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Experience with wet multiple disc friction devices has shown that observed friction levels are substantially higher than those predicted by theoretical models that successfully predict dynamic friction coefficients in journal bearings. Recent experimental results reported by Granick at the molecular level provide a reasonable explanation for this divergence.

Noise has been an annoyance since man began to use friction as an engineering tool. With the advent of lubricated friction devices, many believed that noise would disappear. However, noise in ail-immersed (or “wet”) friction couples continues to be a constant and difficult problem for designers of clutches, brakes, and other frictional devices. While prediction of fractional noise remains difficult, understanding basic hydrodynamic factors that lead to noise can provide insight into this phenomenon. Factors that affect the hydrodynamic state within the friction couple, such as torque, speed, geometery, lubricant, friction material, and temperature, must be understood and controlled to eliminate noise and vibration in these couples. Field and lab experience may be used to provide empirical guidelines for control and prevention of noise and vibration in wet friction couples.

Oil immersed multiple disk brakes (or “wet” disk brakes) are used in a variety of locations in off-highway drivetrains. As a result, such brakes are required to provide different combinations of torque and sliding velocities with respect to the friction material. Increasingly, the versatility and capability of resilient organic friction materials are making these materials the primary choice for such devices. Such brakes are sensitive to different torque-speed combinations, and design of the brakes must take account of these differences. Whenever the brake design is inadequate, failure may occur in the friction material. In general, avoidance of failure may be achieved through brake design. Also, semi-quantitative analysis of material composition suggests that mode of failure and resistance to failure is related to percentages of major constituents in the material, and the nature of these constituents.