Tribological properties of automotive disc brakes with solid lubricants

In automotive brake systems, high temperatures and pressures are generated at the contacting surfaces. This affects the pad and disc materials, creating a friction film between the surfaces, which consists of wear particles and volatile reactants from the pad and disc. To acquire suitable tribological properties, a pad matrix; contains up to 20 different ingredients, mainly selected from experience. In the present report the effect of solid lubricants has been studied in three different pad matrices with relatively few components as compared to commercial brake pads. The components are Cu2S, PbS and Sb2S3, which are known to modify and stabilise the friction coefficient. The friction coefficient and wear rates of the pads are examined on a dynamometer, which simulates series of real-life car brake events. Two different energy levels and two ambient temperatures are included. After these tests, the brake disc surfaces are analysed with energy dispersive X-ray (EDX) and Auger electron spectroscopy (AES) in combination with argon ion sputtering to study the microscopic lateral and in-depth distribution of elements on and below the surface, looking for traces of the friction film. These experiments are used to discuss the correlation between the tribological properties and the external variables - braking temperature, solid lubricants and pad matrix. (C) 1999 Elsevier Science S.A. All rights reserved.