Patent Publication Number: US-2019169520-A1

Title: Lubricant composition

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a National Stage of International Application No. PCT/JP2017/027544 filed on Jul. 28, 2017, which claims priority to Japanese Patent Application No. 2016-150089 filed on Jul. 29, 2016, the entire contents of which are hereby incorporated by reference. 
    
    
     FIELD 
     The present disclosure relates to a lubricant composition. More specifically, the present disclosure relates to a lubricant composition for an internal combustion engine, particularly a lubricant composition for a gasoline engine. 
     BACKGROUND 
     Lubricant compositions are widely used in the automotive field for internal combustion engines, automatic transmissions, gear oils and the like. In recent years, such lubricant compositions are demanded to have a reduced viscosity for improving the fuel efficiency; however, since a reduction in viscosity leads to a reduced oil film thickness, friction cannot be sufficiently reduced. Accordingly, molybdenum dithiocarbamate (MoDTC) capable of reducing friction by yielding molybdenum disulfide under boundary lubrication conditions has been conventionally used. In such cases, MoDTC is usually used in combination with a calcium-based detergent (e.g., Japanese Unexamined Patent Publication (Kokai) No. 2013-199594 (PTL 1)). However, this combination has a limitation in reducing friction and thus cannot sufficiently improve the fuel efficiency. 
     It is also known to use a magnesium-based detergent as a detergent (e.g., Japanese Unexamined Patent Publication (Kokai) No. 2011-184566 (PTL 2) and Japanese Unexamined Patent Publication (Kokai) No. 2006-328265 (PTL 3)). The use of a magnesium-based detergent can reduce friction more than the use of a calcium-based detergent; however, it has a problem of being likely to cause wear. 
     CITATION LIST 
     Patent Literature 
     [PTL 1] Japanese Unexamined Patent Publication (Kokai) No. 2013-199594 
     [PTL 2] Japanese Unexamined Patent Publication (Kokai) No. 2011-184566 
     [PTL 3] Japanese Unexamined Patent Publication (Kokai) No. 2006-328265 
     SUMMARY 
     Technical Problem 
     An object of the present disclosure is to provide a lubricant composition capable of reducing friction while ensuring anti-wear properties even at a reduced viscosity, such as a lubricant composition used in an internal combustion engine, or even a lubricant composition used in a supercharged gasoline engine. 
     Solution to Problem 
     The present inventors intensively studied to discover that the above-described object can be achieved by adding a specific amount of at least one metal salicylate selected from calcium salicylate and magnesium salicylate and a specific amount of a molybdenum-based friction modifier to a lubricant base oil. 
     In other words, the present disclosure is a lubricant composition containing: a lubricant base oil; (A1) a metal salicylate; and (B) a molybdenum-based friction modifier, 
     wherein 
     the amount of component (B) is in a range of 500 to 1,500 ppm by weight in terms of a concentration [B] in ppm by weight of molybdenum in the lubricant composition, 
     component (A1) is any one of calcium salicylate, magnesium salicylate, and a combination thereof, 
     the amount of calcium salicylate is 0 to 1,800 ppm by weight in terms of a concentration [Ca] in ppm by weight of calcium derived from calcium salicylate in the lubricant composition, 
     the amount of magnesium salicylate is 0 to 1,800 ppm by weight in terms of a concentration [Mg] in ppm by weight of magnesium derived from magnesium salicylate in the lubricant composition, and 
     a total of [Ca] and [Mg] is in a range of 200 to 3,000 ppm by weight. 
     In one embodiment of the present disclosure, the lubricant composition further includes at least one of following characteristic features (1) to (10): 
     (1) the lubricant composition comprising (A) a metallic detergent, wherein the lubricant composition comprises the metal salicylate (A1) in an amount of 5 to 100% by weight based on the total weight of component (A) in terms of a ratio of [Ca] and [Mg] based on a total concentration [A] in ppm by weight of metals derived from the metallic detergent in the lubricant composition; 
     (2) the lubricant composition optionally further comprises a metallic detergent other than component (A1) as the metallic detergent (A), wherein the weight of component (A1) based on the total weight of the metallic detergent (A) is in a range of 5 to 100% by weight; 
     (3) the metal salicylate (A1) is magnesium salicylate and calcium salicylate; 
     (4) the metal salicylate (A1) is at least one kind of magnesium salicylate; 
     (5) the lubricant composition further comprises (A2) a metallic detergent other than component (A1) as the metallic detergent (A), component (A2) comprises at least one selected from magnesium, calcium and sodium, and the total content of the metallic detergent (A) satisfies following equation (1): 
       [ A ]/[ B ]≤4.5  (1)
 
     wherein [A] represents a total concentration in ppm by weight of magnesium, calcium and sodium in the lubricant composition; 
     (6) the content of the metal salicylate (A1) satisfies following equation (2): 
       [ A 1]/[ B ]&lt;4.5  (2)
 
     wherein [A1] represents a total concentration ([Ca]+[Mg]) in ppm by weight of magnesium and calcium that are derived from component (A1) in the lubricant composition; 
     (7) the CCS viscosity at −35° C. is 6.2 Pa·s or less; 
     (8) the high-temperature high-shear viscosity (HTHS viscosity) at 150° C. is 1.7 to 2.9 mPa·s; 
     (9) the kinematic viscosity at 100° C. is less than 9.3 mm 2 /s; and 
     (10) the lubricant composition is for an internal combustion engine. 
     The present disclosure also relates to a method of reducing friction while maintaining low-wear properties by using the above-described lubricant composition or the lubricant composition according to any one of embodiments (1) to (10). 
     Effects of Present Disclosure 
     The lubricant composition of the present disclosure is capable of reducing friction while ensuring anti-wear properties even at a reduced viscosity, and can thus be suitably used as a lubricant composition for internal combustion engines, particularly as a lubricant composition for supercharged gasoline engines. 
    
