Measuring and testing – Gas analysis – Gas of combustion
Reexamination Certificate
2002-03-05
2004-05-25
Solis, Erick (Department: 3747)
Measuring and testing
Gas analysis
Gas of combustion
C073S031060, C073S118040
Reexamination Certificate
active
06739177
ABSTRACT:
INCORPORATION BY REFERENCE
The disclosures of Japanese Patent Applications No. 2001-059808 filed on Mar. 5, 2001, No. 2001-074215 filed on Mar. 15, 2001, No. 2001-085662 filed on Mar. 23, 2001, No. 2001-134560 filed on May 1, 2001, No. 2001-188318 filed on Jun. 21, 2001, and No. 2001-327681 filed on Oct. 25, 2001, each including the specification, drawings, and abstract, are incorporated herein by reference in their entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a combustible-gas sensor which detects a concentration of combustible gas such as hydrocarbons based on a concentration of an intake-oxygen, for example, an intake-oxygen concentration sensor, and to a diagnostic device which determines whether or not there is a malfunction in the intake-oxygen concentration sensor. The invention also relates to an air-fuel ratio control device for internal combustion engines which is equipped with an intake-oxygen concentration sensor and which corrects an amount of fuel to be supplied to an engine on the basis of an output from the intake-oxygen concentration sensor.
2. Description of the Related Art
A known air-fuel ratio control device for internal combustion engines has an air-fuel ratio sensor disposed in an exhaust passage of an engine so as to detect an exhaust-gas air-fuel ratio and is designed to perform feedback control of an amount of fuel to be supplied to the engine such that the detected exhaust-gas air-fuel ratio becomes equal to a predetermined target air-fuel ratio. Such an air-fuel ratio control device measures, for example, parameters regarding the amount of intake gas in an engine (e.g., output from an air flow meter, pressure in an intake passage of the engine, and engine speed). On the basis of a relation that is stored in advance using these parameters, the air-fuel ratio control device calculates a base fuel supply amount (base fuel injection amount) such that the exhaust-gas air-fuel ratio coincides with the target air-fuel ratio. Furthermore, the air-fuel ratio control device is designed to actually supply the engine with fuel of an amount which is calculated by correcting the base fuel supply amount such that the exhaust-gas air-fuel ratio detected by an exhaust-gas air-fuel ratio sensor coincides with the target air-fuel ratio.
If the base fuel injection amount is thus subjected to feedback correction on the basis of the actual exhaust-gas air-fuel ratio detected by the air-fuel ratio sensor, it becomes possible to correct errors in regard to detection by a sensor for detecting parameters regarding the amount of intake gas in the engine (e.g., an air flow meter, an intake pressure sensor, and the like) or errors in fuel injection amount resulting from aging or dispersion among individual products in the actual amount of fuel injected from fuel injection valves. Therefore, air-fuel ratio control can be performed with precision.
However, in the case of an engine having an intake passage in which a purging device for purging evaporative fuel flowing from a fuel tank is disposed, the air-fuel ratio of the engine may temporarily deviate from a target air-fuel ratio during purge of evaporative fuel even if feedback control is performed on the basis of an exhaust-gas air-fuel ratio sensor as described above.
That is, if evaporative fuel (hydrocarbons) is introduced into the intake passage through purge, the engine receives evaporative fuel (fuel vapors) together with intake gas in addition to fuel supplied through injection. Thus, while the fuel injection amount of the engine is controlled on the basis of the exhaust-gas air-fuel ratio, the fuel supply amount of the engine increases temporarily. Therefore, the air-fuel ratio of the engine may deviate from the target air-fuel ratio. If feedback control of the fuel injection amount of the engine is performed on the basis of the exhaust-gas air-fuel ratio in spite of the occurrence of such a deviation, the amount of fuel supplied through purge in the engine is corrected, so that the air-fuel ratio of the engine coincides with the target air-fuel ratio. However, a relatively small gain is set for air-fuel ratio feedback control so as to prevent hunting. Therefore, if purge on a large scale is started abruptly, air-fuel ratio feedback control based on the output from the exhaust-gas air-fuel ratio sensor alone inevitably requires a considerable time until the air-fuel ratio of the engine converges to the target air-fuel ratio.
In order to solve this problem, there has been excogitated an air-fuel ratio sensor in which an intake-oxygen concentration sensor for detecting a concentration of oxygen contained in intake gas is disposed in an intake passage of an engine and which is designed to correct a fuel supply amount of the engine on the basis of an output from the intake-oxygen concentration sensor. In order to solve the aforementioned problem, there has been excogitated a control method which is designed to calculate an amount of evaporative fuel introduced into an intake passage of an engine on the basis of a concentration of oxygen contained in intake gas, namely, on the basis of a detection result obtained from an intake-oxygen concentration sensor that is disposed in the intake passage so as to detect a concentration of oxygen contained in intake gas. If evaporative fuel (hydrocarbons) is introduced into the intake passage, it burns in an oxidative catalyst disposed in an oxygen concentration-detecting portion of the sensor, so that the concentration of oxygen in the vicinity of the detecting portion decreases in accordance with the amount of evaporative fuel consumed through combustion (i.e., in accordance with the concentration of evaporative fuel). Therefore, the air-fuel ratio can be controlled with precision even during purge by calculating a concentration of evaporative fuel (vapors) contained in intake gas on the basis of an output from the intake-oxygen concentration sensor, calculating an amount of vapors supplied to the engine on the basis of an amount of intake air in the engine and the concentration of vapors, and decreasingly correcting a fuel injection amount of the engine by an amount corresponding to the amount of vapors.
For instance, Japanese Patent Laid-Open Publication No. 11-2153 discloses an air-fuel ratio control device of this type.
The device disclosed in this publication is designed to calculate an amount of evaporative fuel contained in intake gas during purge on the basis of an output from an intake-oxygen concentration sensor disposed in an intake passage of an engine, and to decreasingly correct a fuel injection amount of the engine by an amount corresponding to the calculated amount of evaporative fuel.
By thus performing purge control so as to calculate an amount of evaporative fuel contained in intake gas on the basis of an output from the intake-oxygen concentration sensor and decrease a fuel injection amount by an amount corresponding to the amount of evaporative fuel, it becomes possible to perform a direct operation of correction in which the fuel injection amount is reduced by the amount corresponding to the calculated amount of evaporative fuel contained in intake gas. Therefore, if purge control based on the output from the intake-oxygen concentration sensor is performed, much higher precision and much higher responding performance can be accomplished in comparison with the case where purge control is performed through air-fuel ratio control that is based on the output from the exhaust-gas air-fuel ratio sensor. Accordingly, in the case of an engine designed to perform purge control on the basis of an output from an intake-oxygen concentration sensor, it is possible to obtain a stable air-fuel ratio even if purge is performed on a large scale. Therefore, it becomes possible to perform purge on a large scale within a short period. As a result, purging operation can be performed efficiently.
It is true that an air-fuel ratio control device designed to perform purge control on the basis of an output from an intake-oxygen concentration
Daido Shigeki
Hyoudo Yoshihiko
Matsubara Takuji
Oyama Naohisa
Sato Fumihiko
Kenyon & Kenyon
Solis Erick
Toyota Jidosha & Kabushiki Kaisha
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