JP2901696B2 - Lubricating oil composition for diesel engines - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a long-life lubricating oil composition, and more specifically, it is possible to effectively remove combustion residues such as soot mixed in oil. The invention relates to a lubricating oil composition for a diesel engine having a long life.

[Description of the Related Art] A diesel engine has a different combustion process from a gasoline engine, and thus is likely to be incompletely burned and to easily generate soot and unburned matter. Most of the generated soot is discharged into the atmosphere as a main component of particulates in exhaust gas.
Soot and unburned materials are mixed as insoluble solids in the lubricating oil together with degraded lubricating oil, and accumulate around the piston and high temperature sliding parts, increase the viscosity of the lubricating oil, and reduce wear and power. This causes problems such as increased losses. How to suppress the above-mentioned problems caused by insoluble solids (hereinafter referred to as combustion residues) mixed in the lubricating oil is one of the major issues in extending the oil exchange period and oil exchange distance. Has become.

As a countermeasure against combustion residues in lubricating oil for diesel engines, a method has heretofore been used to exclusively disperse the combustion residue mixed in the lubricating oil into the lubricating oil finely and uniformly using a detergent and dispersant. Conversely, a method has been proposed in which the dispersibility is moderately suppressed and solid impurities such as combustion residues are captured and removed by a filter (for example, JP-A-60-6790 and JP-A-63-15895). ).

[Problems to be Solved by the Invention] However, in any of these conventional methods, imide-based or amine-based additives such as alkenylsuccinimide and benzylamine are used as ashless dispersants. When trying to capture and remove solid impurities such as combustion residues in a lubricating oil with a filter, such imide-based and amine-based dispersants have high dispersing performance, and the combustion residues are dispersed in extremely fine lumps. Therefore, it becomes easier to pass through the filter. For this reason, even if the addition amount is adjusted by using the dispersant, an appropriate dispersion state cannot be obtained, and it is difficult to efficiently remove the mixed combustion residue with a filter. In addition, since the dispersant is generally used together with a detergent such as a metal sulfonate or a phenate, and has a synergistic action to promote a cleaning action for removing dirt around the piston, the dispersant is dispersed depending on the amount of the dispersant used. Even if an attempt is made to adjust the water solubility, if the amount of the dispersant added is extremely reduced, adverse effects such as a decrease in cleanliness around the piston and a decrease in the total remaining base number will occur.

Therefore, an object of the present invention is to remove the disadvantages of the conventional method, to have a cleaning effect of cleaning dirt around the piston equal to or higher than that of the conventional oil, and to moderately suppress the dispersion performance, and to reduce the combustion residue in the filter. An object of the present invention is to provide a lubricating oil that exhibits excellent performance in capturing oil and has a long oil change period and a long oil change distance.

[Means for Solving the Problems] Among the cleaning dispersants, there are those having an excellent dispersing function, those having an excellent cleaning function, and the like. The characteristics vary depending on the individual dispersing agent. Et al., While maintaining a high cleaning function, moderately suppressed the dispersibility, and searched for a cleaning dispersant having an excellent efficiency of capturing combustion residues in a filter.As a result, hydroxyethyl thiophosphonic acid ester and polyalkenyl succinic acid ester showed the above-mentioned properties. The present invention has been found to exhibit excellent cleaning and dispersing effects when used alone or in combination, thereby completing the present invention.

That is, the present invention relates to a hydroxyethyl thiophosphonic acid ester represented by the general formula (I), wherein a base oil comprising a mineral oil, a synthetic oil or a mixed oil thereof is used. (Where R represents a hydrocarbon group having 6 to 30 carbon atoms) in an amount of 0.5 to 5.0% by weight.

In the present invention, mineral oil and synthetic oil serving as base oils can be used without any particular problem as long as they are usually used as base oils for lubricating oils.
Those having 300 cSt and a viscosity index of 90 or more can be suitably used. Such base oils include mineral oils obtained by a method commonly used in lubricating oil production processes in the petroleum refining industry.
So-called 150-neutral oil, 500-neutral oil, lubricating oil bases such as bright stock, and the like, and as synthetic oils, general poly-α-olefins, ester oils, polyalkylene glycols and the like as lubricating oil bases. No. These substrates can be used alone or in a mixture at an appropriate ratio.

In the present invention, the thiophosphonic acid hydroxyester used as a dispersant is represented by the following general formula (I).

