Patent Application
20180334636
The present invention relates to lubricating oil compositions for internal combustion engines.
Recently, it has been proposed to replace a conventional naturally aspirated engine with an engine having less displacement and equipped with a turbocharger (turbocharged downsized engine), so as to improve fuel efficiency of automobile engines, especially of automobile gasoline engines. Turbocharged downsized engines make it possible to reduce displacement while maintaining engine power, and thus to improve fuel efficiency, owning to the turbocharger.
Disadvantageously, turbocharged downsized engines may suffer a phenomenon that ignition occurs in a cylinder earlier than an expected timing (LSPI: Low Speed Pre-Ignition), when its torque is increased at a low rotation speed. LSPI leads to increase of energy loss, and thus to restriction on fuel efficiency improvement and low-speed torque improvement. Engine oil is suspected to have an influence on occurrence of LSPI. It has been reported that the calcium content in engine oil promotes occurrence of LSPI.
A Ca content in engine oil is derived from a metallic detergent, which is an additive to keep an engine clean, Thus, reducing the Ca content so as to suppress LSPI in turn results in insufficient engine detergency.
An object of the present invention is to provide a lubricating oil composition for an internal combustion engine having improved LSPI suppression performance while having both engine detergency and fuel efficiency.
A first aspect of the present invention is a lubricating oil composition for an internal combustion engine comprising: (A) a lubricant base oil having a kinematic viscosity at 100° C. of 2 to 8 mm2/s and having an aromatic content of no more than 10 mass %; (B) a metallic detergent comprising: (B1) a metallic detergent overbased with calcium carbonate; and (B2) a metallic detergent overbased with magnesium carbonate; and (C) a molybdenum sulfide dithiocarbamate or a molybdenum oxysulfide dithiocarbamate, wherein the composition has a calcium content of no more than 1500 mass ppm on the basis of the total mass of the composition; the composition has a magnesium content of no less than 300 mass ppm on the basis of the total mass of the composition; the composition has a molybdenum content of no less than 600 mass ppm on the basis of the total mass of the composition; and the composition has an HTHS viscosity at 150° C. of no more than 2.7 mPa·s.
In this specification, “kinematic viscosity at 100° C.” means kinematic viscosity at 100° C., which is specified by ASTM D-445; and “HTHS viscosity at 150° C.” means viscosity at a high shear rate and high temperature at 150° C., which is specified by ASTM D4683.
A second aspect of the present invention is a method for suppressing LSPI of an internal combustion engine, the method comprising: operating an internal combustion engine, while lubricating a cylinder of the internal combustion engine by means of the lubricating oil composition according to the first aspect of the present invention.
According to the first aspect of the present invention, a lubricating oil composition for an internal combustion engine having improved LSPI suppression performance while having both engine detergency and fuel efficiency can be provided.
The method for suppressing LSPI of an internal combustion engine according to the second aspect of the present invention uses the lubricating oil composition according to the first aspect of the present invention, which can effectively suppress LSPI of an internal combustion engine.
The present invention will be described hereinafter. Expression “A to B” concerning numeral values A and B means “no less than A and no more than B” unless otherwise specified. In such expression, if a unit is added only to the numeral value B, the same unit is applied to the numeral value A as well A word “or” means a logical sum unless otherwise specified.
<(A) Lubricant Base Oil>
In the lubricating oil composition of the present invention, a lubricant base oil having a kinematic viscosity at 100° C. of 2 to 8 mm2/s and having an aromatic content of no more than. 10 mass % (hereinafter may be referred to as “lubricant base oil of the present embodiment”) is used as a base oil.
Examples of the lubricant base oil of the present embodiment include paraffinic mineral oils, normal paraffinic base oils, isoparaffinic base oils, and mixtures thereof having a kinematic viscosity at 100° C. of 2 to 8 mm2/s and having an aromatic content of no more than 10 mass %, which are obtained by refining lubricant oil fractions that are obtained by atmospheric distillation and/or vacuum distillation of crude oils, through one or more refining processes selected from solvent deasphalting, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, hydrorefining, sulfuric acid washing, clay treatment, etc.
Preferred examples of the lubricant base oil of the present embodiment include a base oil, a raw material of which is any of the following base oils (1) to (8), and which is obtained by recovering lubricant oil fractions derived from refining, through a predetermined refining method, oil of the raw material and/or lubricant oil fractions recovered from the oil of the raw material:
(1) a distillate obtained by atmospheric distillation of paraffin base crude oils and/or mixed base crude oils;
(2) a distillate obtained by vacuum distillation of residual oils of paraffin base crude oils and/or mixed base crude oils (WVGO);
(3) a wax obtained through a lubricant oil dewaxing process (slack wax etc.) and/or synthetic wax obtained through a gas to liquid (GTL) process or the like (Fischer-Tropsch wax, GTL wax, etc.);
(4) a mixed oil of at least one selected from the base oils (1) to (3) and/or a mild hydrocracked oil of the mixed oil;
(5) a mixed oil of at least two selected from the base oils (1) to (4);
(6) a deasphalted oil of the base oil (1), (2), (3), (4) or (5) (DAO);
(7) a mild hydrocracked oil of the base oil (6) (MHC); and
(8) a mixed oil of at least two selected from the base oils (1) to (7).
Preferred examples of the above described predetermined refining method include hydrorefining such as hydrocracking and hydrofinishing; solvent refining such as furfural solvent extraction; dewaxing such as solvent dewaxing and catalytic dewaxing; clay refining by acid clay, activated clay, etc.; and chemical (acid or alkali) washing such as sulfuric acid washing and caustic soda washing. In the present invention, these refining methods may be carried out individually, or at least two refining methods may be carried out in combination. When at least two refining methods are combined, the order thereof is not restricted, and can be suitably determined.
The following base oil (9) or (10) is especially preferable as the lubricant base oil of the present embodiment. The base oils (9) and (10) are obtained by carrying out a predetermined process on a base oil selected from the base oils (1) to (8), or on lubricant oil fractions recovered from any of the base oils (1) to (8):
(9) a hydrocracked base oil obtained by: hydrocracking a base oil selected from the base oils (1) to (8), or lubricant oil fractions recovered from any of the base oils (1) to (8); carrying out a dewaxing process such as solvent dewaxing and catalytic dewaxing on the products thereof, or lubricant oil fractions recovered from the products thereof by distillation or the like; and optionally further distilling the products thereof after the dewaxing process; and
(10) a hydroisomerized base oil obtained by: hydroisomerizing a base oil selected from the base oils (1) to (8), or lubricant oil fractions recovered from any of the base oils (1) to (8); carrying out a dewaxing process such as solvent dewaxing and catalytic dewaxing on the products thereof, or lubricant oil fractions recovered from the products thereof by distillation or the like; and optionally further distilling the products thereof after the dewaxing process. A catalytic dewaxing process is preferable as the dewaxing process.
When the above described lubricant base oil (9) or (10) is obtained, a solvent refining process and/or hydrofinishing process may be further carried out at a suitable stage if necessary.
A catalyst used for the above described hydrocracking or hydroisomerization is not restricted, but a hydrocracking catalyst comprising a metal having hydrogenating ability (such as at least one metal in the VIa group and VIII group of the periodic table) supported on a composite oxide having cracking activity (for example, silica-alumina, alumina-boria and silica zirconia), or on at least one of the composite oxides in combination, bound by binders, as a support; or a hydroisomerization catalyst comprising at least one metal having hydrogenating ability including at least one group VIII metal supported on a support including zeolite (such as ZSM-5, zeolite beta, and SAPO-11) is preferably used. A hydrocracking catalyst and hydroisomerization catalyst may be used in combination by laminating or mixing or the like.
Reaction conditions of hydrocracking and hydroisomerization are not restricted. Preferably, the hydrogen partial pressure is 0.1 to 20 MPa, the average reaction temperature is 150 to 450° C., LHSV is 0.1 to 3.0 hr−1, and the hydrogen/oil ratio is 50 to 20000 scf/b.
The kinematic viscosity of the lubricant base oil of the present embodiment at 100° C. is 2.0 to 8.0 mm2/s, preferably no more than 5 mm2/s, more preferably no more than 4.5 mm2/s, further preferably no more than 4.4 mm2/s, and especially preferably no more than 4.3 mm2/s; and preferably no less than 3.0 mm2/s, more preferably no less than 3.5 mm2/s, further preferably no less than 3.8 mm2/s, and especially preferably no less than 4.0 mm2/s. The kinematic viscosity of the lubricant base oil at 100° C. of more than 8.0 mm2/s might lead to deteriorated low-temperature viscosity properties of the lubricating oil composition, and to insufficient fuel efficiency. The kinematic viscosity thereof of less than 2.0 mm2/s might lead to insufficient oil film formation at lubricating points, which results in poor lubricity, and to large evaporation loss of the lubricating oil composition.
