Apparatus and method for measuring alcohol concentration of liquid blended with alcohol applicable to an automotive vehicle mounted internal combustion engine

• US 5,488,311 A
• Filed: 08/10/1994
• Issued: 01/30/1996
• Est. Priority Date: 05/30/1990
• Status: Expired due to Term

• Current Assignee: Hitachi Automotive Systems Limited (Hitachi, Ltd.)
• Original Assignee: Japan Electronic Control Systems Company Limited, Nissan Motor Co., Ltd.
• Inventors: Takeuchi, Kiyoshi, Kobayashi, Kazumitsu, Shimamura, Masahiko, Kamioka, Hideki
• Primary Examiner(s): Wieder, Kenneth A.
• Assistant Examiner(s): DO, DIEP N
• Application Number:
  US08/288,427
• Time in Patent Office: 538 Days
• Field of Search: 324/674, 324/667, 324/663, 324/681, 324/685, 324/686, 73/61.43, 73/61.44
• US Class Current: 324/674
• CPC Class Codes: G01N 27/221 by investigating the dielectric properties using microwaves G01N22/00; measuring loss factors or dielectric constants per se G01R27/26
• CPC Class Codes: G01N 33/2852 Alcohol in fuels

Abstract

The electrodes of an electrostatic capacitor which is used to determine the alcohol concentration in a mixture of gasoline and alcohol, are connected with a frequency oscillator of the LC type which applies a signal having a frequency which is equal to or greater than 10 MHz. The setting of the oscillation frequency to 10 MHz or more eliminates the amount of change in electrode loss and enables stable and accurate alcohol concentration determination.

Claims

1. An apparatus for measuring an alcohol concentration of a liquid blended with alcohol, comprising:

a) an electrostatic capacitance detector, having electrodes immersed in said liquid, for detecting an electrostatic capacitance between said electrodes;

b) an oscillator coupled to said electrostatic capacitance detector and configured to oscillate at a frequency based on an amount of said electrostatic capacitance detected by said electrostatic capacitance detector, said oscillator oscillates at said frequency in a frequency range of 10 Mhz or more dependent on said alcohol concentration;

c) a frequency divider coupled to said oscillator and configured to divide said frequency from said oscillator and to output a divided frequency indicative thereof; and

d) a frequency-to-voltage converter coupled to said frequency divider and configured to convert said divided frequency into a corresponding voltage.

2. A method for measuring an alcohol concentration of a liquid blended with alcohol, comprising the steps of:

a) forming an oscillation circuit coupled to an electrostatic capacitance sensor having mutually opposing electrodes, said electrodes being immersed in the liquid such that a dielectric constant of said electrostatic sensor is varied with the alcohol concentration of the liquid, wherein an electrostatic capacitance of said electrostatic capacitance sensor is varied with the alcohol concentration, said oscillation circuit outputting an output frequency as an oscillation frequency based on said electrostatic capacitance;

b) dividing the output frequency by a frequency divider and outputting a divided frequency, said divided frequency being at a lower frequency than the output frequency;

c) converting said divided frequency into a first voltage, a level of said first voltage corresponding to the alcohol concentration;

d) detecting a temperature of the liquid; and

e) compensating the level of said first voltage for a variation in the detected temperature to derive a second voltage which indicates the alcohol concentration and which is compensated according to the variation in the temperature of the liquid,

wherein said oscillation frequency of said oscillation circuit is selected to be in a frequency range of greater than 10 MHz but less than 60 MHz when the alcohol concentration ranges from 0% to 100%, such that an electrode loss caused by resonance of said electrodes is reduced and the electrode loss affecting the indicated value of the second voltage is stable.

3. A method for measuring alcohol concentration of a liquid blended with alcohol as recited in claim 2, wherein the frequency range of the oscillation frequency is between 40 MHz and 60 MHz.

4. A method for measuring alcohol concentration of a liquid blended with alcohol as recited in claim 2, wherein the liquid comprises gasoline for an internal combustion engine and the alcohol is methanol.