R is a hydrocarbon group having 6 to 30 carbon atoms, preferably 15 to 25 carbon atoms, such as an alkyl group and an allyl group. 5 carbon atoms
Below, when the solubility is too low and the number of carbons exceeds 30, the viscosity becomes too high, and both are not preferred. Particularly, a polybutenyl group obtained by polymerizing butene is preferable.

In the composition of the present invention, the thiophosphonic acid hydroxyester is added in an amount of 0.5 to 5.0% by weight based on a base oil composed of a mineral oil, a synthetic oil or a mixed oil thereof. If the addition amount is less than 0.5% by weight, a sufficient cleaning effect cannot be obtained, so that it is not preferable. If the addition amount exceeds 5.0% by weight, a highly dispersing agent such as alkenyl succinimide or benzylamine is used. On the other hand, the problem that the dispersibility becomes too good to be captured by the filter does not occur, but the dispersing effect cannot be obtained in proportion to the added amount.

Further, in the present invention, it is preferable to add one or more detergents selected from the group consisting of Ca sulfonate, Ca phenate and Ca salicylate in a total amount of 3 to 10% by weight. These can use what is known as a metal type detergent.

These Ca compounds are mainly added as a detergent, and when used in combination with a dispersant, their performance is further enhanced. In addition, since the action differs depending on the type of Ca compound, it is preferable to add two or more Ca compounds. In addition, even in the case of individual compounds, the rust prevention effect is large due to the base number of each compound in addition to the cleaning action. Since they have different side effects such as those effective for neutralization of acid and acid, it is preferable to add those having different base numbers at an appropriate ratio. The amount of Ca added is preferably in the range of 3 to 10% by weight in total of the Ca compounds, and if it is less than 3% by weight, the cleanliness is insufficient, and the acid generated by combustion and mixed into the lubricating oil is not sufficiently neutralized. On the other hand, if it exceeds 10% by weight, no improvement in the cleaning effect corresponding to it is seen, and it is economically undesirable.

In the present invention, the content of zinc dithiophosphate is preferably 0.5 to 5.0% by weight. Zinc dithiophosphate is a compound represented by the following general formula (II): (However, R is the same or different hydrocarbon group) It acts as an antioxidant that decomposes peroxide and an extreme pressure agent. The amount of zinc dithiophosphate added is 0.
If it is less than 5% by weight, wear resistance is insufficient, and 5.0% by weight.
If the amount exceeds the above range, an effect commensurate with the added amount cannot be obtained.

In the present invention, in addition to the above additives as necessary, for example, polyisobutylene, viscosity index improver such as polymethacrylate, defoaming agent such as silicone oil, phenolic, amine antioxidant Agent or oily agent,
Additives such as extreme pressure agents and corrosion inhibitors can be added as appropriate. However, since the lubricating oil of the present invention requires moderate dispersion suppression without impairing the cleaning effect, a basic dispersant such as polyalkenyl succinimide or benzylamine having a high dispersibility is substantially used. Is preferably not added.

 Hereinafter, the present invention will be described in more detail with reference to Examples.

[Examples] Lubricating oil compositions were prepared by blending various additives into a lubricating base oil, and the cleanliness and trapping of combustion residues were evaluated.

The evaluation test methods for the base oils, the types of additives, and the lubricating oils used in the preparation of the lubricating oil compositions of the examples and comparative examples are as follows.

1. Lubricating base oil In each of the examples and comparative examples, mineral oil prepared by mixing 10 parts by weight of so-called 150 neutral oil and 90 parts by weight of 500 neutral oil obtained from a lubricating oil manufacturing process common in the oil refining industry is used. Using.

2. Additives (1) Thiophosphonic acid ester Texaco Chemical Co., Ltd., TC5986 (2) Polyalkenyl succinimide Nippon Lubrizol Co., Ltd., Lz6418 (3) Detergent Ca sulfonate (with a total base number of 20 and a total base number of 300) , Ca phenate (having a total base number of 100 and a total base number of 250), Ca salicylate (having a total base number of 250) (4) Antioxidant zinc dithiophosphate All of the above are commercially available products.

3.Evaluation tests for lubricating oils Kinematic viscosity: Conducted in accordance with JIS K2283.

Viscosity index: Performed according to JIS K2283.

Total acid value, total base value: Performed according to JIS K2501.