The kinematic viscosity of the lubricant base oil of the present embodiment at 40° C. is preferably no more than 40 mm2/s, more preferably no more than 30 mm2/s, further preferably no more than 25 mm2/s, especially preferably no more than 22 mm2/s, and most preferably no more than 20 mm2/s. On the other hand, the kinematic viscosity thereof at 40° C. is preferably no less than 6.0 mm2/s, more preferably no less than 8.0 mm2/s, further preferably no less than 10 mm2/s, especially preferably no less than 12 mm2/s, and most preferably no less than 14 mm2/s. The kinematic viscosity of the lubricant base oil at 40° C. of more than 40 mm2/s might lead to deteriorated low-temperature viscosity properties of the lubricating oil composition, and to insufficient fuel efficiency. The kinematic viscosity thereof of less than 6.0 mm2/s might lead to insufficient oil film formation at lubricating points, which results in poor lubricity, and to large evaporation loss of the lubricating oil composition.
In this description, “kinematic viscosity at 40° C.” means kinematic viscosity at 40° C. specified by ASTM D-445.
The viscosity index of the lubricant base oil of the present embodiment is preferably no less than 100, more preferably no less than 110, further preferably no less than 120, especially preferably no less than 125, and most preferably no less than 130. The viscosity index thereof of less than 100 tends to lead to not only deteriorated viscosity-temperature characteristics, thermal and oxidation stability, and anti-evaporation performance of the lubricating oil composition, but also an increased friction coefficient, and tends to lead to deteriorated anti-wear properties. The viscosity index in this description means a viscosity index measured conforming to JIS K 2283-1993.
The density of the lubricant base oil of the present embodiment at 15° C. () is preferably no more than 0.860, more preferably no more than 0.850, further preferably no more than 0.840, and especially preferably no more than 0.835. The density at 15° C. in this description means density measured at 15° C., conforming to JIS K 2249-1995.
The pour point of the lubricant base oil of the present embodiment is preferably no more than −10° C., more preferably no more than −12.5° C., further preferably no more than −15° C., especially preferably no more than −17.5° C., and most preferably no more than −20.0° C. The pour point beyond this upper limit tends to lead to deteriorated low-temperature fluidity of whole of the lubricating oil composition. The pour point in this description means a pout point measured conforming to JIS K 25269-1987.
The sulfur content in the lubricant base oil of the present embodiment depends on the sulfur content in its raw material. For example, when a substantially sulfur-free raw material, such as a synthetic wax component obtained through Fischer-Tropsch reaction or the like, is used, a substantially sulfur-free lubricant base oil can be obtained. When a raw material containing sulfur, such as a slack wax obtained through the process of refining the lubricant base oil, and a microwax obtained through a wax refining process, is used, the sulfur content in the obtained lubricant base oil is usually no less than 100 mass ppm. In the lubricant base oil of the present embodiment, in view of further improvement of the thermal and oxidation stability and reduction of the sulfur content, the sulfur content is preferably no more than 100 mass ppm, more preferably no more than 50 mass ppm, further preferably no more than 10 mass ppm, and especially preferably no more than 5 mass ppm.
The nitrogen content in the lubricant base oil of the present embodiment is preferably no more than 10 mass ppm, more preferably no more than 5 mass ppm, and further preferably no more than 3 mass ppm. The nitrogen content beyond 10 mass ppm tends to lead to deteriorated thermal and oxidation stability. The nitrogen content in this description means a nitrogen content measured conforming to JIS K 2609-1990.
Preferably, % CP of the lubricant base oil of the present embodiment is no less than 70, more preferably no less than 80, and further preferably no less than 85; and usually no more than 99, preferably no more than 95, and more preferably no more than 94. % CP of the lubricant base oil under this lower limit tends to lead to deteriorated viscosity-temperature characteristics, thermal and oxidation stability, and friction properties, and further, to decreased effects of an additive when the additive is incorporated to the lubricant base oil. % CP of the lubricant base oil beyond this upper limit tends to lead to decreased solubility of an additive.
Preferably, % CA of the lubricant base oil of the present embodiment is no more than 2, more preferably no more than 1, further preferably no more than 0.8, and especially preferably no more than 0.5. % CA of the lubricant base oil beyond this upper limit tends to lead to deteriorated viscosity-temperature characteristics, thermal and oxidation stability, and fuel efficiency.
Preferably, % CN of the lubricant base oil of the present embodiment is no more than 30, more preferably no more than 25, further preferably no more than 20, and especially preferably no more than 15. Preferably, % CN of the lubricant base oil is no less than 1, and more preferably no less than 4. % CN of the lubricant base oil beyond this upper limit tends to lead to deteriorated viscosity-temperature characteristics, thermal and oxidation stability, and friction properties. % CN thereof under this lower limit tends to lead to decreased solubility of an additive.
In this description, % CP, % CN and % CA mean percentage of the paraffin carbon number to all the carbon atoms, percentage of the naphthene carbon number to all the carbon atoms, and percentage of the aromatic carbon number to all the carbon atoms, respectively, obtained by the method conforming to ASTM D 3238-85 (n-d-M ring analysis). That is, the above described preferred ranges of % CP, % CN, and % CA are based on values obtained according to the above method. For example, the value of % CN obtained according to the above method can indicate more than 0 even if the lubricant base oil does not contain naphthenes.
The saturated content in the lubricant base oil of the present embodiment is preferably no less than 90 mass %, preferably no less than 95 mass %, and more preferably no less than 99 mass %, on the basis of the total mass of the lubricant base oil. The proportion of the cyclic-saturated content to the saturated content is preferably no more than 40 mass %, preferably no more than 35 mass %, preferably no more than 30 mass %, more preferably no more than 25 mass %, and further preferably no more than 21 mass %. The proportion of the cyclic saturated content to the saturated content is also preferably no less than 5 mass %, and more preferably no less than 10 mass %. The saturated content and the proportion of the cyclic-saturated content to the saturated content within these ranges can improve viscosity-temperature characteristics, and thermal and oxidation stability. When an additive is incorporated to the lubricant base oil, functions of the additive can be brought out at a higher level while the additive is sufficiently stably dissolved and retained in the lubricant base oil. Further, friction properties of the lubricant base oil itself can be improved, and as a result, friction-reducing performance can be improved, which leads to improvement of energy efficiency. In this description, the saturated content means a value measured conforming to ASTM D 2007-93.
Any of similar methods from which the same results are obtained can be used for each of a method of separating the saturated content, and the composition analysis of e.g. the cyclic saturated content, and the noncyclic saturated content. Examples thereof include the above method specified in ASTM D 2007-93, the method specified in ASTM D 2425-93, the method specified in ASTM D 2549-91, methods using high performance liquid chromatography (HPLC), and methods obtained by improving these methods.
The aromatic content in the lubricant base oil of the present embodiment is no more than 10 mass %, preferably no more than 5 mass %, more preferably no more than 4 mass %, further preferably no more than 3 mass %, and especially preferably no more than 2 mass %, on the basis of the total mass of the lubricant base oil; and is preferably no less than 0.1 mass %, more preferably no less than 0.5 mass %, further preferably no less than 1 mass %, and especially preferably no less than 1.5 mass %. The aromatic content beyond this upper limit tends to lead to deteriorated viscosity-temperature characteristics, thermal and oxidation stability, friction properties, moreover to deteriorated anti-evaporation performance and low-temperature viscosity properties, and further, when an additive is incorporated to the lubricant base oil, to decreased effects of the additive. Although the lubricant base oil of the present embodiment does not have to contain the aromatic content, the aromatic content of no less than this lower limit can further improve solubility of an additive.
In this application, the aromatic content means a value measured conforming to ASTM D 2007-93. The aromatic content usually includes alkylbenzenes, and alkylnaphthalenes; anthracenes, phenanthrenes, and alkylated compounds thereof; and compounds having four or more fused benzene rings, aromatic compounds having hetero atoms such as pyridines, quinolines, phenols, and naphthols.
A synthetic base oil may be used as the lubricant base oil of the present embodiment. Examples of the synthetic base oil include poly-α-olefins, and hydrogenated products thereof; isobutene oligomers, and hydrogenated products thereof; isoparaffins; alkylbenzenes; alkylnaphthalenes; diesters (such as ditridecyl glutarate, bis(2-ethylhexyl) azipate, diisodecyl azipate, ditridecyl azipate, and bis(2-ethylhexyl) sebacate); polyol esters (such as trimethylolpropane caprylate, trimethylolpropane pelargonate, pentaerythritol 2-ethylhexanoate, and pentaerythritol pelargonate); polyoxyalkylene glycols; dialkyl diphenyl ethers; polyphenyl ethers; and mixtures thereof, having a kinematic viscosity of 2.0 to 8.0 mm2/s at 100° C. and having an aromatic content of no more than 10 mass %. Among them, poly-α-olefins are preferable. Typical samples of poly-α-olefins include oligomers and co-oligomers of C2-C32, preferably C6-C16 α-olefins (such as 1-octene oligomers, decene oligomers, and ethylene-propylene co-oligomers) and hydrogenated products thereof.
