Abstract.Today, road-trains are one of the most widely-spread and multitonnage transport vehicles on road arteries interconnecting countries and cities. The concept of hybrid road-trains mostly meets the widely-spread policy for stepping up the rates of exhaust gas emissions and reducing specific hydrocarbon fuel costs but only an intermediate link in the development of more significant and important design -a driverless roadtrain. This article considers active trailers and their models with different design options for heavy tractor truck propulsion unit drive. The influence of trailer link drive on turning has been studied in "Universal gear" software. Special attention has been given to an electrical drive of active semi-trailer wheels as the most advanced one at the present moment. We have obtained the data intended to be used in design of active trailer chassis and identified the weight and size characteristics of energy accumulators required for movement of a road-train with active trailer. The efficiency factor for different semitrailer drives has been analyzed and calculated, in particular: Low EF of electrical drive. The relevancy of active trailer concept including that for driverless road-trains has been determined on the basis of received data.

The paper considers a digital model of a wheeled agricultural tractor, as well as algorithms for automatic control of the engine and transmission. Simulation of the working conditions was performed in MATLAB and its applications, Simulink, Sim-scape. The tractor model is based on a systemic approach and includes such subsystems as the engine, transmission, undercarriage, hook load, and control actions from the operator, as well as functions of logic and optimisation for gear shifting. With the help of fundamental blocks of the Matlab package, models of tractor physical components are created. The fundamental blocks of the package serve to model the physical components of the tractor: engine, transmission control system, the transmission that includes friction clutches, gears, shafts ties with the necessary characteristics. Simulation of the working processes of a tractor unit is performed with optimisation of the laws of engine and transmission control according to the criterion of fuel efficiency and maximum power usage. The control system parameters were optimised in the transport mode, as well as in the maximum power mode in the traction range. As an illustration of the use of this analysis method, a solution to the problem of optimisation of an agricultural wheeled tractor operating modes is given. The results of this mathematical simulation are presented in this paper. Parameters of tractor operation control algorithm, which provide minimum fuel consumption in tractor operating cycles, are given. The research results showed the effectiveness of the proposed algorithms and the digital model. The presented digital model allows to debug the operating tractor control algorithms and offers an engineering practice for optimising automatic control of the agricultural tractor engine and transmission.