LUBRICATING OIL COMPOSITION

Abstract

A lubricating oil for an internal combustion engine is disclosed. The lubricating oil can provide reduced friction and can cope with environmental regulations requiring a high corrosion-preventing effect. The lubricating oil composition contains a mono or diester of glycerin and a straight-chain or branched fatty acid of C6 to 20 having a saturated hydrocarbyl group; a triazole derivative; and a mixture of primary zinc dialkyl dithiophosphate and secondary zinc dialkyl dithiophosphate.

Description

TECHNICAL FIELD

The present invention relates to a lubricating oil composition and in particular relates to a lubricating oil composition for an internal combustion engine having an improved friction lowering effect and an improved corrosion prevention effect.

BACKGROUND OF THE INVENTION

Strengthening of regulations in regard to environmental protection is currently taking place on a global scale. In particular, with regard to automobiles, fuel-efficiency regulations and exhaust gas restrictions are becoming increasingly severe, due to concerns regarding the environmental problems such as global warming, depletion of oil resources and measures for protection of resources.

To meet demands relating to improved fuel efficiency of automobiles, improvements in the various factors relating to automobiles such as reduction in the weight of the automobile, engine improvements aimed at increasing engine efficiency, and improvements in the efficiency of transmission of drive force, as well as improvements in engine oil in order to prevent frictional losses in the engine have become important. In order to use engine oil to improve fuel efficiency, it is effective to reduce the viscous resistance by lowering engine oil viscosity; however, such lowering of the viscosity of the engine oil increases friction at all points of the engine so excessive lowering of viscosity must be avoided.

In order to improve fuel efficiency, it is effective to reduce friction at metal contact points. However, addition of friction regulators, anti-friction agents or extreme pressure agents etc is necessary and sulphur-containing compounds or phosphorus-containing compounds etc, such as molybdenum dithiocarbamate (MoDTC) are employed for this purpose. However, it is known that the catalyst used to clean the exhaust gas becomes poisoned by such sulphur-containing compounds or phosphorus-containing compounds, degrading the cleaning performance. Therefore it is desirable to minimise the content of sulphur-containing compounds or phosphorus-containing compounds in engine oil.

Also, in view of recent severe restrictions regarding exhaust gases, in diesel engines, reduction of atmospheric pollutants such as particulate material (PM) or nitrogen oxides (NOx) contained in exhaust gas has become a serious problem. Effective measures in this respect are to employ a diesel particulate filter (DPF) to remove PM from automobile exhaust gas and to employ an exhaust gas cleaning device such as a catalyst to reduce the content of NOx (i.e. an oxidation or reduction catalyst).

When conventional engine oil is employed in an automobile in which a DPF is installed, soot adhering to the DPF can be removed by oxidation and combustion. However, since some of the engine oil is burnt in the combustion chamber of the engine and discharged together with the exhaust gas, metallic components in the engine oil are converted to forms such as metal oxides or sulphides and deposited in the DPF, giving rise to the problem of clogging of the DPF. In order to suppress the degradation of performance caused by such plugging of the DPF, restriction of the amount of metal-containing additives in engine oil that are used has been demanded.

Also, in some cases, a coating is applied to the catalyst in the DPF itself, in order to discharge soot that has been deposited in the DPF from the system, by continuous combustion (this is called continuous regeneration of the DPF). However, it is reported that this function of the catalyst is also poisoned by sulphur or phosphorus present in the exhaust gas, causing performance degradation, so in order to suppress such degradation of catalyst function, lowering of phosphorus and sulphur in engine oil has been demanded. Thus, engine oil of reduced metal content (ash content), phosphorus content and sulphur content i.e. engine oil known as low SAPS oil (SAPS: Sulphated-ash, Phosphorus, Sulphur) has become required for vehicles equipped with modern exhaust gas cleaning devices.

Also, in the bearings of diesel engines, not only higher iron-based materials, but also metallic materials such as aluminium, copper, tin, and, in addition, lead-containing metallic materials are sometimes employed. This is because such lead-containing metallic materials have the excellent advantage of showing little fatigue. However, on the other hand, such lead-containing metallic materials have the drawback of large corrosion friction. Various causes of such corrosion friction have been proposed, but, of these, accumulation of peroxides or organic acids generated by degradation of the lubricating oil is considered to be critical.

Sulphur-containing compounds such as zinc dithiophosphate are effective in regard to prevention of corrosion friction of lead-containing materials, and have shown excellent benefits in terms of preventing lead corrosion friction in conventional engine oil.

However, because of the recently heightened demands for low SAPS oil as mentioned above, due to its content of metal, sulphur, and phosphorus, zinc dithiophosphate, which is one of the additives most commonly employed in engine oil, is becoming the subject of restrictions regarding the amount thereof that can be employed in engine oil; a consequent increase in corrosion of lead-containing materials is therefore feared. Also, when fuels whose chief constituent is renewable material i.e. so-called bio-fuels come into use, based on the concept of carbon neutrality as one link in global warming countermeasures, it is projected that oxidation stability of engine oil will be severely impaired. Specifically, accumulation of peroxides and organic acids will occur faster than if gasoline were employed: it is feared that corrosion of lead-containing materials in the engine will thereby be further increased, and suppression of this is therefore an urgent task.

In order to suppress corrosion friction of lead-containing materials, techniques based on triazole derivatives are available (see JP 2009-120735). However, this type of corrosion-preventing agent or rust inhibitor may cause, as a side-effect, considerable degradation of extreme pressure performance and frictional resistance; no methods at all for coping with this have been described.

Also, methods of suppressing corrosion friction of copper-based metals are known (see JP 2003-238982), but the extent thereof is still insufficient and they do not provide a method of addressing lead-containing materials. In other words, establishment of a method for simultaneously suppressing corrosion friction of both copper-based metals and lead-based metals is being demanded.

Various studies have been conducted as to why corrosion-preventing agents and rust inhibitors should severely degrade extreme pressure performance and friction resistance, which are the basic properties of lubricating oils. According to such studies, whereas, normally, extreme pressure agents and anti-wear agents that are added to the lubricating oil composition penetrate into the metal surface of sliding parts under severe sliding conditions, acting to prevent seizure, friction or galling etc by forming an oily film or reactive coating (called an anti-wear coating) by adsorption at the metal surface, the corrosion-preventing agents and rust inhibitors prevent such action of the extreme pressure agents and anti-wear agents.

