Abstract
KEYWORDS – brake energy potential, friction, wear rate, testing, simulation model
ABSTRACT
Braking is a complex stochastic and tribological process characterized by the significant variation of input energy status of a specific tribo-mechanical system whereby energy of motion of vehicle is irrevocably converted into heat and dissipated into the environment. At road vehicles equipped with conventional friction brakes, braking is an extremely unfavorable energy transformation process from energy consumption and recuperation point of view in which energy is irretrievably lost. That is why the question might be raised whether there are any possibilities to manage the brake energy consumption in friction brakes, i.e. would it be possible to manage both work done by the brake and brake wear in order to maximize both the efficiency and life of braking systems and what would be amount of energy that a given brake will transform during its service life? In other words, the question is how big the energy potential of a given brake would be and how to use and/or dissipate it in the best possible manner with no risk to jeopardize achieving of high enough braking performance?
Brake performance evaluation is usually based upon realized deceleration, stopping distance, brake torque and similarly, it does not comprise braking power/energy rate characterization. However, brake performance realization basically depends on “what was available in the brake” i.e. “generic” or initial energy potential/capacity of a given brake and “how this was consumed” under given load conditions and the way brake was used during its service life.
Furthermore, acquiring the quantity of generic energy potential of the given brake one may manage braking process in order to optimize interdependence between brake performance and its service life i.e. wear. Most vehicles are nowadays already equipped with different sensors (speed, application pressure, temperature) and that is why it might be feasible to measure actual value of the brake energy potential in every moment in time of operation. That is how individual brake influencing parameters can be managed simultaneously by means of an appropriate algorithm so as to optimise requested brake performance with the projected brake service life.
Brake energy potential is defined by its performance, service life and friction coefficient stability. It tells us how many braking energy has to be spent before brake lining/pad is reaching its physical wear limit. In order to assess it all influential factors are to be identified and analyzed, and the procedure of doing so is demonstrated in the paper. With this aim, numerous tests were carried out with samples of passenger car disk brakes under laboratory conditions by means of single-ended full-scale inertia dynamometer. Afterwards, results of these tests were used to establish an analytical model which enables us to estimate friction, wear and work done by the brake for a given braking application and the whole service life. Based on the results of experimental and theoretical studies that have been conducted energy potential rate for the given brake may be assessed, and the applied procedure is described in the paper. Finally, the idea for an algorithm of braking management based on the optimization of brake potential is outlined.