Grease Degradation in Constant Velocity (CV) Joints

Abstract

Constant velocity (CV) joints have been widely used for modern vehicles. The sealed grease of CV joints must provide low friction and wear protection for the lifetime use of the vehicle. Grease performance affects the vibration and noise level in the vehicle. Vehicles that have traveled long distances may suffer mechanical and thermal overloads, thus causing the grease to degrade due to changes in its physical and chemical properties. In this article, the grease degradation phenomenon in CV joints is investigated by collecting grease samples from both tripod joints and Birfield joints in actual vehicles that traveled various ranges of distance. In order to analyze the property changes of grease, grease penetration and oxidation induced time are measured using a penetration meter and infrared (IR) spectrometer, respectively. Where oxygen induced time (OIT) is the point that the oxidation occurs in grease. The performance variations of grease are investigated by measuring the friction and wear using linear-oscillation (SRV, Schwingung (oscillation) Reibung (friction) Verschleiss (wear)) test machine as well as the four-ball wear tester. Degradation of properties as well as performance in CV joint grease due to physical and/or chemical changes is identified.

Grease composition influence on friction & starvation

“…The strength will depend on the friction coefficient and implies vibration on the car. These functions which are essential, insure the components have a long life 21 avoiding starvation for example.…”

Thermal Oxidation Mechanism of Polyalphaolefin Greases with Lithium Soap and Diurea Thickeners: Effects of the Thickener

“…Most of the published works were bearing tests that the lubrication life was influenced not only by grease 3 oxidation but also by metal and additive oxidation, wear debris and other changes appeared during the operation [15][16][17][18][19]. Bearing failure at high temperature was caused by grease lubrication failure, but grease lubrication failure was not definitely caused by grease oxidation.…”

“…During the MTM test, the 17 contact was in boundary lubrication phase in which the contact was mainly lubricated by bled oil.…”

Study of the Bearing Friction Inside on a Mobile Coupling Joint

“…The lubricant pressure and film behaviour is studied in [7] depending on the frequency and amplitude of the reciprocating motion of the plunge for a mobile tripod universal joint; the conclusions show that the film thickness increases with the increase of the amplitude and the frequency of the plunge's alternative motions. In [8] is studied the tribological behaviour of a constant velocity mobile joint used in the transmission of the vehicles. The conclusions offer information about the degradation of the grease which lubricates the joint.…”

“…The conclusions offer information about the degradation of the grease which lubricates the joint. A four ball tester and a linear oscillation testing machine is used in [8] in order to study the friction, wear and the grease degradation for constant velocity joint used in the transmission of vehicles that travelled various distances. Regarding the experimental studies oriented on the frictional behaviour of the mobile tripod couplings, the literature presents mainly global friction coefficients averaged for the entire mobile coupling.…”