The method for producing a poly-α-olefin is not restricted. Examples thereof include a method of polymerizing an α-olefin in the presence of a polymerization catalyst such as a catalyst containing a complex of aluminum trichloride or boron trifluoride, and water, alcohol (such as ethanol, propanol, and butanol), a carboxylic acid or an ester.
The lubricant base oil of the present embodiment either may be composed of one base oil component, or may contain a plurality of base oil components, as long as the base oil as a whole has a kinematic viscosity at 100° C. of 2.0 to 8.0 mm2/s and has an aromatic content of no more than 10 mass %.
The content of the lubricant base oil of the present embodiment in the lubricating oil composition of the present invention is normally no less than 70 mass %, preferably no less than 75 mass %, and more preferably no less than 80 mass %; and normally no more than 90 mass %, on the basis of the total mass of the composition when the composition is a multi-grade oil. The content thereof is normally no less than 80 mass %, preferably no less than 85 mass %, and more preferably no less than 90 mass %; and normally no more than 95 mass %, on the basis of the total mass of the composition when the composition is a single-grade oil.
<(B) Metallic Detergent>
The lubricant base oil of the present invention contains (B1) a metallic detergent overbased with calcium carbonate (hereinafter may be referred to as “component (B1)”) and (B2) a metallic detergent overbased with magnesium carbonate (hereinafter may be referred to as “component (B2)”) as (B) a metallic detergent (hereinafter may be referred to as “component (B)”). Examples of the component (B) include phenate detergents, sulfonate detergents and salicylate detergents. These metallic detergents can be used alone or in combination.
Preferred examples of a phenate detergent include overbased salts of alkaline earth metal salts of compounds having the structure of the following formula (1). Examples of alkaline earth metals include magnesium, barium, and calcium, Among them, magnesium and calcium are preferable.
In the formula (1), R1 is a C6-C21 linear or branched, saturated or unsaturated alkyl or alkenyl group; m is a polymerization degree, representing an integer of 1 to 10; A is a sulfide (—S—) group or methylene (—CH2—) group; and x is an integer of 1 to 3. R1 may be combination of at least two different groups.
The carbon number of R1 in the formula (1) is preferably 9 to 18, and more preferably 9 to 15. The carbon number of R1 of less than 6 might lead to poor solubility in the base oil. On the other hand, the carbon number of R1 beyond 21 makes the compound difficult to be produced, and might lead to poor thermal stability.
The polymerization degree m in the formula (1) is preferably 1 to 4. The polymerization degree m within this range can improve thermal stability.
Preferred examples of a sulfonate detergent include alkaline earth metal salts of alkyl aromatic sulfonic acids obtained by sulfonation of alkylaromatics, or basic or overbased salts thereof. The weight-average molecular weight of the alkylaromatics is preferably 400 to 1500, and more preferably 700 to 1300.
Examples of alkaline earth metals include magnesium, barium, and calcium, Magnesium and calcium are preferable. Examples of alkyl aromatic sulfonic acids include what is called petroleum sulfonic acids and synthetic sulfonic acids, Examples of petroleum sulfonic acids here include sulfonated products of alkylaromatics of lubricant oil fractions derived from mineral oils, and what is called mahogany acid, which is a side product of production of white oils. Examples of synthetic sulfonic acids include a sulfonated product of alkylbenzene having a linear or branched alkyl group, obtained by recovering side products in a manufacturing plant of alkylbenzene, which is a raw material of detergents, or by alkylating benzene with polyolefins, Another example of synthetic sulfonic acids includes a sulfonated product of alkylnaphthalenes such as dinonylnaphthalene. A sulfonating agent used when sulfonating these alkylaromatics is not limited. For example, a fuming sulfuric acid or a sulfuric anhydride can be used as the sulfonating agent.
Preferred examples of a salicylate detergent include metallic salicylates or basic or overbased salts thereof. Preferred examples of metallic salicylates here include compounds represented by the following formula (2):
In the above formula (2), each R2 is independently a C14-C30 alkyl or alkenyl group; M is an alkaline earth metal; and n is 1 or 2. M is preferably calcium or magnesium. Preferably n is 1. When n=2, R2 may be combination of different groups.
A preferred embodiment of a salicylate detergent can be an alkaline earth metal salicylate of the above formula (2) wherein n=1, or a basic or overbased salt thereof.
A method for producing alkaline earth metal salicylate is not restricted, and known methods for producing monoalkylsalicylates can be used. For example, an alkaline earth metal salicylate can be obtained by: reacting a metal base such as an oxide and hydroxide of an alkaline earth metal with a monoalkylsalicylic acid obtained by alkylating a phenol as a starting material with an olefin, and then carboxylating the resultant product with a carbonic acid gas or the like, or a monoalkylsalicylic acid obtained by alkylating a salicylic acid as a starting material with an equivalent of the olefin, or the like; once converting the above monoalkylsalicylic acid or the like to an alkali metal salt such as a sodium salt and potassium salt, and then performing transmetallation with an alkaline earth metal salt; or the like.
A method for obtaining an alkaline earth metal phenate, sulfonate, or salicylate overbased with calcium carbonate or magnesium carbonate is not limited. For example, it can be obtained by reacting an alkaline earth metal phenate, sulfonate, or salicylate with a base such as calcium carbonate and magnesium carbonate in the presence of carbonic acid gas.
The metal ratio of the component (B) is a value calculated according to the following formula; preferably no less than 1, more preferably no less than 2, and especially preferably no less than 3; and preferably no more than 50, more preferably no more than 30, and especially preferably no more than 10.
The metal ratio of the component (B)=the valence of the metal element in the component (B)×the metal content in the component (B) (mol)/the soap group content of the component (B) (mol)
Examples of the component (B1) include calcium phenate detergents, calcium sulfonate detergents, calcium salicylate detergents, and combination thereof, which are overbased with calcium carbonate. Preferably, the component (B1) contains at least a calcium salicylate detergent.
Examples of the component (B2) include magnesium phenate detergents, magnesium sulfonate detergents, magnesium salicylate detergents, and combination thereof, which are overbased with magnesium carbonate. Preferably, the component (B2) contains at least a magnesium salicylate detergent, or a magnesium sulfonate detergent.
The content of the component (B1) in the lubricating oil composition is such that the composition has the calcium content of no more than 1500 mass ppm, and preferably has 1400 to 1500 mass ppm, on the basis of the total mass of the composition. The calcium content beyond 1500 mass ppm makes LSPI easy to occur. The calcium content of no less than this lower limit makes it possible to maintain high detergency inside an engine, and to improve base number retainability.
The content of the component (B2) in the lubricating oil composition is such that the composition has the magnesium content of no less than 300 mass ppm, and preferably has 350 to 600 mass ppm, on the basis of the total mass of the composition. The magnesium content of no less than this lower limit can improve engine detergency while suppressing LSPI. The magnesium content of no more than this upper limit can suppress increase of friction coefficients.
<(C) Molybdenum Friction Modifier (MoDTC)>
The lubricating oil composition of the present invention contains a molybdenum sulfide dithiocarbamate or a molybdenum oxysulfide dithiocarbamate as (C) a molybdenum friction modifier (hereinafter may be referred to as “component (C)”). For example, a compound represented by the following formula (3) can be used as the component (C):
In the above general formula (3), R3 to R6 may be either the same or different, and is a C2-C24 alkyl or C6-C24 (alkyl)aryl group, preferably a C4-C13 alkyl or C10-C15 (alkyl)aryl group. This alkyl group may be a primary, secondary, or tertiary alkyl group, and may be linear or branched. It is noted that “(alkyl)aryl group” means “aryl or alkylaryl group”, In an alkylaryl group, the alkyl substituent may be in any position of the aromatic ring. Y1 to Y4 are each independently a sulfur atom or oxygen atom, At least one of Y1 to Y4 is a sulfur atom.
The content of the component (C) in the lubricating oil composition is such that the composition has the molybdenum content of no less than 600 mass ppm, and preferably no less than 700 mass ppm; and preferably no more than 1000 mass ppm, more preferably no more than 900 mass ppm, further preferably no more than 850 mass ppm, and especially preferably no more than 800 mass ppm, on the basis of the total mass of the composition. The molybdenum content of this lower limit or over can improve fuel efficiency and LSPI suppression performance. The molybdenum content of this upper limit or below can improve storage stability of the lubricating oil composition.
