 11 constituting the reference electrostatic capacitance element
A known dielectric substance having zero water content, for example, a fuel having an alcohol concentration of 50% is filled as a dielectric substance 12 (FIG. 1).

As a result, the frequency f _C of the detecting oscillator 46 is
Changes in proportion to the alcohol concentration, whereas the output frequency f _R of the reference oscillator 47 changes depending only on the temperature of the fuel in the sensor. As a result, since the output frequency f _R of the reference oscillator 47 can be used as a signal indicating the fuel temperature, the terminal 52 is separately provided and taken out.

Reference numeral 48 is a gate circuit for switching between up-counting operation and down-counting operation, 49 is an up-down counter, and 50 is a one-shot multivibrator.
The gate circuit 48 includes the one-shot multivibrator 5
When the output of 0 is "L" level, the output of the reference oscillator 46 is switched to the clock input of the up / down counter 49, but when the output of the one-shot multivibrator 50 becomes "H" level, the reference oscillator is switched. 47
Of the up-down counter 49 is switched to the clock input of the up-down counter 49.

The up-down counter 49 performs an up-count operation when the output of the one-shot multi-vibrator 50 becomes "H" level, and performs a down-count operation when the output of the one-shot multi-vibrator 50 is "L" level. When the count value becomes zero, a pulse is generated at the OUT output and the one-shot multivibrator 50 is supplied with a trigger pulse.

The one-shot multivibrator 50 has a predetermined time constant, and normally maintains the "L" level output state, but a predetermined time T _R (hereinafter, this is set every time the trigger pulse from the up / down counter 49 is input). Is referred to as a reference time), and outputs a signal that goes to "H" level.

Next, the operation of this embodiment will be described. When the temperature changes, the relative dielectric constant of the fuel also changes, and as a result, the oscillation frequency characteristic with respect to the alcohol concentration in the fuel changes as shown in FIG. 4, for example. Therefore, when detecting the alcohol concentration in the fuel, the effect of this temperature change must be corrected, but in the embodiment of FIG. 3, this correction operation is obtained as follows. Figure 5
In the operation sequence of the embodiment of FIG. 3 and an explanatory diagram of the temperature correction operation and the alcohol concentration measurement by the operation sequence, the alcohol temperature correction operation by the up / down counter 49 will be described below with reference to this figure.

When an operating voltage is applied to the system, first the oscillators 46 and 47 start oscillating, which causes the up counter 49 to generate a pulse, which triggers the operation sequence. That is, as a result, the output of the one-shot multivibrator 50 first becomes the "H" level, and as a result, the gate circuit 48 is switched so as to supply the output of the reference oscillator 47 to the up / down counter 49, and at the same time up / down. Counter 49 U /
Trigger on the D terminal, switch to up-count operation,
First, the reference oscillation frequency f _R is counted up for the reference time t _R.

Thus, when the reference time t _R elapses, the output of the one-shot multivibrator 50 falls to the "L" level, so that the gate circuit 48 switches to the output of the detecting oscillator 46 at the same time, and at the same time, the up / down counter. 49 switches to the down count operation, and this time counts down at the output frequency f _C of the detection oscillator 46, and when the count value of the up / down counter 49 becomes zero, the up / down counter 49 again generates a trigger pulse. Occurs, and as a result, the operation sequence is restored,
After that, the same operation is repeated.

Therefore, the reference oscillation frequency f _{R at} this time is
The count value when the up-count only reference time t _R as C _1, continue to count down at the frequency f _C of the count value C _1, t ₁ the time until the count value of the up-down counter 49 becomes zero Then, the duty ratio t ₁ / (t _R + t ₁ ) depending on the time t _R and t ₁ per one sequence represents the alcohol concentration with reference to the dielectric 12.

Therefore, the microcomputer 33 (FIG. 2)
Takes in the OUT output of the one-shot multi-vibrator 50 from the terminal 51 (FIG. 3), calculates the duty ratio t ₁ / (t _R + t ₁ ) of this output signal, and obtains the alcohol concentration in the fuel. It controls the air-fuel ratio of the engine.

