Apparatus and method for diagnosing lubricant degradation in internal combustion engine

A method for diagnosing degradation of a lubricant in an internal combustion engine, the method comprising:

• detecting a speed of the engine by a first sensor positioned to measure the speed of the engine and to output a speed detection signal;
• determining a load of the engine by a second sensor configured to detect a load parameter related to torque generated by the engine and configured to output a load detection signal;
• detecting a temperature parameter of the engine with a temperature sensor positioned on the engine, the temperature parameter being proportional to the temperature of a combustion chamber;
• estimating an amount of soot, formed in a predetermined period in the combustion chamber of the internal combustion engine, based on the detected speed of the internal combustion engine and the determined load related to torque generated by the internal combustion engine;
• calculating a cumulative value of the amount of soot estimated;
• and
• determining degradation of the lubricant in the internal combustion engine based on the cumulative value of the amount of soot;
• estimating the temperature of the combustion chamber based on the detected temperature, and correcting the amount of soot estimated into an increased value in response to when the estimated temperature of the combustion chamber is lower than a predetermined first temperature at which fuel injected into the combustion chamber vaporizes less with a decrease in temperature when estimating the amount of soot formed in the combustion chamber;
• and
• actuating an indicator when the corrected amount of estimated soot reaches a predetermined amount.