<(D) Antioxidant>
The lubricating oil composition of the present invention preferably contains an amine antioxidant and/or a phenol antioxidant as (D) an antioxidant (hereinafter may be referred to as “component (D)”). As the amine antioxidant, a known amine antioxidant such as alkylated diphenylamine, alkylated phenyl-naphthylamine, phenyl-α-naphthylamine, and phenyl-β-naphthylamine can be used without any specific limitation. As the phenol antioxidant, a known phenol antioxidant such as 2,6-di-tert-butyl-4-meth ylphenol (DBPC), and 4,4′-methylenebis(2,6-di-tert-butylphenol) can be used without any specific limitation. When the lubricating oil composition of the present invention contains an antioxidant, the content thereof is usually 0.1 to 5 mass % on the basis of the total mass of the composition.
The lubricating oil composition of the present invention preferably contains an amine antioxidant as the component (D). When the lubricating oil composition of the present invention contains an amine antioxidant, the content thereof is preferably 0.01 to 0.1 mass % in terms of nitrogen on the basis of the total mass of the composition. The content of the amine antioxidant in terms of nitrogen of this lower limit or over can further improve lifetime performance of the lubricating oil. The content thereof of this upper limit or below can suppress stain inside an engine.
<(E) Zinc Dialkyldithiophosphate>
The lubricating oil composition of the present invention preferably contains (E) a zinc dialkyldithiophosphate (ZnDTP; hereinafter may be referred to as “component (E)”), For example, a compound represented by the following formula (4) can be used as the component (E):
In the formula (4), R7 to R10 are independently a C1-C24 linear or branched alkyl group, and may be combination of different groups. The carbon numbers of R7 to R10 are preferably no less than 3, preferably no more than 12, and more preferably no more than 8. R7 to R10 may be primary, secondary, or tertiary alkyl groups; and preferably primary or secondary alkyl groups, or combination thereof. Preferably, the mole ratio of primary alkyl group and secondary alkyl group (primary alkyl group:secondary alkyl group) is 0:100 to 30:70. This ratio may be the intramolecular combination ratio of alkyl chains, or may be the mixing ratio of ZnDTP having only primary alkyl groups and ZnDTP having only secondary alkyl groups. When secondary alkyl groups are major, fuel efficiency can be improved.
A method for producing the above zinc dialkyldithiophosphate is not limited. For example, zinc dialkyldithiophosphate can be synthesized by: reacting alcohol(s) having an alkyl group corresponding to R7 to R10 with phosphorus pentasulfide, to synthesize dithiophosphoric acid; and neutralizing the dithiophosphoric acid with zinc oxide.
When the lubricating oil composition of the present invention contains the component (E), the content thereof is preferably 0.03 to 1.0 mass % on the basis of the total mass of the composition. The content of the component (E) is preferably such that the phosphorus content in the composition is 750 to 800 mass ppm on the basis of the total mass of the composition. The phosphorus content in the composition of this lower limit or over can improve not only oxidation stability but also LSPI suppression performance. The phosphorus content therein of this upper limit or below makes it possible to avoid degradation of a base number due to hydrolysis of zinc dialkyldithiophosphate.
<(F) Corrosion Inhibitor or Metal Deactivator>
The lubricating oil composition of the present invention preferably contains (F) a corrosion inhibitor or a metal deactivator (hereinafter may be referred to as “component (F)”). Known corrosion inhibitors can be used as the component (F) without any specific limitation, examples of which include benzotriazole, tolyltriazole, thiadiazole, and imidazole compounds, and known metal deactivators such as imidazolines, pyrimidine derivatives, alkylthiadiazoles, mercaptobenzothiazoles, benzotriazoles and their derivatives, 1,3,4-thiadiazole polysulfide, 1,3,4-thiadiazolyl-2,5-bis(dialkyl dithiocarbanate), 2-(alkyldithio)benzimidazole, and β-(o-carboxybenzylthio) propionitrile. When the lubricating oil composition of the present invention contains the component (F), the content thereof is usually 0.005 to 5 mass % on the basis of the total mass of the composition.
The lubricating oil composition of the present invention preferably contains a sulfur-containing compound as the component (F). Preferred examples of a corrosion inhibitor or a metal deactivator that is a sulfur-containing compound include thiadiazole. Use of a sulfur-containing compound as the component (F) can further improve LSPI suppression performance, and can effectively bring out friction-reducing performance of the component (C), which is a molybdenum friction modifier. When the lubricating oil composition of the present invention contains a sulfur-containing compound as a corrosion inhibitor or a metal deactivator, the content thereof is usually no less than 0.01 mass %, preferably no less than 0.05 mass %, and more preferably no less than 0.1 mass %; and usually no more than 1.0 mass %, preferably no more than 0.5 mass %, and more preferably no more than 0.3 mass %.
The sulfur content in the lubricating oil composition is preferably 0.20 to 0.30 mass %, and more preferably 0.23 to 0.28 mass %, on the basis of the total mass of the composition. The sulfur content therein of this lower limit or more can further improve LSPI suppression performance, and can effectively bring out friction-reducing performance of the component (C), which is a molybdenum friction modifier. The sulfur content therein of this upper limit or below makes it possible to maintain high detergency inside an engine.
<(G) Nitrogen-Containing Ashless Dispersant>
The lubricating oil composition of the present invention may contain a nitrogen-containing ashless dispersant (hereinafter may be referred to as “component (G)”).
Examples of the component (C) include at least one compound selected from the following (G-1) to (G-3):
(G-1) succinimide having at least one alkyl or alkenyl group in its molecule, or derivatives thereof (hereinafter may be referred to as “component (G-1)”);
(G-2) benzylamine having at least one alkyl or alkenyl group in its molecule, or derivatives thereof (hereinafter may be referred to as “component (G-2)”); and
(G-3) polyamine having at least one alkyl or alkenyl group in its molecule, or derivatives thereof (hereinafter may be referred to as “component (G-3)”).
The component (G-1) can be especially preferably used as the component (G).
In the component (G-1), examples of succinimide having at least one alkyl or alkenyl group in its molecule include compounds represented by the following formula (5) or (6):
In the formula (5), R11 is a C40-C400 alkyl or alkenyl group; h represents an integer of 1 to 5, preferably 2 to 4. The carbon number of R11 is preferably no less than 60, and preferably no more than 350.
In the formula (6), R12 and R13 are independently C40-C400 alkyl or alkenyl group, and may be combination of different groups. R12 and R13 are especially preferably polybutenyl groups. In addition, i represents an integer of 0 to 4, preferably 1 to 3. The carbon number of R12 and R13 is preferably no less than 60, and preferably no more than 350.
The carbon numbers of R11 to R13 in the formulae (5) and (6) of these lower limits or over make it possible to obtain good solubility in the lubricant base oil. On the other hand, the carbon numbers of R11 to R13 of these upper limits or below can improve low-temperature fluidity of the lubricating oil composition.
The alkyl or alkenyl groups (R11 to R13) in the formulae (5) and (6) may be linear or branched. Preferred examples thereof include branched alkyl groups and branched alkenyl groups derived from oligomers of olefins such as propene, 1-butene, and isobutene, or from co-oligomers of ethylene and propylene. Among them, a branched alkyl or alkenyl group derived from oligomers of isobutene that are conventionally referred to as polyisobutylene, or a polybutenyl group is most preferable.
Preferred number-average molecular weight of the alkyl or alkenyl groups (R11 to R13) in the formulae (5) and (6) is 800 to 3500.
Succinimide having at least one alkyl or alkenyl group in its molecule includes so-called monotype succinimide represented by the formula (5), where a succinic anhydride terminates only one end of a polyamine chain, and so-called bistype succinimide represented by the formula (6), where succinic anhydrides terminate both ends of a polyamine chain. The lubricating oil composition of the present invention may include either monotype or bistype succinimide, and may include both of them as a mixture.
A method for producing a succinimide having at least one alkyl or alkenyl group in its molecule is not limited. For example, such succinimide can be obtained by: reacting an alkyl succinic acid or an alkenyl succinic acid obtained by reacting a compound having a C40-C400 alkyl or alkenyl group with maleic anhydride at 100 to 200° C., with a polyamine, Here, examples of polyamine include diethylenetriamine, triethylenetetramine, tetraethylenepentamine, and pentaethylenehexamine.
In the component (G-2), examples of benzylamine having at least one alkyl or alkenyl group in its molecule include compounds represented by the following formula (7):
In the formula (7), R14 is a C40-C400 alkyl or alkenyl group; and j represents an integer of 1 to 5, preferably 2 to 4. The carbon number of R14 is preferably no less than 60, and preferably no more than 350.
A method for producing the component (G-2) is not limited. An example of such a method include: reacting a polyolefin such as propylene oligomer, polybutene, and ethylene-α-olefin copolymer, with phenol, to give an alkylphenol; and then reacting the alkylphenol with formaldehyde, and a polyamine such as diethylenetriamine, triethylenetetramine, tetraethylenepentamine, and pentaethylenehexamine, by Mannich reaction.