By the way, the temperature of the fuel is changed, and the temperature T _{1 is} increased by ΔT from the previous temperature T ₁ to obtain the temperature T ₁ + ΔT.
Let's say. Then, the detection capacitance CC,
Since the capacitance of the reference capacitance CR decreases and the oscillation frequencies of the detection oscillator 46 and the reference oscillator 47 increase as shown in FIG. 4, as shown in (2) of FIG. count value when the frequency f _R and only up-count reference time t _R increases from C ₁ to C ₁ + [Delta] C.

However, at this time, the detection oscillator 4
Since the oscillation frequency f _{C of} 6 also increases in the same manner, the time t ₁ from when the count value C ₁ + ΔC at this time is counted down until the count value of the up / down counter 49 becomes zero is As in the case of T _1, the change in temperature is canceled out, and the output signal of the duty ratio t ₁ / (t _R + t ₁ ) corresponding to the alcohol concentration can be obtained.

On the other hand, if the alcohol concentration of the fuel in FIG. 5 (2) is set to a ₁ and this is increased to a ₂ , only the oscillation frequency f _C of the detection oscillator 46 is reduced this time. ), The countdown time by the oscillation frequency f _C of the detection oscillator 46 becomes t ₂ , and as a result, the duty ratio of the output signal becomes t ₂ / (t _R + t ₂ ), and the alcohol concentration a ₂ is It can be detected.

Therefore, according to this embodiment, the temperature-corrected alcohol concentration signal can be directly obtained from the sensor itself, and the accurate alcohol concentration can be easily detected without providing a map in the microcomputer. Therefore, the engine using the alcohol-blended fuel can be accurately controlled.

Instead of the up / down counter 49, the output of the reference oscillator 47 performs forward integration,
It is also possible to use an integrator that performs integration in the negative direction by the output of the detection oscillator 46 and detect the temperature-corrected alcohol concentration by the output of this integrator.

By the way, in the capacitance type alcohol fuel ratio sensor, as shown in FIG. 6, when water is mixed in the fuel, a detection error occurs. Note that FIG. 6 shows the effect of the water composition ratio existing in the fuel on the alcohol concentration-oscillation frequency characteristic. Therefore, in the electrostatic capacity type alcohol fuel ratio sensor like the present invention,
It is necessary to correct the error due to this mixing of water to detect the alcohol concentration, and one embodiment of the present invention in which this water correction is performed will be described below with reference to FIG. 7.

FIG. 7 (1) shows the structure of the detecting oscillator 46 in the embodiment of FIG. 3. Reference numeral 70 denotes an inverter (inversion amplifier circuit), which is combined with a switch S, and this switch S Is switched to the A contact side, the feedback resistance R _F and the electrostatic capacitance CC by the detecting capacitance element are combined with the inverter 70 to form an unstable multivibrator circuit. Capacitance C
An external capacitor having a capacitance of C is connected in parallel to C, and a circuit in which a diode D is connected in parallel to the feedback resistor R _F is combined with the inverter 70 to form an astable multivibrator circuit. To be done. At this time, if water is mixed in the fuel,
The leakage resistance R _L due to this moisture is formed in parallel with the capacitance CC of the detection capacitance element.

First, the oscillation frequency f _C1 when the switch S is switched to the contact A is determined, and then the oscillation frequency f _C2 when the switch S is switched to the contact B side is determined.

The oscillating frequency f _{C2 at} this time is the oscillating frequency in the state where the detecting capacitance CC and the external capacitor having a sufficiently large capacitance are connected in parallel. , The diode D functions so that the electric charge charged in the detection capacitance CC and the external capacitor is discharged only by the leakage resistance R _L , whereby the oscillation frequency f _C2 is less than that of the leakage resistance R _L. The resistance value, that is, the amount of water mixed in the fuel is sufficiently correlated.

Next, these oscillations oscillation frequencies f _C1 and f _C2
Are sequentially loaded into the microcomputer 33 (FIG. 2), and the alcohol concentration table shown in (2) of FIG. 7 stored in the microcomputer 33 in advance is searched by these, and the oscillation frequency f _C1 , F _C2 and the alcohol concentration are read out, and the alcohol concentration in which the error due to the mixing of water is corrected is calculated.

Therefore, for this reason, the switch S is composed of an electronic switch circuit, and is switch-controlled by a control signal from the microcomputer 33.
In response to this, the microcomputer 33 is provided with two kinds of programs, and the switch S is set to the contact A during the temperature-corrected alcohol concentration detection process.
Switch S side, the switch S is used for the process of correcting the error due to the mixing of water and detecting the alcohol concentration.
Is sequentially switched from the A side to the B side, whereby the oscillation frequencies f _C1 and f _C2 are sequentially fetched. The two types of programs may be alternately executed at a predetermined cycle, or may be arbitrarily executed.

