Method and apparatus to limit a midbed temperature of a catalytic converter

A method of limiting a maximum temperature in a catalytic converter which alters exhaust gases produced by combustion of an air/fuel mixture in an internal combustion engine which includes an exhaust pipe for transporting exhaust gases produced by the engine into a catalytic converter, the method comprising the steps of:

• determining an instantaneous temperature value at a midbed point in said catalytic converter by the steps of,
• determining an instantaneous temperature of exhaust gas at a first point on said exhaust pipe as a function of a first value indicative of a steady state temperature at the first point and as a function of a second value indicative of a predetermined temperature rate of change at the first point;
• measuring a mass flow rate of air into an induction system of said engine;
• determining an instantaneous temperature of exhaust gas at an exhaust gas inlet of said catalytic converter as a function of the instantaneous temperature at said first point and a third value indicative of a steady state temperature drop of said exhaust gas from said first point to said exhaust gas inlet;
• determining a steady state temperature at a midbed point in said catalytic converter as a function of said instantaneous temperature of exhaust gas at said exhaust gas inlet and a fourth value indicative of an increase in temperature of said exhaust gas in said catalytic converter;
• determining said instantaneous temperature value at said midbed point as a function of said steady state temperature at said midbed point and a predetermined temperature rate of change of the midbed point which varies as a function of said mass flow rate of air;
• and
• controlling said air/fuel ratio in response to said instantaneous midbed temperature to maintain said midbed temperature within a predetermined midbed temperature range.

In an internal combustion engine comprising a means for generating an air/fuel mixture for combustion within said engine and an exhaust pipe for transporting exhaust gases produced from said combustion of said air/fuel mixture to a catalytic converter, a method of controlling delivery of fuel to a combustion chamber of the engine to generate said air/fuel mixture, which comprises a ratio of air to fuel required to maintain said catalytic converter within a predetermined temperature range, the method comprising the steps of:

• determining an instantaneous temperature value at a midbed point in said catalytic converter;
• altering said air/fuel mixture by the steps of,
• comparing said instantaneous temperature value to a predetermined maximum catalyst midbed temperature range comprising a maximum temperature value and a minimum temperature value and setting a temperature flag to indicate an overtemperature condition if said instantaneous temperature value is greater than said maximum temperature value and setting said temperature flag to indicate an undertemperature condition if said instantaneous temperature value is less than said minimum temperature value;
• setting a first intermediate air/fuel modulation variable equal to a predetermined air/fuel modulation value if said temperature flag indicates said undertemperature condition;
• altering said first intermediate air/fuel modulation variable by an air/fuel modulation alteration value if said temperature flag indicates said overtemperature condition;
• generating a second intermediate air/fuel modulation variable indicative of a ratio of air to fuel in an air/fuel mixture required to generate a predetermined engine response for a predetermined set of engine operating parameters,
• comparing said second intermediate air/fuel modulation variable to said first intermediate air/fuel modulation variable and injecting an amount of fuel to generate an air/fuel ratio corresponding to said second intermediate air/fuel modulation variable if said first air/fuel modulation variable corresponds to a greater proportion of air to fuel than said second air/fuel modulation variable, and injecting an amount of fuel to generate an air/fuel ratio corresponding to said first intermediate air/fuel modulation variable if said first air/fuel modulation variable corresponds to a lesser proportion of air to fuel than said second air/fuel modulation variable.