Roles of Additives to Stabilize Lubricated Rolling–Sliding Contacts

Abstract

Chain continuously variable transmissions (CVTs) are attracting attention as the next-generation practical application, which utilize lubricated rolling/sliding contacts for transmitting the engine power. However, their flexible structure sometimes causes vibration and noise problems which need to be solved. In this study, friction tests were conducted for a rolling/sliding contact lubricated by test lubricants with/without two types of additives (i.e., oleylamine as a friction modifier and tricresyl phosphate as an extreme pressure agent) which are typically used for chain CVT fluids. Besides, based on the minimal model of lubricated rolling/sliding contacts, the stability analysis was conducted to understand the preferable friction characteristics for preventing the vibration and noise problems, under the assumption that the friction force is a function of the instantaneous entrainment speed and the instantaneous slide-to-roll ratio. Consequently, it was found that the combined use of oleylamine and tricresyl phosphate is promising, not only because they provide low friction in the boundary lubrication regime, but also because they provide adequately rough surfaces which increase the lower limit speed of the hydrodynamic lubrication regime, through the mutual inhibitory effects between them.

Additive Formulation for Reducing Noise in Chain CVTs

“…Note that Lubricants FM+EP and FM+EP+DT showed the same viscosity as Lubricant BO, indicating that the additives did not change the performance in the fluid film lubrication. Also note that to observe the fluid film lubrication regime in the ball-on-disc tests, their viscosity was one order of magnitude higher than commercial chain CVT fluids, as in the previous study [10].…”

“…An apparatus shown in Fig. 1 was used for ball-on-disc tests as in the previous study [10]. This commercially-available apparatus (MTM, PCS Instruments) used a rolling/sliding point contact between an AISI 52100 steel ball (diameter: 19 mm; surface roughness: R aA = 0.02 µm and R qA = 0.03 µm) and an AISI 52100 steel disc (diameter: 46 mm; surface roughness: R aB = 0.01 µm and R qB = 0.02 µm), where R aA and R aB are the arithmetic mean roughness of the ball and disc, respectively, and R qA and R qB are the root mean square (RMS) roughness of the ball and disc, respectively.…”

“…The negative slope of friction coefficient for U < U cr generates instabilities in tribosystems [6][7][8][9], which leads to noise and vibration in chain CVTs [10]. In general, noise and vibration likely occur when the negative slope is steep.…”

“…Aiming to overcome the noise and vibration problems in chain CVTs by lubricants, the authors [10] once examined the effect of two additives, oleylamine (kwon as a common friction modifier) and tricresyl phosphate (known as a common extreme pressure agent), on the velocity dependence of friction coefficient in ball-on-disc tests for lubricated rolling/sliding contacts. They found that the additives decreased the friction coefficient in the boundary lubrication regime, which was expected to improve the low-noise and low-vibration performance.…”

An Experimental Study of Surface Damage on Rolling Bearings in Low Lambda Conditions

“…Four types of Durasyn PAO with different viscosities as provided by the manufacturer in Table 2, which are Durasyn 162, Durasyn 164, Durasyn 166, and Durasyn 170, have been chosen. As reported in previous studies [11,12,30,31], additives, such as anti-wear (AW) and extreme pressure (EP) can have a significant effect on tribological surfaces with tribofilm formation, either degrading or protecting the surface [32,33]. Hence, as a preliminary step toward investigating surface damage in low Λ conditions, such effects were eliminated in this study by limiting the base oil properties.…”