In the component (G-3), examples of polyamine having at least one alkyl or alkenyl group in its molecule include compounds represented by the following formula (8):
R15—NH—(CH2CH2NH)k—H (8)
In the formula (8), R15 is a C40-C400 alkyl or alkenyl group; k represents an integer of 1 to 5, preferably 2 to 4. The carbon number of R15 is preferably no less than 60, and preferably no more than 350.
A method for producing the component (G-3) is not limited. An example of such a method include: chlorinating a polyolefin such as propylene oligomer, polybutene, and ethylene-α-olefin copolymer; and then reacting the chlorinated polyolefin with ammonia, or a polyamine such as ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, and pentaethylenehexamine.
Examples of derivatives in the components (G-1) to (G-3) include:
(i) an oxygen-containing organic compound-modified compound where a part or all of the residual amino and/or imino groups is/are neutralized or amidated by reacting the succinimide, benzylamine, or polyamine having at least one alkyl or alkenyl group in its molecule (hereinafter referred to as “the above described nitrogen-containing compound”) with a C1-C30 monocarboxylic acid such as fatty acids, a C2-C30 polycarboxylic acid (such as ethanedioic acid, phthalic acid, trimellitic acid, and pyromellitic acid), an anhydride or ester thereof, a C2-C6 alkylene oxide, or a hydroxy(poly)oxyalkylene carbonate;
(ii) a boron-modified compound where a part or all of the residual amino and/or imino groups is/are neutralized or amidated by reacting the above described nitrogen-containing compound with boron;
(iii) a phosphoric acid-modified compound where a part or all of the residual amino and/or imino groups is/are neutralized or amidated by reacting the above described nitrogen-containing compound with phosphoric acid;
(iv) a sulfur-modified compound obtained by reacting the above described nitrogen-containing compound with a sulfur compound; and
(v) a modified compound obtained by two or more modifications selected from oxygen-containing organic compound-modification, boron-modification, phosphoric acid-modification, and sulfur-modification, on the above described nitrogen-containing compound.
Among the derivatives (i) to (v), using a boronated compound of alkenylsuccinimide, especially a boronated compound of bistype alkenylsuccinimide can further improve the thermal stability of the lubricating oil composition.
The molecular weight of the component (C) is not specifically limited, but preferred weight-average molecular weight thereof is 1000 to 20000.
When the lubricating oil composition of the present invention contains the component (C), the content thereof is, in terms of nitrogen on the basis of the total mass of the lubricating oil composition, preferably no less than 0.01 mass %, and more preferably no less than 0.03 mass %; and preferably no more than 0.15 mass %, more preferably no more than 0.1 mass %, and especially preferably no more than 0.07 mass %. The content of the component (C) of this lower limit or over can sufficiently improve anti-coking performance (thermal durability) of the lubricating oil composition. The content thereof of this upper limit or below makes it possible to maintain high fuel efficiency.
The boron content in the lubricating oil composition is, on the basis of the total mass of the lubricating oil composition, preferably no less than 0 mass ppm, more preferably no less than 100 mass ppm, and especially preferably no less than 200 mass ppm; and preferably less than 400 mass ppm, more preferably no more than 350 mass ppm, and especially preferably no more than 300 mass ppm. The boron content of this upper limit or below makes it possible to maintain high fuel efficiency, while keeping the ash content of the composition low.
<(H) Viscosity Index Improver>
The lubricating oil composition of the present invention preferably contains (H) a viscosity index improver (hereinafter may be referred to as “component (H)”). Examples of the component (H) include non-dispersant or dispersant poly(meth)acrylate viscosity index improvers, (meth)acrylate-olefin copolymers, non-dispersant or dispersant ethylene-α-olefin copolymers or hydrogenated products thereof, polyisobutylene or hydrogenated products thereof, hydrogenated styrene-diene copolymers, styrene-maleic anhydride/ester copolymers, and polyalkylstyrene.
The component (H) preferably contains a poly(meth)acrylate viscosity index improver comprising 10-90 mol % of the structural units represented by the following general formula (9) (hereinafter may be referred to as “viscosity index improver of the present embodiment”) on the basis of the total monomer units in the polymer:
[In the general formula (9), R16 is hydrogen or a methyl group, and R17 is a linear or branched chain hydrocarbon group having a carbon number of 1 to 5.]
In the viscosity index improver of the present embodiment, the content of the (meth)acrylate structural units represented by the general formula (9) in the polymer is preferably 10 to 90 mol %, more preferably no more than 80 mol %, and further preferably no more than 70 mol %; and more preferably no less than 20 mol %, further preferably no less than 30 mol %, and especially preferably no less than 40 mol %. The content of the (meth)acrylate structural units represented by the general formula (9) on the basis of the total monomer units of the polymer beyond 90 mol % may lead to inferior solubility in the base oil, inferior improvement effect on viscosity-temperature characteristics, and inferior low-temperature viscosity characteristics. The content under 10 mol % may lead to inferior improvement effect on viscosity-temperature characteristics.
The viscosity index improver of the present embodiment may be a copolymer comprising another (meth)acrylate structural unit in addition to the (meth)acrylate structural unit represented by the general formula (9). Such a copolymer can be obtained by copolymerizing one or more monomer(s) represented by the following general formula (10) (hereinafter referred to as “monomer (M-1)”), and a monomer other than the monomer (M-1).
[In the formula (10), R18 is a hydrogen atom or a methyl group, and R19 is a linear or branched chain hydrocarbon group having a carbon number of 6 to 18.]
Any monomer can be combined with the monomer (M-1). For example, a monomer represented by the following general formula (11) (hereinafter referred to as “monomer (M-2)”) is preferable. A copolymer of the monomer (M-1) and the monomer (M-2) is a so-called non-dispersant poly(meth)acrylate viscosity index improver,
[In the formula (11), R20 is a hydrogen atom or a methyl group, and R21 is a linear or branched chain hydrocarbon group having a carbon number of 19 or more.]
R21 in the monomer (M-2) represented by the formula (11) is a linear or branched chain hydrocarbon group having a carbon number of 19 or more as described above, preferably a linear or branched chain hydrocarbon group having 20 or more carbons, further preferably a linear or branched chain hydrocarbon group having 22 or more carbons, and more preferably a branched chain hydrocarbon group having 24 or more carbons. The upper limit of the carbon number of the hydrocarbon group represented by R21 is not restricted, but this hydrocarbon group is preferably a linear or branched chain hydrocarbon group having 50,000 or less carbons, more preferably a linear or branched chain hydrocarbon group having 500 or less carbons, further preferably a linear or branched chain hydrocarbon group having 100 or less carbons, especially preferably a branched chain hydrocarbon group having 50 or less carbons, and most preferably a branched chain hydrocarbon group having 25 or less carbons.
One preferred example of the viscosity index improver of the present embodiment is comb-shaped poly(meth)acrylate. Comb-shaped poly(meth)acrylate here means a copolymer of the monomer (M-1) and the monomer (M-2), wherein the monomer (M-2) is a macromonomer including R21 in the formula (11) having a number-average molecular weight (Mn) of 1,000 to 50,000 (preferably 1,500 to 20,000, and more preferably 2,000 to 10,000). Examples of such a macromonomer include a macromonomer derived from a hydrogenated product of a polyolefin obtained by copolymerizing butadiene and isoprene.
In the viscosity index improver of the present embodiment, the polymer may comprise either only one kind of (meth)acrylate structural units corresponding to the monomer (M-2) represented by the general formula (11), or combination of two or more kinds thereof. The content of the structural units corresponding to the monomer (M-2) represented by the general formula (11) is, on the basis of the total monomer units of the polymer, preferably 0.5 to 70 mol %, more preferably no more than 60 mol %, further preferably no more than 50 mol %, especially preferably no more than 40 mol %, and most preferably no more than 30 mol %; and preferably no less than 1 mol %, more preferably no less than 3 mol %, further preferably no less than 5 mol %, and especially preferably no less than 10 mol %, The content of the structural units corresponding to the monomer (M-2) represented by the general formula (11) on the basis of the total monomer units of the polymer beyond 70 mol % may lead to inferior improvement effect on viscosity-temperature characteristics, and inferior low-temperature viscosity characteristics. The content under 0.5 mol % may lead to inferior improvement effect on viscosity-temperature characteristics.
One or more selected from a monomer represented by the following general formula (12) (hereinafter referred to as “monomer (M-3)”), and a monomer represented by the following general formula (13) (hereinafter referred to as “monomer (M-4)”) is/are preferable as other monomers to be combined with the monomer (M-1). A copolymer of the monomer (M-1) and the monomer (M-3) and/or (M-4) is a so-called dispersant poly(meth)acrylate viscosity index improver. This dispersant poly(meth)acrylate viscosity index improver may further contain the monomer (M-2) as constituting monomer.
