Abstract
The friction characteristics of a shock absorber are very complex because the reciprocating motion is not always identical. In this study a device was developed and used to analyze the dynamic friction characteristics under various reciprocating sliding conditions to determine the sliding materials and hydraulic oils that improve the shock absorber performance. This study describes the influence of hydraulic oil additive on the fine reciprocating friction characteristics of steel and copper alloy. Hydraulic oils were prepared by blending a paraffinic mineral oil with zinc dithiophosphate (ZnDTP) and polyhydric alcohol ester as additives. The results show that the dynamic frictional characteristics vary mainly depending on the additive concentration. A specific additive formulation induces a unique amplitude-dependent friction behavior. In addition, the influence of different additives on the lubrication mechanism is investigated based on the instrumental analysis of the friction surface.
Highlights
Nowadays, the cars travel mostly on relatively smooth roads because the road surface has progressively become less irregular due to improved road maintenance
Compared to the base oil, the average friction decreased for the ester at amplitude of ±2.0 mm, but it did not decrease at the fine amplitude of ±0.1 mm
These results reveal that lubrication can be obtained at amplitude of ±2.0 mm with the ester or zinc dithiophosphate (ZnDTP) additive, but at amplitude of ±0.1 mm, there is insufficient lubrication for the ester-only additive and low-concentration ZnDTP, and the friction force becomes large
Summary
The cars travel mostly on relatively smooth roads because the road surface has progressively become less irregular due to improved road maintenance Under such road conditions, a shock absorber, which is a key component in stabilizing car behavior, operates at a fine amplitude of several hundred micrometers to a few millimeters, such that it does not generate sufficient hydraulic pressure for the damping force. No studies have been reported on the dynamic friction properties of friction films focusing on boundary lubrication near zero speed, under boundary lubrication conditions of lubricants with additives in reciprocating motion. Via a newly developed dynamic friction behavior measurement system, the additives used in general lubricating oils and hydraulic oil of shock absorbers are evaluated to investigate the effects of various additives on the lubrication mechanism through instrumental analysis of the friction surface. ZnDTP, which is a multifunctional additive that forms a chemical reaction film, and polyhydric alcohol ester, which is an additive of chemical adsorption film
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