Thermal/Mechanical Measurement and Modeling of Bicycle Disc Brakes

Abstract

Brake induced heating has become more difficult to control as bicycle component mass has been reduced. High-power braking with insufficient cooling or thermal capacitance can create excessive temperatures, boiling brake fluid, performance degradation, and damage. To better understand component heating, a disc braking dynamometer has been constructed with a motor driven disc, hydraulic braking, and a miniature wind tunnel. Disc temperatures are studied for various braking scenarios using infrared techniques and thermocouples. A transient, numerical, MATLAB, lumped parameter thermal/mechanical model is created to predict the impact of key design parameters on braking performance and to understand the heat loss mechanisms from the brake system components. Computational fluid dynamics (CFD) simulations are used to estimate the disc surface convective cooling coefficients for the model. The final model provides transient temperature predictions based on bicycle velocity and braking power, and successfully matches dynamometer experimental data.

Bicycle Disc Brake Thermal Performance: Combining Dynamometer Tests, Bicycle Experiments, and Modeling

“…The temperature match independently validates the friction data curve fits obtained on the dynamometer in this work. Additionally, the agreement of the model temperature to the experimental temperature validates the thermal modeling process described in prior work [1], but now for field conditions. The thermal model predicts that the majority of heat dissipation is from the brake disk surfaces, followed next by the disc spokes (connecting the disc to the hub), and then followed by the brake pads and caliper.…”

“…An example outdoor test, and numerical model thermal prediction is provided for the power organic pads. Prior work [1] only validated the thermal model using the dynamometer, but presented no friction data or model comparison to field tests.…”

“…A previously documented brake dynamometer [1] has been upgraded to include a larger geared electric motor, a brake line pressure transducer, and the ability to convectively heat the brake disc. The updated experimental setup is shown in Figure 1.…”

“…A previously documented transient MATLAB thermal model [1] for bicycle braking was enhanced to include the ability to import braking power data from the outdoor bicycle brake tests (see Section 2.2). The MATLAB thermal model requires brake thermal parameters (convective coefficients, disc geometry) and transient brake power data.…”

“…It outputs a prediction of bicycle disc temperature and the relative contribution of the disc, disc spokes, and brake pad heat rejection capability. Convective coefficients and methods for accounting for disc geometry and heat transfer modeling between components were already derived and presented in the prior work [1]. The disc convective coefficients from the prior work are used here with a modification to account for air density using a Reynolds number to the 4/5th power dependence.…”