# Development of a Simulation Model for HMT of a 50 kW Class Agricultural Tractor
## 5 Conclusions  
In this study, we developed and evaluated the performance of a prototype of an HMT for a 50 kW class agricultural tractor. To evaluate the load data, such as the axle torque, rotational speed, and power transmission efficiency, which are important indicators of transmission for agricultural tractors, we carried out a bench test for the prototype of the HMT. The simulation model for the HMT was developed and analyzed using Rmax DESIGNER. To verify the simulation model, a t-test was carried out between the measured and simulated results based on the gear stages. Finally, the accuracy of the simulation model for the HMT was evaluated by comparing the power transmission efficiency between the measured and simulated results according to the gear stages. The main results of this study are as follows:  
1. The prototype of the HMT for a 50 kW class agricultural tractor was composed of an HSU, compound planetary gear, range shift, spiral level gear, and final reduction gear, and this HMT had three stages and a maximum forward speed of 40 km/h. The simulation model was developed to be the same as the prototype of the HMT. For the performance evaluation, the test bench was installed based on engine conditions of the prototype of the HMT. The axle torque, rotational speed, and power transmission efficiency were measured and simulated according to the gear stages using a bench test and simulation.
2. As a result, the axle torque rapidly decreased in the first gear stage and gradually decreased as the gear stage was increased. We also found that both the measured and simulated axle rotational speed increased constantly, and the measured value decreased slightly in the shifting sections. On the other hand, the power transmission efficiency of the first gear stage appeared to increase, and the power transmission efficiency of the second and third gear stages appeared to decrease after increasing to the maximum point. From the t-test results, there were no significant differences between the measured and simulated load data, such as axle torque, rotational speed, and power transmission of the HMT.
3. The results of linear regression showed an R-squared value of 0.988, an RMSE of 5.461, and an RD of 8.18 in the first gear stage. The results of linear regression at the second gear stage showed an R-squared of 0.971, an RMSE of 1.473, and an RD of 1.84. On the other hand, the results of linear regression at the third gear stage showed an R-squared of 0.980, an RMSE of 1.345, and an RD of 1.84. The trend of power transmission efficiency between the measured and simulated results appeared to be similar in all sections, and we obtained a simulation model with the accuracy of an R-squared value of more than 0.97.  
In conclusion, the measured and simulated results were similar to each other. The results of this study will be useful information for the development of HMT tractors and to improve the power transmission efficiency for the optimal design of agricultural tractors. In a future study, we plan to develop the HMT tractor and measure the load data through agricultural operations, such as plow tillage and rotary operations. In addition, the results of this study are considered to be useful for research on the design of tractor power transmission systems and improvements of HMT for agricultural tractors.  
All authors contributed to the research presented in this work. Their contributions are presented below. Conceptualization, S.-M.B. and Y.-J.K.; methodology, S.-M.B.; software, S.-M.B. and W.-S.K.; validation, Y.-S.K. and S.-Y.B.; writing--original draft preparation, S.-M.B.; writing--review and editing, S.-M.B., S.-Y.B.; supervision, Y.-J.K.; project administration, Y.-J.K.; funding acquisition, Y.-J.K. All authors have read and agreed to the published version of the manuscript.  
This research was supported by the Agricultural, Forestry, Food Research Center Support Program (Project No.: 714002-07), Ministry of Agricultural, Food and Rural Affairs.  
The authors declare no conflict of interest.