Peer-reviewed: Grease degradation in constant velocity (CV) joints

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.