Disc brakes for heavy vehicles: an experimental study of temperatures and cracks

Abstract

A better understanding of the thermomechanical loading of brake discs is important for controlling material fatigue and crack propagation in the disc. In the present study, full-scale drag braking experiments were performed on brake discs made from eight different grey cast iron alloys. The well-performing materials were also tested with an alternative brake pad material. A testing procedure with repeated drag brakings was used. The disc and pad temperatures were registered by thermocouples embedded at selected locations, and the disc surface temperatures by a thermocamera. Extensive analyses of the measured temperatures were performed. The results for the thermocouples at the mid-radius of the disc and at the end of brake applications indicatd that the two sides of the disc have opposite deviations from the mean temperature. The temperature deviations are generally temporally alternating, but also stationary variations can be found. The thermocamera gives the possibility of identifying the phenomena behind the temperature variations found from the thermocouples. Banding of the disc-pads contact with alternating one band and two bands of high temperatures is observed for the studied brake discs exposed to severe braking load cases. Moreover, it was found that hot-spot patterns develop on the disc surface, which are spatially fixed during each brake application. However, they may be either slowly migrating or fixed relative to the disc during consecutive brake applications. Thermal images show that small cracks do not affect hot-spot migration as a hot spot migrates over the crack. However, at a critical length of the crack, the heat becomes localized at the crack and increases its growth, thus limiting the life of the disc. The tests indicate that a combination of hot-spot migration, alternating bands and small temperature differences over the disc are significant factors to be considered when improving the lifespan of the discs.

A coupled approach for vehicle brake cooling performance simulations

“…point 2 and point 4 in Figure 9) can easily vary by more than 100 degrees. Moreover, since higher local temperatures lead to increased thermal expansion and increased wear, these hot spots move with every new load cycle [21]. Figure 10 presents the comparison of brake disc temperatures for the outer radius of the disc from the finger side.…”

Design of a filling ratio observer for a hydraulic retarder: An analysis of vehicle thermal management and dynamic braking system

“…The braking power is then changed abruptly. The temperature increase of coolant circulation is also changed abruptly, as expressed in equation (1). Figure 7(e) shows the speed error when constantspeed driving is activated in 30 s. The result shows that the observer in this study could help the hydraulic control system produce the required braking torque and satisfy the braking requirements of the vehicle.…”

“…Hydraulic retarders (HRs) are auxiliary braking devices of vehicles that can reduce vehicle speed by converting the kinetic energy of vehicle to thermal energy of working fluid. 1,2 Instead of service braking, HR can be used to regulate vehicle speed effectively under nonemergency braking conditions. Compared with other auxiliary braking devices, HR has the advantages of high braking power, durable efficiency, and zero pollution.…”

Aerodynamic and Thermal Modelling of Disc Brakes—Challenges and Limitations

“…Therefore, if some uneven pressure distribution arises at the friction surface, the areas where the pressure is higher experience a higher temperature increase. This, in turn, causes greater local thermal expansion and, thereby, leads to further local pressure increase [29]. Hot-spot positions change with every new load cycle; therefore, measuring the disc temperatures with embedded thermocouples can have serious repeatability issues even when testing in the wind tunnel.…”