    
     DETAILED DESCRIPTION 
     Lubricant Base Oil 
     In the present disclosure, the lubricant base oil is not particularly restricted. The lubricant base oil may be any one of mineral oils and synthetic oils, and these oils can be used singly or as a mixture. 
     Examples of mineral oils include oils obtained by distilling an atmospheric residue, which is generated by atmospheric distillation of crude oil, under reduced pressure and refining the resulting lubricant fraction by one or more treatments, such as solvent deasphalting, solvent extraction, hydrocracking, solvent dewaxing, and hydrorefining; wax-isomerized mineral oils; GTL (Gas-to-Liquid) base oils; ATL (Asphalt-to-Liquid) base oils; vegetable oil-derived base oils; and mixed base oils thereof. 
     Examples of the synthetic oils include polybutenes and hydrogenated products thereof; poly-α-olefins, such as 1-octene oligomer and 1-decene oligomer, and hydrogenated products thereof monoesters, such as 2-ethylhexyl laurate, 2-ethylhexyl palmitate, and 2-ethylhexyl stearate; diesters, such as ditridecyl glutarate, di-2-ethylhexyl adipate, diisodecyl adipate, ditridecyl adipate, and di-2-ethylhexyl sebacate; polyol esters, such as neopentyl glycol di-2-ethylhexanoate, neopentyl glycol di-n-octanoate, neopentyl glycol di-n-decanoate, trimethylolpropane tri-n-octanoate, trimethylolpropane tri-n-decanoate, pentaerythritol tetra-n-pentanoate, pentaerythritol tetra-n-hexanoate, and pentaerythritol tetra-2-ethylhexanoate; aromatic synthetic oils, such as alkylnaphthalenes, alkylbenzenes, and aromatic esters; and mixtures thereof. 
     The kinematic viscosity (mm 2 /s) at 100° C. of the lubricant base oil is not particularly restricted; however, in some embodiments it is 2 to 15 mm 2 /s, 3 to 10 mm 2 /s, 3 to 8 mm 2 /s, or 3 to 6 mm 2 /s. By this, a lubricant composition which not only sufficiently forms an oil film and provides excellent lubricity but also has less evaporation loss can be obtained. 
     The viscosity index (VI) of the lubricant base oil is not particularly restricted; however, in some embodiments it is 100 or higher, 120 or higher, or 130 or higher. By this, the viscosity at low temperatures can be reduced while securing an oil film at high temperatures. 
     (A) Metallic Detergent 
     (A1) Metal Salicylate 
     The lubricant composition of the present disclosure is characterized by comprising, as a metallic detergent (A), a metal salicylate (A1) which is calcium salicylate, magnesium salicylate or a combination thereof in the below-described specific range of amount. The lubricant composition of the present disclosure may further comprise other metallic detergent than calcium salicylate and magnesium salicylate as the metallic detergent (A), and it is appropriate that the weight ratio of component (A1) based on the total weight of the metallic detergent (A), in some embodiments, be in a range of 5 to 100% by weight, 10 to 100% by weight, 15 to 100% by weight, 20 to 100% by weight, or 50 to 100% by weight, in terms of a ratio of [Ca] and [Mg] based on a total concentration [A] in ppm by weight of metals derived from the metallic detergent in the lubricant composition, wherein [Ca] is a concentration in ppm by weight of calcium derived from calcium salicylate in the lubricant composition, and [Mg] is a concentration in ppm by weight of magnesium derived from magnesium salicylate in the lubricant composition. By containing at least one selected from calcium salicylate and magnesium salicylate in a specific amount as the metallic detergent, the lubricant composition can ensure high-temperature detergency and rust inhibition that are required as a lubricant. In addition, the lubricant composition can reduce friction and, therefore, can reduce torque. This is advantageous particularly from the standpoint of fuel efficiency characteristics. 
     As for the amount of component (A1) in the lubricant composition of the present disclosure, in some embodiments the amount of calcium salicylate is 0 to 1,800 ppm by weight, such as 0 to 1,600 ppm by weight, in terms of the concentration [Ca] in ppm by weight of calcium in the lubricant composition; in some embodiments the amount of magnesium salicylate is 0 to 1,800 ppm by weight, such as 0 to 1,600 ppm by weight, in terms of the concentration [Mg] in ppm by weight of magnesium in the lubricant composition; and in some embodiments the value of [Ca]+[Mg] is in a range of 200 to 3,000 ppm by weight, 300 to 2,500 ppm by weight, or 400 to 2,000 ppm by weight. When the amount of component (A1) is greater than the above-described upper limit, excessive wear may occur and a sludge may be generated, whereas when the amount of component (A1) is smaller than the above-described lower limit, the friction-reducing effect is low. 
     In the present disclosure, as described above, at least one selected from magnesium salicylate and calcium salicylate is the metal salicylate. Only a single kind of these metal salicylates may be used, or two or more kinds thereof may be used in combination. For example, a combination of magnesium salicylate and calcium salicylate may be used, or magnesium salicylate alone, or even calcium salicylate alone. 
     When component (A1) is magnesium salicylate alone, in some embodiments it is appropriate that the content thereof in terms of the concentration [Mg] in ppm by weight of magnesium derived from magnesium salicylate in the lubricant composition be in a range of 200 to 1,800 ppm by weight, 250 to 1,500 ppm by weight, 300 to 1,200 ppm by weight, or 400 to 1,000 ppm. When component (A1) is calcium salicylate alone, in some embodiments it is appropriate that the content thereof in terms of the concentration [Ca] in ppm by weight of calcium derived from calcium salicylate in the lubricant composition be in a range of 200 to 1,800 ppm by weight, 300 to 1,600 ppm by weight, or 500 to 1,400 ppm by weight. When component (A1) is a combination of magnesium salicylate and calcium salicylate, in some embodiments it is appropriate that a total of [Ca] and [Mg] satisfy a range of 200 to 3,000 ppm by weight, 300 to 2,500 ppm by weight, or 400 to 2,000 ppm by weight. Particularly, in some embodiments it is appropriate that [Mg] be in a range of 100 to 1,600 ppm by weight, 150 to 1,400 ppm by weight, 200 to 1,200 ppm by weight, or 300 to 1,000 ppm, and that [Ca] be in a range of 100 to 1,600 ppm by weight, 300 to 1,500 ppm by weight, or 500 to 1,400 ppm by weight. 
     In some embodiments, the magnesium content in magnesium salicylate and the calcium content in calcium salicylate are each 0.5 to 20% by weight, 1 to 16% by weight, or 2 to 14% by weight. The amount of component (A1) to be added is adjusted such that magnesium and calcium are incorporated into the lubricant composition in the above-described respective ranges of amount. 
     In some embodiments, the metal salicylate (A1) is an overbased metal salicylate, such as a combination of magnesium salicylate and calcium salicylate, or even overbased magnesium salicylate. By this, acid neutralization performance required for a lubricant can be ensured. When overbased magnesium salicylate is used, a neutral magnesium- or calcium-based detergent may be mixed therewith. When overbased calcium salicylate is used, a neutral calcium-based detergent may be used in combination. 
     The total base number of the metal salicylate (A1) is not restricted; however, in some embodiments it is 20 to 600 mg KOH/g, 50 to 500 mg KOH/g, or 100 to 450 mg KOH/g. By this, acid neutralization performance, high-temperature detergency and rust inhibition that are required for a lubricant can be ensured. When two or more metal salicylates are used as a mixture, the base number of the mixture is in the above-described range in some embodiments. 
     In some embodiments, the amount of component (A1) in the lubricant composition satisfies following equation (2): 
       [ A 1]/[ B ]&lt;4.5  (2)
 