[In the formula (12), R21 is a hydrogen atom or a methyl group, R23 is an alkylene group having a carbon number of 1 to 18, E1 is an amine residue or heterocyclic residue having 1 to 2 nitrogen atoms, and 0 to 2 oxygen atoms, and a is 0 or 1.]
Specific examples of an alkylene group having a carbon number of 1 to 18 represented by R23 include ethylene group, propylene group, butylene group, pentylene group, hexylene group, heptylene group, octylene group, nonylene group, decylene group, undecylene group, dodecylene group, tridecylene group, tetradecylene group, pentadecylene group, hexadecylene group, heptadecylene group, and octadecylene group (each alkylene group may be either a linear or branched chain).
Specific examples of a residue represented by E1 include dimethylamino group, diethylamino group, dipropylamino group, dibutylamino group, anilino group, toluidino group, quinolidino group, acetylamino group, benzoylamino group, morpholino group, pyrrolyl group, pyrrolino group, pyridyl group, methylpyridyl group, pyrrolidinyl group, piperidinyl group, quinolyl group, pyrrolidonyl group, pyrrolidono group, imidazolino group, and pyrazino group,
[In the formula (13), R24 is s a hydrogen atom or a hydrocarbon group, and E2 is a hydrocarbon group, or an amine residue or heterocyclic residue having 1 to 2 nitrogen atoms, and 0 to 2 oxygen atoms]
Specific examples of a group represented by E2 include dimethylamino group, diethylamino group, dipropylamino group, dibutylamino group, anilino group, toluidino group, quinolidino group, acetylamino group, benzoylamino group, morpholino group, pyrrolyl group, pyrrolino group, pyridyl group, methylpyridyl group, pyrrolidinyl group, piperidinyl group, quinolyl group, pirrolidonyl group, pyrrolidono group, imidazolino group, and pyrazino group.
Preferred specific examples of the monomers (M-3) and (M-4) include dimethylaminomethyl methacrylate, diethylaminomethyl methacrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, 2-methyl-5-vinylpyridine, morpholinomethyl methacrylate, morpholinoethyl methacrylate, N-vinylpyrrolidone, and mixtures thereof.
Although the copolymerization molar ratio of the copolymer of the monomer (M-1) and the monomers (M-2) to (M-4) is not restricted, monomer (M-1):monomers (M-2) to (M-4) is preferably approximately 20:80 to 90:10, more preferably 30:70 to 80:20, and further preferably 40:60 to 70:30.
The viscosity index improver of the present embodiment may be produced by any method. For example, they can be easily obtained by radical solution polymerization of the monomer (M-1) and/or (M-2), and one or more selected from the monomers (M-3) to (M-4) under presence of a polymerization initiator such as benzoyl peroxide.
PSSI of the viscosity index improver of the present embodiment measured by the diesel injector method is preferably no more than 40, more preferably no more than 10, further preferably no more than 5, especially preferably no more than 3, and most preferably no more than 1, The PSSI greater than 40 means low shear stability, and may lead to deteriorated fuel efficiency at the initial stage of use so as to maintain a certain level of kinematic viscosity and HTHS viscosity after use. The lower limit of the PSSI of the viscosity index improver of the present embodiment is not restricted, but usually greater than 0. “PSSI” in this description means a permanent shear stability index of a polymer calculated based on data measured according to ASTM D 6278-02 (Test Method for Shear Stability of Polymer Containing Fluids Using a European Diesel Injector Apparatus), conforming to ASTM D 6022-01 (Standard Practice for Calculation of Permanent Shear Stability Index).
The weight-average molecular weight (Mw) of the viscosity index improver of the present embodiment is usually 10,000 to 700,000, preferably no less than 20,000, more preferably no less than 50,000, further preferably no less than 100,000, and especially preferably no less than 120,000; and preferably no more than 500,000, more preferably no more than 400,000, and further preferably no more than 300,000. When the weight-average molecular weight is under 10,000, not only viscosity index improvement effect is small and fuel efficiency and low-temperature viscosity characteristics deteriorate when the viscosity index improver is dissolved in the lubricant base oil, but also the cost might rise. When the weight-average molecular weight is over 700,000, not only viscosity increase effect is too large, and fuel efficiency and low-temperature viscosity characteristics deteriorate, but also shear stability, the solubility in the lubricant base oil, and storage stability deteriorate.
The ratio of the weight-average molecular weight to PSSI (Mw/PSSI) of the viscosity index improver of the present embodiment is preferably no less than 1.0×104, more preferably no less than 2.0×104, further preferably no less than 5.0×104, and especially preferably no less than 8.0×104. Mw/PSSI of less than 1.0×104 may lead to deteriorated fuel efficiency and low temperature startability, that is, deteriorated viscosity temperature characteristics and low-temperature viscosity characteristics.
The ratio of the weight-average molecular weight (Mw) to the number-average molecular weight (Mn) (Mw/Mn) of the viscosity index improver of the present embodiment is preferably no more than 4.0, more preferably no more than 3.5, further preferably no more than 3.0, especially preferably no more than 2.0, and most preferably no more than 1.5; and preferably no less than 1.0, more preferably no less than 1.05, and further preferably no less than 1.1. Mw/Mn beyond 4.0 leads to deteriorated solubility and deteriorated improvement effect of viscosity temperature characteristics, which may lead to failure to maintain sufficient storage stability and fuel efficiency.
The content of the component (H) inclusive of diluent in the lubricating oil composition of the present invention is, on the basis of the total mass of the composition, usually 0.1 to 30 mass %, preferably no less than 1 mass %, more preferably no less than 3 mass %, and further preferably no less than 5 mass %; and preferably no more than 20 mass %, and more preferably no more than 15 mass %. The content of less than 0.1 mass % may lead to deteriorated fuel efficiency, and insufficient low temperature characteristics. The content beyond 30 mass % may lead to deteriorated fuel efficiency and shear stability of the composition.
<Other Additives>
Other additives that are commonly used in lubricating oil can be incorporated in the lubricating oil composition of the present invention according to its purpose in order to further improve its performance. Examples of such additives include additives such as friction modifiers other than the component (C), anti-wear agents (or extreme-pressure agents), anti-rust agents, demulsifiers, and defoaming agents.
Examples of friction modifiers other than the component (C) that can be used here include one or more friction modifier selected from ashless friction modifiers and organic molybdenum compounds other than the component (C). The content of the friction modifier other than the component (C) is preferably 0.01 to 2.0 mass % on the basis of the total mass of the lubricating oil composition. Containing the friction modifier other than the component (C) can further improve fuel efficiency.
Examples of organic molybdenum compounds other than the component (C) include molybdenum dithiophosphate; complexes of molybdenum compounds (examples thereof include: molybdenum oxide such as molybdenum dioxide and molybdenum trioxide; molybdenum acids such as orthomolybdic acid, paramolybdic acid, sulfurized (poly)molybdic acid; molybdic acid salts such as metal salts and ammonium salts of these molybdic acids; molybdenum sulfides such as molybdenum disulfide, molybdenum trisulfide, molybdenum pentasulfide, molybdenum polysulfide; thiomolybdic acid; metal salts and amine salts of thiomolybdic acid; and molybdenum halides such as molybdenum chloride), and sulfur-containing organic compounds (examples thereof include: alkyl (thio)xanthate, thiadiazole, mercaptothiadiazole, thiocarbonate, tetrahydrocarbylthiuram disulfide, bis(di(thio)hydrocarbyldithiophosphonate) disulfide, organic (poly)sulfide, and sulfurized ester) or other organic compounds; and sulfur-containing organic molybdenum compounds such as complexes of sulfur-containing molybdenum compounds such as the above described molybdenum sulfides, sulfurized molybdic acids, and alkenylsuccinimide. These organic molybdenum compounds may be either mononuclear molybdenum compounds, or polynuclear molybdenum compounds such as binuclear or trinuclear molybdenum compounds.
An organic molybdenum compound which does not contain sulfur as a constituting element can be used as an organic molybdenum compound other than the component (C). Specific examples of an organic molybdenum compound which does not contain sulfur as a constituting element include molybdenum-amine complex, molybdenum-succinimide complex, molybdenum salt of organic acids, and molybdenum salt of alcohols. Among them, molybdenum-amine complex, molybdenum salt of organic acids, and molybdenum salt of alcohols are preferable.
When an organic molybdenum compound is used as the friction modifier other than the component (C), the content thereof is preferably 0.01 to 2.0 mass % on the basis of the total mass of the composition. When an organic molybdenum compound is used as the friction modifier other than the component (C), the molybdenum content in the lubricating oil composition is, on the basis of the total mass of the composition, no less than 600 mass ppm, and preferably no less than 700 mass ppm; and preferably no more than 1000 mass ppm, more preferably no more than 900 mass ppm, further preferably no more than 850 mass ppm, and especially preferably no more than 800 mass ppm as well. The content below this lower limit tends to lead to insufficient friction reducing effect despite addition of the compound, and insufficient fuel efficiency, and thermal and oxidation stability of the lubricating oil composition. On the other hand, the content beyond this upper limit does not bring the effect corresponding thereto, and tends to lead to deteriorated storage stability of the lubricating oil composition.