In other words, it is reported that, since the rate of absorption of the corrosion-preventing agents or rust inhibitors to the metal surface is high and their affinity for the metal is great, these additives are more strongly adsorbed onto the metal surface of the sliding parts than the extreme pressure agents or anti-wear agents: the extreme pressure agents or anti-wear agents therefore cannot form an anti-wear coating and, as a result, damage or increased friction occurs.

In such circumstances, an object of the present invention is to provide a lubricating oil composition of a type meeting environmental regulations and with improved friction-reducing effect and corrosion-preventing effect, with low ash, low phosphorus and low sulphur, not containing a molybdenum-based friction-reducing agent, that may be used in an internal combustion engine such as a gasoline engine, a diesel engine, or dimethyl ether-fuelled engine or the like, or a gas engine.

SUMMARY OF THE INVENTION

As a result of meticulous studies aimed at achieving the above object, the present inventors discovered that, while maintaining the friction-reducing effect, the problems of lead corrosion and copper corrosion could be solved by conjoint use in the lubricating oil base oil of (a) specified fatty acid glyceride compounds and (b) specified triazole derivatives in a certain ratio, and including (c) specified zinc dialkyl dithiophosphates, each of these being present in small quantities.

The invention provides a lubricating oil composition containing, as constituent (a), 0.5 to 1.5 mass % of a mono or diester of glycerin and a straight-chain or branched fatty acid of carbon number 6 to 20 having a saturated hydrocarbyl group; as constituent (b), 0.1 to 0.5 mass % of a triazole derivative represented by general formula (1):

wherein R₁ is hydrogen or a hydrocarbyl group of carbon number 1 to 3, R₂ and R₃ are respectively independently hydrogen or a hydrocarbyl group of carbon number 1 to 20, which may contain an oxygen atom, sulphur atom or nitrogen atom;
and, as constituent (c), 0.01 to 0.2 mass %, calculated as phosphorus, of a mixture of primary zinc dialkyl dithiophosphate whose alkyl group is a primary hydrocarbyl group (hereinbelow sometimes referred to as primary ZnDTP) and secondary zinc dialkyl dithiophosphate whose alkyl group is a secondary hydrocarbyl group (hereinbelow sometimes referred to as secondary ZnDTP); wherein the ratio of constituent (a)/constituent (b) is 1.5 to 8.

With the present invention, by the use of a mixture containing the aforementioned (a) specified fatty acid glyceride compounds, (b) conjoint use of a specified fraction and specified ratio of a specified triazole derivative and (c) blending primary ZnDTP and secondary ZnDTP in a specified ratio, the problem of corrosion of lead and copper can be simultaneously suppressed, while also achieving lowering of friction due to improved fuel efficiency and the synergistic effect achieved by the combination of the various additives. This lubricating oil composition constitutes a lubricating oil composition for internal combustion engines of a type conforming to environmental regulations, which need not contain a molybdenum-based friction reducing agent, which has low ash, low phosphorus and low sulphur, and improved friction reduction effect, oxidation stability and corrosion-preventing effect; specifically, this lubricating oil composition can be widely employed with internal combustion engines such as gasoline engines, diesel engines, or engines whose fuel is dimethyl ether, or gas engines or the like.

DETAILED DESCRIPTION OF THE INVENTION

For the base oil that is employed in the lubricating oil composition according to the present invention, mineral oils, synthetic oils, or various mixtures of these that are normally employed in lubricating oil may be suitably used: base oils of group 1, group 2, group 3, group 4 and group 5 in the base oil category of the API (American Petroleum Institute) may be employed alone or in the form of mixtures thereof; in particular, base oils of group 2, group 3 and group 4 are preferably employed.

Group 1 base oils comprise for example paraffin-based mineral oils obtained by suitable combination of refining means such as solvent refining, hydrogenation refining and dewaxing, in respect of lubricating oil fractions obtained by reduced-pressure distillation of crude oil. The viscosity index may be 80 to 120, preferably 95 to 110. The dynamic viscosity at 100° C. is preferably 2 to 40 mm²/s, more preferably 3 to 15 mm²/s. The total nitrogen content may be less than 100 ppm, preferably less than 50 ppm. In addition, oil of aniline point 80 to 150° C., preferably 90 to 135° C. may be employed.

Group 2 base oils comprise for example paraffin-based mineral oils obtained by suitable combination of refining means such as hydrogenation refining and dewaxing, in respect of lubricating oil fractions obtained by reduced-pressure distillation of crude oil. Group 2 base oils refined by the hydrogenation refining method of for example the Gulf Company are of total sulphur less than 10 ppm, aromatics less than 5 mass % and can be applied to the present invention. The viscosity of these base oils is not particularly restricted, but the viscosity index may be 80 to 120, preferably 100 to 120. The dynamic viscosity at 100° C. may preferably be 2 to 40 mm²/s, more preferably 3 to 15 mm²/s, and particularly preferably 3.5 to 12 mm²/s. Also, oil of total sulphur less than 300 ppm, preferably less than 100 ppm and even more preferably less than 10 ppm may be employed. The total nitrogen may also be less than 10 ppm, preferably less than 1 ppm. In addition, oil of aniline point 80 to 150° C., preferably 100 to 135° C. may be employed.

Of these group 2 base oils, base oils, called group 2 plus base oils are preferable, whose viscosity coefficient is at least 115.

As group 3 base oils, for example in regard to the lubricating oil fraction obtained by reduced-pressure distillation of crude oil, there are available paraffin-based mineral oils manufactured by high-hydrogenation refining, base oils refined by the ISODEWAX process, in which wax generated by the dewaxing process is converted to isoparaffins and these are dewaxed, or base oils refined using the Mobil WAX isomerisation process: these also may suitably be employed in the present invention.

There is no particular restriction on the viscosity of these base oils, and a viscosity index of 120 to 160, preferably 120 to 150, may be employed. The dynamic viscosity at 100° C. is preferably 2 to 40 mm²/s, more preferably 3 to 15 mm²/s, and particularly preferably 3.5 to 12 mm²/s. Also, the total sulphur may be less than 300 ppm, preferably less than 100 ppm and even more preferably less than 10 ppm. The total nitrogen may also be less than 10 ppm, preferably less than 1 ppm. Furthermore, oil whose aniline point is 80 to 150° C., preferably 110 to 135° C. may be employed. Of these group 3 base oils, preferable base oils, called group 3 plus base oils, may be mentioned, which have a viscosity index of at least 130.