     In equation (2), [A1] represents a total concentration (i.e. [Ca]+[Mg]) in ppm by weight of magnesium and calcium that are derived from the magnesium salicylate and calcium salicylate (A1) in the lubricant composition, and [B] is as described above. 
     In some embodiments, the value of [A1]/[B] is less than 3.0, less than 2, less than 1.8, or less than 1.5. When the value of [A1]/[B] is greater than the above-described upper limit, the torque-reducing effect may be low. In some embodiments, the lower limit value of [A1]/[B] is 0.1, 0.2, or 0.3. 
     In one embodiment, as described above, the lubricant composition of the present disclosure comprises only magnesium salicylate as the metal salicylate (A1), or a combination of magnesium salicylate and calcium salicylate as component (A1). The lubricant composition of the present disclosure may further contain (A2) a metallic detergent other than the calcium salicylate and magnesium salicylate (A1) as the metallic detergent (A). In this case, as described above, in some embodiments it is appropriate that the weight ratio of component (A1) based on the total weight of the metallic detergent (A) be 5 to 100% by weight, 10 to 100% by weight, 15 to 100% by weight, 20 to 100% by weight, or 50 to 100% by weight, in terms of the ratio of [Ca] and [Mg] based on the total concentration [A] in ppm by weight of metals derived from the metallic detergent in the lubricant composition. In some embodiments, it is appropriate that the percentage (% by weight) of magnesium salicylate based on the total weight of the metallic detergent (A) be 5 to 100% by weight, 10 to 80% by weight, 10 to 60% by weight, or 10 to 40% by weight, in terms of the percentage of [Mg] based on the total concentration [A] in ppm by weight of metals derived from the metallic detergent in the lubricant composition. In another embodiment, the lubricant composition of the present disclosure comprises only magnesium salicylate, or only a combination of magnesium salicylate and calcium salicylate, as the metallic detergent (A). 
     (A2) Metallic Detergent Other than Metal Salicylate 
     In the lubricant composition of the present disclosure, as component (A2) which is a metallic detergent other than the metal salicylate (A1), a conventionally known metallic detergent containing at least one selected from magnesium, calcium and sodium can be used in combination. Examples of component (A2) include metal sulfonates. A metal sulfonate may be used singly, or two or more thereof may be used in combination. By incorporating a metal sulfonate, high-temperature detergency and rust inhibition that are required for a lubricant can be better ensured. The amount of component (A2) varies depending on the amount of component (A1); however, in some embodiments it is 0 to 5,000 ppm by weight, 0 to 2,000 ppm by weight, or 0 to 1,000 ppm by weight, in terms of a concentration [A2] in ppm by weight of metals derived from component (A2) in the lubricant composition. 
     Examples of the metal sulfonate include magnesium sulfonate, calcium sulfonate, and sodium sulfonate. 
     Further, a commonly-used metallic detergent other than the above-described ones can also be used within a range that does not adversely affect the effects of the present disclosure. For example, magnesium phenate, calcium phenate, and/or a sodium-based detergent may be incorporated. Sodium sulfonate, sodium phenate, and sodium salicylate may be used as the sodium-based detergent. These sodium-based detergents may be used singly, or in combination of two or more thereof. By incorporating a sodium-based detergent(s), high-temperature detergency and rust inhibition that are required for a lubricant can be ensured. The sodium-based detergent(s) can be used in combination with the above-described magnesium-based detergent and optional calcium-based detergent. 
     In some embodiments, the total amount of the metallic detergent (A) in the lubricant composition satisfy following equation (1): 
       [ A ]/[ B ]≤4.5  (1)
 
     In equation (1), [A] represents a total concentration in ppm by weight of magnesium, calcium and sodium in the lubricant composition, and [B] represents a concentration in ppm by weight of molybdenum in the lubricant composition. 
     In some embodiments, the value of [A]/[B] is 3.0 or less, 2.8 or less, 2.6 or less, or 2.5 or less. When the value of [A]/[B] is greater than the above-described upper limit value, excessive wear may occur. In some embodiments, the value limit value of [A]/[B] is 0.2, 0.5, or 1. 
     (B) Molybdenum-Based Friction Modifier 
     The molybdenum-based friction modifier is not particularly restricted, and any conventionally known molybdenum-based friction modifier can be used. Examples thereof include sulfur-containing organic molybdenum compounds, such as molybdenum dithiophosphate (MoDTP) and molybdenum dithiocarbamate (MoDTC); complexes of a molybdenum compound and a sulfur-containing organic compound or other organic compound; and complexes of an alkenylsuccinimide and a sulfur-containing molybdenum compound, such as molybdenum sulfide or sulfurized molybdic acid. Examples of the molybdenum compound include molybdenum oxides, such as molybdenum dioxide and molybdenum trioxide; molybdic acids, such as ortho-molybdic acid, para-molybdic acid, and sulfurized (poly)molybdic acid; molybdates, such as metal salts and ammonium salts of these molybdic acids; molybdenum sulfides, such as molybdenum disulfide, molybdenum trisulfide, molybdenum pentasulfide, and molybdenum polysulfide; sulfurized molybdic acid, and metal salts and amine salts thereof; and molybdenum halides, such as molybdenum chloride. Examples of the sulfur-containing organic compound include alkyl(thio)xanthate, thiaziazole, mercaptothiadiazole, thiocarbonate, tetrahydrocarbyl thiuram disulfide, bis(di(thio)hydrocarbyldithiophosphonate)disulfide, organic (poly)sulfides, and sulfurized esters. In some embodiments, organic molybdenum compounds, such as molybdenum dithiophosphate (MoDTP) and molybdenum dithiocarbamate (MoDTC), are used. 
     Molybdenum dithiocarbamate (MoDTC) is a compound represented by following formula [I], and molybdenum dithiophosphate (MoDTP) is a compound represented by following formula [II]. 
     
       
         
         
             
             
         
       
     
     In above-described formulae [I] and [II], R 1  to R 8  may be the same or different from each other and each represent a monovalent hydrocarbon group having 1 to 30 carbon atoms. The hydrocarbon group may be linear or branched. Examples of the monovalent hydrocarbon group include linear or branched alkyl groups having 1 to 30 carbon atoms; alkenyl groups having 2 to 30 carbon atoms; cycloalkyl groups having 4 to 30 carbon atoms; and aryl groups, alkylaryl groups and arylalkyl groups, which have 6 to 30 carbon atoms. In the arylalkyl groups, an alkyl group may be bound at any position. More specifically, examples of the alkyl group include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group, a tridecyl group, a tetradecyl group, a pentadecyl group, a hexadecyl group, a heptadecyl group, and an octadecyl group, as well as branched alkyl groups thereof. In some embodiments, the alkyl groups have 3 to 8 carbon atoms. Further, X 1  and X 2  each represent an oxygen atom or a sulfur atom, and Y 1  and Y 2  each represent an oxygen atom or a sulfur atom. 
     As component (B), a sulfur-free organic molybdenum compound can also be used. Examples thereof include molybdenum-amine complexes, molybdenum-succinimide complexes, molybdenum salts of organic acids, and molybdenum salts of alcohols. 
     Moreover, as the friction modifier (B) in the present disclosure, the trinuclear molybdenum compounds described in U.S. Pat. No. 5,906,968 can be used as well. 
     In some embodiments, component (B) is added in such an amount that allows the concentration [B] in ppm by weight of molybdenum in the lubricant composition to be in a range of 500 to 1,500 ppm by weight, such as 600 to 1,200 ppm by weight. When the amount of component (B) is greater than the above-described upper limit, the detergency may be deteriorated, whereas when the amount of component (B) is less than the above-described lower limit, there are cases where friction cannot be sufficiently reduced or the detergency is deteriorated. 
     As described above for component (A), in some embodiments the amount of component (B) satisfies following equation (1): 
       [ A ]/[ B ]≤4.5  (1)
 
     In equation (1), [A] represents a total concentration in ppm by weight of magnesium, calcium and sodium in the lubricant composition, and [B] represents a concentration in ppm by weight of molybdenum in the lubricant composition. 
     In some embodiments, the value of [A]/[B] is 3.0 or less, 2.8 or less, 2.6 or less, or 2.5 or less. In some embodiments, the lower limit value of [A]/[B] is 0.2, 0.5, or 1.0. 
     As described above for component (A1), in some embodiments the amount of component (B) satisfies following equation (2): 
       [ A 1]/[ B ]&lt;4.5  (2)
 
