Solid anti-friction devices – materials therefor – lubricant or se – Lubricants or separants for moving solid surfaces and... – Heavy metal or aluminum in an organic phosphorus compound...
Reexamination Certificate
2001-06-05
2002-07-30
Howard, Jacqueline V. (Department: 1764)
Solid anti-friction devices, materials therefor, lubricant or se
Lubricants or separants for moving solid surfaces and...
Heavy metal or aluminum in an organic phosphorus compound...
C508S372000, C508S378000, C508S403000, C508S408000, C508S421000, C508S438000, C508S442000
Reexamination Certificate
active
06426323
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a lubricating oil composition for continuously variable transmission, and more particularly, to a lubricating oil composition used in a push belt type of continuously variable transmission. More specifically, the invention relates to a lubricating oil composition which ensures a high coefficient of boundary lubrication friction and an excellent wear preventing property in a push belt-type continuously variable transmission.
BACKGROUND OF THE INVENTION
The push belt-type continuously variable transmission (which may be sometimes referred to as belt-type CVT hereinafter) rapidly increases in number because it is effective in improving a fuel cost and also drivability of automobiles. However, the belt-type CVT is difficult in obtaining a large transmission torque capacity, and has been mounted only on a small automobile whose displacement is 1600 cc or below. The improvement in the transmission torque capacity is a serious problem on the belt-type CVT.
With the belt-type CVT, a torque is transmitted by means of a friction force between a belt element and a pulley. Thus, the transmission torque capacity is determined depending on the coefficient of friction between the metals of the belt element and the pulley and the urging force of the pulley. The coefficient of friction between the metals is influenced by the property of a lubricating oil. The shortage of the coefficient of friction between the metals may lead to the slippage between the belt and the pulley and may cause a disadvantage in that the belt is broken out.
On the other hand, an electromagnetic clutch has been hitherto used as a starting mechanism of the belt-type CVT. In order to cope with an increasing transmission torque accompanied by the tendency toward a great displacement and improve the drivability, there has been now used a wet clutch or and a torque converter with a lock-up clutch. These wet clutch, torque converter and CVT make use of a common lubricating oil. Accordingly, it has become important how to adapt the lubricating oil for continuously variable transmission (CVT oil) to the wet clutch or torque converter.
Under these circumstances, an automatic transmission oil (referred to as ATF) has been frequently used for the CTV oil. This is because with an existing automobile of a small displacement, the transmission torque is so small that a required level of the coefficient of friction between metals is not so high, under which if an oil having a relatively high coefficient of friction between metals is selected among ATF's, the performance can be satisfied. The merit of making use of ATF includes actual results on the adaptability with a wet clutch and also on adaptability on other types of materials. However, if the belt-type CVT is mounted in an automobile of a large displacement, a required level of the coefficient of friction between metals increases. The mere use of ATF does not result in a satisfactory performance, and an oil only for the CVT has to be used.
Further, in order to efficiently transmit an engine output by means of the belt-type CVT, it is necessary to prevent slippage between a belt and a pulley. When a belt for preventing the slippage is inserted at an increased pressure, it is more liable to wear out. To avoid this, there has been required not only an improvement in device, but also a lubricating oil that can prevent the slippage between a belt and a pulley and can also prevent the belt and pulley from being worn out.
Hitherto, lubricating oils for continuously variable transmission have been proposed including, for example, a lubricating oil composition of Japanese Patent Application Laid-open No. Hei 2-175794 wherein a wear preventive, a metal detergent and a carboxyl group-bearing friction modifier are formulated, a composition for continuously variable transmission of Japanese Patent Application Laid-open No. Hei 9-100487 wherein a sulfur-based extreme pressure agent, a phosphorus-based extreme pressure agent, and a metal-based detergent are formulated, a lubricating oil composition for continuously variable transmission of Japanese Patent Application Laid-open No. Hei 10-8081 wherein an ashless dispersant, a sulfur-based extreme pressure agent and a phosphorus-based extreme pressure agent are formulated, a lubricating oil composition for belt-type CVT automatic transmission of Japanese Patent Application Laid-open No. Hei 10-306292 wherein a Ca sulfonate and a phosphite ester having a specified range of a total base number are formulated, a lubricating oil composition for belt-type continuously variable transmission of Japanese Patent Application Laid-open No. Hei 11-80772 which has a coefficient of friction within a specified range and wherein a metal detergent and a zinc dialkyldithiophosphate are formulated, and a lubricating oil composition for continuously variable transmission of Japanese Patent Application Laid-open No. Hei 11- 181464 wherein a polymethacrylate or the like, an imide compound and a zinc alkyldithiophosphate are formulated. In spite of these proposals, however, a satisfactory, high level of a coefficient of friction between metals and an excellent wear preventing property against the belt and pulley have not be realized. Especially, a high coefficient of friction between metals is required for the belt-type continuously variable transmission lubricating oil (CVT oil) is required, for which a metal detergent is formulated. Among metal detergents, there are known some detergents that impede the wear preventing property depending on the amount thereof. On the other hand, a wear preventive formulated to improve the wear preventing property is unsatisfactory for wear proofing owing to the interaction with the metal detergent if its amount is too small. In contrast, when the amount is too much, there arises the problem that a coefficient of friction between metals lowers.
Applicants invention addresses the needs with respect to such lubricating oils.
SUMMARY OF THE INVENTION
Embodiments of the invention relate to a lubricating oil composition wherein at least two specific types of compounds are formulated in a lubricating base oil.
The lubricating oil compositions have both a high coefficient of friction between metals and an enhanced wear preventing property against a belt and a pulley as required for a belt-type CVT oil.
Applicants have found that when at least two additives including a metal detergent (A) having a ratio of a metal content and a total base number within a specified range, and a phosphorus-based wear preventive (B) are formulated in a lubricating base oil in such a way that a ratio between the metal content in the metal detergent (A), i.e. a calcium content, and a phosphorus content in the phosphorus-based wear preventive (B) is within a specified range, whereby a lubricating oil composition for continuously variable transmission which can realize both a high coefficient of friction between metals and an excellent wear preventing property required as the lubricating oil for continuously variable transmission can be obtained.
More particularly, according to an embodiment of the invention, there is provided a lubricating oil composition for continuously variable transmission, which comprises a metal detergent (A) and a phosphorus-based wear preventive (B), characterized in that a ratio between a content (ppm) of a metal derived from said metal detergent (A) and based on the total weight of the lubricating oil composition and a total base number (mg KOH/g) ranges 0.75-4.5 (ppm/mg KOH/g), and a ratio between the content (ppm) of the metal derived from said metal detergent (A) and a content of phosphorus derived from the phosphorus-based wear preventive (B) ranges 0.5-2.0 (ppm/ppm).
Preferred embodiments include those set forth below.
(1) A lubricating oil composition for continuously variable transmission, wherein a continuously variable transmission is a push belt-type continuously variable transmission.
(2) A lubricating oil composition for continuously variable transmission, wherein the phos
Kugimiya Takanori
Sato Takehisa
Howard Jacqueline V.
Scuorzo Linda M.
TonenGeneral Sekiyu K.K.
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