Abstract
This paper briefly describes some analysis of a car braking process — the peculiarities of car wheel-to-road adhesion, the influence of distiibution of braking forces on car stability between front and rear axles. The requirements of EU Directive 71/320/EEC to braking force coefficients of car front and rear axles are exposed. Structural designs of braking systems are analyzed with respect to their meeting the EU standards. Experimental measurements ofbraking force coefficients for some models of cars which are used in Lithuania, are presented with the analysis how these coefficients meet the EU standards. The analysis of test results, suggestions for the ratio of braking forces of car front and rear axles are presented.
Highlights
The most effective braking can be reached in the case when the longitudinal force coefficient
With the goal ofexamination how the main car braking systems meet the 71/320/EEC Directive the longitudinal force coefficients J..l-!f and J.l.x,. for front and rear axles were measured in 26 cars
The obtained results were used for drawing J.l._if = f(z) and J.l.xr = f(z) for these cars together with the braking efficiency limits ).1~fmax and J..lxrmax for front and rear axles established by the EU standards
Summary
The most effective braking can be reached in the case when the longitudinal force coefficient (braking force coefficient (see section 2) ofthe car front wheel axle equals the coefficient of the rear wheel axle. During the intensive braking higher reliability of wheel locking at first exists for the rear axle, because the braking force coefficient of the rear wheels usually can sooner reach and exceed the value of the wheel-to-road adhesion coefficient in comparison with the braking force coefficient of the front wheels [1] This factor is negative from the point of view of traffic safety - the car becomes unstable. Taking into account the described problems the car must be designed and made so that locking of rear wheels would not occur earlier than that of front wheels during the emergency braking. Most of them do not meet the technical requirements prescribed For these reasons the authors made efforts to study how the parameters of such used cars meet the 71 /320/EEC Directive for ratio of braking forces of front and rear axles. The analysis of the test results and proposals for the improvement of car brake control are presented in the conclusions of this paper
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