     In equation (2), [A1] represents a concentration in ppm by weight of metal(s) derived from component (A1) in the lubricant composition. In some embodiments, the value of [A1]/[B] is less than 3.0, less than 2.0, less than 1.8, or less than 1.5. When the value of [A1]/[B] is greater than the above-described upper limit, the torque-reducing effect may be low. In some embodiments, the lower limit value of [A1]/[B] is 0.1, 0.2, or 0.3. 
     In the lubricant composition of the present disclosure, the above-described lubricant base oil and components (A1) and (B) are indispensable, and the lubricant composition may also comprise known anti-wear agent, ashless dispersant and viscosity index improver as optional components. 
     As the anti-wear agent, known anti-wear agents can be used. In some embodiments, a phosphorus-containing anti-wear agent may be used, for example, a zinc dithiophosphate (ZnDTP (also referred to as “ZDDP”)) represented by the following formula may be used. 
     
       
         
         
             
             
         
       
     
     In this formula, R 1  and R 2  may be the same or different from each other and each represent a hydrogen atom or a monovalent hydrocarbon group having 1 to 26 carbon atoms. The monovalent hydrocarbon group is a primary or secondary alkyl group having 1 to 26 carbon atoms; an alkenyl group having 2 to 26 carbon atoms; a cycloalkyl group having 6 to 26 carbon atoms; an aryl, alkylaryl or arylalkyl group having 6 to 26 carbon atoms; or a hydrocarbon group containing an ester bond, ether bond, alcohol group or carboxyl group. In some embodiments, R 1  and R 2  are each a primary or secondary alkyl group having 2 to 12 carbon atoms, a cycloalkyl group having 8 to 18 carbon atoms or an alkylaryl group having 8 to 18 carbon atoms, and R 1  and R 2  may be the same or different from each other. In some embodiments, R 1  and R 2  are each a zinc dialkyldithiophosphate, and the primary alkyl group has 3 to 12 carbon atoms, such as 4 to 10 carbon atoms. In some embodiments, the secondary alkyl group has 3 to 12 carbon atoms, such as 3 to 10 carbon atoms. The above-described zinc dithiophosphate may be used singly, or two or more thereof may be used as a mixture. In addition, zinc dithiocarbamate (ZnDTC) may be used in combination. 
     Further, at least one compound selected from phosphate-based and phosphite-based phosphorus compounds represented by following formulae (3) and (4) as well as metal salts and amine salts thereof can also be used. 
     
       
         
         
             
             
         
       
     
     In above-described formula (3), R 3  represents a monovalent hydrocarbon group having 1 to 30 carbon atoms; R 4  and R 5  each independently represent a hydrogen atom or a monovalent hydrocarbon group having 1 to 30 carbon atoms; and m represents 0 or 1. 
     
       
         
         
             
             
         
       
     
