Механика машин, механизмов и материалов (Sep 2022)
Selection of the Range of Gear Ratios of the Mechanical Part of the Electromechanical Power Train of the Tractor
Abstract
A method has been developed for selecting the gear ratio of the mechanical part of the power train (MPPT) to work on agricultural operations of a tractor of the 5th drawbar class equipped with an electromechanical power train with a traction induction electric motor (TIM). It is assumed that there are two gears: the high one (n-th) for operation in transport mode and the low one (n–1st) for operation in operational and technological modes. The gear ratio MPPT uМЧТ,n, corresponding to the nth gear, is determined from the condition of ensuring the required maximum velocity of the tractor. The gear ratio of the MPPT uМЧТ(n–1), corresponding to the n–1st gear, must be in the range from the uМЧТ(n–1),р, at which the minimum plowing velocity will be provided at the nominal value of the voltage frequency supplied to the TIM, to the uМЧТ(n–1),max, determined by from the condition of providing the maximum possible velocity range of the tractor with only the n-th gear without overlapping its n–1st gear. A formula is also proposed for determining the value of the uМЧТ(n–1),v, at which the tractor can operate with the maximum velocity permissible for a given agricultural operation. If uМЧТ(n–1),v < uМЧТ(n–1) < uМЧТ(n–1),р, then the entire velocity range for a given agricultural operation will be provided when working in the n–1st gear. In order to determine the uМЧТ(n–1) with the best traction efficiency, it is proposed to carry out tractor traction calculation for the values of uМЧТ(n–1) taken in the range from uМЧТ(n–1),р to uМЧТ(n–1),max with a certain step. After that, for the selected value uМЧТ(n–1), it is necessary to calculate the TIM losses during tractor operation in the entire velocity range provided by the n–1st gear. If the thermal mode of the TIM is not performed when the tractor is moving at low velocities in the n–1st gear, then it is necessary either to take a larger value of the uМЧТ(n–1) at which it is performed, or in case of a small excess of the permissible power losses of the TIM, do not increase the uМЧТ(n–1), but take this into account when designing the TIM cooling system.
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