Of group 4 base oils, there are available polyolefin base oils, called poly-α-olefin (PAO) oils. There is no particular restriction concerning the viscosity; the dynamic viscosity at 100° C. is preferably 2 to 40 mm²/s, more preferably 3 to 15 mm²/s, and particularly preferably 3.5 to 12 mm²/s.

As group 5 base oils, there may be mentioned by way of example polyolefins apart from the aforementioned PAO, alkyl benzenes, alkyl naphthalenes, esters, polyoxyalkylene glycols, polyphenyl ethers, dialkyl diphenyl ethers, fluorine-containing compounds (perfluoropolyethers, fluorinated polyolefins etc), and silicones. As polyolefins, polymers of various types of polyolefins or hydrides of these are included. Any desired olefin may be employed: examples include ethylene, propylene, butene, or α-olefins of carbon number 5 or more. Regarding the manufacture of polyolefins, one of the aforementioned olefins may be used alone, or two or more may be used in combination.

The GTL (gas to liquid) base oil that is synthesised by the Fischer-Tropsch method in the technique of converting natural gas to liquid fuel has much lower sulphur and aromatics then mineral oil base oil refined from crude oil and has an extremely high paraffin composition ratio, giving it excellent oxidation stability and extremely small evaporation loss: such base oil can therefore be suitably employed as base oil in the present invention. There are no particular restrictions regarding the viscosity of the GTL base oil but, as a typical example, the viscosity index may be 115 to 180, preferably 125 to 175 or more preferably 130 to 160. Also the dynamic viscosity at 100° C. may be 2 to 12 mm²/s, preferably 2.5 to 8.5 mm²/s. Also, as a typical example, the total sulphur is less than 10 ppm and the total nitrogen is less than 1 ppm. An example of a commercial product of such a GTL base oil is SHELL XHVI (Registered Trademark).

As described above, as the base oil, oil of various types may be employed alone, or may be employed in the form of a suitable mixture: the sulphur of such a base oil may be less than 50 ppm, preferably less than 10 ppm; even more preferably, the degree of freedom in blending design may often be increased by making the sulphur content 0 ppm.

Regarding the viscosity of the aforementioned base oil, as mentioned above, there is no particular restriction; base oil of suitable viscosity may be employed, depending on the application of the lubricating oil composition; usually, the dynamic viscosity at 100° C. is 2 to 40 mm²/s, preferably 3 to 15 mm²/s and particularly preferably 3.5 to 12 mm²/s. If the dynamic viscosity at 100° C. is 2 mm²/s or more, there is little evaporation loss, and if it is less than 40 mm²/s, loss of power due to lowered viscosity is suppressed: a beneficial effect in terms of improved fuel efficiency may therefore be obtained.

The aforementioned (a) according to the present invention are fatty acid glyceride compounds, and are mono or diesters of glycerin and fatty acids of carbon number 6 to 20 having a straight-chain or branched saturated hydrocarbyl group. Of these, there may be mentioned as preferred examples mono or diesters of glycerin and fatty acids of carbon number 6 to 12 having a straight-chain saturated hydrocarbyl group and fatty acids of carbon number 14 to 20 having a branched saturated hydrocarbyl group. As examples of these, there may be mentioned glyceryl mono-isostearate and mixtures of glyceryl mono-octanate and dioctanate. The fatty acid glyceride compounds of (a) may be employed on their own or in the form of a combination of two or more of these. Also, the blending amount thereof is preferably at least 0.5 mass %, more preferably at least 0.7 mass %, from the point of view of the friction reduction effect. Regarding the upper limit of the blending amount, this is less than 1.5 mass %, from the point of view of metal corrosion, oxidative degradation of the lubricating oil and economy.

The triazole-based compounds of (b) according to the present invention are represented by the following general formula (1):

In the above equation (1), R₁ is hydrogen or a hydrocarbyl group of carbon number 1 to 3, preferably hydrogen. R₂ and R₃ are respectively independently hydrogen or hydrocarbyl groups of carbon number 1 to 20, preferably hydrocarbyl groups of carbon number 6 to 12, which may contain an oxygen atom, sulphur atom, or nitrogen atom. Preferably, R₂ and R₃ do not contain an oxygen atom, sulphur atom, or nitrogen atom. R₂ and R₃ may be respectively the same or different. Regarding the above (b) triazole derivative, from the point of view of the beneficial effect thereof, 0.1 to 0.5 mass % may be used. Also, for this triazole derivative, a single type thereof may be employed, or two or more types thereof may be employed in combination. In addition, this may be employed in combination with other metal deactivators.

As constituent (c) of the present invention, zinc dialkyl dithiophosphate (ZnDTP) is employed. This ZnDTP is represented by the following general formula (2):

In the above formula (2), R⁴, R⁵, R⁶ and R⁷ are respectively independently straight-chain or branched saturated hydrocarbyl groups of carbon number 3 to 20. The carbon number of the saturated hydrocarbyl groups is preferably 3 to 12, and more preferably 3 to 8.

The carbon numbers of R⁴ to R⁷ are respectively independent, but their structure is the same. Specifically, in the case where R⁴ is a primary hydrocarbyl group, the remaining R⁵ to R⁷ are also primary hydrocarbyl groups, and, in the case where R⁴ is a secondary hydrocarbyl group, the remaining R⁵ to R⁷ are also secondary hydrocarbyl groups. Also, primary zinc dialkyl dithiophosphates (primary ZnDTP) where the R⁴ to R⁷ are primary hydrocarbyl groups and secondary zinc dialkyl dithiophosphates (secondary ZnDTP) where the R⁴ to R⁷ are secondary hydrocarbyl groups may be mixed. R⁴ to R⁷ may be respectively the same or different.

The contents of the mixture of primary ZnDTP and secondary ZnDTP may be 0.01 to 0.2 mass %, referred to (calculated as) the amount of phosphorus, preferably 0.05 to 0.15 mass %, more preferably 0.05 to 0.12 mass %. If the content of primary and secondary ZnDTP is too small, sufficient friction preventing performance is not obtained; if it is too large, not only is the additive effect saturated and so uneconomic, but also there is a considerable effect of the phosphorus component on exhaust gas catalytic activity, giving rise to a risk of problems regarding catalyst poisoning.

