Air-fuel ratio estimating/detecting device

An air-fuel ratio estimating/detecting device, comprising:

• a pulse generating unit configured to generate a crank pulse for each predetermined rotation angle of a crankshaft of an engine;
• a crank angular speed calculating unit configured to calculate a first crank angular speed based upon an interval of two continuous crank pulses at a compression top dead center or above the compression top dead center of the engine, and to calculate a second crank angular speed based upon an interval of two continuous optional crank pulses in a compression stroke;
• an intake air volume estimating unit configured to calculate charging efficiency that is a function of an intake air volume from a difference between the first crank angular speed and the second crank angular speed, which are calculated by the crank angular speed calculating unit;
• a fuel injection amount estimating unit configured to estimate an amount of fuel injected for each cycle based upon driving time of a fuel injection valve;
• an oxygen concentration detecting element that has an output transition region where detection output according to a concentration of oxygen remaining in a combustion gas is generated and the detection output changes in a stepwise fashion in accordance with the concentration of the remaining oxygen corresponding to a theoretical air-fuel ratio;
• and
• a proportional constant determining unit configured to determine a proportional constant of an air-fuel ratio and the theoretical air-fuel ratio by using the intake air volume estimated by the intake air volume estimating unit when an output value of the oxygen concentration detecting element is in the output transition region and the amount of fuel injected estimated by the fuel injection amount estimating unit,
• wherein when the output value of the oxygen concentration detecting element is not in the output transition region, the air-fuel ratio is estimated from the proportional constant determined by the proportional constant determining unit, the charging efficiency, and the amount of fuel injected.

An air-fuel ratio estimating/detecting device comprising:

• intake air volume estimating means for estimating intake air volume introduced into a cylinder of an engine;
• fuel injection amount estimating means for estimating the amount of fuel injected for each cycle on the basis of driving time of a fuel injection valve;
• an oxygen concentration detecting means for detecting oxygen concentration, said oxygen concentration element having an output transition region where detection output according to concentration of oxygen remaining in a combustion gas is generated and the detection output changes in a stepwise fashion in accordance with the concentration of the remaining oxygen corresponding to a theoretical air-fuel ratio;
• and
• proportional constant determining means for determining a proportional constant of an air-fuel ratio and the theoretical air-fuel ratio by using the intake air volume estimated by the intake air volume estimating means when an output value of the oxygen concentration detecting means is in the output transition region and the amount of fuel injected estimated by the amount of fuel injected estimating means,
• wherein when the output value of the oxygen concentration detecting means is not in the output transition region, the air-fuel ratio is estimated from the proportional constant determined by the proportional constant determining means, the intake air volume, and the amount of fuel injected.

An air-fuel ratio estimating/detecting device, comprising:

• pulse generating means for generating a crank pulse for each predetermined rotation angle of a crank shaft of an engine;
• crank angular speed calculating means for calculating a first crank angular speed based upon an interval of two continuous crank pulses at a compression top dead center or above the compression top dead center of the engine, and for calculating a second crank angular speed based upon an interval of two continuous optional crank pulses in a compression stroke;
• intake air volume estimating means for calculating charging efficiency that is a function of an intake air volume from a difference between the first crank angular speed and the second crank angular speed, which are calculated by the crank angular speed calculating means;
• fuel injection amount estimating means for estimating an amount of fuel injected for each cycle based upon driving time of a fuel injection valve;
• oxygen concentration detecting means for detecting oxygen concentration, said oxygen concentration detecting means having an output transition region where detection output according to a concentration of oxygen remaining in a combustion gas is generated, and the detection output changes in a stepwise fashion in accordance with the concentration of the remaining oxygen corresponding to a theoretical air-fuel ratio;
• and
• proportional constant determining means for determining a proportional constant of an air-fuel ratio and the theoretical air-fuel ratio by using the intake air volume estimated by the intake air volume estimating means when an output value of the oxygen concentration detecting means is in the output transition region and the amount of fuel injected estimated by the fuel injection amount estimating means,
• wherein the output value of the oxygen concentration detecting means is not in the output transition region, the air-fuel ratio is estimated from the proportional constant determined by the proportional constant determining means, the charging efficiency, and the amount of fuel injected.

A method for detecting an air-fuel ratio, said method comprising:

• estimating intake air volume introduced into a cylinder of an engine;
• estimating an amount of fuel injected for each cycle based upon a driving time of a fuel injection valve;
• generating a detection output according to concentration of oxygen remaining in a combustion gas, wherein the detection output changes in a stepwise fashion in accordance with a concentration of the remaining oxygen corresponding to a theoretical air-fuel ratio;
• and
• determining a proportional constant of an air-fuel ratio and the theoretical air-fuel ratio by using the estimated intake air volume when an output value of the detection output is in the output transition region, and the estimated amount of fuel injected, wherein when the detection output is not in the output transition region, the air-fuel ratio is estimated from the proportional constant, the intake air volume, and the amount of fuel injected.