Vehicle mounted engine control apparatus

A vehicle mounted engine control apparatus, to which are connected

• a pair of upstream and downstream exhaust gas sensors that are arranged in an upstream position and a downstream position of a catalyzer which is arranged in an exhaust passage of the internal combustion engine, and each generate a nonlinear or linear detection signal voltage corresponding to an air fuel ratio of an exhaust gas in the exhaust passage, and
• a pair of upstream and downstream heaters to which electric power is supplied at the time when a predetermined requirement is satisfied, in order to activate the upstream and downstream exhaust gas sensors at an early stage,
• the vehicle mounted engine control apparatus comprising:
• a microprocessor that cooperates with a program memory to execute a fuel injection control unit, an upstream air fuel ratio control unit and a downstream air fuel ratio control unit;
• and
• a heater control circuit that includes a pair of upstream and downstream switching elements which are driven and controlled by the microprocessor so as to supply electric power to the upstream and downstream heaters, and a pair of current sensing resistors for supplying heater current detection signals to the microprocessor;
• wherein the fuel injection control unit adjusts the valve opening time of a injector, which is an electromagnetic coil for driving a fuel injection electromagnetic valve, thereby to control an amount of fuel injection, in proportion to the amount of intake air, which is detected by an air flow sensor arranged in an intake passage of the internal combustion engine, or which is arithmetically calculated from the detection value of a rotation sensor which generates a pulse signal corresponding to the rotational speed of the internal combustion engine and the detection value of a negative pressure sensor which is arranged in an intake pipe, whereby the amount of fuel supply is controlled so as to obtain a predetermined voluntary target air fuel ratio;
• wherein the upstream air fuel ratio control unit generates to the fuel injection control unit a correction command to increase or decrease the amount of fuel supply in such a manner that an air fuel ratio in an upstream position corresponding to the detection signal voltage obtained from the upstream exhaust gas sensor matches a first target voltage which is a target air fuel ratio in the upstream position;
• wherein the downstream air fuel ratio control unit corrects the first target voltage in such a manner that an air fuel ratio in a downstream position corresponding to the detection signal voltage obtained from the downstream exhaust gas sensor matches a second target voltage which is a target air fuel ratio in the downstream position;
• wherein at the time when the supply current to the upstream heater declines to a predetermined value or less in accordance with a temperature rise of the upstream heater to which electric power has first been supplied, the supply of electric power to the downstream heater is started even if the upstream exhaust gas sensor is still in its unactivated state;
• wherein the value of the voluntary target air fuel ratio of the fuel injection control unit is set to a first initial value in which the exhaust gas becomes a fuel rich state, until the resistance value of an internal resistance of the upstream exhaust gas sensor decreases to generate an upstream side detection signal voltage;
• and
• wherein the first target voltage for the upstream air fuel ratio control unit is set to a second initial value in which the exhaust gas becomes a fuel rich state, until the resistance value of an internal resistance of the downstream exhaust gas sensor decreases to generate a downstream side detection signal voltage.