Abstract
This study was a continuous investigation of the roles played by the tribofilm on dry automotive clutch system performance. Tribological experiments were performed by the addition of wear debris at the beginning of tribometer tests and by reducing the surface roughness of a cast iron counter-face. The initial surface conditions of cast discs were 0.2 and 1.2 µm. The pin-on-disc tests were carried out at three different PV levels: 3.08, 7.88, and 10.09 MPa·ms−1, and the current results were correlated to those previously obtained in the standard tribometer procedure. When the wear debris was added into the tribosystem, the friction coefficient level dropped drastically while the assembly wear rate rose. In contrast, the modified cast discs provided a reduced wear rate of assembly and a higher and more stable friction coefficient level. These improvements were obtained in a severe condition where higher temperature levels were reached. For the tests with added debris, SEM observations revealed a more intense tribofilm development over the worn surfaces of the clutch friction material. The smoothest cast disc did not damage the developed tribofilms and maintained them more stably due to a reduction in contact area stresses at the highest tribometer test.
Highlights
During the clutch system engagement of an automotive car, sliding contact occurs between a polymeric compound and a metallic counter-face
According to Bahadur [1], when polymeric materials slide against metallic counter-faces, material transfer occurs invariably from polymer to metal, and the counter-face roughness plays an important role both in the transfer process and in the tribofilm development
The higher average coefficient of friction (COF) value achieved in the severe tribometer test condition might be associated with the glass fibers exposures (Figure 5f,h)
Summary
During the clutch system engagement of an automotive car, sliding contact occurs between a polymeric compound and a metallic counter-face. According to Bahadur [1], when polymeric materials slide against metallic counter-faces, material transfer occurs invariably from polymer to metal, and the counter-face roughness plays an important role both in the transfer process and in the tribofilm development. In order to optimize the tribological performance of dry friction materials intended for automotive applications, innovative algorithms have been developed [2,3,4,5]. These algorithms are able to predict the wear properties of polymer-matrix composites. Neither the material transference nor the role that the tribofilm plays on the system performance has been investigated. In order to develop more efficient clutch systems, it has become necessary to achieve better control over their tribological characteristics
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