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Brake pad compressibility is a parameter which is commonly utilized within the braking industry for design and production considerations. With a number of procedures relying on the accurate measurement of this metric, Greening Testing Laboratories, Inc. undertook to examine the extent to which different intrinsic or extrinsic factors may affect these measurements. This paper is a status update on continuing efforts by our laboratory in this area, first reported in early 2022. The primary goal of this study was to measure how brake pad compressibility changed as a function of the environmental humidity in which they were stored in prior to testing, due to the absorption of moisture. To properly evaluate these deviations, it was also necessary to evaluate and compensate for how compressibility values may change over the course of repeated testing due to material characteristics alone - a parameter which may be of significance in its own right.

The wet clutch system (WCS) is a complex combination of friction plates, separator plates and fluid (lubricant). The basic function of the WCS is to transfer torque under various operating conditions such as slipping, shifting, start/launch and/or torque converter clutch (TCC) operation. Under these conditions the slope of the coefficient of friction (μ or COF) versus slip speed (μ-v) curve must be positive to prevent shudder of the WCS, a highly undesirable condition in the lubricated friction system. An extended durability duty cycle test procedure is required to evaluate the WCS during which the μ-v curve is monitored for a negative slope, a condition indicating the potential for shudder. The friction plates, separator plates, and lubricant must be tested together and remain together during the test to be properly evaluated as a WCS.

The brake caliper piston plays a key role in caliper function, taking significant responsibility for qualities such as fluid consumption, insulation of the brake fluid from heat, seal rollback function, and brake torque variation sensitivity to disc thickness variation. It operates in a strenuous environment, being routinely subjected to high stresses and elevated temperatures. Given all of the demands on this safety-critical component (strength, stiffness, wear resistance, stable friction against rubber, thermal stability, machinability, manageable thermal conductivity, and more), there are actually relatively few engineering materials suitable for use as a caliper piston, and designs tend to be limited to steel, aluminum, and engineered plastics (phenolic composites). The lattermost - phenolic composites - has been of especial interest recently due to mass savings and possible reduction in brake corner judder sensitivity to disc thickness variation.

Mountainous routes provide a challenge to foundation brakes in both fade and wear attributes. Brake dynamometers test programs are employed to emulate different overland routes. These programs are often created from time-based recordings of vehicle data and do not incorporate the topography of the route. Greening Testing Laboratories, Inc. has developed a new technique to incorporate elevation profiles and defined “rules” to create dynamometer simulation programs for various vehicle test routes, including those that contain significant grade changes. The introduction of distance-based rules is advantageous because it allows the creation of a dynamometer control program based upon mathematical inputs, therefore eliminating the need for an instrumented vehicle run prior to developing a dynamometer simulation for that route.