On the Effect of DLC and WCC Coatings on the Efficiency of Manual Transmission Gear Pairs

Abstract

An experimentally validated tribo-dynamic model has been developed to predict the gear teeth frictional losses considering the properties of the diamond-like-carbon (DLC)-coated and tungsten carbide carbon (WCC)-coated surface. The operating conditions used are snapshots of the Real Driving Emissions (RDE) driving cycle. The results demonstrate that the use of these coatings can improve the frictional losses up to 50%. The gear teeth boundary friction model is enriched by experimentally measured coefficients of the surface asperity boundary shear strength using an atomic force microscope (AFM). The computationally efficient model enables the efficiency prediction in a complete transmission. Such an approach, considering the contact mechanics of coated gear and their effect on the viscous and boundary friction, has not been hitherto reported.

Effects of Diamond-like Carbon and Tungsten-Carbide Carbon Coatings on Tribological Performance of Cam–Tappet Conjunction

“…It is the asperity level equivalent of the coefficient of friction which is expanded to macro-level (conjunction level) using the Greenwood and Tripp approach presented in Section 2.5. The values of this coefficient for surfaces of this study are investigated and obtained using an Atomic Force Microscope (AFM) by Laderou et al [33]. The simulations performed are representative of a four-stroke engine at a speed of 3000 RPM and evaluate the behaviour of the system over two complete engine cycles.…”

Tribological enhancement of piston skirt conjunction using graphene-based coatings

“…In total, nine normal loads are applied from 10 to 80 nN, typical for measuring the nano-frictional response of coatings with these AFM probes, such as can be observed in previous works. 7,44,45,51,66,67 The lower limit of this range is usually specified by sensitivity of the machine, not being able to control lower values. The higher limit is governed by the fact that plastic deformation should be avoided in frictional measurement.…”

A test rig for the experimental characterization of the mechanical energy dissipation due to the propagation of elastic waves during the impact of cylinders

“…Usually, unless proper dissipative devices are implemented, the damping quantification is challenging and often uncertain, and full-scale tests have to be performed to characterize the transmission. As a consequence, several models have been proposed to study the energy dissipation due to not-conservative forces, such as friction on the tooth flanks, friction on the supports of the shafts, windage, oil spreading, dissipative properties of the gear materials [1], and the presence of small and limited plastic or viscous strains in the contact region [2]. All these models assess the mechanical energy dissipated and, even if several processes can be involved, the global effect is usually collected into a unique damping parameter [3,4].…”