Next, the process of calculating the alcohol concentration in which the detection error due to water is corrected from these oscillation frequencies f _C1 and f _C2 will be described with reference to FIG. In the figure,
The upper curve A ₀ is for the case where the water composition ratio is 0%, and the curve A ₅ is for the case of 5%, and the switch S is switched to the A side.
Further, it is a characteristic curve when the resistance value of the feedback resistance RF is 6.1 kΩ, and the lower curve B ₀ has the same water composition ratio of 0%.
In the case of, the curve B ₅ is also 5%, the case where the switch S is switched to the B side, the capacitance of the external capacitor C is 1000 pF, and the diode D is connected in parallel with the feedback resistor RF. It is a characteristic curve.

First, when the detection oscillation frequency f _C1 is obtained, the detection oscillation frequency f _C1 has two curves A ₀ and A ₅
Request a _5-point and a ₀ point that matches. However, at this stage, the alcohol concentration is determined by the detection oscillation frequency f.
_It can only be specified that _C1 is in the range between the points a ₅ and a ₀ which coincide with the two curves A ₀ and A ₅ . Accordingly, next, the alcohol concentration represented by these a _5-point and a ₀ point, determine the b _0, b ₅ point coincident with the two curves B _0, B ₅ of the lower, between these points Find the connecting straight line b ₀₅ .

Next, when the detection oscillation frequency f _C2 was obtained, a point b _{n at} which this frequency f _C2 intersects the straight line b ₀₅ was obtained. This was corrected for the detection error due to moisture at this time. Alcohol concentration. Therefore, in this way, the values obtained successively for the fuel of which the water content and the alcohol concentration are known are stored in the table of the microcomputer and the alcohol concentration table as shown in FIG. 7 (2) is created. Thereafter, by the processing of the microcomputer 33, the alcohol concentration in which the detection error due to water is arbitrarily corrected can be detected. Therefore, according to this embodiment, even when the alcohol-containing fuel contains water, , The alcohol concentration can always be detected accurately, and the air-fuel ratio of the engine can be accurately controlled.

As another method for specifying the water composition ratio, the change in the time constant Δτ / τ of the discharge from the electrostatic capacitance for detection is calculated by replacing the feedback resistance with a large one during discharge and f
The alcohol concentration can also be obtained from C1 and Δτ / τ using a table of the microcomputer.

Next, regarding still another embodiment of the present invention,
This will be described with reference to FIG. In this embodiment shown in FIG. 9, the sensor according to the present invention is integrated with a regulator for adjusting fuel injection pressure. Is the reference capacitance element, and the detection capacitance element 5
The capacitance value CC according to 6 and the reference capacitance CR according to the reference capacitance element 57 are taken into the signal processing circuit 20 mounted on the printed circuit board 19 and processed there to generate a signal representing the alcohol concentration. Will be output.

According to the embodiment shown in FIG. 9, the space factor in the engine room can be improved by integrating with the regulator, and it is advantageous in simplifying the fuel piping layout.

[0058]

According to the present invention, the temperature dependence and the water content dependence of the alcohol concentration can be accurately corrected by the reference capacitance, so that the alcohol fuel ratio sensor having the required accuracy can be constructed in a compact circuit configuration. It will be possible to easily provide a sensor that is well balanced in terms of performance, reliability, cost, and usability. Can greatly contribute to

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of an alcohol fuel ratio sensor according to the present invention.

FIG. 2 is a configuration diagram showing an example of an alcohol fuel engine control system to which the alcohol fuel ratio sensor according to the present invention is applied.

FIG. 3 is a configuration diagram showing an embodiment of a signal processing unit in the alcohol fuel ratio sensor of the present invention.

FIG. 4 is a characteristic diagram showing temperature dependence of an alcohol-blended fuel.

FIG. 5 is an explanatory diagram of an alcohol concentration detecting operation according to an embodiment of the present invention.

FIG. 6 is a characteristic diagram showing a water composition dependency of an alcohol mixed fuel.

FIG. 7 is an explanatory diagram showing the configuration of another embodiment of the alcohol fuel ratio sensor according to the present invention and the configuration of a table.

