Method for determining minimum lubricating oil-film thickness under operating engine conditions using electrical capacitance

Claim 1

A method for determining the minimum oil-film thickness of a lubricating oil composition under operating engine conditions comprising: (a) placing the lubricating oil composition being evaluated in an operating engine wherein a selected bearing of said engine is electrically isolated; (b) obtaining an instantaneous signal relating to capacitance between the entire bearing and shaft and measuring the capacitance using capacitance measuring means, said capacitance measuring means employing a high enough frequency to avoid the ambiguous effect of oil conductivity and a low enough potential to avoid electrical discharge between the surfaces; and (c) converting said capacitance signal developed between said bearing and shaft to a value indicative of the minimum oil-film thickness between said bearing and shaft at the particular time said capacitance signal is obtained by using the formula: ##EQU6## where: is the radial clearance K is a constant (0.08854) A is the area of the plate Σ is the dielectric constant of the material between the plates C is capacitance.

Claim 2

A method for determining the minimum oil-film thickness of a lubricating oil composition under operating engine conditions comprising: (a) placing the lubricating oil composition being evaluated in an operating engine wherein a selected bearing of said engine is electrically isolated; (b) obtaining an instantaneous signal relating to capacitance between the entire bearing and shaft and measuring the capacitance using capacitance measuring means, said capacitance measuring means employing a high enough frequency to avoid the ambiguous effect of oil conductivity and a low enough potential to avoid electrical discharge between the surfaces; and (c) converting said capacitance signal developed between said bearing and shaft to a value indicative of the minimum oil-film thickness between said bearing and shaft at the particular time said capacitance signal is obtained by using the formula: ##EQU6## where: is the radial clearance K is a constant (0.08854) A is the area of the plate Σ is the dielectric constant of the material between the plates C is capacitance.

Claim 3

A method for determining the minimum oil-film thickness of a lubricating oil composition under operating engine conditions comprising: (a) placing the lubricating oil composition being evaulated in an operating engine wherein a selected bearing of said engine is electrically isolated; (b) applying an alternating current between the crankshaft of said engine and said entire bearing, said current being applied at a frequency which is high enough to avoid the ambiguous effect of oil conductivity and said current being low enough to avoid electrical discharge between the two surfaces, (c) measuring the potential developed between said shaft and bearing at any selected time during an engine cycle, said measurement directly relating to the capacitance therebetween, and (d) converting the capacitance to a value indicative of the minimum oil-film thickness between said shaft and said bearing at the particular selected time by using the formula: ##EQU7## where: s is the radial clearance K is a constant (0.08854) A is the area of the plate Σ is the dielectric constant of the material between the plates C is the capacitance.

Claim 4

A method for determining the minimum oil-film thickness of a lubricating oil composition under operating engine conditions comprising: (a) placing the lubricating oil composition being evaulated in an operating engine wherein a selected bearing of said engine is electrically isolated; (b) applying an alternating current between the crankshaft of said engine and said entire bearing, said current being applied at a frequency which is high enough to avoid the ambiguous effect of oil conductivity and said current being low enough to avoid electrical discharge between the two surfaces, (c) measuring the potential developed between said shaft and bearing at any selected time during an engine cycle, said measurement directly relating to the capacitance therebetween, and (d) converting the capacitance to a value indicative of the minimum oil-film thickness between said shaft and said bearing at the particular selected time by using the formula: ##EQU7## where: s is the radial clearance K is a constant (0.08854) A is the area of the plate Σ is the dielectric constant of the material between the plates C is the capacitance.

Claim 9

A method for determining the minimum oil-film thickness of a lubricating oil composition under operating conditions comprising: (a) placing the lubricating oil composition being evaluated in an operating engine wherein the crankshaft is electrically isolated; (b) obtaining an instantaneous signal relating to capacitance between the shaft and bearings of said engine and measuring the capacitance using capacitance measuring means, said capacitance measuring means employing a high enough frequency to avoid the ambiguous effect of oil conductivity and a low enough potential to avoid electrical discharge between the surfaces; and (c) converting said capacitance signal developed between said shaft and bearings and which is indicative of the relative capacitance between said surfaces, to a value indicative of the relative minimum oil-film thickness between said surfaces by using the forula: ##EQU8## where: s is the radial clearance K is a constant (0.08854) A is the area of the plate Σ is the dielectric constant of the material between the plates C is capacitance.

Claim 10

A method for determining the minimum oil-film thickness of a lubricating oil composition under operating conditions comprising: (a) placing the lubricating oil composition being evaluated in an operating engine wherein the crankshaft is electrically isolated; (b) obtaining an instantaneous signal relating to capacitance between the shaft and bearings of said engine and measuring the capacitance using capacitance measuring means, said capacitance measuring means employing a high enough frequency to avoid the ambiguous effect of oil conductivity and a low enough potential to avoid electrical discharge between the surfaces; and (c) converting said capacitance signal developed between said shaft and bearings and which is indicative of the relative capacitance between said surfaces, to a value indicative of the relative minimum oil-film thickness between said surfaces by using the forula: ##EQU8## where: s is the radial clearance K is a constant (0.08854) A is the area of the plate Σ is the dielectric constant of the material between the plates C is capacitance.