Any compound usually used as an ashless friction modifier for lubricating oil can be used as an ashless friction modifier without particular limitation. Examples of ashless friction modifiers include compounds each having one or more heteroatoms selected from oxygen, nitrogen, and sulfur in its molecule, and each having a carbon number of 6-50. More specific examples thereof include ashless friction modifiers such as amine compounds, fatty acid esters, fatty acid amides, fatty acids, aliphatic alcohols, aliphatic esters, urea compounds, and hydrazide compounds, each of which has at least one C6-C30 alkyl or alkenyl group, especially a linear alkyl group, a linear alkenyl group, a branched alkyl group, or a branched alkenyl group each having 6-30 carbons, in the molecule.
When the lubricating oil composition contains an ashless friction modifier, the content thereof is preferably no less than 0.01 mass %, more preferably no less than 0.1 mass %, and further preferably no less than 0.3 mass %; and preferably no more than 2 mass %, more preferably no more than 1 mass %, and especially preferably no more than 0.8 mass %, on the basis of the total mass of the lubricating oil composition. The content of an ashless friction modifier of less than 0.01 mass % tends to lead to insufficient friction reducing effect despite addition thereof. The content thereof beyond 2 mass % tends to inhibit effect of anti-wear additives or the like, or to lead to deteriorated solubility of additives.
Any anti-wear agents (or extreme-pressure agents) used for lubricating oil can be used as an anti-wear agent (or an extreme-pressure agent) without particular limitation. Examples thereof include sulfur-based, phosphorus-based, and sulfur-phosphorus-based extreme pressure agents, and specifically, phosphorous esters, thiophosphorous esters, dithiophosphorous esters, trithiophosphorous esters, phoshphate esters, thiophosphate esters, dithiophosphate esters, trithiophosphate esters, amine salts thereof, metal salts thereof, derivatives thereof, dithiocarbamate, zinc dithiocarbamate, disulfides, polysulfides, sulfurized olefins, and sulfurized oils. Among them, addition of a sulfur-based extreme-pressure agent, especially sulfurized oil is preferable. When the lubricating oil composition contains an anti-wear agent (or extreme-pressure agent), the content thereof is preferably 0.01 to 10 mass % on the basis of the total mass of the composition.
Examples of anti-rust agents include petroleum sulfonate, alkylbenzenesulfonate, dinonylnaphthalenesulfonate, alkenylsuccinate esters, and polyol esters. When the lubricating oil composition contains an anti-rust agent, the content thereof is preferably 0.01 to 10 mass % on the basis of the total mass of the composition.
Examples of demulsifiers include polyoxyalkylene glycol-based nonionic surfactants such as polyoxyethylene alkyl ether, polyoxyethylene alkylphenyl ether, and polyoxyethylene alkylnaphthyl ether. When the lubricating oil composition contains a demulsifier, the content thereof is preferably 0.01 to 10 mass % on the basis of the total mass of the composition.
Examples of defoaming agents include silicone oil having kinematic viscosity at 25° C. of 1000 to 100,000 mm2/s, alkenylsuccinimide derivatives, esters of polyhydroxy aliphatic alcohol and long-chain fatty acid, methyl salicylate, and o-hydroxybenzylalcohol. When the lubricating oil composition contains a defoaming agent, the content thereof is preferably 0.01 to 10 mass % on the basis of the total mass of the composition.
<Lubricating Oil Composition>
The kinematic viscosity of the lubricating oil composition of the present invention at 100° C. is preferably 4.0 to 12 mm2/s, more preferably no more than 9.3 mm2/s, further preferably no more than 8.2 mm2/s, especially preferably no more than 7.1 mm2/s, and most preferably no more than 6.8 mm2/s; and more preferably no less than 5.0 mm2/s, further preferably no less than 5.5 mm2/s, especially preferably no less than 6.1 mm2/s, and most preferably no less than 6.3 mm2/s. The kinematic viscosity of the lubricating oil composition at 100° C. under 4.0 mm2/s may lead to insufficient lubricity. The kinematic viscosity thereof beyond 12 mm2/s may lead to insufficient low-temperature viscosity and fuel efficiency.
The kinematic viscosity of the lubricating oil composition of the present invention at 40° C. is preferably 4.0 to 50 mm2/s, more preferably no more than 40 mm2/s, further preferably no more than 35 mm2/s, further preferably no more than 32 mm2/s, especially preferably no more than 30 mm2/s, and most preferably no more than 28 mm2/s; and more preferably no less than 15 mm2/s, further preferably no less than 18 mm2/s, further more preferably no less than 20 mm2/s, especially preferably no less than 22 mm2/s, and most preferably no less than 25 mm2/s. The kinematic viscosity of the lubricating oil composition at 40° C. under 4 mm2/s may lead to insufficient lubricity. The kinematic viscosity thereof beyond 50 mm2/s may lead to insufficient low-temperature viscosity and fuel efficiency.
The viscosity index of the lubricating oil composition of the present invention is preferably 140 to 400, more preferably no less than 160, further preferably no less than 180, especially preferably no less than 200, and most preferably no less than 210. The viscosity index of the lubricating oil composition under 140 might make it difficult to improve fuel efficiency while keeping the HTHS viscosity at 150° C., and further, to reduce the low-temperature viscosity (for example, at −35° C. that is measurement temperature of the CCS viscosity specified in the SAE viscosity grade 0W-X, known as viscosity grades of fuel-economy oil), When the viscosity index of the lubricating oil composition is beyond 400, the evaporation loss might increase, and troubles due to insufficient solubility of additives and compatibility with seal materials might occur.
The HTHS viscosity of the lubricating oil composition of the present invention at 100° C. is preferably no more than 5.5 mPa·s, more preferably no more than 5.0 mPa·s, further preferably no more than 4.9 mPa·s, especially preferably no more than 4.8 mPa·s, and most preferably no more than 4.6 mPa·s; and preferably no less than 3.5 mPa·s, more preferably no less than 4.0 mPa·s, further preferably no less than 4.4 mPa, and especially preferably no less than 4.5 mPa·s. In this description, the HTHS viscosity at 100° C. means high temperature high shear viscosity at 100° C., specified in ASTM D4683. The HTHS viscosity at 100° C. under 3.5 mPa·s may lead to insufficient lubricity. The HTHS viscosity at 100° C. beyond 5.5 mPa·s may lead to insufficient low-temperature viscosity and fuel efficiency.
The HTHS viscosity of the lubricating oil composition of the present invention at 150° C. is no more than 2.7 mPa·s, preferably no more than 2.65 mPa·s, and especially preferably no more than 2.35 mPa·s; and preferably no less than 1.95 mPa·s, more preferably no less than 2.1 mPa·s, further preferably no less than 2.2 mPa·s, and especially preferably no less than 2.25 mPa·s. In this description, the HTHS viscosity at 150° C. means high temperature high shear viscosity at 150° C., specified in ASTM D4683. The HTHS viscosity at 150° C. under 1.95 mPa·s may lead to insufficient lubricity. The HTHS viscosity at 150° C. beyond 2.7 mPa·s may lead to insufficient fuel efficiency.
The ratio (X100/X150) of the HTHS viscosity at 100° C. (X100) to the HTHS viscosity at 150° C. (X150) of the lubricating oil composition of the present invention is preferably no more than 2.0. The ratio of the HTHS viscosity X100/X150 of no more than 2.0 makes it possible to achieve high fuel efficiency while maintaining anti-wear performance. The lower limit of the ratio of the HTHS viscosity X100/X150 is not specifically restricted, but is preferably no less than 1.8. The ratio of the HTHS viscosity X100/X150 of no less than 1.8 makes it possible to maintain high base oil viscosity, which is advantageous in view of evaporation loss and anti-wear performance.
The evaporation loss of the lubricating oil composition according to the present invention is, as NOACK evaporation loss at 250° C., preferably no more than 20 mass %, further preferably no more than 15 mass %, and especially preferably no more than 14 mass %. When the NOACK evaporation loss is beyond 20 mass %, the evaporation loss of the lubricating oil is large, which causes viscosity increase and the like, and is not preferable. The NOACK evaporation loss in the present description is evaporation loss of the lubricating oil measured conforming to ASTM D 5800. The lower limit of the NOACK evaporation loss of the lubricating oil composition at 250° C. is not restricted, but normally no less than 5 mass %.