     In above-described formula (4), R 6  represents a monovalent hydrocarbon group having 1 to 30 carbon atoms; R 7  and R 8  each independently represent a hydrogen atom or a monovalent hydrocarbon group having 1 to 30 carbon atoms; and n represents 0 or 1. 
     In formulae (3) and (4), examples of the monovalent hydrocarbon groups having 1 to 30 carbon atoms that are represented by R 3  to R 8  include alkyl groups, cycloalkyl groups, alkenyl groups, alkyl-substituted cycloalkyl groups, aryl groups, alkyl-substituted aryl groups, and arylalkyl groups. In some embodiments, R 3  to R 8  are each an alkyl group having 1 to 30 carbon atoms or an aryl group having 6 to 24 carbon atoms, for example, an alkyl group having 3 to 18 carbon atoms, such as an alkyl group having 4 to 15 carbon atoms. 
     Examples of the phosphorus compounds represented by formula (3) include phosphorous acid monoesters and hydrocarbyl phosphonites, which have one of the above-described hydrocarbon groups having 1 to 30 carbon atoms; phosphorous acid diesters, monothiophosphorous acid diesters and (hydrocarbyl)phosphonous acid monoesters, which have two of the above-described hydrocarbon groups having 1 to 30 carbon atoms; phosphorous acid triesters and (hydrocarbyl)phosphonous acid diesters, which have three of the above-described hydrocarbon groups having 1 to 30 carbon atoms; and mixtures thereof. 
     Metal salts or amine salts of the phosphorus compounds represented by formula (3) or (4) can be obtained by allowing, for example, a metal base (e.g., a metal oxide, a metal hydroxide, a metal carbonate, or a metal chloride) or a nitrogen compound (e.g., ammonia, or an amine compound having only a hydrocarbon group or hydroxyl group-containing hydrocarbon group having 1 to 30 carbon atoms in the molecule), to act on a phosphorus compound represented by formula (3) or (4) and subsequently neutralizing some or all of residual acidic hydrogens. Examples of a metal in the above-described metal base include alkali metals, such as lithium, sodium, potassium, and cesium; alkaline earth metals, such as calcium, magnesium, and barium; and heavy metals (excluding molybdenum), such as zinc, copper, iron, lead, nickel, silver, and manganese. In some embodiments, alkaline earth metals, such as calcium and magnesium, and zinc are used. 
     In the lubricant composition, the anti-wear agent is incorporated in an amount of usually 0.1 to 5.0% by weight, such as 0.2 to 3.0% by weight. 
     Examples of the ashless dispersant include nitrogen-containing compounds having at least one linear or branched alkyl or alkenyl group having 40 to 500 carbon atoms, such as 60 to 350 carbon atoms, in the molecule, and derivatives thereof; Mannich dispersants; mono- or bis-succinimides (e.g., alkenylsuccinimides); benzylamines having at least one alkyl or alkenyl group having 40 to 500 carbon atoms in the molecule; polyamines having at least one alkyl or alkenyl group having 40 to 400 carbon atoms in the molecule; and modified products thereof obtained by modification with a boron compound, carboxylic acid, phosphoric acid or the like. Any one or more of these ashless dispersants can be arbitrarily selected and incorporated. In some embodiments, the lubricant composition may comprise an alkenylsuccinimide. 
     A method of producing the above-described succinimides is not particularly restricted and, for example, the succinimides can be obtained by allowing a compound having an alkyl or alkenyl group having 40 to 500 carbon atoms to react with maleic anhydride at 100 to 200° C. and subsequently allowing the resulting alkyl succinate or alkenyl succinate to react with a polyamine. Examples of the polyamine include diethylenetriamine, triethylenetetramine, tetraethylenepentamine, and pentaethylenehexamine. Examples of the derivatives of nitrogen-containing compounds exemplified above as the ashless dispersant include compounds modified with a so-called “oxygen-containing organic compound”, which are obtained by allowing a monocarboxylic acid having 1 to 30 carbon atoms (e.g., a fatty acid), a polycarboxylic acid having 2 to 30 carbon atoms (e.g., oxalic acid, phthalic acid, trimellitic acid, or pyromellitic acid) or an anhydride thereof, an ester compound thereof, an alkylene oxide having 2 to 6 carbon atoms, or a hydroxy(poly)oxyalkylene carbonate to act on the above-described nitrogen-containing compounds and subsequently neutralizing or amidating some or all of residual amino groups and/or imino groups; so-called “boron-modified compounds”, which are obtained by allowing boric acid to act on the above-described nitrogen-containing compounds and subsequently neutralizing or amidating some or all of residual amino groups and/or imino groups; so-called “phosphate-modified compounds”, which are obtained by allowing phosphoric acid to act on the above-described nitrogen-containing compounds and subsequently neutralizing or amidating some or all of residual amino groups and/or imino groups; sulfur-modified compounds obtained by allowing a sulfur compound to act on the above-described nitrogen-containing compounds; and modified compounds obtained by performing a combination of two or more types of modifications selected from modification with an oxygen-containing organic compound, boron modification, phosphate modification and sulfur modification on the above-described nitrogen-containing compounds. In some embodiments, boric acid-modified compounds of alkenyl succinimides, particularly boric acid-modified compounds of bis-type alkenylsuccinimides, can further improve the heat resistance when used in combination with the above-described base oil. 
     In some embodiments, the amount of the ashless dispersant is 20% by weight or less, 15% by weight or less, or 5% by weight or less, based on the total amount of the composition. As the ashless dispersant, a boron-containing ashless dispersant can also be used as a mixture with a boron-free ashless dispersant. When a boron-containing ashless dispersant is used, the content ratio thereof is not particularly restricted; however, in some embodiments it is appropriate that the amount of boron contained in the composition be 0.001 to 0.2% by weight, 0.003 to 0.1% by weight, or 0.005 to 0.05% by weight, based on the total amount of the composition. 
     In some embodiments, the number-average molecular weight (Mn) of the ashless dispersant is not less than 2,000, not less than 2,500, not less than 3,000, or not less than 5,000, but not higher than 15,000. When the number-average molecular weight of the ashless dispersant is less than the above-described lower limit value, sufficient dispersibility is not attained in some cases. Meanwhile, when the number-average molecular weight of the ashless dispersant is higher than the above-described upper limit value, an excessively high viscosity makes the fluidity insufficient, causing an increase in deposits. 
     Examples of the above-described viscosity index improver include those containing a polymethacrylate, a dispersion-type polymethacrylate, an olefin copolymer (e.g., a polyisobutylene or an ethylene-propylene copolymer), a dispersion-type olefin copolymer, a polyalkylstyrene, a hydrogenated styrene-butadiene copolymer, a styrene-maleic anhydride ester copolymer, a star isoprene or the like. Further, a comb-shaped polymer which contains, in its main chain, at least a repeating unit based on a polyolefin macromer and a repeating unit based on an alkyl (meth)acrylate containing an alkyl group having 1 to 30 carbon atoms, can also be used. 
     The viscosity index improver is usually composed of the above-described polymer and a diluent oil. In some embodiments, the content of the viscosity index improver is 0.01 to 20% by weight, 0.02 to 10% by weight, or 0.05 to 5% by weight, in terms of the polymer amount based on the total amount of the composition. When the content of the viscosity index improver is less than the above-described lower limit value, the viscosity-temperature characteristics and the low-temperature viscosity characteristics may be deteriorated. Meanwhile, when the content of the viscosity index improver is higher than the above-described upper limit value, not only the viscosity-temperature characteristics and the low-temperature viscosity characteristics may be deteriorated, but also the production cost is largely increased. 
     In the lubricant composition of the present disclosure, in order to improve the performance thereof, other additive(s) may further be incorporated in accordance with the intended purpose. As other additives, additives that are commonly used in lubricant compositions can be used, and examples thereof include an antioxidant, a friction modifier other than above-described component (B), a corrosion inhibitor, a rust inhibitor, a pour-point depressant, a demulsifier, a metal deactivator, and an anti-foaming agent. 
     Examples of the antioxidant include phenolic and amine-based ashless antioxidants, and metal-based antioxidants, such as copper-based and molybdenum-based antioxidants. Examples of the phenolic ashless antioxidants include 4,4′-methylene-bis(2,6-di-tert-butylphenol), 4,4′-bis(2,6-di-tert-butylphenol) and isooctyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, and examples of the amine-based ashless antioxidants include phenyl-α-naphthylamine, alkylphenyl-α-naphthylamine, and dialkyldiphenylamine. The antioxidant is incorporated into the lubricant composition usually in an amount of 0.1 to 5% by weight. 
     Examples of the friction modifier other than above-described component (B) include esters, amines, amides, and sulfurized esters. The friction modifier is incorporated into the lubricant composition usually in an amount of 0.01 to 3% by weight. 
     Examples of the corrosion inhibitor include benzotriazole-based, tolyltriazole-based, thiadiazole-based, and imidazole-based compounds. Examples of the rust inhibitor include petroleum sulfonates, alkylbenzene sulfonates, dinonylnaphthalene sulfonates, alkenylsuccinic acid esters, and polyhydric alcohol esters. The rust inhibitor and the corrosion inhibitor are each incorporated into the lubricant composition usually in an amount of 0.01 to 5% by weight. 
     As the pour-point depressant, for example, a polymethacrylate-based polymer that is compatible with the lubricant base oil to be used can be selected. The pour-point depressant is incorporated into the lubricant composition usually in an amount of 0.01 to 3% by weight. 
     Examples of the demulsifier include polyalkylene glycol-based nonionic surfactants, such as polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, and polyoxyethylene alkylnaphthyl ethers. The demulsifier is incorporated into the lubricant composition usually in an amount of 0.01 to 5% by weight. 
     Examples of the metal deactivator include imidazolines, pyrimidine derivatives, alkylthiadiazoles, mercaptobenzothiazoles, benzotriazoles and derivatives thereof, 1,3,4-thiadiazole polysulfides, 1,3,4-thiadiazolyl-2,5-bisdialkyl dithiocarbamates, 2-(alkyldithio)benzimidazoles, and β-(o-carboxybenzylthio)propionitrile. The metal deactivator is incorporated into the lubricant composition usually in an amount of 0.01 to 3% by weight. 
     Examples of the anti-foaming agent include silicone oils having a kinematic viscosity at 25° C. of 1,000 to 100,000 mm 2 /s, alkenylsuccinic acid derivatives, esters of a polyhydroxy aliphatic alcohol and a long-chain fatty acid, methyl salicylate, and o-hydroxybenzyl alcohols. The anti-foaming agent is incorporated into the lubricant composition usually in an amount of 0.001 to 1% by weight. 
     As other additive, an alkali borate-based additive can be added. The alkali borate-based additive contains an alkali metal borate hydrate and can be represented by the following formula: 
       M 2 O. x B 2 O 3   .y H 2 O 
     In this formula, M represents an alkali metal; x represents 2.5 to 4.5; and y represents 1.0 to 4.8. 
     Specific examples of the alkali borate-based additive include lithium borate hydrate, sodium borate hydrate, potassium borate hydrate, rubidium borate hydrate and cesium borate hydrate. In some embodiments, potassium borate hydrate and sodium borate hydrate are used. The average particle size of these alkali metal borate hydrate particles is generally 1 micron (μ) or smaller. In the alkali metal borate hydrate used in the present disclosure, the ratio of boron to alkali metal is in a range of about 2.5:1 to 4.5:1 in some embodiments. The amount of the alkali borate-based additive to be added is 0.002 to 0.05% by weight in terms of boron amount based on the total amount of the lubricant composition. 
     The CCS viscosity at −35° C. of the lubricant composition of the present disclosure is not restricted; however, in some embodiments it is 6.2 Pa·s or less, 5.0 Pa·s or less, 4.0 Pa·s or less, or 3.5 Pa·s or less. 
     In some embodiments of the lubricant composition of the present disclosure, the amount of molybdenum contained therein and the CCS viscosity at −35° C. satisfy following equation (5): 
       [CCS viscosity]/[ B ]≤0.01  (5)
 