FIG. 8 is an explanatory diagram of an alcohol concentration detecting operation according to another embodiment of the present invention.

FIG. 9 is a sectional view showing still another embodiment of the alcohol fuel ratio sensor according to the present invention.

[Explanation of symbols]

 1 inner electrode (electrostatic capacity for detection) 2 outer electrode 3 flow hole 4, 5 insulating support member 6 lead terminal 8 metal container 10 inner electrode (reference electric capacity) 11 outer electrode 12 known dielectric 13 inlet 14 flow Exit 20 signal processing circuit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Naoki Minami 2520 Takaba, Takata, Ibaraki Prefecture Inside Hitachi Automotive Engineering Co., Ltd. (72) Inventor Takao Sasayama 4026 Kuji Town, Hitachi City, Ibaraki Hiritsu Co., Ltd. Hitachi Research Laboratory (72) Inventor Kazuo Kato 4026 Kuji-cho, Hitachi City, Ibaraki Prefecture Hitachi Research Institute, Ltd. (72) Inventor Norio Hasegawa, Katsuta City, Ibaraki 2520 Takaba, Automotive Engineering Research Association

Claims (9)

[Claims] 1. A capacitance type alcohol fuel ratio sensor for detecting an alcohol concentration according to a change in relative permittivity of fuel, wherein a metal container arranged in a fuel supply path to an engine and a metal container arranged in the metal container. The electrode pair for detection, which is made into a dielectric by circulating the fuel in the container, and the reference electrode pair, which is placed in the metal container and made to be a dielectric by encapsulating a substance of known properties, are provided for the detection. An alcohol fuel ratio sensor, wherein the alcohol fuel ratio sensor is configured to detect the alcohol concentration by comparing the electrostatic capacity of the electrode pair for use with the electrostatic capacity of the reference electrode pair. 2. The invention according to claim 1, wherein the detection electrode pair and the reference electrode pair are each configured by coaxially arranging a rod-shaped inner electrode and a tubular outer electrode. An alcohol fuel ratio sensor characterized in that all of the electrode pairs are vertically arranged in the metal container and are dimensioned so as to reach from the inner ceiling surface to the bottom surface of the container. 3. The alcohol fuel ratio according to claim 1, wherein each of the detection electrode pair and the reference electrode pair is covered with a film of a fluororesin material having a thickness of 20 to 300 μm. Sensor. 4. The alcohol fuel ratio sensor according to claim 1, wherein the fuel outlet passage from the metal container is arranged at a position close to the bottom surface of the metal container. 5. The detection and reference oscillators according to claim 1, wherein the capacitances of the detection electrode pair and the reference electrode pair are used as frequency determining elements, respectively.
Up-counted by the output of the reference oscillator,
An alcohol fuel ratio sensor, comprising: an up-down counter which is down-counted by the output of the detecting oscillator, and the temperature-corrected alcohol concentration is detected by the output of the up-down counter. 6. The oscillator for detection and reference, each of which uses the capacitance of the electrode pair for detection and the electrode pair for reference as a frequency determining element.
The output of the reference oscillator performs positive direction integration, and the output of the detection oscillator performs negative direction integration, and an integrator is provided to detect the temperature-corrected alcohol concentration by the output of the integrator. An alcohol fuel ratio sensor, which is configured as described above. 7. The alcohol fuel ratio sensor according to claim 1, wherein the metal container comprises a pressure control chamber of a pressure regulator arranged in a fuel supply system of an engine. 8. The astable multivibrator according to claim 1, wherein the detecting electrostatic capacity of the detecting electrode pair is used as a frequency determining element, and a diode is connected in parallel to a feedback resistor of the astable multivibrator. And a switch means for connecting a capacitor having a known electrostatic capacity to the detection electrostatic capacitance in parallel with the detection electrostatic capacitance, and an unstable multivibrator when the detection electrostatic capacitance is used as a frequency determining element. An alcohol fuel ratio characterized by being configured to detect the water-corrected alcohol concentration by comparing the output frequency with the output frequency of the astable multivibrator when the diode and the capacitor are connected by the switch means. Sensor. 9. The alcohol fuel ratio according to claim 8, wherein the water-corrected alcohol concentration detection process and the temperature-corrected alcohol concentration detection process are sequentially performed. Sensor.