Also, in the mixture of the above primary ZnDTP and secondary ZnDTP, the ratio of primary ZnDTP may be 10 to 60 mass % of the total ZnDTP referred to (calculated as) the amount of phosphorus, preferably 30 to 55 mass %, and more preferably 33 to 50 mass %, while the ratio of secondary ZnDTP may be 40 to 90 mass %, preferably 45 to 70 mass % and more preferably 50 to 67 mass %.

In a lubricating oil composition containing the aforementioned (a), (b) and (c) constituents, the ratio (a/b) of the aforementioned constituent (a) and constituent (b) may be made about 1.5 to 8: a synergistic effect is thereby achieved, and an excellent friction reduction effect and corrosion preventing effect, which cannot be achieved by these on their own are simultaneously obtained.

In the lubricating oil composition according to the present invention, in a range such as not to impair the object of the present invention, if necessary, other additives apart from the constituents (a), (b), (c) may be suitably blended, such as, for example, viscosity index improvers, pour point depressants, metal cleaning agents, ashless dispersants, antioxidants, friction modifiers, metal deactivators, anti-wear agents or extreme pressure agents, rust inhibitors, surfactants or anti-emulsifiers or defoamers.

As viscosity index improvers, there may be mentioned by way of example non-dispersion type polymethacrylate, dispersion type polymethacrylate, non-dispersion type olefin-based copolymers (such as for example ethylene-propylene copolymer), or dispersion-type olefin-based copolymers, styrene-based copolymers (such as for example styrene-diene copolymers, or styrene-isoprene copolymers). From the point of view of the beneficial effect of such blending, the blending amount of these viscosity index improvers will usually be about 0.1 to 15 mass %, referred to the total amount of the lubricating oil composition. Also, as pour point depressants, there may be mentioned by way of example polymethacrylates of weight average molecular weight about 5000 to 50,000.

As metal cleaning agents, any of the alkaline earth metal cleaning agents that are employed in lubricating oils may be used, such as for example alkaline earth metal sulphonates, alkaline earth metal phenates, alkaline earth metal salicylates and mixtures of two or more of these. As the alkaline earth metals of the aforementioned alkaline earth metal sulphonates, alkaline earth metal phenates, or alkaline earth metal salicylates, magnesium or calcium, preferably calcium, may be employed. As these metal cleaning agents, apart from neutral salts as mentioned above, for example basic salts, over-based salts and mixtures of these may be employed: in particular, calcium salicylate is preferable on account of its cleaning performance and anti-wear properties.

The content of the aforementioned metal cleaning agents is usually less than 1 mass %, calculated in terms of the metallic element, and preferably less than 0.5 mass %. Preferably the content thereof is less than 0.3 mass %, in order to keep the sulphated ash in the lubricating oil composition below 1 mass %. Also, in order to obtain oxidation stability, and maintain the total base number and high-temperature cleaning performance, the content should be at least 0.05 mass %, preferably at least 0.1 mass %. The aforementioned sulphated ash is a value measured by “5. Method of testing sulphated ash” of JIS K 2272 and is chiefly due to additives containing metals: based on this, it is possible to learn the amount of metal additives in the composition.

As regards the ashless dispersants, there is no particular restriction as to their type, and any conventionally typically employed ashless dispersant may be used: examples include succinimide-based compounds of the mono-imide type or bis-imide type, benzylamine-type compounds, or alkenamine-type compounds. Preferably succinimide-type compounds and particularly preferably alkenyl succinimides are employed. The aforementioned ashless dispersants are present in the content of 0.1 to 15 mass %, preferably 0.2 to 10 mass % in the composition. If the aforementioned content is less than 0.1 mass %, a sufficient beneficial effect is not found; if the content exceeds 15 mass %, the beneficial effect is saturated and further addition is economically disadvantageous. A single type of the aforementioned ashless dispersants may be employed, but it is also possible to employ a mixture of two or more types thereof in a suitable ratio.

As the aforementioned antioxidants, there may be employed for example phenolic antioxidants, amine-based antioxidants, molybdenum amino complex-based antioxidants, or sulphur-based antioxidants.

As phenolic antioxidants, there may be mentioned for example 4,4′-methylenebis (2,6-di-t-butylphenol), 2,2′-methylenebis (4-methyl-6-t-butylphenol), 4,4′-bis(2,6-di-t-butylphenol), 4,4′-bis(2-methyl-6-t-butylphenol), 2,2′-methylenebis (4-ethyl-6-t-butylphenol), 4,4′-isopropylidene-bis(2,6-di-t-butylphenol), 4,4′-butylidenebis (3-methyl-6-t-butylphenol), 2,2′-methylenebis (4-methyl-6-nonylphenol), 2,2′-isobutylidenebis (4,6-dimethyl phenol), 2,2′-methylenebis (4-methyl-6-cyclohexylphenol), 2,6-di-t-butyl-4-methyl phenol, 2,6-di-t-butyl 4-ethyl phenol, 2,4-dimethyl-6-t-butylphenol, 2,6-di-t-amyl-p-cresol, 2,6-di-t-butyl-α-dimethyl-amino-p-cresol, 2,6-di-t-butyl-4-(N,N′-dimethyl amino methyl phenol), 4,4′-thiobis (2-methyl-6-t-butylphenol), 4,4′-thiobis (3-methyl-6-t-butylphenol), 2,2′-thiobis (4-methyl-6-t-butylphenol), bis(3-methyl-4-hydroxy-5-t-butyl benzyl) sulphide, bis (3,5-di-t-butyl 4-hydroxybenzyl) sulphide, n-octyl-3-(4-hydroxy-3,5-di-t-butyl phenyl) propionate, n-dodecyl 3-(4-hydroxy-3,5-di-t-butyl phenyl) propionate, n-octadecyl 3-(4-hydroxy-3,5-di-t-butyl-phenyl) propionate, 2,2′-thio[diethyl-bis-3-(3,5-di-t-butyl-4-hydroxyphenyl) propionate], and hexamethylene glycol bis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]. Of these, in particular phenolic antioxidants are suitable which are of the bisphenolic type or ester-group-containing phenolic type; also, a mixture of two or more of these may be employed.

