System for diagnosing deterioration of catalyst

A diagnostic apparatus for diagnosing a deterioration state of a catalyst in an engine, comprising:

• a memory for storing a preset criterion value;
• and
• a processor connected to the memory for obtaining an index value indicative of a conversion efficiency of the catalyst;
• receiving a value of a state variable of the engine that correlates with a physical quantity affecting a catalytic action of the catalyst;
• modifying the index value to a value in a standard state of the catalyst previously set as to the physical quantity using the value of the state variable;
• and determining the deterioration state of the catalyst by comparing the modified index value with the preset criterion value, wherein the processor gives the index indicative of the conversion efficiency of the catalyst based on signals received from a first oxygen concentration sensor provided upstream side of the catalyst and a second oxygen concentration sensor provided downstream side of the catalyst.

An engine control unit, which controls an engine by receiving a value of the state variable of said engine from a sensor for detecting said value of the state variable of said engine, comprising:

• a memory for storing a preset criterion value;
• and
• a processor connected to the memory for obtaining an index value indicative of a conversion efficiency of the catalyst;
• receiving a value of a state variable of the engine that correlates with a physical quantity affecting a catalytic action of the catalyst;
• modifying the index value to a value in a standard state of the catalyst previously set as to the physical quantity using the value of the state variable;
• and determining the deterioration state of the catalyst by comparing the modified index value with the preset criterion value.

A diagnostic system for diagnosing a deterioration state of a catalyst in an engine, comprising:

• a first oxygen concentration sensor provided upstream side of said catalyst,
• a second oxygen concentration sensor provided downstream side of said catalyst,
• a memory for storing a preset criterion value and a predetermined range for a state variable of the engine that correlates with a physical quantity affecting a catalytic action of the catalyst;
• and
• a processor operatively connected to the memory for obtaining an index value indicative of a conversion efficiency of the catalyst, receiving a value of the state variable of the engine, suspending a determination of the deterioration state of the catalyst if the value of the state variable is outside the predetermined range, and determining the deterioration state of the catalyst by comparing the index value with the preset criterion value if the value of the state variable is within the predetermined range.

A diagnostic system for diagnosing a deterioration state of a catalyst in an engine, comprising:

• a first oxygen concentration sensor provided upstream side of said catalyst,
• a second oxygen concentration sensor provided downstream side of said catalyst,
• a memory for storing a preset criterion value;
• and
• a processor connected to the memory for obtaining an index value indicative of a conversion efficiency of the catalyst;
• receiving a value of a state variable of the engine that correlates with a physical quantity affecting a catalytic action of the catalyst;
• modifying the index value to a value in a standard state of the catalyst previously set as to the physical quantity using the value of the state variable;
• and determining the deterioration state of the catalyst by comparing the modified index value with the preset criterion value.

A method of diagnosing a deterioration state of a catalyst in an engine, comprising:

• (a) storing a preset criterion value;
• (b) obtaining an index value indicative of a conversion efficiency of the catalyst;
• (c) detecting a value of a state variable of the engine that correlates with a physical quantity affecting a catalytic action of the catalyst;
• (d) modifying the index value to a value in a standard state of the catalyst previously set as to the physical quantity using the value of the state variable;
• and
• (e) determining the deterioration state of the catalyst by comparing the modified index value with the preset criterion value, wherein steps (d) and (e) are carried out by using a processor which obtains the index value and the state variable from a memory which stores a predetermined range for the state variable.

A method of diagnosing a deterioration state of a catalyst in an engine, comprising:

• (a) storing a preset criterion value;
• (b) obtaining an index value indicative of a conversion efficiency of the catalyst;
• (c) detecting a value of a state variable of the engine that correlates with a physical quantity affecting a catalytic action of the catalyst;
• (d) modifying the index value to a value in a standard state of the catalyst previously set as to the physical quantity using the value of the state variable;
• and
• (e) determining the deterioration state of the catalyst by comparing the modified index value with the preset criterion value.