Abstract
Typical constructive solutions of drum brake mechanisms for motor vehicles are presented in this paper. It's been emphasized that calculation methods and investigation of those mechanisms are given in numerous published papers. However, based on conducted analysis, it's been proven that there is no general accepted method for evaluation of characteristics and output parameters of drum brake mechanisms. Intensive development of computer technique, numeric methods and measurement techniques gives a significant contribution in that sense. In the case of analytical methods, problem of defining the input parameters, i.e. the forming the function of pressure distribution on friction linings of brake shoes is solved by assuming the form of pressure changes (in the literature, the most common form is cosine). In most cases, determination of position of the greatest wear of linings has shown agreement with this assumption. Drum brake subsystem with the input-pressure of brake fluid in the brake cylinder and output-brake torque is presented in the paper. The obtained results showed that a time delay (»0.1 s) between the output and input exist, due to a response of a drum brake mechanism. This points out to the deficiency of determining performance of brake in time domain, because, in comparison, there are no adequate excitations and response of the system. Hence, dynamic mode is observed in the analysis of drum brake subsystem. Dynamic analysis determines behaviour of a system in the transitional period, which comprises the process of transition of the system from one steady state to another steady state. Mathematical model that describes the dynamic components of the system in dynamic mode takes into account the time variations in input and output values. Analysis of the dynamic behaviour of the system is done in time and frequency domain. Transfer and frequency characteristics contain all important information about the behaviour observed in the frequency domain as follows: the input gain and attenuation effects, the phase positions and so on. With pre-known transfer characteristics of a system, response in relation to the specified inputs (excitations) may be determined, which is a good basis for determination of correlation between the results obtained by different methods of identification and under different test conditions. According to a given algorithm, complex characteristics of different solutions of brake mechanisms are formed, effectiveness and stability parameters are determined and, in that way, a reliable base for their categorization and selection has been created.
Keywords: Drum Brakes, Experimental Research, Mechanical Characteristics, Data Processing