Lubricant composition for automobile driving system

Abstract

A lubricant composition having a 40° C. dynamic viscosity of 40 mm2 / s or less that has wear resistance equal to or better than a lubricant having a 40° C. dynamic viscosity of 76 mm2 / s is achieved by providing a base oil with a zinc dithiophosphate and alkaline earth metal salt in an amount to provide a ratio of elemental zinc to alkaline earth metal in the oil in the range of 0.2 to 1.0.

Description

[0001] This application claims the benefit of Japanese Patent Application 2004-163106 filed Jun. 1, 2004 (Patent Applicants: Tonen General Sekiyu K.K. and Toyota Motor Corporation). FIELD OF THE INVENTION [0002] The present invention pertains to a lubricant composition for an automobile driving system. More specifically, the present invention pertains to a lubricant composition for automobile gears, especially for a manual speed-change gear. BACKGROUND OF THE INVENTION [0003] In recent years, as a measure for preventing global warming, various schemes for protecting the environment have been proposed. One said scheme calls for development of an environmentally friendly lubricant. An environmentally friendly lubricant for use in automobiles, is required to have an excellent effect in improving gas mileage to reduce the amount of carbon dioxide exhaust from internal combustion engines. In order to increase the mileage with the lubricant, two methods have been under study, that is, a m...

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Benefits of technology

[0008] In order to solve the aforementioned problems, the present inventors have performed extensive research. As a result of this research, it was found that when an alkaline earth metal salt and zinc dithiophosphate are mixed at a prescribed ratio, it is possible to obtain a lubricant composition that has a 40° C. dynamic viscosity of 40 mm2 / s or lower, and, at the same time, that has excellent wear resistance for steel parts and, especially, for aluminum parts, equal to or better than the wear resistance of a conventional commercially available lubricant with a 40° C. dynamic viscosity of 76 mm2 / s. The present invention was achieved based on this finding.

[0014] As explained above, according to the present invention, by adding an organic acid alkaline earth metal salt, especially magnesium sulfonate, in a prescribed quantity in a base oil with a low viscosity, and by mixing said organic acid alkaline earth metal salt and zinc dithiophosphate at a prescribed ratio, it is possible to obtain a type of lubricant for a manual speed-change gear that can display significant wear resistance for not only steel parts but also aluminum sliding parts, and that has an excellent effect in increasing mileage.

[0043] As the alkaline earth metal sulfonate, magnesium sulfonate is especially preferred. In the low-viscosity state, when it is used together with zinc dithiophosphate, excellent wear resistance can be displayed in a manual speed-change gear having sliding aluminum parts.

[0092] From the results of the friction width listed in Table 1, significant effects can be displayed for the oil samples prepared with a low 40° C. dynamic viscosity of 30 mm2 / s, corresponding to an excellent effect in increasing the mileage, with the quantity of elemental Mg in the oil at a prescribed value, and with the ratio of the quantity of elemental Zn in the oil to the quantity of elemental Mg in the oil in the prescribed range of 0.2-1. Example 1 was compared with Comparative Examples 2 and 3 with the same quantity of elemental Mg. In Example 1, the ratio of the quantity of elemental Zn in the oil to the quantity of elemental Mg in the oil is 0.67, that is, within the aforementioned prescribed range. On the other hand, in Comparative Examples 2 and 3, the ratio of the quantity of elemental Zn in the oil to the quantity of elemental Mg in the oil is 1.33, that is, outside the aforementioned range, and the wear resistance is much worse.

[0094] The lubricant composition for a manual speed-change gear of the present invention contributes to protection of the environment since it is an environmentally friendly lubricant by realizing low viscosity. Also, it can be used as a high-quality lubricant for an automobile driving system, such as a manual transmission, manual transmission axle, etc. Consequently, it greatly contributes to the petroleum and automobile industries with regard to manufacture and application.

Problems solved by technology

In order to realize smooth operation of the synchronization device, lowering of the friction coefficient is undesirable because if only the viscosity is reduced, the oil film becomes thinner, and wear is facilitated.

Aluminum parts adopted for reducing the weight of the driving system device are especially more prone to wear than are steel parts, and they are more easily affected by a reduced viscosity.

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