Grease Composition For Use In Constant Velocity Joints

Abstract

In order to provide for a grease composition which has a good compatibility with boots made of rubber or thermoplastic elastomer, and which also gives low wear and low friction, a grease composition for use in constant velocity joints is suggested, comprisinga) a base oil composition;b) at least one tri-nuclear molybdenum compound of the formulaMo3SkLnQz,wherein L are independently selected ligands having organo groups with a sufficient number of carbon atoms to render the compound soluble or dispersible in the oil, n is from 1 to 4, k varies from 4 though 7, Q is selected from the group of neutral electron donating compounds such as amines, alcohols, phosphines, and ethers, and z ranges from 0 to 5 and includes non-stoichiometric values;c) at least one urea derivative thickener.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application claims priority of International Patent Application No. PCT / EP2006 / 009718, filed Oct. 7, 2006, and which is incorporated in its entirety by reference.FIELD OF THE INVENTION[0002]The present invention relates to a lubricating grease which is intended primarily for use in constant velocity universal joints, especially ball joints or tripod joints, which are used in the drivelines of motor vehicles.BACKGROUND OF THE INVENTION[0003]The motions of components within constant velocity joints (CVJ) are complex with a combination of rolling, sliding and spinning. When the joints are under torque, the components are loaded together which can not only cause wear on the contact surfaces of the components, but also rolling contact fatigue and significant frictional forces between the surfaces. The wear can result in failure of the joints and the frictional forces can give rise to noise, vibration and harshness (NVH) in the driveline. ...

AI Technical Summary

Benefits of technology

The present invention provides a grease composition for use in constant velocity joints that has good compatibility with rubber or thermoplastic elastomer materials. The grease composition should also have low wear and low friction in use in constant velocity joints. The grease composition includes a base oil composition, at least one tri-nuclear molybdenum compound, and at least one urea derivative thickener. The tri-nuclear molybdenum compound should have at least 21 carbon atoms among the ligands. The base oil composition can be any kind of base oil or a blend of mineral oils and synthetic oils. The urea derivative thickener used in the grease composition can be a urea complex thickener or a mixture of urea derivative thickener with other thickeners such as calcium or lithium-based thickeners or complex thickeners. The use of the present invention provides a grease composition that reduces friction and wear in constant velocity joints.

Problems solved by technology

When the joints are under torque, the components are loaded together which can not only cause wear on the contact surfaces of the components, but also rolling contact fatigue and significant frictional forces between the surfaces.

The wear can result in failure of the joints and the frictional forces can give rise to noise, vibration and harshness (NVH) in the driveline.

Otherwise there is a degradation of the boot material which causes premature failure of the boot, allowing the escape of the grease and ultimately failure of the CVJ.

Both mineral and synthetic base oils extract the plasticisers and other oil soluble protective agents from the boot materials, Paraffinic mineral oils and poly-α-olefin (PAO) synthetic base oils diffuse very little into especially boots made of rubber material causing shrinkage, but on the other hand naphthenic mineral oils and synthetic esters diffuse into boot materials and act as plasticisers and can cause swelling.

The exchange of plasticiser or plasticiser compositions for the naphthenic mineral oil can significantly reduce the boot performance, especially at low temperatures, and may cause the boot to fail by cold cracking, ultimately resulting in failure of the CVJ.

If significant swelling or softening occurs, the maximum high speed capability of the boot is reduced due to the poor stability at speed and / or excessive radial expansion.

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