A Coupled, Multi-Physics Model of the Automotive Brake System with Focus on Dynamic Torque Prediction
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Date
2009-12
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Publisher
The Ohio State University
Abstract
High speed brake judder is one of the common vibration problems in the automotive industry. Judder has been described as an unacceptable vibration/shake experienced in the vehicle when the brakes are applied. This vibration is generally felt at the steering wheel, seat track, and brake pedal. In severe cases, vibration of the entire chassis has been observed. The phenomenon generally occurs if the vehicle is traveling above a threshold speed (roughly 60 mph); the corresponding maximum vibration level occurs at or around 14 Hz.
The fundamental source of the judder problem is the disc-caliper brake system, specifically the brake torque variations T(t) (BTV) and brake pressure variations P(t) (BPV) occurring within the brake system. Disc thickness variation y(t) (DTV) is attributed as the primary source of T(t) in the mechanical system, but it is possible that the dynamic torque acting structurally on the hydraulic system (or the hydraulic system dynamics in general) introduces an additional contribution or feedback to the T(t) level. The purpose of this research was thus to formulate a coupled mechanical and hydraulic multi-physics disc-caliper brake system model, predict the dynamic torque history T(t), and investigate parameter sensitivity with regards to y(t) and T(t).
A new multi-physics software AMESim Image.Lab (by LMSĀ©) is used to formulate the coupled mechanical and hydraulic system model. Using this dynamic model and a three tier sensitivity analysis of the system parameters, several fundamental questions are posed, investigated, and answered. It is demonstrated that a resonance around 20 Hz exists in the system, that a larger y(t) amplitude induces higher brake torque variations, and that run out creates %60 as much T(t) as y(t) does. Results show that there is a mechanical and hydraulic coupling acting on the 2nd mode (about 20 Hz) of the system, and that the addition of an accumulator into the hydraulic system could possibly reduce the dynamic torque levels.
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Keywords
Brake Modeling, Brake Judder