     wherein [CCS viscosity] represents a value (Pa·s) of the CCS viscosity at −35° C. of the lubricant composition, and [B] represents the concentration in ppm by weight of molybdenum in the lubricant composition. 
     In some embodiments, the value of [CCS viscosity]/[B] is 0.008 or less, such as 0.005 or less. When this value is larger than 0.01, the torque reduction ratio may be reduced and the detergency may be deteriorated. The lower limit value of [CCS viscosity]/[B] is not restricted; however, in some embodiments it is 0.002, such as 0.003. 
     The high-temperature high-shear viscosity (HTHS viscosity) at 150° C. of the lubricant composition of the present disclosure is not restricted; however, in some embodiments it is 1.7 to 2.9 mPa·s, such as 2.0 to 2.6 mPa·s. 
     The kinematic viscosity at 100° C. of the lubricant composition of the present disclosure is not restricted; however, in some embodiments it is less than 9.3 mm 2 /s, such as less than 8.2 mm 2 /s. 
     The lubricant composition of the present disclosure has sufficient friction characteristics and wear characteristics and exerts an effect of attaining a high torque reduction ratio even at a low viscosity; therefore, the lubricant composition of the present disclosure can be suitably used for internal combustion engines as well as supercharged gasoline engines. 
     EXAMPLES 
     The present disclosure will now be described in more detail by way of Examples and Comparative Examples thereof; however, the present disclosure is not restricted to the below-described Examples. 
     Materials used in Examples and Comparative Examples are as follows. 
     Lubricant Base Oil 
     Lubricant base oil: Fischer-Tropsch-derived base oil, kinematic viscosity at 100° C.=4.1 mm 2 /s, VI=127 
     (A) Metallic Detergents 
     (A1) Metal Salicylates 
     (A1-1) magnesium salicylate (total base number: 340 mg KOH/g, magnesium content: 7.5% by weight) 
     (A1-2) calcium salicylate 1 (total base number: 350 mg KOH/g, calcium content: 12.0% by weight) 
     (A1-3) calcium salicylate 2 (total base number: 220 mg KOH/g, calcium content: 8.0% by weight) 
     (A2) Metal Sulfonates 
     (A2-1) magnesium sulfonate (total base number: 400 mg KOH/g, magnesium content: 9.0% by weight) 
     (A2-2) calcium sulfonate (total base number: 300 mg KOH/g, calcium content: 11.6% by weight) 
     (B) Molybdenum-Based Friction Modifier 
     Molybdenum-based friction modifier: MoDTC (a compound represented by above-described formula [1], wherein X 1  and X 2  are both O, and Y 1  and Y 2  are both S; molybdenum content: 10% by weight) 
     Anti-Wear Agents 
     Anti-wear agent 1: pri-ZnDTP (primary alkyl group) 
     Anti-wear agent 2: sec-ZnDTP (secondary alkyl group) 
     Other Additives 
     Antioxidant: phenolic antioxidant 
     Ashless dispersant: succinimide 
     Viscosity index improver: polymethacrylate 
     Anti-foaming agent: dimethyl silicone 
     Examples 1 to 12 and Comparative Examples 1 to 8 
     Lubricant compositions were each prepared by mixing the respective components in the amounts indicated in Tables 1 and 3. The amounts of the magnesium-based detergent, calcium-based detergent and molybdenum-based friction modifier indicated in Tables 1 and 3 are concentrations in terms of the contents (ppm by weight) of magnesium, calcium and molybdenum based on the total amount of each lubricant composition ([Mg], [Ca] and [B] in the order mentioned), respectively. The amounts of the anti-wear agent and other additives are in parts by weight based on the total amount (100 parts by weight) of each lubricant composition. It is noted here that the amount of the magnesium-based detergent and that of the calcium-based detergent were controlled such that the total molar amount of magnesium and calcium contained in these detergents was as constant as possible in all of Examples and Comparative Examples. For the thus obtained compositions, the below-described tests were conducted. The results thereof are presented in Tables 2 and 4. 
     In Tables 1 and 3 below, [A] represents a total concentration in ppm by weight of all magnesium and calcium contained in each lubricant composition (i.e. including Mg and Ca derived from magnesium sulfonate and calcium sulfonate, respectively), and [A1] represents a total concentration in ppm by weight of magnesium and calcium derived from the metal salicylate(s) (A1) contained in each lubricant composition (i.e. [Ca]+[Mg]). Further, [A1]/[A] represents a ratio (% by weight) of [A1], which is the total concentration in ppm by weight of magnesium and calcium derived from the metal salicylate(s), based on [A], which is the total concentration in ppm by weight of all magnesium and calcium contained in each lubricant composition. 
     (1) High-Temperature High-Shear Viscosity at 150° C. (HTHS150) 
     The high-temperature high-shear viscosity at 150° C. was measured in accordance with ASTM D4683. 
     (2) CCS Viscosity at −35° C. (CCS Viscosity) 
     The CCS viscosity at −35° C. was measured in accordance with ASTM D5293. 
     (3) Kinematic Viscosity at 100° C. (KV100) 
     The kinematic viscosity at 100° C. was measured in accordance with ASTM D445. 
     (4) Torque Reduction Ratio 
     Using the lubricant compositions obtained in Examples and Comparative Examples as test compositions, the torque was measured in a motoring test with a gasoline engine. A TOYOTA 2ZR-FE 1.8L in-line 4-cylinder engine was used as the engine, and a torque meter was arranged between a motor and the engine to measure the torque at an oil temperature of 80° C. and an engine speed of 700 rpm. The torque was also measured in the same manner using a commercially available GF-5 0W-20 oil as a standard oil. The torque (T) of each test composition was compared with the torque (T 0 ) of the standard oil, and the reduction ratio from the torque of the standard oil, ({(T 0 −T)/T 0 }×100) (%), was calculated. A higher reduction ratio indicates superior fuel efficiency. A reduction ratio of 5.5% or higher was regarded as satisfactory. 
     (5) Diameter of Shell Wear Scar 
     The diameter of shell wear scar was measured in accordance with the shell four-ball test (ASTM D4172), except that the rotation speed, the load, the testing temperature and the testing time were set at 1,800 rpm, 40 kgf, 90° C. and 30 minutes, respectively. A wear scar diameter of 0.7 mm or smaller was regarded as satisfactory. 
     (6) Hot Tube Test (Evaluation of High-Temperature Detergency) 
     Each lubricant composition and air were allowed to continuously flow in a glass tube of 2 mm in inner diameter for 16 hours at rates of 0.3 mL/hr and 10 mL/sec, respectively, while maintaining the temperature of the glass tube at 270° C. A lacquer adhered to the glass tube was compared with a color chart and evaluated with a score of 10 when the lacquer was transparent or a score of 0 when the lacquer was black. A higher score indicates superior high-temperature detergency. A score of 5.0 or higher was regarded as satisfactory. 
     
