Determining quality of lubricating oils in use
Resistivity ρ values of a lubricating oil are repeatedly determined at a predetermined temperature (range) as it is in use in a working mechanism such as a vehicle engine. Such accumulated properties over operating time of the working lubricant can be plotted graphically to display a curve with, for example, a first portion where dρ/dt>0, a maximum ρ max at a time t 1 where dρ/dt=0, a second portion where dρ/dt<0, a minimum ρ min at a time t 2 where dρ/dt again is zero, and a third portion where dρ/dt>0. Furthermore, there can exist another time t 3 , where dρ/dt exhibits a discontinuous change (increase) with time. Characteristics of the ρ vs. t curve, including, the values of t 1 , t 2 , t 3 , ρ max , ρ min , and the ratio ρ max /ρ min can be compared with like data on like lubricant oils in estimating the remaining useful life of the present operating lubricant oil.
1. A method of determining remaining useful life of a quantity of oil in use in fluid lubrication of an operating mechanism, the method comprising:
repeatedly determining resistivity (ρ) values of the oil at an predetermined oil temperature during operating time intervals of the mechanism;
recording a resistivity-time ρ(t) history of the oil such that, as successive resistivity values starting with an initial value are accumulated with elapsed operating time, a continuous ρ(t) linear curve is formulated that includes; (1) a first portion with a slope of dρ/dt>0 up to a first time t 1 during which values of ρ increase and (2) a maxima at t 1 where dρ/dt=0 with a corresponding ρ max ,
comparing, from time to time, the then existing portion of the ρ(t) curve with like predetermined data on a like or functionally comparable oil composition;
using the comparison to predict the remaining useful life of the oil;
continuing to record a resistivity-time ρ(t) history of the oil so that a continuous ρ(t) linear curve is formulated that further includes; (3) a second portion with a slope of dρ/dt<0 during which values of ρ decrease up to a second time t 2 , (4) a minima at t 2 where dρ/dt=0 with a corresponding ρ min , and (5) a third portion where dρ/dt>0 ;
continuing to compare, from time to time, the then existing portions of the ρ(t) curve with like predetermined data on a like or functionally comparable oil composition and using the comparison to predict the remaining useful life of the oil;
continuing to record a resistivity-time ρ(t) history of the oil in the third portion of the ρ(t) curve until time t 3 when there is a sudden increase in the value of the time derivative of the resistivity indicating that the useful life of the oil has been depleted; and then
generating a signal indicating that the useful life of the oil has been depleted.
2. A method as recited in claim 1 in which the oil comprises a mineral-based oil derived from petroleum.
3. A method as recited in claim 1 in which the oil comprises a synthetic oil comprising carbon-based and/or silicon-based materials.
4. A method as recited in claim 1 in which the mechanism is a hydrocarbon fueled engine.
5. A method as recited in claim 1 in which the oil in the mechanism operates at temperatures above about 100° C.
6. A method as recited in claim 1 in which t 2 /t 1 is about 10 or greater.
7. A method as recited in claim 1 in which t 1 is used to predict remaining useful life of the oil.
8. A method as recited in claim 1 in which t 1 and t 2 are used to predict the remaining useful life of the oil.
9. A method as recited in claim 1 in which ρ max is used to predict remaining useful life of the oil.
10. A method as recited in claim 1 in which ρ min and/or ρ max are used to predict remaining useful life of the oil.
11. A method as recited in claim 1 in which the ratio ρ max /ρ min is used to predict remaining useful life of the oil.
12. A method as recited in claim 1 in which the oil is contained in an impedance sensor with a known resistivity constant, and the sensor is powered with an input voltage by an AC frequency generator in a time varying electric field at frequencies in the range of about 100 MHz to 0.1 Hz;
the sensor output current and phase angle between the output current and input voltage are detected;
the impedance amplitude, resistance and reactance of the sensor-oil combination are determined from the input voltage, output current and phase angle; and
the electrical resistivity of the oil at the predetermined temperature is determined from the determined resistance and sensor resistivity constant.
13. A method of determining remaining useful life of a quantity of oil in use in fluid lubrication of an operating mechanism, the method comprising:
repeatedly determining resistivity (ρ) values of the oil at a predetermined oil temperature under a time-varying electric field during operating time intervals of the mechanism;
recording a resistivity-time ρ(t) history of the oil such that, as successive resistivity values starting with an initial value are accumulated with elapsed operating time, a continuous ρ(t) linear curve is formulated that includes; (1) a first portion with a slope of dρ/dt>0 up to a first time t 1 during which values of ρ increase, (2) a maxima at t 1 where dρ/dt=0 with a corresponding ρ max , (3) a second portion with a slope of dρ/dt<0 during which values of ρ decrease up to a second time t 2 , (4) a minima at t 2 where dρ/dt=0 with a corresponding ρ min , and (5) a third portion where dρ/dt>0 ;
comparing, from time to time, the then existing portions of the ρ(t) curve with like predetermined data on a like or functionally comparable oil composition;
repeatedly using the comparison to predict the remaining useful life of the oil;
continuing to record a resistivity-time ρ(t) history of the oil in the third portion of the ρ(t) curve until time t 3 when there is a sudden increase in the value of the time derivative of the resistivity indicating that the useful life of the oil has been depleted; and then
generating a signal indicating that the useful life of the oil has been depleted.
14. A method as recited in claim 13 in which the oil is a mineral-based oil derived from petroleum.
15. A method as recited in claim 13 in which the oil is a synthetic oil comprising carbon-based and/or silicon-based materials.
16. A method as recited in claim 13 in which the mechanism is a hydrocarbon fueled engine.
17. A method as recited in claim 13 in which the oil in the mechanism operates at temperatures above about 100° C.
18. A method as recited in claim 13 in which t 1 and t 2 are used to predict the remaining useful life of the oil.
19. A method as recited in claim 13 in which ρ min and/or ρ max are used to predict remaining useful life of the oil.
20. A method as recited in claim 13 in which the ratio ρ max /ρ min is used to predict remaining useful life of the oil.
21. A method as recited in claim 13 in which the oil is contained in an impedance sensor with a known resistivity constant, and the sensor is powered with an input voltage by an AC frequency generator in a time varying electric field at frequencies in the range of about 100 MHz to 0.1 Hz;
the sensor output current and phase angle between the output current and input voltage are detected;
the impedance amplitude, resistance and reactance of the sensor-oil combination are determined from the input voltage, output current and phase angle; and
the electrical resistivity of the oil at the predetermined temperature is determined from the determined resistance and sensor resistivity constant.