Braking Impact of Normal Dither Signals

Abstract

Dither control is a method of introducing high-frequency control efforts into a system to suppress a lower-frequency disturbance. One application of dither control is the suppression of automotive brake squeal. Brake squeal is a problem that has plagued the automotive industry for years. Placing a piezoceramic stack actuator in the piston of a floating caliper brake creates an experimental normal dither system. Many theoretical models indicate a reduction in the braking torque due to the normal dither signal. Using a Hertzian contact stiffness model, the loss in friction is due to lowering 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. A particular approach considering a single-degree-of-freedom friction oscillator predicts a maximum friction reduction of 10%, occurring at the primary resonance of the system. This paper will concentrate on validating this claim by experimentally determining braking torque reduction for a variety of dither control signals. Several dither control frequencies were chosen at system resonances, while others were chosen at frequencies most likely to provide control of the system. These frequencies were chosen based on previous squeal suppression research. The results indicate that dither control frequencies at system resonances have a greater impact on the braking system’s performance. In general, dither control reduces braking torque by no more than 2%.

Dynamics and bifurcations of nonsmooth systems: A survey

“…a second-order differential equation involving a sign function. The time periods that stable regimes spend sticking to the switching manifold appear to be in direct relation to the break squeal level, see Badertscher-Cunefare-Ferri [20] and Ibrahim [177]. Studying grazing bifurcations in dry friction oscillators is a possible way to understand the properties of such sticking phases.…”

“…A significant growth in the subject has been due to the understanding that nonsmooth systems display a wealth of complex dynamical phenomena, that must not be disregarded in applications. Some applications that illustrate the relevance of nonsmooth dynamics include the squealing noise in car brakes [20,177] (linked to regimes that stick to the switching manifold determined by the discontinuous dry friction characteristics), loss of image quality in atomic force microscopy [357,382,263,293] (caused by new transitions that an oscillator can undergo under perturbations when it just touches an elastic obstacle), and, on a more microscopic scale, the absense of a thermal equilibrium in gases modelled by scattering billiards [360,197,198] (whose ergodicity can be broken by a small perturbation as soon as the unperturbed system possesses a closed orbit that touches the boundary of the billiard).…”

Characterisation of friction reduction with tangential ultrasonic vibrations using a SDOF model

“…Superposition of high-frequency vibrations on low-frequency disturbances or dither control has been proposed for suppressing squeal in automotive brakes (Cunefare and Graf, 2002;Badertscher et al, 2007;Hagerdorn et al, 2005;Jearsiripongkul and Hochnelert, 2006;Hagedorn and von Wagner, 2004). Active or smart pads have been developed (Michaux et al, 2007) which include embedded piezoelectric elements between the brake pad material and the metallic backing plate to generate a normal harmonic force.…”