       
         
           
               
               
               
               
               
               
               
               
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Exam- 
                 Exam- 
                 Exam- 
                 Exam- 
                 Exam- 
                 Exam- 
                 Exam- 
                 Exam- 
                 Exam- 
                 Exam- 
                 Exam- 
                 Exam- 
               
               
                   
                 ple 1 
                 ple 2 
                 ple 3 
                 ple 4 
                 ple 5 
                 ple 6 
                 ple 7 
                 ple 8 
                 ple 9 
                 ple 10 
                 ple 11 
                 ple 12 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Lubricant base oil 
                 balance 
                 balance 
                 balance 
                 balance 
                 balance 
                 balance 
                 balance 
                 balance 
                 balance 
                 balance 
                 balance 
                 balance 
               
               
                 (A1-1) magnesium 
                 300 
                 600 
                 300 
                 0 
                 300 
                 1,100 
                 300 
                 0 
                 900 
                 600 
                 600 
                 1,500 
               
               
                 salicylate ([Mg], 
               
               
                 ppm by weight) 
               
               
                 (A2-1) magnesium 
                 0 
                 0 
                 0 
                 300 
                 0 
                 0 
                 0 
                 300 
                 0 
                 0 
                 0 
                 0 
               
               
                 sulfonate ([Mg], 
               
               
                 ppm by weight) 
               
               
                 (A1-2) calcium 
                 1,400 
                 900 
                 1,400 
                 1,400 
                 0 
                 0 
                 1,400 
                 1,400 
                 500 
                 0 
                 1,400 
                 1,300 
               
               
                 salicylate 1 ([Ca], 
               
               
                 ppm by weight) 
               
               
                 (A1-3) calcium 
                 0 
                 0 
                 0 
                 0 
                 1,400 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 salicylate 2 ([Ca], 
               
               
                 ppm by weight) 
               
               
                 (A2-2) calcium 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 900 
                 0 
                 0 
               
               
                 sulfonate ([Ca], 
               
               
                 ppm by weight) 
                   
               
               
                 [A1] total ([Ca] + 
                 1,700 
                 1,500 
                 1,700 
                 1,400 
                 1,700 
                 1,100 
                 1,700 
                 1,400 
                 1,400 
                 600 
                 2,000 
                 2,800 
               
               
                 [Mg]) 
               
               
                 [A1]/[A] 
                 100 
                 100 
                 100 
                 82 
                 100 
                 100 
                 100 
                 82 
                 100 
                 40 
                 100 
                 100 
               
               
                 (% by weight) 
               
               
                 (B) molybdenum- 
                 700 
                 700 
                 700 
                 700 
                 700 
                 1,000 
                 1,000 
                 1,000 
                 700 
                 700 
                 700 
                 700 
               
               
                 based friction 
               
               
                 modifier 
               
               
                 Anti-wear agent 1 
                 1 
                 1 
                 — 
                 — 
                 — 
                 1 
                 — 
                 — 
                 1 
                 1 
                 1 
                 1 
               
               
                 Anti-wear agent 2 
                 — 
                 — 
                 1 
                 1 
                 1 
                 — 
                 1 
                 1 
                 — 
                 — 
                 — 
                 — 
               
               
                 Antioxidant 
                 0.6 
                 0.6 
                 0.6 
                 0.6 
                 0.6 
                 0.6 
                 0.6 
                 0.6 
                 0.6 
                 0.6 
                 0.6 
                 0.6 
               
               
                 Ash-free dispersant 
                 3.6 
                 3.6 
                 3.6 
                 3.6 
                 3.6 
                 3.6 
                 3.6 
                 3.6 
                 3.6 
                 3.6 
                 3.6 
                 3.6 
               
               
                 Viscosity index 
                 8.7 
                 8.7 
                 8.7 
                 8.7 
                 8.7 
                 8.7 
                 8.7 
                 8.7 
                 8.7 
                 8.7 
                 8.7 
                 8.7 
               
               
                 improver 
               
               
                 Anti-foaming agent 
                 0.1 
                 0.1 
                 0.1 
                 0.1 
                 0.1 
                 0.1 
                 0.1 
                 0.1 
                 0.1 
                 0.1 
                 0.1 
                 0.1 
               
               
                 [A]/[B] 
                 2.4 
                 2.1 
                 2.4 
                 2.4 
                 2.4 
                 1.1 
                 1.7 
                 1.7 
                 2.0 
                 2.1 
                 2.9 
                 4.0 
               
               
                 [A1]/[B] 
                 2.4 
                 2.1 
                 2.4 
                 2.0 
                 2.4 
                 1.1 
                 1.7 
                 1.4 
                 2.0 
                 0.9 
                 2.9 
                 4.0 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
               
               
               
               
               
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 Exam- 
                 Exam- 
                 Exam- 
                 Exam- 
                 Exam- 
                 Exam- 
                 Exam- 
                 Exam- 
                 Exam- 
                 Exam- 
                 Exam- 
                 Exam- 
               
               
                   
                 ple 1 
                 ple 2 
                 ple 3 
                 ple 4 
                 ple 5 
                 ple 6 
                 ple 7 
                 ple 8 
                 ple 9 
                 ple 10 
                 ple 11 
                 ple 12 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Evalu- 
                 KV100 
                 mm 2 /s 
                 6.8 
                 6.7 
                 6.8 
                 6.8 
                 6.7 
                 6.6 
                 6.9 
                 6.9 
                 6.6 
                 6.6 
                 6.7 
                 6.9 
               
               
                 ation 
                 HTHS150 
                 MPa · s 
                 2.3 
                 2.3 
                 2.3 
                 2.3 
                 2.3 
                 2.3 
                 2.3 
                 2.3 
                 2.3 
                 2.3 
                 2.4 
                 2.4 
               
               
                 results 
                 CCS viscosity 
                 Pa · s 
                 3.2 
                 3.1 
                 3.4 
                 3.3 
                 3.3 
                 3.4 
                 3.4 
                 3.4 
                 3.1 
                 3.0 
                 3.1 
                 3.2 
               
               
                   
                 Torque 
                 % 
                 5.99 
                 7.71 
                 8.04 
                 6.40 
                 7.40 
                 7.43 
                 7.45 
                 8.66 
                 7.50 
                 7.29 
                 7.40 
                 6.90 
               
               
                   
                 reduction ratio 
               
               
                   
                 Diameter of 
                 mm 
                 0.64 
                 0.63 
                 0.68 
                 0.55 
                 0.62 
                 0.61 
                 0.66 
                 0.66 
                 0.63 
                 0.52 
                 0.61 
                 0.61 
               
               
                   
                 shell wear scar 
               
               
                   
                 Hot tube 
                 270° C. 
                 7.5 
                 7.5 
                 6.5 
                 5.5 
                 5.5 
                 8.5 
                 5.5 
                 5.5 
                 7.5 
                 6.0 
                 5.5 
                 8.0 
               