In addition, as amine-based antioxidants, there may be mentioned by way of example: alkyl-substituted phenylaniline-based antioxidants such as hexyl phenylaniline or octyl phenylaniline; bis(alkyl-substituted phenyl) amines such as bis(butylphenyl) amine, bis(neopentylphenyl) amine, bis(hexylphenyl) amine, bis(heptylphenyl) amine, bis(octylphenyl) amine, or bis(nonylphenyl) amine; bis(dialkyl-substituted phenyl) amines such as bis(dibutylphenyl) amine, bis (di-hexylphenyl) amine, bis(di-octylphenyl) amine, or bis(dinonylphenyl) amine; and naphthylamine-based antioxidants, specifically, 2-naphthylamine, N-2-naphthylamine, or N-alkyl-substituted phenyl-2-naphthylamines such as N-butylphenyl-2-naphthylamine, N-pentylphenyl-2-naphthylamine, N-hexylphenyl-2-naphthylamine, N-octylphenyl-2-naphthylamine, or N-nonylphenyl-2-naphthylamine. Of these, bis(alkylphenyl) amines and naphthylamines are ideal.

As molybdenum amino complex-based antioxidants, there may be mentioned hexavalent molybdenum compounds such as for example compounds obtained by reaction of molybdenum trioxide and/or molybdic acid with an amine compound. There is no particular restriction regarding the amine compounds that may be reacted with the hexavalent molybdenum compound: examples that may be mentioned include monoamines, diamines, polyamines, alkanolamines, or heterocyclic compounds such as imidazoline, the alkylene oxide adducts of these compounds, and mixtures of these. There may also be mentioned by way of example sulphur-containing molybdenum complexes of succinimide.

As the aforementioned sulphur-based antioxidants, there may be mentioned by way of example: dialkyl sulphides such as didodecyl sulphide, or dioctadecyl sulphide; thiodipropionic acid esters such as didodecyl thiodipropionate, or dioctadecyl thiodipropionate, dimyristyl thiodipropionate, or dodecyl octadecyl thiodipropionate, 2-mercaptobenzo imidazole, phenothiazine, pentaerythritol-tetrakis-(3-lauryl thiopropionate), or methylenebis (dibutyl dithiocarbamate).

Apart from the zinc dialkyl dithiophosphates of the aforementioned constituent (c), any compound that is ordinarily employed as an anti-wear agent or extreme pressure agent in lubricating oil may be employed as an anti-wear agent or extreme pressure agent: examples include zinc phosphate, zinc dialkyl phosphate, zinc dialkyl monothiophosphate, zinc dithiocarbamine, disulphides, vulcanised olefins, vulcanised fats and oils, vulcanised esters, thiocarbonates, thiocarbamates or the like sulphur-containing compounds, phosphorus-containing compounds such as phosphorous acid esters, phosphoric acid esters, phosphonic acid esters and the amine salts or metal salts or the like thereof, or sulphur and phosphorus-containing anti-wear agents such as thiophosphorous acid esters, thiophosphoric acid esters, thiophosphonic acid esters, and the amine salts or metal salts or the like thereof, alkali metal borates and their hydrates.

Apart from the aforementioned constituent (a), any compound that is ordinarily employed as a friction-reducing agent in lubricating oil may be employed: examples include ashless friction-reducing agents such as fatty acid esters, aliphatic amines, acid amides, fatty acids, aliphatic alcohols, or aliphatic ethers having at least one alkyl group or alkenyl group in the molecule, of carbon number 6 to 30. Metal-containing friction-reducing agents such as molybdenum complexes having an organic ligand may also be mentioned.

Apart from the aforementioned constituent (b), any compound that is ordinarily employed as a metal deactivator in lubricating oil may be employed: examples include oxazole-based compounds, thiazole-based compounds, benzotriazole-based compounds, tolyl triazole-based compounds, thiadiazole-based compounds, indazole-based compounds, imidazole-based compounds and pyrimidine-based compounds.

As rust inhibitors, petroleum sulphonates, alkyl benzene sulphonate, dinonyl naphthalene sulphonate, alkenyl succinic acid esters, or polyhydric alcohol esters and the like may be mentioned by way of example.

Also, as surfactants or anti-emulsifiers, there may be mentioned by way of example polyalkylene glycol-based non-ionic surfactants, such as polyoxyethylene alkyl ether, polyoxyethylene alkylphenyl ether, or polyoxyethylene alkylnaphthyl ether. As defoaming agents, there may be mentioned by way of example silicone oil, fluorosilicone oil and fluoroalkyl ethers.

While various types of additives may be employed in the lubricating oil composition according to the present invention, the sulphur content in the lubricating oil composition should be kept below 0.5 mass %, preferably below 0.4 mass %. If the sulphur content is less than 0.5 mass %, deterioration of performance of the exhaust gas cleaning catalyst can be suppressed. Also, the phosphorous content should be kept to 0.01 to 0.2 mass %, preferably 0.05 to 0.15 mass % and more preferably 0.05 to 0.12 mass %. If the phosphorus content is less than 0.2 mass %, as mentioned above, deterioration of performance of the exhaust gas cleaning catalyst can be suppressed. Also, the sulphated ash should be kept below 1.1 mass %, preferably below 1.0 mass %. If the sulphated ash is less than 1.1 mass %, the drop in performance of the DPF can be suppressed. Specifically, the amount of ash deposited in the DPF is small, making it possible to suppress clogging of this filter by the ash, and so making it possible to prolong the useful life of the DPF.

EXAMPLES

The invention is described in more detail with reference to practical examples, but the invention is not restricted to these examples in any way.

Lubricating oil compositions according to practical examples and comparative examples were prepared having the compositions shown in Table 1 to Table 3. The constituents used in preparation of the lubricating oil compositions were as follows.

