Patent ID: 8464576

Claim:
A device for estimating an antioxidant performance of engine oil, which is used as an indicator for determining degradation of engine oil, comprising: fuel concentration-acquiring means for acquiring a concentration of fuel in the engine oil; and antioxidant performance-estimating means for estimating an antioxidant performance of engine oil, based on the acquired concentration of fuel; wherein said antioxidant performance-estimating means comprises: first antioxidant performance-estimating means for estimating an antioxidant performance of an antioxidant contained in the engine oil as a first antioxidant performance; and second antioxidant performance-estimating means for estimating an antioxidant performance of a peroxide decomposer contained in the engine oil as a second antioxidant performance, and calculates the antioxidant performance based on the estimated first antioxidant performance and second antioxidant performance; wherein said first antioxidant performance-estimating means calculates a rate of change in oxidation induction time corresponding to the antioxidant in the engine oil by a following equation (A), and calculates the oxidation induction time corresponding to the antioxidant as the first antioxidant performance, by integrating the calculated rate of change, and wherein said second antioxidant performance-estimating means calculates a rate of change in oxidation induction time corresponding to the peroxide decomposer in the engine oil by a following equation (B), and calculates the oxidation induction time corresponding to the peroxide decomposer as the second antioxidant performance, by integrating the calculated rate of change, d[OIT] AH /dt=k 1 +k 2 ×[NOx] 2 +k 3×[FUEL] 2 (A) d[OIT] zN /dt=[OIT] zN x ( k 4 +k 5 ×[NOx] 2 +k 6×[FUEL] 2 ) (B) wherein d[OIT] AH /dt: rate of change in the oxidation induction time corresponding to the antioxidant, d[OIT] zN /dt: rate of change in the oxidation induction time corresponding to the peroxide decomposer, [OIT] ZN : oxidation induction time corresponding to the peroxide decomposer, k 1 to k 6 : reaction rate coefficients, [NOx]: NOx concentration in the crankcase, and [FUEL]: concentration of fuel in the engine oil.