Lubricants with enhanced thermal conductivity containing nanomaterial for automatic transmission fluids, power transmission fluids and hydraulic steering applications

Abstract

A lubricant composition having an enhanced thermal conductivity, up to 80% greater than its conventional analogues, and methods of preparation for these fluids are identified. One preferred composition contains a base oil, nanomaterial, and a dispersing agent or surfactant for the purpose of stabilizing the nanomaterial. One preferred nanomaterial is a high thermal conductivity graphite, exceeding 80 W / m in thermal conductivity. The graphite is ground, milled, or naturally prepared to obtain a mean particle size less than 500 nm in diameter, and preferably less than 100 nm, and most preferably less than 50 nm. The graphite is dispersed in the fluid by one or more of various methods, including ultrasonication, milling, and chemical dispersion. Carbon nanostructures such as nanotubes, nanofibrils, and nanoparticles are another type of graphitic structure useful in the present invention. Other high thermal conductivity carbon materials are also acceptable. To confer long-term stability, the use of one or more chemical dispersants or surfactants is useful. The thermal conductivity enhancement, compared to the fluid without graphite, is proportional to the amount of nanomaterials added. The graphite nanomaterials contribute to the overall fluid viscosity, partly or completely eliminating the need for viscosity index improvers and providing a very high viscosity index. Particle size and dispersing chemistry is controlled to get the desired combination of viscosity and thermal conductivity increase from the base oil while controlling the amount of temporary viscosity loss in shear fields. The resulting fluids have unique properties due to the high thermal conductivity and high viscosity index of the suspended particles, as well as their small size.

Description

[0001]This application is a Continuation-In-Part of copending U.S. application Ser. No. 10 / 737,731 filed on Dec. 16, 2003 which claims priority from U.S. application Ser. No. 10 / 021,767 filed on Dec. 12, 2001 which claims priority from U.S. Provisional Application Ser. No. 60 / 254,959 filed on Dec. 12, 2000; PCT Application S.N. PCT / US02 / 16888 filed on May 30, 2002; U.S. nonprovisional application Ser. No. ______ filed on Dec. 8, 2003; and claims priority from U.S. Provisional Application Ser. No. 60 / 433,798 filed on Dec. 16, 2002 all of which are incorporated by reference in their entirety.[0002]This application is part of a government project, Contract No. W031-109-ENG-38 by the Department of Energy. The Government has certain rights in this invention.BACKGROUND OF THE INVENTION[0003]1. Field of the Invention[0004]The invention relates to the field of providing lubricants and functional fluids containing nanomaterial dispersed within automatic transmission fluids, power transmissio...

AI Technical Summary

Benefits of technology

[0018]To confer long-term stability, an effective amount of one or more chemical dispersants or surfactants is preferred, although a special grinding procedure in base oil will also confer long term stability. The thermal conductivity enhancement, compared to the fluid without graphite, is proportional to the amount of nanomaterials added. The graphite nanoparticles or nanotubes contribute to the overall fluid viscosity, partly or completely eliminating the need for viscosity index improvers and providing a very high viscosity index. Particle size and dispersing chemistry is controlled to get the desired combination of viscosity and thermal conductivity increase from the base oil while controlling the amount of temporary viscosity loss in shear fields. The resulting fluids have unique properties due to the high thermal conductivity and high viscosity index of the suspended particles, as well as their small size.

[0050]It is an object of the present invention to provide a uniform and stable dispersion where the thermal conductivity and heat transfer capability of the fluid is at least more than 20% improved compared to conventional mineral oil based automatic transmission fluids.

Problems solved by technology

Often designers will desire a fluid with higher thermal conductivity than the conventional oil, but are restricted to oil due to the many other parameters the fluid must meet.

While there have been various patents filed on lubricants containing graphite, e.g. U.S. Pat. No. 6,169,059, there are none which specifically rely on graphite to improve the thermal conductivity of the fluid formulated for specific applications.

Furthermore, there are none which teach specifically the use of nanometer-sized graphite with mean particle size much significantly less than 1000 nm in order to increase thermal conductivity and that reducing particle size improves thermal conductivity.

While graphite-containing automotive engine oil was once commercialized (Arco graphite), the potential to use graphite as a heat transfer improving material in this oil was not realized.

On the other hand, the use of graphite in lubricants for recirculating systems was made unpopular, partly due to evidence that micron size graphite could “pile up” in restricted flow areas in concentrated contacts, thereby leading to lubricant starvation.

Previously, naturally formed “nano-graphites” have not been available in the marketplace at all.

Additionally, the heat transfer requirements in transmissions and pumps are significant.

It is generally necessary to use some form of cooling for the transmission fluid, and some designs of transmissions are prevented due to insufficient capability to eliminate waste heat.

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