Shear stable functional fluid with low brookfield viscosity

Abstract

A functional fluid of low Brookfield Viscosity comprising a mixture of at least two different base stocks with shear stable viscosity modifier polymers, and also containing performance additives.

1 . A functional fluid comprising: 
 (A) a mixture of at least two base stocks, said mixture comprising    (i) at least one first base stock having a kinematic viscosity of at least 4.5 to about 8.0 mm 2 /sec at 100° C., a viscosity index of at least 120 to about 160, a pour point of about −12° C. maximum, a saturates content of greater than about 98 mass %;    (ii) at least one second base stock having a kinematic viscosity of about 2.0 to about 4.5 mm 2 /sec at 100° C., a viscosity index of about 100 to about 120, a pour point of about −12° C. maximum, a saturates content of greater than about 98 mass %;    wherein the first base stock is present in the amount of about 40 vol % to about 90 vol % based on the stock,    wherein the second base stock is present in the amount of about 10 vol % to about 60 vol % based on the stock,    wherein the first base stock (i) and second base stock (ii) are not the same; and    (B) said base oil mixture (being a blend of base stocks as defined above) has a kinematic viscosity of about 4.0 to about 5.5 mm 2 /sec at 100° C., a viscosity index of about 120 to about 150, a pour point of about −12° C. maximum;    (C) at least one viscosity index improver having a shear stability index (SSI) less than 35, as measured in the KRL Tapered Roller Bearing Tester according to procedure CEC-L-45-T-93, said SSI being defined by the equation            SSI   =         (       μ   i     -     μ   f       )       (       μ   i     -     μ   0       )       *   100             where    μ i —Initial fluid viscosity @ 100° C. (fully blended ATF)    μ f —Final after-shear fluid viscosity @ 100° C. (fully blended ATF)    μ 0 —Base oil viscosity @ 100° C. (blend of two or more base stocks without any additives);    (D) an additive package;    (E) the resulting additized functional fluid having, a kinematic viscosity of about 5.0 to about 6.5 mm 2 /sec at 100° C., a viscosity index of about 120 to about 180, a pour point of about less than −42° C. maximum, and a Brookfield viscosity of about 15,000 cP or less at −40° C.;    (F) the resulting additized functional fluid having, an after KRL shear parameter (SP) of about 4.9 to about 5.6 mm 2 /sec at 100° C. as defined by            SP   =       (       μ   f     +     μ   0       )     2             where    μ f —Final after-shear fluid viscosity @ 100 ° C. (fully blended ATF)    μ 0 —Base oil viscosity @ 100 ° C. (blend of two or more base stocks without any additives).    
     
     
         2 . The functional fluid of  claim 1  wherein base stock (i) has a kinematic viscosity of about 4.5 to about 7.0 mm 2 /s at 100° C., a viscosity index in the range of about 125 to about 150, a pour point of less than about −15° C.  
     
     
         3 . The functional fluid of  claim 1  wherein base stock (i) has a kinematic viscosity of about 5.0 to about 7.0 mm 2 /s at 100° C., a viscosity index in the range of about 125 to about 150, a pour point of less than −18° C.  
     
     
         4 . The functional fluid of  claim 1  wherein base stock (ii) has a kinematic viscosity of about 2.5 to about 4.0 mm 2 /s at 100° C., a viscosity index in the range of about 100 to about 115, a pour point of less than −15° C.  
     
     
         5 . The functional fluid of  claim 2  wherein base stock (ii) has a kinematic viscosity of about 2.5 to about 4.0 mm 2 /s at 100° C., a viscosity index in the range of about 100 to about 115, a pour point of less than −15° C.  
     
     
         6 . The functional fluid of  claim 3  wherein base stock (ii) has a kinematic viscosity of about 2.5 to about 4.0 mm 2 /s at 100° C., a viscosity index in the range of about 100 to about 115, and a pour point of less than −15° C.  
     
     
         7 . The functional fluid of  claim 1  wherein base stock (ii) has a kinematic viscosity of about 2.5 to about 3.5 mm 2 /s at 100° C., a viscosity index in the range of about 100 to about 110 and a pour point of less than −18° C.  
     
     
         8 . The functional fluid of  claim 2  wherein base stock (ii) has a kinematic viscosity of about 2.5 to about 3.5 mm 2 /s at 100° C., a viscosity index in the range of about 100 to 110 and a pour point of less than −18° C.  
     
     
         9 . The functional fluid of  claim 3  wherein base stock (ii) has a kinematic viscosity of about 2.5 to about 3.5 mm 2 /s at 100° C., a viscosity index in the range of about 100 to 110, and a pour point of less than −18° C.  
     
     
         10 . The functional fluid of claims  1 ,  2 ,  3 ,  4 ,  5 ,  6 ,  7 ,  8  or  9  wherein the viscosity index improver has a shear stability index (SSI) of less than 25.  
     
     
         11 . The functional fluid of  claim 1 ,  2 ,  3 , 4 ,  5 ,  6 ,  7 ,  8  or  9  wherein the additized functional fluid has an after KRL shear parameter (SP) of about 4.95 to about 5.4 mm 2 /s at 100° C.  
     
     
         12 . The functional fluid of  claim 10  wherein the additized functional fluid has an after KRL shear parameter (SP) of about 4.95 to about 5.4 mm 2 /s at 100° C.  
     
     
         13 . The functional fluid of  claim 1 ,  2 ,  3 ,  4 ,  5 ,  6 ,  7 ,  8  or  9  wherein the additized functional fluid has an after KRL shear parameter (SP) of about 4.98 to about 5.2 mm 2 /s at 100° C.  
     
     
         14 . The functional fluid of  claim 10  wherein the additized functional fluid has an after KRL shear parameter (SP) of about 4.98 to about 5.2 mm 2 /s at 100° C.  
     
     
         15 . The functional fluid of  claim 1 ,  2 ,  3 ,  4 ,  5 ,  6 ,  7 ,  8  or  9  wherein the base oil mixture (B) has a kinematic viscosity of at least about 4.5 to about 5.5 mm 2 /s at 100° C.  
     
     
         16 . The functional fluid of  claim 10  wherein the base oil mixture (B) has a kinematic viscosity of at least about 4.5 to about 5.5 mm 2 /s at 100° C.  
     
     
         17 . The functional fluid of  claim 11  wherein the base oil mixture (B) has a kinematic viscosity of at least about 4.5 to about 5.5 mm 2 /s at 100° C.  
     
     
         18 . The functional fluid of  claim 12  wherein the base oil mixture (B) has a kinematic viscosity of at least about 4.5 to about 5.5 mm 2 /s at 100° C.  
     
     
         19 . The functional fluid of  claim 13  wherein the base oil mixture (B) has a kinematic viscosity of at least about 4.5 to about 5.5 mm 2 /s at 100° C.  
     
     
         20 . The functional fluid of  claim 14  wherein the base oil mixture (B) has a kinematic viscosity of at least about 4.5 to about 5.5 mm 2 /s at 100° C.  
     
     
         21 . The functional fluid of  claim 1  wherein the viscosity index improver is a PAMA.