Analysis and verification of power transmission characteristics of the hydromechanical transmission for agricultural tractors

In this study, we developed a network model of a Hydromechanical transmission (HMT) for tractors. We verified the developed network model using commercial software and analyzed the power transmission characteristics of an HMT-equipped tractor based on the verified network model. We developed a network model considering the power losses of the transmission elements to analyze the power transmission characteristics of the HMT’s main shift. Using this model, we analyzed the power transmission characteristics of the main shift and confirmed that the power of the main shift can be split and circulated depending on the stroke of the Hydrostatic unit (HSU). We then used the model to analyze the HSU stroke, the power transmission efficiency, and the wheel torque, all of which comprise the power transmission characteristics of an HMT-equipped tractor. As a result, the HMT changed the driving speed of the tractor by continuously varying the HSU stroke. The tractor efficiency increased with the driving speed at each mode and decreased after having reached its maximum efficiency. To verify the developed network model, we compared the analysis results of the tractor’s power transmission efficiency and wheel torque with those obtained from commercial software. From the comparative analysis, we confirmed that the power transmission efficiency and wheel torque of the two models coincided. Therefore, we conclude that the developed network model is highly suitable for analyzing the power transmission characteristics of the HMT.