The braking capacity of reducing the speed or even keeping the vehicle stoped is extremely important in the design of any brake system, as more than meeting legislation requirements; it directly affects the safe operation of the vehicle and its users. A fundamental component, which requires notable attention, is the friction material, which is designed to establish a compromise between mechanical properties, friction coefficient, noise propensity, deformation, wear, among others. However, braking capacity is a combined response for several of these friction material properties, along with the performance of other brake system components, such as the brake chamber, disc and caliper. This work aims to analyze firstly the influence of the friction material deformation and secondly the brake system deformation on the total stroke of the brake chamber. To the first one, three different formulations of friction material, applied to commercial vehicles, were selected. For these materials, compressibility measurements were performed, according to ISO 6310, and also subjected to static test for measuring the total stroke of the brake chamber, in an inertial dynamometer. The static test performed consists of a pressure ramp application on the brake pad with the measurement of the total chamber stroke for each of the pressures. To the second one, static test was performed using steel pads (copying the brake pad shape), with thickness simulating new and end-of-life pads. The friction material and the brake system showed a significant pressure sensitivity, with a small contribution at low pressures, increasing its contribution with pressure increase. More than it, this work allowed to understand that the formulation, pad compressibility, material thickness, brake system stiffness, temperature and chamfered pads show a significant influence on the performance, fuel consumption and reduction of pollutants), there are also improvements to be made on braking performance and reduction of early wear. These improvements must also be applied to commercial vehicles such as trucks and buses, where the brake system is subjected to heavy loads and long routes. For this type of vehicle is very important to obtain maximum brake pad durability, in order to reach customer satisfaction.
For commercial vehicles, the use of disc brakes has been increasing gradually, once it is already widely applied in Europe and there is a gradual growth in North American and Asian markets. Brazil tends to follow the same path as Europe, only slower, due to drum brakes costs, which are much lower than disc brake costs. Disc brake system has greater advantages compared to the drum brake system, such as: higher braking efficiency, even on higher application temperatures; greater dissipative energy capacity during braking and, finally, greater comfort during brake pedal actuation [2].
Pedal force and displacement are important factors for the driver to modulate, regarding safety and braking efficiency. It shows that soft pedal feeling is not only unsafe due to lack of vehicle control and accidental brake lock, but can also generate longer stopping distances [3].
Technically, the term known as Pedal Sensitivity means the relationship between the force applied to the pedal, the pedal travel and the deceleration achieved by the vehicle. Normally, the vehicle's brake capacity is evaluated on a field test, considering different conditions of deceleration, force and chamber stroke.