Method and apparatus for detecting a non-operational status of a catalyst in an engine exhaust conduit

1. A method of sensing and signalling a non-operational status of a catalyst in a catalytic converter in an exhaust conduit of a combustion engine, the engine having a fuel charge supply apparatus providing a fuel charge to combustion chambers of the engine with a predetermined air/fuel ratio in response to a pre-catalyst oxygen sensor in the exhaust conduit, the method comprising the steps:

providing a post-catalyst temperature sensor in the exhaust conduit;

reading the post-catalyst temperature sensor to provide an initial sampled exhaust gas temperature;

providing a quantity of unburned fuel through at least one of the combustion chambers to the catalytic converter during an idle period of engine operation while temporarily suspending a response of the fuel charge apparatus to the pre-catalyst oxygen sensor;

monitoring the post-catalyst temperature sensor at a predetermined propagation delay time after providing the quantity of unburned fuel to provide an additional sampled exhaust gas temperature;

comparing a temperature difference between the additional sampled exhaust gas temperature and the initial sampled exhaust gas temperature with a predetermined reference value; and

signalling a non-operational status of the catalyst if the temperature difference does not exceed the predetermined reference value.

2. The method of claim 1 wherein the step of providing a quantity of unburned fuel through at least one of the combustion chambers is repeated for selected events in the at least one of the combustion chambers for a predetermined intrusive action time, wherein a frequency of the selected events is determined by an event counter.

3. The method of claim 1 wherein the engine has a plurality of banks of combustion chambers each with its own exhaust conduit, catalytic converter and post-catalyst temperature sensor and the method prevents its own operation on more than one of the banks simultaneously.

4. The method of claim 1 further comprising the step of determining that the post-catalyst temperature sensor is indicative of a stable catalyst temperature prior to the step of reading the post-catalyst temperature sensor to provide an initial sampled exhaust gas temperature.

5. The method of claim 1 further comprising the step of determining that the post-catalyst temperature sensor is indicative of a fully warmed up catalyst temperature prior to the step of reading the post-catalyst temperature sensor to provide an initial sampled exhaust gas temperature.

6. The method of claim 1 wherein the combustion engine includes spark ignition apparatus for igniting the fuel charges within the combustion chambers and the step of providing a quantity of unburned fuel through at least one of the combustion chambers comprises withholding spark ignition from the at least one of the combustion chambers to cause a misfire therein.

7. The method of claim 6 wherein the quantity of fuel in the fuel charge provided to the at least one of the combustion chambers when the spark ignition is withheld is greater than the quantity of fuel that would have been provided in the fuel charge if the spark ignition had not been withheld.

8. The method of claim 1 wherein the combustion engine provides direct injection of fuel into the combustion chambers and the step of providing a quantity of unburned fuel from at least one of the combustion chambers comprises injecting the quantity of unburned fuel into the at least one of the combustion chambers during an exhaust cycle thereof, whereby the quantity of unburned fuel reaches the catalytic converter in an unburned state.

9. The method of claim 8 wherein the quantity of unburned fuel is added to combustion products of a combustion event within the at least one of the combustion chambers during the exhaust of those combustion products therefrom.

10. A catalyst operational state monitoring system for use with a combustion engine having an exhaust conduit with a catalytic converter and further having a fuel charge supply apparatus providing a fuel charge to the combustion chambers with a predetermined air/fuel ratio in response to a pre-catalyst oxygen sensor in the exhaust conduit, the monitoring system comprising:

a post-catalyst temperature sensor in the exhaust conduit; and

a digital processor adapted to:

read the post-catalyst temperature sensor to provide an initial sampled exhaust gas temperature,

provide a quantity of unburned fuel through at least one of the combustion chambers to the catalytic converter during an idle period of engine operation while temporarily suspending a response of the fuel charge apparatus to the pre-catalyst oxygen sensor,

monitor the post-catalyst temperature sensor at a predetermined time after providing the quantity of unburned fuel to provide an additional sampled exhaust gas temperature,

compare a temperature difference between the additional sampled exhaust gas temperatures and the initial sampled exhaust gas temperature with a predetermined reference value, and

signal a non-operational status of the catalyst if the temperature difference does not exceed the predetermined reference value.

11. The catalyst operational state monitoring system of claim 10 further comprising a digital processor adapted to determine that the post-catalyst temperature sensor is indicative of a stable catalyst temperature prior to reading the post-catalyst temperature sensor to provide an initial sampled exhaust gas temperature.

12. The catalyst operational state monitoring system of claim 10 further comprising a digital processor adapted to determine that the post-catalyst temperature sensor is indicative of a fully warmed up catalyst temperature prior to reading the post-catalyst temperature sensor to provide an initial sampled exhaust gas temperature.