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In a mixture control system having an exhaust gas sensor located in an exhaust system of an internal combustion engine for controlling the air-fuel ratio of the mixture supplied to the engine, a detection system for detecting when the temperature of the exhaust gas sensor is within its normal operat

In a mixture control system having an exhaust gas sensor located in an exhaust system of an internal combustion engine for controlling the air-fuel ratio of the mixture supplied to the engine, a detection system for detecting when the temperature of the exhaust gas sensor is within its normal operating range. A deviation signal is derived from the exhaust gas sensor to represent the deviation of the air-fuel ratio within the exhaust system from a desired air-fuel ratio. The peak value of the deviation signal is detected and stored in a storage circuit and compared with a threshold which represents the normal operating temperature of the exhaust gas sensor to provide a disabling signal for the mixture control system to suspend feedback control operation when the temperature of the sensor falls below its normal operating temperature. The exhaust gas sensor is then supplied with a current in response to the presence of the disabling signal so that the voltage across the sensor\s internal impedance increases because of its high impedance value at low sensor temperatures. The output from the gas sensor is compared with a preset value higher than the maximum output level of the sensor when operating at or above its normal operating temperature but lower than the minimum output level of the sensor when operating below its normal operating temperature with the current being fed. When the gas sensor output falls below the preset value, the system determines that the temperature of the gas sensor has risen above its normal operating temperature to resume feedback control operation.

대표청구항 ▼

In a mixture control system for an internal combustion engine having an exhaust gas sensor for supplying a control signal to the mixture control system, a detection system for detecting when the temperature of the gas sensor is at or above its operating temperature to allow said mixture control syst

In a mixture control system for an internal combustion engine having an exhaust gas sensor for supplying a control signal to the mixture control system, a detection system for detecting when the temperature of the gas sensor is at or above its operating temperature to allow said mixture control system to operate said engine in a closed-loop control mode and detecting when the temperature of the gas sensor is below its operating temperature to allow said mixture control system to operate the engine in an open-loop control mode, wherein said sensor is operable at a high temperature for generating a voltage signal representative of the concentration of a predetermined constituent gas in the exhaust gases, said sensor having an internal impedance varying inversely with the temperature of said sensor from a very high impedance at its low, nonoperable temperature to a very low impedance at its high operating temperature, said detection system comprises: exhaust gas sensor output circuit means for generating a signal representative of the deviation of said concentration representative voltage signal from a predetermined voltage level representing a desired air-fuel ratio; storage circuit means for detecting the peak value of said deviation representative signal and storing the most recent peak value of the deviation representative signal; a first detector for determining the relative voltage level of the output of said storage circuit means to the voltage level of a first threshold representing the normal operating temperature of said exhaust gas sensor to cause said mixture control system to operate in the feedback control mode when the output of said storage circuit means is greater than said threshold level or cause said mixture control system to operate in the open control mode when the output of said storage circuit means is smaller than said threshold level; means for supplying a current flow to said exhaust gas sensor in response to the presence of said disabling signal to thereby increase the voltage across its internal impedance; and a second detector for determining the relative voltage level of the output of said exhaust gas sensor to the voltage level of a second threshold higher than the maximum output level of the exhaust gas sensor when operating at or above the normal operating temperature, and lower than the minimum output level of the exhaust gas sensor when operating below its normal operating temperature in the presence of said current flow, for switching the control modes of said mixture control system from the open to closed modes when the increased voltage output of said exhaust gas sensor falls below said second threshold as the output of said gas sensor decreases inversely with the temperature of the gas sensor.