Hydraulic fluid change indicating device for automatic transmission

A hydraulic fluid change indicating device for an automatic transmission for a vehicle, comprising:

• fluid temperature detecting means for detecting the temperature of a hydraulic fluid for said automatic transmission;
• engine speed detecting means for detecting the rotational speed of an engine;
• input shaft speed detecting means for detecting the rotational speed of an input shaft in said automatic transmission;
• output shaft speed detecting means for detecting the rotational speed of an output shaft in said automatic transmission;
• heat amount detecting means for detecting the amount of heat generated in a torque converter;
• first deterioration rate calculating means for obtaining a first deterioration rate according to the temperature of the hydraulic fluid for said automatic transmission detected by said fluid temperature detecting means;
• deterioration acceleration coefficient calculating means for obtaining a deterioration acceleration coefficient according to the amount of heat generated in said torque converter detected by said heat amount detecting means;
• means for calculating a thermal hydraulic fluid deterioration according to said first deterioration rate and said deterioration acceleration coefficient;
• second deterioration rate calculating means for obtaining a second deterioration rate according to the rotational speed of said engine, the rotational speed of said input shaft in said automatic transmission, and the rotational speed of said output shaft in said automatic transmission;
• means for calculating a mechanical hydraulic fluid deterioration according to said second deterioration rate;
• determining means for determining whether a greater one of said thermal hydraulic fluid deterioration or said mechanical hydraulic fluid deterioration is greater than a predetermined hydraulic fluid change threshold;
• and
• indicating means for indicating a warning to change said hydraulic fluid when said determining means determines that said greater of said thermal hydraulic fluid deterioration or said mechanical hydraulic fluid deterioration is greater than said hydraulic fluid change threshold.