Patent ID: 6850865

Claim:
A method of monitoring the condition of the fluid in an automatic transmission in real time comprising: (a) disposing a pair of spaced electrodes in the fluid in the transmission; (b) exciting one of said electrodes sequentially with a first relatively low frequency alternating voltage for measuring the effect of electrochemical interaction at the electrode surface through impedance variation and at a second relatively high frequency alternating voltage for measuring the effect of bulk fluid impedance; (c) measuring the current in the other of said electrodes at said first and second frequencies and computing the difference in impedance ΔZ at said frequencies; and determining the temperature corrected value of the impedance difference ΔZ TC from a known relationship of ΔZ as a function of temperature; (d) determining a parameter selected from the group consisting of (i) ASTM D-664 TAN (ii) ASTM E168 Oxidation and (iii) ASTM D-5483 HPDSC Induction time from a lookup table of values of ΔZ TC as a function of one of (i), (ii) and (iii); and, (e) providing an end of life (EOL) indication for the fluid when one of said TAN, Oxidation and HPDSC time reaches a predetermined limit.