Furthermore, the diesel engine was actually turned on, and the practical performance of the lubricating oil was evaluated in a cleanliness test and a filter test for capturing combustion residues.

Cleanliness In-line 4-cylinder, swirl chamber type, 2.2 diesel engine operated under the following operating conditions, rotation speed 4000rpm output 56PS oil temperature 120 ℃ test time 100hr After engine stop, open to block piston ring groove and ring gland The deposit was evaluated for cleanliness of the test lubricating oil in accordance with the Land Diesel Engine Piston Evaluation Method (JPI-55-15-85). In this engine test, only a full flow filter was installed as an oil filter.

Combustion residue trapping performance An in-line 4-cylinder, direct-injection, 3.3-diesel engine was operated under the following operating conditions, with a rotation speed of 2,000 rpm, an output of 75 PS, an oil temperature of 90 ° C, and a test time of 100 hours. It was supplemented by an oil filter installed in the lubrication oil circulation system. The concentration of the combustion residue in the combustion residue and oil was quantified to evaluate the trapping property of the combustion residue in the oil filter.

The specifications of the oil filter used in this engine test are as follows.

The combustion residue capture rate of the filter and the combustion residue concentration in oil are
It was determined as follows. The oil filter after the engine test was collected, then the weight of the dry filter after removing the oil using n-hexane was measured, and the difference between the weight of the dry filter and that of a new oil filter was defined as the trapped amount of the combustion residue. Then, the combustion residue capture rate (%) of the filter was determined by the following equation.

The concentration of the combustion residue in the oil was determined by diluting the lubricating oil containing the combustion residue with n-hexane after a predetermined engine test, and performing centrifugation at 12400 G for 3 hours. The recovered weight percentage of the solid obtained by removing the hexane by evaporation was defined as the concentration of the combustion residue in the oil.

Examples 1 to 3 Lubricating oil compositions were prepared by adding various additives to the above-mentioned lubricating base oil at the ratios (% by weight) shown in the upper part of Table 1. The physical properties of the obtained lubricating oil composition are as shown in the lower part of Table 1. Table 2 shows the results of engine tests performed to evaluate the practical performance of these lubricating oils. The upper part of the table shows the test results of cleanliness, together with the increase in total acid value and the remaining total base number, and the lower part shows the results of the trapping test.

Comparative Examples 1 and 2 A lubricating oil composition containing a polyalkenyl succinimide corresponding to a conventional CD-grade engine oil was prepared, and was designated as Comparative Example 1. Further, the succinimide added in Comparative Example 1 was used in an amount of 0.
The composition reduced to 5% was used as Comparative Example 2 and compared with the results of Examples 1 to 3, respectively. The results are shown in Tables 1 and 2.

As is clear from the results in Table 2, the lubricating oil of the present invention (Examples 1 to 3) has a higher engine cleanability and a residual total base number than the conventional lubricating oil for diesel engines (Comparative Example 1). It can be seen that the performance is equal to or more than that, and the performance of capturing the combustion residue is improved 3 to 4 times. On the other hand, in Comparative Example 2 in which the amount of succinimide added was smaller than the amount added to the conventional oil, although the capture performance was improved due to the reduction in the amount of succinimide, it did not reach the level of the present invention. In addition, engine cleanliness has deteriorated.

[Effect of the Invention] The present invention relates to a lubricating oil for a diesel engine,
The addition of a specific amount of a dispersant with a moderately suppressed dispersibility greatly improves the efficiency of capturing solids in the oil filter. Of course, since it does not deteriorate even after long-term use, the oil exchange distance of the lubricating oil for diesel engines, which is inevitably mixed with the combustion residue, is extended, and the lubricating oil life is significantly improved. .

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Claims (2)

(57) [Claims] 1. A thiophosphonic acid hydroxyethyl ester represented by the general formula (I) is added to a base oil comprising a mineral oil, a synthetic oil or a mixed oil thereof. (Where R represents a hydrocarbon group having 6 to 30 carbon atoms) in an amount of 0.5 to 5.0% by weight. (2) 0.5-5.0% by weight of zinc dithiophosphate,
And (2) a lubricating oil composition for a diesel engine according to claim 1, wherein a total of 3 to 10% by weight of one or more detergents selected from the group consisting of Ca sulfonate, Ca phenate and Ca salicylate is added.