Lubricant Additives for Improving the Performance of Metal V-Belt Type CVTs

Abstract

Lubricants for metal V-belt type CVTs (B-CVTFs) must be able to produce a higher metal-metal friction coefficient and give excellent anti-shudder properties for lock-up clutch used in B-CVTs. This study intends to optimize various kinds of lubricant additive such as anti-wear additive, detergent and friction modifier (FM) for improving these performances of B-CVTs. In addition, contact mode atomic force microscopy was utilized to investigate links between friction performance and the morphology of tribofilms formed from candidate additives. As a result, an additive formulation consisting of a phosphorus additive, calcium detergent and dispersant showed a higher friction coefficient between the metals. The results of the surface analysis on the wear scar indicate that calcium tribofilm species formed fine depositions on the rubbing surface, which might attribute to a higher friction between the metals. Moreover, it is found that a sort of friction modifier gave an excellent anti-shudder performance for wet clutch with keeping higher friction coefficient between the metals, which would result in improving the performance of B-CVTs.

Lubricants for Metal Belt Continuously Variable Transmissions

“…Some friction test methods to reproduce the friction characteristics of an actual belt CVT in the laboratory have been proposed [2,3]. Figure 3 shows a block on ring type friction tester evaluating the friction characteristics between metals [9]. This test procedure is based on JASO M358 High load condition [13] and has been previously shown to be a valid method of assessing the torque capacity in a CVT between a candidate oil and a reference oil.…”

“…This test implies that using a greater load results in a better anti-seizer property for the test oils. Figure 5 shows the metal-metal friction characteristics tested by LFW-1 [9]. Table 1 shows the compositions of the test oils.…”

“…These additives are normally used in CVTFs in order to keep the transmission clean and also known to play an important role in controlling friction-velocity performance in lock-up clutch [9]. Figure 6 illustrates the contact force Atomic Force Microscopy (AFM) topographic images of the post-test blocks derived from the tested oils [9]. Note that the brighter parts in the AFM images represent higher positions on the surface.…”

“…It is assumed that the friction coefficient is dependent on the shearing force based on the characteristics of the boundary lubrication film formed by the additives and the EHL (elastohydrodynamic lubrication) film. The authors reported the effect of lubricant additives in B-CVTFs exert on the friction properties between the metals [9,10], and the effect of base stocks on the actual CVT transmission torque capacity [11]. This report reviews the results obtained from these studies.…”

Development of Fluids for Chain Type CVTs

“…8). It is supposed that those islands promote a shift from the fluid lubrication area to the boundary lubrication area, contributing to a higher friction coefficient [8].…”