Analysis of the Braking Process of a Vehicle with an O2-Category Trailer

Abstract

The paper considers the emergency braking of a vehicle combination consisting of a towing vehicle and an O2-category trailer with regard to directional stability. It is shown that the widely used constant distribution of the total braking force between the axles of the road train does not ensure braking efficiency and may cause premature wheel lock on individual axles. The object is the vehicle–trailer road train in braking mode; the aim is to develop a planar mathematical model for determining normal reactions on the wheels, forces in the coupling and the conditions for simultaneous approach of all wheels to the lock limit.

The model is based on equilibrium equations of forces and moments for the towing vehicle and the trailer, taking into account braking-force distribution coefficients, coordinates of centers of mass, dynamic tyre radii and the height of the coupling point. Analytical expressions are derived for normal reactions on all axles and for vertical and horizontal reactions in the coupling, which makes it possible to evaluate redistribution of axle loads during deceleration.

It has been established that the braking force acting on the trailer axles causes a more intensive change of reactions on the wheels of the rear axle of the towing vehicle than on the front axle, which reduces the adhesion coefficient at which the rear wheels lock. Conditions for simultaneous attainment of the lock limit by all wheels of the combination have been obtained, as well as the optimum share of the total braking force that should be assigned to the trailer axles. The proposed model can be used when choosing mass and braking-system parameters of vehicles with O2-category trailers to ensure stable and efficient braking without anti-lock systems.

Keywords: vehicle combination; towing vehicle; O2-category trailer; emergency braking; distribution of braking forces; normal reactions; coupling device; adhesion coefficient; wheel lock; mathematical model.