The inventors have examined operation of a turbocharged testing engine under operation conditions such that LSPI easily occurs, and have found that occurrence frequency of LSPI has a negative correlation with an autoignition point in differential scanning calorimetry (DSC) under an air or oxygen atmosphere at a pressure of 10 atm.
In the engine test, so as to exclude influence of deposits formed in a combustion chamber, preconditioning operation at partial load was carried out at 4000 rpm for 30 minutes, and thereafter the throttle position, rotation speed, injection timing, air-fuel ratio, etc. were changed to operation conditions such that LSPI easily occurs (throttle: fully opened, rotation speed: 1800 rpm), Then the number of occurrence of LSPI within 1 hour was measured by means of combustion pressure sensors attached to each cylinder of the engine.
In the DSC measurements, 5 mg of an engine oil sample was heated together with a standard material, under an air or oxygen atmosphere at a pressure of 10 atm, at a temperature increase rate of 10 K/min, to obtain a function of difference of input energy against temperature. In the obtained function, an autoignition point was determined as the lowest temperature at which an exothermic peak begins.
The DSC (10 atm oxygen atmosphere) autoignition point of the lubricating oil composition of the present invention is preferably no less than 213° C., more preferably no less than 215° C., further preferably no less than 217° C., and especially preferably no less than 220° C. The upper limit thereof is not specifically restricted, but usually no more than 300° C., and typically no more than 280° C. The DSC (10 atm oxygen atmosphere) autoignition point of this lower limit or over can effectively suppress the occurrence frequency of LSPI.
The lubricating oil composition of the present invention preferably has a parameter rs represented by the following mathematical formula (1) of no less than 1.08, more preferably no less than 1.10, further preferably no less than 1.15, and especially preferably no less than 1.20. The parameter rs is preferably no more than 3.00, more preferably no more than 2.00, and especially preferably no more than 1.50.
r
s=([S]+[Mo]+[Zn])/([Mg]+2×[Ca]) (1)
(in the mathematical formula (1), [S] represents the sulfur content derived from additives (unit: mass ppm); [Mo] represents the molybdenum content of the composition (unit: mass ppm); [Zn] represents the zinc content of the composition (unit: mass ppm); [Mg] represents the magnesium content of the composition (unit: mass ppm); and [Ca] represents the calcium content of the composition (unit: mass ppm).)
The parameter rs within the above described range makes it possible to achieve well-balanced fuel efficiency, engine detergency, and LSPI suppression performance.
The lubricating oil composition of the present invention preferably has a parameter rs′ represented by the following mathematical formula (2) of no less than 1.00, more preferably no less than 1.02, further preferably no less than 1.05, especially preferably no less than 1.10, and most preferably no less than 1.15. The parameter rs′ is preferably no more than 2.50, more preferably no more than 2.00, and especially preferably no more than 150.
r
s′=([S]′+[Mo]+[Zn])/([Mg]+2×[Ca]) (2)
(in the mathematical formula (2), [S]′ represents the sulfur content derived from additives other than any sulfonate detergent (unit: mass ppm); [Mo] represents the molybdenum content of the composition (unit: mass ppm); [Zn] represents the zinc content of the composition. (unit: mass ppm); [Mg] represents the magnesium content of the composition (unit: mass ppm); and [Ca] represents the calcium content of the composition (unit: mass ppm).)
The parameter rs′ within the above described range makes it possible to achieve well-balanced fuel efficiency, engine detergency, and LSPI suppression performance.
<Method for Suppressing LSPI of Internal Combustion Engine>
The method for suppressing LSPI of an internal combustion engine according to the second aspect of the present invention includes a step of operating an internal combustion engine, while lubricating a cylinder of the internal combustion engine by means of the above described lubricating oil composition according to the first aspect of the present invention. In the method for suppressing LSPI of the present invention, the lubricating oil composition of the present invention is used for at least lubrication of the cylinder, and a portion of the internal combustion engine other than the cylinder may be lubricated together with the cylinder by means of the lubricating oil composition of the present invention. Known lubricating oil supply mechanisms can be employed for lubricating the cylinder of the internal combustion engine by means of the composition, without particular limitation, Lubricating the cylinder of the internal combustion engine by means of the composition of the present invention effectively suppresses LSPI in the internal combustion engine.
Hereinafter the present invention will be more specifically described based on. Examples and Comparative Examples. It is noted that the present invention is not limited to these examples.
Each of the lubricating oil compositions of the present invention (Examples 1 to 8) and for comparison (Comparative examples 1 to 5) was prepared using the following base oil and additives. In Tables, “inmass %” means mass % on the basis of the total mass of the base oil, “mass %” means mass % on the basis of the total mass of each composition, and “mass ppm” means mass ppm on the basis of the total mass of each composition.
(Base Oil)
O-1: Group III base oil, kinematic viscosity (100° C.): 4.15 mm2/s, aromatic content: 0.2 mass %
(Metallic Detergent)
B1-1: CaCO3-overbased Ca salicylate, Ca content: 8.0 mass %, metal ratio: 3.0, base number (perchloric acid method): 225 mgKOH/g, sulfur content: 0.0 mass %
B1-2: CaCO3-overbased Ca sulfonate, Ca content: 12.75 mass %, base number (perchloric acid method): 325 mgKOH/g, sulfur content: 2.0 mass %
B2-1: MgCO3-overbased Mg sulfonate, Mg content: 9.3 mass %, base number (perchloric acid method): 400 mgKOH/g, sulfur content: 2.0 mass %
(Molybdenum Friction Modifier)
C-1: molybdenum (oxy)sulfide dithiocarbamate, alkyl group: combination of C8 and C13, Mo content: 10.0 mass %, sulfur content: 10.8 mass %
(Antioxidant)
D-1: amine antioxidant, nitrogen content: 3.6 mass %
D-2: phenol antioxidant
(Zinc Dithiophosphate)
E-1: zinc dialkyldithiophosphate (alkyl group: secondary C6, Zn content: 9.25 mass %, phosphorus content: 8.5 mass %, sulfur content: 17.6 mass %)
(Ashless Dispersant)
G-1: polybutenylsuccinimide, bis-type, number-average molecular weight of polybutenyl group: 1300, nitrogen content: 1.75 mass %
G-2: boronated polybutenylsuccinimide, bis-type, number-average molecular weight of polybutenyl group: 1300, nitrogen content: 1.5 mass %, boron content: 0.78 mass %
(Viscosity Index Improver)
H-1: polymethacrylate viscosity index improver, weight-average molecular weight: 500,000, PSSI: 5
(Other Sulfur-Containing Additives)
I-1: alkyldithiothiadiazole, sulfur content: 36.0 mass %
I-2: sulfurized olefin, sulfur content: 46.0 mass %
(Evaluation of Lubricating Oil Compositions)
For each of the lubricating oil compositions of Examples 1 to 6 and Comparative examples 1 to 4, the amount of deposits in a hot tube test (HTT290 deposit) was measured, and a friction coefficient (SRV friction coefficient) was measured by means of an SRV friction testing machine. For each of the lubricating oil compositions of Examples 3 to 6, HTHS viscosities at 100° C. and 150° C., kinematic viscosities at 100° C. and 40° C., and a viscosity index were further measured. The results are shown in Tables 1 and 20 For each of the lubricating oil compositions of Examples 1, 7 and 8, and Comparative examples 4 and 5, a DSC (10 atm oxygen atmosphere) autoignition point was also measured. The results are shown in Table 3. Measurement methods were as follows:
(1) HTT290 deposit: a hot tube test was carried out at 290° C., conforming to JPI-5S-55-99, to measure the weight of deposits (unit: mg) adhering to the inner wall surface of a tube having a predetermined bore and length. Less deposits means higher engine detergency.
(2) SRV friction coefficient: a cylinder-on-disk test was carried out t a temperature of 100° C. at a load of 400 N at an amplitude of 1.5 mm at a frequency of 50 Hz by means of an SRV reciprocating friction wear testing machine (manufactured by Optimol Instruments), to measure a friction coefficient.
(3) HTHS viscosity: measured conforming to ASTM D-4683.
(4) kinematic viscosity: measured conforming to ASTM D-445.
(5) viscosity index: measured conforming to JIS K 2283-1993.
(6) DSC autoignition point: differential scanning calorimetry was carried out under an oxygen atmosphere at a pressure of 10 atm at a temperature increase rate of 10° C./min by means of a pressure differential scanning calorimeter (manufactured by TA Instruments), to determine an autoignition point as a temperature at which the peaks began. A higher autoignition point means less LSPI occurrence frequency.
The lubricating oil composition of the present invention has improved LSPI suppression performance, and is superior in engine detergency and fuel efficiency. Thus, the lubricating oil composition of the present invention can be preferably used for lubrication of turbocharged gasoline engines which tend to suffer LSPI, especially for lubrication of turbocharged direct-injection engines.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2015-238434 | Dec 2015 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2016/086160 | 12/6/2016 | WO | 00 |
