Internal combustion engine with oxygen sensor heater control

In combination:

• an internal combustion engine having fuel supply and exhaust means;
• an oxygen sensor in the exhaust means, said sensor being effective to generate an output voltage in response to engine exhaust content, said sensor further being characterized by an associated internal capacitance and including a separate resistive heater element with a leakage current path between the heater element and internal capacitance;
• closed loop control means effective to periodically sample the oxygen sensor output voltage at predetermined times and generate therefrom a fuel control signal for application to the fuel supply means;
• electric power supply means characterized by a variable output supply voltage and effective to supply electric current to the resistive heater element during received heater control signal pulses with consequent charging of the sensor internal capacitance through the leakage current path;
• means effective to generate the heater control signal pulses, each pulse beginning shortly after a sampling of the oxygen sensor output voltage and ending at least a predetermined time before the next such sampling, said means being further responsive to the output supply voltage of the electric power supply means to vary the duration of the heater control signal pulses to maintain a constant average power in the resistive heater element, whereby a controlled power is supplied to the sensor heater element in pulses allowing discharge of the sensor internal capacitance before each sampling of the sensor voltage for an accurate sampling thereof.