Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Lumped type parameters
Reexamination Certificate
1999-03-18
2001-11-20
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Lumped type parameters
Reexamination Certificate
active
06320393
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a dielectric constant sensing device for sensing a dielectric constant of a fluid to discriminate the property of the fluid and a method employing the same and, more particularly, a device for measuring an alcohol containing rate of an alcohol blended fuel employed in an engine of an automobile, etc. and a method employing the same.
2. Description of the Prior Art
In recent years, in order to promote the employment of the alternative fuel, automobiles which can use the fuel which is prepared by blending alcohol such as methanol, ethanol, etc. into a gasoline are being introduced. If an engine can employ the alcohol blended fuel is controlled, the air-fuel ratio of the engine, the ignition timing, or the like must be changed according to the alcohol concentration in the fuel in order to clean an exhaust gas or to extract a sufficient engine power, unlike the case where an engine can only employ the gasoline is controlled. Since the dielectric constant of the alcohol blended fuel is changed according to the alcohol concentration, the alcohol concentration can be detected by measuring the dielectric constant. For this purpose, in the prior art, for example, the dielectric constant sensing device disclosed in U.S. Pat. No. 5,255,656 has been proposed.
This device will be explained with reference to
FIGS. 8
,
9
, and
10
hereinbelow.
FIG. 8
is a plan view, partially broken away, showing a dielectric constant sensing device in the prior art.
FIG. 9
is a cross sectional view showing the dielectric constant sensing device in the prior art.
FIG. 10
is a block diagram showing a circuit configuration of the dielectric constant sensing device in the prior art.
In
FIG. 8
, a reference
301
denotes an input pipe into which the fuel is introduced;
302
, an output pipe for discharging the fuel;
303
, a sensor portion; and
304
, a sensor circuit chamber (omitted partially) in which a sensor circuit
400
for processing signals from the sensor portion
303
is built. In
FIG. 9
, a reference
305
denotes an outer wall of the sensor portion
303
formed of resin, and an electrode
306
which is formed of double layers of copper and nickel by the plating is provided on an entire inner surface of the outer wall
305
. A reference
307
denotes a chamber which is filled with the fuel, and a reference
308
denotes a cylindrical coil which is provided in a coaxial manner relative to an inner surface of the outer wall
305
and has the inductance L
0
. This cylindrical coil operates as an electrode, and has a capacitor of capacitance C
0
which is a sum of a stray capacitance formed between the coil wires and a capacitance formed between the electrode
308
and the electrode
306
.
In
FIG. 10
, the electrode
306
is connected electrically to ground of the sensor circuit
400
. Both ends of the cylindrical coil
308
are connected to the resonator circuit
401
which is composed of a CMOS inverter. An output of the resonator circuit
401
is connected to the output circuit
402
. A reference
403
denotes a power supply circuit
403
for supplying a constant stabilized voltage to the overall sensor circuit, and a reference
404
denotes a temperature measuring circuit which has a thermistor used to execute the temperature compensation.
Next, an operation will be explained. The inductance L
0
of the cylindrical coil
308
and the stray capacitance C
0
constitute a parallel resonance circuit which can resonate at a resonance frequency Fr given by
Fr
=
1
2
π
LoCo
(
1
)
Since the resonance circuit
401
is formed to feed back positively at the resonance frequency Fr, oscillation at the resonance frequency is continued. This resonance frequency is divided by the output circuit
402
and then transmitted to an engine control device (not shown).
If the fuel is filled in the chamber
7
, the stray capacitance C
0
is changed by the dielectric constant and thus the resonance frequency is changed according to Eq. (1). Therefore, the dielectric constant of the fuel can be detected by sensing the resonance frequency. Since the dielectric constants of the gasoline and the methanol are given as about 2 and about 32 respectively in the methanol blended fuel, change in the methanol concentration contributes significantly to change in the dielectric constant of the fuel. Hence, if the dielectric constant of the fuel can be detected, an alcohol blended ratio can be detected, so that appropriate engine control can be achieved.
However, since the dielectric constant sensing device in the prior art is constructed in the following, there have been problems described later.
Since size of the sensor
3
is not increased so much with regard to the mountability as the engine control device for the automobile, the magnitude of the stray capacitance being formed is limited by itself. In the prior art set forth above, the stray capacitance C
0
of the cylindrical coil
308
is only 26 pF. In contrast, the input portion has the stray capacitance having the unnegligible magnitude. For example, if the voltage at the terminal of the cylindrical coil
308
is input into any IC, the input capacitance of several pF exists for every IC. In addition, if the wirings are provided on the circuit substrate, there is the case where the capacitance of several pF is generated only by tne wirings. The stray capacitance at the input portion of the sensor circuit
400
is input in parallel with the stray capacitance C
0
of the cylindrical coil
308
in circuit, the stray capacitance C
0
is changed correspondingly to thus change the resonance frequency Fr of the sensor.
In addition, such stray capacitance is not a controlled and stabilized capacitance and thus varied easily by the peripheral temperature and the deterioration of the durability. Therefore, there has been the problem that such stray capacitance becomes a factor to cause the error in the sensor output.
In order to employ the cylindrical coil
308
as the inductor as a circuit element, i.e., as a circuit element for generating a voltage, which is proportional to the time differential of the current flowing through the element, between both terminals of the element, both terminals of the cylindrical coil
308
must be connected to the sensor circuit
400
. Therefore, there has been the problem that the number of the terminals is increased.
In addition, there has been the problem that, since several electronic parts are needed at the minimum in order to constitute the resonator circuit, a circuit scale is enlarged.
SUMMARY OF THE INVENTION
The present invention has been made to overcome the above problems and it is an object of the present invention to provide a fluid dielectric constant sensing device which is able to attain high precision by a simple structure.
It is another object of the present invention to provide a fluid dielectric constant sensing device which is able to sense a dielectric constant with high precision not to cause re-reflection of a signal.
It is still another object of the present invention to provide a fluid dielectric constant sensing device which is resistant to disturbance.
It is yet still another object of the present invention to provide a fluid dielectric constant sensing device which is resistant to changes in the environment.
It is further object of the present invention to provide a fluid dielectric constant sensing device which is able to sense the dielectric constant in a short time.
It is still further object of the present invention to provide a fluid dielectric constant sensing method which is able to attain high precision simply.
It is yet still further object of the present invention to provide a fluid dielectric constant sensing method which is able to sense a dielectric constant with high precision not to cause re-reflection of a signal.
It is an additional object of the present invention to provide a fluid dielectric constant sensing method which is resistant to changes in the environment.
It is still additional
Nagano Susumu
Ono Mitsuhiro
Yasui Katsuaki
Kerveros J
Metjahic Safet
Mitsubishi Denki & Kabushiki Kaisha
Sughrue, Mion, Zion, Macpeak & Seas, PLLC
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