Effects of Altitude and Road Gradients in Boosted Hydraulic Brake Systems

Brake systems are strongly related with safety of vehicles. Therefore a reliable design of the brake system is critical as vehicles operate in a wide range of environmental conditions, fulfilling different security requirements. Particularly, countries with mountainous geography expose vehicles to aggressive variations in altitude and road grade. These variations affect the performance of the brake system. In order to study how these changes affect the brake system, two approaches were considered. The first approach was centered on the development of an analytical model for the longitudinal dynamics of the vehicle during braking maneuvers. This model was developed at system-level, considering the whole vehicle. This allowed the understanding of the relation between the braking force and the altitude and road grade, for different fixed deceleration requirement scenarios. The second approach was focused on the characterization of the vacuum servo operation. This characterization was developed at component-level. An experimental methodology was used for the characterization of the vacuum servo operation under different atmospheric pressure conditions. A relation between the mechanical gain of the vacuum servo and the altitude was found when considering the relation between atmospheric air pressure and altitude. A complete model was obtained by merging the two approaches. As a case study, a given vehicle was considered, taking into account its specific parameters. A mechanical gain for the complete brake system was found. The braking performance of the vehicle as a function of altitude and road grade was assessed.