INFLUENCE OF DESIGN AND OPERATIONAL FACTORS ON THE STABILITY OF THE CAR WITH TRAILER OF CATEGORY O2 DURING BRAKING MODE
Authors: Sakhno Volodymyr , Onyshchuk Vasyl , Stelmashchuk Stanislav 
Published: November 2024

In recent years, enterprises and private manufacturers in Ukraine have mastered the production of a wide range of towed vehicles. Significant attention is given to the issues of road safety for road trains, particularly those of category M1, which have found widespread use not only among state and private enterprises but also among amateur motorists. Ensuring the safety of such road trains is a pressing task.
The movement characteristics of a road train fundamentally differ from those of a single vehicle. This difference is explained by the presence of additional forces in the articulated connections of the vehicle components, as well as the forces and moments acting on its individual components, which influence the movement of the vehicle as a whole. This influence is particularly noticeable during the braking of a road train, which can be accompanied by the folding of components and a loss of vehicle stability. Ensuring the safety of such road trains is a pressing task that requires a more detailed analysis of the impact of the distribution of braking forces on the stability of the road train’s movement. Such research was conducted on a spatial mathematical model of the road train.
To determine the longitudinal and lateral forces acting on the wheels of a road train during braking, the normal reactions of the support surface on the wheels of the vehicle and trailer were determined. These reactions, along with the specific braking forces, determine the braking forces acting on the wheels of the vehicle and trailer. For example, with a deceleration of 6.0 m/s², the normal reaction of the support surface on the twin axle of the trailer decreases by 25%. In the absence of an anti-lock braking system in the trailer’s brake drive, wheel lockup and loss of road train stability are possible. Therefore, it is advisable to brake the road train with decelerations not exceeding 4.0 m/s². In this case, the initial braking speed that ensures the stability of the road train’s movement is higher than its maximum speed. When changing the trailer’s load while the vehicle’s load remains unchanged at a speed of 25 m/s, the road train remains stable throughout the entire range of the trailer’s total mass variation, whereas at a speed of 30 m/s, the critical mass of the trailer remains at 2500 kg. This is explained by the fact that the trailer’s mass affects the magnitude of the maximum braking force created by the braking system and the braking force that can be realized. The loading of the trailer, particularly the side loading of its wheels, is very important as it can lead to uneven braking forces on the trailer’s axles. It is shown that with the nominal loading of the vehicle and trailer, increasing the unevenness of the braking forces on the trailer’s axles up to 30% reduces the initial braking speed, which still ensures the stability of the road train’s movement, by almost half from 35.3 to 19.7 m/s. Therefore, the unevenness of the braking forces on the trailer’s axles should be limited to 15%. This will ensure the stability of the road train’s movement and the safety of its operation.
Keywords: аutomobile, trailer, road train, side and axle load, braking, initial speed, movement stability.