The dynamic characteristics of shock absorbers, key components of suspensions, significant impact on the vehicle's driving performance, including stability and ride comfort. The damping force of a shock absorber is composed of both hydraulic damping force and friction. Notably, when switching between reciprocating motions, the dynamic friction force becomes the dominant factor. This study found that dynamic performance can be improved by controlling the friction waveform during reciprocating motion through the combination of ZDDP and ester additives with different valences. It was found that the dynamic performance can be improved by controlling the friction waveform during reciprocating motion by combining ZDDP with ester additives of different valences. The aim of this study was to clarify the mechanism by which the friction waveform changes depending on the valence of the ester additive. To achieve this, we investigated the adsorption behavior using a Quartz Crystal Microbalance (QCM), observed the film formation process with Atomic Force Microscopy (AFM), and evaluated friction characteristics using a macro friction tester. This approach allowed us to link nano- and macro-scale characteristics. The results suggest that the reaction of ZDDP on the sliding surface was influenced by changes in the adsorption behavior of the ester additive, which varied depending on its valence. This change in adsorption behavior controlled the friction waveform.

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In electric railways, current collecting materials such as contact wire and contact strip are subject to wear due to friction and current. It has been reported that the friction and wear properties of these materials differ even at the same sliding speed and current. Previously, the authors focused on a bulk temperature of the contact strip, which varies with the history of the sliding conditions, and reported that the heat transfer properties that governing the temperature rise of the contact strip may vary depending on the mechanical wear modes under unelectrified conditions. However, there have been no reports on the heat transfer properties under electrified conditions, nor on the relationship between the properties and wear modes. In this paper, the authors carry out wear tests under electrified conditions and analyze the heat transfer properties, then discuss the relationship between the properties and wear modes. The results show that the influence of current on the heat transfer properties is small when the contact loss ratio is small. They also show that these properties have a certain range of values depending on the transferred material and the roughness of the wear surface that changes depending on the wear modes.

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