               
                   
                 [CCS 
                   
                 0.0046 
                 0.0044 
                 0.0049 
                 0.0047 
                 0.0047 
                 0.0034 
                 0.0034 
                 0.0034 
                 0.0044 
                 0.0043 
                 0.0044 
                 0.0046 
               
               
                   
                 viscosity]/[B] 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
               
               
               
               
             
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                 Compar- 
                 Compar- 
                 Compar- 
                 Compar- 
                 Compar- 
                 Compar- 
                 Compar- 
                 Compar- 
               
               
                   
                 ative 
                 ative 
                 ative 
                 ative 
                 ative 
                 ative 
                 ative 
                 ative 
               
               
                   
                 Exam- 
                 Exam- 
                 Exam- 
                 Exam- 
                 Exam- 
                 Exam- 
                 Exam- 
                 Exam- 
               
               
                   
                 ple 1 
                 ple 2 
                 ple 3 
                 ple 4 
                 ple 5 
                 ple 6 
                 ple 7 
                 ple 8 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 Lubricant base oil 
                 balance 
                 balance 
                 balance 
                 balance 
                 balance 
                 balance 
                 balance 
                 balance 
               
               
                 (A1-1) magnesium 
                 0 
                 0 
                 0 
                 300 
                 600 
                 1,900 
                 0 
                 0 
               
               
                 salicylate ([Mg], 
               
               
                 ppm by weight) 
               
               
                 (A2-1) magnesium 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 600 
                 0 
               
               
                 sulfonate ([Mg], 
               
               
                 ppm by weight) 
               
               
                 (A1-2) calcium 
                 1,900 
                 1,900 
                 1,900 
                 1,400 
                 900 
                 0 
                 0 
                 0 
               
               
                 salicylate 1 ([Ca], 
               
               
                 ppm by weight) 
               
               
                 (A1-3) calcium 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 salicylate 2 ([Ca], 
               
               
                 ppm by weight) 
               
               
                 (A2-2) calcium 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 900 
                 1,700 
               
               
                 sulfonate ([Ca], 
               
               
                 ppm by weight) 
                   
               
               
                 [A1] total ([Ca] + 
                 1,900 
                 1,900 
                 1,900 
                 1,700 
                 1,500 
                 1,900 
                 0 
                 0 
               
               
                 [Mg]) 
               
               
                 [A1]/[A] 
                 100 
                 100 
                 100 
                 100 
                 100 
                 100 
                 0 
                 0 
               
               
                 (% by weight) 
               
               
                 (B) molybdenum- 
                 700 
                 1,000 
                 1,000 
                 300 
                 300 
                 700 
                 700 
                 700 
               
               
                 based friction 
               
               
                 modifier 
               
               
                 Anti-wear agent 1 
                 1 
                 1 
                 — 
                 1 
                 1 
                 1 
                 1 
                 1 
               
               
                 Anti-wear agent 2 
                 — 
                 — 
                 1 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Antioxidant 
                 0.6 
                 0.6 
                 0.6 
                 0.6 
                 0.6 
                 0.6 
                 0.6 
                 0.6 
               
               
                 Ash-free dispersant 
                 3.6 
                 3.6 
                 3.6 
                 3.6 
                 3.6 
                 3.6 
                 3.6 
                 3.6 
               
               
                 Viscosity index 
                 8.7 
                 8.7 
                 8.7 
                 8.7 
                 8.7 
                 8.7 
                 8.7 
                 8.7 
               
               
                 improver 
               
               
                 Anti-foaming agent 
                 0.1 
                 0.1 
                 0.1 
                 0.1 
                 0.1 
                 0.1 
                 0.1 
                 0.1 
               
               
                 [A]/[B] 
                 2.7 
                 1.9 
                 1.9 
                 5.7 
                 5.0 
                 2.7 
                 2.1 
                 2.4 
               
               
                 [A1]/[B] 
                 2.7 
                 1.9 
                 1.9 
                 5.7 
                 5.0 
                 2.7 
                 0.0 
                 0.0 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
               
               
               
               
             
               
                   
                 TABLE 4 
               
               
                   
                   
               
               
                   
                 Compar- 
                 Compar- 
                 Compar- 
                 Compar- 
                 Compar- 
                 Compar- 
                 Compar- 
                 Compar- 
               
               
                   
                 ative 
                 ative 
                 ative 
                 ative 
                 ative 
                 ative 
                 ative 
                 ative 
               
               
                   
                 Exam- 
                 Exam- 
                 Exam- 
                 Exam- 
                 Exam- 
                 Exam- 
                 Exam- 
                 Exam- 
               
               
                   
                 ple 1 
                 ple 2 
                 ple 3 
                 ple 4 
                 ple 5 
                 ple 6 
                 ple 7 
                 ple 8 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Evalu- 
                 KV100 
                 mm 2 /s 
                 6.8 
                 6.9 
                 6.9 
                 6.7 
                 6.8 
                 6.8 
                 6.4 
                 6.5 
               
               
                 ation 
                 HTHS150 
                 MPa · s 
                 2.3 
                 2.3 
                 2.3 
                 2.3 
                 2.3 
                 2.4 
                 2.3 
                 2.3 
               
               
                 results 
                 CCS viscosity 
                 Pa · s 
                 3.2 
                 3.4 
                 3.4 
                 3.3 
                 3.3 
                 3.2 
                 3.0 
                 3.0 
               
               
                   
                 Torque 
                 % 
                 0.86 
                 2.91 
                 5.30 
                 1.70 
                 3.40 
                 6.00 
                 4.50 
                 4.20 
               
               
                   
                 reduction ratio 
               
               
                   
                 Diameter of 
                 mm 
                 0.53 
                 0.63 
                 0.61 
                 0.54 
                 0.62 
                 0.81 
                 0.63 
                 0.60 
               
               
                   
                 shell wear scar 
               
               
                   
                 Hot tube 
                 270° C. 
                 6.5 
                 6.5 
                 4.0 
                 3.0 
                 4.0 
                 9.0 
                 1.0 
                 1.0 
               
               
                   
                 [CCS 
                   
                 0.0046 
                 0.0034 
                 0.0034 
                 0.0110 
                 0.0110 
                 0.0046 
                 0.0043 
                 0.0043 
               
               
                   
                 viscosity]/[B] 
               
               
                   
               
            
           
         
       
     
     As indicated in Table 4, the compositions of Comparative Examples 1 to 3 in which the content of calcium salicylate (A1) was high had a low torque reduction ratio, and the composition of Comparative Example 6 containing a large amount of magnesium salicylate (A) caused a large wear. Further, the compositions of Comparative Examples 4 and 5 in which the amount of the molybdenum-based friction modifier (B) was less than the lower limit of the present disclosure had a low torque reduction ratio and exhibited poor high-temperature detergency. Moreover, the compositions of Comparative Examples 7 and 8 which did not contain any metal salicylate not only had a low torque reduction ratio but also exhibited poor high-temperature detergency. 
     On the other hand, as indicated in Table 2, the lubricant compositions according to the present disclosure caused only a small wear and exhibited a high torque reduction ratio and excellent high-temperature detergency, despite having a low kinematic viscosity at 100° C.