(1) Base oil 1: group 3 base oil of Fischer-Tropsch origin (characteristics: 100° C. dynamic viscosity 3.979 mm²/s, viscosity index 131, % CA no more than 1, sulphur content less than 10 ppm)

(2) Base oil 2: group 3 base oil of Fischer-Tropsch origin (characteristics: 100° C. dynamic viscosity 7.565 mm²/s, viscosity index 145, % CA no more than 1, sulphur content less than 10 ppm)

(3) Base oil 3: group 3 base oil (characteristics: 100° C. dynamic viscosity 4.250 mm²/s, viscosity index 125, % CA no more than 1, sulphur content 40 ppm)

(4) Base oil 4: group 3 base oil (characteristics: 100° C. dynamic viscosity 7.600 mm²/s, viscosity index 133, % CA no more than 1, sulphur content 10 ppm)

(5) Base oil 5: group 2 base oil (characteristics: 100° C. dynamic viscosity 5.357 mm²/s, viscosity index 109, % CA no more than 1, sulphur content less than 100 ppm)

(6) Base oil 6: group 2 base oil (characteristics: 100° C. dynamic viscosity 12.22 mm²/s, viscosity index 113, % CA no more than 1, sulphur content less than 100 ppm)

(7) Secondary ZnDTP: mixture of ZnDTP having secondary hydrocarbyl groups of carbon number 3 and ZnDTP having secondary hydrocarbyl groups of carbon number 6. P content 10.0%

(8) Primary ZnDTP: ZnDTP having primary hydrocarbyl group of carbon number 5. P content 9.5%

(9) Glyceride 1: glyceryl mono-isostearate (GM I)

(10) Glyceride 2: mixture of glyceryl mono-octanate and dioctanate, mono-units: di-units 4:6 to 6:4

(11) Glyceride 3: glyceryl mono-oleate (GMO)

(12) Triazole compound: 1-(di-(2-ethyl hexyl) aminoethyl) 1,2,4-triazole (Irgamet 30 manufactured by BASF)

(13) Benzotriazole compound: 1-(di-(2-ethylhexyl)aminoethyl)-4-methylbenzotriazole (Irgamet 39 manufactured by BASF)

(14) Ca salicylate: Ca content 8% by mass, total base number 230 mgKOH/g

(15) Ca sulphonate: Ca content 12.5 mass %, total base number 320 mgKOH/g

(16) Other additives: contains succinimide dispersant, phenolic antioxidant, amine-based antioxidant and viscosity index improver.

In order to investigate the performance of the practical examples and comparative examples described above, a reciprocatory movement friction test as described below, a copper and lead corrosion test, a friction characteristic test based on a traction test, an oxidation stability test, an anti-wear test and a hot tube test, indicating the engine cleaning performance, were conducted. The results of the tests that were carried out are shown in Table 1 to Table 3.

Reciprocatory Movement Friction Test

In order to ascertain the frictional performance, an evaluation was conducted using a PLINT testing machine (PLINT.TE77 testing machine). For the upper test piece, a cylindrical test piece manufactured in accordance with SK-3, of diameter 6 mm, length 16 mm was employed; for the lower test piece, a test plate manufactured in accordance with SK-3 was employed, with a test temperature of 100° C., load 300N, vibration amplitude 15 mm, reciprocatory frequency 10 Hz, duration of test 10 min: the coefficient of friction obtained was used as an index of fuel efficiency.

As the pass value in this test, a coefficient of friction of 0.115 or less was specified.

Copper and Lead Corrosion Test

This was based on the lubricating oil oxidation stability test for internal combustion engines (ISOT) of JIS K2514: a 250 ml sample of the lubricating oil composition was placed in a glass beaker and a steel plate, copper plate and lead plate were immersed in this test oil, and an oxidation stability test was conducted for 168 hours at 150° C.: the amounts (ppm) of copper and lead leached into the degraded test oil after the test were measured. The copper and lead contents in the oxidation-degraded oil were measured in accordance with Japanese Petroleum Association Standard JPI-5S-38-92.

Lower leached contents of copper and lead indicate a smaller corrosion effect in respect of copper and lead. Pass values in respect of this test are as follows.

Copper content: 50 ppm or less.

Lead content: 30 ppm or less.

Frictional Performance Test

In order to evaluate the frictional performance of the various test oils, the traction of the test oils was measured with a combination of a ½ inch steel ball and traction measurement steel disc provided by PCS Instruments, using an EHL thin-film thickness measurement device manufactured by PCS Instruments. The test conditions were set as: sliding/rolling ratio 20%, load 20N (0.82 GPa), oil temperature 120° C.; a traction coefficient of 0.06 or less at a sliding speed of 0.01 m/s was regarded as a pass. If the traction coefficient exceeds 0.06, friction becomes large and fuel efficiency is adversely affected.

Oxidation Stability Test

In order to evaluate the oxidation stability of the various test oils, the test was conducted using test equipment based on “Piston under-crown cumulative test device for lubricating oil” as set out in JP 2004-092601.

The test conditions were set as: piston top and temperature 275° C., oil temperature 100° C., oil spray rate 90 ml/minute, and test time 48 hours; the percentage increase of the 40° C. dynamic viscosity after the test was measured: values below 5% were regarded as pass values.

Anti-Wear Test

As the test for evaluating anti-wear properties of the various sample oils, in accordance with ASTM D 4172-94 “Standard Test Method for Wear Preventive Characteristics of Lubricating Fluid (Four-Ball Method)”, a test was conducted under the conditions: rotational speed 1200 rpm, load 40 kgf, oil temperature 75° C., test time 1 hour; a pass was specified as being that the average diameter of three wear marks should be less than 0.50 mm.

Hot Tube Test

In order to evaluate the high-temperature cleaning performance, which constitutes an index for the measurement of piston cleaning performance, of each of the sample oils, a hot tube test was conducted, based on the “engine oil-hot tube test method” of Japanese Petroleum Association Standard JPI-5S-55-99.

The test conditions were set as: test temperature 208° C., test time 16 hours, sample oil feed rate 0.3 ml/hour, air flow rate 10 ml/hour; a colour phase evaluation (merit points) of at least 7.0 points in respect of the discoloured section of the glass tube after completion of the test was regarded as a pass.

The practical examples 1 to 4 and comparative examples 1 to 4 shown in Table 1 show the results of measurement of the coefficients of friction in a reciprocatory friction test and the copper concentration (leached amount) in the oil and lead concentration in the oil in the copper and lead corrosion test (ISOT), by varying the added amounts of glyceride 1 (glyceride mono-isostearate) and glyceride 2 (C8 mono-diglyceride) and the added amount of triazole compound keeping the amounts of secondary and primary ZnDTP, Ca salicylate and other additives (including succinimide dispersant, phenolic and amino antioxidant and viscosity index improver) fixed at the same amounts. The primary and secondary ZnDTP were employed mixed in a ratio of 1:2, referred to the amount of phosphorus. The ratio: glycerides 1,2/triazole compound was 2.5 to 5.

