Evaluation of the influence of brake mechanisms characteristics stability on the braking vehicles process

Abstract

The purpose of the article is to evaluate the influence of the stability of the characteristics of brake mechanisms on the process of braking of passenger vehicles. In the article, using the example of a mixed braking system of a passenger vehicle of segment C, an assessment was made of the influence of the stability of the characteristics of its braking mechanisms on the braking process. The results obtained allow us to conclude that with "cold" and "cooled" brake mechanisms of the vehicle, the values of the mathematical expectation of the friction coefficient and the dispersion of its values are approximately the same. The performed calculation shows that when the friction coefficient changes by 8-20%, the braking torque changes by 20-30%. In this case, the difference between the largest and smallest braking torque can be 50%. Given that the left and right brake mechanisms (due to various reasons) may have different coefficients of friction of the friction surfaces, then the unevenness of the braking forces on the rear axle of the vehicle under consideration can be up to 50%. In order to prevent advanced blocking of the rear wheels during vehicle braking in the event that the actual coefficient of distribution of braking forces between the axles deviates from the calculated value due to the instability of the brake mechanisms, it is necessary to ensure the fulfillment of the condition according to the dependence given in the work. The results obtained can be used in the design of braking systems and the assessment of the braking properties of vehicles, as well as in the examination of road accidents.
The instability of the braking torques on the wheels does not have a significant effect on the reduction of the total braking force (braking efficiency) in the presence of amplifiers in the drive, but it significantly affects the stability of the vehicle during braking, since it causes a significant change in the coefficient of distribution of braking forces between the axles and the appearance of their onboard unevenness. The statistical analysis of the coefficients of friction of friction pairs (on the example of a passenger vehicle of segment C) showed their wide spread, which significantly affects the onboard and axial unevenness of the braking forces; for example, for friction linings DTM, the average difference between the friction coefficients on the left and right wheels is 0.17, and the standard deviation is ± 0.08. The difference in the coefficients of friction of friction pairs of different types of brake mechanisms, due to the use of friction linings from different manufacturers, can lead to a change in the coefficient of distribution of brake forces over a wide range.