Abstract
Keywords - brake, judder, disc, DTV, casting
Brake judder is one of the most serious problems in automotive-brake systems. It has not been eradicated despite all the efforts that many researchers and engineers have made to reduce it by studying its causes and mechanisms. Brake discs play a significant role in judder. We therefore pursued the development of homogeneous brake discs to reduce judder from various viewpoints in terms of both product and process engineering. We focused on three specific approaches:
- Precise and accurate machining,
- A design strategy for less thermal coning with an outer-hat disc configuration, and
- An integrated process for improving material homogeneity to reduce on-brake DTV growth.
The first approach is precise and accurate machining. The higher geometric accuracy of finished brake discs reduces the off-brake growth of disc thickness variations (DTV) and resulting cold judder. We achieved 20 m in lateral runout (LRO) and 10 m in DTV or even greater precision by using turning operations alone. With an additional grinding operation to correct the geometric dimensions of friction plates, we obtained a higher accuracy of 5 m in DTV.
The second approach is a design strategy to reduce thermal coning. We carried out a series of computer-aided engineering (CAE) experiments based on Taguchi methods with the assistance of our original brake-disc-design system. We determined the critical parameters for reducing thermal coning and proposed a strategy for designing outer-hat brake discs with less coning. Thermal coning and resulting hot judder have been reduced in discs designed with this strategy.
The third approach is improved material homogeneity to reduce on-brake DTV growth and resultant judder. We studied the relationship between DTV and casting-material properties and clarified that the circumferential homogeneity of brake discs had significant effects on brake judder. As a solution to this, we established an integrated system for developing and manufacturing discs with material homogeneity to reduce judder. This system consists of three elements: foundry engineering to obtain material homogeneity, an original flake graphite structure index (K-FGI) to measure disc homogeneity, and an accelerated wear test on a brake dynamometer to estimate the potentials of on-brake DTV growth.
By integrating these approaches from R&D through manufacturing as described above, we have provided homogeneous and robust brake discs to reduce judder.