As shown in Table 1, in the case of practical examples 1 to 4, the frictional coefficients in the reciprocatory frictional test were 0.106 to 0.114, satisfying the pass criterion (0.115 or less). Also, in the copper and lead corrosion test, the copper concentration was 6 to 14 ppm and the lead concentration was 3 to 17 ppm: in both cases, the pass criteria for copper corrosion (no more than 50 ppm) and lead corrosion (no more than 30 ppm) were satisfied. In contrast, comparative example 1 contained a triazole compound: although in the reciprocatory frictional test the frictional coefficient satisfied the pass criterion, the copper corrosion and lead corrosion in the copper and lead corrosion tests were severe, so the pass criteria were not satisfied. Comparative example 2 is a prescription in which the ratio of glyceride and triazole compound was more than 8: the frictional coefficient in the reciprocatory frictional test satisfied the pass criterion, but the amount of leached copper and the amount of leached lead in the copper and lead corrosion test did not satisfy the pass criteria. Comparative example 3 is a prescription in which the ratio of glyceride and triazole compound was less than 1.5: the amount of leached copper and the amount of leached lead in the copper and lead corrosion tests satisfied the pass criteria, but the frictional coefficient in the reciprocatory frictional test did not satisfy the pass criterion. Also, in comparative example 4, no glyceride was added: the amount of leached copper and the amount of leached lead in the copper and lead corrosion tests satisfied the pass criteria, but the frictional coefficient in the reciprocatory frictional test did not satisfy the pass criterion. It can thus be seen that none of comparative examples 1 to 4 satisfied the pass criteria.

It can thus be seen that the difference between practical examples 1 to 4 and comparative examples 1 to 4 lies in that, if glyceride 1 (GMI) is employed without adding triazole compound, as in comparative example 1, the leaching of copper and lead into the oil in the copper and lead corrosion test overshoots the pass criteria i.e. there is severe metal corrosion. In the case of comparative example 2, by addition of 0.1 mass % of triazole compound, leaching of copper and lead is suppressed compared with comparative example 1, but the corrosion criteria are still not satisfied. In comparative example 3, by addition of 0.5 mass % of GMI and 0.5 mass % of triazole compound, the leached amounts of copper and lead are reduced to a level satisfying the pass criteria, but the frictional coefficient does not satisfy the pass criterion. Also, even if triazole compound is used, as in comparative example 4, if GMI is not added, the frictional coefficient is high, so that the pass criterion is not satisfied. Thus, by studying the various addition ratios of glyceride 1 (GMI) and triazole compound, it can be seen that, as shown by the results of practical examples 1 to 4 and comparative examples 1 to 4, frictional performance and leaching of copper and lead can be effectively suppressed if the ratio of glycerides 1, 2 and triazole compound are in a suitable range (2.5 to 5 in the practical examples).

As shown in Table 2 and Table 3, in practical examples 5 to 9, just as in the case of practical example 1, the ratio of glycerides 1, 2 and the triazole compound is fixed at 5; in practical example 10, this ratio is 6: in both cases, the pass criterion is satisfied in each of the tests. As shown in practical example 7 and practical example 8, it can be seen that, if the conditions of the present invention are satisfied, the pass criteria of each of the items are satisfied, irrespective of the type of base oil. Practical example 9 shows a case where primary ZnDTP and secondary ZnDTP are blended in a ratio of 1:1 referred to the phosphorus content: just as in the cases where the blending ratio is 2:1, in the other practical examples, each of the criteria are satisfied, and there is no effect for example on wear performance.

Comparative example 5 and comparative example 8 show cases in which the ratio of glycerides 1, 2 and triazole compound is 5: however, in a prescription in which only primary ZnDTP is employed as the ZnDTP, the pass criterion is not met in the anti-wear test, while, in a prescription in which only secondary ZnDTP is employed as the ZnDTP, the pass criterion is not met in the frictional performance test (traction coefficient); from this it can be seen that a combination of primary ZnDTP and secondary ZnDTP is important in satisfying the pass criteria of both the anti-wear test and the traction coefficient. It can also be seen that the glyceride 2 shown in practical example 5 satisfies the pass criterion in respect of each of the test items, in the same way as glyceride 1. In comparative example 6, glyceride 3 (GMO having an unsaturated hydrocarbyl group) is employed instead of glycerides 1,2: none of the pass criteria of the copper corrosion test, oxidation stability test, or hot tube test are satisfied; thus high-temperature cleaning properties and metal corrosion suppression capability, which are fundamental characteristics of engine oil, are greatly inferior. In comparative example 7, a benzotriazole compound, which is widely employed as a copper deactivator, is employed instead of the triazole compound: it can be seen that the copper and lead corrosion test criteria are not met and there is no beneficial effect in terms of corrosion suppression. In comparative example 9, secondary ZnDTP and glyceride 3 (GMO) were employed: while the pass criterion is satisfied in the traction test, the high-temperature cleaning performance in the hot tube test does not satisfy the pass criterion: thus it was found that cleaning performance, which is one of the vital properties for engine oil, is adversely affected in the case of GMO. In comparative example 10, glyceride 3 (GMO) was excluded from the prescription of comparative example 9 and in fact no glyceride is present: while the high-temperature cleaning performance in the hot tube test and the copper and zinc corrosion test satisfy the test criteria, the traction coefficient in the wear performance test is large, so that the pass criterion is not satisfied: it can thus be seen that fuel efficiency is degraded. Also, in practical example 6, some of the Ca salicylate of practical example 5 is substituted by Ca sulphonate: nevertheless, the pass criterion of each item is satisfied, showing that Ca sulphonate can be employed as a metal cleaning agent.

It should be noted that the entries “not done” in Table 3 indicate that the test in question was not in fact carried out, since it was known that the pass criteria in the tests that had already been implemented were not satisfied.

