About the project

The use of forestry machinery in modern wood harvesting technologies involves some risk to the health of the operator and damage to the forest ecosystem in terms of soil compaction, erosion, damage to trees and root systems, air, soil, water resources pollution, etc. On the other hand, forestry machinery has to do heavy work and meet the demands for higher productivity while reducing operating costs. This applies primarily to forest vehicles moving on forest soil.
The skidder is, according to ISO 6814:2000 norm, defined as a self-propelled, articulated forest vehicle for skidding trees or parts of trees. The skidding is the removal of entire trees or parts of the tree (trunk, wood assortment) from the felling and processing site to the roadside landing. Due to the necessary technical requirements for performing the skidding operations in forest terrain, the skidder uses a forestry winch to skid parts of the trees from the felling and processing site to the skid road, and then, when traveling along the skid road, one end of the load is lifted off the ground and rested on the rear end of the vehicle while the other end of the load is dragged on the ground. Due to the use of winches in the skidding process, the skidder is mainly driven on the skid roads, which significantly reduces damage to forest soil and young trees.

There are increasing demands in terms of reducing the cost of running forest machines, together with regulatory pressures for lower emissions of exhaust gases and noise, which calls into question the future of a skidder that uses a diesel engine as its sole power source. Therefore, forestry machinery manufacturers are interested in the electrification of the propulsion, which can already be seen with the appearance of certain hybrid and electric forest vehicles (e.g. forwarders and harvesters), but for the time being, such propulsions are not present in the skidder. The hybrid drive, which is thought to be a solution that can meet the requirements for low exhaust emissions, can use a smaller diesel engine, with an additional power source (e.g. battery) allowing it to operate in a more favorable mode, while retaining high drive performance over fully electric drive, extended autonomy, and less energy storage requirements, resulting in lower mass and total cost.

The future development of electrified forest vehicles is a very important topic of scientific research in the field of forestry engineering. It is a prerequisite for the precise determination of the energy consumption of different types of forest vehicles at different work tasks and under different terrain conditions. For this purpose, it is necessary to carry out field measurements on existing vehicles, and then to carry out an adequate analysis of the collected data, which is, after processing, used as a basis for the development of hybrid and electric forest vehicles. The parameterization and verification of the mathematical models of the skidder’s drive are achieved on the basis of the processed measured data. Using mathematical drive models with defined working cycles obtained by measurement, the structure of the hybrid drive and the dimensions of the hybrid drive elements (internal combustion engine, electric motor, batteries…) are determined using modern optimization methods which, as a result, give the optimal hybrid drive of the skidder for the selected working cycles (e.g. for hilly or mountainous terrain, or for universal use). For the optimal operation of each drive component, an optimal control strategy for the proposed hybrid drive is designed.

For the optimal operation of each drive component, an optimal control strategy for the proposed hybrid drive is designed. The aforementioned forest winch is an important element in the operation of the skidder and is a significant energy consumer. Existing skidders use hydraulic or mechanical winch drive. The hybrid winch drive is designed to use an electric or electro-hydraulic winch for greater energy-saving potential due to a better degree of efficiency and greater control over its operation. The project envisages the development of an experimental setup of an electro-hydraulic winch in order to produce a precise mathematical model intended to select a suitable winch drive that will fit into the hybrid drive of the skidder and to design the operation of such a winch.
Finally, the goal of the project is to offer a conceptual design of a hybrid skidder that will be the basis for a prototype that can be further marketed as an innovative product of high added value. The hybrid skidder is a step up from the current state of the market, where only conventional-powered skidders are offered. In addition to the innovative skidder solution, other project goals are also being achieved like increasing the market-oriented activities of scientific organizations and strengthening the model of technology transfer to the business sector.

Some outcomes of project elements, such as the results of measuring and analyzing data of real working cycles in different terrains, a mathematical model of conventional and hybrid skidder propulsion, and management of hybrid skidder and winch are results that will be applicable to related areas and will have a scientific value.