A two-mass dynamic model of an electric vehicle is considered to obtain analytical dependences describing the gearshift process in a shaft-planetary gearbox. The calculations are based on the optimal diagram of shifting gears from low to high without interruption of the power flow from the electric motor. At the stage of gear shifting, at which the kinematic gear ratio of the gearbox changes from u1 to u2, Lagrange equations of the second kind are used to determine the time dependences of angular velocities of the input and output shafts of gearbox. An example is given for calculating the gearshift time from low gear to high one for the MAZ-4381EE delivery electric truck, as well as a refined calculation for a multi-mass dynamic scheme is carried out.
Введение. Современные электромеханические силовые установки электромобилей в большинстве случаев оснащаются высокооборотными тяговыми электродвигателями и 1-ступенчатыми понижаю-УДК 629.33; 621.3 С.Н. ПОДДУБКО, канд. техн. наук, доц.
With all advantages, electric vehicles have a significant disadvantage — a relatively small driving range on a single charge of the traction battery compared to cars using hydrocarbon fuel. The solution to the issue is to choose a rational structural scheme of an electromechanical power unit to obtain its high energy efficiency regardless of the operating conditions. A significant number of electric vehicles produced today either do not contain gearboxes or contain single-speed reducers. The use of a multi-speed gearbox solves the problem of adapting the working processes of a traction electric motor to the loading conditions, bringing its efficiency as close as possible to the range of highly efficient values. Calculated estimation of energy consumption of the MAZ-4381EE electric delivery truck is carried out in the paper for various versions of the mechanical part of power unit: without a reducer, with the use of a reducer and two types of two-speed gearboxes (shaft and shaft-planetary). The evaluation is made based on consideration of the European test driving cycle NEDC, taking into account the use of efficiency maps of the traction induction electric motor. The calculation results showed that the use of two-speed gearboxes can reduce the total energy consumption by more than 1.8 times compared to a power unit with a high-torque motor and without a gearbox.
The aim of this work is to assess the compliance of the estimated lifetime of the planetary gearbox of hydromechanical transmission of a BELAZ mining dump truck with the actual operational one based on the results of accelerated (forced) bench tests. Preliminary strength calculations were carried out for the two most stressed modes of movement of a mining dump truck in a quarry on the rise, where the most significant damage to gear trains takes place: for maximum productivity (power) and maximum torque. Investigations showed that the gears limiting the lifetime of the gearbox are the sun gear and satellites of the 3rd planetary series. As a result of the tests, the estimated operating time of the planetary gearbox on the bench was achieved, which guarantees an operational life of at least 400,000 km of the dump truck run.
Technical condition diagnostics of the planetary reducers of motor wheels in mining dump trucks electromechanical power units requires the study of dynamic processes caused by shock pulses in gearings when tooth remating. The levels of the occurring vibrations are determined by the natural frequencies and natural modes of reducer. The article describes calculation method based on the study of the developed dynamic model of a two-row planetary reducer of a motor wheel, describing the torsional vibrations of its elements and differing from the known ones by taking into account the compound motion of the planetary row satellites, the axes of which rotate together with the carrier. The calculation of natural frequencies and modes of vibrations is reduced to the computation of eigenvalues and eigenvectors of a matrix of special form based on the application of the iterative numerical method of Jacobi rotations. As an example, the calculation is given for gears of the motor wheel reducer of BELAZ mining dump trucks of the 7530 and 7531 series with a load capacity of 220 and 240 tons, respectively. The calculation of the natural frequencies of reducer performed makes it possible to determine those harmonic components of vibration-inducing disturbances in the form of shock pulses which cause resonance phenomena in the mechanism contributing to a significant increase of dynamic loads levels and accelerating the processes of lifetime expense of gear trains. In addition, the analysis of natural modes parameters makes it possible to determine the reducer elements with the highest vibration activity and monitor during vibration monitoring the technical condition of gear trains that limit the reliability of the mechanism.
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