	TABLE 1
	Practical	Practical	Practical	Practical	Comparative	Comparative	Comparative	Comparative
	example 1	example 2	example 3	example 4	example 1	example 2	example 3	example 4
Base oil 1	60	60	60	60	60	60	60	60
Base oil 2	Balance	Balance	Balance	Balance	Balance	Balance	Balance	Balance
Secondary	0.8	0.8	0.8	0.8	0.8	0.8	0.8	0.8
ZnDTP
Primary ZnDTP	0.4	0.4	0.4	0.4	0.4	0.4	0.4	0.4
Glyceride 1	1	1.25	0.75		1	1	0.5	0
Glyceride 2				1
Triazole	0.2	0.3	0.25	0.4	0	0.1	0.5	0.2
compound
Ca salicylate	2.7	2.7	2.7	2.7	2.7	2.7	2.7	2.7
Other	17	17	17	17	17	17	17	17
additives
Total	100	100	100	100	100	100	100	100
Ratio of	5	4.17	3	2.5	∞	10	1	0
glyceride 1
or 2/triazole
compound
Coefficient	0.111	0.106	0.114	0.110	0.111	0.109	0.121	0.123
of friction
in
reciprocatory
dynamic
friction test
Copper and	9	6	14	11	680	126	7	12
lead
corrosion
test: copper
concentration
in oil [ppm]
Lead	3	4	7	17	110	84	11	9
concentration
in oil [ppm]

	TABLE 2
	Practical	Practical	Practical	Practical	Practical	Practical	Practical
	example 1	example 5	example 6	example 7	example 8	example 9	example 10
Base oil 1	60	60	60			60	60
Base oil 2	Balance	Balance	Balance			Balance	Balance
Base oil 3				60
Base oil 4				Balance
Base oil 5					70
Base oil 6					Balance
Secondary ZnDTP	0.8	0.8	0.8	0.8	0.8	0.6	0.8
Primary ZnDTP	0.4	0.4	0.4	0.4	0.4	0.4	0.4
Glyceride 1	1		1	1	1	1	1.2
Glyceride 2		1
Glyceride 3
Triazole compound	0.2	0.2	0.2	0.2	0.2	0.2	0.2
Benzo-triazole compound
Ca salicylate	2.7	2.7	1.2	2.7	2.7	2.7	2.7
			1
Other additives	17	17	17	17	17	17	17
Ratio of glyceride 1 or	5	5	5	5	5	5	5
2/triazole compound
Frictional characteristics	0.043	0.054	0.053	0.043	0.050	0.045	0.041
test: traction coefficient
Copper and lead corrosion	9	8	49	40	48	42	15
test: copper concentration
in oil [ppm]
Lead concentration in oil	3	12	4	10	10	7	7
[ppm]
Oxidation stability test:	2.9	1.4	4.8	3.0	3.8	2.9	2.9
percentage change of 40° C.
dynamic viscosity [%]
Anti-wear test: wear mark	0.45	0.46	0.45	0.46	0.47	0.47	0.46
diameter [mm]
Hot tube test: merit points	7.5	7.0	7.5	7.0	7.0	7.0	7.5

	TABLE 3
	Practical	Practical	Practical	Practical	Practical	Practical
	example 5	example 6	example 7	example 8	example 9	example 10
Base oil 1	60	60	60	60	60	60
Base oil 2	Balance	Balance	Balance	Balance	Balance	Balance
Base oil 3
Base oil 4
Base oil 5
Base oil 6
Secondary ZnDTP		0.8	0.8	1.2	1.2	1.2
Primary ZnDTP	1.2	0.4	0.4
Glyceride 1	1		1	1
Glyceride 2
Glyceride 3		1			1
Triazole compound	0.2	0.2		0.2	0.2	0.2
Benzo-triazole compound			0.2
Ca salicylate	2.7	2.7	1.2	2.7	2.7	2.7
Ca sulphonate
Other additives	17	17	17	17	17	17
Ratio of glyceride 1 or 2/triazole	5	0	—	5	0	0
compound
Frictional characteristics test:	0.042	0.050	0.045	0.067	0.042	0.089
traction coefficient
Copper and lead corrosion test:	Not done	73	310	5	Not done	4
copper concentration in oil [ppm]
Lead concentration in oil [ppm]	Not done	9	30	9	Not done	16
Oxidation stability test:	2.8	13	3.1	0	Not done	Not done
percentage change of 40° C. dynamic
viscosity [%]
Anti-wear test: wear mark diameter	0.52	Not done	Not done	Not done	Not done	Not done
[mm]
Hot tube test: merit points	7.0	5.5	7.5	7.5	6.0	7.5

Claims

1. A lubricating oil composition comprising: wherein R1 is hydrogen or a hydrocarbyl group of carbon number 1 to 3, R2 and R3 are respectively independently hydrogen or a hydrocarbyl group of carbon number 1 to 20, which may contain an oxygen atom, sulphur atom or nitrogen atom; and, wherein the ratio of constituent (a)/constituent (b) is 1.5 to 8.

as constituent (a), 0.5 to 1.5 mass % of a mono or diester of glycerin and a straight-chain or branched fatty acid of carbon number 6 to 20 having a saturated hydrocarbyl group;

as constituent (b), 0.1 to 0.5 mass % of a triazole derivative represented by general formula (1):

as constituent (c), 0.01 to 0.2 mass %, calculated as phosphorus, of a mixture of primary zinc dialkyl dithiophosphate whose alkyl group is a primary hydrocarbyl group and a secondary zinc dialkyl dithiophosphate whose alkyl group is a secondary hydrocarbyl group;

2. A lubricating oil composition according to claim 1, wherein said constituent (a) is a mono or diester of glycerin and a fatty acid of straight-chain of carbon number 6 to 12 or branched saturated hydrocarbyl group of carbon number 14 to 20.

3. A lubricating oil composition according to claim 2, wherein said constituent (a) is a mixture of glyceryl mono-isostearate or glyceryl mono-octanate and dioctanate.

4. A lubricating oil composition according to claim 1, wherein the alkyl group of the primary zinc dialkyl dithiophosphate and of the secondary zinc dialkyl dithiophosphate of said constituent (c) is a straight-chain or branched saturated hydrocarbyl group of carbon number 3 to 20.

5. A lubricating oil composition according to claim 1, wherein the mixing ratio of the mixture of the primary zinc dialkyl dithiophosphate and the secondary zinc dialkyl dithiophosphate of said constituent (c) is 10 to 60 mass % of the primary and 40 to 90 mass % of the secondary, referred to the phosphorus content.

6. A lubricating oil composition according to claim 1, wherein said lubricating oil base oil contains at least 50 mass %, referred to the total amount of the composition, of a base oil belonging to group 2, group 3 or group 4 in the base oil category established by the American petroleum Institute (API), or a mixture of these.

7. A lubricating oil composition according to claim 6, wherein said lubricating oil base oil is of Fischer-Tropsch synthetic origin, its dynamic viscosity at 100° C. being 2.5 to 8.5 mm2/s.

8. A lubricating oil composition according to claim 1 wherein said lubricating oil composition is employed in a lubricated mechanism wherein the lubricating oil is in contact with copper and/or lead-containing metallic material in an internal combustion engine.