Circuit and control method for electrically heating a catalyst

In an exhaust system of a engine including a power source and a plurality of vehicle loads, an apparatus for electrically heating a catalyst, the apparatus comprising:

• a multi-phase alternator electrically coupled to the power source, the multi-phase alternator rectifying AC to DC by a diode rectifier bridge internal to the multi-phase alternator;
• similar means for switching DC from the diode rectifier bridge of the multi-phase alternator to an electrically heated catalyst and cutting off DC supplied to the power source from the multi-phase alternator, the switching means electrically coupled to the multi-phase alternator;
• an electrically heated catalytic converter for receiving DC supplied by the multi-phase alternator electrically coupled to the singular switching means, the catalytic converter including a catalyst for purifying exhaust gases of the engine and a heating element for bringing the catalytic converter expediently within peak operating temperature;
• an Electronic Control Unit (ECU), the ECU including a microprocessor, memory capabilities, and at least one bus line for energizing and de-energizing the singular switching means, the ECU electrically coupled to the singular switching means;
• a temperature sensor in close proximity to the catalytic converter heating element for reading a temperature of the heating element and having outputs, the temperature sensor outputs in communication with the ECU and for imparting an electrical signal representation of the catalyst temperature to the ECU;
• and
• whereby the multi-phase alternator alternatively supplies DC to the power source and the catalyst heating element of the catalytic converter via the singular switching means.

In a engine and associated catalyst performance control system having an Electronic Control Unit (ECU), the ECU including a microprocessor, memory capabilities, and at least one bus line, a battery, a multi-phase alternator, an electrically heated catalyst, and a relay connecting the multi-phase alternator and catalyst, a method for heating an electrically heated catalyst to a desired temperature, the catalyst disposed within an exhaust chamber of the engine, the method comprising the steps of:

• determining when a minimum engine RPM is reached and a battery voltage is above a minimum threshold;
• energizing a relay coil for cutting off a current path from the alternator power output to the battery such that all output power from the multi-phase alternator is provided to the electrically heated catalyst;
• increasing in graduated steps the output power from the multi-phase alternator;
• monitoring a voltage across the electrically heated catalyst to determine whether the voltage is within a specified range;
• terminating the current methodology if the electrically heated catalyst voltage is not within the specified range and storing a fault code in ECU memory to indicate a shorted electrically heated catalyst;
• comparing an engine load before and after ramping the output power of the alternator to determine whether an open electrically heated catalyst circuit has occurred;
• terminating the current methodology if the electrically heated catalyst voltage is not within the specified range and storing a fault code in ECU memory to indicate the open electrically heated catalyst circuit;
• providing a current path from the multi-phase alternator power output to the battery for a specified time such that all output power from the multi-phase alternator is provided to the electrically heated catalyst if a short or open catalyst circuit has not occurred;
• limiting the voltage of the electrically heated catalyst to a specified level by controlling a duty cycle of the multi-phase alternator;
• determining whether heater voltage, battery voltage, and engine RPM falls below a specified range;
• terminating the current methodology if the heater voltage, battery voltage, and engine RPM falls below the specified range and storing a fault code in ECU memory to indicate the open electrically heated catalyst circuit;
• and
• de-energizing the relay coil if the heater voltage, battery voltage, and engine RPM does not fall below the specified range wherein the output power from the multi-phase alternator to the electrically heated catalyst is disconnected and the multi-phase alternator output power to the to the battery and engine loads is connected.