Estimating the air volume washing the friction pairs of the drum brake mechanism during forced cooling

The aim was to determine the volume of air washing the heated surfaces of friction pairs in automobile drum-pad brake devices, which represent a closed-type friction unit, during forced cooling. The research object was a standard automobile drum-pad brake device of a closed type. Simulation experiments were performed using the main hydraulic dependencies accounting for local and linear losses. The Microsoft Excel package and mathematical statistics methods were used to analyze forced cooling of the standard friction unit under study. The air volume and flow passing between the gap of the working friction pairs of the drum-pad brake were accepted as criteria. A cooling model was developed, taking into account local aerodynamic (resistance at the entrance and exit from the brake mechanism cavity) and linear losses (friction, heating, and eddy formation). The developed model showed that, under forced cooling in the temperature range from 65 to 300°C (1st regime), the airflow rate varied from 0.0000086 to 0.000021 m³/s. At the same time, under forced cooling and a constant temperature range (2nd regime), the airflow rate increased by 63.7%. When increasing the input and output holes in the cavity of the brake mechanism from 0.0025 to 0.005 m and from 0.005 to 0.01 m, respectively, the air consumption under the 1st regime increased by 14%, and under the 2nd regime - by 22%. To implement the 2nd regime, a design was proposed for a forced cooling system built in in a drum-pad brake device, which allows the cooled air to be delivered directly into the gap between the friction pairs, bypassing the drum-pad brake shield. The developed model provides a quantitative assessment of the cooling efficiency of the friction unit of a drum-pad brake device depending on changes in the design parameters (the diameter of the input and output holes in the brake mechanism cavity, the internal diameter of the brake drum, the gap between the working surfaces of the friction unit), thus facilitating the development of new friction units.

volume, air flow rate, thermal boundary layer, vortex formation, forced cooling