Improvement of the traction calculation methodology for the electric drive design of hybrid agricultural modular platforms

RELEVANCE of this study stems from the methodological gap between the agrotechnical requirements for self-propelled modular platforms (drawbar pull, operating speed, mass) and the parameters necessary for designing traction electric motors using the finite element method (external speed characteristic (ESC), CPSR). Existing methods do not account for the specifics of individual electric drives and the modern possibilities of mass variation.

THE PURPOSE. To develop an algorithmic traction calculation methodology that transforms the initial agrotechnical parameters into a well-founded external speed characteristic of a traction electric motor for hybrid agricultural modular platforms with series transmission.

METHODS. The methodology is based on traction balance equations, classical tractor theory, and analysis of empirical dependencies. A key feature is the introduction and systematic consideration of the operational mass range coefficient and the overload capability coefficient, enabling a transition from discrete mass settings to a continuous range. The calculation includes determining the required power, efficiency (taking into account energy efficiency classes), reduction gear ratios, and constructing the desired external speed characteristic.

RESULTS. A family of external speed characteristics of traction electric motors was obtained, demonstrating the influence of varying parameters on the required Constant Power Speed Ratio (CPSR). It was found that increasing the design operating speed from 4 to 8 km/h with a fixed operational mass range coefficient of 1.66 reduces the required CPSR from 11.1 to 5.5. Based on the traction balance equations, a dimensionless complex for CPSR was derived, generalizing the influence of the speed factor, adhesion factor, ballasting factor, and overload factor. A strategy for unifying traction motors within a model series is substantiated: a single motor size covers the requirements of the entire series by software shifting of the base point on the ESC without recalculating the electromagnetic system.

CONCLUSIONS. The developed methodology bridges the methodological gap between mechanical and electromagnetic modeling, acting as a crucial link in a closed-loop digital design cycle. It enables the formulation of accurate technical specifications for designing electric machines, optimizes the traction motor design for real operating conditions with variable mass and dynamic loads, and significantly reduces iteration time between interrelated engineering disciplines.

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