5. A fuel injection quantity control system for an internal combustion engine which is injected with fuel which includes a mixture of gasoline and alcohol, said fuel being injected to said internal combustion engine by a plurality of fuel injectors, said system comprising:

sensor means for determining speed and load of said internal combustion engine;

an alcohol concentration sensor for sensing an amount of alcohol contained in said fuel having a concentration of said alcohol ranging from 0% to 100%, said alcohol concentration sensor having electrodes which are immersed in said fuel to integrally define a capacitor;

an oscillator operatively coupled to said electrodes together with the alcohol concentration sensor and configured to provide a oscillation signal having a frequency of more than 10 MHz;

a frequency divider coupled to said oscillator and configured to divide the frequency of said oscillation signal and to output a divided frequency signal as a result thereof, said divided frequency signal having a frequency less than the frequency of the oscillation signal; and

circuit means responsive to said divided frequency signal provided from said frequency divider for determining an appropriate pulsewidth of a fuel injection signal to be applied to said plurality of fuel injectors,

wherein said oscillation signal produced by said oscillator varies according to the concentration of said alcohol,

and wherein the pulsewidth of said fuel injection signal determines an amount of said fuel to be injected into said internal combustion engine by said fuel injectors.

6. A fuel injection quality control system as recited in claim 5, wherein, when said signal having a frequency higher than 10 MHz is produced by said oscillator coupled to said electrodes, an electrode loss due to resonance of said electrodes is reduced.

7. A fuel injection quality control system as recited in claim 6, wherein said signal produced by said oscillator has a frequency in a range from 40 MHz to 60 MHz.

8. A fuel injection quality control system as recited in claim 5, wherein said oscillator comprises an LC circuit having a capacitance including said electrodes.

9. A fuel injection quality control system as recited in claim 8, further comprising:

a temperature sensor immersed in said fuel for detecting a temperature of said fuel and outputting a temperature detection signal therefrom; and

temperature correcting means connected to said frequency-to-voltage converter and said temperature sensor for correcting said voltage signal indicative of a value of alcohol concentration output from said frequency-to-voltage converter according to said temperature detection signal output from said temperature sensor.

10. A method for measuring an alcohol concentration of a liquid blended with alcohol, comprising the steps of:

a) measuring an electrostatic capacitance of said liquid;

b) determining an oscillation frequency according to said electrostatic capacitance, said oscillation frequency varying according to a level of said electrostatic capacitance;

c) dividing said oscillation frequency into a divided frequency;

d) converting said divided frequency into a first voltage, said first voltage indicating the alcohol concentration of the liquid;

e) detecting a temperature of the liquid; and

f) adjusting said first voltage based on the detected temperature to derive a second voltage which indicates the alcohol concentration and which is compensated according to the variation in the temperature of the liquid,

wherein said oscillation frequency is selected to be in a frequency range of greater than 10 MHz but less than 60 MHz when the alcohol concentration ranges from 0% to 100%, such that an electrode loss caused by resonance of said electrodes is reduced and the electrode loss affecting a value of said second voltage is stable.

11. A fuel injection quantity control system for an internal combustion engine which is injected with fuel which includes a mixture of gasoline and alcohol, said fuel being injected to said internal combustion engine by a plurality of fuel injectors, said system comprising:

a sensor circuit connected to said internal combustion engine and configured to determine a speed and load of said internal combustion engine and to output a sensor signal indicative thereof;

an alcohol concentration sensor configured to sense an amount of alcohol contained in said fuel having a concentration of said alcohol ranging from 0% to 100%, said alcohol concentration sensor having electrodes which are immersed in said fuel to integrally define a capacitor;

an oscillator operatively coupled to said alcohol concentration sensor and configured to produce a fixed frequency signal having a frequency of more than 10 MHz, said frequency of said fixed frequency signal being proportional to the amount of alcohol sensed by said alcohol concentration sensor;

a frequency divider coupled to said oscillator and configured to divide said frequency of said fixed frequency signal and to output a divided frequency signal as a result thereof; and

a signal generation circuit means coupled to receive said divided frequency signal from said frequency divider and said sensor signal from said sensor circuit and configured to determine a pulsewidth of a fuel injection signal to be applied to said plurality of fuel injectors,

wherein said fixed frequency signal produced by said oscillator varies according to the concentration of said alcohol, and the pulsewidth of said fuel injection signal determines an amount of said fuel to be injected into said internal combustion engine by said fuel injectors,

and wherein when said fixed frequency signal is output from said oscillator, an electrode loss due to resonance of said electrodes is reduced.