Design of Vehicle Road Testing Method for Determination of Brake Pad Friction Characteristics

Abstract

Friction material of brake pads is one of the most important elements of the brake because it has great influence on performance of basic tasks of braking. The following friction material properties are generally desirable: high, stable and predictable static and dynamic coefficient of friction, minimum wear characteristics combined with frictional properties that inhibit counter surface wear, adequate corrosion resistance, absence of vibration and squeal noise, acceptable costs of raw materials, processing and manufacturing technologies. Testing of material friction characteristics demands delicate procedure, because their features can not be estimated based on their chemical structure, configuration but exclusively based on experimental methods. There are two basic ways for testing of friction properties: within the brake itself or on samples, i.e. friction materials test tubes. Frequently, laboratory tests of friction characteristics are not enough, but it is necessary to subject friction materials to a series of vehicle tests on a test track or on the road before they are released as commercial products. Analysis of brake pad friction characteristic obtained by the road testing of vehicle is presented in this paper. The influence of variations of pressure in brake cylinder and vehicle speed on friction coefficient during tests is analyzed. Also, variation of friction coefficient during braking is monitored, starting with the assumption of cosine distribution of surface pressure along the brake pad.