Experimental Investigation of Dither Control on Effective Braking Torque
Badertscher, Jeff (Jeffrey William)
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Dither control is a method of introducing high frequency control efforts into a system to suppress a lower frequency disturbance. Dither control is an effective means of suppressing automotive brake squeal. Brake squeal is a problem that has plagued the automotive industry for years. In fact many makers of materials for brake pads spend up to 50% of their engineering budgets on noise, vibration and harshness issues. A normal dither signal may be introduced to an automotive braking system by placing a piezoceramic stack actuator in the piston of a floating caliper brake. Many theoretical models indicate a reduction in the braking torque due to the dither signal. Under the assumption of Hertzian contact stiffness the loss in braking torque is due to lowering of the average normal force. There are also theories that the dither signal eliminates the stick-slip oscillation causing an effective decrease in the friction force. Yet another theory indicates that the effective contact area is reduced, lowering the mean coefficient of friction. It is not apparent whether any of these models accurately portrays the interaction of the brake pads and rotor.