Abstract
This paper proposes a new transmission scheme of hydromechanical continuously variable transmission (HMCVT) for tractors. The HMCVT has 4 working ranges in each of the front and rear directions. The speed characteristic and the torque characteristic of HMCVT are theoretically derived. On the basis of HMCVT power flow direction, the Крейнeс formula is used to calculate the transmission efficiency. Then, the image analysis method is used to study the influence of parameters on the transmission efficiency of HMCVT, and the main influencing factors are found. The results of theoretical derivation demonstrate that, by coordinating control of the HST displacement ratio and the engagement conditions of shifting clutches, the stepless speed regulation of HMCVT at the tractor speed of 0–50 km/h can be realized. The proposed HMCVT has the ability to continuously transmit and change torque over all working ranges. The overall transmission efficiency of HMCVT is at a high level. To verify the theoretical derivation, Amesim simulation software is used for the modeling and simulation of HMCVT. The simulation results are consistent with the theoretical analysis results. Therefore, the HMCVT proposed in this paper has the advantages of compact structure and high transmission efficiency, and it is suitable for matching tractors.
Highlights
In addition to transportation, the main function of tractors is to drive agricultural machinery needed for agricultural production, which needs the transmission of tractors to provide constantly changing speed and torque to adapt to frequent external load changes [1].In this context, the use of a continuously variable transmission (CVT) for tractors has become a trend. e most common type of CVTs is the hydraulic static transmission (HST) [2]; it mainly includes hydraulic pumps, hydraulic motors, and control mechanism
In order to overcome the above shortcomings, the HST is connected in parallel with the mechanical components to form a hydromechanical continuously variable transmission (HMCVT) [3,4,5,6]
HMCVT transmits only part of the power through the HST; the remaining power is transmitted through the mechanical components, so the efficiency is much higher than HST
Summary
The main function of tractors is to drive agricultural machinery needed for agricultural production, which needs the transmission of tractors to provide constantly changing speed and torque to adapt to frequent external load changes [1]. HMCVT can realize stepless speed regulation through the HST, while relying on mechanical components to achieve high efficiency transmission. Literature [8] first proposes a transmission scheme for single-row planetary gears with two hydromechanical working ranges. E author of [15] proposes a transmission scheme in which a single-row planetary gear is connected in series with a mechanical stepped transmission. E single-row planetary scheme helps to reduce the size of the transmission, but the hydraulic motor needs to be reversed quickly at the moment of switching, which needs high performance of the hydraulic motor. It includes the input shaft, pump-motor hydraulic system, planetary gear mechanism, gear pairs, shifting clutches, and directional clutches.
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