Sensor control device and air fuel ratio detecting apparatus

A sensor control apparatus for controlling a gas sensor element which generates a detection signal that changes in accordance with air-fuel ratio while making use of exhaust gas of an internal combustion engine, the sensor control apparatus comprising output means,

• wherein, as ranges for air-fuel ratio, first, second, and third zones are defined,
• the first zone ranging from a first lower limit within a rich region to a first upper limit in a lean region,
• the second zone ranging from a second lower limit in the rich region, the second lower limit being located between the first lower limit and a stoichiometric air-fuel ratio, to a second upper limit in the lean region, the second upper limit being located between the first upper limit and the stoichiometric air-fuel ratio, and
• the third zone ranging from a third lower limit in the lean region, the third lower limit being equal to the second upper limit or being located between the second upper limit and the stoichiometric air-fuel ratio, to a third upper limit between the second upper limit and the first upper limit, and
• wherein the output means outputs first, second, and third output signals,
• the first output signal changes in accordance with the detection signal corresponding to an air-fuel ratio at least within the first range,
• the second output signal changes in accordance with the detection signal corresponding to an air-fuel ratio at least within the second range, the second output signal changing to a greater degree than the first output signal in response to a change in the detection signal, and
• the third output signal changes in accordance with the detection signal corresponding to an air-fuel ratio at least within the third range, the third output signal changing to a greater degree than the first output signal in response to a change in the detection signal,
• wherein the output means includes:
• a first amplification circuit which is selectively brought into one of a first state in which the first amplification circuit amplifies the detection signal with a first gain and outputs the first output signal and a third state in which the first amplification circuit amplifies the detection signal with a third gain greater than the first gain and outputs the third output signal;
• a second amplification circuit which amplifies the detection signal with a second gain greater than the first gain and outputs the second output signal, and
• the first amplification circuit comprises changeover means for switching a gain of the first amplification circuit, by changing a resistance of a feedback resistor, to one of the first and third gains.

A sensor control apparatus for outputting a detection signal that changes in accordance with an air-fuel ratio while making use of exhaust gas of an internal combustion engine, the sensor control apparatus comprising:

• an amplification circuit which can be selectively brought into a first state and a second state through switching of a gain of the amplification circuit by changing a resistance of a feedback resistor;
• and
• a current detection resistor which has a predetermined resistance and detects current flowing through the gas sensor element,
• wherein
• in the first state, the amplification circuit amplifies the detection signal with a relatively small gain and outputs a first output signal which changes in accordance with the detection signal corresponding to an air-fuel ratio within a relatively wide first air-fuel ratio zone;
• in the second state, the amplification circuit amplifies the detection signal with a relatively large gain and outputs a second output signal which changes in accordance with the detection signal corresponding to an air-fuel ratio within a relatively narrow second air-fuel ratio zone contained in the first air-fuel ratio zone, and
• a voltage generated across the current detection resistor is used as the detection signal.