Lubricant Composition for a 4-Stroke Marine Engine

Abstract

The invention relates to a grade SAE 30 or 40 lubricant oil for marine four-stroke engines, comprising: (a) 50 to 95% by weight of an oil of mineral or synthetic origin, (b) at least one nanoparticulate detergent of a quantity sufficient for the neutralisation of the acid compounds formed by oxidation of the sulphurous compounds in the fuel supplying the engine, (c) 1 to 20% by weight of at least one polyisobutylene which is soluble in the base oil, with a number average molecular weight of 500 to 8000 inclusive and a kinematic viscosity (at 100° C.) of 50 to 50,000 mm 2 /s inclusive, preferably 200 to 6,000 mm 2 /s, (d) 0.05 to 5.0% of at least one aminated anti-oxidant agent active at a temperature of or above 180° C. and the use of said oil for lubrication of a four-stroke marine engine.

1 . An SAE 30 or 40 grade lubricating oil for 4-stroke marine engines, comprising:
 (a) 50 to 95% by weight of a base oil of mineral or synthetic origin;   (b) at least one nanoparticulate overbased detergent in an amount sufficient to neutralize the acid compounds formed by oxidation of the sulfur compounds in the fuel supplied to the engine;   (c) 1 to 20% by weight of at least one polyisobutylene soluble in the base oil, having a number-average molecular weight between 500 and 8000 and a kinematic viscosity (at 100° C.) between 50 and 50 000 mm 2 /s, preferably between 200 and 6000 mm 2 /s; and   (d) 0.05 to 5.0% of at least one amine antioxidant active at a temperature of 180° C. or above.   
     
     
         2 . The lubricating oil as claimed in  claim 1 , characterized in that the amine antioxidant active at a temperature of 180° C. or above is an aromatic amine. 
     
     
         3 . The lubricating oil as claimed in  claim 1 , characterized in that it has a kinematic viscosity at 100° C. of between 10 and 15 mm 2 /s, preferably between 13.5 and 14.5 mm 2 /s. 
     
     
         4 . The lubricating oil as claimed in  claim 1 , characterized in that it has a total base number between 3 and 100 mg of KOH/g. 
     
     
         5 . The lubricating oil as claimed in  claim 1 , characterized in that the overbased detergent or detergents are chosen from phenates, salicylates and sulfonates. 
     
     
         6 . The lubricating oil as claimed in  claim 2 , characterized in that the amine antioxidant agent is an aromatic monoamine of formula:
   R 1 R 2 R 3 N   where R 1  and R 2  each represent, independently of each other, a hydrogen atom, a C 1-20 , preferably C 4-16 , aliphatic group, or an aromatic or heteroaromatic, monocyclic or condensed polycyclic, substituted or unsubstituted group, R 3  is an aromatic or heteroaromatic, monocyclic or condensed polycyclic, unsubstituted group or a group carrying a C 1-20  alkyl substituent, or R 1  and R 3  together form an aromatic or heteroaromatic, monocyclic or condensed polycyclic group.   
     
     
         7 . The lubricating oil as claimed in  claim 6 , characterized in that the amine antioxidant is an alkylarylamine. 
     
     
         8 . The use of an oil as claimed in  claim 1  as a lubricating oil for 4-stroke marine engines. 
     
     
         9 . The use of the combination of:
 (a) at least one polyisobutylene soluble in the base oil, having a number-average molecular weight between 500 and 8000 and a kinematic viscosity (at 100° C.) between 50 and 50 000 mm 2 /s; and   (b) at least one amine antioxidant active at a temperature of 180° C. or above,   in order to slow down the increase, over the course of time, of the kinematic viscosity of a 4-stroke marine engine lubricating oil comprising a base oil of synthetic or mineral origin and at least one nanoparticulate overbased detergent.