Braking Impact of Normal Dither Signals

[+] Author and Article Information
Jeff Badertscher

 Georgia Institute of Technology, 771 Ferst Drive, Love Building, Room 205, Atlanta, GA 30332gtg437d@prism.gatech.edu

Kenneth A. Cunefare

 Georgia Institute of Technology, 771 Ferst Drive, Love Building, Room 113, Atlanta, GA 30332ken.cunefare@me.gatech.edu

Aldo A. Ferri

 Georgia Institute of Technology, 771 Ferst Drive, Love Building, Room 107, Atlanta, GA 30332al.ferri@me.gatech.edu

J. Vib. Acoust 129(1), 17-23 (May 19, 2006) (7 pages) doi:10.1115/1.2346689 History: Received August 22, 2005; Revised May 19, 2006

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%.

Copyright © 2007 by American Society of Mechanical Engineers
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Figure 1

Single-degree-of-freedom friction oscillator

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Figure 2

Time response with and without normal dither signal

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Figure 3

Single-degree-of-freedom model using a Hertzian contact stiffness

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Figure 4

Average friction for varying system mass

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Figure 5

Dither control actuator

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Figure 6

Brake dynamometer

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Figure 7

Pre-load capable PZT dither actuator

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Figure 8

Numbered circles indicate data acquisition locations for transfer function measurements

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Figure 9

Static transfer function, selected dither frequencies: 4.6, 6.3, 12, and 25.6kHz

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Figure 10

Dynamic transfer function, selected dither frequencies: 2.9, 4.5, 11.3 18.66, and 24.5kHz

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Figure 11

Raw percent difference in braking torque: ◻is T1, 엯 is T2, ▵ is Temp

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Figure 12

Raw percent difference in brake line pressure ◻: is T1, 엯 is T2, ▵ is Temp

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Figure 13

Final percent change in braking torque:엯 is T1, ◻ is T2

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Figure 14

Comparison of torque impact of excitation at static vs dynamic peak response frequencies: 엯 Static (Ave −0.60%), ◻ Dynamic (Ave −1.97%)




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