Exhaust gas sensor electrical circuit improvement

An improved exhaust gas sensor electrical circuit employing a sensor of the type having a first negative-temperature-coefficient variably resistive element adapted to produce an electrical resistance change, as a function of the composition of the exhaust gases produced by the combustion of a rich or lean (with respect to stoichiometry) air/fuel mixture supplied to an internal combustion engine, in a circuit including a second negative-temperature-coefficient variably resistive element that is connected in series with the first variably resistive element, the improved exhaust gas sensor electrical circuit comprising:

• the first element being formed from metal oxide ceramic material having spaced first and second electrical leads connected thereto, the metal oxide material having between the leads connected thereto an electrical resistance that varies both as a function of the temperature of the metal oxide material and as a function of the partial pressure of oxygen in the exhaust gases to which the metal oxide material is exposed;
• the second element being formed from metal oxide ceramic material having, as compared to the metal oxide material of the first element, a longer time rate of response to variations in the partial pressure of oxygen in the exhaust gases from an internal combustion engine supplied with an air/fuel mixture changed from rich to lean and vice versa, the second element having spaced first and second electrical leads connected thereto, the second electrical lead of the first element having a junction formed with the first electrical lead of the second element;
• a source of electrical energy having first and second electrical leads;
• circuit means for connecting the first and second elements in a series-circuit between the first and second electrical leads of the source of electrical energy;
• and
• circuit means for inhibiting reduction in the magnitude of the change in voltage, measured between one of the leads of the source of electrical energy and the junction between the first and second elements, which magnitude change would otherwise result from prolonged exposure of at least the second element to exhaust gases produced by combustion of a rich air/fuel mixture prior to change to a lean air/fuel mixture or vice versa.