The necessity of increasing the efficiency of logging road trains by reducing the transport costs spent on hauling timber in existing road and climatic conditions is substantiated. A review of scientific research by foreign scientists is presented, which made it possible to identify the most significant factors influencing transportation costs. A promising design of a recuperative pneumohydraulic fifth wheel coupling device has been proposed, which makes it possible to reduce transportation costs by reducing the amount of fuel used by a road train, to increase the reliability of a logging road train by reducing the dynamic loads that occur between its links when driving over uneven surfaces of a logging road. The mathematical model of the movement of a timber tractor with a semi-trailer equipped with the proposed coupling device, under conditions of frequent accelerations and decelerations, over the unevenness of the logging road has been improved, which makes it possible to perform a preliminary assessment of the energy recovery by the proposed device in various modes of transient processes, as well as to investigate the influence of the main parameters of the recuperative pneumohydraulic fifth wheel coupling device for performance indicators. Two computer programs have been developed to study the performance indicators of a recuperative pneumohydraulic fifth wheel coupling under various transient modes of movement of a logging road train with given parameters of roughness of a logging road. It has been established that the use of the proposed coupling device in a logging road train makes it possible, when driving with randomly repeated decelerations and accelerations, to regenerate power up to 6.5 kW, and also to achieve a value of longitudinal acceleration of the semi-trailer relative to the tractor of 0.72 m/s2. Computer modeling made it possible to establish the value of the optimal diameter of the hydraulic cylinder, which provides the highest value of recuperated power at the lowest value of the acceleration of the semi-trailer relative to the tractor.

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The place and importance of the use of timber trucks among all types of timber transport involved in the process of removing timber from the felling site to consumers is described. The main advantages and disadvantages of using a timber tractor with a dismantling trailer for transportation of long timber while driving on insufficiently equipped timber roads are considered. The most significant drawback is revealed, which consists in the structural imperfection of the conical structure of the timber tractor. A promising design of a recuperative conic device of a timber road train is proposed. It describes its main advantages from installation on a timber tractor with a dismantling trailer, as well as the effect of such a design of a bent device on the operating efficiency of a timber road train.

The importance of using timber road transport in the technological process of harvesting and hauling timber has been substantiated. The influence of the design flaws of fifth-wheel couplings on the safety indicators of the road train, its stability, productivity, and fuel consumption, which are manifested during the operation of timber tractors with semitrailers, has been revealed. The work of foreign authors aimed at improving the efficiency of using fifth-wheel couplings used in the designs of tractors with saddle trailer has been considered. The advantages of using the proposed recuperative spring-hydraulic fifth-wheel coupling device in a timber lorry train have been described. They consist in ensuring a simultaneous increase in the reliability of road train, recuperating energy of the working fluid, reducing the magnitude of dynamic loads, as well as ensuring favorable working conditions for the driver. On the basis of the developed mathematical and simulation functioning models of a timber tractor with a saddle trailer equipped with the proposed design of a recuperative spring-hydraulic fifth wheel coupling, computer experiments have been carried out, which made it possible to obtain the dependence of the influence of the inner diameter of the hydraulic cylinder, the stiffness of the springs used in the recuperative spring-hydraulic fifth wheel coupling on the longitudinal acceleration of the semitrailer and the average value of the recovered power. It was revealed that the optimal spring stiffness of the recuperative spring-hydraulic fifth wheel coupling, which is in the range from 150 to 200 kN/m, makes it possible to achieve the value of the average recovered power in the range from 7 to 8.4 kW

The necessity of increasing the efficiency of timber trucks by improving the designs of their suspensions has been substantiated. The main disadvantages of traditional suspension structures used in modern logging trucks have been described. A promising design of a modular independent tubular torsion bar suspension for a logging truck has been proposed. The aim of the research consisted of two stages. At the first stage, a mathematical model for the functioning of the proposed torsion bar suspension has been developed. At the second stage, a computer program for a preliminary assessment of the effectiveness of the functioning of this suspension (when driving on an insufficiently equipped forest road) has been made. Time dependences of the angular positions of suspension arm fork and ends of the tubular torsion bars were obtained. The regularities of the influence of the movement speed, average height of irregularities, coefficient of dry friction on the relative spread of vertical loads and suspension indicators of vibration dispersions were revealed.